AUGUST 2022 IN THIS ISSUE: REMOVING THE GUESSWORK ANDCUTSCAN,CORE 42 Sustainable Concrete: From theory and standards to practical use. PHOTO CREDIT: ROOTSTOCKS / ISTOCK / GETTY IMAGES
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XRADAROFCOURTESYPHOTOS
T he most common reason to perform a concrete scan is to detect objects embedded within the concrete slab, and more often than not, these scans are done because there is a need to cut, drill or core into the concrete. And this is not an unusual task; it happens every day on a vast variety of construction projects. There might be a need to install utilities like water pipes or sewer lines, or phone and computer lines may be needed for a specific area. In these instances, a concrete scanning technician can be brought in to image the area to identify which objects are buried within the slab, and at what depths.
SCAN(ORCUTCORE)BEFOREYOU
Many troubles can be avoided when modern scanning methods are combined to provide a clear picture of what’s happening below the surface.
on-sitemag.com / 39 CUTTING & CORING
BY JESSE HODGINS
THE BENEFITS OF SCANNING BEFOREHAND Existing concrete infrastructure can be riddled with embedded objects. These are often planned, as is the case with electrical conduits, radiant heating lines, post-tension cables, rebar and wire mesh, but knowledge of their exact, precise positioning is rarely available, and even with a layout in hand, there is a possibility that something may have shifted during the concreteElectricalpour. conduits usually measure between 20 and 50 mm in diameter, and are commonly found within a concrete
There are several methods used to scan concrete, each with its own set of advan tages and limitations. Known throughout the industry as non-destructive testing, the most widely used methods are Ground Penetrating Radar (GPR), Ultrasonic Pulse Echo (UPE), X-ray, Half-Cell Potential (HCP), and Ultrasonic Pulse Velocity (UPV). Ground Penetrating Radar
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METHODS OF SCANNING AND MAPPING
structure. If one of these conduits is severed, power outages can occur, internet access can go down, and coring technicians run the risk of being electrocuted. Cutting into post-tension cables, rebar, or wire mesh can cause significant structural damage to a building. In addi tion to potentially compromising building safety, repairing the damage can result in project delays and risingThankfully,costs. all of the above scenarios can be avoided by simply scanning before any cutting is performed. With a detailed report in hand, coring techni cians will be able to cut confidently without risking their own health and safety of the structure. Safety is one thing; efficient project planning is another. In addition to preventing damage to objects beneath the surface, concrete scans can help guide next steps at various stages of construction. Professional companies, like the one I work for, can produce accurate and detailed surveys, along with accurate as-built drawings. These comprehensive reports can detail slab thickness, reinforcement cover, spacing, rebar diameter and foundations. Structural drawings provide valuable information that allow engineers to make data-driven decisions for planning and construction phases. Raw data, maps and CAD-ready files can easily incorporate existing as-built slab conditions into structural design and analysis.Thebenefits of concrete scanning are far-reaching. Having a scan done prior to cutting and coring concrete can save time, help make informed decisions, prevent costly mistakes, and ensure safe measures are being taken.
Ultrasonic Pulse Echo UPE is able to provide accurate readings at larger depths than GPR. It is an advanced imaging technique that can vividly map out honeycombing, large cracks and voids. This method can determine the thickness of reinforced concrete structures up to eight feet in depth. It runs up against issues when testing on rough or unfinished concrete, however. X-ray Using X-ray to scan concrete results in a direct image of the subsurface. It provides a great snapshot of the objects within the slab but is restrictive, expensive and can be very time-consuming.
CUTTING & CORING
The most established method for concrete scanning and imaging, GPR works by transmitting high-frequency electromagnetic waves into the structure via an antenna. It’s quick, efficient and relatively affordable, but its findings require a high level of interpretation.
Jesse Hodgins, C.Tech, has worked with Xradar, a leading provider of concrete scanning services in Canada, since 2017. He recently spearheaded the company’s expansion into Ottawa.
