Experimental Study And Numerical Simulation On Crack Of Autoclaved Fly Ash Brick Wall

Autoclaved fly ash brick is one of new wall materials vigorously promoted in ourcountry, which often shows crack in the wall once it is applied to practical engineering.For general masonry structure, temperature is one of the primary causes of wall crack.Water absorption rate and water loss rate of autoclaved fly ash brick is slower thanordinary clay brick owing to their own characteristic, and the dehydration process cantrigger larger shrinkage deformation. As a result, temperature variation and dryshrinkage deformation are two main reasons of crack in autoclaved fly ash brick walls.So far, many scholars have carried out a thorough research on the dryingshrinkage deformation of autoclaved fly ash brick wall in our country. However, mostexperiments are based on the local natural environment conditions, without consideringeffect of cold environment on drying shrinkage deformation. The main purpose of thisstudy is to promote the application of autoclaved fly ash brick in northeast cold regionbecause the deformation behavior of crack in the usual nature environment conditionmay not be appropriate for that of cold environment. So the deformation properties ofautoclaved fly ash brick wall in the cold natural environment are mainly discussed inthis paper. A series of researches in this paper mainly include performance of autoclavedfly ash brick and its special mortar, the influence of high calcium fly ash on theproperties of special mortar, the free drying shrinkage behavior of autoclaved fly ashbrick wall under standard curing environment with temperature20℃and relativehumidity60%. Besides, the deformation performance of wall built by autoclaved fly ashwas also studied when there are temperature differences on the both sides of the wall inwhich the wall outside exposed in the cold winter and the inside lateral the indoorheating environment. The main results are as follows.The water absorption rate and water loss rate of autoclaved fly ash brick were bothslow, and the latter is much slower which just reached equilibrium moisture contentrequiring more than50days in the nature environment condition. With regard to thebrick, the shrinkage rate adopting the fast drying way is greater than the long-term dryshrinkage rate in the indoor natural environment. In addition, the initial moisturecontent and environment relative humidity will affect brick equilibrium moisturecontent and drying shrinkage.High calcium fly ash equal replacing cement in the special mortar can improve themechanical performance and restrain shrinkage percentage of mortar. When the specialmortar added high calcium fly ash, the shrinkage percentage was also lessened andmeanwhile the frost resistance was enhanced.The wall shrinkage law and factors in the standard curing environment is inaccordance with most of conclusions. The temperature has a great effect on the outer surface of the wall exposed in the cold natural environment. The wall outside surfacetowards to different directions accept different amount of solar radiation, making thenorth and the south wall surface difference temperatures, which lead to non-consistentshrinkage and larger the shrinkage of the north wall surface. The temperature of the wallinside and outside are in different environment, with different shrinkage mechanisms,further non-consistent deformation and the larger shrinkage deformation of the outsidesurface.Moreover, numerical simulations on the shrinkage stress of the top and the bottomin the restrained wall during cooling process and shrinkage equivalent temperaturedifference process with finite element software ANSYS Workbench are discussedrespectively.