Estimation of shrinkage of high-strength concrete including autogenous shrinkage

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(1) As autogenous shrinkage of concrete occurs in cement paste phase, it is less than that of cement paste itself because of the presence of aggregate particles. It is assumed that concrete can be expressed by a two-phase model, where aggregate particles are dispersing in cement paste matrix as inclusions. It has been proved that influence of aggregate on autogenous shrink-age can be estimated with an existing two phase model, such as Hobbs' model, for mortar and concrete with different volume concentration of aggregate(2) The total strain including autogenous shrinkage and drying shrinkage decreases with increasing duration of sealed curing for specimen with 0.2 and 0.3 water-cement ratio. But the difference decreases with increasing age, although data for a very long time has not been obtained. For specimen with 0.4, 0.5, and 0.6 water-cement ratios, the duration of sealed curing dose not have significant effect on the total strain at later ages.(3) For the specimens with 0.4, 0.5 an … More d 0.6 water-cement ratios, shrinkage is observed at any atmospheric condition with relative humidity ranging form 40% to 90%, and shrinkage increases with decreasing relative humidity. For specimen with 0.2 w/c, on the other hand, slight expansion is observed at 80% and 90% of relative humidity. For specimen with 0.3 water-cement ratio, volume change is hardly observed at 90 % relative humidity.(4) It can be seen that autogenous shrinkage at early ages increases with specimen size, which is explained by temperature effect and that ultimate value is not considerably influenced by specimen size.(5) Shrinkage of high-strength concrete cannot be precisely estimated form existing models such as JSCE model and RILEM French Chapter model, so prediction model for shrinkage of high-strength concrete has to be established.(6) Shrinkage decreases with increasing ambient relative humidity and expansion can be recorded when ambient relative humidity is more than a certain value that is dependent on water-cement ratio. The value of the specific ambient relative humidity (ρo) at which neither drying shrinkage nor expansion is not recorded, can be determined as a function of water-cement ratio, and coincides with the intemal relative humidity of the concrete Less