concrete VOLUME 55 ISSUE 1 MARCH/APRIL 2011
Pervious Concrete How concrete with holes in it makes perfect sense
Endless Possibilities Peter Fell COLOURS concrete across commercial, civic and residential applications
Concrete Treasure Trove CCANZ talks with a reflective Len McSaveney
THE MAGAZINE OF THE CEMENT AND CONCRETE ASSOCIATION OF NEW ZEALAND
UPFRONT
concrete MAGAZINE
Although several weeks have passed since my oped piece appeared in the Christchurch Press and numerous developments have occurred in relation to the Christchurch earthquake, my sentiments remain, and warrant underlining in this issue of Concrete magazine.
Editor/Advertising: Adam Leach +64 4 915 0383 adam@ccanz.org.nz
With the myriad lessons from 22 February 2011 (and 4 September 2010) yet to be fully assessed, it has been somewhat disturbing to see opinions rushed into print that pointlessly pitch one building material against another or that ignore the realities of 21st-century building technology.
Subscriptions:
The position held by CCANZ on matters related to the Christchurch earthquake is that we will pull out all the stops in support of the Royal Commission, the Department of Building and Housing and the Canterbury Earthquake Recovery Agency (CERA).
by CCANZ (Cement & Concrete
This assistance might include acting as a conduit between industry and the earthquake authorities, providing expert concrete-related information and supporting any assessment of the seismic performance of buildings.
PO Box 448
At this point in time, CCANZ does not believe it is useful to speculate, as some have, about what a conceptual city made of timber would be like, any more than it would be to speculate about what an entire city made only of concrete would be like. Such speculation ignores the fact that both timber and concrete building materials are integral components of almost all building projects.
NEW ZEALAND
New Zealand is fortunate to have academic experts in a range of building materials, who, when exercising academically neutral opinions, can give real balance to the arguments about the strengths of different materials for different contexts.
Email: admin@ccanz.org.nz
Kylie Henderson +64 4 499 8820 admin@ccanz.org.nz concrete is published quarterly
Supporting one-sided arguments is of no help. It is better to allow genuinely independent expert opinions to be given equal space, and for the best of both worlds to inform each other by focusing on furthering New Zealand’s reputation as a developer of world-class engineering solutions. To inform debate and help ensure confidence in concrete is not undermined, CCANZ will, over the coming months, focus its attention on highlighting the advantages of concrete construction across residential and multi-storey applications. The next issue of Concrete will feature an overview of concrete’s performance during both earthquakes. Within the residential space CCANZ will seek to clarify that the poor performance of some concrete slab foundations during the earthquakes resulted from poor design (no reinforcement) as well as placement on land prone to liquefaction. Amongst a series of recommendations, CCANZ will be advising that all residential concrete slab-on-ground floors for timber frame buildings that are to be placed on ‘good’ ground, as specified in NZS 3604: 2011, should be reinforced. This work will take place within a wider residential campaign currently under development - see page 6. Designed to showcase the advantages of using concrete to create comfortable, stylish and strong homes, the campaign will utilise video, print and web resources when it comes online in July 2011.
Association of New Zealand)
Level 6, 142 Featherston St Wellington
Tel: +64 4 499 8820 Fax: +64 4 499 7760. Website: www.ccanz.org.nz ISSN: 1174-8540 ISSN: 1179-9374 (online) Disclaimer: The views expressed in concrete are not necessarily those of the Cement & Concrete Association of New Zealand. While the information contained in the magazine is printed in good faith, its contents are not intended to replace the services of professional consultants on particular projects. The Association accepts no legal responsibility of any kind for the correctness of the contents of this magazine, including advertisements. © Copyright 2011 CCANZ (Cement & Concrete Association of New Zealand)
Key to CCANZ work from a multi-storey perspective will be raising awareness of PREcast Seismic Structural Systems (PRESSS) within an inevitable wider public discussion on the merits of emerging building technologies. The Southern Cross Hospital building in Christchurch, which survived the earthquakes without structural damage, and the Alan MacDiarmid building in Wellington, both employ PRESSS, and will undoubtedly inform the next phase of determining how we build commercial buildings in the future. As analysis of building performance continues and reconstruction plans begin to take shape we would all be best served to remember that building technology has not advanced in the ways that it has, and continues to do, without the weight of evidence. Let’s focus on that. Rob Gaimster CCANZ, CEO
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Cover photo: New Lynn War Memorial Library, courtesy Golden Bay Cement
NEWS FORMER NZCS PRESIDENT HONOURED Wayne Raymond has been elected a Fellow of IPENZ for contributing to the advancement of engineering practice and innovation in the creation of engineering works. Wayne is recognised for helping advance structural engineering construction practice. By applying innovative construction methodologies in multi-storey building construction he has helped enhance productivity. He has contributed to codes of practice for using pre-cast concrete as a building material and was a key contributor to the 2003 IPENZ Structural Engineering Task Force. Among other bodies, he was active for many years in the New Zealand Concrete Society.
INGHAM TO HEAD NZ FIB DELEGATION New Zealand Concrete Society Vice President Jason Ingham has been nominated as the New Zealand delegate for fib following the resignation of Len McSaveney. The International Federation for Structural Concrete (fib fédération internationale du béton) advances knowledge of concrete construction on technical, aesthetic, economic and environmental levels. Len McSaveney was New Zealand’s fib delegate for 15 years. See pages 8-11 for CCANZ CEO Rob Gaimster’s discussion with Len.
DBH EARTHQUAKE REPAIR GUIDANCE DOCUMENT The Department of Building and Housing (DBH) has issued guidance on the repair and rebuild of houses in land-damaged areas of Canterbury. The guidance is part of the Department’s ongoing work supporting long-term recovery in the Canterbury area. A consistent approach to repair and reconstruction in landdamaged areas is vital to minimise delays and aid the recovery. This guidance only applies to houses directly affected by the Canterbury earthquake. The focus is on foundation and floor elements but it also covers common areas of ‘above the floor’ damage such as chimneys. The recommendations have been developed in cooperation with technical experts and will help to safeguard people and homes in future earthquakes. Guidance on House Repairs and Reconstruction Following the Canterbury Earthquake can be downloaded from the DBH website. See page 4 for changes to Building Code compliance documents for Clause B1 Structure.
Energy Efficient Our Insulated Masonry System incorporates 40/60 or 80mm insulation board to concrete structures providing a complete thermal envelope. This System provides for the premium Rockcote flashing suite, and plaster coatings to provide a durable, low maintenance, and most importantly energy efficient structure now and into the future.
HOMESTAR PARTNER CCANZ has become a Supporting Partner of the Homestar™ residential rating tool. Homestar is the product of a Joint Venture partnership between BRANZ, Beacon Pathway and the NZGBC. Led by these organisations coordinated input from industry stakeholders and government has combined to develop a single residential rating tool for NZ’s new and existing homes. Visit www.homestar.co.nz
www.rockcote.co.nz 0800 50 70 40
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BUZZ from the Beehive IMMEDIATE CHANGES TO SEISMICITY AND FOUNDATION DETAILS FOR CHRISTCHURCH Canterbury Earthquake Recovery Minister Gerry Brownlee recently announced changes to Building Code documents to increase the seismic hazard factor for Canterbury and to require stronger foundations for buildings. The Department of Building and Housing has decided to increase the seismic hazard factor for the design of all buildings by 35 per cent from 0.22 to 0.3 based on the best scientific and structural engineering advice available. In addition, concrete floor foundations for housing will need to be tied and reinforced. This change was signalled in guidance on foundation repairs provided to the construction sector after the September 4 earthquake. These changes are likely to increase costs for new residential building work in the order of $2,000 to $9,000 per property, depending on the size of the house, the foundation option chosen and the state of the ground. “Residential homes built in Christchurch will be required to have increased bracing and foundations and be more resistant to bowing or cracking,” said Mr Brownlee. “These changes will mean new buildings are constructed better to withstand any future severe earthquakes.” The changes will take effect from Thursday 19 May 2011 in the three local authority areas in greater Christchurch: Christchurch City, Waimakariri, and Selwyn District Councils. The seismic hazard factor for buildings in much of the Selwyn District, closer to the Alpine Fault, is already greater than 0.3.
NEW ONLINE TOOL BOOSTS LICENSED BUILDER SCHEME On 5 May Building and Construction Minister Maurice Williamson announced a new on-line service that will allow licensed building practitioners to register their skills and expertise online. As part of the Licensed Building Practitioner (LBP) Scheme, the on-line service has been launched through the Department of Building and Housing website at www.dbh.govt.nz/lbp where licensed building practitioners can register online, edit their profiles and update their skills and expertise. The database will double as a tool for consumers to check if practitioners are licensed and to obtain the latest information about them. “The public needs to have confidence in the building industry and in the quality of their work, especially given the rebuilding being undertaken in Christchurch,” said Mr Williamson. Already 8300 licences have been issued putting the scheme on track to hit the target of 14,000 by March 2012. EXPERTS APPOINTED TO ASSIST INVESTIGATION Leading New Zealand engineering companies will assist the Department of Building and Housing with the technical investigation into the performance of the Canterbury Television, Pyne Gould Corporation, Forsyth Barr and Hotel Grand Chancellor buildings, Building and Construction Minister Maurice Williamson announced in early April. The companies are Beca Consultants; Dunning Thornton Ltd; StructureSmith; and Hyland Fatigue and Earthquake Engineering.
“The aim is to improve safeguards for people occupying the buildings and reduce personal harm and damage to property from any future earthquakes.”
The Department has also appointed a panel of experts, chaired by construction law expert Mr Sherwyn Williams, which will provide guidance on the methodology of the investigations and peer review the findings.
Mr Brownlee commented that the changes to the seismic hazard factor and foundation requirements needed to be made promptly so that commercial building owners and homeowners could get on with rebuilding or repairing properties as quickly as possible.
“The investigation is underway and is expected to be completed by 31 July 2011,” Mr Williamson said. “However, it is important to get this right rather than simply on time. It may be that more time is needed to undertake the work properly.”
Building and Construction Minister Maurice Williamson believes the changes are based on the best available science and the advice of recognised seismic and structural engineering experts.
“The investigation will establish and report on: the original design and construction of the buildings; the impact of any alterations; how the buildings performed in the 4 September 2010 earthquake and the aftershocks; what assessments of the buildings’ stability/ safety were made; and why the buildings collapsed or suffered serious damage on 22 February 2011.”
The Department also worked closely with the Christchurch City Council in developing the new seismic hazard factor. “Ground shaking in Christchurch on 22 February was very violent and exceeded Building Code design requirements for buildings in the area,” said Mr Williamson. “The scientific assessment of the earthquakes and how buildings performed in them does not support an increase in the seismic hazard factor above the 0.3 level.” The new Compliance Document for Clause B1: Structure of the Building Code, along with an Information sheets summarising the changes, can be found at www.dbh.govt.nz/news-index.
