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Research: Coal Ash Strengthens Concrete

Friday, November 1, 2019

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Concrete, well known for requiring precise mixing conditions and components, can be susceptible to faults if these conditions are not met. Recently, Drexel University researchers say that they've developed an additive out of coal ash that can both help make concrete more durable and crack-free.

The research, recently published in Cement and Concrete Composites, was led by principal investigator Yaghoob Farnam, PhD, an assistant professor in Drexel’s College of Engineering. Farnam worked in collaboration with faculty members from Drexel’s Civil, Architectural and Environmental Engineering Department, Grace Hsuan, PhD, and Sabrina Spatari, PhD, as well as E.J. Garboczi, PhD, from the National Institute of Standards and Technology.

Product Development

According to the university, this additive can also shorten the time it takes for concrete to harden. In order for the building material to reach its greatest durability, the cement needs to mix thoroughly with water during the curing process.

“This is a very important part of the process because if the concrete dries too quickly during its curing, due to added water shortage, it can form cracks and other flaws,” said Farnam. “These drying shrinkage cracks cause the surface to be susceptible to aggressive fluid ingress creating concrete durability problems such as corrosion, salt damage or freeze-thaw damage.”

Drexel University

Concrete, well known for requiring precise mixing conditions and components, can be susceptible to faults if these conditions are not met. Recently, Drexel University researchers say that they've developed an additive out of coal ash that can both help make concrete more durable and crack-free.

Though the use of lightweight aggregates has proven to be a benefit in producing the building material, the concrete industry has limited access to both natural and synthetic lightweight aggregates due to limited sources of material, noted Farnam. The aggregate the team wanted to develop would ideally have strong properties for strength, mixing and porousness, as well as be made from a commonly found waste material.

“The solution we came up with involved recycling this waste product, coal ash, into a porous, lightweight aggregate with excellent performance characteristics that could be produced at a lower cost than current natural and synthetic options,” said Farnam.

“This material and process would not only benefit the concrete industry by improving the quality of their products, but it could also help keep coal ash out of landfills.”

Coal Ash Additive

The material the team developed, known as spherical porous reactive aggregate, or SPoRA for short, was produced by combining ash with chemicals that help with aggregate sintering and bonding, then forming the material into tiny spheres and baking them at 1,160 degrees Celsius for a short period. The end result can hold almost half its weight in water and can also release the liquid into the cementing mix at a regular rate. Testing also indicated that two types of SPoRA performed better than more traditional aggregates like shale, clay and slate and foamed glass, in terms of shape, porousness, relative weight and ability to absorb and release water.

“As the concrete begins to cure on the outside, the aggregate pellets are also releasing their moisture to help it cure from the inside out as well,” said Balapour said.

“This approach can help to maximize the durability of the concrete. And the SPoRA-making process is simple enough to produce aggregates of any size and water capacity, so we believe it could be used for a number of applications in the construction industry.”

Previously, Farnam also worked on using paraffin wax in concrete to successfully melt snow and ice off of road-like surfaces, revealing an enviornmentally friendly deicing alternative.

   

Tagged categories: Additives; Colleges and Universities; concrete; NA; North America; Program/Project Management; Research and development

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