Obst, Drew (2023) Use of Harvested Ash as Replacement for Fine Aggregate in Concrete. [USQ Project]
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Abstract
Many years of heavy reliance on coal combustion for energy production has resulted in the generation of large amounts of waste ash material. Some of this ash is commonly used for beneficial purposes, such as fly ash in concrete, but the coarser bottom ash is less frequently utilised and predominantly ends up in storage ponds.
This research project seeks to determine if coal bottom ash in these ponds can be harvested and used to replace a portion of fine aggregate in concrete. This possible use for harvested ash (HA) has been investigated in numerous studies from around the world with mixed results pertaining to how the incorporation of HA affects concrete performance. A key finding from review of the existing literature is that physical and chemical properties of HA vary significantly depending on the source of the ash. The literature review also reveals there is very limited research into replacing fine aggregate in concrete with ash from sources within Australia.
This project investigates how physical properties of concrete are impacted when a portion of the fine aggregate is replaced with HA from a power station in Millmerran, Queensland. The experimental programme involves the batching of five concrete mixes having fine aggregate replaced with HA at rates of 0%, 12.5%, 25%, 50% and 75% by volume. The concrete properties tested in this project include workability, concrete density, and compressive, splitting tensile and flexural strength. Material testing was also conducted on the HA to determine the properties required for mixing in concrete and to help characterise the ash from this specific source.
The results of the research suggest up to 25% of the fine aggregate in concrete can be replaced by HA without significantly affecting the concrete’s strength performance. The testing also indicates the workability of concrete reduces significantly as the amount of HA replacement increases. Scanning electron microscope (SEM) analysis of the hardened concrete samples reveal negligible difference in the microstructure of concrete containing 25% HA while the 75% HA mix shows significantly less crystalline structure development.
The report concludes that replacing a portion of the fine aggregate in concrete with HA shows potential as a way of removing coal bottom ash from storage ponds and having a positive impact on the natural environment. While the results of this research project show significant promise, the report also suggests further research that would be required before the use of HA as fine aggregate in concrete is considered commercially viable.
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| Item Type: | USQ Project |
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| Item Status: | Live Archive |
| Faculty/School / Institute/Centre: | Current – Faculty of Health, Engineering and Sciences - School of Engineering (1 Jan 2022 -) |
| Supervisors: | Lokuge, Weena |
| Qualification: | Bachelor of Engineering (Honours) (Civil) |
| Date Deposited: | 30 Sep 2025 05:14 |
| Last Modified: | 30 Sep 2025 05:14 |
| Uncontrolled Keywords: | harvest ash; concrete replacement |
| URI: | https://sear.unisq.edu.au/id/eprint/52983 |
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