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Urban concrete - requisites and remedies Concrete has an important role to play in the rapid urbanisation that is taking place
URBAN CONCRETE - REQUISITES AND REMEDIES
The current world population of 7.6 billion is expected to reach 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion in 2100, according to a recent United Nations report, with roughly 83 million people being added to the world’s population every year. We are witnessing rapid urbanisation and there will be major relocation of populations to urban areas in the near future. Urbanisation brings with it a lot of challenges, with a thrust on basic needs such as food supply, transport, utilities, shelter and infrastructure. With shelter and infrastructure being among the basic requirements, construction industry professionals need to be innovative in meeting this increasing demand, and in this process, concrete plays an important role. The concrete industry, by and large, is still ‘hand-crafted’ and depends heavily on manual work and on-site construction, which leads to large amount of material wastage and workforce inefficiency. Hence, we must look at newer, energy-efficient, environment-friendly materials and technologies that minimise skill inputs and deliver faster results at affordable prices. The swift shift in the dynamics of concrete, in recent years, has posed a lot of challenges for concrete technologists and concrete professionals across the globe. In the process of making modern concrete, one needs to pay greater attention not only to aspects such as the mix design but also to its performance with respect to handling, pumping, placing, finishing and curing. Durability and sustainability are the buzz words in the world of modern concrete. Durability is at the forefront in the making of modern concrete. Hence, it is essential to have better know-how on concrete-making materials, such that one can extract the best potential from these ingredients. For obvious reasons, concrete has been different in the past and is in the present, and will be in the future. Emerging trends in construction and construction practices, such as the use of alternative aggregates, demand a holistic approach by various stakeholders in the construction industry for successfully specifying and making urban concrete. Poor rheology, stickiness, workability retention, pumpability and placement of modern concrete are some of major pain points which need immediate attention. Advancements in concrete technology due to newly developed materials, such as chemical admixtures, have assisted in improving the properties of concrete and address most of the above-mentioned pain points. This article will set out to explain the requisites for making urban concrete and the remedies for overcoming challenges in this effort.
INTRODUCTION
Infrastructural development, urbanisation and demographic changes are some of megatrends globally and they will bring with them enormous challenges in the immediate future. Whilst an estimated population of 11.2 billion by 2100 on Planet Earth is seen as a challenge by most of us, on the other hand, this can also be considered as an opportunity for many sectors such as agriculture, construction, electronics, finance, and so on. Seventy percent of the world’s population is expected to stay in cities. This will create a demand for more smart megacities. Currently, America and Asia have the most megacities and it is interesting to note that by 2100, Asia and Africa will have the most megacities, as we estimate 80% of world’s population will be based in Asia and Africa. The future megacities are expected to be much larger and smarter than the current megacities. Infrastructure is one of the important elements of the economy, for a community or country to function competitively and to improve the standard of living of
its people. It comprises the basic framework; facilities; water, sewerage, transport, power and communications networks; and buildings. There are enormous renovation needs in developed countries. However, in emerging markets, infrastructure and urbanisation are essential for reaching the essential goals. Another reason for a surge in infrastructure spending that encourages urbanisation is the intention of political leaders to boost economic prospects in as many regions as possible and underpin growth through job creation. It is time now for construction professionals to align themselves with emerging technologies and make use of advancements in building materials, construction equipment and construction methods, to address the needs of affordable housing; well-functioning infrastructure for water, traffic, energy, sanitation and waste treatment; environmental protection; smart and green cities; efficient modes of transport; and so on. The construction industry is the pivotal element in infrastructure development. Due to the high demand for infrastructure, the industry needs more resources such as manpower, materials and machinery, and on the other hand, the construction industry is facing a scarcity of resources. Resource efficiency is and will be a challenge for the construction fraternity. The construction sector is playing an essential role as a solution provider that will address these challenges. Construction is the second largest industry, next only to agriculture, in most of the developing countries. The construction industry in developing countries has been a labour-intensive industry, although changes in favour of modernisation and automation are now discernible in certain fields. Ready-mixed concrete is one such field. Cement is an intermediate product in construction, as it requires further processing to get the end product - that is concrete. As per the latest statistics, 1 m3 of concrete is consumed per person per annum. In construction, concrete plays a vital role and in concrete, admixtures play a vital role. Concrete is the second most-used material in the world, next to water. In civil construction, which could be as old as human civilisation, over the years, concrete has emerged as a versatile construction material. Today, with modern infrastructure demanding good construction practices, it is rather difficult to imagine any infrastructure development that does not use or require concrete.
