Abstract
In this paper, it is shown that Class F fly ash (FA) can be effectively used in high volumes as a supplementary cementitious material (SCM). High volume use of FA is of interest in promoting the development and application of green materials. In South Africa, there is little or no literature on high volume incorporation of locally available FA in concrete. In this investigation, six different concrete mixes of water/cementitious ratios (w/cm’s) = 0.3 and 0.45, were used. The mixtures consisted of 0, 30, 50 and 70% FA. Tests carried out were workability, bleeding, compressive strength and heat of hydration. Large 300 mm cubes were
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used to study hydration heat development in fresh concrete. As expected, concrete strength decreased as FA content increased owing to the slower rate of strength development in FA mixtures. It was found that heat of hydration generated in HVFA mixes gave lower peak temperatures compared to mixes without FA, producing reductions of 27% to 43.5% in peak temperatures for mixtures containing 50% and 70% FA respectively. Temperature simulation using ConcreteWorks gave predictions correctly depicting the measured temperature profiles but with slight under-estimation of peak temperatures.