Study On The Hydration Mechanism Of Sulphate Aluminate-silicate Cement-dopant Composite Cementitious Materials

Nowadays,the compounding of sulfo-aluminate cement and ordinary silicate cement has become one of the hot spots in the field of construction materials,and the compounding of two types of cement can play their respective advantages and complement each other’s shortcomings.Mineral admixtures and chemical additives as cement "seasoning",can improve the performance of cement,but also can reduce the cost of cement use.The study in this paper is based on the composite cementitious material system of sulfo-aluminate cement-ordinary silicate cement,and investigates the standard consistency water consumption,setting time,flexural and compressive strength of cementitious sand,drying shrinkage,drying mass change rate,carbonation resistance and freeze-thaw damage resistance of the base material system by incorporating mineral admixture and boric acid,supplemented by XRD and SEM to explain the macroscopic phenomena and explain the relevant mechanism,and draws relevant conclusions:(1)In the sulphate aluminate cement-ordinary silicate cement composite cementitious material system,with the increase of sulphate aluminate cement admixture,the standard consistency water consumption first increases and then decreases,and the setting time decreases and the initial and final setting time interval is shortened;with the increase of mineral admixture,the standard consistency water consumption increases and the setting time is slightly extended;the increase of boric acid admixture makes the sulphate aluminate-silicate-mineral admixture The increase in the amount of boric acid makes the standard consistency water consumption of the composite cementitious material system decrease,and the setting time is prolonged.(2)The compounding of two kinds of cement in any proportion makes the strength lower compared with the single kind of cement,but the stability is qualified;the blending of mineral dopants makes the early strength lower and the later strength higher,and the effects are from high to low: silica fume > mineral powder > fly ash;the blending of boric acid makes the strength of ternary composite cementitious material system higher,and the best effect is when the blending amount is 0.2%.(3)The compounding of the two cements improves the drying shrinkage and drying mass change rate compared with the single cement;the fly ash and mineral powder in the mineral admixture make the drying shrinkage and drying mass change rate decrease,while the silica fume makes the drying shrinkage and drying mass change rate increase;the admixture of boric acid can effectively improve the drying shrinkage of the ternary composite cementitious material system,making the drying shrinkage and drying mass change rate decrease.The drying shrinkage rate and the drying mass change rate change synchronously.(4)Two kinds of cement compounding make the anti-carbonation performance and anti-freeze-thaw performance improved;the incorporation of mineral dopants makes the anti-carbonation performance and anti-freeze-thaw performance more excellent than the binary composite cementitious material system,and the incorporation of silica fume is the most excellent;the incorporation of boric acid makes the anticarbonation performance and anti-freeze-thaw performance of the ternary composite cementitious material system more excellent.(5)The basic properties and mechanical properties results and laws of the sulfur aluminate cement-ordinary silicate cement-mineral powder-silica fume composite cementitious material system obtained through the test are the same as those of the ternary composite cementitious material system,and no fundamental changes are found,and the superposition effect of mineral admixture is not obvious.(6)The incorporation of mineral dopants and boric acid does not cause the composite cementitious material to produce new hydration products,the main hydration products are AFt,C3 S and C2 S.The mineral dopants are involved in different stages of the hydration reaction,making the amount of hydration products at each stage different,boric acid will slow down the early hydration rate,but help the later hydration reaction.