Research On The Anti-freezing Of Autoclaved Fly Ash Brick

Autoclaved fly ash brick is an ideal substitute for the traditional burnt clay brick,with the character of energy conservation and environmental friendship. Especially, thecorresponding law on banning using of burnt clay brick was issued, and furtheraccelerated the application of autoclaved fly ash brick in China. However, theanti-freezing performance put serious restrict on the application in cold area ofautoclaved fly ash brick. Therefore, the paper researched the effect of differentingredients on the anti-freezing durability of autoclaved fly ash brick and thecorresponding numerical model was established.The results showed that, the lowest apparent porosity was33%as the mass percentof cement reached14%, and the decreasing region rapidly of conductivity changed from-10oC to-20oC, the pore structure was optimized by incorporating cement into theautoclaved fly ash brick. The frozen temperature of autoclaved fly ash brick was-10oC^-15oC according to the rapidly decreasing zone of conductivity.The mechanical strength of autoclaved fly ash brick with different lime content,decrease then increase with the freeze-thaw cycle increasing. The results indicated thatthe autoclaved fly ash brick rapid hydrated on the condition of high temperature andpress, and formed the density cover surrounding fly ash.When the autoclaved fly ash brick was frozen in different temperature, and tissurface was thawed rapidly, the large temperature difference between exterior andinterior induced the crack of autoclaved fly ash brick, and therefore lowed itsanti-freezing durability. However, autoclaved fly ash brick with above10%cementoccur cracking damage in large temperature difference and was benefit for itsanti-freezing durability.The corresponding damage model was established on the basis of the experimentalresearch, the calculated results showed that the elastic-modulus damage model wasmore safe in evaluating anti-freezing durability of autoclaved fly ash brick, and thecorresponding formula was:y=γ₁7.604e^-0.05N+γ₂⊿R_d, and γ₁,γ₂were constantcorrelate with cement and lime content. Based on the service life of autoclaved fly ash brick in engineering, the freeze-thawtest over-evaluated the anti-freezing durability of autoclaved fly ash brick. Therefore,the crack, induced by the large temperature difference between exterior and interior hadserious negative effect on the anti-freezing durability of autoclaved fly ash brick, andthe corresponding revised factor is0.1F （C）, the formula was,t=0.1F（C） t₅.