Research On The Effect Of Slow-release Water Reducing Agent On The Performance Of Recycled Aggregate Concrete

Rapid urbanization has led to billions of tons of building and demolition wastes growing annually.The traditional way to dispose of building wa stes is simply to pile them up.This will not only occupy valuable land resources,but also bring a series of environmental pollution problems.In order to alleviate this problem,some scholars try to break the building waste into recycled aggregate to replace part of natural aggregate for mixing new concrete,which can effectively save the very scarce natural sand and stone resources,on the other hand,can maximize the recycling of building waste.Up to now,the replacement rate of recycled aggregate in structural concrete without any pretreatment is generally less than 30%,while for non-structural concrete,the utilization rate of recycled aggregate can reach 100%.At the same time,for fresh concrete,slump and expansion are important indexes to measure its flowability and working performance.For concrete,different water consumption will seriously affect its working performance,strength and durability.The research emphasis of this paper is the influence of the polycarboxylic acid slow-release water reducer on the performance of recycled concrete,including the influence of the dosage of the recycled concrete and the influence of the polycarboxylic acid slow-release water reducer on the compressive strength,splitting tensile strength and durability of recycled concrete under the premise of the slump of 200-250 mm.The results are as follows:(1)As the replacement ratio of recycled aggregate increases,the amount of water reducing agent is also increasing.For C30,C45,C60 and other low design strength concrete,the amount of water reducer needed to meet the slump and expansion requirements of industrial pumping under the same replacement rate of recycled aggregate is not much different.However,for C70,C80 and other high design strength concrete,the role of water reducer is very obvious.(2)The strength of recycled concrete can be improved by adding water reducing agent.When the replacement ratio of recycled aggregate is 100%,the compressive strength of recycled aggregate can reach 90% of the reference concrete.(3)The addition of water reducer can not effectively improve the splitting tensile strength of recycled aggregate concrete,which is due to the inherent defects of recycled aggregate,so that it can not form an effective bond with the surrounding cement paste.(4)The superplasticizer has a great influence on the performance of high strength concrete,and the change of recycled aggregate replacement ratio in concrete mix proportion will cause the change of durability of concrete test blocks,which are negatively correlated.To sum up,adding slow-release water reducer can improve the initial fluidity of concrete,and for compressive strength has a relatively obvious enhancement effect,which is conducive to the practical application of recycled aggregate in building engineering.