Size Effect Of Water Permeability Of Concrete

Water plays a very important role in the deterioration of the properties of concrete.The water permeability is an important index for the durability assessment and design of concrete.In many industrial problems,it is essential to evaluate the permeability resistance of concrete.However,the size effect of water permeability will affect the practical applications of experimental results.The water permeability of cement paste and concrete specimens with different sizes is studied in this paper through the steady-state flow method.Based on the extreme value theory,the size effect,main influential factors,and critical size of the water permeability of cement paste and concrete are analyzed.The test results show that the water permeability of cement paste increases with the increase of the cross-sectional area.When the cross-sectional area reaches 0.015 m~2,the water permeability approaches to a constant.The water permeability of concrete first decreases with increasing the cross-sectional area.When the specimen diameter is larger than 150 mm,the effect of aggregation of coarse aggregates can be neglected and the water permeability of concrete increases with the increase of the cross-sectional area but with a gradually reduced rate.When the cross-sectional area reaches 0.025 m~2,the water permeability approaches to a constant.The theoretical analyses indicates that,within a certain scale,the distribution of the water permeability rate of concrete elements obeys the type-II extreme value distribution,which is the main cause of the size effect.When the size of the concrete specimen is smaller that the critical size,the water permeability is a power function of the cross-sectional areas and the size effect rate can obtained by fitting experimental results.The size effect of the water permeability of concrete is related to the distribution of the permeability rates of concrete elements.The more easily the maximum value of the water permeability appears,the more significant the size effect is.As the size of the concrete specimenincreases,the distribution of the water permeability rate changes from the extreme value distribution trends to the Gauss one,which is the main cause of the critical size.