Five percent of CO2 emissions produced by humans comes from making cement. Cement is used in making concrete. Currently, one ton of CO2 is released while making one ton of cement for concrete. Using rice husks would cut the CO2 emitted into the atmosphere.
Rice husks are rich in silicon dioxide (SiO2) which is an essential ingredient in concrete. Unfortunately, burning the husks has previously left ash too “contaminated by carbon” to be useful.
Researchers in Plano, Texas have discovered that burning the husks at very high temperatures in a furnace, 800 degrees centigrade (1,472 degrees Fahrenheit), gets rid of the carbon leaving only pure silica particles behind. Some CO2 is emitted by the process but that is easily offset by the amount of CO2 absorbed into rice paddies each year.
Concrete has been made using waste materials like: “slag from steel mills, coal fly ash and silica fume, a leftover from the silicon metal industry”. Rice husks have been avoided because burning them left such a high carbon content.
Now that a way has been found to reduce rice husks to carbon-free silica particles, the husks can replace 20 percent of the cement normally used to make concrete. Using rice husks will also cut down on the overall carbon emissions from the concrete industry. Being able to use rice husks will be especially useful in countries like China, India and Japan where rice is a staple crop and concrete is a common building material.
Rajan Vempati of ChK Group, Inc., and his research team are continuing to test and refine their method. If everything goes as planned, the team will build a furnace big enough to burn 15,000 tons of rice husks annually.
Building with concrete and concrete forms has been advocated as providing a stronger home, with lower energy bills and less maintenance. Concrete houses will withstand strong storms with less damage. However, the immense amount of carbon dioxide produced during the process has kept green builders from completely embracing it as a green solution. With rice husks cutting down on the amount of CO2 produced, green builders might change their opinions.