Coal gangue, an industrial waste, is rich in silicon and aluminum phase and may be used as a mineral admixture in concrete after moderately stimulating activity, allowing for efficient solid waste utilization. This study used a mortar strength and activity evaluation method to investigate single or compound activation methods to find the optimum activation method of coal gangue. FLIR, XRD, and SEM were used to investigate the activation mechanism of different modes, providing a theoretical foundation for the study of coal gangue as a concrete admixture. Results showed that mechanical ball milling, microwave, and chemical activator could activate coal gangue, and the composite activation effect was the best. The fineness of the coal gangue powder was more than 300 mesh, according to the optimal compounding method. Accordingly, the particle surface was smooth, the internal defects were reduced, and the microwave irradiation temperature was 700°C–800°C, causing the coal gangue particles to form a bonding surface and gradually agglutinate and densify. Meanwhile, the layered structure of kaolin minerals was destroyed, and a significant amount of glassy active SiO₂ and Al₂O₃ was produced, enhancing the gel ability and activity of coal gangue. Finally, 8% Ca(OH)₂ was added in the production of mortar specimens, which increased the alkalinity of the slurry, stimulated the rapid cracking and secondary hydration of the coal gangue, and enhanced the strength of mortar. At this time, the activity rate of coal gangue powder reached the highest, which was 90.5%.

Although manifold empirical studies have identified the mechanical properties of crumb rubber concrete (CRC), a comparative analysis of economic and environmental benefits between CRC and ordinary Portland cement concrete (OPCC) is not explored. In this paper, a quantitative meta-analysis between CRC and OPCC is conducted to explore optimized design strength, and a comparative analysis of the economic and environmental benefits of the two materials is undertaken. Considering cost price as the economic index and CO₂ emissions per cubic meter of concrete as the environmental index in the materialization stage, CRC and OPCC were compared with different mix designs to achieve grades of similar strengths. Upon replacing less than 20% of natural fine aggregates in concrete with crumb rubber, while retaining the cement content, an increase of 6% in the cost price was achieved for CRC with 30–40 MPa strength grade. Apart from the aspect of mining and transportation of natural aggregates, the reduction of CO₂ emissions by means of CRC adoption was verified in the treatment process of waste tire incineration. The results show that CO₂ emissions from CRC decreased by 15–17% when compared with OPCC for 30~40 MPa grade concrete. The research conclusion can serve as a theoretical basis for the engineering application of CRC with the same strength, and make certain contributions to the industrial application of crumb rubber aggregates and the sustainable treatment of waste tires.

Driven by capillary adsorption, moisture and aggressive media can easily intrude into unsaturated concrete and shorten the service life of concrete structures. In the present study, gangue-based concrete (GBC) was produced by replacing cement (substitution rate 0%, 10%, 20% and 30%) with mechanical-microwave activated coal gangue powder (ACGP) to explore the effect of freeze-thaw damage on the water absorption performance of GBC. ACGP improved the frost resistance of GBC, but the frost resistance declined at 30% mixing. The water absorption performance of GBC was promoted by freeze-thaw damage. Besides, the water absorption performance of GBC decreased first and then enhanced with the growth of ACGP content, especially the weakest at 20% content. The correlation analysis between the macroscopic characteristics of freeze-thaw damage and water absorption performance suggested that the coefficient of capillary absorption was highly linearly correlated with the damage layer thickness (R² > 0.9). The pore structure of GBC was optimized by the increase of small pores as well as the decrease of large pores after ACGP mixing. Furthermore, the coefficient of capillary absorption showed an apparent positive correlation with the transitional pores.

Compared with ordinary concrete, coal gangue concrete (CGC) is limited by its poor mechanical properties and frost resistance, which seriously restricts its wide application in cold regions. In order to improve the resource utilization rate of coal gangue, this paper takes advantage of the ‘overlapping effect’, ‘micro-aggregate filling effect’ and ‘volcanic ash effect’ of fly ash (FA) and silica fume (SF) and the anti-cracking effect of basalt fiber (BF) to study their effects on the macro performance of CGC and the micro modification mechanism. Modified CGC was prepared by replacing cement with 20% total mineral additives and adding BF. Taking different fly ash and silica fume incorporation ratios (F/S) and the BF content as variables, the research was carried out from two scales of macro performance and microstructure. The results show that the mechanical properties and frost resistance of CGC can be significantly improved by adding mineral additives and BF, and the modification effect is better with a decrease in F/S. When F/S = 1, the compressive strength, splitting tensile strength and flexural strength of the specimens increased by 13.73%, 8.37% and 4.27%, respectively. After 300 freeze–thaw cycles, the specimen was still not damaged by freezing and thawing. At the same time, keeping F/S = 3 unchanged and changing the BF content, it was found that the optimal content of BF was 0.15 vol% under the combined action of BF, FA and SF. In terms of microstructure, the addition of mineral additives and BF segregates and fills the macropores in the structure, greatly reducing the harmful pores and turning them into harmless and less harmful pores. When F/S = 1, the number of multi-harmful pores decreased by 16.89%, and the number of harmless pores and less harmful pores increased by 9.19%, which greatly optimized the pore structure and pore gradation.