The Rheological Characteristics And Workability Control Methods Of Pumped High-strength Lightweight Concrete

High-strength lightweight concrete(HSLC) is a cement-based material whose normal aggregates are partially or totally replaced by lightweight aggregates with a dry surface density less than 1950kg/m3 and a strength degree above LC30. HSLC has some characteristics of lightweight, thermal and heat insulation, absence of alkaline aggregate reaction and promises tremendous economical potential and wide application in tall buildings, long-span bridges, etc. Meanwhile, the segregation of lightweight aggregate in HSLC tends easily to undermine the homogeneity of the concrete and further decrease its workability sharply. Consequently, the rheology and homogeneity of HSLC demand a systematic research to meet the requirement of modern pumping construction.Based on the analysis of rheological characteristics and mechanism of segregation movement in HSLC, The paper established an aggregate segregation control model and put forward the values of slump, spreading, segregation as the evaluation standards and technical methods to control the segregation of HSLC.The influence of the types and dosages of mineral admixtures, water reducing admixtures and viscosity enhancing admixtures on the fluidity of HSLC was studied. The mathematical relationship between the fluidity parameters of HSLC and the corresponding cement paste was established and the range of rheological parameters to obtain a good workability was put forward.The influence of the types, pre-wetting extent and shape coefficient of light aggregate on the rheology of HSLC was studied. The paper also analysized the influence of the interference of blended aggregates on the segregation of HSLC, established the mathematical model of interference of blended aggregates based on the Law of Conservation of Momentum, and finally investigated and quantified the impact value of volumetric sand ratio, water absorption and paste viscosity on the movement velocity of aggregate by studying the conditions for a notable interference of blended aggregates.The paper put forward preparation technologies, mixing techniques and technical routes of high strength ultra lightweight concrete which was prepared with a dry surface density less than 1400kg/m~3, 28d compressive strength of 23MPa, a high fluidity, good homogeneity and no bleeding and segregation and was successfully pumped in the new terminal of Wuhan TianHe Airport.