The Research On The Influence Of Water Content On The Mechanical Properties Of Autoclaved Aerated Concrete

Autoclaved aerated concrete(AAC)is a new type of green building material rapidly developed nowadays.Due to its strong hygroscopicity,the moisture content plays a significant effect on its physical and mechanical properties.At present,the current specification only provides the moisture content range of AAC mechanical performance test conditions is 8%～12%,and when the external environment humidity changes,the moisture content of AAC may not be within the above-mentioned range,and plays a significant impact on its mechanical properties.At present,domestic and foreign literatures rarely report the change of mechanical properties when the internal moisture content of AAC is not between 8%and 12%,which will restrict the promotion and application of AAC and the revision and improvement of relevant standards and regulations.In this study,based on the research results of cement-based composite materials and the mechanism of the influence of moisture content on cement-based materials,by adjusting the internal moisture content of AAC,the variation of mechanical properties of AAC block masonry under different water content conditions was discussed in-depth,and studied the AAC uniaxial and biaxial compression characteristics and masonry through-seam shear resistance,established and perfected AAC block masonry constitutive model database,which provides a theoretical basis for the development and improvement of the structural design of AAC block masonry.The main research results obtained in this paper are as follows:(1)The uniaxial compression characteristics of AAC under different water content conditions were studied.The influence rule of water content on the main mechanical performance parameters of AAC was analyzed,and the corresponding fitting equation was established.The moisture content played a significant effect on the failure mode of AAC.Micro-cracks are first generated from the bottom or top of the specimen.When the moisture content of AAC is less than 10%,brittle failure existed and accompanied by a large splitting noise.When the specimen was damaged,it presented obvious vertical cracks in the middle and presents splitting failure mode.When the water content of AAC was larger than 10%,its failure mode was "splayed"or corner failure.The three-stage constitutive relationship equation of AAC under uniaxial compression under different water content conditions was established,which has important reference value for in-depth study and exploration of the mechanical properties and durability of AAC,and can also provide revision and improvement of corresponding codes and regulations reference.(2)The biaxial compression performance of AAC under four different lateral pressure levels with a water content of 10%was studied.The results show that when the confining pressure value is small,the failure mode of AAC specimens under biaxial compression is similar to that under uniaxial compression,showing a split failure mode;With the increase of the confining pressure,the tensile strain of the test piece is generated on the free surface.The main cracks generally appear in the direction of 20° to 30° with the principal stress direction,and the shear failure mode or inclined layered failure mode of the inclined section.At the same time,the influence law of the confining pressure value on the peak stress,peak strain and elastic modulus of AAC is also found;and the AAC biaxial compressive strength envelope equation is established and the biaxial compressive failure criterion suitable for AAC is proposed.(3)The effect of water content on the shear resistance of AAC masonry joints was studied.The results show that the shear strength of AAC masonry increases first and then decreases with the increase of water content;The length of the soaking time plays a significant effect on the damage form of AAC.At the same time,the formula for the shear strength of AAC masonry joints considering the effect of water content is established.The research results can provide a reference for the seismic and collapse performance and safety performance evaluation of AAC buildings in service under different environmental humidity or immersion environment conditions.