Relationship Between Internal Relative Humidity And Drying Shrinkage Of Concrete

In modern, the cracking caused by shrinkage has become an important factorof the durability of the concrete, and the drying shrinkage is the most commonand most primary reason of the concrete cracking. In the real situation, especia llyin a larger size concrete structure, its overall drying shrinkage is not uniform.There is a certain drying shrinkage gradient with different positions, and thisdrying shrinkage gradient will cause. The self-restraint shrinkage stress willaccelerate the cracking of the concrete and reduce durability of the concrete. Themost important reason of causing drying shrinkage of concrete is their respectiverelative humid ity changes in their own positions. Therefore, it is necessary tostudy the relative humidity distribution of the concrete’s own and the dryingshrinkage and the relationship between them.Three kinds of strength classes of the concrete are compounded in this paper,and the specimens are placed in the relative humidity of RH20%，RH40%，RH60%begin to conduct the single-sided drying test. The paper studied the relativehumidity distribution inside the concrete. And then we pick out the data of25mm、50mm、200mm of the position from measured humidity data to control theenvironment humid ity of shrinkage specimens. At last, the drying shrinkage datacan be got.The results showed: in the case of single-sided drying, drying process of theconcrete specimen consist two aspects: water loss and their own the consumptionof the hydration. This situation creates the decline of overall humidity ofconcrete specimen with the growth of the age, at the same time. The inner layerhas sma ll decline of relative humid ity and the outer layer has a large decrease ofrelative humidity. The concrete with lower strength class, with mixing fly ash andwith higher humid ity of environment has sma ller humidity gradient and higheroverall humidity.Experiments show that: The concrete with lower strength class, with mixingfly ash and with higher humid ity of environment has smaller overall dryingshrinkage and has sma ller drying shrinkage difference between the position of25mm and200mm. The relative humid ity of the concrete has significant influence to the drying shrinkage of the concrete. A good linear relat ionship isshowed between them. The sensitivity of the drying shrinkage to the relativehumidity and the final shrinkage value of the concrete can be gained withanalysis of the regression equation.