THE STUDY OF THE EARLY HYDRATION OF CEMENT PASTE USING MICROWAVE TECHNIQUE

Abstract

Microwave technique is used to study the early hydration of the OPC, OPC/PFA blended cement as well as OPC/HAC mixes by measuring the changes in dielectric constant ? and the electrical conductivity ? of hydrating cement pastes. An excellent correlation is established between the microwave results and the results of conventional calorimetric measurement. However, microwave results can also provide information about the microstructure development of cement paste. Thus it can be used as a more powerful method to monitor the cement hydration. The hydration processes of OPC/HAC mixes with various HAC contents is found to be highly dependent on the relative proportion of the OPC and HAC. The fast setting takes place in the mixes containing 20 - 30% HAC. The results suggest that the early hydration process and the setting behavior of OPC/HAC pastes can be controlled by the correct choice of the relative proportion of OPC and HAC. PFA is found to act almost as an inert filler in OPC/PFA blends during the early hydration and thus retards the early hydration. Both Ca(OH), and Na2SO4 can accelerate the early hydration of OPC/PFA blends , while NaOH is unsuitable for this purpose. The investigation of the apparent activation energy of cement hydration using microwave technique is attempted. The apparent activation energy of the OPC is found to be 38.10 KJ/mol and this result is in good agreement to that obtained by using conventional calorimetric method. The similarity of the apparent activation energy of OPC/PFA blend with 60% PFA to that of the 100% OPC confirms the latency of the PFA in the early hydration of OPC/PFA blends.