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The Department is inviting members of the public to supply photographs, video recordings, and first-hand accounts of the state or performance of each building prior to, during, and after 22 February 2011. The investigation Terms of Reference are available at www.dbh.govt.nz. CHRISTCHURCH ROYAL COMMISSIONERS ANNOUNCED Attorney-General Christopher Finlayson confirmed on 11 April that the Government will recommend Sir Ron Carter and Associate
Professor Richard Fenwick as commissioners for the Royal Commission of Inquiry into Building Failure caused by Canterbury Earthquakes. When those appointments are signed off by the GovernorGeneral, they will join chair Justice Mark Cooper on the Royal Commission. The two have considerable experience in analysis, problem solving and the engineering sector. Sir Ron Carter has a considerable background in the engineering sector, as a former managing director of Beca Carter Hollings and Ferner Ltd. He is a current director of Rugby New Zealand 2011 and has extensive governance experience, including chairing the Civil Aviation Authority. He has led a number of high profile reviews, including the 1999 review on the management of New Zealand’s borders. He is a Distinguished Fellow of the Institution of Professional Engineers. Richard Fenwick is an Adjunct Associate Professor in Civil Engineering at the University of Canterbury. He is a leader in the field of earthquake engineering and is internationally renowned for his work in the design of seismic-resistant reinforced concrete structures. He was made a Companion of the New Zealand Order of Merit in 2010 for services to engineering. The Royal Commission’s terms of reference have also been finalised. The terms of reference require the Commission to look at two major areas:
1. It will inquire into buildings in the Christchurch CBD, looking specifically at what factors led some buildings to fail severely; why some buildings’ failure caused extensive injury and death, and why buildings differed as to the extent to which they failed and caused injury or death. That will mean looking at, among other things, the characteristics of buildings which may have led to failure (for example age, location, whether buildings conformed to earthquake risk best practice). 2. It will also inquire into the adequacy of current legal and best-practice requirements for the design, construction and maintenance of buildings in central business districts in New Zealand. The Royal Commission will report its findings by 11 April 2012, but will release an interim report after six months. The report will also include the Royal Commission’s recommendations for: 1. any measures necessary or desirable to prevent or minimise the failure of buildings in New Zealand due to earthquakes; 2. the cost of those measures, and 3. the adequacy of legal and best-pravctice requirements for building design, construction and maintenance, in as far as those requirements apply to managing risks of building failure caused by earthquakes. The Commission will be supported administratively by the Department of Internal Affairs.
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Concrete solutions
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Zooming in on Concrete CCANZ’s latest project for promoting the story of concrete is a campaign focused on the benefits of using concrete in residential construction - from floor slabs through to fully concrete homes. Initial work on this campaign, which currently has the working title of ‘Coming Home To Concrete’, has begun with a series of brief video vignettes being filmed at locations ranging from a suburban family home to the larger scale rural setting of a home being built amongst the vines of a Martinborough winery.
Typically the spectrum of answers feature aspects such as concrete’s ability, through thermal mass, to deliver a warm home, closely followed by such advantages as durability and fire resistance, along with a growing appreciation of aesthetic and acoustic characteristics achievable with concrete.
A focus has also been placed on homes in Christchurch, with filming at locations in areas hard hit by earthquake after earthquake (see stories opposite).
During the remainder of 2011 the candid views being expressed on camera will be edited into thematically arranged sequences and made available via the CCANZ website as ‘web clips’, as well as a compilation on DVD. Those themes will also be mirrored in a reader-friendly companion brochure-format publication, again cross-referencing to the CCANZ website and more in-depth technical resources.
Interview subjects for the campaign have so far included homeowners, builders, architects and engineers, with interviews loosely structured around topics such as the attributes of concrete that are of most importance for each interviewee.
Director and cameraman Darryn Smith films Winifred and David Bull at the site of their tilt slab concrete home being built at the Cabbage Tree Vineyard near Martinborough. (pictured at top of page)
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Watch this space for campaign developments.
Cameraman Chris Terpstra films Andrew Simpson, of Parsonson Architects, and Jared Torrington, construction foreman of A. Sparks Ltd as they discuss plans for a new build at a site office in residential Karori, Wellington.
Building Trades tutor Eddie Brownlee, at centre, holds a sample of the no-fines concrete that has held together the family home of Doreen and Grahame Fraser.
FROM THE HILLS ABOVE CHRISTCHURCH
STANDING THE TEST OF TIME (AND EARTHQUAKES)
For Christchurch architect Roger
For Dr Grahame Fraser, a senior fellow
Buck (pictured ABOVE) the Canterbury
in physics at Canterbury University, his
earthquakes have put a range of issues
house in Mount Pleasant is a testament to
into stark perspective.
the durability of no-fines concrete and
An immediate consequence of the massive city-changing jolt on 22nd February was that the CBD office of Buck Architects, the practice that Roger founded two decades ago, became off limits due to damage in surrounding buildings. On the day of the quake Roger was at home and had what might be termed a ringside seat overlooking the worst affected suburbs from his perch in Kakariki Lane high above Sumner. This benchmark set of homes safely nestled on the hillside of Kakariki Lane are Roger’s legacy project and a fulfilment of many of his beliefs in sustainable high mass solar homes consisting of 80-100% concrete. The latest addition, the Teear House, has only been occupied since August 2010 and collected an award in CCANZ’s 2010 Concrete3 Sustainability Awards for Excellence in Residential Concrete Construction. The fact that Kakariki Lane houses have remained virtually unscathed through the quakes indicates that while this group of houses and its community might be ‘unconventional’, that very approach has proven to be much more of a success than what passes for ‘conventional’. Roger’s passion for Kakariki Lane is certainly undiminished and he continues to collect facts and to graph the high performance achieved within buildings where concrete is the primary building material. He is also certain to be one of the voices that should be listened to most closely in the efforts required to rebuild a city on principles of true sustainability and energy efficiency.
the building nous of the firm of T.R. (Tom) Brownlee and Sons when the house was built 46 years ago. Motivated by the fact that the house and its 25 cm concrete walls emerged from major earthquakes with only minor internal damage, Grahame wrote to CCANZ to “put in a plug” for the durable and safe nature of his “humble family home”. Furthermore, Grahame invited CCANZ to visit the house he and wife Doreen have raised their family in to see the proof in person, joined by Eddie Brownlee - son of Tom and a long time tutor in Building Trades at the Christchurch Polytechnic Institute of Technology. An additional bonus of our visit was being able to see a carefully put together family history of the house, complete with photos of its original construction as taken at the time by Doreen Fraser. Over the years T.R. Brownlee and Sons built as many as thirteen houses and one panel beating shop using no-fines concrete, based on Tom Brownlee’s opinion - as paraphrased by Grahame that “given Christchurch sat on hundreds of feet of gravel it was a very appropriate basis for construction”. Eddie remembers his father as a relentless innovator in varying his use of cement mixes and no-fines concrete and, moving with the times, Eddie has built himself a tilt slab concrete home which has been favourably assessed by the Earthquake Commission (EQC). As with so much that has happened in Christchurch these stories serve to illustrate the lesser told aspects of the very often random and land-related damage that has occurred - quite regardless of house materials.
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Concrete Treasure
Trove
CCANZ CEO ROB GAIMSTER CHATS WITH A REFLECTIVE (and soon to retire) LEN MCSAVENEY ABOUT PROBLEM SOLVING, INNOVATION, ALONG WITH THE IMPORTANCE OF EDUCATION, TRAINING, INTERNATIONAL NETWORKING AND TRADE ASSOCIATIONS. RG: Len, thank you for taking time out to chat with Concrete magazine. LM: My pleasure. RG: Before we begin, let me just quickly summarise what has been a long and distinguished career in the concrete industry, spanning some forty years.
After graduating from Canterbury University in 1964 with a degree in Civil Engineering, you went to work for what is now Holmes Consulting Group. However, the urge to travel became too strong, and you left to see the world, ending up in Canada. Initially employed in the oil industry, you moved to Toronto in 1970 and began your involvement with (precast) concrete. By 1974 you were back in New Zealand, but now with your Canadian bride Marilyn, working for R.T. Scott Limited in Blenheim, a company later bought by Stresscrete, which in turn became part of the Fletcher organisation. This began your long association with Fletchers, that has included various roles at Firth Industries (chief engineer and market development manager), and which is culminating with the role of Market Development Manager at Golden Bay Cement for civil and structural applications.
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Throughout the various stages of your career in concrete what one key personal attribute has been your greatest asset? LM: Having the ability to innovate, being an innovator. Although that has a bit of a negative connotation in the concrete industry. RG: Do you think? LM: In parts of the concrete industry that are afraid of new ideas. So I would say, being a problem solver. Really, when I think of the innovations I have been responsible for and the patents I have registered in my name, things generally start with a problem, in response to which you ask “How do I overcome that?” RG: So, innovation is part of the problem solving process? LM: Yes. Usually those ideas come in the middle of the night. You’ll be thinking about a problem before you go asleep. Then it hits you. For me, it’s just like a picture coming into focus. Then there’s the answer! RG: So what would you say has been the biggest problem you have helped solve? LM: Getting drilling rigs up to the Canadian Artic. We had to break them down to fit on a Hercules, then land on the ice, when it’s thick enough, but not so bunched up with pressure ridges that the planes can’t land. So you have a very short weather window when you can get in and everything has to come together.
However, from a concrete perspective it would have to be the Westpac Stadium in Wellington. Which was a project that posed many challenges.
RG: Such as? LM: First and foremost, Fletchers wanted to win it. They didn’t want an Australian contractor coming in here and building such a prestigious stadium. But it was the decision to go with lightweight concrete that was significant.
meant we could get more units on a truck. Ken said you do the business case and I guarantee I will get you the money.
So although we were going to save $1 million on construction costs, we were going to spend about $1 million on lightweight aggregate. You usually wouldn’t do that, but from the Concrete Group’s perspective, beyond the construction issues, it was important to see how lightweight concrete fitted in the New Zealand market, and to prove to the Stadium Trust that Fletchers were serious.
To me there was no risk as it had been widely used in North America and we had visited a number of stadiums there where designers had said lightweight concrete was the obvious choice because of the crane issues. The Dodgers stadium in LA was built of lightweight concrete in the 1960s, and has survived a number of earthquakes including the Northridge one. So we knew it performed well.
However, when you promote an idea such as lightweight concrete, and it gets accepted, there are still people who seek to undermine it.
RG: What made you pursue the lightweight solution? LM: In terms of construction on the site, which was so close to the fault-line and on weak ground, piling was uncertain. So the lighter we could make the stadium the less risk there was. In my mind it was always going to be lightweight concrete or structural steel, never normal density concrete, and yet there was a battle from concrete interests to make sure it was normal density concrete. RG: So there was quite strong resistance to the use of lightweight concrete? LM: Oh yes - even after it was finished. RG: So where exactly was the lightweight concrete used? LM: All of the precast concrete was lightweight, made by Stresscrete. We used an expanded shale aggregate imported from California, where it had been widely used for close to 80-years. Texas Industries supplied the aggregate.
RG: It seems to me that typifies the concrete industry the world over – an initial mistrust of innovation amongst certain groups.
LM: Yes – people waiting around to say “I told you so.”
I went to Ken Howard, who was running the Fletchers Concrete Group at that time, and said we think lightweight concrete is going to work in this stadium because there is a crane issue, and the bigger you make the pieces, the fewer joints, and the faster it goes together. It was precast at Otaki and transported by trucks, so being lightweight
RG: Are there other innovations you are particularly proud of, one that you perhaps consider to be your legacy? LM: That would be the concrete power poles that replaced the old hardwood poles for secondary transmissions lines
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across the middle of the North Island. The thing about hardwood is that is rots from the middle, meaning it can’t be treated. This meant that there were a lot of rotten wooden poles holding up critical power lines. So Electro Corp, as it was in those days, called for tenders for the supply of hollow concrete poles. We won the contract on the basis of importing some equipment from Germany. However, during the 18-months it took Electro Corp to privatise we figured out a better way of supplying the poles. This involved creating an outer mould and a rotating inner mandrel, tapered, from which we cast the poles. This saved over $1 million in equipment costs, and enabled production to begin quickly - which is still continuing today. RG: Tell me a bit about the Self-Compacting Concrete [SCC] at the Tauranga Harbour Link Stage 2 project. LM: The bid team for Fletchers phoned me and said can you make a concrete that gives a 100-year life with 40 mm of cover? At the same time fib [International Federation for Structural Concrete] had just published their state-of-the-art report on durability design for concrete. I said, well the Europeans say it can be done with micro silica and fly ash, but we haven’t tested our materials. We commenced a testing programme and sure enough we proved that we could achieve exactly the same numbers as they had in Europe.
