MORPHOLOGY AND MICROSTRUCTURE OF TRICALCIUM ALUMINATE HYDRATE PASTES AFTER HYDRATION IN PRESENCE OF INORGANIC ADMIXTURES

Tricalcium aluminate is considered as one of the most important material in the main inorganic compounds that constitute the cement. It plays an important role in controlling hydraulic characteristics for cement and leads to strength of concrete. Although its percent do not exceed (7-12%), of the total essential compounds constituting cement material , but it acquired special importance through its capability of reserving cement in a form paste, it can be handled easily during construction when water is add to cement. It is responsible of setting time in cement mixture so can be adjusted according to different whether conditions. To adjust setting time, organic or inorganic compounds must be added to cement mix in the presence of water to accelerate or retard hydration process according to the type of added admixture. In this study, the effect of inorganic admixtures (Ca(OH)2, Al(OH)3,CaCl2 and CaSO4.2H2O)on the hydration of tricalcium aluminate hydrate pastes after different periods was investigated using scanning electron microscope (SEM) . The results indicated that Al(OH)3 accelerate the hydration process while mixture of Ca(OH)2 and CaSO4.2H2O retard this process. Presence of Al(OH)3 with CaCl2 accelerate the hydration process . Presence of Al(OH)3 with mixture of Ca(OH)2 and CaSO4.2H2O decreased the retarding effect of this mixture on hydration process.