Properties’ Difference Between Surface Layer And Internal Area Of Concrete

For the whole life cycle of concrete.Firstly,in the forming stage,the boundary effect of formwork and aggregate makes the mortar aggregate to the surface of concrete.Secondly,in the early curing stage,the temperature and humidity of concrete surface are lower and fluctuate greatly,which makes the hydration speed of concrete surface slow and uneven.And during the service period,the surface of concrete will be affected by carbonization,etc.The above reasons will lead to differences between the surface and the interior of concrete Properties.Such differences often lead to inaccurate detection methods based on surface concrete and other issues.However,the existing research on the difference between surface and internal properties of concrete has some limitations,lack of quantitative analysis,and limited research on improving methods.In order to further study the difference between the surface and internal properties of concrete and the improvement measures.In this paper,the influence of strength grade,admixture and early curing method on rebound strength,microhardness,chloride ion penetration resistance and water absorption of concrete surface and interior were studied by means of slice or drilling.Main results are as follows:(1)The effects of strength grade,fly ash or slag powder on the surface and internal properties of concrete were studied.The results show that increasing the strength grade of concrete and incorporating appropriate amount of fly ash or slag powder into concrete can improve the difference between surface and internal Properties of concrete.Moreover,the difference between the surface and internal properties of concrete can not be eliminated by changing the strength grade,adding fly ash or slag powder.(2)The effects of early standard curing,covering film curing,sprinkler curing and natural drying on the difference of surface and internal properties of concrete were studied.The results show that the difference between surface and internal properties of concrete is the greatest under natural drying.Early curing of concrete can improve the difference between surface and internal properties of concrete.Sprinkler curing has better effect on improving high-strength concrete,while cover curing has better effect on improving low-strength concrete.(3)By the range analysis of test results.The results show that among the same concrete,the difference of water absorption between surface layer and interior layer is the greatest,followed by chloride ion penetration resistance and the difference of resilience strength is the smallest.The main factor affecting the difference between surface and internal performance of concrete is the early maintenance mode,followed by the strength grade of concrete.