The magic thing about SCC is that the surface is so dense. You don’t have to vibrate so you don’t have that little space of trapped water around the aggregate, the result being very low sorptivity on the surface. We were advised by Professor Bartos from Paisley University that during SCC testing sorptivity levels should be examined because if you can reduce them from 8 mm to 0.8 mm then you have a magic start in terms of your 100-year life. That idea saved Fletchers close to $20 million on the Tauranga Harbour Link job by allowing the spans to be lighter and longer, meaning fewer piers. SCC also meant reduced labour costs.
RG: What I don’t understand, and I guess there are issues of vertical integration, is that in Europe that idea would have been proposed by a ready mix company not a cement company. LM: A cement company wants to sell magic fillers for concrete, so we have to take the initiative in that area. In fact, there was some opposition to the use of SCC from the ready mixed concrete supplier, who considered it too risky, and preferred conventional concrete. In fact, it wouldn’t have worked in conventional concrete as the beams would have been beyond the lifting capacity of the available cranes. RG: What do you see as the big challenges facing the cement and concrete industry? LM: When you look at what’s happening to the rest of the world I would have to say low carbon / low energy, within the wider context of sustainability.
I presented a paper at the Transitions to Sustainability conference in Auckland recently, at which I was the only one talking about concrete. In my session one of the five speakers was unable to attend, so during his slot the panel was available for questions, all of which were directed towards me - “why is cement manufactured this way?”, “why does concrete behave this way?” We talked
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through the issues, and all of a sudden the audience could understand the rationale behind cement and concrete processes, and appreciate the efforts being made by the industry to enhance its environmental performance.
I spent some time explaining inorganic polymers, and how we would use them if possible, but that currently such was not the case. That inorganic polymer concrete is structurally sound, but questions remain over its durability because it is very permeable and therefore does not protect the reinforcing like conventional construction concrete.
RG: How is low carbon / low energy going to be achieved? LM: Fletchers just spent about $120 million on achieving it at Golden Bay Cement. Blended cement in one technology that has been heavily invested in, as evidenced by the new plant at Eastport in Auckland. Alternative, carbon-neutral fuels is another technology. RG: And recycled materials? LM: Yes. I’ve been working with Graeme Norton from a company called the 3R Group who deal in product stewardship, a concept that involves taking a product back and finding uses for it. A key initiative from a concrete perspective is Resene’s Paint Wise scheme, which feeds into Golden Bay Cement and Firth Industries’ “Paintcrete” product for masonry blockfill. RG: How is the development of “Paintcrete” progressing? LM: Well let’s just say that I was reading an article recently from the American Concrete Institute which suggested that it is a typical male characteristic to instinctively not believe what other people think. Men think, global warming, it’s just part of a natural cycle, and maybe there’s nothing that mankind can do to prevent it. Whereas women don’t think that way. So I think there’s hope. RG: I know you have a very keen interest in education and training. Is that something which has developed over time, or has it always been important to you? LM: I have always considered it important. If you want your product to be widely used and in an appropriate manner, the easiest market to reach is the student body. Once they have graduated and entered practice they are equipped with the necessary set of skills to utilise that product. RG:
As an industry, do you think we’ve done enough in that space?
LM: Well Fletcher Building certainly has, but I’m not sure if others within the industry appreciate the opportunities that can be created and fulfilled through contact with students. RG: Your involvement with fib has been extensive, dating back to 1996. Are such professional organizations important from a New Zealand perspective? LM: Yes. Discussing topics of common interest with colleagues from around the world can yield extremely useful outcomes. What we see as a problem in New Zealand is really of only minor concern compared to international issues. For instance, the terms of reference for the new fib Special Activity Group (SAG 8) on sustainability, led by Professor Koji Sakai from Japan, are very ambitious and far reaching, cutting across a huge range of cement and concrete concerns.
RG: What specific outcomes has your involvement with fib produced for New Zealand? LM: We succeeded in getting PRESSS technology written into our concrete structural design standard, NZS 3101:2006. We also got fibre reinforced concrete in as part of normal structural concrete design, while lightweight concrete is better served that it had been previously. We are fortunate to be able to present to New Zealand standard committees documentation from European research. That makes it very easy for developments to be accepted here. In Australia they don’t have that advantage. RG: In a similar vein, where do you see trade associations such as CCANZ benefitting the industry? Do they serve a purpose? LM: Lobbying the Department of Building and Housing, and all those other entities in Wellington is important. As is the coordination of pan-industry projects. Activities
Protect your property against graffiti
that for instance Golden Bay Cement or Fletchers wouldn’t undertake by themselves. They’re best done through CCANZ.
The CCANZ library is a wonderful resource. Although a lot of people now prefer to search for information on the internet, I like to use the library. If I have a problem I’m trying to solve I go to the library shelf, pull out a book on my topic, then I’ll see a related book that I’ll consult, and then along-side that book will be another that interests me, even though it may be on a different subject. People talk about reading the bible and flipping it open and there’s your answer to your day’s problem. Visiting the library and reading concrete textbooks is similar to that. It starts ideas going around in your mind and before you know it you’ve solved the problem.
RM: With retirement pending do you look back on your career in the concrete industry and wonder what would have happened if you had taken a different path? LM: No. I’ve watched guys move into management roles and do quite well because their engineering skills have equipped them well. But then they get to the point where they’re bored, people problems mainly. The fun goes out of the job. And I thought “I’m not going to let that happen to me”. I resisted the move to the corporate ladder on the administrative side and just focused on being the best I could at engineering and keeping up to date with that. RM: Your late wife, Marilyn, tragically passed away recently. Obviously a terrible moment in your life. I had dinner with you shortly after the funeral and was struck by your fortitude. I just wondered how you managed to cope? LM: I think it’s just the family, friends, work colleagues. I also think I came out of it stronger, but it’s painful. RM: How will you occupy your time during retirement? You have never struck me as the type of man able to sit still for very long. LM: I’ve got hobbies at home and have six grandchildren. I will do some wood working, gardening and tidy things up around the house. I also plan to see the pyramids. I do a bit of consulting. I still want to stay involved with Auckland University and work with Fletchers in terms of securing research funding. I’m currently on the supervising panel for a PhD student. RG: Do you have a message for young people thinking of entering the concrete industry?
Unsightly graffiti over your property not only looks bad, but it is likely to attract more graffiti. New Resene Uracryl GraffitiShield is a high performance low VOC waterborne two pack urethane designed to provide a clear protective finish to protect your property against graffiti. Once cured, if graffiti does occur, it can be removed using Resene Graffiti Cleaner without the need to repaint the area. Graffiti is often called a gateway crime – left unaddressed, taggers often progress to more serious crimes, so it pays to tackle any graffiti that you do see promptly. For more information on Resene Uracryl GraffitiShield see Data Sheet RA58 or your Resene ColorShop.
LM: It’s a dynamic industry. There is a perception amongst government that concrete is an “old technology” and should therefore be excluded from research funding. Well that’s just crazy. The concrete industry is evolving, and keeping up with the times. RG: A last word? LM: Don’t be scared of change. It’s inevitable. RG: Thank you Len. Good luck.
0800 RESENE (737 363 www.resene.co.nz
18674 GraffitiShield Concrete 1/3v ad.indd 16/03/11 11 12:20 PM volume 55 issue 1 MARCH/APRIL 2011 1 || concrete
THE ROB ROY HOTEL THERE AND BACK AGAIN
The Victoria Park Tunnel project is the first of the Government’s seven roads of national significance to be built. The project will upgrade 2.2km of State Highway 1, from the Auckland Harbour Bridge to the Wellington Street motorway over bridge, and will remove the last remaining traffic bottleneck on the central Auckland motorway system – but one modest, though not insignificant building, stood in its way. 12 concrete
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It is anticipated that the Victoria Park Tunnel project will deliver significant growth benefits to the Auckland region when it is finished, by improving access to markets and giving freight operators more reliable access across the Waitemata Harbour and through to the Auckland CBD and Port. The project comprises a 450 m cut and cover tunnel under Victoria Park for three northbound traffic lanes, widening the motorway through St Marys Bay by one lane in each direction, and refurbishment of the Victoria Park viaduct to carry four southbound traffic lanes. Standing in the way of the tunnel component was the historic Rob Roy Hotel (more recently known as the Birdcage), constructed in 1885 and listed as a Category II Historic Place. Resource Management Act designation conditions required that the listed building be preserved and the New Zealand Transport Agency [NZTA] agreed that the building should be relocated away from the path of the motorway tunnel. After consultation with the community, the NZTA decided to go beyond the designation conditions and return the building to its original position, once the tunnel has been completed. The Victoria Park Alliance, made up of constructors Fletcher Construction and Higgins, designers Beca and Parsons Brinkerhoff as well as the NZTA, invited Dunning Thornton Consultants to carry out the detailed strengthening and moving design because of their previous experience moving the Museum Hotel in Wellington and the Waihi Pumphouse. The first step in the process was to strengthen the building structure to current seismic code requirements – this would also provide the strength and stiffness it required for the move. Together with improving the timber floor and ceiling diaphragms, the rear walls of the building were sprayed with concrete to create shear walls – the primary bracing element for the building. The detailing of the shearwalls resulted in minimal intervention to the heritage fabric. The rear brick walls had originally been rendered (plastered) and (now back in the initial location) the new concrete has been rendered to reinstate the original appearance. The next step was to support each of the brick walls at ground level with concrete “sandwich” beams; matching parallel beams on each side of the wall, post-tensioned together to carry the loads from the walls to 14 sliding bearings. These bearings were located on four, stiff, precision-cast concrete ‘runway’ beams. These deep T-beams were required to span variable, soft ground and large culverts without succumbing to differential settlement. The brick building needed a level runway to avoid subsidence cracking. The beams performed well, with measured deflections less than 2 mm. The building made the journey in a slow and measured manner over a two day period from 31 August to 1 September 2010, without incident and without any damage to its precious heritage façade. Following the completion of the southern portal of the tunnel the building was returned to its original position on 12 April 2011, although it was rotated seven degrees, anti-clockwise, for one side to be parallel to the new alignment of Franklin Road. Across both legs the project captured the interest of the media and the public at large. The result has been a win for the community with the sustainable retention, recycling and re-use of an important Auckland heritage icon for future generations to enjoy. Dunning Thornton won the Excellence in Concrete for the Community Award for their work on moving the Rob Roy Hotel at the 2010 Concrete3 Sustainability Awards.
