Study Of Preparation And Properties Of Alkali-activated Slag-Red Mud Materials For Repair Materials

Red mud is an industrial solid waste discharged in the process of alumina production.Its small particle size and high alkali content restrict its resource utilization.Because red mud contains a large amount of aluminosilicate material,it has the condition of alkali excitation reaction.Therefore,by using the high alkalinity of red mud and adding additional alkali to stimulate the red mud,and then compounding it with the more active slag,we can prepare a repair material with excellent mechanical properties,corrosion resistance and strong bonding.However,there are also shortcomings such as brittleness,high water absorption,easy alkali flooding and large drying shrinkage,which has become a bottleneck limiting the application of alkaliinspired repair materials in practical engineering.In this thesis,the alkali-slag-red mud repair mortar was prepared by using slag and red mud as cementitious materials and studying the effects of different factors on the performance of the repair mortar with reference to the standards of building materials industry,and the alkali-slag-red mud repair mortar meeting the requirements of the standards was prepared.In order to reduce the water absorption,calcium stearate and silane coupling agent were used to modify the alkali-inspired repair materials.The hydration process and microstructure of the repair materials modified by calcium stearate and silane coupling agent were investigated based on the test analysis of porosity,hydration products and microstructure.Finally,on the basis of the above study,the durability performance was evaluated and analyzed by drying shrinkage,degree of alkali flooding and resistance to sulfate erosion.The basic laws revealed by the study are as follows:(1)Using slag and red mud as raw materials and water glass as activator the best ratio design is determined by a single variable: 30% red mud doping,70% slag doping,modulus selection of 1.6,5% alkali activator,and fixed water-cement ratio of 0.45,which can prepare alkali-activated repair materials with good workability and mechanical properties.(2)The internal doping of calcium stearate can effectively reduce the water absorption rate of the alkali-activated repair material,improve the bond strength and reduce the compression-folding ratio,but the mechanical properties are slightly reduced.This is mainly because the air-entraining effect of calcium stearate leads to the formation of more stable closed pores in the system,which makes the pore connectivity reduced,thus blocking the transport of ions from inside and outside the slurry.At the same time,calcium stearate forms a calcium stearate layer film on the inner wall of the introduced pores,and the hydrophobicity of the capillary wall makes the capillary water absorption rate greatly reduced.(3)The internal doping of silane coupling agent contributes to the dispersion of early slag and red mud particles,which accelerates hydration and makes the strength increase and dense network structure.At the same time,the silane coupling agent can be closely combined with alkali-slag-red mud specimens to generate hydrophobic film on the surface of the slurry,which greatly reduces the rate of water absorption.(4)The incorporation of both calcium stearate and silane coupling agent improves the durability of the repair material,effectively reduces drying shrinkage,inhibits the phenomenon of alkali flooding,and improves the coefficient of sulfate erosion resistance.The 28 d drying shrinkage of 1.5% calcium stearate reduced by about 25%compared with AASR,and the 90 d erosion resistance coefficient reached 127%;the28 d drying shrinkage of 1.5 wt.% silane coupling agent reduced by about 40%compared with AASR slurry,and the 90 d erosion resistance coefficient reached 104%.