Roughly two billion tonnes of Portland cement is produced every year; accounting for approximately five per cent of man-made CO2 emissions.
There is a need to find new ways to reduce carbon emissions in building, and increase sustainability and this might be achieved is by embracing new cement technology.
The traditional cement industry is pursuing a number of different strategies: blending pozzolans with Portland cement, adding mineraliser additives to reduce process temperatures, and CO2 sequestration or storage.
One of the initiatives that resulted from this was a new type of cement, subsequently branded ‘Eco-Cement’ developed in Australia.
Eco-Cement, based on magnesium carbonate as opposed to calcium carbonate (used in Portland), is used to make permeable concretes.
It was one of the first products of its kind on the market, absorbing CO2 and water from the atmosphere during the natural setting process.
Eco-Cement is made by heating magnesite in a kiln to produce reactive magnesium oxide (magnesia).
The magnesia powder is then added to a conventional Portland cement mix which, in turn, can be mixed with aggregates, in the usual fashion, to make Eco-Cement.
Eco-Cement hydrates in permeable substrates, using mix water, then carbonates. The more magnesia added and the more permeable it is, the more CO2 the Eco-Cement absorbs.
An Eco-Cement concrete block typically takes up to one year to carbonate fully, occurring quickly at first and then slowing as the process continues.
At its end-of-life or become obsolete, any Eco-Cement structure are can be almost fully recycled back into cement.
The material’s major environmental benefit comes from the fact that Eco-Cement can effectively incorporate large amounts of waste matter into its mixture – including carbon-based wastes that would otherwise rot or be burned.
Manufacturing Portland cement is one of the most energy intensive industry manufacturing processes.
Ordinary Portland cement is made by heating limestone or clay to around 1,500ºC – the extreme heat required to operate kilns creates a significant demand for energy.
Approximately six million BTUs are required to produce one tonne of Portland cement.
The process itself releases 0.8 tonnes of CO2 per tonne of cement.
When this is mixed with water to make concrete, however, each tonne can absorb up to 0.4 tonnes of CO2 which is an overall carbon footprint of 0.4 tonnes of CO2 per tonne of cement.
Producing Eco-Cement, the kilns do not need to be run so hot. Magnesium carbonate converts to magnesium oxide at around 650ºC.
Like Portland, Eco-Cement absorbs around 0.4 tonnes of carbon per tonne, but carbon absorbed in Portland cement reacts with calcium to deposit calcium carbonate crystals, which weaken the strength of the concrete.
Eco-Cement, which is magnesium-based, actually gains strength from the magnesium carbonate crystals that are the result of the equivalent reaction.
Given the ubiquity of cement use, this is bound to be an attractive answer to the needs of construction companies, especially in Middle Eastern countries where an ongoing steam of very large, hugely ambitious infrastructure and construction projects appears to be underway and where there are very few practical alternatives to cement.
More research is needed, but the fact that people are working on solutions of this kind is certainly a hopeful one.
The environmental benefits that might result from commercialising the concept are huge.
(this article published in 1BINA.my)
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