混凝土水灰质量比与其早期收缩关系的研究

研究早龄期收缩对于解决混凝土工程,尤其是高性能混凝土的早期开裂具有重要意义.采用新研制的非接触式微位移传感器法对不同水灰质量比的混凝土从成型6 h到3 d龄期内的自收缩、单面干燥条件下的总收缩进行测量,同时监测混凝土试件内部温度变化.结果表明:随着水灰质量比的降低,混凝土的自收缩、干燥条件下的总收缩及自收缩在总收缩中所占比例都明显增加,早期自收缩与水灰质量比的关系呈二次曲线关系;当水灰质量比较低时,早龄期的混凝土因表面干燥引起的水分散失会在一定程度上阻碍水泥水化进程,因而这时的总收缩并不是干燥收缩与自收缩的简单叠加.

Study on Relationship between Water-cement Mass Ratio and Early Age Shrinkage of Concrete

The research of early age shrinkages of concrete is very important for the solutions of early age cracking of concrete engineering,especially for high performance concrete. In this paper,autogenous shrinkage under sealed condition and total shrinkage under dry condition of concretes with different water-cement mass ratio were measured from 6 hours to 3 days age with a newly-developed method. This method adopts a type of micro-displacement sensor and the concrete need not be touched during testing. The temperature changes in the concrete specimens were monitored at the same time. As a result, it is shown that autogenous shrinkage, total shrinkage under dry condition and the ratio of autogenous shrinkage in total shrinkage of concretes during early ages increase evidently with the decreasing of water-cement mass ratio and the relation between early age autogenous shrinkage and water-cement mass ratio can be figured by a cubic equation. It is also demonstrated that the total shrinkage under dry condition can' t be considered as the simple addition of drying shrinkage and autogenous shrinkage when the water-cement mass ratio of concrete is low because water loss of concrete due to drying at early age may counteract the hydration process of cement in a certain degree.