Study On Impermeability Of Recycled Concrete With Admixture

With the rapid economic development in the twenty-first century,natural aggregates are widely excavated to be used as raw materials for infrastructure development works.This large-scale excavation has resulted in the gradual depletion of natural aggregates.Moreover,a huge amount of waste concrete adversely affects earth’s environmental balance and causes a lot of waste of resources.Flood and waterlogging in Jiangxi is frequent.It needs a lot of water conservancy projects such as the construction of dikes and dams.With the increasingly prominent contradiction between these problems,the emergence of recycled concrete will undoubtedly provide a good solution to these problems.As the most basic of mechanical properties,the compressive strength of the cubes must be considered in the study of recycled concrete with admixtures.At the same time,in order to make sustainable use of recycled concrete,it is necessary to consider the key impermeability of recycled concrete service life.In view of the large amount of waste concrete and the weak impermeability of recycled concrete,this paper mainly studies the impermeability of recycled concrete with admixture.In this paper,fly ash content,silica fume content,mineral content and different water-cement ratio as well as recycled aggregate replacement rate have been used as variable factors in recycled concrete.The content of superplasticizer was fixed.16 groups of orthogonal tests were designed and 96 impermeability test specimens were made.The impermeability of recycled concrete with admixture was studied.The following were the main conclusions:(1)Through the analysis of the results of orthogonal tests,the optimum mix ratio of recycled concrete to the admixture was obtained.The optimum mix ratio of recycled concrete was 0.43,the replacement ratio of recycled aggregate was 50%,and the fly ash content was 5%,silica fume content was 2%,mineral powder content was 4%,and superplasticizer content was 1.5%.(2)According to the analysis of the results of the orthogonal test,it is concluded that the influencing factors are in the order of water-cement ratio,fly ash content,iron content,replacement rate of recycled aggregate and silica fume.It shows that the primary and secondary factors affecting the impermeability performance of recycled concrete with admixtures are: water-cement ratio,fly ash content,mineral content,replacement rate of recycled aggregate and silica fume content,i.e.water-cement ratio is the main factor influencing the impermeability of recycled concrete followed by fly ash content,iron content and recycled aggregate replacement rate while silica fume had minimal impact.(3)According to the analysis of variance of test results,the order of main and secondary factors affecting the impermeability of recycled concrete was obtained which is: the water-cement ratio,fly ash content,mineral content,recycled aggregate and silica fume content.The effect of water-cement ratio on the test is very significant.The effect of fly ash content on the test is remarkable.The mineral content has a significant influence on the test while the replacement rate of recycled aggregate has a certain influence on the test.The effect of silica fume content on the test is not significant.(4)In the case of recycled concrete with admixtures the specimens for which the water-cement ratio of the recycled concrete was 0.48 and 0.58,the compressive strength increased first and then decreased.For the specimens with water-cement ratio 0.43,the compressive strength first decreased and then increased.This is because admixtures added to the recycled aggregate concrete reduces the water content thereby improving the cube compressive strength.With the increase in the replacement rate of recycled aggregates,the compressive strength decreases because the recycled aggregate itself has small defects in the form of cracks,so that it needs more water which reduces the aggregate strength.The increase in compressive strength of recycled concrete in the later period is due to the addition of appropriate amounts of admixtures into the recycled concrete.