Experimental Study On Mechanical Performance And Durability Of Recycled Aggregate Based Alkali Activated Slag Concrete

In recent decades,economy of China has been rapidly developed.The construction industry,as one of the pillar industries in our country,has played an important role in the economic development.However,at the same time,it has also broughtproblems including environmental pollution and resource shortage.The massive use of cement results in a large amount of carbon dioxide emissions,which cause green-house effect.Overexploitation of natural aggregates results in a shortage of non-renewable resources such as stoneand river sand and.On the other hand,the overall utilization rate of slag produced in the industrial production process is limited;the conversion rate of waste concrete resources is low,and large-scale stacking has resulted in soil pollution,air pollution and other malignant effects.The appearance of alkali activated slag concrete and recycled aggregates promotes the solution of the above problems to a certain extent,but they also have their own limitation in performance.The combination of the two materials has certain theoretical possibilities,but the research on this new material at present,especially in the use of low concentration alkali activator and the introduction of recycled fine aggregate is limit.In this paper,slag is used as the main cementitious material replace of cement,and recycled coarse and fine aggregates are used to replace natural aggregates.The properties of alkali-activated slag recycled concrete with different concentration of alkali activator,different recycled coarse aggregate and fine aggregate substitution rate are studied.(1)The basic properties of alkali-activated slag recycled concrete were investigated.The slump of concrete was tested to measure the working performance of this material.The density and water absorption of different approaches of concrete and conventional aggregate mixtures were compared under different replacement rates of recycled aggregate,and the compactness of this concrete was analyzed;the dynamic elastic modulus of concrete was measured to comprehensively analyze the micro-structure of this material.(2)The effects of different variables on the cubic compressive strength,flexural strength and splitting tensile strength of alkali-activated slag recycled concrete were investigated.The cubic compressive strength of concrete at different ages was compared.When the concentration of alkali activator was 0,0.5%,1% and 3%,the cubic compressive strength of concrete under different curing conditions was compared.The development of cubic compressive strength of 3% group with age growth and replacement rate of recycled coarse aggregate and fine aggregate was explored;the 28-day flexural strength and Splitting tensile strength and cubic compressive strength of concrete were measured.Degree,and comprehensive strength values were compared.(3)The shrinkage,carbonation resistance and sulfuric acid corrosion resistance of alkali-activated slag recycled concrete were studied.The shrinkage values of concrete with 0.5% alkali activator and 3% recycled aggregate were measured,and the shrinkage properties of concrete with recycled aggregate were evaluated.The carbonation resistance tests of concrete with 0.5% alkali activator and 3% recycled aggregate were carried out,and the effects of the concentration of alkali activator and the replacement rate of recycled aggregate on the carbonation depth of concrete were studied.The changes of appearance,mass change rate and sulfuric acid resistance of concrete were measured.This paper evaluates and summarizes the performance of this material in different application environments,which provides a theoretical reference for future specific applications.(4)The microstructure and composition of alkali-activated slag recycled concrete were analyzed.The double transition zone(ITZ)in the interior structure was found,and the micro-morphology difference between the ordinary geopolymer concrete and the recycled geopolymer concrete was compared.The composition of different micro-regions was analyzed by energy spectrum.The macroscopic performance of the material is explained from the micro level.