Research On The Mix Ratio, Engineering Performance And Pore Structure Of Alkali Slag Foamed Concrete

Alkali activated slag foamed concrete is a new type of green lightweight concrete prepared by using alkali activated slag as cementing material.Compared with ordinary cement foamed concrete,it not only has the characteristics of light weight,thermal insulation,sound insulation and fire prevention,but also has the advantages of energy saving,waste utilization,short setting time and high strength are in line with the development concept of new building materials.In this paper,the mix design,macroscopic properties,hydration products and pore structure of alkali activated slag foamed concrete with water glass as the activator were studied.Taking dry density,compressive strength and thermal conductivity as performance indicators,slag content,alkali concentration and activator cement ratio as parameters,three-factor and three-level orthogonal tests were carried out to explore the optimal mixproportion of alkali activated slag foamed concrete and the influence of three factors on performance;the influence of the addition of metakaolin,swelling agent and super absorbent polymer(SAP)on the shrinkage performance of alkali activated slag foamed concrete was investigated.And the SEM,XRD and FTIR were used to analyze the effects of different components on the hydration products.Based on the stereological principle and fractal theory,the pore structure parameters of alkali activated slag foamed concrete were studied.And established a connection between pore structure and macro performance.This paper aims to solve some of the factors that restrict the development of alkali activated slag foamed concrete through experiments,and play a positive role in its promotion and development.The main research results of this paper are as follows:1.Using the range analysis method to analyze the orthogonal test results,the primary and secondary order of the influence of three factors on the properties of alkali activated slag foamed concrete is obtained.alkali concentration > activator cement ratio > slag mass coefficient;When the alkali concentration is 9%,the activator cement ratio is 0.46,and the slag mass coefficient is 1.4,the properties ofalkali activated slag foamed concrete is optimal.When the modulus of water glass is fixed,the alkali concentration has a great influence on the properties of alkali activated slag foamed concrete.When the alkali concentration is in the range of 5% to9%,with the increase of alkali concentration,the hydration progress of slag is accelerated,and the early compressive strength higher,the foam that is mixed in the slurry is less likely to be lost,the obtained foamed concrete is more stable,and the dry density can better meet the design value;when the alkali concentration is more than9%,the alkali slag slurry has a faster setting speed and a lower fluidity,which affects the uniformity of the mixing and destroys the pore structure and ultimately affects various properties.2.Metakaolin,expansion agent and SAP can effectively reduce the shrinkage and thermal conductivity of alkali activated slag foamed concrete,but the effect on dry density and compressive strength is quite different.The higher the density grade,the smaller the shrinkage of alkali activated slag foamed concrete,the greater compressive strength and thermal conductivity;the incorporation of metakaolin will slow down the hydration process and reduce the early compressive strength,but with the hydration,28 d compressive strength increases first and then decreases with the increase of metakaolin content.The addition of expansion agent and SAP will also reduce the early compressive strength.When the blending amount is small,it will have little effect on the 28 d compressive strength.Larger ones will affect the hydration process and pore structure,affecting the final dry density and compressive strength.3.The SEM/EDS,XRD and FTIR microscopic testing methods were used to analyze the microstructure and hydration products of alkali activated slag foamed concrete.The incorporation of metakaolin makes the hydration product more compact and the cracks are reduced.The resulting zeolite-like product improves the stability and strength of the solid phase;although the incorporation of the expansion agent hinders the early strength development,as the hydration progresses,The hydration product becomes dense and stable,and the ettringite crystal acts as a"micro-aggregate" in the gel product,limiting the shrinkage rate and increasing the late strength;although the SAP does not produce new hydration products,it can play the role of "internal maintenance",effectively reducing the shrinkage and thermal conductivity.4.The dry density of alkali activated slag foamed concrete is mainly related to the type of cementitious material and the characterization of porosity.When the cementitious materials are the same,the linear relationship between the porosity and the dry density is dominant,which plays a leading role in the dry density.Within a certain range,the dry density decreases with the increase of the porosity;the average roundness factor and the average pore diameter It has a great influence on the fractal dimension,but has little effect on the dry density.Therefore,when the composition affecting the pore size and shape of the pore is incorporated,the fractal dimension does not reflect the change trend of the dry density well.5.The compressive strength of alkali activated slag foamed concrete is closely related to the types of cementitious materials and the parameters of pores.In the case of the same cementitious material,the smaller the porosity,the average roundness factor,and the smaller the average pore size,the larger the proportion of the small pores,the smaller the fractal dimension,and the greater the compressive strength of the alkali activated slag foamed concrete;Dimension can reflect the combined effect of multiple parameters of pore structure well,and establish the relationship between pore structure and compressive strength.When the density grade changes,there is a good correlation between compressive strength and dry density.But at the same density level.the change in the average roundness factor and the average pore diameter of the pores causes a change in the compressive strength,and at this time,the correlation cannot express the relationship between the compressive strength and the dry density.6.When the density grade is different,the thermal conductivity of alkali activated slag foamed concrete mainly depends on the solid phase composition and porosity,and the thermal conductivity decreases with the increase of porosity;at thesame density level,the thermal conductivity decreases with the decrease of pore diameter,roundness factor and the proportion of large pores.