Pore Structure Design And Performance Optimization Of Dry Pervious Concrete

Dry pervious concrete products have some advantages of pouring pervious concrete,such as good decorative effect,simple construction,no on-site maintenance problems,and easy maintenance when there is clogging or damage.However,at present,the study of dry pervious concrete for products is mostly focused on the application technology,but the theoretical research is few.The lack of theoretical guidance for the production of permeable products makes it difficult to coordinate the contradictory relationship between permeability coefficient and strength by controlling porosity.In addition,the characteristics of high porosity of pervious concrete make people doubt its frost resistance.Nevertheless,the test method for evaluating the frost resistance of pervious concrete is not consistent with the actual application conditions,and the study of how the porosity affects the frost resistance of pervious concrete is relatively small.Resulting in the uneven quality of permeable products,which hinders its popularization and application.In view of this,the pore structure design method and performance optimization measures of dry pervious concrete were systematically studied in this paper.A porosity based mixture proportion design method is proposed.According to the compressible packing model,the dry packing density of graded aggregate under the vibratory compact packing process was calculated.And the correlation between the packing density in the dry pervious concrete and the dry packing density of graded aggregate was discussed.Based on this,the packing density and the content of the graded aggregate in the dry pervious concrete were calculated.And the content of cement and water was calculated by combining the water cement ratio and the designed porosity.The mixture proportion design method proposed in this paper takes into account the effect of the molding process and aggregate gradation on the porosity of permeable concrete,and the results show that it can be used to control the total porosity of dry pervious concrete with good applicability.The correlation between pore structure and dry pervious concrete properties was studied.Based on the discrimination of flow patterns,the Kozeny-Carman equation was modified to study the correlation between the permeability and the effective porosity and the average pore size.The Griffith fracture mechanics theory was modified to study the correlation between the strength of the pervious concrete and the total porosity and the average pore size,and the correlation between the frost resistance of pervious concrete and the porosity was studied.The results show that the permeability coefficient is more related to the effective porosity,and the permeability can be predicted by the modified Kozeny-Carman equation through the effective porosity.Through the modified Griffith fracture mechanics formula,the flexural strength can be predicted well,and the prediction of the compressive strength is uncertain.The main reason is that it is impossible to determine the effect of the pore size on the compressive strength.And there is little correlation between porosity and frost resistance of dry pervious concrete.The performance optimization of dry pervious concrete has been carried out.The theoretical measures to increase the strength of pervious concrete were proposed according to the established dry pervious concrete structure model.Combined with the freeze-thaw damage characteristics of pervious concrete,it was concluded that the modified cement slurry method was the easiest way to increase the strength and improve the frost resistance without reducing the permeability.Then the performance optimization results of cement paste modification such as adding superplasticizer,latex,silica fume and compound silica fume and superplasticizer were studied.The results show that the performance of dry pervious concrete is the best by adding 5% latex under the condition of dry/wet combined curing.