Conventional asphalt patching contains bitumen, a sticky black residue left after the distillation of petroleum. The conventional patch contains polycyclic aromatic hydrocarbons (known as PAHs) which are a risk to human health. A patch formulated with sand eliminates this environmental concern because its matrix is composed of calcium and magnesium oxides that are non-toxic to humans.
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"We came up with an idea to divert sand from landfill wastewater and turn it into a marketable product".says Zhongzhe Liu, Ph.D., who presents the paper. "We formulated it into a ceramic mortar that could be used as a patch to repair potholes.". The substance, known as a sand-assisted patch (GAP), is ultimately safer for the environment than hydrocarbon-based asphalt.
But sand, a heavy, non-biodegradable solid, requires processing to become GAP.
First, wastewater containing sewage, food leftovers and other waste is processed in treatment plants. The result is clean water that is released into the waterways, but also solids from the preliminary treatment which are mainly sand and gravel, and this is known as sand. Because sand contains pathogens and impurities that make it unsuitable for direct recycling, it is usually taken to a landfill and buried.
Liu, who is based at California State University, Bakersfield, and his collaborators they were looking for ways to make the sand usefulperhaps as a road material. They decided to incorporate it into a chemically bonded phosphate ceramic (CBPC). CBPCs are commonly used to treat hazardous or radioactive waste for disposal, but no one had yet used them in wastewater products.
So far, researchers have analysed the performance of GAP in the laboratory, demonstrating that it has a compressive strength comparable to asphalt pavement.They believe its longevity will be superior to that of asphalt-based patches. The group has filed a patent for GAP based on these initial findings. In the meantime, they are working to further improve the compressive strength of GAP, so it could be used for other applications, such as the construction of wheel stops at the end of parking spaces.
