A typical composition of Ordinary Portland Cement combines calcareous materials (or calcium carbonate) and argillaceous substances (silicates of alumina) crushed and ground together above 1500º C to form a uniform powder (in the dry process) or a homogenous paste (through the wet process).6 Figure illustrates the principle ingredients of cement whose characteristic properties are described as follows:
Their proportion controls the chemical properties of cement in terms of strength and settling properties. Most cements are hydraulic in nature, ie, they set in the presence of water and release heat due to reactions between these components. A certain category of cement is non-hydraulic where they set in dry form and reaction occurs in the presence of carbondioxide in the air. The latter category is meant for specialised applications such as resistance to chemicals, etc. This section highlights the chemical process associated with commonly used Portland cement, which is a form of a hydraulic type of cement. The following steps illustrate chemical reactions, which govern the settling and hardening properties of the cement when applied to a construction structure.9
These materials can be added to the concrete as they contribute to the hardening process due to their hydraulic and pozzolanic properties. The most commonly used SCMs are:
The Cement industry is the only industry that demonstrates a great example of converting ‘waste to wealth’ by making use of rejects from other industries. Over time, the Cement Industry has created several opportunities around the optimisation of resources and energy inputs. The Indian Cement sector is at the forefront of energy and fuel efficiency related innovation with a performance at par with the best available technologies globally. Moving forward, supporting policy frameworks will enable more advances in the sector.