Cities dont have to be so... gray

The gray color of a giant city. Standing in the middle of downtown New York, one can see the many hues of cement that color the world of massive building construction. It's a consequence of the color of Portland Cement. Gray slabs of concrete have defined our skylines, bridges, runways, and highways. (To be more precise, the characteristic gray to brown color of ordinary cement derives from a number of transitional elements in its chemical composition. These are, in descending order of coloring effect, chromium, manganese, iron, copper, vanadium, nickel and titanium.)

But imagine a slightly prettier world where our cement was white, instead. Of course, there is a such thing as white cement already, but it's a little pricey and a lot of energy goes into reducing the presence of certain beneficial elements.

One solution, was presented by R.K. Vempati and his colleague Prasad Rangaraju from Clemson University, at the 13th ACS Green Chemistry & Engineering Conference in College Park, Maryland. The researchers propose using rice hull ash (RHA) to dramatically whiten cement. RHA is made from the controlled combustion of rice hulls—the hard outsides of rice that must be removed before we can cook and consume rice.

Drs. Vempati and Rangaraju had managed to substitute 20% by mass of cement with RHA. They saw significant compressive strength as well as a substantially whiter end product (thanks to biogenic silica from the rice hull). The end product is described as carbon neutral, which is of course, of great importance to today's modern building infrastructure. The researchers point out that the production of one ton of regular cement produces one ton of CO₂ and that there is 1 yard³ per person of cement produced every year—making concrete the second most widely used material on earth (water is the first). So by taking a second look at how we use and produce building materials, there's much more to gain than just the beautification of our cities and highways.