Pothole repair made eco-friendly using grit from wastewater treatment


Date:
August 18, 2020
Source:
American Chemical Society
Summary:
Potholes are aggravating to drive over, and they can cause billions
of dollars of damage every year to automobiles. Now, scientists
report a brand-new way to repair roads that's also eco-friendly
-- by using a remnant of wastewater treatment called grit that's
usually disposed of in landfills.



FULL STORY ========================================================================== Potholes are aggravating to drive over, and they can cause
billions of dollars of damage every year to automobile wheels,
tires and suspensions. Currently, road crews fill in these holes with hydrocarbon-containing asphalt, but that material can leach out, polluting
the environment. Now, scientists report a brand-new way to repair roads
that's also eco-friendly -- by using a remnant of wastewater treatment
called grit that's usually disposed of in landfills.


==========================================================================
The researchers will present their results today at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo.

"We had an idea to divert wastewater grit from landfills and turn it into
a marketable product," says Zhongzhe Liu, Ph.D., who is presenting the
work. "We formulated it into a ceramic mortar that could be used as a
patch for pothole repair." The substance, known as grit assisted patch
(GAP), is ultimately safer for the environment than hydrocarbon-based
asphalt.

But grit, a heavy, unbiodegradable solid, requires processing to
become GAP.

First, wastewater containing sewage, food scraps and other waste is
processed at treatment plants. The result is clean water that is released
into waterways, but also solids from the preliminary treatment that are
mostly sand and gravel, and this is referred to as grit. Because grit
contains pathogens and impurities that make it unsuitable for direct
recycling, it is usually taken to a landfill and buried.

Liu, who is at California State University-Bakersfield, and his
collaborators were looking for ways to make grit useful, perhaps as a
road material. They decided to incorporate it into a chemically bonded phosphate ceramic (CBPC).

CBPCs are routinely used to treat hazardous or radioactive waste for
disposal, but no one had used this yet on wastewater products.

Because a CBPC contains ingredients that would inactivate microbes,
the researchers thought this could be a good way to kill pathogens and
end up with a material that could be safely applied to roads. "In the
first step of making a CBPC, we mix the wet grit with calcium oxide
and magnesium oxide, which form an alkaline grit slurry that prevents
the proliferation of pathogens," Liu says. "The second step is to add a
weak acid, potassium dihydrogen phosphate, into the pathogen-minimized
alkaline slurry to form the grit-CBPC mortar." Conventional asphalt patch contains bitumen, a sticky, black residue left over after petroleum distillation. The conventional patch contains polycyclic aromatic
hydrocarbons (known as PAHs) that are a risk to human health. A grit- formulated patch eliminates this environmental concern because its matrix
is composed of calcium and magnesium oxides that are not toxic to people.

So far, the researchers have analyzed GAP performance in the lab,
showing it has a compressive strength comparable to asphalt pavement,
and 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 on improving GAP's compressive strength even further, so it could potentially be used for other
applications, such as building wheel stops at the end of parking spots.

The next step for getting GAP on the market as a pothole patch is
to evaluate its bond strength when in contact with existing pavement
and its durability when exposed to environmental extremes. The team
is currently working on demonstration-scale experiments to field test
GAP on an operational roadway with regular traffic. If necessary, they
will explore additives to further improve the mechanical properties
and durability of the new material. In addition, they plan to conduct a side-by-side comparison of GAP and conventional patch to gain a thorough understanding of the advantages it provides in terms of carbon footprint
and economic benefit.


========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/08/200818094032.htm

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