Study On The Properties Of Pervious Concrete Mixed With Silica Fume And Metakaolin And The Pore After Freeze-thaw Cycle

The construction of "sponge city" can greatly improve the ecological environment of the city and reduce the cost of urban construction,application and maintenance.Sponge city can also collect rainwater and use it to solve the problem of urban water shortage to some extent."Sponge city" enables the ecological environment to be flexibly adjusted,and alleviates the "heat island effect" through effective "accumulation,infiltration and purification".Building permeable concrete pavement is one of the main ways to build "sponge city".However,the special pore structure inside the permeable concrete leads to its poor freeze-thaw resistance,which limits its application in the construction of "sponge city" in cold areas.Therefore,the key to the construction of "sponge city" in cold region is to prepare pervious concrete with high frost resistance.In this paper,9 groups of 27 specimens were prepared by adding silica powder,metakaolin and polypropylene fiber into concrete.The strength of the specimen is C20 and the target porosity is 15%.The optimum ratio of admixture was determined by range analysis.The strength and permeability tests were carried out,and the results showed that the addition of silica powder,metakaolin and polypropylene fiber into the pervious concrete did not affect the porosity of the specimens.Seventeen groups of 51 specimens were prepared for rapid freeze-thaw test of permeable concrete.The relation curves of mass loss rate,relative dynamic modulus,compressive strength loss rate and freeze-thaw were established.Taking the reduction rate of compressive strength of 20%as the standard,the maximum freeze-thaw times of the samples doped with silica powder,metakaolin and polypropylene fiber can reach 90 times,higher than the maximum freeze-thaw times of the samples without admixture in the literature which is25 times.It is suggested that the change of porosity after freeze-thaw should be used as a reference index to measure the freeze-thaw heat of pervious concrete.CT scanning method is used to detect the porosity of pervious concrete after freeze-thaw,and the numerical comparison with gravimetric method proves that CT scanning method can quickly and accurately detect the porosity of pervious concrete.