Study On Mechanical Properties And Shrinkage Characteristics Of Alkali Activated Fly Ash And Slag

The shrinkage deformation of alkali activated fly ash and slag concrete is significantly higher than that of cement concrete with the same strength.At present,there is no reasonable shrinkage prediction model,which limits the engineering application.In order to explore the shrinkage mechanism of alkali activated fly ash slag and seek a reliable shrinkage prediction numerical model.Combined with the micro performance tests such as X-ray diffraction(XRD),Fourier transform infrared absorption spectroscopy(FTIR),hydration heat,mercury injection(MIP),internal humidity and saturation,this paper expounds the influence mechanism of raw material mix ratio on the mechanical properties and shrinkage characteristics of alkali activated fly ash slag slurry;based on the mechanism of pore pressure,the drying shrinkage of alkali activated fly ash slag slurry is quantitatively calculated,compared with the measured results,and the following conclusions are obtained:(1)CaO content of raw materials,activator modulus and alkali content are all important factors affecting alkali activated reaction,among which CaO content of raw materials has the most significant influence,The increase of CaO content in the raw material will accelerate the alkali activated reaction,gradually compact the pore structure,and then improve the mechanical properties of the slurry.When the alkali content level is high,the increase of activator modulus will inhibit the alkali activated reaction and weaken the mechanical properties of the slurry.The effect of alkali content on the reaction is not monotonous.When the alkali content level is low,increasing the alkali content will accelerate the alkali activated reaction and improve the mechanical properties of the slurry;When the alkali content level is high,the situation is just the opposite;There is a significant correlation between elastic modulus and compressive strength of alkali activated fly ash slag slurry.(2)In general atmospheric environment,pore tension is the driving force of autogenous shrinkage and drying shrinkage.The finer the pore diameter of alkali activated fly ash slag slurry,the greater the capillary pore stress generated in the process of desiccation and self-desiccation,which will accelerate the shrinkage deformation.At the same time,the ability of slurry to resist deformation will be improved,which can inhibit the shrinkage deformation.In the process of pore water loss,the effects of pore tension and deformation modulus on shrinkage are in dynamic equilibrium.CaO content of raw materials,modulus of activator and alkali content will have an important impact on autogenous shrinkage and drying shrinkage.Among them,CaO content has the most significant impact,which is negatively correlated with drying shrinkage(modulus change is dominant)and positively correlated with autogenous shrinkage(capillary stress change is dominant).(3)The self-desiccation effect of alkali activated fly ash slag slurry in the curing period and the water loss in the drying shrinkage process lead to the decrease of its internal humidity.The resulting capillary stress develops rapidly,which makes it enter the non-linear elastic viscous stage earlier.The measured shrinkage of the slurry is about 2-4 times that of the elastic shrinkage,and the elastic shrinkage is basically completed in the first 7 day after the drying test.The growth of the latter depends mainly on the creep behavior of the gel.The creep of slurry is significantly affected by the self-desiccation stress during the curing period,especially in the group with high CaO content.