CHALLENGES FOR THE READY-MIX INDUSTRY
Modern infrastructural concrete is very different and demanding compared to the concrete produced and placed in the past. Cast-in-situ concrete is almost replaced by ready-mix concrete. Despite several technological advancements in the field of ready-mix, the ready-mix business is still a diverse and demanding sector with its own requirements and challenges. Ready-mix operations are always local, with key factors such as financial resources and transportation playing a central role in decision making. In essence, we can classify the challenges into three categories: • Operational challenges • Supply Chain challenges • Technical Challenges Strength, durability and placeability are at the forefront of the challenges faced by ready-mix concrete producers, along with the need for concrete that is aesthetically pleasing, more sustainable and safer to use. Hence, there is need for technologically advanced concrete admixtures for the ready-mix industry, that meet industry codes and meet or exceed the demands of challenging construction applications and adverse placement conditions. Project delays can be extremely costly, which is why we complement our product offerings with one-on-one customer support. Through our technical and site support services, we work to anticipate and overcome challenges before they occur, by selecting the appropriate custom-based product solution for increased production efficiency and speed of construction. One of the wishes in the wish list of ready-mix producers is to have the right admixture partner who has a broadbased range of product solutions which can provide added value, to increase the service life of concrete, speed of construction and environmental efficiency, as well as liquid colouring products for aesthetically pleasing architectural concrete.
INNOVATIVE ADMIXTURE TECHNOLGIES
Today, in the field of concrete technology, there is a revolutionary shift, resulting in the ability to achieve any property of concrete (green or grey), without much difficulty. This has been aided by developments in the field of construction chemicals, especially admixtures. More than 35 years ago, Mr V M Malhotra had said, “There have been very few major developments in concrete technology in recent years. The concept of air entrainment in the 1940s was one; it revolutionised concrete technology in North America. It is believed that the development of superplasticisers is another major breakthrough which will have a significant effect on the production and use of concrete, in years to come”. The prediction on superplasticisers has proven to be correct. Ready-mix concrete is characterised by a great number and variety of different mix designs, utilising different types of fillers, cements and binders, as well as complying with the increasing trend towards more performance- and durability-based concrete specifications. At the same time, ready-mix producers must maintain their profitability in the face of rising material, labour and equipment costs. As a result, producers are optimising their production and logistics costs. Innovative admixture systems, from Master Builders Solutions of BASF, support these goals by providing the capability of delivering high quality concrete at any time to the job site. This new concept facilitates the production of concrete with both
Process Step
Materials
Mixing
Transit
Placing
Admixture Solutions for:
1. Higher Usage of Manufactured Sand 2. More Sustainable Concrete Mixtures
3. Faster Mixing Times 4. Production of Ultra High Strength
5. Improved Slump Retention
6. Reduction of Concrete Stickiness 7. Easier & Faster Placement of Concrete
Hardening 8. Faster Early Strength Development
Hardened Properties 9. Reduction in Shrinkage and Cracking 10. Replacement of Steel Reinforcing
Table 1: Urban concrete challenges addressed using innovative admixture.
Figure 1: Building blocks used in PolyCarboxylate Ether (PCE) superplasticiser technology.
extended workability and a low water/cement ratio. Cost savings in production may be realised through mix design optimisations for cement types and aggregate composition. As a result, these technologies enable ready-mix producers to optimise inventory, facilitate logistics and reduce investments in tanks and dispenser equipment and thus also decrease maintenance costs.
ADVANCEMENTS IN CONCRETE ADMIXTURES Extended workability retention
As shown in Figure 1c), SuperPlasticiser-Super Retaining Polymer (SP-SRP) contains a large amount of building block A, responsible for workability retention. Hence, the composition should qualify this admixture for ready-mix concrete applications where long transportation times are typically encountered, under severe conditions like hot weather or difficult aggregate or cement conditions. We decided to apply SP-SRP in a 30 MPa strength class concrete, where the designed slump upon delivery to site is 10 cm - 14 cm. In this case, SP-SRP enables the RMC station to adjust initial slump at the batching station to the designed slump at delivery. The perfectly flat performance of SP-SRP ensures that, no matter when the concrete arrives at the site (as long as it is within 2 hours), the specification is matched. Retarded naphthalene-based superplasticisers, however, cannot be treated that way. Due to the severe slump loss, the batching plant would have to adjust to a slump higher than the specification requires, with consequences for the mix proportion. Furthermore, due to the slope of the slump loss curve, the actual slump delivered on site is dependent on the actual transportation time, which makes it challenging to hit a tight specification like in the example given, and re-tempering at the jobsite eventually has to occur.
