The global annual consumption of concrete – the most extensively used material on Earth after water is in excess of four billion tons. The production of cement and the curing process during concreting releases substantial amounts of CO2 – over 8% of the global greenhouse gas emissions. New technology allows use of sequestered CO2 to manufacture cement resulting in 70% less CO2 emission and additional sequestering benefits. There is a need for urban planners to ensure that concrete used for various infrastructure projects are sustainable.
The National Infrastructure Pipeline is an ambitious project launched by Prime Minister Narendra Modi and by some estimates, it is believed that around 16% of this will be used to upgrade and build new urban infrastructure in Indian cities. The National Smart Cities Mission is a key element for realising this vision by providing solutions for urban renewal and retrofitting key infrastructure projects to make sustainable cities for the future.
But geographically, India is a vulnerable nation in the current climate crisis. The heart of the climate crisis is the excessive production of carbon dioxide (CO₂). With more CO2 produced, it increases the greenhouse effect, trapping heat and warming the Earth’s oceans and atmosphere resulting in profound changes to the world’s climate ecosystem. The result is that we have harsher droughts in the summer and more erratic weather phenomena like cyclones, cloudbursts, hailstorms, typhoons and hurricanes.
Therefore, it becomes imperative that cities start to build resilience from the brick level.
The ClimateSmart Cities Assessment Framework has identified the need to build green buildings for the future. The National Institute of Urban Affairs (NIUA), the Indian government’s research and training for urban development has come out with a manual for urban planners on sustainable construction and demolition waste management. The manual identifies that city planners may face challenges to implement sustainability goals local urban bodies, private players and state government bodies. The manual suggests that planners refer to the National Building Code of India 2016 to encourage the use of recycled construction materials and demolished waste and it prescribes that planners should explore technology options when it comes to building materials.
With this context, it is worth noting the advancements in concrete and cement technology to advance sustainable development of cities.
The global annual consumption of concrete – the most extensively used material on Earth after water is in excess of four billion tons. The key material in concrete, cement, works like a binder. Both the production of cement and the curing process during concreting releases substantial amounts of CO2. As a consequence of its intrinsic chemistry, approximately one ton CO2 is emitted for every ton of cement produced. Cement is responsible for 8% of the global greenhouse gas emissions. The Cement Action Plan under the World Business Council for Sustainability Development suggests removal of eight billion ton CO2 each year to achieve negative emission by 2050.
City planners need to be up to date with new types of concrete which reduce the amount of CO2 emissions. For example, SOLIDIA, an American cement producer, has invented a process that results in 40% less CO2 emission. Further, the new process uses 30% less energy, and produces more cement for the same raw material input. SOLIDIA’s research shows that injecting CO2 instead of water in fresh concrete increases compressive strength, expedites curing, and obviates use of water for curing. It is thus estimated that 15kGs of CO2 can be sequestered per cubic-meter of Ready-Mix Concrete (RMC), and 15-23kGs per cubic-meter of precast structures.
Needless to add that higher strength in concrete can result in reduced cross sections of concrete structures, better space utilization, and enhanced economy. Reduction in water consumption is a boon for water starved developing countries in Asia, Middle East, etc., where infrastructure development is a political and aspirational priority. It is significant to note here that globally three trillion litres of water is used for curing of concrete. Add to that power consumed in pumping this water.
Cement industry and infrastructure developers could possibly take a u-turn in carbon emission if they succeed in commercial utilization of sequestered CO2, together with steel slag and industrial waste, to replace limestone – a significant ingredient in manufacture of cement. Referred to as synthetic limestone, every ton produced would capture 440kgs of CO2.
Another technique under research involves recycling demolished concrete and blending it with fresh concrete while injecting sequestered CO2. Advantages of casting concrete by this method are substantial , viz.,
- Sequestration of CO2;
- Less energy consumption;
- Reduction in reaction time in the setting process;
- Extra structural strength – reduced cross section of structural member;
- Substantial reduction in curing water;
Overall, concreting this way would result in 70% less CO2 emission from current levels, and at the same time sequestering CO2 already released. These technologies are in their nascent stage undergoing scrutiny on the techno-economics. Parameters of strength and curing process are the key. Indian cement manufacturers jointly with their technology partners too are exploring commercial viability.
However, on a policy level, there is a need for urban planners to ensure that concrete used for various infrastructure projects are sustainable. The NIUA’s manual and the National Building Code of 2016 are welcome guideposts for the entire construction industry. There is a need for the private sector, who are on the forefront of building material sciences to interface more with government bodies and regulators to make new best practices.
This article has been authored by Arvind Rastogi (consultant, sustainability) and Shashidhar KJ (consultant, editorial operations).