Construction is a part of a growing economically emerging country like India. Every day new buildings and roads are being constructed and the key to all this construction is a powdered grey coloured binder known as Cement. Seldom used on its own, cement is used to bind the construction materials together by adhering to them as it sets and hardens. When it is mixed with fine aggregate the resulting mixture is mortar which is used for masonry. Mixing of cement with sand and gravel produces concrete for construction task.
The most common variation of cement used is the Portland cement which sets like an adhesive due to a chemical reaction between the dry cement and water. Each passing year witnesses millions of tonnes of cement being produced and consumed worldwide. China, India and USA are the top three producers as well as consumers. Cement is a vital part of industries like chemical, cement, industrial and real estate and construction. But with its convenience comes the baggage of its effect on the environment. The production of cement involves heating or roasting of limestone and clay at high temperature in giant kilns releasing tonnes of carbon dioxide in the air. Dry cement powder causes severe eye and respiratory irritation and a long duration exposure can cause diseases like tuberculosis. It is highly alkaline and the setting process i.e. mixing with water makes it even more corrosive and can severe skin burns on contact. The reaction also produces some carcinogenic and toxic chemicals. So while Cement may be a boon to construction, it seems to be a bane to the environment and human beings.
Looking into cement’s unwanted effects, scientists have long been searching for safer, cheaper and viable alternatives. The recent result of this research is Green Cement. It is defined as “A cementitious material that meets or exceeds the functional performance capabilities of ordinary Portland cement by incorporating and optimizing recycled materials, thereby reducing consumption of natural raw materials, water, and energy, resulting in a more sustainable construction material.”
Right now there is no fixed recipe to produce green cement. Individual researches have created substances that set like cement and are as sturdy. The whole idea behind Green cement is making a product that reduces carbon emission, requires less energy for manufacturing uses industrial wastes as raw materials, has high long-term strength and higher ductility, reduced porosity and enhanced mechanical strength. These goals are achieved by using alternative fuels i.e. fuel other than petrochemical or coal, using ground limestone which reduces cost and carbon emission, using Ground granulated blast furnace slag which uses less energy and works at low heat.
Other ideas are based on the use of resource efficient cement mixes. This includes:
Calcium Sulfoaluminate cements which use comparatively lesser energy and release less carbon;
Calcium aluminate and calcium alumina–silicate cement which is comparatively quick to produce and produces less carbon;
Magnesium-oxide based cement which requires less energy to produce and form a carbon-negative cement meaning it absorbs more than it releases carbon in the process.
Alkali-activated cement which is competitive with regular cement in terms of performance and cost, produce very less carbon, have a longer life and use industrial waste as raw material thus helping in recycling.
Commercially, many companies in the USA and Australia are now manufacturing green cement for worldwide consumption. They differ on various points but are aimed towards providing a cleaner and greener alternative to cement. A company uses seawater to make calcium carbonate out of the carbon emissions to be used as Portland cement substitute. Yet another one uses superheated steam to modify cement particles which are more reactive and separates and captures carbon emitted in the process. Zero-carbon footprint claims a cement manufacturer, which is made of fly ash and liquid additives.
Construction is essential for humankind and so is cement. The idea now is how to reduce if not reverse the damage that has been caused by the popular methods of construction. With every industry in need to go green and sustainable, it is important for cement manufacturers to look for an alternative that help them take up the cause. The need to deliver an alternative that suffices, if not supersedes, the current virtues of Portland cement soon, persists on the scientific minds.