Research On High Strength Semi-lightweight Concrete And It's Application

High strength semi lightweight concrete (HSSC) is a kind of new concretematerial which refers to the coarse aggregates compounded with normal weightaggregate and lightweight aggregate. Its dry apparent density between 1950 kg/m³and 2300kg/m³ and compressive strength higher than 50Mpa and modulus can bedesigned. HSSC has many merits such as high compressive strength, small dead load,good volume stability and excellent durability. So it is economic to use ttSSLC inhigh-rise buildings and long-span bridges, and the prospect of its application is veryextensive. The relation between the composition, construe and performance of HSSCand the key application technology of HSSC in the practical engineering werestudied systematically in this paper. The research achievement supplied the theoryand technology for the design, preparation and application of HSSC.The originality innovation of this thesis is summarized as following:The relation between the inner humidity and self-shrinkage of high strengthconcrete was studied systematically. Based on the relation, the compensated theoryand design method of inner humidity of high strength concrete were presented. It canbe concluded that the HSSC possessed the good volume stability because thelight-weight aggregate and normal aggregate played the roles as the humiditycompensation and confining shrinkage, respectively. At the same time, the strengthdesign theory model of HSSC was established and the mixture proportion designmethod was presented. The equation for the relation between compressive strengthand tensile strength of HSSC is as following, f_t=0.0519f_cu^1.0467. The equation for therelation between compressive strength, appearance density and elastic modulus ofHSSC is as following, E=0.02554×f_cu^1.44×ρ^0.23. This laid a theory foundation forthe design, preparation and application of HSSC.The rheologic and workability performance of HSSC was studiedsystematically by means of the different effecting factors. And the rule was provedup: the yield value of shear stress and the viscosity of cement paste decreased withthe increasing of volume ration of normal aggregate in the concrete: but thedivergence and the slump constant were inversed. Then the experimental methodsfor the uniform performance of HSSC and the workability index of the pumpingHSSC were established. It realized, the application of the pumping HSSC andsupplied the rule for raw materials and workability performance designing of HSSC. The composition, construction and durability of HSSC were studied by theXRD, SEM, EDXA and durability experiment. The excellent durability of HSSCresulted from the higher hydrated degree and more dense construction of the cementstone and the lower content and orientation index of Ca(OH)₂ in the interfacebetween the stone and aggregate because of the inner humidity compensation oflight-weight aggregate.It is studied systematically on the flexural and shearing mechanical propertiesof the SC60 HSSC beams. The results showed that HSSC beam has the similardestructive characteristic to the normal concrete beams. The flexivity and limiterload of HSSC is close to of the normal concrete beams with the same strength grade.Comparing the crack of the HSSC beams with the normal concrete beams, the spacebetween them is smaller and the distribution is more homogeneous, which isindicated that the bonded strength between HSSC beams and reinforcing steel bar ishigher and the synchronize distortion capability is better. With increasing of the ratioof reinforcement, the ductility of HSSC beams decreases and the limited load withcracking increases slightly. The stirrup of HSSC beams has few effects on theslanting crack and flexivity. The flexivity of HSSC beam increased with the shearspan ratio increasing. This laid a theory foundation for the design of HSSC appliedin the practice engineering.It was originality reported on the engineering practice of HSSC. It was firstlypresent for the optimum design method of steel-box beam bridge surfacingconstruction base on HSSC and the gradient design method of lightweight hollowbeam used HSSC. The characteristic of the surfacing system of steel-box beambridge and the prestressed lightweight hollow beam was analyzed by finite-elementmethod. A new unit-construction system for the pavement of steel-box beambridge was established, which make the surfacing system with the consistentdistortion and high durability performance. Another new construction form was alsoestablished, which make the stress of both ends of the prestressed lightweight hollowbeam is obviously improved so that the split phenomenon of ends can be voided andthe using performance and safety of the construction get improvement.The research achievement was successfully applied in the engineering ofTuanshan river bridge of Xiao-Xiang highway and of steel-box beam bridge of theWuhan middle circle line and of Wuhan east-west lake road. The world puzzleincluding traction, bellying and breakage of the steel-box beam bridge surfacing pavement and the dehiscence of both ends of the prestressed lightweight hollowbeam was solved completely. At the same time, we have possess a unitizedtechnology with independence knowledge property right for the steel-box beambridge and prestressed lightweight hollow beam.