Experimental Study On Compressive Performance Of Alkali Slag Ceramsite Concrete Under Freeze-thaw Cycles

In cold areas,freezing damage of concrete is an important factor affecting durability of buildings.During the freezing process,the pore water in concrete will freeze and cause volume expansion.During the melting process,ice melting into water causes volume shrinkage.Under the action of freeze-thaw cycles,the alternating transformation of concrete pore water phase transformation will produce alternating stress on the internal structure,induce the initiation and expansion of cracks,and cause different degrees of damage.In our country,there are a large number of coal gangue stacking every year which causes environmental pollution,meanwhile blast furnace ironmaking also produces a large number of slag by-products.The preparation of alkali slag concrete with coal gangue ceramsite can achieve the recycling effect of solid wastes of coal gangue and slag.Hence,it is of great significance to study the compressive performance of alkali slag ceramsite concrete under freeze-thaw cycles.Taking alkali slag ceramsite concrete as the research object,this paper prepared alkali slag ceramsite concrete samples with the volume of ceramsite content of 0%,25%,50%,75% and 100%,and measured the physical properties of concrete with different ceramsite content,such as slump,density and capillary water absorption at room temperature,and the longitudinal wave velocity of concrete with different moisture content and ceramsite content under freeze-thaw cycles.Uniaxial compression tests were carried out on alkali slag ceramsite concrete with different ceramsite content under normal temperature and freeze-thaw cycles.The stress-strain curves characteristics were analyzed,and the effects of moisture content,ceramsite content,freeze-thaw cycles period and freeze-thaw lower limit temperature on the compressive performance of alkali slag ceramsite concrete under freeze-thaw cycles were discussed.Meanwhile,the freeze-thaw damage mechanism of alkali slag ceramsite concrete was preliminarily revealed by SEM test.The main conclusions are as follows:(1)Under the action of freeze-thaw cycles,the P-wave velocity of alkali slag ceramsite concrete decreases with the increase of ceramsite content and moisture content.This is mainly due to the loose porous ceramsite particles and the volume expansion of the free water inside the concrete after freezing.Moreover,the volume shrinkage after the solid ice melting,resulting in more pores and channels inside the concrete.The more the moisture content,the wider the coverage of the ice crystals,the greater the damage.(2)Under different ages and ceramsite content,the stress-strain curves of alkali slag ceramsite concrete have experienced four stages: compaction stage,elastic stage,crack development stage and failure stage.The slope of failure stage descent curve becomes steeper with the increase of age,which reflects the characteristics of brittle failure.Because the addition of ceramsite retards the rapid failure of the specimen caused by stress concentration,the slope of failure stage decreases with the increase of ceramsite content.(3)Under the action of freeze-thaw cycles,the compressive strength of samples decreases obviously with the increase of moisture content.With the increase of freeze-thaw cycles,the compressive strength of samples first decreases and then increases.With the lower limit of freeze-thaw temperature decreasing,the compressive strength of ceramsite concrete does not decrease significantly,indicating that ceramsite concrete is less sensitive to temperature.Based on the uniaxial compression test results under freeze-thaw cycles,the prediction formula of compressive strength of alkali slag ceramsite concrete is established.(4)SEM images show that the cracks in the samples evolve wider and more with the increase of moisture content under freeze-thaw cycles.With the decrease of the lower limit temperature of freeze-thaw cycles,the cracks inside the samples changed from no cracks to cracks,and then the cracks widened,and finally the structure becomes loose.(5)Under the same freeze-thaw cycles,the input energy density of the sample is negatively correlated with the lower freeze-thaw limit temperature.The lower the lower freeze-thaw limit temperature is,the lower the input energy density of the sample is.This is because the upper limit of freeze-thaw temperature is fixed,and the lower the lower limit of freeze-thaw temperature,the greater the positive and negative temperature difference,the greater the damage to the sample,and the lower the input energy density required when the sample is damaged.Figure [51] Table [4] Reference [90]...