Microcalorimetric Study On Calcium Aluminate Cement Hydration

Calcium aluminate cement (CAC) is very versatile special cement used for specific applications. During the hydration of CAC a large quantity of heat is liberated within one day that causes a considerable increase of temperature in material. This paper examines the hydration of three samples (A, B and aged B) of commercial CAC ISTRA 40 (producer: Istra Cement, Pula, Croatia). The rate of heat generation of cement pastes due to the hydration reactions was measured at several temperatures with differential micro-calorimeter. In the experiments water to cement ratio was also varied and in one sample quartz sand was added. When CAC and water first come in contact far less heat is liberated, than for Portland cement. Higher water to cement ratio increases the heat evolved at later ages due to higher quantity of water available for hydration. Cement mortar prepared with milled quartz sand showed 1.2 h shorter setting time than corresponding neat CAC paste. This could be explained by more germination sites available for the nuclei to start the hydration precipitation. Except for the change in the setting time there are no other significant differences in the kinetics of hydration when compared to original cement sample. Due to a water and CO2 uptake from the environment the aged sample has a greater weight loss on ignition, shorter setting time, lower hydration rate and lower heat of hydration evolved in comparison to original sample. Contrary to previous reports in literature acceleration of CAH10 formation was observed in 5 to 10 oC temperature range. Heat generation data obtained could not be satisfactory fitted by the Avrami-Erofe’ev nucleation and growth kinetic model