Research On Rheological Properties Of Cement Based Materials Based On Particle Characteristics

Mixture rheological performance directly determines construction quality.So rheological properties is modern concrete mix design as one of the most important technical indicator. At present, at home and abroad most of the research and the existing concrete in design specification for the design and adjustment of the rheological properties is mainly based on empirical formula, without taking into account the actual raw material particle characteristics that produces the important influence, leading that different researchers findings were inconsistent and concrete design is not economic. Therefore, this topic based on particle packing and suspension theory, from three levels of cement paste, mortar, concrete mixture study the cementitious materials, fine aggregate, coarse aggregate particle composition have different influences on the rheological properties of mixing material. Determining the correspondence between particles and rheological properties lays a theoretical foundation on concrete with ratio optimization design.In cement paste system, we have different dosage, different fineness of fly ash and slag powder instead of cement to change the cementitious material system, particle composition and characteristics. The results show that in a certain range, increasing the mixing amount of the fly ash will reduce the viscosity of cement paste, improve the degree of fluidity of cement paste. When incorporated of fine fly ash, fluidity of cement paste is unfavorable. With the increase of slag content, the fluidity of cement paste becomes larger, and the viscosity is smaller. There is a good correlation between S1 and S2 and rheology of cement paste as the area of Fuller and the particle curve of the composite cementitious material. The bigger S1, the smaller the fluidity of the cement paste, the bigger the viscosity; the bigger S2, the bigger the fluidity of the cement paste, the smaller the viscosity.When the fineness modulus of sand is in a small range, the fluidity of cement mortar is not bigger with the fineness modulus of sand becoming larger. This shows that even if the fineness modulus of sand is same, if content of each fraction of fine particles is different, the fluidity of the cement mortar will have significant differences. So when researching fine aggregate sand havs influence on the rheology of cement mortar, we not only use the fineness modulus of sand as a reference, should also consider the particle size distribution of the sand. The yield shear stress and plastic viscosity all increase, fluidity is bigger with increasing surplus coefficient of slurry; when the surplus coefficient of slurry increases to a certain value, the trend is no longer obvious.the voidage of aggregates and the aggregate total ratio surface area become bigger with the increase of the content of flat and elongated particles, which leads differences in the same mix ratio of concrete; design of concrete with ratio should be elongated coarse aggregate content control in less than 10%, choosing good particle shape of coarse aggregate particles, which significantly improve the concrete mixture rheological properties. Under the same conditions, concrete slump and expansion value are bigger with the surplus coefficient of mortar increasing, but after the surplus coefficient of mortar reaching 2.5, concrete slump and expansion value are not obviously bigger like before.