Reader Response Draft #2

The NaturalBlaze.com article, "Researchers Turn Waste from Coal Power Plants into Concrete" (2019), reports that researchers from Drexel University have discovered that recycling coal ash is a sustainable solution to protect the natural environment and improve the built environment. Millions of tons of coal ash, a less harmful by-product of coal-fired power plants, end up in landfills each year. The article also states that by turning the waste product into a special concrete additive, and adding it to a concrete mixture, will improve its durability and quality (as cited in the journal “Cement and Concrete Composites”). The article also asserts that proper mixing and curing is required to use concrete without any drawbacks. Hence, the special concrete additive will shorten the time for concrete to harden. Using this method will reduce the amount of coal ash in landfills and benefit the concrete industry.

From the journal article, “Cements and Concrete Composites”(2020), coal ash, or coal bottom ash used in the study, is turned into a lightweight aggregate (LWA) called “spherical porous aggregate” (SPoRA). This aggregate is then used as an additive for concrete mixture which increases the workability of concrete, have better sorption properties to absorb and desorb water, and have a glassy surface to provide surface reactivity. This indicates that the coal bottom ash has the potential to be an effective LWA that can be used as an internal curing for concrete.

Based on the NaturalBlaze.com article, turning coal bottom ash into an additive for concrete mixture is a possible solution for environmental preservation and is beneficial to the concrete industry. However, the article fails to address the disadvantages of coal bottom ash on the key properties of concrete.

One of the disadvantages of using coal bottom ash in concrete is that it increases the water absorption rate in concrete. According to the article, “Potential Use of Malaysian Thermal Power Plants Coal Bottom Ash in Construction” (2012), coal bottom ash’s high water absorption rate, angular shape and porous surface, it requires higher water content to achieve the “degree of lubrication” for a workable mix. This increase in water demand has a medium effect on the early stages of bottom ash concretes.

 From the article, “Researchers Turn Waste from Coal Power Plants into Concrete" (2019), it Is stated that concrete requires the exact amount of moisture inside it as once the powder and aggregates form a strong  “cementing matrix”, it becomes difficult for moisture to penetrate once it begins to dry. As coal bottom ash is used as an internal curing for concrete, it requires the right amount of water content in order for it to effectively cure the concrete from the inside. This mixture also needs a high percentage of water in order for the coal bottom ash to be able to mix with the cement mixture.

As a result, it is a necessity to balance the amount of water in coal bottom ash to mix with the cement mixture as well as getting the proper water content inside the concrete to cure within it.

Another disadvantage is the resulting lower compressive and flexural strength. According to a study, “Use of Bottom Ash as Fine Aggregate in Concrete: A Review” (2016), it was found that the compressive strength of bottom ash concrete had “lower than the control concrete specimens at all the ages”. It is also noted that the bottom ash concrete gained strength slower and only acquired strength rapidly after 28 days. The study also stated that the bottom ash concrete gained flexural strength comparable but lesser than that of controlled concrete.