Study On Optimization Of Retarders Of Cementitious System In Modern Concrete

So far, concrete is the largest building materials. With the development ofscience and technology, cementitious system in modern concrete has changed verymuch. In order to ensure the performance of cement and concrete, retarder is anindispensable component. According to characteristics in the modern concrete, thispaper study the appropriate content the retarder(gypsum)in cement itself andcementitious materials of concrete, and coordinated role of gypsum and other retarderin eventual cementitious system. The basis of choosing material would be provided incement and concrete production.First of all, Portland cement of different admixture, cementitious system (withoutand with chemical admixtures) would be researched. The change of different gypsumto the setting time and strength and fluidly would be analysis. Take setting time andliquidity and strength for principle, the appropriate gypsum range would be obtained.And further hydration would be studied with appropriate gypsum content.For A, B and C three Portland cement with different admixture, when gypsumcontent respectively are2.2%,1.3%,1.1%, systems can satisfy the requirements thatthe initial setting time is not less than45min, the final setting time is not more than600min. When setting time is stable, the gypsum contents are6.1%,4.05%and2.79%. As system performance is excellent, the range of gypsum is4~7%.Common cementitious system in concrete (without chemical admixtures), thesetting time is significantly delayed with mineral admixtures. When gypsum contentis higher than1%, the initial setting time is more than120min and final setting timeis more than240min. When setting time was stable, the gypsum contents are3.26%,2.35%,3.25%. The range of gypsum is3~6%when system performance is excellent.In the cementitious system with PC and retarder, when the gypsum content ismore than2%, liquidity reduces obviously with gypsum increasing. Gypsum has goodcompatibility in Poly-napthalen and retarder system. When gypsum content is higherthan1%, the initial setting time is more than200min and final setting time is morethan400min. Under the condition of the excellent performance, the gypsum of2%~6%is for best quantity.When there is no gypsum in system, the hydration process is lower. Whengypsum content is appropriate, hydration heat release rate tends to accordance. Whengypsum content is appropriate, the species of hydration products is similar in cementitious system. Mineral admixtures and additives do not affect system ofadmixture hydration role.