Influence Of Mineral Admixture On The Hydration Performance Of Calcium Aluminate Cement

Due to the existence of the transformation problem,which causes the decrease of the compressive strength,the application and development of the calcium aluminate cement is restricted.The effects of mineral admixtures such as silica fume,slag and fly ash on setting time,compressive strength,resistivity,chemical shrinkage and hydration products of aluminate cement were studied.The use of mineral admixtures to inhibit the transformation of calcium aluminate cement was explored,the conclusion are as follows:?1?Silica fume can shorten the setting time of calcium aluminate cement paste..When the silica fume content is 20%,the compressive strength of the hardened cement paste does not shrink during the 365 d.With the increase of silica fume content,the phase transition period determined by the electrical resistivity curve is gradually advanced and weakened.In addition,the electrical resistivity of the cement paste at 24 h is also increased,with a decreasing internal temperature peak and an advancing time of temperature peak appeared.The chemical shrinkage of calcium aluminate cement paste decreases with the addition of silica fume.Silica fume can inhibit the transformation of CAH₁₀0 and C₂AH₈ to C₃AH₆.Therefore,silica fume can accelerate the hydration reaction and inhibit the transformation of calcium aluminate cement.?2?The slag retarded the setting time of calcium aluminate cement.Appropriate content of slag is beneficial to promote the strength development and inhibit the late strength decreasing of calcium aluminate cement.20%slag content has the highest contribution to late compressive strength.With the increase of slag content,the electrical resistivity at 24 h is gradually decreased,and the induction period remained unchanged.The chemical shrinkage of cement paste decreases with the increase of slag content.There is a good correlation between the calcium aluminate cement and chemical shrinkage after adding slag.In the early stage of hydration,slag do not participate in the hydration process of calcium aluminate cement.The slag promotes the formation of stable hydration product C₂ASH₈,and can inhibit the transformation.?3?The fly ash retarded the setting time of calcium aluminate cement.The compressive strength of hardened calcium aluminate cement paste all shrinks at90 d,and the shrinkage amplitude is larger than that of control sample.The incorporation of fly ash can't effectively promote the development of late strength.With the increase of fly ash content,the induction period of cement hydration is obviously shortened,and the 24 h electrical resistivity of cement paste is also gradually reduced.The incorporation of fly ash does not affect the growth trend of chemical shrinkage of calcium aluminate cement paste,whose characteristics are first rapid growth,then gradually slow down,but the total amount of chemical shrinkage decreases with the increase of fly ash.In the early stage of hydration,fly ash does not participate in the hydration process of calcium aluminate cement.The effect of fly ash on inhibiting transformation is not significant.