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DECORATIVE CONCRETE
COLOUR IS KEY
Herne Bay Villa Renovation Key to the complete renovation of this villa in one of Auckland’s most sought-after suburbs was the creation and extension of a contemporary living area at the rear of the property which utilised Peter Fell coloured concrete both inside and out. One of the benefits of concrete is its durability, which enables it to be used in both interior and exterior settings to create a seamless flow. Typically, coloured concrete features in those parts of the house with high requirements in terms of wear, such as the kitchen or dining room. Here, coloured concrete is used in the laundry and kitchen, then flows out onto the deck. By using a 150 mm deep drainage channel there was no need for a step-down from the house to the deck, enabling an uninterrupted transition between the indoor and outdoor space. Using the same coloured concrete also contributed to a sense of continuous space, as did a seamless joint between the concrete and timber internal floor areas. The result is an open and uncluttered living environment, leading to an expansive outlook across the garden. The concrete steps present a slight overhang on both the side and front edges which gracefully lifts their appearance. The front step 14 concrete
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of the house was also similarly cast in concrete to ensure subtle continuity across the villa. All the concrete areas are elevated through the use of the Hibond flooring system. Permanent formwork systems such as Hibond enable rapid construction, a tidy soffit and are suitable for exterior work. Simple and modern, this villa extension is an excellent example of how quality detailing can lift a project from acceptable to exceptional. Key to its success was the ability of functional and elegant coloured concrete floors to merge interior and exterior environments, as well as allow the heritage and modern elements of the villa to integrate with ease. Architect: Salmond Reed Contractor: Shore Build Ltd
FOR BOTH INTERIOR AND EXTERIOR USE, ACROSS RESIDENTIAL, COMMERCIAL AND CIVIC APPLICATIONS, DECORATIVE CONCRETE OFFERS AN ALMOST UNLIMITED RANGE OF OPTIONS TO CREATE AESTHETIC APPEAL. WHAT BETTER WAY TO EXPERIENCE THE POSSIBILITIES ACHIEVABLE IN CONCRETE COLOUR, TEXTURE AND FINISH THAN TO TAKE A LOOK AT RECENT PROJECTS INVOLVING WELL RESPECTED CONCRETE COLOUR SPECIALISTS PETER FELL LTD, WHO HAVE BEEN PRODUCING EXCEPTIONAL COLOURED CONCRETE ENVIRONMENTS FOR 20-YEARS.
Wairakei International Golf Course As with concrete floors, the use of colour, texture and finish can combine to produce absolutely unique wall panels. While the decorative possibilities of concrete wall panels has not yet been fully realised in New Zealand, the dramatic results on display at Wairakei International Golf Course’s new shop will go someway towards advancing their uptake. Seeking a different expression within the facility but with materials that complimented existing buildings, architect Neville King from Rosetta Stone Architects chose precast concrete panels.
to ensure no warping or twisting, and most importantly, no leakage. Heated casting beds and curing blankets helped achieve uniform curing to minimise potential colour variation.
Strict attention was paid to the concrete colour palette, with both client and architect working closely with the Peter Fell team to choose the most appropriate colour for the wall panels.
The outcome is a deceptively simple and striking building that reflects the brand values of the course. The client is thoroughly pleased, and rightly so as it is a tremendous job that all involved can be proud of.
Within the shop the coloured panels line the entrance, which also boasts a floor of the same colour. The 125 mm thick panels were produced at the Palmer Mill precast yard in Taupo with concrete supplied by Firth. The timber surface effect was created by using rough sawn 150 mm board laid very tightly within the Reid Swift Form system
Client: Wairakei International Golf Course Architect: Rosetta Stone Architects Building Contractor: C.J. Fisher LTD Precast Concrete: Palmer Mill Construction LTD
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Greenmeadows New World Supermarket, Hawkes Bay Seeking to reinterpret the typical supermarket design and present an entirely fresh image, this bold and innovative addition to the New World collection of stores consists of a building with a total floor area of 3852 m2, as well as a feature mezzanine. The new building provides the Foodstuffs group with a fantastic show piece – demonstrating to the public that New World is committed to providing a total shopping experience. The success of the overall project is testament to the client’s clean vision, and is a superb example of how collective skills and experience can result in a perfectly executed design that is stunning and original.
maintenance. Secondly, colour. Selected from Peter Fell’s comprehensive range, the earthy shade was specifically chosen to create a sense of welcome and contribute to the overall visual theme. Thirdly, finish. A light salt and pepper grind was used to ensure flatness and increase durability. Finally, sealer. The Retroplate system was used to improve density and seal the floor.
The use of a more natural flooring aesthetic, including warm colours and a sophisticated material palette, provides shoppers with a relaxed and inviting environment. Key is the concrete floor, the innovative specification for which came about following a fact finding mission to the US by Foodstuffs staff and their consultants, which yielded four primary stipulations.
Due to poor ground conditions, approximately 450 timber piles were driven into the ground as a means to support the structure and floor slab. In-situ concrete foundations support precast panels, columns and structural steel frames with a Longrun Dimond 630 Roof.
Firstly, a post tensioned floor slab. Constructed by Conslab, the slab provides a joint free finish eliminating the need for sawcuts while providing an anticipated reduction in long-term 16 concrete
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Client: Foodstuffs Properties (Wgtn) Ltd Architect: Architecture HDT Ltd Contractor: Mainzeal Property and Construction Ltd Flooring subcontractor: Conslab LTD Ready Mixed Concrete: Allied Concrete LTD
Wairepo Swamp Walk Initiated by the public art team at Auckland City Council, the striking new Wairepo Swamp Walk opened in December 2010. Combining audacious design and precise execution, the walk is one of the outstanding civic projects of 2010 to utilise concrete. The walkway represents exceptional urban design principles and practices, advanced by Auckland City in partnership with renowned artist Billy Apple. Engaged by the Council to develop a concept for the walkway that runs between Sandringham Road and the Eden Park stadium, Apple drew inspiration from ‘the golden ratio’ as well as New Zealand’s two most famous sporting colours. The resulting walk, the first purpose built shared zone in Auckland City, unequivocally sets the scene for an Eden Park experience, particularly with Rugby World Cup on the horizon. Contrax Ltd specified the concrete mix design, utilising Peter Fell’s Super Black for the intense dark sections of the walkway, and Peter Fell titanium dioxide for the white sections. The aggregate is North Island basalt and South Island silica, making for a truly New Zealand proprietary aggregate mix design. The formwork and stainless edge system was specially designed by Contrax to achieve the required accuracy. Executing the pours
was a challenge given the amount of rain during the construction. At one point marquees had to be erected to protect the concrete. The attention to detail and workmanship demonstrated by Grant O’Sullivan of Contrax deserves special mention. The Wairepo Swamp Walk is an example of how a high profile project can ensure success through the early involvement of a knowledgeable contractor, whose experience with coloured architectural concrete meant an appropriate specification was followed from the project’s beginning. Client: Auckland City Council Artist: Billy Apple Consulting Designers: Opus International Consultants Main Contractor: Fulton Hogan Ltd Concrete Contractor/Design Consultant: Contrax Ltd
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concrete 17
PERVIOUS CONCRETE: AN introduction
Image courtesy National Ready Mix Concrete Association (U.S.)
Image courtesy SvR Design – Civil Engineer and Landscape Architect
Pervious Concrete…. Past, Present and Future Rob Green, Manager / Engineer - Concrete Division, Higgins Group Holdings Limited Imagine a concrete pavement that will reduce the flow rate of water entering the stormwater system, filter out stormwater contaminants, and help reduce urban temperatures. Pervious concrete pavements will do all this, and more. Also referred to as porous concrete or no-fines concrete, pervious concrete achieves its high porosity through an interconnected network of voids, and is used primarily in pavement applications. Pervious concrete contains little or no fine aggregate (sand) and just enough cement paste to bind the coarse aggregate while preserving a void interconnectivity of around 15-25% in its hardened form.
Past The earliest use of no-fines concrete can be traced back to the UK, when in 1852 several houses and a 61 m long / 2 m high sea barrier were constructed.1 The use of no-fines concrete remained confined to occasional building construction and other limited non-pavement applications until after World War II. In the wake of an acute housing shortage post-war, which led to an unprecedented demand for bricks that could not be met, the European construction industry looked increasingly towards no-fines concrete as it required considerably less cement per volume than conventional concrete. The growing adoption of no-fines concrete for building purposes in turn led to trials of its use in alternative applications. During the mid 1960’s an experimental no-fines surface pavement layer was cast over a conventional rigid pavement in Nottinghamshire, England, with the intention of exploiting the drainage properties of no-fines concrete. Initially the pavement performed well, but after 10 years, deterioration as a result of freeze-thaw and hydraulic pumping actions was considerable. Despite the outcome, the potential for no-fines concrete in pavement applications was sufficient for engineers elsewhere to begin further trials. In Florida, experiments involving no-fines concrete pavements were conducted for use in parking lots, one of which was patented as “Porous Pavement”, and included a pavement design and the
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PERVIOUS CONCRETE: AN introduction
40% EVAPO TRANSPIRATION
38% EVAPO TRANSPIRATION
10% RUNOFF
20% RUNOFF
25% DEEP INFILTRATION
25% SHALLOW INFILTRATION
NATURAL GROUND COVER
21% DEEP INFILTRATION
21% SHALLOW INFILTRATION
10% – 20% IMPERVIOUS SURFACE
35% EVAPO TRANSPIRATION
30% EVAPO TRANSPIRATION
30% RUNOFF
20% SHALLOW INFILTRATION
55% RUNOFF
15% DEEP INFILTRATION
35% – 50% IMPERVIOUS SURFACE
10% SHALLOW INFILTRATION
5% DEEP INFILTRATION
75% – 100% IMPERVIOUS SURFACE
Figure 1: Schematic model of the impact of urbanisation on storm water (Source: Environmental Building News, 1994)
use of a proprietary adhesive. Later, another no-fines concrete was promoted in Florida, resulting in the term “Pervious Concrete” being patented. Around this time, experimentation with the use of porous concrete for edge drains and hard shoulders was also being carried out in France and in the USA. In the 1980’s the use of no-fines concrete pavements and permeable bases began to become more widespread across the USA with pavements being laid in many states including, Florida, New Mexico, Utah, California, Illinois, Oklahoma and Wisconsin. This steady growth in demand stimulated and encouraged the current phase of pervious concrete pavement development.
Present Stormwater Management The primary attribute of pervious concrete is the interconnected void structure which allows the passage of water from the surface through to the sub-base when used in pavement applications. Urbanisation has led to the rapid growth of impermeable paved areas which require large scale stormwater management systems. This has a distinct influence on natural stormwater pathways - see Figure 1. Specifically, as the area of permeable land diminishes following urbanisation, the ratios of evapotranspiration, run-off, shallow penetration and deep penetration of storm water changes dramatically. Urban stormwater carries with it hydrocarbon pollutants such as oil and fuel which have been deposited on pavements from motor vehicles. Standard impermeable pavements direct this contaminated stormwater in the direction of natural waterways, with detrimental effect. Pervious concrete pavements can however, help to minimise such pollution. As stormwater flows through the network of voids to penetrate the soil beneath, pollutants
are reduced through natural attenuation and/or biological degradation until they become inert.2 The environmental benefits of this filtration process are a key contributor towards wider sustainable development. Increasing the percentage of pervious concrete pavements in urban design therefore constitutes an effective means of restoring natural stormwater pathways, and thus reducing the need for large-scale stormwater management systems. Heat Island Effect Urbanisation has resulted in the increased concentration of the built environment over greater areas. Comprised of structures and pavements constructed predominantly using high mass materials, the built environment has in essence become a gigantic heat store. During the day it collects solar radiation in the form of heat energy, and then releases it at night, increasing air temperatures, particularly where there is little wind to disperse this radiating heat. A direct consequence of this phenomenon, known as the heat island effect, is the increased uptake of energy intensive space cooling devices such as air conditioning units. The high albedo effect of pervious concrete means it absorbs much less solar heat than darker surfaces such as asphalt. In addition, the open pore structure of pervious concrete compared to standard concrete, results in even less heat being absorbed and subsequently released. Both these characteristics of pervious concrete help to lessen the impact of the heat island effect. A further positive environmental benefit of pervious concrete in terms of minimising the heat island effect is its ability to enable successful tree planting in built-up urban areas. The open pore structure of pervious concrete allows for trees roots to have ample access to water and air that will ensure their well-being, and in turn provide the cooling effect of the tree’s shade.
