Concrete is a leading contributor to global warming, producing as much as one-tenth of industry-generated greenhouse-gas emissions. A new study suggests a simple way in which those emissions could be reduced by more than half while producing a stronger, more durable material.
The study, described in the journal Nature Communications, suggests that reducing the ratio of calcium to silicate would not only cut emissions, but would actually produce better, stronger concrete.
Concrete is a mixture of sand, gravel, water and cement. Cement is made by cooking calcium-rich material, usually limestone, with silica-rich material, typically clay, at temperatures of 1,500ºC. This yields a hard mass called “clinker” which is ground into a powder.
In conventional cement, the standard calcium-to-silica ratio is 1.7. But the molecular structures of differing ratios have never been scientifically studied. The researchers built a database of different chemical formulations. They found that the optimum mixture was not the 1.7 used today but about 1.5. At that point the material can achieve twice the mechanical strength.
Because the CO2 emission in cement production come from the production of calcium, any reduction in the calcium content has a large effect on emissions. Reducing the ratio from 1.7 to 1.5 could reduce CO2 emissions by as much as 60%.