The Research On The Thermal Performance Of Autoclaved Aerated Concrete Under Coupling Factors

Autoclaved Aerated Concrete(AAC)as a new self-insulating wall material has been vigorously promoted and applied in building envelope structure,and achieved remarkable results.The thermal performance of AAC is not only the premise of its durable performance design,but also the basis of its energy saving and environmental protection energy consumption calculation.However,the test conditions of AAC thermal conductivity and thermal storage coefficient given in the existing codes are mainly concentrated in the absolute dry state and water content between 0%and 18%,but no other thermal parameters are given.As a result,the performance and service life of AAC materials cannot be comprehensively evaluated.In this thesis,the change rule of AAC thermal performance under different environmental factors was discussed by means of unsteady state test method.The microstructures of AAC were tested by means of material science research methods in order to reveal the degradation mechanism of thermal properties of AAC under different influencing factors.Moreover,the database of the physical properties of heat and moisture transfer of AAC block was established and perfected in order to lay a theoretical foundation for further optimization design of AAC block in the future.The main conclusions of this thesis are as follows:(1)The relationship between the thermal performance of AAC and three single erosion factors,namely,moisture content,carbonization and acid rain,was established.The results show that the moisture content is the key factor affecting the thermal performance of AAC,and the power function can be used to describe the relationship between the thermal conductivity,thermal resistance and thermal storage coefficient of AAC with the moisture content.With the increase of carbonization age,the thermal performance of AAC degrade significantly.With the increase of acid rain cycle times,the thermal insulation performance of AAC decreases gradually.(2)The effects of coupling factors such as moisture-carbonization,acid rain-carbonization and bulk density-moisture on the thermal performance of AAC were investigated.The results show that the increase of moisture promotes the carbonization reaction of AAC,and acid rain can inhibit the carbonization of AAC.The smaller the bulk density of AAC,the better its thermal performance,and the more significant the influence of moisture content on it will be.(3)The influence mechanism of carbonation corrosion on thermal performance of AAC was revealed.Based on Fick’s diffusion law and concrete carbonization model,the prediction model of thermal conductivity of AAC under the coupling action of moisture and carbonization was established.(4)The macro and micro pore characteristics of AAC were tested by means of material science research method,and its water absorption and moisture absorption characteristics were studied.The results show that the water absorption process of AAC satisfies the time kinetics,and the smaller the bulk density of AAC is,the greater the dynamic moisture content and the ultimate equilibrium moisture content will be.(5)The thermal conductivity of the matrix was reasonable identified by extrapolation of the thermal conductivity dependence on the porosity to the zero porosity value.Moreover,the geometric parameter k of the Lichtenecker’s model was optimized and the prediction model of effective thermal conductivity of AAC was constructed.