Low-strength Self-compacting Concrete Optimal Mix Design

With further development of walling material in our country,the structure system of concrete minitype hollow building blocks with constructional colum is playing an important role in the multi-storey building.However,in this system,because of having more constructional eolums,there will not only have more work done but being more difficult to have concrete densely vibrated by using normal concrete according to present operation rules,and it is sure that vibrating can easily result in dislocation of building block around constructional colum and under ring beam.This is one of reasons which can lead to dehiscence between building blocks.Harden SCC has good mechanical property and durability, less construction noise and faster construction velocity.What's more,it can fill up the moulding board and hold reinforced bar under its own weight without vibration.With good liquidity, good construction and stuffing property.In addition, it is not easy for SCC to produce segregation with additives. So it can solve the problem of dehiscence between building blocks.Up to now the research of SCC mainly concentrates on the strength degree of C40 and above. Meanwhile, SCC is mainly used at the reinforced concrete construction with densely-packed concrete reinforced bar.The study of SCC used at constructional colum and ring beam of bearing building blocks is rarely found.In this thesis,local materials and industrial byproduct fly ash are used to produce the low-strength SCC (C25,C20). A conclusion, which is that influence degree of fly ash dosage,mortar ratio, superplasticizers dosage and thickening agent dosage to fresh concrete workability and strength is made through using orthogonal testing method and regarding slump,slump flow,7d and 28d strength as feedback indexs, and making range analysis to experimental results. At last, according to synthesis balance method,the author successfully obtained low-strength SCC with high liquidity,no vibration,which has the characters of slup≥240mm,slup flow≥550mm,middle difference≥25mm and enough 28d strength.And meanwhile,the author made primary analysis to concrete slump and slump flow loss with different additives and additives admixture.In theend,the author made primary study to concrete shrinkage.