Study On Physical And Mechanical Properties And Frost Resistance Of Hybrid Fiber Permeable Concrete

Pervious concrete instead of ordinary concrete as pavement material is an important way to alleviate the heat island effect in cities and towns,effectively utilize rainwater resources and supplement groundwater resources.Compared with ordinary concrete,permeable concrete has loose internal structure and low strength,so it can not be used in heavy-duty pavement,severe cold area and saline alkali land area for a long time.Based on the fact that the hybrid fiber can improve the permeability,toughness and frost resistance of pervious concrete.This paper studies the influence of the monofilament polypropylene fiber and basalt fiber on the physical properties and the mechanical property of pervious concrete,expounds the mechanism that HFPC has higher toughness and frost resistance than single incorporation fiber pervious concrete.Uses Cox regression analysis and Grey correlation method as the theoretical basis,based on the frost resistance predicted the service life of hybrid fiber permeable concrete（HFPC）.The main conclusions are as follows:（1）The slump of HFPC decreases greatly with the increase of basalt fiber content,while the effect of polypropylene fiber on the slump of pervious concrete is relatively low;Compared with ordinary permeable concrete,when the ratio of basalt fiber to monofilament polypropylene fiber is 2:1,1:2 and 1:1,the porosity increases by 45.77%,21.65% and16.29% respectively.When the ratio is 2:1,the permeability increases by 63%.（2）In the pervious concrete with single fiber,the compressive strength of pervious concrete decreases with the increase of the content of polypropylene fiber.When the content of basalt fiber is 0.4%,the compressive strength of pervious concrete reaches a maximum;When the mixing ratio of basalt fiber to monofilament polypropylene fiber is 1:1,the loss rate of compressive strength of HFPC is the largest,which is 42.02%;When the hybrid ratio was 1:2,the flexural strength of HFPC increased by 122.34%;Compared with polypropylene fiber,basalt fiber is more closely combined with cement-based materials.Combined with the analysis of composite material theory and fiber spacing theory,basalt fiber enhances the bonding between polypropylene fiber and cement-based materials.At the same time,the addition of basalt fiber reduces the fiber spacing,so HFPC has stronger toughness and crack resistance than polypropylene fiber permeable concrete alone.（3）When polypropylene fiber is added alone,the frost resistance of pervious concrete is improved obviously,with an increase range of about 50% ～ 100%,while basalt fiber has little effect on the frost resistance of pervious concrete;When the two fibers are mixed,the frost resistance of pervious concrete is greatly improved,and the number of freeze-thaw cycles is more than 150 times,which is about three times more than that of ordinary pervious concrete;Hybrid fiber improves the crack resistance of permeable concrete,slows down the damage rate in the middle stage of freeze-thaw failure（crack development stage）,and prolongs the damage development time in the second stage;Based on Cox regression analysis and Grey correlation method,the frost resistance of fiber pervious concrete is evaluated,and the results of indoor freeze-thaw test are connected with the actual working conditions.Predicted the frost resistance life of pervious concrete which mixed with hybrid fibers.The frost resistance life of ordinary pervious concrete is 14 years,and that of HFPC with hybrid ratio of 1:2 is 34 years.