As has been stated in the past on this blog, the manufacture of concrete, specifically cement, is a incredibly energy intensive/dirty process that accounts for about 5% of the annual global CO2 emissions generated as a result of human activity. For every ton of cement produced, a ton of greenhouse gas is released into the atmosphere.
For a while now various industrial waste products from coal fly ash to steel slag have been used in concrete to reduce the amount of Portland cement needed. Now, researchers in Plano, Texas have developed a method that turns rice husks into a material that can be used as a partial replacement for the cement content in concrete.
Rice husks contain high amounts of silicon dioxide which is an essential component in concrete. Though scientists have been trying to utilize the silicon in rice husks (for use in concrete) for decades, the resulting ash created, when the rice husks are burned, has been to high in carbon to be useful as a cement substitute.
Burn Baby Burn
The ChK Group’s research has developed a technique using an oxygen-free furnace to heat the rice husks to over 800 degrees centigrade that drives away all of the carbon and leaves only pure silica in the ash. This ash can comprise up to 20% of the total content of concrete and not only makes the material stronger, but enables it to far better resist corrosion.
Currently this method is lab tested only, but there are plans to build a full sized processing plant within the next couple of years. If this new method were to utilize all of the rice husks produced in the United States, it could produce 2.1 million tons of ash each year. This method has even greater potential in developing countries such as China and India, where rice and concrete consumption are much higher.
So How Is This Better?
Though on the surface this method of using the silica in rice husks in lieu of cement sounds as if it’s environmentally more friendly (cause it’s coming from organic matter), in reality the process really isn’t that necessary nor environmentally friendly. The total cement content that can be replaced with rice husk ash is essentially the exact same amount replaced by nastier by-products like coal fly ash and steel slag. Though the properties of these waste products are slightly different from those found in rice husk ash, these more toxic substances perform the same function in concrete, i.e. cement replacement, strengtheners, etc. So it somewhat begs the question as to why taking an organic by-product, (that can biodegrade) and spending fossil-fuel-based energy to transport and burn it, makes better environmental sense than using a more troublesome to dispose of industrial waste product that results from unrelated processes that transpire regardless of concrete production.
The Good: A process that utilizes organic waste to reduce the cement content in concrete; thereby reducing the emissions resulting from its production. Developing countries that have enormous rice production may be able to use this process to lessen the carbon footprint of their concrete.
The Bad: This process is seemingly unnecessary when there are already industrial by-products being recycled into concrete that perform the same function as rice husk ash. Producing rice husk ash requires fossil-fuel-based energy and produces greenhouse gases.
The Bottom-Line: While there may now be a method that can utilize rice husks for concrete, its use, from an environmental perspective, isn’t really necessary considering it will only take the place of other more polluting industrial by-products.
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