Papers by Keyword: Semi-Adiabatic Curing Test

Abstract: Condensed silica fume (CSF) is often added into concrete mixes to enhance the properties of concrete. However, the effect of CSF on the heat evolution and temperature rise of concrete is not clearly known. Test results in the literature are insufficient and sometimes contradictory to enable any conclusion to be drawn regarding the role of CSF in heat generation behaviour of concrete. Moreover, since the chemical reactions of cement and CSF both involve water and hence cement and CSF are competing with each other in reacting with water, the water to binder (W/B) ratio may affect the temperature rise characteristics of concrete. This paper reports an experimental study of adiabatic temperature rise of CSF concrete conducted at The University of Hong Kong. Five concrete mixes without CSF and 10 concrete mixes with CSF dosages at 5% and 10% were tested with the recently developed semi-adiabatic curing test method. The adiabatic temperature rise was obtained by applying heat loss compensation to the test results. It was found that the addition of CSF could suppress the adiabatic temperature rise of concrete. At the same time, the strength of concrete could be enhanced. Based on the experimental results, prediction formula and design chart of adiabatic temperature rise of CSF concrete were developed.

Abstract: Owing to the less exothermic pozzolanic reaction of pulverized fuel ash (PFA) compared to cement hydration, the addition of PFA can reduce the heat generation of concrete during its hardening. However, as the water to binder (W/B) ratio would affect the proportions of cement and PFA that could react with water, the conventional practice of determining concrete temperature rise solely based on the cement and PFA contents may not yield accurate estimations. An experimental programme was launched to investigate the adiabatic temperature rise of PFA concrete mixes. Seven concrete mixes without PFA added and 14 concrete mixes with PFA dosages at 20% and 40% were tested with the recently developed semi-adiabatic curing test method. The adiabatic temperature rise was obtained by applying heat loss compensation to the test results. It was found that the incorporation of PFA could suppress the adiabatic temperature rise by 4°C to 14°C. The test results revealed the dependence of adiabatic temperature rise on both PFA dosage and W/B ratio, whose combined effects can be accurately addressed via the prediction formula and design chart developed herein.

Abstract: The temperature rise of concrete during hardening is intimately related to the mix proportion, among which the cement content is a major factor. However, high-strength concrete mixes are often proportioned with low water contents which leads to incomplete hydration of cement contained therein. Hence, the conventional rule of determining concrete temperature rise solely based on the cement content may not yield accurate estimations. An experimental program has been launched to investigate the coupled effects of cement and water contents on the adiabatic temperature rise of concrete. Eighteen concrete mixes were tested with a newly developed semi-adiabatic curing test method and their adiabatic temperature rise obtained by applying heat loss compensation to the test results. The results revealed that, when the water/cement ratio is lower than 0.36, both cement and water contents have effects on the adiabatic temperature rise of concrete. Prediction formula and design chart of adiabatic temperature rise, which are accurate to ±1.3°C compared with the test results, are developed. Furthermore, prediction formula of the degree of hydration of concrete is recommended.