INVESTIGATION ON STRENGTH AND SHRINKAGE RATE OF ALKALI-ACTIVATED TUFF POWDER AND AGGREGATES COMPOSITE

Under the carbon peaking and carbon neutrality goals,seeking green cementitious materials from natural geomaterials is widely focused. The fine tuff powder is a solid waste produced in the process of manufactured sand production,and is a natural silica-aluminum geopolymer. There are few studies on the strength and shrinkage properties of tuff powder and aggregate composite. We select quartz tuff powder,blast furnace slag,sand,gravel and hydrophobic agent as raw materials to prepare alkali activated tuff powder slurry,tuff powder mortar and tuff-based concrete. After 60℃curing,the compressive strength,splitting tensile strength and shrinkage of the composites are investigated. The influences of each component on their physical and mechanical properties are analyzed. The results showed that the compressive strength of alkali activated tuff powder without additive is 12.7MPa and is higher than that of tuff powder and aggregate composite (of 4.4~7.0MPa). The results are attributed to the weak interfaces formed by the aggregate adding and different thermal expansion rates of aggregate and paste. The compression modulus of samples also is reduced when the sand and crushed stone are added in the composite. The mineral composition of tuff powder is similar to that of tuff aggregate. Due to the depolymerization and polymerization reaction under the action of alkali activator,the hydrated calcium aluminosilicate and hydrated sodium aluminosilicate are formed on particle surface. Then,the strengths of tuff powder and tuff aggregate composite are higher. With the addition of sand and gravel,the shrinkage of the sample decreases. The minimum shrinkage is 0.4% for the tuff powder,quartz sand and tuff gravel composite. For the hydrophobicity,bonding strength weakening and surface reaction preventing,the Lotus leaf hydrophobic agent(LHG) and Boiled wood oil(BWO)reduce the strength of tuff based geopolymer and tuff powder-sand-gravel composite. The strength of samples with shrinkage reducing agent(SRA)is higher than that of LHG and BWO groups,which is attributed to the water retention capacity of SRA. The shrinkage migration effects of LHG,BWO and SRA on tuff powder geopolymer are not significant. For the tuff powder and sand composite,the shrinkage ratio of samples with SRA is 0.9% and lower than that of LHG and BWO groups. For the tuff powder,sand and gravel composite,the shrinkage rate of samples without additives is lower,indicating that the volume shrinkage of the powder-sand-gravel composite is mainly influenced by the skeleton supporting. Based on the above analysis,the optimum proportions of each groups are suggested.