Cement is a strong binding agent or adhesive, which serves as the primary ingredient in concrete. Concrete plays an elementary role in construction as a critical component in foundations, structures, roads, bridges, highways, embankments, and more. Given its key role in construction and urban development, the production levels of cement continue to rise every year. At present, the annual production levels of Ordinary Portland Cement (OPC) amount to about 3.6 billion metric tons. According to Columbia University’s Earth Institute, the annual growth rate of cement production is 2.5%. According to present findings, the cement manufacturing industry produces more than 2.55 billion tons each year. By 2050, it is assumed that the yield of cement will surpass 4.5 million tons.
As important as cement is, the process to manufacture it is also a major cause of industrial air pollution. The production of clinker, a key ingredient in cement, is a chief source of emission of noxious gases, especially carbon dioxide.
In the cement manufacturing process, a mixture of limestone and clayey materials is fed to a kiln operating at 1400⁰C. After the thermal process, the processed material is ground, forming a lumpy and solid substance known as clinker. Finally, gypsum is mixed with clinker, forming cement. The clinker production process is highly energy-intensive and releases gaseous effluents. For 1 tonne of cement produced, 0.6 to 1 tonne of carbon dioxide is released. In addition to clinker production, there are other processes in cement manufacture that give off CO2. But cement is so indispensable in all walks of life, it is hard to imagine a world without cement production. Can there be a viable substitute for cement?
Green Cement Offers the Solution
As an initiative to bring down the threats produced by emission, the manufacturing process of cement can be suitably altered to bring down the emission levels significantly. Green cement is a form of cement produced with the help of a “carbon-negative manufacturing process.” In other words, cement produced as the final product of a technologically advanced process, such that emissions during unit operations (like clinker production) are minimized, is referred to as green cement. Green cement is an eco-friendly product which resolves serious environmental issues and minimizes the carbon footprint of cement production.
The prefix green before green cement represents anything that is environment friendly or contributes to making the environment greener. The significance of green cement is being continually realized by all nations, thanks to the international symposiums raising awareness about sustainability and climate change. There are multiple technologies and mechanisms for green cement manufacture, patented by different manufacturing agencies.
However, greater awareness about green cement and its potential is needed in the present scenario. Manufacturers and consumers often consider it a financially risky venture to invest in an innovative product or production technology. Significant changes in industrial set-ups also lead to raised financial expenses. The national governments need to support green cement production for meeting construction requirements. Manufacturing companies and investors must be given incentives for adopting green cement manufacturing processes. Appointment of home inspectors will help keep records of buildings made of green cement, so that such buildings could be certified and builders rewarded.
One international company that has embarked on the promising initiative successfully and set benchmarks in the international market is
Ceratech, a cement manufacturer from the United States. The feed mixture used in its manufacturing process constitutes 95% recycled fly ash and 5% renewable liquid additives. The system adopted known as hydraulic cement system complies with stringent technical specifications like International Code Council (ICC) and United States Green Building Council (USGBC). According to the standards of Environmental Product Declaration (EPD), cement manufactured at Ceratech has almost zero carbon footprint. The process reduces consumption of virgin resources by 95%, while water requirement is reduced by half.
Hydration of Ceratech’s green cement results in an extremely dense crystalline material known as calcium silicate aluminate hydrate (CASH). Its desirable properties include resistance to sulphate attack, high early strength, resilience, durability, crack resistance, and low chloride permeability. Its corrosion resistance is three to four times that of Ordinary Portland Cement (OPC). It is two times more resistant to freeze-thaw. Pre-heating of the raw material is a step adopted in the modified process. It leads to energy savings and also makes the manufacturing plant environmentally friendly.
Scope of Green Cement
Green cement making reduces cement intake, and its major raw materials include discarded industrial wastes like blast furnace slag and fly ash. Hybrid green cements are specialized forms of green cement characterized by attractive parameters like high long-term strengths and higher ductility. In the manufacturing process of green cement, carbon dioxide emitted during the manufacturing process is significantly reduced. Green cement can reduce the carbon footprint by 40%.
Apart from reducing carbon dioxide emissions, the green cement manufacturing process also helps maintain cement strength. Composed of calcined clay and powdered limestone, green cement has desired characteristics such as reduced porosity and enhanced mechanical strength. Green taxes can be levied on traditionally produced cement, raising OPC prices by two times. Hence, green cement has a great scope for the future and will offer price and quality benefits.