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This type of measurement can gauge the potential for corrosion, and thus, the durability of concrete reinforcement. HCP is advantageous when working with concrete structures like parking lots, concrete piers, docks and tunnels. Ultrasonic Pulse Velocity UPV can be used to assess the quality of concrete structures, such as beams, columns, walls and slabs. With this technology, ideally there is access to both sides of the structure, but even if access to the structure is one-sided, indirect transmission can be used.
Although conventional GPR scanning is a proven method for concrete scanning, it has its shortcomings. Take slab-on-grade for example—the bottom layer is often quite weak or can be laying on a range of base materials. When scanning slab-ongrade with GPR, a technician will likely have difficulty determining the depth of the slab or getting a reliable read. By making use of a combination of the varying methods, based on the project assigned and deliverables required, it is possible to retrieve an accurate reading for slab-on-grade that more conventional single-method scanning cannot match. When methods are combined, it becomes possible to “see” through wire mesh, and the technician is able to distinguish between specific objects. The postscan report will show if the slab contains electrical conduits, radiant heating lines, rebar, or post-tension cables. It might even have them all!
The two main limitations to this method of scanning are that X-rays are unable to provide the depth of embedded objects, and access to both sides of the slab is required. X-ray cannot be used with concrete slab on grade. Half Cell Potential
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SCAN TO VISIT OUR WEBSITE
COMBINING THE POWERS
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SUSTAINABILITY
Concretesolutions
Finding low-emission paths to concrete production.
“In Canada, we’re in a really inter esting phase of the climate discussion,” says Adam Auer, president and CEO of the Cement Association of Canada. “So much of the climate discussion over the past number of years is really focused on carbon pricing as the primary instrument for decarbonization, both on the consumer side and on the industrial side. It feels like that sort of background policy is now wellButunderstood.”thepathto decarbonization is more complicated than simply dollars on a ledger. And Auer says that the cement and concrete industry have been leaders in helping find solutions. “If you understand the construction value chain, it’s quite complicated,” he explains. “If you want to decarbonize that chain, it’s not just about material manufac ture, which is obviously a big component, but it’s also about codes and standards. It’s about the willingness of architects, develop ers and specifiers to accept innovation and try new things. It’s about the willingness for the market to pay more for really lead ing-edge stuff. It’s about thinking through things like material efficiency in the same way that we’ve thought through things like energy efficiency.”
He says that government instruments like capital funding through the Net Zero Accelerator Initiative (NZA)—that’s the investment tax credit for carbon capture, utilization and storage—can help accelerate the pace of “They’rechange.talking about some really innovative instruments around carbon price certainty through things like carbon contracts,” he says, adding that programs like NZA help encourage the adoption of earlier stage, more capital-intensive tech nologies like carbon capture and storage.
BY ANDREW SNOOK
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42 / AUGUST 2022 When 196 parties signed on to The Paris Agreement at the end of 2015, the level of public and political attention given to greenhouse gas emission produc tion spiked dramatically. With that commit ment to limit global warming through the lowering of emissions, certain industries, including the concrete industry, were going to be impacted, and potentially pressured, far more than others to find sustainable solutions for their products—and sooner rather than Fortunatelylater.for the sector, many compa nies, research organizations and govern ments around the world have been hard at work for many years to help make concrete production more sustainable.
Some of these options, such as moving away from carbonized fuel supplies, are already happening, but the sector is still in the early stages, and some of the avail able technologies are expensive, making it difficult to build a business case to support their use without government incentives.
“In cement in particular, and I think it probably applies to a lot of other heavy manufacturing sectors, there’s really no silver bullet,” he says. “There’s a menu of technologies and policies, and they all come together to work.”
He says that governments need to think more horizontally across their own portfolio about how the different levers they have on the policy side must work together to pave the way for industry to be able to make big investments in the technologies that are needed.
There are some impressive technologies related to carbon utilization in cement and concrete that are currently being created.
Auer pointed to carbon capture technol ogies from companies like Carbon Upcy cling Technologies and Blue Planet Systems as examples of how innovative aggregate and additives can be part of the discussion.
