Anchoring technology is a common measure for geotechnical reinforcement, capable of fully mobilizing and enhancing the inherent strength and self-stabilizing capacity of tunnel surrounding rock, thereby effectively controlling deformation of the surrounding rock. It has become one of the most economical and effective methods for improving geotechnical engineering stability and solving complex geotechnical problems. As an important component of the anchoring structure, the grout body plays a significant role in improving the load-bearing performance of anchor bolts (cables). Among these, improving the fluidity, setting time, mechanical strength and other indicators of grouting materials is the primary means of enhancing grouting reinforcement performance.

To this end, the Construction Process Mechanics Research Team of the Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, developed a novel early-high-strength grouting material based on materials such as calcium sulfoaluminate cement clinker, ordinary Portland cement, anhydrite and limestone powder. Through macroscopic and microscopic testing techniques including uniaxial compression tests, X-ray diffraction tests, thermogravimetric analysis tests and mercury intrusion porosimetry tests, the team systematically studied the evolution laws of performance indicators such as mechanical strength, hydration products, expansion rate and microstructure of the grouting material, revealed its early hydration mechanism, and verified the anchoring performance of the early-high-strength grouting material through numerical simulation and on-site anchor bolt pull-out tests. The results show that the initial setting time of the early-high-strength grouting material is only 25 min, the final setting time is 40 min, and the fluidity reaches 282 mm. The free expansion rate shows a non-linear growth trend, with an average growth rate of 4.51 ‰/d within the 14-day age period. The uniaxial compressive strength reaches 40.3 MPa at 1 day of age, increases to 61.7 MPa at 7 days of age, and then remains stable. The main hydration products of the high-strength grouting material are ettringite and aluminum hydroxide gel, and the phase content remains stable after 1 day of hydration. Due to the rapid increase in hydration product content and volume expansion, the pore structure of the high-strength grouting material becomes denser. Numerical simulation and field tests show that the early-high-strength grouting material significantly improves the anchoring performance of prestressed anchor bolts compared with ordinary Portland cement. The novel grouting material exhibits excellent characteristics of early strength, high strength and slight expansion in the early stage of hydration, making it suitable for engineering needs such as anchoring grouting and ground reinforcement.

The research results were published in Construction and Building Materials, a top journal in the field of civil engineering. The research was funded by the Second Tibetan Plateau Scientific Expedition and Research Program (No. 2019QZKK0904), a major project of the National Natural Science Foundation of China (No. 51991392), and projects of the National Key Research and Development Program (No. 2021YFC3100805, 2021YFC3100802).

Paper link: https://doi.org/10.1016/j.conbuildmat.2023.134324