Research On Performance Of Alkali Activated Slag-metakaolin Composite Cementitious

Alkali activated slag cement with the excellent physical mechanical properties and durability property is a kind of environmentally friendly materials with the function of saving energy, making use of waste, protecting environment, thus become one of the active investigated field in cement material. Alkali activated slag cementation material have the feature of condensation faster and shrinkage larger, which is one of the importance of technical problem to restricted its application and development. In comparison, alkali activated metakaolin cementation material with the main products Na2O.x Al2O3.ySiO2.zH2O (zeolite minerals) have the longer setting time,better high temperature performance and smaller deformation. Partial replacement of slag with metakaolin to form alkali activated- slag - metakaolin binder system expected to improve the concrete properties,especially reducing the shrinkage by adjusting the composition of the solid state dispersed. Thus,in this paper,the dry shrinkage ,the condensation hardening perporties and resistance to erosion of AASMC were studied. The result shows that:①AASMC has the better dimensional stability than AASC.When the sodium silicate modulus was 1.5 and alkali content was 4%,shrinkage rate of 90 days age was from 0.27% to 0.16% with the increase of metakaolin content in the range of 10% to 50%. The degree of decrease was 40.7%. The reduction of shrinkage rate was due to the incorporation of metakaolin changed the composition and structure of hydration products of AASC.②The dry shrinkage was impacted by the alkali component and solution to slag quantity ratio. When the alkali content was in the range of 3% to 5%,sodium silicate modulus was in the range of 1.0 to 2.0,Solution to slag quantity ratio was in the range of 0.40 to 0.50,the dry shrinkage was increased with the alkali content or sodium silicate modulus or solution to slag quantity ratio was increased.The characteristics were similar with AASC.③The effect was not obvious to improve the setting time as the metakaolin content was increased.When the sodium silicate modulus was 1.5 and alkali content was 4%,the initial setting time was still less than 30mins with the metakaolin content in the range of 10% to 50%.The setting time of AASMC may be related with C/S involved in the chemical reaction.Metakaolin brought forth negative impact on the strength of AASMC. When the content exceeds 30%,the strength was greatly reduced.④Alkali component,solution to slag quantity ratio also affected the basic performance of AASMC.The compressive strength was enhanced and setting time was decreased with the alkali content increased in the range of 3% to 5%. The setting time was decreased and the compressive strength was increased firstly and then decreased with the sodium silicate modulus was increased in the range of 1.0 to 2.0.The compressive strength was deceased and setting time was increased with the solution to slag quantity ratio was increased in the range of 0.40 to 0.50.⑤The AASMC has the better corrosion resistance than AASC.The flexural strength growth rate of AASMC was 3.9%,5.5% and the flexural strength growth rate of AASC was 1.5%,3.7% when the spencimens soaked in the solution of 5% MgSO4,5%Na2SO4 for 180 days.AASC and AASMC had the high strength remanent ratio and weight remanent ratio soaked in the acid solution for 90 days.The strength remanent ratio was 98.89% and the weight remanent ratio was 99.15% when the specimens of AASMC soaked in the acid solution of pH=1.0 for 90 days. The strength remanent ratio was 97.78% and the weight remanent ratio was 98.89% when the specimens of AASMC soaked in the acid solution of pH=1.0 for 90 days.Thus The AASMC has the better corrosion resistance.