| Since the beginning of summer in 2021,Henan and Shanxi province have suffered flood disasters one after another,causing huge casualties and property losses.Although these disasters were caused by extreme weather,many problems and deficiencies have been exposed in a concentrated manner.The higher the place,the more serious the flood disaster.This phenomenon is ultimately because a large amount of land in the city is replaced by high-rise buildings and urban hardened pavement,which seriously damages the ecological function of the soil,causing problems such as difficult urban drainage and lack of groundwater resources.,and pervious concrete has excellent ventilation and water permeable functions,and it can be used as an urban paving material to alleviate this problem.However,due to the small amount of cementitious materials and many internal pores of pervious concrete,its characteristics of low compressive strength and poor frost resistance have seriously affected its large-scale promotion in the cold climate regions of northern my country.Aiming at some problems existing in the practical application of pervious concrete,based on the laboratory test,the mix ratio was designed by the controlled variable method,the pervious concrete test block was prepared and its performance was tested.the influence of the forming process of pervious concrete and the changes of various factors in the mixing proportions（Aggregate particle size,water-binder ratio,glue-bone ratio,target porosity,admixture content,admixture content,fiber content,etc）on the mechanical properties,water permeability,anti-clogging performance and anti-freezing performance of pervious concrete were studied respectively and the effect of mix proportions on the working performance of pervious concrete was summarized.The main research results are as follows:（1）Four methods of manual tamping molding,vibrating table vibrating molding,surface vibrating instrument vibrating molding and press static pressure molding were used respectively,and their advantages and disadvantages were compared.The results showed that the pervious concrete test block prepared by static pressure molding（5MPa）Under the condition of satisfying certain water permeability（1.56mm/s）,its compressive strength is better than that of permeable concrete formed by other molding methods and molding parameters;（2）The test uses compressive strength and water permeability coefficient as evaluation indicators to explore the influence of various factors of mix ratio on the performance of permeable concrete.The results show that the target porosity is 15%,the water-binder ratio is0.35,the content of silica fume is 8%,and the water reducing agent is mixed with water.When the amount is about 0.5%,the comprehensive performance of the test block is the best,and when the ratio of cement to bone is greater than 0.25,the compressive strength of the test block can reach above C20;（3）The permeability coefficient of pervious concrete decreases with the increase of the number of plugging cycles,and the decay rate of the permeability coefficient is positively correlated with the porosity of pervious concrete.With the increase of the number of plugging cycles,the larger the target porosity of the pervious concrete,the faster the permeability coefficient decreases;（4）The increase of the flexural strength of permeable concrete is much greater than the improvement of the compressive strength by the addition of fibers,and the mechanical properties of the polypropylene fiber permeable concrete test block are generally better than those of basalt when the fiber length and dosage are the same.Fiber permeable concrete test block,the appropriate dosage of both fibers is about 4kg/m~3;（5）The target porosity and water-binder ratio were negatively correlated with the frost resistance of pervious concrete;the cement-bone ratio and the content of silica fume were positively correlated with the frost resistance of pervious concrete.Based on the influence laws of the various factors of the mixing ratio on the anti-compression,water permeability and anti-freezing performance,the following ratios are proposed:When the target porosity is15%,the water-binder ratio is 0.35,the silica fume content is 8%,the water reducing agent content is 0.5%,and the fiber content is 4kg/m~3,Pervious concrete can meet a certain permeability coefficient（0.97mm/s）,and its compressive strength can reach above C20.And after 25 freeze-thaw cycles,its compressive strength loss rate and mass loss rate can meet the requirements of the specification,and the frost resistance is excellent. |
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