Precast applications
SuperPlasticiser-High Early Strength (SP-HES) molecules are rapidly adsorbed on the surface of the cement grains and act through electrostatic and steric repulsion to powerfully disperse the individual particles of cement. The molecular structure of PolyCarboxylate Ether (PCE) polymers is essential for the early development of strength. With conventional PCE superplasticisers, the molecules cover the entire surface of the cement grain and build a barrier against contact with water. Therefore, the hydration process takes place slowly. The unique, proprietary molecular structure of SP-HES exposes a larger surface area of the cement grains to react with water. Therefore, it is possible to obtain earlier development of the heat of hydration, faster development of the hydration products and, as a consequence, higher strengths at a very early age. This advantage can even be utilised at low temperatures. The unique mechanism of this new polymer technology allows it to be adsorbed into the cement without inhibiting the hydration of the cement. Thanks to this technology, SP-HES exhibits 10% - 20% higher early strength development than traditional technology while providing good slump retention. The composition of SP-HES indicates that the performance would be useful in precast applications, where workability retention requirement is often only for less than 1 hour, due to the batching plant being in the proximity of the precast yard. In fact, SP-HES provides sufficient slump retention in the actual application under hot climate conditions. Applying SP-HES in a high slump concrete, leads to a slump loss not greater than 4 cm after 1 hour, even at 35º C ambient temperature. The slump retention of conventional PCE admixture, on the contrary, is only for approximately 20 minutes.
With the slump life extended, one would anticipate early strength to be inferior in the case of SP-HES. However, SP-HES shows not only equal early strength compared with conventional PCE, but after 28 days at standard curing conditions, the strength exceeds the benchmark by 12%. It is noteworthy that, due to the chemical nature of the mechanism of the new admixtures, its effect is quite dependent on the cement composition. Apparently, even though the early strength development can differ significantly, it is always improved, and differences are levelled out at later ages, where a strength increase of up to 15% can be expected, compared to the conventional PCE admixture. The mechanism behind the difference in strength development, which is dependent upon the cement composition, is currently under investigation and remains unclear at this point of time.
Concrete rheology enhancement
In the case of urban concrete, given the expected service life of structures, authorities and consultants specify a stringent durability requirement. In the process of making urban concrete, one needs to pay greater attention not only to aspects such as the mix design but also to its performance with respect to handling, pumping, placing, finishing and curing. Durability and sustainability are the buzz words in modern concrete world. Durability is at the forefront in the making of urban concrete. To achieve the desired durability requirements, concrete technologists must make use of higher amounts of supplementary cementitious materials, ingredients like micro silica become essential, and lower water content in concrete mixes is mandatory. Such concretes with lower water and higher powder create enormous challenges in batching and mixing of concrete. Longer mixing times reduce the operational efficiency and the concrete stickiness will be a major issue during pumping, placing and finishing of concrete. The concrete technologist has limited options to reduce the stickiness of mixes given the lower water-binder ratio and higher binder contents which are essential to achieve the desired durability parameters. This creates a demand for a solution to minimise the stickiness and hence concrete rheology is one of the important parameters when it comes to making urban concrete. Aided by advancements in polymer science and innovation, scientists have developed a new generation of polymers, that is characterised by the ability to significantly improve the rheological properties of concrete. Urban concrete mixes often demonstrate a higher viscosity due to their low water contents. Although having a high level of workability, the concrete often appears harsh, sticky and therefore difficult to pump and process. This is especially true for engineering concrete with low water/cement ratios optimised towards having a low environmental impact. To overcome these challenges, BASF has developed MasterEase, a new admixture range developed for low-viscosity concrete, With the new technology, plastic viscosity can be reduced by up to 30%, which results in a substantial reduction of pumping pressure required to pump the concrete at the construction site. Placing and finishing of the concrete is much easier, faster and hence more economical than using standard concrete. The ease is experienced in terms of mixing, pumping, placing, levelling and finishing of concrete. Concrete producers and users benefit in many ways from the new technology, which is flexible and adaptable, to produce concrete with improved workability retention. It can adapted to challenging situations such as those with temperature variations. Moreover, the high level of rheology and workability retention minimises jobsite addition of water. This is a real added value for the contractors in terms of concrete durability. The concrete is easy to place, trowel and pump. Utilising this concrete saves time and cost in every single construction project. It improves the utilisation of the transportation fleet and equipment and reduces the wear of mixers, pumps and pipelines. In addition, the possibility to reduce mixing water even further without impacting the concrete rheology, opens new possibilities for improvement in concrete mix designs. Less water in concrete mixes implies higher performance and better durability. The new technology is particularly suitable for concrete mixes which are optimised for advanced engineering properties and sustainability. High strength concrete with low water/cement ratios, as well as mixes with higher levels of secondary cementitious materials, reduce the CO2 footprint and are easier to produce and place. This helps engineers and investors to improve sustainability ratings of their projects.