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concrete 19
PERVIOUS CONCRETE: AN introduction
Maintenance Clogging and ravelling are two characteristics of pervious concrete pavements perceived as barriers to its more widespread uptake. However, through appropriate maintenance practices these issues can be effectively managed. Clogging occurs when the voids at, or near, the surface of pervious concrete pavements become blocked with sand, soil, leaves and other similar debris carried into the void structure through compression or stormwater flow. Clogging can reduce the pavement’s capacity to allow stormwater to drain through to the sub-base. Typical permeability flow rates through pervious concrete range from 120 l/m²/min to 320 l/m²/min.3 A recent study4 indicated that clogging with sand has a minimal effect on the permeability of pervious concrete pavements even when subjected to 100-year rain event simulations. A similar study5 also suggested that clogging is primarily the result of poor routine maintenance, or where there were inappropriate mix-design and placement, such as excessively wet mix or over compacted mixes, have occurred. Maintenance systems for pervious concrete pavements are still under development, but vacuuming the pavement surface is a recommended means of removing loose debris. Other potential cleaning options include power blowing and pressure washing. In fact, the US National Ready Mixed Concrete Association6 has reported that pressure washing of clogged pervious concrete pavements can restore between 80-90% of original permeability. The dislodgement of aggregate from the surface of pervious concrete pavements is referred to as ravelling. Although recommended practice in terms of prevention and rehabilitation is relatively unclear, surface ravelling has been identified more commonly occurring within the first few months of a pervious concrete pavement’s use. Potential causes range from the tyre action of turning heavy vehicles or where the mix was too dry at the time of placement.7 Surface ravelling may also occur at sawn or formed joints.
The continuing development of pervious concrete as a pavement medium is ensuring its potential to make a considerable contribution towards a sustainably built environment. 1 Ghafoori, N. & Dutta, S. (1995). Development of No-Fines Concrete Pavement Applications, Journal of Transportation Engineering, May/June 1995. 2 Kevern, J., Wang, K. & Schaefer V. (2008). Pervious Concrete in Severe Exposures, Concrete International, July 2008. 3 Tennis P.D., Leming M.L. & Akers D.J. (2004). Pervious Concrete Pavements, Portland Cement Association, 2004. 4 Haselbach, L.M., Valavala, S. & Montes, F. (2006). Permeability Predictions for Sand Clogged Portland Cement Pervious Concrete Pavement Systems, Journal of Environmental Management Systems 81 (2006). 5 Delatte, Prof N. (2007). Portland Cement Pervious Concrete Pavement: Field Performance Investigation on Parking Lot and Roadway Pavements, Final Report, Cleveland State University, December 2007. 6 National Ready Mixed Concrete Association. (2008). Pervious Concrete When it rains…it drains, Pervious Concrete Frequently Asked Questions, 2008, http://www.perviouspavement.org/benefits,%20structural.htm 7 Delatte, Prof N. (2007a). Portland Cement Pervious Concrete Pavement: Field Performance Investigation on Parking Lot and Roadway Pavements, Final Report, Cleveland State University, December 2007, p 8. 8 Wang, K., Schaefer, V.R., Kervern, J.T. & Suleiman, M.T. (2006). Development of Mix Proportion for Functional and Durable Pervious Concrete, NRMCA Concrete Technology Forum: Focus on Pervious Concrete, Nashville, TN, May 2006. 9 Kevern, J., Wang, K. & Schaefer V. (2008). Pervious Concrete in Severe Exposures, Concrete International, July 2008.
Future Most development of pervious concrete pavement technology has taken placed since the 1980’s, primarily driven by environmental concerns. The acceptance of pervious concrete as a LEED® accredited pavement material demonstrates its success in providing genuine construction solutions with a positive environmental benefit. The aesthetic potential for pervious concrete pavement surfaces cannot be matched by standard impervious pavements, a characteristic that proponents of pervious concrete pavement are eager to exploit through the introduction of colour and texture as a means to add value to an already highly credentialed pavement material. There is, however, continuing doubt about the performance of pervious concrete in terms of strength and durability, with attempts to improve these characteristics generally met by reductions in permeability. Trials undertaken included the addition of fibres8 9, viscosity modifying admixtures, hydration stabilisers10, styrene-butadiene rubber11, epoxy vinyl acrylic emulsions12, latexmodified portland cement13 and waste latex paint.14
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Test methods used for “normal” concrete are not often applicable to pervious concrete, while specific pervious concrete tests and specifications are still under developmental. In a 2007 conference paper Mark Offenberg, lead editor for ACI Committee 522 on pervious concrete outlined future priorities, “…the greatest need in the pervious concrete industry today is for researchers to study test methods for this material…….Basic test methods will ensure the quality of pavements placed, give owners and regulators a sense of comfort in the product, and allow the industry to improve and optimise the concrete mixtures.”15
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10 Bury, M. & Mawby, C. (2006). Pervious Concrete Mixes: The Right Ingredients And Proportions Are Critical to Success, Concrete Construction, April 2006, http://www.concreteconstruction.net/ industrynews.asp?sectionID=707&articleID=283260 11 Youngs, A. (2006). Pervious Concrete. The California Experience, 2006, http://www.ecst.csuchico.edu/__depts/cim/documents/Youngs_Pervious_ Concrete_2006.pdf 12 Monahan, A. (1981). Porous Portland cement concrete; the state of the art, U.S. Army Engineer Waterways Experiment Station, Structures Laboratory, Vicksburg, Mississippi, 1981. 13 Walters, D.G. (2006). Significance of Tests and Properties of Concrete, Ed. Lamond & Pielert, ASTM International, May 2006. 14 Mohammed, A., Nehdi, M. & Adawi, A. (2008). Recycling Waste Latex Paint in Concrete with Added Value, ACI Materials Journal, Technical Paper 105-M42, July-August 2008. 15 Offenberg, M. (2007). The Future of Pervious Concrete Pavements, 23rd Biennial Conference of the Concrete Institute of Australia, Adelaide, Australia, October 2007.
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A NEW ZEALAND INVESTIGATION
THE FIRST STEPS DOWN A PERVIOUS PATH STEVE CROSSLAND, SALES ENGINEER, FIRTH INDUSTRIES LIMITED
Established in 2010 by CCANZ, the Master Concrete Placers’ Association and a number of concrete suppliers, the Pervious Concrete Industry Committee seeks to raise awareness and advance the uptake of pervious concrete. This task will involve the development of suitable mix designs, testing methods, placement procedures, and ultimately a standard specification.
The committee’s initial 3-stage work programme was comprised of a series of trials, culminating with the installation of a pervious concrete footpath in Albany on Auckland’s North Shore. 1. Laboratory Trials - Design and test an appropriate mix using local aggregates, and in so doing begin to develop an understanding of what is most ideal for New Zealand conditions. 2. Trial Panels – Cast a set of panels to provide experience in batching, mixing and handling pervious concrete. Also determine the appropriate water content, mix consistency at discharge, and surface texture of the compacted material. 3. Trial Footpath - Prepare and install a pervious concrete footpath, with an emphasis on placement and workability, compaction method, surface texture, curing process, in-situ permeability, and cross section analysis of core samples.
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concrete 21
NZ PERVIOUS CONCRETE
Background and Methods Prior to beginning the series of trials a literature review was conducted. Key amongst the resources gathered was the American Concrete Institute’s (ACI) Report on Pervious Concrete: 522R-10, which provided the trials’ initial mix design calculation procedure. Currently there are a limited number of ASTM (American Society for Testing and Materials) Standards specifically for use with pervious concrete. However, the ASTM Subcommittee Committee C09.49 on Pervious Concrete is developing test methods for compressive strength, flexural strength, in place density/porosity, and in place permeability. The BS 1881-113:1983 Testing Concrete. Method for Making and Curing No-Fines Test Cubes was used but with cylinders instead of cubes. ASTM C1688/C1688M-10a Standard Test Method for Density and Void Content of Freshly Mixed Pervious Concrete and ASTM C1701/C1701M-09 Standard Test Method for Infiltration Rate of in Place Pervious Concrete were also used to test the material. Laboratory Trials The laboratory trials were conducted at Firth Industries using an initial mix design based on ACI Report on Pervious Concrete: 522R-10. Three separate laboratory trials were conducted to determine the mix design that would be used for the subsequent panels and footpath. During the trial mix process adjustments to aggregate, sand and cement content were required. BS 1881-113:1983 was adopted to test compressive strength, although standard 100 mm diameter test cylinders were used instead of test cubes. This standard also prescribes the use of a Proctor hammer to consolidate the pervious concrete. However, for the purposes of the trial the standard Proctor hammer was modified by welding a circular steel plate to the bottom. The curing process consisted of stripping the test cylinders after 2-days and submerging them in water until the bubbles ceased to rise. They were then allowed to drain, put in a sealed plastic bag and placed in the curing tank at a standard temperature of 21±2°C. ASTMC 1688/C1688M-10a was used to give an indication of void and density of the freshly mixed pervious concrete. The test method involves filling a standard yield pot in two layers, then consolidating with a Proctor hammer (20 blows per layer), and then filling the pot with water. The only variation for the trial was the use of the modified Proctor hammer. Description
Compressive Strength 7 days
Compressive Strength 28 days
Trial Mix 1
8.7 MPa
16.6 MPa
Trial Mix 2
11.7 MPa
14.0 MPa
Trial Mix 3
20.7 MPa
19.6 MPa
Table 1. Compressive strength results for trial mix designs
During the laboratory trials the correct cement content of the mix in its plastic state was determined, while an indication of the strength of the paste in the hardened mix was gauged by looking at the compressive strength test failure mode. It also became apparent that there was a very fine line between too little and too much water when mixing. Only 80% of the total
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water content was initially mixed, with careful water addition thereafter. It was observed both in the laboratory and at the plant that some mixes started to “ball” in the mixer, requiring subsequent cautious water addition to achieve the correct workability. Casting the test cylinders to BS 1881-113:1983 with the modified Proctor hammer formed a noticeable joint between the layers. However, due to its midway location, the joint was deemed not to have any significant influence on compressive strength. Trial Panels Prior to carrying out the trials on the footpath, two panels were poured using the selected trial mix. Placed on plastic sheeting, on top of a concrete slab, the trial panels were 2 m x 1 m long and 100 mm thick. Workability was checked using the “balling” method, which verified the precise amount of water in the mix. The concrete was screeded with a 10 mm riser strip, hand troweled, and then hand rolled longitudinally and laterally to remove any undulations in the surface. The panels where immediately covered with plastic following finishing, and left for 10-days. Description
Compressive Strength 7 days
Compressive Strength 28 days
Panels
12.7 MPa
18.1 MPa
Table 2. Compressive strength results for trial panels
The production of the panels revealed that the mix consistency and the paste for the surface texture were good. Compressive strength results were satisfactory. Permeability tests were not conducted. The trial was invaluable as preparation for the batching and placing of pervious concrete for the footpath. Trial Footpath The section of footpath on the North Shore selected for the pervious concrete trial was approximately 21 m long and 1.5 m wide. Scalar penetrometer tests of the sub grade revealed it to be sandy clay and extremely hard. The existing concrete footpath was removed and the sub base excavated to accommodate a 100 mm subgrade of 2-5 mm clean chip, which was laid on a single layer of Syntex GNP Class-A filter cloth. A 75 mm diameter Novaflow drain was laid along the full length of the path and also wrapped in the filter cloth. During placement the concrete truck was able to chute directly on to the sub grade. The pervious concrete was screeded and racked off using 10 mm riser strips, and then consolidated longitudinally with a mechanical roller screed, and across its width with a hand roller. The saw cut joints were made using a “Pizza Cutter” roller. It was observed during placing that the mechanical roller screed could have been heavier, which may have resulted in better consolidation of the concrete and in turn higher compressive strength results. Installing the footpath also reiterated the importance of using hydration stabilisers and retarders to ensure the concrete was workable when it arrived on-site. Description
Compressive Strength 7 days
Compressive Strength 28 days
Footpath
16.8 MPa
17.5 MPa
Table 3. Compressive strength results for trial footpath
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The curing procedure saw the pathway covered with 150 micron plastic sheeting within 20 minutes of being finished, and left for 10-days. No curing compounds were used. ASTMC 1701/C1701M-09 was used to determine infiltration testing. As part of the pre-wet procedure 3.6 litres of water was poured on the test area and timed. If the 3.6 litres of water takes less than 30 seconds to flow from the surface the test requires a further 18 litres of water, if greater than 30 seconds then only 3.6 litres of water is used. For this trial 18 litres of water were required. The test results were satisfactory. Two cores were taken adjacent to where the infiltration tests were conducted in order to demonstrate correlation between the infiltration rates and the densities of the cored concrete. The cores yielded the results in the table below.
