Study On Mechanical Properties Of Polypropylene Fiber Modified Nano-silica Permeable Concrete

In recent years,the country has vigorously promoted the construction of "sponge cities",and permeable concrete has become more and more widely used as a permeable pavement material.The internal pores have the functions of water absorption and water storage,which can alleviate the urban heat island effect and supplement groundwater,but the existence of a large number of pores affects the strength and durability of permeable concrete.In this paper,nano-silicon and polypropylene fibers are added to permeable concrete to study the influence of both on the performance of permeable concrete.The main research contents are as follows:(1)Based on a single porosity of 23%,two aggregate grades G1 and G2 with different thicknesses were prepared,and the optimal grade was determined by physical and mechanical properties.The test data shows that on the basis of the same porosity,the compressive strength of the coarse grade G2 specimen is better than that of the fine grade G1 specimen.(2)Through the cement paste test,determine the standard consistency water consumption after adding four different proportions of nano-silicon particles,so as to determine the appropriate water-binder ratio,and then determine the optimal nano-silicon blending ratio through physical and mechanical performance tests.The test data shows that the amount of water used increases significantly after the addition of nano-silicon,and the greater the water-to-binder ratio,the better the performance of the specimen.When the nano-silicon addition ratio is 0.5%,the compressive strength of the specimen is the highest.(3)Based on the addition of 0.5%nano-silicon,the effects of the length and amount of polypropylene fiber on the compressive and flexural strength of permeable concrete are studied.The analysis shows that the addition of nano-silicon and polypropylene fibers can better improve the mechanical properties of permeable concrete,and with the increase in the proportion of polypropylene fibers,the porosity increases.In terms of compressive strength,when adding 0.5%nanometer silicon+1.0kg/m3 of 18mm polypropylene fiber,the compressive strength is the highest.In terms of flexural strength,the effect of single addition of 0.5%nanometer silicon on the flexural strength of permeable concrete Smaller,when mixed with 0.5%nanometer silicon+1.5kg/m3 18mm polypropylene fiber,polypropylene modified nanometer silicon permeable concrete has the highest flexural strength,reaching 4.43MPa.(4)The anti-freezing properties of polypropylene fiber modified nano-silicon permeable concrete were studied.The test results show that nano-silicon alone and nano-silicon+polypropylene fiber can significantly improve the frost resistance of pervious concrete.After 75 freeze-thaw cycles,the mechanical properties of the specimens in each group decreased slowly.At this time,the anti-freeze performance of the permeable concrete mixed with 0.5%nano-silicon+1.0kg/m3 polypropylene fiber was the best;after 300 freeze-thaw cycles,The test pieces of each group showed different reductions,the mechanical properties of ordinary permeable concrete declined the fastest,and the anti-freezing performance of the permeable concrete mixed with 0.5%nanometer silicon+1.5kg/m3 polypropylene fiber was the best.