Concrete strength enhancement
Given the fluctuations in concrete-making materials and the concreting practices, achieving the desired concrete strength today is a new challenge. Inferior concrete workability at the time of placing encourages the workforce to add water, which in turn reduces the concrete strength. Inconsistency in concrete-making ingredients and variations in the materials, from batch to batch, is a major pain point for concrete professionals. Switching from natural/river sand to alternative ingredients such as crushed rock fines/manufactured sand can impact concrete strength, if appropriate changes in concrete mix design are not adopted. Urban concrete and its durability requirements will demand higher replacement by supplementary cementitious materials. Not only due to the higher proportion of supplementary cementitious materials but also to accommodate the inconsistency of these materials, concrete professionals need a whole new approach to mix design, to achieve the desired strength of concrete. Hence a robust solution to address the concrete strength issues is the need of the hour.
With the advancements in chemistry and concrete admixture science, BASF Mater Builder solutions have developed a revolutionary technology that redefines concrete strength and durability. It allows concrete producers to expand concrete performance while reducing the environmental impact. Master X-Seed STE is an innovative, strength-enhancing admixture solution for the construction industry, which significantly improves both early and late-age strength development in concrete. The new solution, Master X-Seed STE, also helps to make production of concrete more efficient. The concept originated from BASF’s X-Seed, a unique seeding technology used to promote cement hydration and speed up concrete hardening. Master X-Seed STE further enhances concrete’s strength development and performance characteristics. Specially formulated for the Asia Pacific concrete market, Master X-Seed STE admixture utilises calcium silicate hydrate (CSH) nanoparticles, along with other technologies (admixture solutions), to facilitate and improve strength development at all ages of the concrete. Master X-Seed STE enables the increased use of supplementary cementitious materials, thus helping to reduce the carbon footprint associated with concrete production. Master X-Seed STE admixture allows concrete producers to expand the performance space of a given concrete mixture and optimise the cementitious content, by permitting a strength safety factor up to 15%. This allows earlier stripping of forms to improve production efficiency. It is recommended for use in ready-mix and precast concrete and Self-Consolidating Concrete (SCC).
CONCLUDING REMARKS
While we build more and more urban cities to accommodate the needs of future urbanisation, the importance of concrete as a building material is clear. In fact, the innovative use of concrete can only become even more important. For infrastructure businesses to increase their commercial viability and their relevance, contractors and builders in the market need to look beyond the traditional boundaries defined by existing construction practices, market segments and structures built. A holistic approach from all the stakeholders in the construction industry to address these urban construction and concrete-related challenges is the need of the hour. New and rapid developments in nano chemistry can certainly aid in the progress of concrete technology. This, in turn, can help in the construction processes by making them more efficient, faster and economical. The admixtures described in the article have the potential to minimise the cost related to wastage and energy. More importantly, these factors contribute towards achieving construction practices with lower carbon footprints. Cost and time savings remain the twin objectives of project owners, developers, contractors and ready-mix companies. Today, the construction industry awaits a breakthrough solution that addresses the escalating need for speed and sustainable development. Modern architecture, large-scale and high-rise constructions demand building materials that provide durability and energy efficiency. The growth of infrastructure is unstoppable. The innovative admixture technologies will be the driving force for the development and growth of infrastructure. The Master Builder solutions from BASF meet most of challenges and requirements of concrete in infrastructure development.
REFERENCES
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