According to foreign media, the concrete is made from a mixture of cement, aggregates (such as gravel) and water. If the mixture dries too quickly, cracks will form in it when cured. But now, scientists have determined that the use of coal ash balls could prevent this from happening.
Typically, to ensure that the poured concrete does not dry too quickly, the contractor takes measures such as covering the concrete with film or spraying it with water.
However, getting these things done can be cumbersome, which is why some research groups have developed lightweight porous aggregates that initially absorb water and then slowly release it into concrete substrates. The idea is that by using these materials, concrete will dry at a more controlled and uniform rate without covering or spraying.
Researchers at Drexel University in the United States are looking for a cheaper, richer form of such porous aggregates, turning to “fly ash” waste from burning coal in power plants. The team, led by Associate Professor Yaghoob Farnam, combined fly ash with bonded chemicals to form tiny spheres and then bake them for a few minutes at 1160oC.
The resulting material, called SPoRA, represents a “spherical porous reactive aggregate”. Not only is it cheap, easy to manufacture, but it absorbs almost half the water weight – much better than some commercially available aggregates. As the water is dried, it gradually spreads from the sphere into the concrete matrix, ensuring that no cracks do occur.
“The solution we’ve proposed involves recycling this waste (coal ash) into a porous lightweight aggregate with excellent performance at a lower cost than current natural and synthetic options,” says Farnam. This material and process will not only benefit the concrete industry by improving the quality of its concrete products, but will also help to exclude coal ash from landfills. “
A paper on the study was recently published in the journal Cement and Concrete Composites.
In addition, scientists at Rice University have previously reported that fly ash can also be used as an ecological alternative to traditional Portland cement.