Mix Design And Performance Study Of Geopolymer Pervious Concrete

With the advent of the "sponge city" concept,maximizing the potential of urban green spaces,roads,water systems,and other elements in absorbing,storing,and releasing rainwater has become a popular research topic.Permeable concrete with a large number of internal pores has emerged as a viable solution.However,traditional permeable concrete production involves the use of cement as the binder material,which results in high energy and resource consumption and generates significant greenhouse gas emissions.In this study,metakaolin-based geopolymer was used to partially replace cement as the binder material in the production of permeable concrete.Orthogonal experiments were conducted to verify the feasibility of the mix proportion design method based on the volume method,and the significance of the factors affecting each index was analyzed.Single-factor experiments were designed to conduct an in-depth analysis of the factors that have the most significant influence on each index of geopolymer permeable concrete and to investigate the variation laws of permeability performance,strength,durability,and other indices under different target porosity levels.Furthermore,the plane structure of geopolymer permeable concrete sections was analyzed using image processing methods,and the effects of pore area,equivalent diameter,shape parameter,and other factors on the strength and permeability performance of geopolymer permeable concrete under different target porosity levels were discussed.The study’s primary objectives and results are summarized below.(1)Orthogonal tests were conducted to investigate the effects of various factors on the strength and permeability performance of geopolymer pervious concrete,and the results were ranked.The target porosity and water-cement ratio were identified as the two most important factors affecting its performance.ANOVA showed that the target porosity had a significant effect on the 7-day compressive strength and an effect on the 28-day compressive strength and permeability coefficient.The optimal combination of a watercement ratio of 0.6,target porosity of 25%,partial kaolin percentage of 55%,and alkali equivalent of 9% was obtained using the total efficacy factor method,considering the strength and permeability of the geopolymer pervious concrete.With this combination,the 7-day compressive strength of the ground polymer pervious concrete reached 14.33 MPa,the 28-day compressive strength reached 17.5 MPa,and the permeability coefficient reached 2.02 mm/s.(2)Based on the results of orthogonal experiments,single-factor experiments were conducted to further explore the factors that have the greatest impact on the performance of geopolymer permeable concrete.The effects of target porosity on the workability,strength,permeability,durability,and friction coefficient of geopolymer permeable concrete were studied,and prediction models for quantitative indexes such as measured porosity,permeability coefficient,and friction coefficient were established by taking the target porosity as the independent variable.(3)To further investigate the effects of cementation surfaces and planar pores on the macroscopic properties of geopolymer pervious concrete at different target porosities,sections of polymer pervious concrete test blocks were prepared from various locations at different target porosities.The cementation surfaces between the geopolymer pervious concrete aggregates and cementing materials were observed by optical microscopy at 30×and 60× magnification,and parameters such as pore area,equivalent diameter,and shape coefficient of each cut surface were extracted by image processing to investigate the effect of variation of target porosity on the performance of geopolymer pervious concrete at a fine microscopic scale.