Estimation of shrinkage of high-strength concrete including autogenous shrinkage

(1)混凝土的自收缩发生在水泥浆体阶段，由于骨料颗粒的存在，混凝土的自收缩小于水泥浆体本身的收缩。假定混凝土可以用两相模型来描述，其中骨料颗粒以夹杂物的形式分散在水泥净浆基质中。对于不同骨料体积浓度的砂浆和混凝土，骨料对自收缩龄期的影响可以用现有的两相模型(如Hobbs模型)来估算。(2)对于水灰比为0.2和0.3的试件，总应变(包括自收缩和干缩)随着密封养护时间的增加而减小。但这种差异随着年龄的增长而减小，尽管很长一段时间没有数据。对于水灰比为0.4、0.5和0.6的试件，密封养护时间对后期总应变没有显著影响。(3)对于水灰比为0.4、0.5和…的试件，密封养护时间对后期总应变没有显著影响当水灰比大于0.6时，在相对湿度为40%~90%的任何大气条件下都会出现收缩现象，且收缩随相对湿度的降低而增大。另一方面，对于0.2w/c的样品，在80%和90%的相对湿度下观察到轻微的膨胀。对于水灰比为0.3的试件，在90%相对湿度下几乎没有观察到体积变化。(4)可以看出，早期自收缩随着试件尺寸的增加而增加，这是由温度效应解释的，极限值不受试件尺寸的显著影响。(5)高强混凝土的收缩不能用现有的模型，如JSCE模型和Rilem法国章模型来精确估计。因此，必须建立高强混凝土收缩的预测模型。(6)收缩随环境相对湿度的增加而减小，当环境相对湿度大于一定值时会出现膨胀现象，这与水灰比有关。既不记录干燥收缩也不记录膨胀的特定环境相对湿度(ρo)的值可以作为水灰比的函数来确定，并且与混凝土的内部相对湿度重合较少。

(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