Influence Of Heating Treatment On The Structure And Properties Of Foamed Concrete

As cement based porous material,foamed concrete has been rapidly developed and applied in construction and building field because of the superior heat preservation,energy absorbing,anti-seismic and fire resistance properties.However,the structure and function failure of foamed concrete might occur under fire disaster and high temperature furnace conditions,which make it the key issue to evaluate the structure and properties evolution of foam concrete through high temperature thermal treatment.In this paper,foamed concrete with density of 300-700kg/m3 was prepared by using physical foaming method.The changes of appearance,mass loss,compressive strength loss,thermal conductivity and water absorption of foamed concrete were studied after thermal treatment at different temperature point.Besides,the changes of pore structure,phase composition and micro-structure of the foamed concrete were also analyzed.On the basis of above,the effects of mix design on high temperature resistance of foamed concrete were studied.The results showed the trend of increasing in the mass loss,water absorption,thermal conductivity and decreasing in compressive strength with increasing of temperature.The density had a great influence on the performance of foamed concrete after heating treatment.The compressive strength loss and the water absorption offoamed concrete with density of 300-400kg/m3 are higher than the others.However,the thermal conductivity firstly decreased at 200?but increased with higher temperature.At 800?,the performance of the foamed concrete with different density grade is consistent:the mass loss rate is 200%,the mass water absorption is 65%-70%,the thermal conductivity is about 0.30-0.33,and the compressive strength residual rate is 20%.The porosity of the foamed concrete increased and the pore diameter changed a little through thermal treatment.No obvious changes were observed for the hydration products and species of foam concrete with different density.In foam concrete,free water escaption,calcium silicate hydrates(C-S-H)and ettringite decomposition occured below 200?,then the ettringite completely decomposited at 400?,portlandite decomposited at 600 ?,the decomposition of calcium carbonate and accompanied by the formation of dicalcium silicate occured at 800?.The increasing of water-cement ratio increased the mass loss of foam concrete before 800?,but has little effect at 800?.And the residual strength of the foamed concrete with water-cement ratio of 0.50-0.55 was higher than that of the others through high temperature thermal treatment.The addition of fly ash and metakaolin could reduce the mass loss of foamed concrete and improves the residual strength.The addition of silica fume is not conducive to the improvement of residual strength.