Experimental Study On Strength And Freeze-Thaw Durability Of Pervious Concrete

Pervious concrete is a water-permeable concrete obtained from water,cement,a certain grade of aggregate and admixture according to a certain mixing ratio and molding process.Compared with ordinary concrete,the biggest advantage of pervious concrete is that it has excellent water permeability.When pervious concrete is used in pavement,it can play the role of flood control,drainage,noise reduction,and alleviation of urban heat island effect.Therefore,pervious concrete has been more and more widely used in recent years,especially in the construction of “sponge city”,pervious concrete plays a very important role.In this paper,the reasonable water-to-binder ratio and the amount of water reducing agent for making pervious concrete are determined by the trial mixing method.Pisolite and basalt gravel with a particle size of 5 ~ 10 mm were used as the aggregate of pervious concrete,silica fume and fly ash are used as admixtures for pervious concrete.The admixture was blended into the pervious concrete in different proportions,and the pervious concrete specimens with different aggregates and admixtures were obtained.The effective permeability,permeability coefficient,compressive strength and splitting tensile strength test of the prepared pervious concrete,as well as the freeze-thaw cycle test in clear water and 3%,5%,and 10% sodium sulfate solution were carried out,and the specimens were scanned by microscopic electron microscopy after the freeze-thaw cycle.Also,the microscopic mechanism analysis of the experimental results was carried out.The test results show that the type and amount of the admixture have a significant effect on the permeability,strength and freeze-thaw durability of pervious concrete.In this paper,the freeze-thaw compression coefficient is proposed to quantitatively evaluate the freeze-thaw durability of pervious concrete.It is show that the type and amount of admixture are the root causes of the permeability,strength and freeze-thaw durability of pervious concrete through qualitative analysis of freeze-thaw durability by mass loss rate,relative dynamic elastic modulus and relative compressive strength,also,through quantitative analysis of freeze-thaw durability using durability coefficient and freeze-thaw compression coefficient.And there is a negative correlation between permeability and strength,freeze-thaw durability.The pervious concrete incorporating silica fume has smaller effective porosity and permeability coefficient,higher strength and freeze-thaw durability than the same amount of fly ash and double-mixing samples.The effective porosity and permeability coefficient of double-mixing samples will increase with the increase of total content,but the strength and freeze-thaw durability will decrease.The pervious concrete with 10% silica fume shows the excellent strength and freeze-thaw durability under the premise of satisfying permeability.The freeze-thaw cycle medium will affect the freeze-thaw durability of pervious concrete.Compared with the freeze-thaw cycle in clear water,the freeze-thaw durability of pervious concrete in sodium sulfate solution is worse,and the freeze-thaw durability of the sample was most degraded during the freeze-thaw cycle in a 5% sodium sulfate solution.It was found that the freeze-thaw durability of samples in the 5% sodium sulfate solution were 30% weaker than that in water through the quantitative analysis of the durability coefficient and the freeze-thaw compression coefficient.The experimental results show that the strength and freeze-thaw durability of pervious concretes can be improved by optimizing the admixture and minimizing the porosity of the samples under the premise of satisfying the permeability.When quantitatively evaluating the freeze-thaw durability,the durability coefficient is similar to the freeze-thaw compression coefficient,and the freeze-thaw compression coefficient is more accurate,and it is more suitable for quantitative evaluation of freeze-thaw durability in engineering.