“There’s a huge opportunity to use concrete as a vehicle to sequester carbon,” he says, adding that other technologies are also under development, and in need of support. “It’s about making sure that
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BIOPRODUCT SOLUTIONS
The calculations used in the CarbonStar standard are designed to account for the emitted and sequestered carbon per unit of concrete. It was created to limit global warming to 1.5°C by 2050.
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“We see that there’s a lot of improve ments when adding the fibres,” says Helen Lentzakis, manager of the Biomaterials Division at FPInnovations. To date, only small amounts of fibres have been added to concrete mixes with a variety of different fibre types being used in the recipes. Some of the mixes include the additions of Thermomechanical Pulp (TMP) fibres, Bleached Chemi-ThermoMechanical Pulp (BCTMP) fibres, softwood, and North Bleached Softwood Kraft (NBSK) fibres, as well as Crystalline Nanocellulose (CNC) and Cellulose Filaments (CF). With each mix, Lentzakis says her team has discovered different types of improvements.
44 / AUGUST 2022 when we look at the suite of options that are available for decarbonization, that we’ve gotten the right kind of policy, and support for each of those different stages.”
“Additionally, AI can be used to optimize the packing of the particles, reducing the amount of binder needed. However, these technologies are in limited usage,” Riley says.
One of the solutions to help make concrete production more sustainable may come from the forestry sector.
Of course, there’s no sense in waiting, since even a small step is a step in the right direction. As Auer says, “Let’s not wait for the silver bullets, like carbon capture utili zation. Yes, we’re investing in those things. But in the interim, there’s a lot of things we can do today.”
SUSTAINABILITY
To ensure that the standard is being met, the concrete manufacturer will also be required to provide an Environmental Product Declaration (EPD) for its concrete mix and to document the EPD so that the airport and other stakeholders can record the embedded carbon. Riley, who is CEO of the World Cement Association, says that concrete suppliers are mainly using blends to lower the CO2 in the concrete they are producing and supplying to meet requirements like those requested by the SFO. “Concrete suppliers are reducing their CO2 footprints mainly by using blended cements instead of OPC [Ordinary Portland Cement], since these have lower carbon footprints and supplementary cementitious products such as slag, fly ash and natural pozzolans,” he says. New technologies may include geopoly mer concretes, mainly with slag (some times fly ash, red mud and other materials) and no cement; as well as synthetic aggre gates made from sequestered CO2, such as those created by Blue Planet.
Biomaterials Division has the capabilities to measure all the properties of the concrete from the fresh state to the hardened states. They test all
HIGHER STANDARDS
“The major improvement is during the curing process to control cracking behaviours. By adding these fibres, we can control the amount that the shrinkage occurs, and ultimately, the cracking,” she explains. “What happens, especially with high-performance fibres for high-perfor mance concrete, is that you don’t have a large amount of water, which increases the shrinkage.”Ifthe porous network of the concrete doesn’t have enough free water, the cellu lose fibres release water to the concrete. “This is how you’re reducing the shrinkage, and ultimately, the cracking,” she says. “That’s an interesting property improvement that we’ve FPInnovations’seen.”
One of the tools now available in the war on greenhouse gas emissions is the CarbonStar standard. Initially developed for Canada and the U.S., this standard offers governments and companies “a rigorous, transparent way to quantify, specify, and then reduce the carbon intensity of concrete based on a standard simple way to measure, report and specific CO2 intensity,” according to Decarbonising our Built Environment, Concrete Block by Concrete Block, written by Greg Kats of Smart Surfaces and the World Cement Association’s Ian Riley and Manon Burbidge.
For the past five years, FPInnovations, a private not-for-profit organization that specializes in the creation of solutions in support of the Canadian forest sector’s global competitiveness, has been research ing ways to introduce wood pulp fibres to improve concrete recipes.
The first implementation of the CarbonStar standard is underway at the San Francisco International Airport (SFO), which has adopted the standard to reduce the warming impact of the concrete it plans to use on its upcoming building and infrastructure projects. The airport lists three levels of CO2 intensity in its specifications for concrete, using the CarbonStar rating system with the minimum requirement being no more than 200 pounds of CO2 per cubic yard (119 kg/m3), and ramping up to a best case of not more than negative-200 pounds per cubic yard — or 60 per cent below the current industry average.
