Compressive Strength And Size Effect Research On Pervious Concrete

With the substantial application of "sponge City" materials,pervious concrete has shown excellent permeability,wear resistance,anti-skid and environmental protection,easy maintenance,sound absorption and noise reduction and other advantages,the road paved by it has become a "breathing" town landscape road,pervious concrete materials have begun to be valued and applied.Pervious concrete has the same composition as general concrete,mainly incloud cement,water,coarse aggregate and additives,but it has high permeability,with porosity between 10% and 35%.Its high permeability also limits the improvement of mechanical properties,and because of the large number of pores in the pervious concrete,its failure forms become more complex.Stress concentration often occurs around the pore.Before reaching the ultimate strength,the concrete around the pore has taken the lead in destroying and destabilizing,which makes it difficult to predict the strength of the pervious concrete.Because of the "wall effect" in the forming process of pervious concrete,the so-called "wall effect" means that the larger size aggregates of pervious concrete will surge around the test block in the forming process.When subjected to force,these aggregates tend to contact with less aggregates,forming a certain weak area.In addition,because of the large number of pore in pervious concrete,when the size of test block increases,the number of pore increases,and the probability of sudden structural instability increases,which also leads to the size effect of pervious concrete is larger and more complex than that of ordinary concrete.Therefore,it has great significance to study the mix ratio and size effect of pervious concrete.In this research,the effects of target porosity,aggregate size,water cement ratio and water reducer content on the compressive strength and permeability of pervious concrete are studied by orthogonal experimental design,and the optimum mix proportion of relevant factors is obtained.Based on this,the influence of different porosity on compressive strength and different sizes are further studied.At the same time,the finite element software is used to simulate and compare with the experiment.The main conclusions were summarized as follows:(1)Through orthogonal test,the optimum mix ratio of pervious concrete is determined: target porosity is 10%,water cement ratio is 0.31,aggregate size is 5-10 mm,water reducer is 1.1%.It is found that permeability coefficient increases rapidly with the increase of porosity.Therefore,it is more meaningful to study the influence of other factors on the strength of pervious concrete on the premise that porosity is not less than 15%.(2)The influence of aggregate size on the strength of pervious concrete is studied.The compressive strength of pervious concrete with aggregate size of 5-10 mm is close to that with aggregate size of 10-15 mm.When aggregate size increases to 15-20 mm,the compressive strength of pervious concrete decreases significantly compared with the other two sizes.(3)The influence of water-cement ratio on the compressive strength of pervious concrete is studied.The compressive strength of pervious concrete increases first and then decreases when the water-cement ratio is 0.28,0.31 and 0.34.The water cement ratio should be kept near 0.31.(4)The pervious concrete with different porosity is studied by ANSYS.With the increase of porosity,the compressive strength decreases,and the stress concentration around the pore appears,which is consistent with the experimental results.