The Effects of Waterborne Polyurethane-Modified Cement on the Mechanical Characterization of Grouting Concretion Stone

To improve the safety and stability of tunnel structures, developing grouting materials suitable for cold regions with excellent performance is crucial. Herein, waterborne polyurethane (WPU) was used to modify cement grouting materials. Through orthogonal testing analysis, the optimal mixing ratio of the modified cement grouting materials was determined to be as follows: a water-cement ratio of 0.5, hydroxypropyl methyl cellulose (HPMC) content of 0.05%, WPU content of 5%, water-reducing agent (WRA) content of 0.2%. Furthermore, the dynamic mechanical properties of grouting concretion stones were studied. The influence of various external parameters on the compressive strength of the grouting concretion stones cured for different ages was evaluated. The influence degree of stone particle size on the dynamic compressive strength of the grouting stone body was d_{5-10 mm} > d_{5-20 mm} > d_{5-30 mm}. The split Hopkinson pressure bar experiment was performed to show that for the same strain rate, the absorbed energy and energy utilization rate first increase and then decrease with increasing stone particle size. When the stone particle size was 5-20 mm, the absorption energy and energy utilization rate of the grouting stone body were the highest.