The ‘Hard’ Truth: Concrete’s Role in Building a Sustainable Future
Concrete has been the building block of the world’s civilisation. But the production process of cement, the main ingredient of concrete, leads to considerable carbon dioxide emissions which makes a strong case for finding and using more sustainable alternatives. In this episode of the WSP Anticipate Podcast, Laith Haboubi, Associate Director at WSP, is joined by Dr. James Aldred, Adjunct professor at Australia’s New South Wales University, to explore several aspects with regards to the different alternatives of concrete components.]
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The challenges and opportunities of using cement replacements
Cement replacements do not only reduce our consumption of cement and in turn its environmental impact, but they also have great durability benefits. The cost, availability, and consistency of quality of these materials are aspects that need to be considered and that make the use of these alternatives sometimes only possible for certain applications.
Pulverised Fuel Ash (PFA) or simply fly ash, for example, is a coal combustion by-product and is used as a cement replacement especially in countries where coal-fired power plants are a major source of electricity. Inconsistencies in the quality and quantities of fly ash produced make it a less reliable alternative compared to other materials such as granulated blast furnace slag which is easier to get and produce. Dr. Aldred says: “A power plant does not produce fly ash. It produces power and fly ash is just an uncomfortable side effect. So, they are not going to go out of their way to make sure that it is fit for concrete.”
High cost can also be an impediment to adopting some cement alternatives. Calcium aluminate cement for example is expensive but it is great for high-heat refractory applications. It can also be used for moderate acid-resistant applications. Geopolymers can be a better alternative for aggressively acidic environments as they show remarkable resistance to acidic attacks compared to Portland cement.
Is there a foreseeable future without concrete?
For every tonne of cement produced, one ton of carbon dioxide is emitted. However, “There is no foreseeable future that we can see without concrete.” says Dr. Aldred. Concrete is sustainable in the sense that it has less embodied energy and carbon than most other building materials (excluding timber). What perhaps is causing the problem is the sheer scale of the amount of concrete that we use as it is the second most used product by man after water!
A lot can be done to raise the sustainability indicators of concrete. The construction industry should be made aware that more cement in the concrete mix does not mean more durability for instance. Reducing cement can have a great positive impact on both the environment and the constructed projects. The use of recycled aggregates is also helpful in enhancing the sustainability of concrete. Many engineers and architects,
however, voice their concerns over nominal reductions in concrete quality because of recycled aggregates. The way to deal with this is to use the right grades of concrete for the right applications.
To combat corrosion, waterproofing admixtures, stainless steel, stainless steel clad, epoxy-coated rebar, and fibre reinforcement are used among other alternatives. Some of these non-ferrous reinforcements have a huge potential while some can lead to serious issues. The strength, durability, and lightweight that can be achieved with carbon fibres for example are very impressive. On the other hand, a small defect or scratch in Epoxy coated rebar can lead to very quick degradation. Other alternatives such as stainless steel face a different challenge. “The global supply of stainless steel is very small compared to the massive amount of reinforcement used in concrete.” Says Dr. Aldred. Hence, the use of stainless steel should be for elements and structures that cannot be maintained easily.
Technology and the future of concrete
New advances in the production and processing of concrete will make huge positive impacts on the construction industry. Concrete 3D printing for instance will make it easier to build intricate and complex structures. Another breakthrough in progress is carbon cure (i.e. injecting waste carbon dioxide into concrete) which has a great potential in reducing the environmental impacts associated with cement production. A third example is direct pumping which enables the production of concrete on site and improves the capacity of pumping with no disruption to traffic.