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46 / AUGUST 2022 the fresh properties including rheology properties, isothermal calorimetry, and most of the mechanical properties as well, including the flexural strength and the tensile strength as well as major concrete durability indicators. So, what are the bene fits of adding these various fibres? “The benefit is to increase the dura bility, especially the freeze-thaw resis tance, which obviously is an important property in Canada,” says Lentzakis. “We test freeze-thaw cycles, and we see that there’s an improvement with the addition of theFPInnovationsfibres.” has not yet fully assessed the CO2 impact because they are working with such small amounts of fibres, but the benefit of increased durability in concretes certainly makes for an argument for more sustainable concrete production. Also, cellulose filaments (CF) make it possible to use local, lower quality sand sources without compromising performance. “Because you’re improving the mechanical properties, such as a structural toughness, the advantage would be to use less concrete,” Lentzakis says. “Concrete is usually classified by compressive strength, so if you can increase the classification and have less concrete, and replace some concrete with fibres, you can have a signifi cantFPInnovationsimpact.” has also found that the use of these fibres in the concrete have helped with preventing corrosion in rein forced“Weconcrete.did corrosion activity monitoring
While the industry has the ability to provide products and solutions with a lower embodied carbon, these products are sometimes at odds with traditional or boiler plate specs and, in some of these cases, these newer designs go against what has “always been done,” which is why there is a need for alignment across all players in the construction value chain to achieve more sustainable“Well-intentionedoutcomes. policies may run up against practices that are built on years of experience, and rightfully so,” says Ian Paine, director of Ready Mix Performance, Western Canada, at Lafarge Canada. “We greatly appreciate that the people responsible for our infrastructure are exceedingly conservative.” As he says, the performance of the concrete material in a building or structure will always be the primary concern driving the material selection process, but once the appropriate level of performance for a mix has been demonstrated, there needs to be an ability to work these newer products into the specifications stream.
SUSTAINABILITY
“We find that we have to repeat that process,” Paine says. “It takes extraordinary resources. That kind of time and manpower will require the industry. We strongly encourage that cross-knowledge transfer of experience.”He’shoping that industry associations can press for changes to that process, to make it less cumbersome for industry players.“Iwould strongly encourage associa tions within the country to make sure that they’re using their platforms to talk about successes across geography,” he says. “So that maybe when someone in Ontario has agreed that a pilot was successful, then Alberta or Manitoba looks at that data and says, ‘That’s good enough for us.’”
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on outdoor reinforced concrete elements by applying chloride, and we saw that the fibres helped with retarding the corrosion that’s usually caused by chloride,” says Lentzakis. “We managed to have the 26 elements with different types of fibres of TMP, CNC, CF, BCTMP and NBSK fibres at different loading, and we saw with the improvement in corrosion there was a differ ence between how much fibre we are using. So, when you use too much fibre, you don’t see improvement in corrosion mitigation, but when you use less fibres, you see that improvement in corrosion, so that’s pretty interesting as well.”
While engineers may see increased risk, companies like Lafarge have thoroughly tested their newer mixes and designs and stand by the performance of these materials in the same manner as they do with their traditional mixes. “While we fully appreciate the responsibilities of the stakeholders around the table, we are also very open to agreeing to an innovation process,” he says. Even where there is a pathway for innovative products to be specified, a major challenge is the need to prove processes in multiple jurisdictions, duplicating efforts. Even when one jurisdiction in Canada approves a particular process or product, it can take several years for other jurisdictions to adopt it.
Andrew Snook is a freelance writer and editor.
While there are new technologies and products available and coming to market, one of the biggest roadblocks to the imple mentation of modified concrete products is human in nature. It can be difficult to convince engineers to change their specifi cations in a project away from long proven building materials. The same can be said for codes and standards as well.
BARRIERS TO IMPROVEMENT
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