HEAT EVOLUTION AND HYDRATION MODELLING OF GGBS CEMENT

The advisability of controlling peak temperature of concrete at early-age is well recognised, and the choice of appropriate low heat cement with suitable heat of hydration characteristics can assist in this control. This is particularly pertinent with respect to water-retaining and massive concrete structures where the need to prevent early-age thermal cracking is paramount. PC/ggbs combinations are often used in these structures since they have low heat of hydration but achieve strength rapidly enough to meet most strength classes. The paper describes tests carried out to assist in the modelling of the hydration of PC/ggbs combinations for use in estimating the early-age temperature of concrete structures. Two sources of ggbs were used; one regarded as a standard ggbs typical of most use in UK, and the other specifically selected as a high fineness ggbs. Systematic isothermal conduction calorimetry tests for PC/ggbs combinations were carried out over a range up to 90% ggbs content by mass in the combination, at temperatures of 5°C, 20°C, 40°C and 60°C. The curves of rate of heat evolution against time and cumulative heat were analysed and a mathematical model based on the test results was proposed. In general, the relationships appeared to be double peak curves, which were considered to result from an initial Portland cement reaction, followed by a later ggbs reaction activated by the lime made available during hydration of the Portland cement. A further refinement can be achieved by considering co-reactivity effects of PC and additions.

• INTRODUCTION

• EXPERIMENTAL PROGRAMME

• EXPERIMENTAL RESULTS

• HYDRATION MODELLING

• CONCLUSIONS

• ACKNOWLEDGEMENTS

• REFERENCES