Cement has been the cornerstone of human civilisation development since its discovery by Joseph Aspdin in the early nineteenth century. Ordinary Portland Cement (OPC) has been historically produced by grinding clinker (95%) with gypsum (5%). Over the past few decades, the Indian Cement Industry has been increasingly substituting clinker with industrial byproducts having hydraulic properties such as ground granulated blast furnace slag (byproduct of iron and steel industry) and fly ash (byproduct of power industry) towards development of greener alternatives such as Portland Slag Cement (PSC) and Portland Pozzolana Cement (PPC) respectively. Replacement of clinker leads to a direct reduction in emissions associated with thermal and electrical energy consumption and a clinkerisation process. Clinker substitution is widely recognised as the key lever for promoting decarbonisation in the Cement Industry and realising a circular economy of industrial byproducts, which are commonly considered an environmental hazard.
Table highlights the gradual increase in the production of greener alternatives such as PPC and PSC in India. At 65% (2017), PPC is the dominant variety of cement produced in India. While in percentage terms the share of PSC in the cement portfolio is declining, the absolute production of PSC has been on the rise. Other value added application based cements make up 1% of the total cement produced.
The historical increase in the production of PPC and PSC have been strongly aided by the availability of fly ash and slag in India, which continues in the present times. Steel production in the upcoming decade is projected to increase in line with cement. The rising recycling levels and adoption of scrap based electric arc furnaces in the Steel Sector, however, could reduce the future availability of blast furnace slag. In COP26, India has increased its target of renewable energy to 500 GW by 2030. The consequential decarbonisation of the electricity grid would tend to impact the availability of fly ash. While the Cement Industry has started exploring alternative clinker chemistry and assessing/utilising alternative materials such as ground limestone, calcined clay, rice husk ash, and silica fume, the overall substitution potential of these alternatives remains limited.
The quantum of clinker that can be substituted in the final cement product depends largely on the characteristics of the alternative raw material and end use application. Voluminous legacy waste and annual generation of significant quantum of cementitious materials presents both an opportunity and an environmental concern, which necessitates immediate action towards utilisation into large volume applications. Adoption of Polluter Pays Principle can help provide the necessary impetus towards adequate pre-processing and transportation of the required substitute cementitious materials from source plants located in various nooks and corners of the Country. Additionally, it is important to increase awareness amongst consumers on the durability and reliability of these green cements as suitable alternatives to OPC. Procurement of blended cement in public infrastructure projects would go a long way in instilling confidence among individual home builders/project owners/consumers to adopt greener alternatives. Concrete is the 2nd most consumed material after water and transitioning towards such greener alternatives like PPC and PSC would help build a more sustainable society.