Experimental study on preparation and optimization of high-performance cement grouts mixed with chemical additives for capsule grouting technology

With the development of underground space, underground construction inevitably affects the safety of surrounding structures. Capsule grouting technology (CGT) is proposed to protect adjacent structures from the impact of underground construction. This study developed a high-performance cement grout (HPCG) for CGT using chemical additives. The orthogonal test was performed to optimize the material composition and study the synergistic effect of cement additives of HPCG. Then, the microstructure of HPCG was further analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results show that the water-cement ratio shows a significant influence on flowability, bleeding, and compressive strength of HPCG. Then, the retarder presents a dramatic effect on prolonging the setting time (more than 70 h) by hindering the hydration reaction process. As the polycarboxylate superplasticizer content increases from 0 to 0.2%, the flowability of HPCG increases by 81.7%, while the bleeding increases 115.4%. However, the influence of each factor on the performance is not a single target but a synergistic influence, so a comprehensive analysis should be considered to determine the optimal dosage of additives. Accordingly, the optimal design of HPCG can be recommended that 1.0 for water-cement ratio, 0.45% for retarder, 0.2% for polycarboxylate superplasticizer, and 3% for fluid loss additive, which shows high performance for CGT, with the flowability of 28.3 cm, bleeding rate of 1.61%, initial setting time of 71.1 h, 7 days compressive strength of 2.3 MPa.