influence density, void ratio and in turn permeability. Also, a laboratory infiltration or percolation test could potentially be trialed. As an initial step towards developing an enhanced understanding of pervious concrete technology within a New Zealand environment, along with a set of robust guidelines for production, installation and maintenance, the trials have provided valuable information. 1. Laboratory trials - Cylinder compaction with modified Proctor hammer 2. Laboratory trials - Sealed cylinder in curing tank 3. Laboratory trials - Mode of failure 4. Trial panels - Screeding off using 10mm Riser strip 5. Trial panels - Rolling longitudinally 6. Trial panels - “Balling” 7. Trial footpath – Filtercloth, wrapped Novaflow drain and 2-5 mm chip sub base
Description
Compressive Strength 28 days
8. Trial footpath - Mechanical roller screed
Footpath Core O
10.5 MPa
9. Trial footpath – Pizza cutter control joint
Footpath Core X
8.5 MPa
10. Trial footpath – Plastic sheet cover for curing
Table 4. Compressive strength results for trial footpath cores
11. Trial footpath – Infiltration test 12. Trial footpath – Core samples (bottom of core at top)
Next Steps Overall the series of trials was very encouraging, and the Pervious Concrete Industry Committee is currently formulating a follow-up work programme. Possible objectives for subsequent trials may be to investigate how different methods of on-site compaction
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Producing Pervious Pavements Hints for the engineer, contractor on placement of pervious concrete – BY MATTHEW 0FFENBERG If you flip through the pages of a typical issue of Concrete International (the ACI’s monthly journal) or any other concrete industry journal, you’ll see articles about supplementary cementitious materials, high-performance concrete, self-consolidating concrete, vapor retarders, and strength acceptance testing. This article, however, is not typical. It covers a low strength, dry, porous concrete that is so simple, it’s complicated. Although its properties may make pervious concrete a tricky material to work with, they can also make it a developer’s friend. 24 concrete
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Fig. 1 (left): Pervious concrete can be cast on an open-graded gravel base where subgrade soils are primarily clay
One of the key features of pervious concrete is that it can be used to create a structurally sound pavement that drains stormwater thereby reducing runoff and replenishing groundwater supplies. Construction of pervious concrete pavements is different from construction of plain concrete pavements in that the contractor is responsible for an extra level of quality control. Acceptance of the material is not based on strength, smoothness, and thickness but on porosity, smoothness, and thickness. Therefore, it takes a different mindset. Pervious concrete is actually no-fines (or low fines) concrete with a low water-cement ratio and is typically used in low volume applications. Hardened pervious concrete can have a compressive strength ranging from 1000 to 4000 psi (7 to 28 MPa). More important, though, is the void content - pervious concrete pavements have been placed with 15 to 35% void ratios. Every party involved in the construction of a pervious concrete pavement should keep in mind the functions of the pavement: structural support and stormwater management. The process starts with proper planning and design in the engineer’s office, continues through proper staging and job - site control with the general contractor, and finishes with proper construction by the concrete contractor. This article helps to identify each party’s responsibility and identify the keys for their success. However, we will focus primarily on the concrete contractor’s role in the success of the pervious pavement. WHY PERVIOUS CONCRETE? In recent years, the engineering and environmental communities have noticed troubling effects caused by development - major changes to stream, lake, and river depths caused by uncontrolled stormwater runoff from developed real estate. Rainwater tends to run off of developed sites (rather than being retained by soil or vegetation), causing stream bank erosion, waterway pollution, and downstream flooding. The government now requires control of storm water runoff for developed sites. A typical fix is to use stormwater retention ponds to slow the rate of stormwater discharge from the site. These ponds work well but are costly to the developers as they consume large amounts of valuable real estate. Pervious concrete allows parking areas to be covered with a material that allows stormwater to pass through. This reduces stormwater runoff rates, allows infiltration of the precipitation, and facilitates the recharge of groundwater supplies. Another common use of pervious concrete pavements is to reduce the impact of development on trees. A pervious concrete pavement allows the transfer of both water and air between the roots and the ground surface. Pervious concrete pavements have been successfully placed inside the drip line of urban trees without adversely affecting their health. To ensure the success of this type of system, it is imperative that the roots of the tree are not damaged during construction operations, especially during earthwork and grading operations. TYPICAL SECTIONS As with plain concrete, pervious concrete may be built on an opengraded base course, or on suitable site soils. In Florida, the material is often placed on the native sandy soils, which allow percolation and infiltration of the stormwater. In other states, where subgrade soils may be clay, the pervious concrete is cast on an open-graded gravel base such as a No. 57 (ASTM C 33)1 rock (Fig. 1). This allows a large volume of retention under the pavement and provides extra
structural support. It is important that the structural support chosen for the pervious pavement not be greatly affected by moisture penetrating lower pavement layers. CONSTRUCTION BASICS As mentioned earlier, construction of a pervious concrete pavement is quite different from ordinary concrete. There are four key elements to the success of a pervious pavement surface: 1. Subgrade preparation. The subgrade should be uniform and properly compacted; 2. Concrete mixing water. The concrete should have the correct amount of water; 3. Concrete compaction/finishing. The concrete should be compacted and finished without excessive effort; and 4. Sufficient curing. Curing should be performed in a timely manner and of sufficient duration. Just like any other pavement system, uniform subgrade compaction is critical for a successful pervious concrete pavement. Further, it is important not to over compact the subgrade soils. A key design feature of a pervious concrete pavement system is its permeability. The permeability of subgrade soils decreases nonlinearly with increases in density. Thus, if subgrade soils are compacted beyond their design limits, then the infiltration rate of the soil will decrease and the pavement will not drain the desired amount of runoff. The Florida Concrete and Products Association,2 for example, recommends compaction to only 92 to 96% of the modified proctor maximum density (ASTM D 1557)3 for sandy subgrades. Where this might seem quite soft compared with typical compactive efforts, uniformity is key. For silty or clay soils, the level of compaction will depend on the specifics of the pavement design. Further, care should be taken, in this situation, not to over compact a soil with swelling potential. As with any concrete pavement, the subgrade should be moistened before concrete placement, and wheel ruts from the concrete trucks should be raked and recompacted. The most complicated skill for a pervious concrete contractor to acquire is judging the proper quantity of mixing water in the fresh, no-fines concrete. This material is sensitive to minor changes in water content, so field adjustment of the fresh mixture is almost always necessary. Having the proper quantity of water in the concrete is critical because too much water causes the pores to collapse, and too little water prevents proper curing of the concrete, which will lead to a premature surface raveling failure. Corrective action for either of these scenarios is removal and replacement of the concrete. Experienced contractors learn to judge the proper water content in the fresh concrete by visual inspection. Key characteristics to note include the presence of open pore space in the compacted concrete and a light sheen from the free water in the concrete. The concrete supplier should take some responsibility in this as well. Drivers should be trained to understand the basics of pervious concrete. A pervious concrete pavement may be placed with either fixed forms or a slipform paver. Nevertheless, the simplest approach to placing pervious concrete is to cast it in forms that have a riser strip on the top of each form such that the strike off device is actually 3/8 to 1/2 in. (10 to 13 mm) above the final elevation of the pavement. As the concrete leaves the truck, it should be
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raked to an approximate elevation (Fig. 2). Strike off may then be performed by truss screed, roller screed, or straight edge (for small areas). After striking off the concrete, the riser strips are removed and the concrete is rolled to the proper elevation. Rolling compacts the fresh concrete to provide strong bond between the paste and aggregate and creates a smooth riding surface. Caution should be exercised in rolling to prevent excessive force, which would cause the voids to collapse. Test panels, local experience, or both will provide necessary information on proper riser strip thickness and rolling technique. In any case, rolling should be performed immediately after strike off. The roller itself should be specially designed to roll pervious concrete in that it is weighted properly, protected from warping, and covers the entire lane width. It should be noted that it is possible to roll slip-formed pavement; however, if formed properly, the pavement will be adequately compacted and have the necessary surface smoothness. Sod rollers are not practical for rolling pervious concrete in warm climates. Sod rollers require an extended finishing time to achieve a sufficiently flat and smooth surface, which lengthens the time (to greater than 20 min.) before curing may start.
