Cement, Energy and Environment

2  The per capita consumption of cement was apparently more than 550 kg, which happened to be more than the per capita consumption of food in the world.  The resultant cement-based construction materials including concrete can be tentatively estimated at 2 m 3 or 4.5 tonnes per person, which is second only to consumption of water. APPROACHES FOR MINIMIZING CO 2 EMISSION FROM CONCRETE APPLICATIONS Almost about two decades back Prof. P K Mehta of University of California, Berkeley, had suggested three primary tools as the basic strategy for reducing the impact of CO 2 emission in concrete construction as depicted in Fig.2. The following tools suggested looked apparently simple but in a way they were interlinked and each tool required many activities to precede its implementation :  Reduce concrete us e in construction  Reduce cement proportion in making concrete  Reduce clinker content in making cement. Later Prof. P. Aitcin of University of Sherbrooke, Canada, elaborated the strategy further by adding a few more conceptual steps to the above basic tools as mentioned below:  More clinker with less limestone and coal  More cement with less clinker  More concrete with less cement  More kN’s in concrete with less cement and aggregate  More durable structure with longer life cycle. The above segmental approaches are explained in the following sections. More Clinker with Less Limestone and Cal As we all know, the carbon dioxide emission continues to remain a major concern for the Portland cement manufacturing process. The concern emanates from the release of about 535 kg CO 2 per tonne of clinker from the limestone calcination and about 330 kg CO 2 per tonne of clinker from the fuel combustion, resulting in direct emission of 835 kg CO 2 per tonne of clinker. The corresponding figure for cement would vary, depending on the quantity of clinker used in making a tonne of cement and the grinding technology adopted. In this context, the industry at large has adopted the following key levers to reduce the CO 2 emission level at the clinker-making stage:  Use of alternative non-carbonate calcium-rich raw materials  Enhancing use of alternative fuels in place of conventional coal  Making unit operations more energy efficient  Generating electricity with waste heat  Increase in the use of renewable energy. With these measures, the average specific electricity consumption and specific heat consumption in India have come to 82 kWh/t of cement and 725 kcal/kg of clinker against the corresponding global consumption Fig.1. Comparison of cement and steel production with growth in population during the last six and half decades. Fig.2. Basic tools for minimizing CO 2 emission in concrete application.