Experimental Study On Physical And Mechanical Properties And Durability Of Autoclaved Lightweight Concrete At High Temperature

The high temperature of fire is a major threat to the safe use of buildings today,so it is urgent to study the thermal insulation and fire resistance of building materials.Autoclaved lightweight concrete(ALC)has good high temperature resistance and meets the actual needs of engineering.In this paper,the basic physical and mechanical properties test,permeability test,freeze-thaw cycle test and microstructure test of ALC specimens after high temperature treatment were carried out to study the physical and mechanical properties and durability of autoclaved lightweight concrete at high temperature.The following conclusions are obtained:(1)The basic mechanical properties of ALC specimens after high temperature were tested.It was found that the compressive and tensile strength of ALC specimens decreased continuously,the elastic modulus decreased and the energy absorption decreased after constant temperature treatment for more than 1h.The compressive strength of ALC specimens is affected by different cooling methods,and decreases with the increase of temperature and constant temperature time.(2)When the temperature increases and the constant temperature time prolongs,the damage of ALC specimens increases.When the temperature is low,the damage degree of spray cooling specimen is less than that of natural cooling specimen.After a long time of constant temperature at higher temperature,the damage of spray cooling specimens is more serious..(3)It was found that the maximum capillary water absorption and capillary water absorption coefficient of ALC specimens increased.The capillary water absorption resistance of the spray cooling specimens decreased significantly after high temperature treatment.The free chloride ion content and chloride ion diffusion coefficient increased with the increase of treatment temperature.After 400℃ high temperature,the microcracks inside the spray cooling specimens increased,and the permeability resistance was significantly lower than that of the natural cooling specimens.(4)Freeze-thaw cycle test was carried out on ALC specimens.The relative wave velocity of the specimen decreased significantly and the compressive strength decreased.The damage of chloride salt freeze-thaw cycle specimens is larger than that of water freeze-thaw cycle specimens,and the mechanical properties decrease greatly.The frost resistance of ALC specimens is affected by different freeze-thaw methods,and increases with the increase of temperature and constant temperature time.(5)Microstructure test and pore structure parameter analysis showed that the surface lattice structure of ALC specimens was destroyed and the compactness decreased after high temperature.Crack propagation in the specimen after freeze-thaw cycles.The porosity,fractal dimension,average pore diameter and most probable pore diameter of ALC specimens increase with the increase of temperature and constant temperature time.It is calculated by grey relational analysis that the average pore size,the most probable pore size and porosity have great influence on the physical and mechanical properties,permeability and frost resistance after high temperature.Figure [51] Table [7] Reference[108]...