Fig. 2: Concrete should be raked to an approximate elevation as it leaves the truck Fig. 3: Pervious concrete should be cross-rolled when fresh to smooth it out
Occasionally, extra steps are necessary to provide the desired finish on pervious concrete. Where ride quality is an issue, the fresh concrete should be cross-rolled to smooth out any flatness deviations (Fig. 3). Additionally, it may be necessary to float the edges of the concrete. It is common to see the rollers not compacting sufficiently at the edges, so the concrete is hand floated to ensure quality all the way up to the form. Pervious concrete can also be tooled. A rounded edge may be desired, for example, adjacent to a sidewalk (Fig. 4). Each of these steps would be done after the initial rolling, but before jointing. Jointing pervious concrete pavement follows the same rules as for an unreinforced concrete pavement,4 with a few exceptions. With less water in the fresh concrete, shrinkage of the hardened material is reduced. Thus, joint spacings may be wider. The rules of jointing geometry, however, remain the same (Fig. 5). Rather than saw cutting, joints in pervious concrete are tooled with a rolling/ jointing tool (Fig. 6). This allows joints to be cut in short time, and allows curing to continue uninterrupted. Proper curing is essential to the structural integrity of a pervious concrete pavement. Curing ensures sufficient hydration of the cement paste to provide the necessary strength in the pavement section. Further, insufficient curing will cause the surface to ravel, in extreme cases, to the full depth of the pavement. Therefore, curing should begin within 20 min. of concrete placement. Plastic sheeting is typically used to retain moisture in the pavement mass for curing (Fig. 7). It should be secured with reinforcement or lumber such that it will be able to stay in place for the full 7-day curing period, in any weather. As pervious concrete should not be specified by design strength, at no time should acceptance be based on strength. More important to the success of a pervious pavement is void content. Thus, acceptance should be based on the unit weight of the in-place pavement being within 5 lb/ft3 (80 kg/m3) of the design unit weight. Density (unit weight) is the only field test required for fresh pervious concrete. Slump and air content tests for conventional concrete are not applicable to a no-fines concrete mixture. If the pervious concrete pavement is an element of the site’s stormwater management plan, the designer should certify that it is functioning 26 concrete
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properly through visual observation of its drainage characteristics before opening of the facility. TROUBLESHOOTING One can imagine a number of things going wrong when placing a concrete pavement. Unfortunately, as with any construction, problems do arise. Minor issues such a slight cracking, discoloration, and deviations from flatness can be resolved by a number of means. There are, however, three major construction field problems with pervious concrete that require removal and replacement as the only option to repair the deficiency: 1. Too much water in the concrete mixture; 2. Not enough water in the concrete mixture; and 3. Insufficient curing of the concrete. The first problem is easy to diagnose, and can usually be caught before the concrete has hardened. If there is too much water in the mixture, the cement paste will fill the voids and seal the surface of the concrete. If the contractor notices this happening with the fresh concrete, the load should be immediately rejected, and the concrete producer notified of the problem. Additionally, the fresh material should be removed before hardening. If this problem is not noticed until after the concrete has hardened, it will adversely affect the stormwater management features of the pavement. Again, the only way to fix it is to remove the deficient section and replace it with new material.
USA PERVIOUS CONCRETE
Fig. 4: The owner may prefer the look of a rounded edge adjacent to a sidewalk
Fig. 6: A rolling/jointing tool may be used on pervious concrete, rather than saw cutting
Fig. 5: Rules about jointing are the same with pervious concrete as with any concrete
Fig. 7: Plastic sheeting is typically used to retain moisture in the pavement mass for curing
The second and third problems can look similar in hardened concrete. These issues create symptoms of a raveling surface. In some situations, it will even look like a loose gravel pavement. The difference between the two can be diagnosed by looking at the edge of the pavement. If there was too little water in the mixture, the pavement will be weak throughout its depth, to the point it can be crumbled by hand. If there was too little curing, only the top will be deficient and the lower half of the pavement will be sound. In either situation, the only remedy is to remove the affected area, to the full depth, and replace it with new concrete. RESPONSIBILITIES Beyond contract documents and technical specifications, each party involved in building a pervious concrete pavement has several responsibilities to ensure the success of the pavement and storm water management system. These should be discussed in a preconstruction meeting between all of the stake holders to ensure each party understands the importance of their duties. General Contractor
• Keep all traffic off pervious concrete until cured • Protect pervious concrete pavement from damage during construction • Hire only qualified contractors to place pervious concrete
Concrete contractor
• Provide proper subgrade • Use adequate equipment • Cure and protect the concrete for minimum of 7 days
• P rovide trained drivers, batch operators, and dispatchers who understand pervious concrete • Provide properly batched material • Provide material only to qualified finishers
Concrete producer
REFERENCES 1. ASTM International, “Standard Specification for Concrete Aggregates (ASTMC 33-99),” W. Conshohocken, PA, 1999, 8 pp. 2. “Pervious Pavement Manual,” Florida Concrete and Products Association, Orlando, FL, 1990. 3. ASTM International, “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (ASTMD1557-02e1),”W. Conshohocken, PA. 4. ACI Committee 330, “Guide for Design and Construction of Concrete Parking Lots (ACI 330R-01),” American Concrete Institute, Farmington Hills, Ml,2001, 32 pp. Matthew Offenberg is the Pavement Promotion Manager with Rinker Materials in Orlando, FL. He is Secretary of ACI Committee 330, Concrete Parking Lots and Site Paving, and Lead Editor for ACI Committee 522, Pervious Concrete. Offenberg received his bachelor’s and master’s degrees from the School of Civil Engineering at Purdue University. He is a registered professional engineer in Arizona and Florida, Article reproduced with kind permission from the author and ACI’s Concrete International magazine. volume 55 issue 1 MARCH/APRIL 2011
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Figure 1: Infiltration of water through PCPC.
Figure 3: Zero slump PCPC.
Pervious concrete a sustainable drainage solution
M.T. Bassuoni of the Department of Civil Engineering, University of Nottingham and M. Sonebi of the Centre for Built Environment Research at Queen’s University Belfast discuss the testing and results of a research project on the performance of Portland cement pervious concrete as a solution to drainage problems. With population growth, continual urbanisation has led to an increase of impervious surface areas, which block the percolation of precipitation from rainfall and snow down through the ground.
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reduces surface run-off and the need for separate storm water retention ponds and/or large storm sewers. Its open-cell structure permits storm water to readily filter through the pavement into the underlying soil, thereby helping to capture pollutants and preserve water quality in streams and rivers, and recharging groundwater supplies.2 3 4 In addition, PCPC is produced at low cost and thus can be considered among the most attractive SUDS. Mix design The porous structure of PCPC is obtained by limiting or eliminating fine aggregate, using controlled proportions of gap-graded or single-sized coarse aggregate and providing an adequate volume of cementitious paste. The paste provides a thin layer encapsulating and binding together the coarse aggregate, while maintaining the interconnectivity of millimetre-size voids, creating an open structure through which air and water can readily infiltrate. The relatively low volume of paste and high porosity reduce the strength of PCPC compared to normal concretes; typically the compressive strength is in the range 5–17 MPa, which is adequate for applications such as lightly trafficked pavements.2 3 4 While the use of PCPC has been increasing in the USA, it is not widely used in Europe, perhaps due to the limited research data and the absence of national and international Standards. Comprehensive research programmes are needed to develop systematic guidelines and specifications based on performance tests. Currently mix design is mainly driven by the experience of local contractors, which varies according to the location and availability of local materials. A research project has assessed the performance of PCPC (strength and permeability) based on key mix design parameters (water:cement ratio and contents of cement and coarse aggregate). Materials and testing methods This increases the potential for excess surface run-off, which can lead to downstream flooding, bank erosion and possibly transport of pollutants into potable water supplies. The UK Government has recently issued the Flood and Water Management Act 20101 which includes requirements for sustainable urban drainage systems (SUDS) for all new construction works that prevent direct infiltration of water through natural soil. The Act generally describes sustainable drainage as the management of precipitation from rainwater, snow or other sources to reduce the risk of flooding, improve water quality and protect the environment and health and safety. Portland cement pervious concrete (PCPC) is characterised by an interconnected pore structure and high void content typically in the range 15–35% by volume, thus allowing direct infiltration of water through its structure (Figure 1). While its constituent materials are similar to those of normal concrete, PCPC contains little or no fine aggregate.2 3 PCPC – also known as no-fines concrete, permeable concrete, porous concrete or enhanced porosity concrete – has been used in a variety of applications, especially lightly trafficked areas such as parking lots. PCPC can effectively solve drainage problems and reduce the risk of flash flooding. PCPC pavements are now being used in sustainable developments in the USA, where its high permeability
Mixes were prepared with CEM I 42.5N cement and nominal 20 mm single-sized crushed basalt aggregate, sourced from a local quarry. Water:cement (w/c) ratio was in the range 0.28–0.4, cement content 350–415 kg/m3 and coarse aggregate 1200–1400 kg/m3. For each mix, triplicates of 100 × 200 mm cylinders and 100 × 100 × 100 mm cubes were prepared. Excessive tamping was avoided in order to prevent blockage of the open pore structure. Currently there are no standard procedures for the preparation of PCPC laboratory specimens. The specimens were demoulded after 24 hours, and stored in a curing tank maintained at a temperature of 20±2°C until the time of testing. In addition to assessing the fresh properties (slump and unit weight) of the mixes, compressive strength, void ratio and permeability tests were conducted on the hardened specimens. The infiltration rates were determined using a falling head permeability test (Figure 2) after 28 days. To examine the effect of compaction, the infiltration rate (k) was calculated for cross-sections cut from the top and bottom of cylindrical specimens. Fresh properties Most combinations produced stiff mixes as indicated by almost zero slump values (Figure 3), which is typical for this type of concrete. However, the slump test is not a proper indicator for
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the workability of PCPC and should not be prescribed as an acceptance measure.3 The fresh density was in the range 1920– 2200 kg/m3, which is lower than that of normal concrete due to the significantly higher volume of voids. The fresh density is reasonably correlated to the hardened void ratio as shown in Figure 4.
Figure 4: Relationship between fresh density and void ratio of PCPC.
Hardened properties The void ratio ranged from 13 to 23% and the cube compressive strength from 21 to 13 MPa. The average infiltration rate of corresponding cylindrical specimens was in the range 0.30–1.42 cm/s and were thus within, or higher than, typical flow rates for pervious concrete (0.20–0.54 cm/s).2 3 4 The relationship between void ratio and compressive strength followed the typical trend of normal concrete (ie, the increase in void ratio led to a corresponding reduction of compressive strength). The majority of cubes failed at the contact points between the cement paste and the aggregate, which suggests that the interfacial zone is a key parameter controlling the strength.
Figure 5a: Isoresponse curves for PCPC cubes: (a) 28-day compressive strength (MPa), and (b) void ratio (%).
There was a difference in the distribution of voids through the height of the cylindrical specimens with the top being less porous than the bottom. The void ratios at the top were in the range 15–18% (infiltration rate 0.30–0.68 cm/s) and at the bottom 18–23% (infiltration rate 0.43–1.42 cm/s). In the majority of the specimens, the hardened density was higher at the top due to surface compaction and finishing, which led to lower void content and permeability. This agrees with results obtained from cores taken from cast-in-situ PCPC pavements in South Carolina5 and highlights the sensitivity of PCPC to surface compaction.
Figure 5b
Effect of variables Figure 5a shows the effect of w/c on the 28-day cube compressive strength. At constant coarse aggregate and cement contents, the increase of w/c from 0.28 to 0.40 led to an increase in compressive strength. This is in contrast to the typical trend exhibited by normal concretes. Increasing the w/c produced a higher volume of paste that was in excess of that needed to encapsulate the aggregate. Surplus paste clogged the open pore structure, thus reducing the void ratio and increasing compressive strength. Reducing the w/c (up to 0.28) led to an increase in the void ratio with higher infiltration rates.
Figure 6: Isoreponse curves for the infiltration rates (cm/s) of PCPC cylinders.
In the same way, increasing the cement content from 350 to 415 kg/m3 at a fixed w/c and coarse aggregate content reduced the void ratio (Figure 5b), and in turn the infiltration rate due to the higher volume of paste. At a fixed cement content and w/c (ie, constant paste volume), the increase of coarse aggregate content from 1200 to 1400 kg/m3 led to a significant increase in the void ratio and infiltration rate (Figure 6). This can be ascribed to the larger specific surface of the higher aggregate content, which was optimally encapsulated by the cement paste, thus maximising the open-cell structure.
Figure 7: Relationship between void ratio and infiltration rate of PCPC.
