The Influence Of Micron And Nano Scale Admixture On The Hardening Properties And Microstructure Of Alkali Activated Slag Cementing Materials

Based on the alkali activated slag cementious materials(AASC),the influence of different activator modulus,alkali content and water to binder on the mechanical properties and workability of AASC was systematically investigated using orthogonal experimental design.To improve hardening and microstructural properties of AASC at the nanoscale,nano-silica(NS)was introduced,and its effect on ASCC macro-mechanical properties,micro-mechanical properties,shrinkage properties,reaction products and microstructure was also studied using a variety of advanced material testing methods(such as:nano-indentation,SEM-EDS with BSE and MIP with XCT).Besides,the effect of AASC performance was studied at different curing conditionss.Meanwhile,at the micro-scale,WEP-AASC mechanical properties,products and reaction heat were investigated with the replacement of mineral powder(waste expanded perlite,WEP),and analysis of the environmental impact and cost of the AASC with the addition of waste materials was evaluated.Therefore,the feasibility of WEP replacing slag was validated.Based on the above studies,a modified method for AASC was finally obtained that the incorporation of nano-materials improved the mechanical properties of AASC,while the incorporation of WEP improved the environmental and cost performance of AASC.Based on the above research objectives,the specific content and conclusions of this study include the following aspects:Based on orthogonal experiment design,the influence of three factors on the mechanical properties and workability of AASC were studied in the range of activator modulus 1.0-2.0,alkali contents 3%-6%,and water to binder 0.35-0.45.Based on the fluidity,compressive strength and flexural strength at 28 days,it was found that the best proportion ratio of AASC was modulus 1.2,alkali content 4%and water to binder in 0.40.The highest strength of NS-AASC could be achieved by adding 2%NS in this study,and the incorporation of 2%NS slightly suppressed the shrinkage of NS-AASC.In addition,under different curing conditions(wet and dry),it is more conducive to the growth of NS-AASC strength under wet conditions.The results of AASC reaction products by XRD,SEM-EDS and BSE showed that the incorporation of 2%NS optimized the micro-morphology and structure,reduced the width and number of AASC cracks,and made the reaction products denser.Basd on the nano-indentation test,the additive of 2%NS increased the micro-mechanical properties of AASC,the micro-elastic modulus and micro-hardness increased about 2GPa and 0.14GPa,respectively;the proportion of C(N-A)-S-H increased,indicating that NS promoted the polymerization process,increased the polymerization rate and produces more C(N-A)-S-H;Based on the tests of the NS-AASC pore structure using XCT and MIP,the porosity distribution intervals at both the micron and nanometer levels were obtained.And the incorporation of 2%NS was obtained,which reduced the porosity of AASC,optimized the structure of pore and reduced the presence of harmful pore.With 10-50%WEP replacement,the total heat of reaction was reduced.Based on TGA and XRD studies on WEP-AASC polymerization products,the substitution of 0-50%WEP slightly reduced the proportion of C-S-H;Based on the analysis of the environmental and cost of WEP-AASC,the replacement of slag with WEP can reduce CO2 emissions and costs.