Avanish Singh, M.tech, Maulana Azad National Institute of Technology, Bhopal
Kanchan Kushwaha, M.Tech, Samrat Ashok Technological Institute, Vidisha
Dr. Rakesh Kumar, Head & Senior Principal Scientist, Rigid Pavement Division, CSIR-CRRI, New Delhi
Ordinary Portland Cement (OPC) has been ruling the cement-based construction industry since 18th century i.e. start of its commercial production. In last two decades, the manufacturing rate has grown from 1.5 billion metric tonnes in 2000 to over 4 billion metric tonnes in 2018 . Global cement production is expected to increase from 4 billion metric tonnes in 2018 to 4.83 billion metric tonnes by 2030. Figure 1 shows the global production of OPC over last 8 years. Ordinary Portland cement (OPC) has stabilized itself as an essential and tactical commodity material . Because of reliance on OPC, its global cement production has now reached to over 4 billion tonnes per year due to fast infrastructural development in emerging economies . Approximately, 50% of world’s OPC is consumed to produce over 11 billion tonnes of concrete annually, while rest 50% is used for other applications such as mortars, screeds, coatings etc . Today sustainable, economical and durable concrete is more desirable with increasing infrastructure and building demands . As per an estimate, the global demand of cement is expected to increase over 12-15% by 2050 . In past few years Middle East regions, Northern Africa and developing countries such as China and India have seen enormous growth. Presently, China is leading the cement industry by manufacturing 58% of the total global demand . U.S. Geological Survey estimates that over 4 billion tonnes of cement produced annually and approximately 0.9 tonne of CO2 is released per one tonne of cement produced as shown in figure 2 [3,7]. As per this estimation over 3.5 billion tonnes of CO2 annually is being produced by the cement industry. Therefore, cement industry is responsible for nearly 5–7% of global CO2 emissions . Besides releasing CO2 from cement plants, SO2 (sulfur dioxide), NOx (nitrous oxides) are also being thrown in to atmosphere causing acid rain and greenhouse effect . Excluding these gas emissions, cement manufacturing also roots to the depletion of natural resources. It is accepted that around 1.5 tonnes of raw materials is required to manufacture 1 tonne of OPC [10,11]. Furthermore, manufacturing of clinkers encompasses gigantic energy . Hence, cement industry is facing massive challenges such as conservation of natural resources, escalating costs of energy sources, CO2 emission reduction etc, with the current growing global demand [13,14].
Figure1: Global Cement Production from 2010-2018 
Cement requirements can be reduced through measures like optimized dosage of cement in concrete, recycling and reuse of construction and demolish waste, and increasing the design life of roads, buildings and other infrastructures.
Figure 2: Amount of CO2 Emission from 1 tonne of Cement ProductionThe CO2 emission from cement production has increased 0.3% per year from 2014 to 2017 which is forcing the cement industry to find alternatives of OPC. In past few decades many alternatives for OPC were made to partly/fully replace OPC with eco-friendly binding materials to diminish the hostile environmental effect of construction industry. One of the common substitutes is application of industrial by-products (fly ash, slag, silica fume) as partial replacement of OPC [15–18]. Key strategies to cut carbon emissions from construction industry as shown in figure 3 includes carbon capture and storage from cement production, recycling and reuse of building materials, clinker substitution in cement production and making the industry alternative cements friendly which emits less CO2 than OPC [19-22].
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