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[Display omitted] • Effect of CA on the working performance of Portland cement-sulfoaluminate cement-based grouting materials ware studied. • Mechanisms of in-situ polymerization modification of CA on the properties of grouting materials were analyzed. • The damage constitutive equation of grouting materias under the CA was established. To enchance the toughness of ordinary Portland cement-sulfoaluminate cement-based grouting material and minimize the secondary damage of road structure caused by stone body destruction under vehicle load. In this paper, the development laws of setting time, fluidity, and mechanical strength of grouting material, and the characteristics of stone damage under the action of calcium acrylate are systematically analyzed. The mechanism by which in-situ polymerization of improves the toughness improvement of ordinary Portland cement-sulfoaluminate cement-based grouting material is then revealed. In-situ polymerization of calcium acrylate delays the setting time, and an appropriate calcium acrylate content improves the flowability. The addition of calcium acrylate largely enhances the mechanical strength of the stone body, improving the 1-day compressive strength and flexural strength by 279.18% and 301.64%, respectively. Calcium acrylate also increases the flexural compression ratio of the stone body. The highest flexural compression ratio at 28d is 0.5592. The microscopic analysis reveals that calcium acrylate promotes hydration, and forms stable calcium polyacrylate in the stone body, which connects the hydration products into a more densely cement-calcium polyacrylate composite structure. Consequently, the toughness of the stone body improves. By analyzing the stress–strain curve, the stone body still exhibits a capacity to resist damage after the peak stress under the action of calcium acrylate. Finally, a damage constitutive equation of the stone body with different damage factors is established, which has excellent agreement with the test curve and can predict the mechanical properties of cement-based grouting material modified by in-situ polymerization of calcium acrylate. The findings provide a theoretical framework for designing the strength of grouting materials and evaluating road stability. [ABSTRACT FROM AUTHOR]

• A new strength enhancement method for red mud-based grout was proposed. • Workability of red mud-based grout was investigated. • Mechanism of fibres on the properties of red mud-based grouts was analyzed. Grouting materials are subjected to high stress during underground engineering construction and are easily damaged. To overcome the shortcomings of red mud-based geopolymer grout, systematic experiments were conducted to analyse the workability, mechanical properties and failure mode of red mud-based grouts reinforced with polypropylene, glass and basalt fibres. Micro-structural analysis was conducted to reveal the mechanism of the effects of fibres on the geopolymer grouts, and the results show that the yield stress of the red mud-based grouts increased with the fibre content. The addition of polypropylene, glass and basalt fibres increased the mechanical strength of the grouts by 27.5%, 32.6% and 27.3% and increased the flexural strength by 16.07%, 30.35% and 35.36%, respectively. Moreover, all fibre-reinforced red mud-based grouts exhibited higher elastic modulus and low porosity, as revealed by the longitudinal wave velocity performance and mercury intrusion porosimetry. Micro-structural analysis of the grouts revealed an effective interfacial bonding between the fibres and the geopolymeric binder. The obtained grouts overcome the shortcomings of red mud-based geopolymer grouts and exhibit an improved utilisation rate of red mud in geotechnical engineering. [ABSTRACT FROM AUTHOR]

• Effect of retarders on red mud-based geopolymer cementitious materials is proposed. • The mechanism retarder on hydration process systematically discussed. • The microstructure and mechanism of retarder on the mechanical strength is analyzed. The effects of sodium gluconate, sodium hexametaphosphate, and sodium tripolyphosphate on the hydration process, rheological properties, and mechanical strength of red mud-based geopolymer cementitious materials were studied by hydration microcalorimeter, infrared spectrometer, and X-ray diffraction. The results show that all the three retarders can delay the hydration and hardening rate of the slurry of red mud-based geopolymer cementitious materials, and sodium gluconate has the most significant effect on the hydration rate. The rheology of the slurry shows the Herschel-Buckley model. The introduction of retarders will reduce the yield stress and increase the shear thickening characteristics of the slurry. Under the action of retarder, the 3-days compressive strength of red mud-based geopolymer cementitious materials decreases significantly, while the 28-days compressive strength has little change. Sodium gluconate can improve the 28-days compressive strength to a certain extent. Microscopic analysis showed that retarding agent blocked the hydration rate of red mud-based polymer gel mainly through adsorption, encapsulation and complexation. [ABSTRACT FROM AUTHOR]

• The nonlinear mathematical model for the mechanical strength was developed using RSM. • Optimization of pore structure was the key to improve the performance of filling materials. • The karst filling materials efficiently utilizes limestone tailings. Karst areas are prone to collapse under the action of hydrodynamic forces, which has become an essential geological disaster to constrain mineral resources exploitation, underground space development, and infrastructure construction in karst areas. The cemented filling can effectively improve the stability of the karst structure, which is an effective method to control karst collapse. In this paper, limestone tailings-based cementitious materials are prepared from limestone tailings, desulfurized gypsum, slag, cement clinker, and sodium hydroxide. The impact of various factors on compressive strength in cementitious materials is evaluated through the response surface method (RSM), and the optimized ratio is as follows: cement clinker 9.97%, desulfurization gypsum 6%, limestone tailing powder 50%, blast furnace slag 34.03%, NaOH 3%. Karst filling material is prepared by cementing the limestone tailing sand with the optimized limestone tailing-based cementing material. The experiment reveals the mechanism of fineness modulus, cement-sand ratio and slurry concentration on the fluidity and strength of karst filling material. Optimization of pore structure is the key to improve the performance of filling materials. The karst filling materials efficiently utilizes limestone tailings with a utilization rate of 87.5%–93.75%. [ABSTRACT FROM AUTHOR]