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Greener cement production starts soon

Posted: 24/01/2008

A factory on the outskirts of Melbourne, Australia could be about to provide a big step forward for green building. It's the first commercial enterprise in the world dedicated to transforming waste from power stations and blast furnaces into geopolymer concrete, said by the manufacturer to offer significant savings in carbon emissions compared to normal cement based concrete.

The factory, owned by the company Zeobond, is due to start operations in February.

Geopolymers, the basic substance of Zeobond's E-crete are a type of inorganic polymer formed at room temperature by using industrial waste, fly ash and bottom ash from power stations, blast furnace slag from iron making plants, and recycled cement waste to form a solid binder that looks like and performs a similar function to ordinary Portland cement.

According to the World Business Council for Sustainable Development (WBCSD), “Concrete is the most widely used material on earth apart from water, with nearly three tons used annually for each man, woman, and child.” Cement is made by burning fossil fuels when the limestone and clay are heated to over 1300°C and CO2 is liberated from the decomposed limestone.

The hugely energy intensive calcination step is a necessary key to cement production. Therefore, the focus of reductions in CO2 emissions during cement manufacturing is on energy use.

However, emissions reduction is ultimately limited by two factors: (1) the high temperature needed to drive the calcination of limestone, and (2) 60% of CO2 produced in cement manufacture arises from the calcination reaction itself.

The manufacture of cement produces about 0.9 kilograms of CO2 for every kilogram of cement. At least 4% of global CO2 emissions result from cement manufacture, making this product one of the more polluting activities undertaken by mankind.

One of the primary advantages of geopolymers over traditional cements from an environmental perspective is largely associated with the much lower CO2 emissions from geopolymer manufacture compared to OPC production. This is mainly due to the absence of the high-temperature calcination step in geopolymer synthesis.

While the activators used in geopolymers do reintroduce some CO2 cost, the overall CO2 saving due to widespread geopolymer utilisation is in the order of 80-90% when compared with Portland cement.

Zeobond is currently involved in an accreditation process and Life Cycle Analysis with a view to having the environmental benefits of geopolymers officially acknowledged by the relevant Australian and international bodies.

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