Influence Of Early Strong Mineral Additive On Mixed Portland Cement Performance

In this paper, C4A3S single mineral is made of pure chemical reagents, and the influence of C4A3S mineral additive on the physical properties and hydration properties of Portland cement and mixed Portland cement is discussed. Fly ash, limestone and gypsum are used to synthesize the mineral additive, and the influence of temperature, iron content and SO3content on which formation and burning performance is also studied. Influences of mineral admixture on the Portland cement’s and admixture Portland cement’s physical properties and hydration properties are discussed as well.The results show that C4A3S single mineral formed at1300℃is the best. A certain amount of C4A3S single mineral can obviously improve the setting time and strength of Portland cement and mixed Portland cement. With the increase of C4A3S single mineral, the setting time is significantly shortened and the water requirement of normal consistency is significantly increased. When the addition amount of C4A3S single mineral is up to10%, quick setting will occur. When the amount of C4A3S single mineral is up to3%, the strength of cement at different ages will be greatly improved. Especially, the early strength of Portland slag cement grows from41MPa to48MPa, and the late strength grows from86MPa to94MPa.In order to contribute to the formation of minerals in the C4A3S admixture, the temperature should be controlled at1300℃, the content of aluminoferrite mineral should be limited at3-7%, and an excess3%of SO3is preferred. High temperature can cause the decomposition of the main mineral C4A3S; while low temperature leads to small mineral crystal particles, decreased yield, and unstable high temperature C2S state. High content of Fe phase in the admixture can produce too much liquid phase during sintering, which leads to the decomposition of C4A3S mineral. However, low Fe content in the admixture makes the sinter process difficult, and thus the yield decreases. The decomposition of gypsum at high temperature finely makes up the volatility of SO3during high-temperature calcinations, and provides important support for the formation of C4A3S mineral.C4A3S mineral additive is added to Portland cement and mixed Portland cement as a certain proportion. The results show that the setting time is shortened and the water requirement of normal consistency is increased with the increasing amount of C4A3S mineral additive, which is mainly attributed to the quick hydration of C4A3S mineral. Hydration process needs a large amount of water. When the added amount of C4A3S mineral additive is fixed, the more amount of mixing materials is, the shorter the setting time of composite cement. The fewer water requirement of normal consistency is needed. The strength of3d and28d of Portland cement doped with C4A3S mineral admixture increase in the early age and then decrease with the increasing amount of it. When added content of C4A3S mineral admixture is10%, the early strength is improved by about10MPa, the later strength also increases steadily. In addition, adding a certain content of C4A3S single mineral or admixture replacing cement to mixed Portland cement can improve the strength more substantially in the early time than adding that to cement. This is mainly due to the existent of C4A3S mineral, which helps the formation of AFt and C-S-H gel at early hydration, and obviously decreases the content of Ca(OH)2. Moreover, it can change the hydration product type in hardened cement paste and matching relations, benefit the development of early strength cement, and improve the hydration of slag fly ash mixed material, etc. If appropriate amount of C4A3S single mineral or its additive is added to cement that have two or more than two kinds of components, the increasing degree of composite cement’s strength is greater than that of cement mixed with single mixture, because of the double effect of the compound effect and the accumulation effect. Thus, it can be conclude that, when with significant mixing amount of mixed materials, good performance of Portland cement can be achieved with the addition of C4A3S single mineral or C4A3S mineral additive.