Controllable Preparation and Enhancement Mechanism of Al₂O₃ Nanomaterial-Modified Ultrafine Cement Composite Grouting...

Using ultrafine silicate cement as the cementitious material, and admixtures such as expansion agent, rapid-setting agent and water reducer as additives, a new type of composite grouting material with high early strength and high toughness was obtained by modification with nano-Al₂O₃ (NA). The influence of NA content on the mechanical properties, flowability, bleeding behavior, setting time, volume shrinkage, and microstructure was investigated for composite grouting materials. The results show that, as the NA content increases, the flowability of the paste decreases, the bleeding rate reduces, and the setting time increases first and then decreases. Appropriate NA can effectively improve the mechanical strength of the composite grouting material. Especially at the condition of 3% NA, the composite grouting material reached the highest early compressive strength and toughness. Compared with the control group, the compressive strength of the specimen increases by 39.54% and 6.83% respectively at 1 d and 21 d, and the flexural strength increased by 55.41% at 1 d. XRD, FTIR, SEM and hydration heat analysis confirm that the NA can promote the early hydration heat of ultrafine cement, and shorten the induction period. Moreover, more C-A-H gel products will be generated by consuming Ca(OH)₂ with active NA, leading to an improvement in the matrix compactness. Such an outstanding mechanical property can be mainly attributed to the triple coupling mechanism of the hydration regulation, microstructure and filling effect of superfine cement by nano-Al₂O₃ in combination with multi-component admixtures.