Study On Properties And Microstructure Of Geopolymer Permeable Concrete

As an environmentally friendly material,permeable concrete has been widely used in urban road construction to alleviate congestion disasters in recent years,and has provided much-needed help to improve the "block effect of heat ",maintain the ecological balance and build a " sponge city ".However,due to its large pores and low strength,permeable concrete has not been widely used as a coating material on a large scale.Therefore,it is necessary to study the coordination of the performance of permeable concrete.In this article,the combination of geopolymers,a new inorganic material,uses slag and fly ash as cement materials,and water glass and sodium hydroxide as alkaline excitation solutions to prepare concrete permeable to geopolymers.The characteristics of orthogonal test are used to test all kinds of composition,factor ratio and other important data,so as to understand the influence of mechanical strength and permeability of permeable concrete at different ages of 7d,14 d and 28 d.The reaction mechanism,hydration products and morphological characteristics of the reaction mechanism,hydration products and morphological characteristics were analyzed using modern microscopic SEM and XRD test methods.The main research contents and achievements are as follows:(1)During the test,four kinds of factors,namely sodium silicate modulus,alkali content,slag-fly ash ratio and porosity were tested,and their effects on compressive strength,Flexural strength,water permeability and porosity of concrete permeable to geopolymers were discussed.It is concluded that when the target porosity of slag-fly ash geological polymer permeable concrete is 18%,the optimal mix ratio is 1.4 of water glass modulus and 75% of slag-fly ash ratio.The alkali content is 8%.Under this combination,the test data of compressive strength can reach 23.96 MPa,the flexural capacity can reach 4.0MPa,and the permeability coefficient of pores is1.76mm/s.(2)Changes in mechanical properties and water permeability under the influence of four factors: sodium silicate modulus,alkali content,slag-fly ash ratio and porosity are investigated and analyzed.Specifically,as the porosity,alkali content and modulus of sodium silicate increase,the compressive strength and flexural strength of permeable concrete will first increase and then decrease;As the slag to fly ash ratio increases,there is a tendency to decrease first and then increase.In terms of water permeability,it is similar to the tendency of change in compressive strength.Only the increase in the slag / fly ash ratio will lead to a decrease in water permeability.The increase in water glass modulus and alkali concentration all show different trends.(3)Through the microscopic test and analysis of XRD and SEM,combined with the macroscopic observation of permeable concrete,the reaction mechanism,hydration products and surface morphology of geopolymer permeable concrete were analyzed.It is concluded that in the strong alkali environment,the early hydration of slag and fly ash is not complete,and the hydration products in the later stage tend to be denser,thus forming dense C-S-H cementation,which is consistent with the conclusion of macroscopic analysis.