The Research On Hygroscopic And Mechanical Properties Of Autoclaved Aerated Concrete In Forest Environment

Autoclaved Aerated Concrete(AAC),as a new type of wall material to replace the traditional solid clay brick,has many advantages such as light weight and durability,heat preservation and insulation,sound absorption and sound insulation,fire retardant and flame retardant,and becomes the national vigorously promotes wall material.In recent years,with the vigorous promotion of China's ecological civilization construction and the full implementation of the national strategy of rural revitalization,the forest health industry has become an effective way to promote the vigorous development of rural revitalization and high-quality forest buildings are an important part of the health industry.Therefore,AAC has gradually become a commonly used wall material in forest buildings.However,AAC appears water and mildew,deformation and cracking,and thermal insulation performance decreases in actual use due to the high humidity in the forest area and the heavy acid rain pollution in some areas,which has affected the durability and aesthetics of the wall materials in the forest area.So through carrying out research on the degradation mechanism of AAC under the condition of forest environment characteristics,it has important guiding significance to optimize the preparation technology and quality guarantee system of AAC,it will provide important technical support for further enriching and improving AAC's existing application technology standards in order to achieve the same lifespan of AAC's new enclosure wall materials and the main structure.This thesis takes AAC as the research object,takes the humidity,temperature,acid rain p H and sulfate concentration of the forest area as the basic working conditions,based on the combination of survey analysis,theoretical research,indoor accelerated test,macro test and micro analysis,studied separately the moisture absorption and desorption performance,volume stability and mechanical properties of AAC under three different working conditions of dry-wet circulation,sulfate attack and sulfate dry-wet circulation respectively,and carried out comparative analysis for the change of microstructure before and after AAC degradation.The main innovative results are as follows:(1)Study on the moisture adsorption and moisture liberation of AAC under three different conditions of dry-wet circulation,sulfate attack and sulfate dry-wet circulation.Based on isothermal hygroscopic curves and hygroscopic rate curves,hygroscopic properties of AAC under different operating conditions are investigated.The results show that model of double exponential function as moisture adsorption model,and midilli model law conforms to the moisture liberation model.Meanwhile,the law of moisture transport in AAC conforms to Fick diffusion theorem.Based on the analysis of finite element software,the predict results of AAC moisture absorption and drainage process are in good agreement with the test results.(2)Wet expansion and dry shrinkage of AAC under dry-wet circulation,sulfate attack and sulfate dry-wet circulation are tested by dynamic method.The results show that the value of wet expansion and dry shrinkage increased by the times of dry-wet circulation,concentration of soaking and the times of sulfate dry-wet circulation.The value of wet expansion and dry shrinkage balance to the time of absorbing water(or lossing water).Based on the multiple linear regression method,the AAC's wet expansion model under different working conditions is established.The bazant-panula model is modified by the characteristic parameters of water content and relative humidity of the specimen,and establish the dry shrinkage model of AAC under three working conditions.The error value between the predict results and the test results is less than 10%.(3)The mechanical performance and failure characteristics of AAC under three working conditions for dry-wet circulation,sulfate attack and sulfate dry-wet circulation are studied.It conclud that the AAC's compressive strength and splitting tensile strength with the times of dry-wet circulation,concentration of sulphate attack and the times of sulfate dry-wet circulation,prove the characteristic parameters of AAC stress-strain full curves with the times of dry-wet circulation,concentration of sulphate attack and the times of sulfate dry-wet circulation,the mechanical failure mechanism of AAC under three operating conditions is revealed.Uniaxial compressive stress-strain whole curve equation of AAC set up under different working conditions.Based on finite element software simulation,goodness of fit between the predict results and the test results is 95%.(4)Using SEM,XRD as characteristics of internal microstructure and method of DIP technology for quantitative characterization,ascertain the change rule of microstructure,hydration products and internal pore structure of AAC under three working conditions of dry-wet circulation,sulfate attack and sulfate dry-wet circulation.Establish the relationship between porosity fractal dimension of AAC and compressive strength,splitting tensile strength,wet bilge drying shrinkage based on fractal theory.And the mechanical properties of AAC and volume stability properties and microscopic properties provide prophase research foundation,the relationship among soaking and and the degradation mechanism of AAC under different working conditions for dry-wet circulation,sulfate attack and sulfate dry-wet circulation conditions is revealed.