Alternatively, the equivalent amount of paste coating a lower aggregate content reduced the void ratio and permeability because of a surplus amount of paste clogging the pore structure. Correlation between void ratio and infiltration rate The relationship between the void ratio and infiltration rate of all the mixes tested is shown in Figure 7. The non-linear behaviour is attributed to the dependence of the infiltration rate on the
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A
Concrete B
Solutions Figure 2: Falling head permeability test set-up. A
Perspex Cylinder
B
Sleeve surrounding PCPC cylinder allowing vertical drainage
percentage of voids as well as their interconnectivity. Since a good correlation exists between the fresh density and void ratio (Figure 4), it is suggested that the fresh density test can act as a viable quality control or acceptance measure for PCPC. Concluding remarks At present, the use of pervious concrete in the UK and Europe is limited. There is still need to establish material properties and develop standard tests to explore its full potential. The most important advantage is its ability to permit water infiltration through its open structure, making it among the best sustainable urban drainage systems. The characteristics comply with the current environmental regulations in UK and provide cost-effective SUDS. PCPC is a technology that can help property owners, designers and planning regulators meet the latest challenges of ‘green’ building standards. By controlling the w/c and the contents of cement and coarse aggregate, the required properties (high void ratio and permeability) can be readily achieved, with the fresh density test providing a reliable acceptance measure.
Rockcote’s MultiStop range of premium construction mortars are designed for ease of use as sandable or non sandable patch, repair, & finishing plasters to achieve the best result over concrete substrates.
References 1. Office of Public Sector Information (OPSI). Acts of the UK Parliament and Explanatory Notes, Flood and Water Management Act 2010 c.29. 2. Tennis, P.D., Leming, M.L. and Akers, D.J. Pervious Concrete Pavements. EB302.02, Portland Cement Association, Skokie, IL, and National Ready Mixed Concrete Association, Silver Spring, MD, USA, 2004. 3. Obla, K. Pervious Concrete for Sustainable Development. Proceedings of the First International Conference on Recent Advances in Concrete Technology, September 2007, Washington, DC, USA, 6pp.
Always Start with a Better Finish
4. Schaefer, V.R., Wang, K., Sulieman, M.T. and Kevern, J. Mix Design Development for Pervious Concrete in Cold Weather Climates. Final Report, National Concrete Pavement Technology Center, Iowa State University, Ames, IA, USA, 2006. 5. Haselbach, L. and Freeman, R. Vertical Porosity Distributions in Pervious Concrete Pavements, Materials Journal, American Concrete Institute (ACI), Vol.103, No.6, pp.452–458. Article reproduced with kind permission from the author and the UK Concrete Society’s Concrete magazine.
www.rockcote.co.nz 0800 50 70 40
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ACI 522R-10 Report on Pervious Concrete American Concrete Institute (ACI) This report provides technical information on pervious concrete’s application, design methods, materials, properties, mixture proportioning, construction methods, testing, and inspection. The term “pervious concrete” typically describes a near-zero-slump, open-graded material consisting of portland cement, coarse aggregate, little or no fine aggregate, admixtures, and water. The combination of these ingredients will produce a hardened material with connected pores, which in application helps to reduce stormwater runoff, improve stormwater quality, recharge groundwater supplies, and reduce the impact of the urban heat island effect. ABSTRACT. www.concrete.org/bookstorenet ACI 522.1-08 Specification for Pervious Concrete Pavements American Concrete Institute (ACI) This specification covers materials, preparation, forming, placing, finishing, jointing, curing, and quality control of pervious concrete pavement. Provisions governing testing, evaluation, and acceptance of pervious concrete pavement are included. This reference specification can be made applicable by citing it in Project Specifications. The Architect/Engineer supplements this reference specification as needed by designating or specifying individual project requirements. ABSTRACT. www.concrete.org/ bookstorenet PCP: Pervious Concrete Pavements by Paul D. Tennis, Michael L. Leming, David J. Akers Portland Cement Association (PCA) Pervious concrete as a paving material has seen renewed interest due to its ability to allow water to flow through itself to recharge groundwater and minimize stormwater runoff. This introduction to pervious concrete pavements reviews its applications and engineering properties, including environmental benefits, structural properties, and durability. Both hydraulic and structural design of pervious concrete pavements are discussed, as well as construction techniques. ABSTRACT. www.cement.org/bookstore Pervious Concrete: Hydrological Design and Resources CD Portland Cement Association (PCA)
PERVIOUS CONCRETE RESOURCES THE RESOURCES OUTLINED BELOW ARE AN IDEAL STARTING POINT FROM WHICH TO EXPLORE THE POTENTIAL OF PERVIOUS CONCRETE. EACH IS AVAILABLE TO PURCHASE FROM THE PUBLISHER, OR BORROW FROM THE CCANZ LIBRARY. EMAIL LIBRARY@CCANZ.ORG.NZ
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A timely update to the useful reference tool on pervious concrete. Filled with technical and promotional resources materials addressing specifying, proportioning, production, and placement of pervious concrete. The CD also contains an analysis tool on hydrological design. The hydrological analysis program is intended solely to illustrate the behaviour of pervious concrete systems in relatively simple situations. ABSTRACT. www.cement.org/ bookstore Pervious Concrete: When it Rains….it Drains [website] Compiled by the National Ready Mixed Concrete Association (NRMCA) and the Portland Cement Association (PCA), this site focuses on pavement applications for pervious concrete. www.perviouspavement.org Image courtesy Portland Cement Association (PCA)
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CCANZ Library Listed below is a small selection of recently acquired material by the CCANZ library. email library@ccanz.org.nz Sustainable Concrete Architecture by David Bennett Based on new thinking and real world evidence Sustainable Concrete Architecture offers a rational method for accounting for the carbon impact of concrete in contemporary architecture. Highly illustrated and detailed in scope, the book marries technical know-how with inspirational case studies. A technical front section looks at recent innovations in concrete technology with a comprehensive, balanced account of the material’s embodied energy and impact-in-use. Often maligned as environmentally unfriendly, the technical evidence about concrete reveals its legitimate place in the current lexicon of low carbon building design. The second half of the book sets out a series of cutting-edge case studies of different building types constructed in concrete. Solid States: Concrete in Transition edited by Michael Bell and Craig Buckley By far the most pervasive and affordable building material in the world, concrete has undergone ever-more widespread dissemination, standardization, and technological innovation in the last twenty-five years. Experts consider it the quintessential “engineered� material, with recent scientific breakthroughs yielding composites stronger than steel, lighter than water, and as beautiful as natural stone. In Solid States: Concrete in Transition, a group of architects, historians, theorists, engineers, fabricators, and materials scientists explore the past, present, and future possibilities of this highly calibrated, fluid material.
Library Quiz To go in the draw to win a copy of Solid States: Concrete in Transition edited by Michael Bell and Craig Buckley answer the following simple question: Completed in 1982, what was cutting-edge about the design of Wellington’s William Clayton Building? Email your answer to library@ccanz.org.nz. Entries close Friday 24 June 2011.
Congratulations to Bill Peck of Firth Industries Limited, who correctly answered the Dec 10/Jan 11 Library Quiz to receive a copy of The Sustainable Concrete Guide - Applications edited by Andrea J. Schokker.
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CONTACTS New Zealand Ready Mixed Concrete Association Ph (04) 499 0041 Fax (04) 499 7760 Executive Officer: Rob Gaimster President: Jon Hambling www.nzrmca.org.nz New Zealand Concrete Masonry Association Ph (04) 499 8820 Fax (04) 499 7760 Executive Officer: David Barnard President: Jason Savage www.nzcma.org.nz Precast NZ Inc. Ph (09) 638 9416 Fax (09) 638 9407 Email: ross.cato_precastnz@xtra.co.nz Executive Officer: Ross Cato President: Andrew Sinclair www.precastnz.org.nz New Zealand Concrete Society Ph (09) 536 5410 Fax (09) 536 5442 Email: concrete@bluepacificevents.com Secretary/Manager: Allan Bluett President: Dene Cook www.concretesociety.org.nz New Zealand Master Concrete Placers Association Ph (06) 873 4428 Fax (06) 873 4429 Email: office@mcpa.org.nz www.mcpa.org.nz
News from the Associations New Zealand Concrete Society (NZCS) ROTORUA NEW VENUE FOR INTERNATIONAL SYMPOSIUM The International Symposium on High Performance Concrete and the NZ Concrete Industry Conference which were to be held in Christchurch will now be in Rotorua. Both events will be held at the Energy Event Centres on the same dates as originally scheduled - Concrete Conference - 8 August; Symposium - 9-11 August . An outstanding response to the call for papers - more than 250 abstracts from 44 countries bodes well for attendance numbers at what will be the largest international conference ever hosted by the New Zealand Concrete Society. The 9th International Symposium on High Performance Concrete - Design, Verification and Utilization is expected to attract up to 300 international delegates and will feature six keynote speakers and 11 invited speakers. It will be preceded by a one-day NZ Concrete Conference. Conference organiser Michael Khrapko says the conference gives New Zealanders in the concrete industry a unique opportunity to meet leading world experts in the field of highperformance concrete and to learn where concrete technology is heading. The keynote speakers are as follows: • Pierre-Claude Aïtcin - University of Sherbrooke • Michael Collins, University of Toronto, • Mitsutaka Hayakawa, Tokyo Polytechnic University, Japan • Olafur Wallevik, Innovation Center Iceland, Reykjavik University • Joost Walraven, TU Delft, Holland • Francis Young, University of Illinois Symposium delegates will have the option of attending Concrete Conference 2011. Book by 15 May for earlybird registration. The symposium is to be hosted by NZCS with support from: FIB (Federation Internationale du Beton), RILEM, JCI (Japan Concrete Institute), ACI (American Concrete Institute), JSCE (Japan Society of Civil Engineers), and Concrete Institute of Australia. For information on keynote and invited speakers, social and partners’ programmes, accommodation and the technical programme, visit: www.hpc-2011.com
Technical Information
NEW ONLINE RESOURCE
Your one-stop, online resource that has everything you need to know about Pipeline, Watermain, Drainage and Environmental products
www.humes.co.nz/technical
Check it out now! volume 55 issue 1 MARCH/APRIL 2011
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application innovation. Duomix Fire anD Dramix, the right Fibre For each application. www.bosfa.com
Duomix Fire and Dramix breaking new ground – Victoria Park tunnel. Duomix Fire m6 – passive fire resistance, precast panels Duomix Fire M6 are 18 μm diameter, 6mm long synthetic fibres and were used as passive fire protection in the precast wall panels, an effective and reliable measure against explosive spalling. Research has shown that the fineness of the fibre and ultimately the number of fibres per cubic meter of concrete is a dominant factor controlling their effectiveness.
Dramix – crack control, primary shotcrete lining Dramix steel fibre reinforced concrete (Grade 30MPa FL 3.0/2.5; nZS3101:2006) was used in combination with traditional reinforcing in the watertight shotcrete layer; this can significantly reduce crack width and or the required amount of reinforcement.
other suitable applications For Dramix combineD with traDitional reinForcing:
REALISE GREATER EnGInEERInG EFFICIEnCY WITHOUT COMPROMISInG QUALITY On YOUR nEXT PROJECT. TALk TO THE LEADER IN FIBRE REINFORCED CONCRETE ENGINEERING CALL 1300 665 755 (AUS), 0800 665 755 (nZ) OR vISIT bOSFA.COM
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– Liquid tight structures; basement slabs, industrial slabs with hygiene requirements or subjected to hazardous liquids – To limit the number of joints in roads and in commercial slabs – Where SLS crack control is critical and governs over ULS design