Reducing Carbon Emissions in Concrete

Climate change is a rapidly escalating emergency, with the building and construction industry responsible for 39%⁽¹⁾ of all carbon emissions in the world.

While operational emissions accounting for 28% are being addressed through energy efficiency and renewal energy, the remaining 11% comes from upfront or embodied carbon emissions associated with construction materials and processes. As new construction is expected to double the world’s building stock by 2060, addressing upfront or embodied carbon emissions is critical in combating climate change and limiting global temperature rise to 1.5^oC as per the Paris climate accord.

Much of the embodied carbon emissions come from concrete, the most widely consumed man-made material in existence (second only to water). Cement, the major constituent of concrete, has a massive carbon footprint - one ton of cement represents about one ton of CO₂ emissions. Cement accounts for about 8% ⁽²⁾ of the world’s CO₂ emissions, which is more than all the trucks in the world put together. If cement were a country, it would be the third largest emitter of CO₂ emissions behind USA and China! In parallel, cement also depletes natural resources from our planet - such as limestone, clay and other materials.

Coal combustion products and steel slag are low carbon construction materials derived from industrial waste streams - coal-fired thermal power plants and blast furnace steel plants respectively - which can reduce pure cement usage, hence reducing embodied carbon emissions and enabling sustainable construction. Specifically, India being a coal-power driven economy, produces 200M+ metric tons of fly ash every year. Unutilised ash is dumped into ponds, resulting in economic (non-productive land use), environmental (air pollution, heavy metal leaching, impact on agriculture and contamination of water table) and social (lung and respiratory diseases, cancer and neurological disorders) implications. For example, fly ash contributed to about 37% PM10 and about 26% PM2.5 pollution ⁽³⁾ in Delhi – the capital of India. However, the right quality fly ash and value added products can be productively utilised in construction, with an array of technical advantages in addition to economic, environmental and social benefits.