This paper presents a systematic investigation into the long-term mechanical property development, water absorption behavior, and microstructural characteristics of hybrid glass and polypropylene fiber-reinforced concrete (HGPFRC). The findings provided valuable engineering construction solutions for holistically considering the improvement effect of hybrid fibers on concrete performance and for the durability design of concrete materials. The main conclusions of the study are as follows: the water-to-binder ratio (w/b) and the hybrid fiber content significantly influenced the development rate of compressive strength in concrete. Compared to the control group without fibers, the compressive strength of HGPFRC increased more rapidly during the curing stage from 7 to 28 days. HGPFRC with different w/b and fiber contents exhibited significant differences in water absorption rates at various testing stages. In this study, the water absorption of HGPFRC reached 60% to 86% of the total absorption on the first day, 6% to 23% from the second to the fourth day, and 3% to 18% from the fifth to the thirty-first day. Considering the compressive strength, water absorption performance, and microstructure observed via SEM, the optimal mix proportion for the HGPFRC in this study was determined to be a w/b of 0.35 and a hybrid fiber content of 1.8%. The hybrid glass and polypropylene fiber content of 2.7% used in this study exceeded the optimal dosage, and the resulting concrete could not meet engineering construction requirements.

Concrete components in highways and bridges are susceptible to freeze–thaw deterioration in cold regions, compromising their service safety. Alkali-activated fly ash-slag concrete (AAFSC), which fully replaces Portland cement with industrial by-products, offers promising environmental and application benefits. However, research on its freeze–thaw damage remains limited, hindering its use in cold-region infrastructure. This study presents a systematic experimental and theoretical investigation into the freeze–thaw deterioration of AAFSC. For the first time, the damage process is described within the Kachanov–Rabotnov evolution framework, establishing an exponential damage model with well-defined physical boundary conditions—extending continuum damage mechanics to freeze–thaw action in concrete. The model quantitatively captures damage progression in AAFSC and demonstrates broad applicability across various concrete types reported in the literature. This work provides important guidance for predicting the freeze–thaw durability of AAFSC-based transportation infrastructure components in cold regions.

Polyurethane cement (PUC) is a high-performance composite that combines the high toughness of polymers with the durability of cementitious materials, showing potential in the field of structural strengthening. However, when used alone, its crack confinement capability is limited. To investigate the strengthening effect of wire mesh–polyurethane cement (WM-PUC) composite on the shear performance of damaged reinforced concrete (RC) beams, static loading tests were conducted on four RC beams. All strengthened beams were preloaded to induce initial damage and subsequently retrofitted on the sides using the two composite materials. Their shear performance was evaluated through single-point monotonic loading. The failure modes, load–displacement curves, shear capacity, and crack development patterns of the strengthened beams were analyzed in detail. The experimental results indicated that after strengthening with PUC and WM-PUC, the shear capacity of the damaged beams was effectively enhanced. The ultimate loads of the damaged beams strengthened with PUC and WM-PUC were 360 kN and 390 kN, respectively, representing increases of 12.5% and 21.88% compared to the unstrengthened beam. Compared to the PUC-strengthened beam, the ultimate load of the WM-PUC-strengthened beam increased by 8.3%, indicating that the incorporation of wire mesh further enhanced the strengthening effectiveness of the polyurethane cement composite. In terms of crack control, WM-PUC strengthening was more effective than PUC strengthening in restraining the initiation and propagation of diagonal cracks. The findings demonstrate that WM-PUC composite exhibits favorable applicability for the shear strengthening of damaged RC beams, with overall performance superior to that of PUC-only strengthening, thereby providing a technical reference for high-performance shear strengthening of existing concrete structures.

This study addresses the calculation of subgrade settlement over shallow, old longwall goafs under traffic loads. Based on the spatial distribution characteristics of the additional stress field, the total settlement is first decoupled into four components: the subgrade settlement and foundation settlement directly induced by traffic loads, and the residual settlement and reactivated settlement specific to the old goaf. Subsequently, a comprehensive model for calculating the total subgrade settlement is developed by integrating the probability integration method, elasticity theory, and the layerwise summation method under a “component-based calculation and dynamic superposition” framework. The results indicate that the total subgrade settlement over shallow old longwall goafs consists of four components: subgrade settlement, foundation settlement, goaf residual settlement, and goaf reactivation settlement; neglecting traffic-load-induced subgrade settlement, foundation settlement, and goaf reactivation settlement will significantly underestimate the total settlement.The proposed model can dynamically combine the relevant settlement components according to varying load levels and structural stability states. This capability quantitatively characterizes the entire settlement response process, from a “structurally stable” state to a state of “progressive reactivation.” This model addresses the limitations of conventional methods, which often homogenize the old goaf and overlook these traffic-load-induced settlements. It significantly enhances the rationality and systematic nature of the calculations, offering a novel method for evaluating and predicting subgrade settlement over abandoned goaf areas beneath highways.