Research On Hydration Exothermic Regularity Of High Volume Mineral Admixtures Cementitious Systems

Hydration heat of cementitious material system is the main cause of concrete temperature cracking.It has two main methods to reduce the hydration heat of the cementitious material which are using ordinary portland cement with large amount of mineral admixture or low heat Portland cement,respectively.At present,there are few reports about the difference between the two methods on the hydration heat release of cementitious materials.Therefore,in this paper,the hydration exothermic curve of cementitious material system is measured,which are low heat Portland cement,different mineral additives and admixture.The exothermic curves are analyzed,and emphatically compared the difference between the law of hydration heat and analyze hydration process of both combined with the hydration kinetics model of Krstulovic-Dabic.Specifically as follows:（1）Cementitious material system of portland cement with different mineral admixtures and admixtures on hydration heat were tested by direct determination of cement hydration heat,respectively.Test results found:the content of mineral admixtures and retarder can reduced system of cementitious materials and with the increasing material content of mineral admixture,hydration heat reducing effect was more obvious.（2）The law of hydration between low heat Portland cement and ordinary portland cement with a large amount of mineral admixtures were comparatively analyzed and the difference of hydration law were found.Comparative analysis shows that:when the mineral admixture was 40%⁵0%,the 3d hydration heat of the cementitious material system was lower than the same period of hydration heat of low heat Portland cement,but the 7d hydration heat would be more than that of hydration heat of low heat Portland cement;when the mineral admixture was more than 60%⁷0%,the 3d and 7d hydration heat of cementitious material were lower than that of hydration heat of low heat Portland cement.（3）Cementitious system of Portland cement mixed with 45%and 50%mineral admixture and low heat Portland cement were as the research object,Respectively.The dynamics model of Krstulovic-Dabic hydration was used.In terms of the hydration rate（K₁’,K₂’,K₃’）and the degree of hydration the turning point（α₁,α₂）etc.of crystal nucleation and growth phase,boundary phase and diffusion stage,the hydration process on 0³d,3d⁷d of the ordinary portland cement with high volume mineral admixtures and low heat Portland cement were further explored.The results show that:compared with ordinary portland cement,the hydration rate of cementitious materials of ordinary portland cement with high volume mineral on the crystal nucleation and growth phase and boundary phase were slow,so the 3d hydration heat were low;the hydration rate of those on diffusion stage were fast,so the 7d hydration heat were high.