Year

2012

Degree Name

Master of Engineering - Research

Department

School of Civil, Mining and Environmental Engineering

Abstract

This study aims to investigate the effects of unburned carbon in coal combustion fly ash on the properties of concrete. One of the most important effects of unburned carbon on concrete is its tendency to absorb the Air Entrainment Agent (AEA) in concrete. Because of this effect, the American Society for Testing and Materials (ASTM) and Australian standards (AS) restrict using fly ashes to those with Loss on Ignition (LOI) lower than 6% and 4% respectively. This study aims to compare the effects of LOI and particle size distribution of fly ash particles on the amount of AEA required for the concrete. The evidence suggests that particle size distribution has a stronger correlation to the AEA demand rather than the amount of unburned carbon in fly ash as measured by LOI test. Foam Index (FI) tests were also done on the fly ash samples to measure the degree of interaction between unburned carbon in fly ash and AEA.

Three different fly ashes were collected from different power stations in New South Wales. Two fly ash samples were collected from Earing power station and the other one was collected from Wallerawang power station. All samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Mastersizer 2000 to find the chemical composition, mineralogy, morphology and particle size distribution. LOI tests were also performed on the fly ash samples. After that, concrete mixes were produced in the laboratory to examine effects of LOI and particle size of fly ashes on the properties of concrete including air content, compressive strength and drying shrinkage.

The aforementioned tests showed that LOI values did not correlate strongly with the AEA demand in concrete. The FI results in this study showed a satisfactory correlation to the AEA demand in concrete. The results suggest that FI is a good indicator of AEA demand because as the FI increases, the required amount of AEA also increases. This finding supports the hypothesis that FI of the fly ash controls AEA demand rather than LOI.

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