Study On Mechanical Properties And Frost Resistance Of C30 Pervious Concrete

Pervious concrete is a widely used pavement material in sponge city construction,but its strength is still difficult to meet the engineering requirements to a certain extent,and the addition of mineral admixtures can improve the mechanical properties and durability of pervious concrete to some extent.In this paper,the pervious concrete mixed with mineral admixtures was taken as the research object,and the blank groups were set up.The mechanical properties and frost resistance of the permeable concrete with single admixture and compound admixture were studied in depth.The main research contents and achievements include:1.The porosity and permeability coefficients of pervious concrete at 7,28 and 56 days of curing age were analyzed under four conditions:single admixture of fly ash(5%,10%,15%),single with the same dosage(10%)of fly ash,silica fume and mineral powder,compound admixture of fly ash and mineral fume,and compound admixture of fly ash and silica fume.The results show that the porosity and permeability coefficients of pervious concrete increase with the addition of mineral admixtures.With the increase of the dosage and the increase of curing age,the"permeability reduction"effect is not obvious,but it can basically meet the standard requirements.2.The compressive strength and flexural strength of pervious concrete at curing age of7,28 and 56 days under four conditions were studied.The results show that compared with the blank group,adding fly ash alone can be reduced the strength of permeable concrete for7d,28d and increased the strength of 56d,while the mineral powder and silica fume can improve the strength of permeable concrete at all ages.Among them,the best modification effect of mineral powder is achieved,and its 56d compressive strength can reach C30grade.For pervious concrete with mineral admixtures,its 56d compressive strength can reach C30 grade or above,which can meet the needs of light motor vehicle pavement.3.The hydration samples of pervious concrete with single and compound mineral admixtures for 28 and 56 days were tested by SEM and XRD,and the macroscopic conclusion was further proved by microscopic analysis.The results show that the volcanic ash reaction of mineral powder and silica fume is mainly in the early stage,while the volcanic ash reaction of fly ash is mainly in the late stage.The surface of the pervious concrete mixed with 5%fly ash and 10%mineral powder is arranged orderly,and the hydration reaction is more thorough.A large amount of C-S-H gel is generated.The internal micropores are filled,the structure becomes dense,and the permeability is reduced.The strength is the largest,which is consistent with the macroscopic analysis results.4.The mass loss and relative dynamic elastic modulus changes of pervious concrete with single and compound mineral admixtures under freeze-thaw cycles are compared and analyzed.The results show that mineral admixtures can enhance the freeze-thaw resistance of pervious concrete and reduce the mass and relative dynamic elastic modulus loss during freeze-thaw process.With the increase of total mineral admixtures,the loss rate of cyclic mass and relative dynamic elastic modulus of pervious concrete decreases gradually.Among them,the freeze-thaw resistance of pervious concrete is most improved by adding 5%fly ash+10%mineral powder.5.The damage model of relative dynamic elastic modulus and freeze-thaw cycle exponential function of pervious concrete with mineral admixtures under freeze-thaw conditions was established,and the freeze-thaw damage evolution equation of pervious concrete with mineral admixtures was obtained.The correlation coefficient R~2 is greater than 0.97.