To improve the deformation performance of recycled concrete with tailings (TRC), its carbonization characteristics and deterioration mechanism with different polypropylene fiber content were analyzed macroscopically and microscopically. The results showed that the fiber had little effect on the compressive strength, which increased first and then decreased, with the optimum content being 0.6%. The splitting tensile strength first increased and then tended to be stable, with the optimum dosage ranging from 0.6% to 0.9%. The more the content, the higher the peak strain and the lower the elastic modulus. The rising section of its constitutive curve changed little, while the falling section became more gentle. Carbonization made the relative dynamic elastic modulus change small with a trend of first increasing and then decreasing, and the optimum content was 0.6–0.9%. When the fiber content was small, the influence on the carbonization depth did not remain significant, but when it was large, the depth increased obviously, and this critical content was about 0.6%. Microscopically, through nuclear-magnetic resonance (NMR) and scanning electron microscope (SEM) analysis, due to the strong tensioning effect of the fiber, when a small amount was added, the porosity and pore structure had not been significantly changed, so the impact on its resistance to carbonization was not obvious. However, after excessive addition, the interface transition zone (ITZ) between different materials became larger, resulting in a significant increase of its harmful cracks and a great impact on the anti-carbonization ability, with the optimal content being about 0.6%. This study provides a theoretical reference for the deformation performance improvement measure of TRC, which would be helpful for the rapid promotion and application of green concrete in engineering practice.

To improve the utilization efficiency of iron tailings (IOT) and recycled coarse aggregate (RCA), the mechanical properties, erosion depth and other erosion characteristics of recycled aggregate concrete (RAC) with different IOT amounts were studied in salt spray erosion environments and the erosion mechanisms were analyzed by SEM technology. The results showed that at the same erosion age, IOT caused the compressive strength and splitting tensile strength of RAC to tend to first increase and then decrease, with the optimum mixing amount being approximately 40%. Under the same conditions, the erosion depth of RAC was much higher than that of ordinary concrete. The erosion depth first decreased and then increased with an increasing amount of IOT. When the IOT content was 30–40%, the salt spray erosion depth reached its minimum. The solidification coefficient K₁ first decreased and then increased with the increase in iron tailings content. At its lowest point, the iron tailings content was approximately between 30% and 50%, which demonstrated that the higher the salt spray erosion age, the larger the solidification coefficient. Through SEM microscopic images, it could be seen that the appropriate amount of iron tailings caused the formation of salt spray erosion crystals and that the effect of physical expansion pressure caused a reduction in the porosity of RAC and a slight increase in its mechanical properties and salt spray erosion resistance. When the iron tailings content was large, the optimal mix ratio of the concrete also changed and then harmful pores and cracks were regenerated. Therefore, resistance to salt spray erosion was weakened. The research in this paper provides a theoretical basis for the engineering application of recycled concrete with tailings in salt spray environments.

Economic development and infrastructure improvement will inevitably lead to the accumulation of construction waste and tailings, which has not only a huge impact on the environment but is also a waste of resources. Recycling these resources and making green concrete is an effective way to solve these problems. In this study, the salt spray erosion characteristics and erosion mechanism of tailings recycled concrete (TRC) with polypropylene fibers were studied through macro and micro methods. The results showed that its compressive strength and splitting tensile strength increased at first and then decreased, with the optimum content of 0.6–0.9%, and the strength increase coefficient reached its maximum value at the erosion period being 14 d to 28 d. Under the same erosion cycle, when the fiber content was low (≤0.6–0.9%), the erosion depth hardly fluctuated. While the fiber content changed from 0.6% to 1.2%, the erosion depth and curing ability (erosion for 90 days) increased by 16.29% and 11.20%, which implied that its erosion resistance decreased sharply. Through SEM microscopic analysis, it could be observed that when the fiber content was low, the matrix structure and porosity had little change; while the fiber content was excessive, the porosity increased greatly. The longer the erosion period was, the greater the cumulative expansion of salt crystals was, and the larger the porosity was, whose results were in good agreement with the experimental results. This research provides a significant theoretical basis for the application of TRC in engineering.

This study addresses the critical challenge of low reactivity and environmental leaching associated with high-volume phosphogypsum by implementing an ettringite seed induction strategy to optimize foam concrete performance. These issues may lead to insufficient mechanical reliability, weak structural integrity, and environmental safety concerns in engineering applications. The results demonstrate that an optimal 2% seed dosage increases the 28-day compressive strength to 4.7 MPa, which represents a 150% improvement over the control while maintaining mass loss below 3.0% after 15 wet–dry cycles. Microstructural analysis reveals that the seeds serve as heterogeneous nucleation sites that help mitigate the inhibitory effects of phosphogypsum impurities to facilitate the growth of a dense 3D interlocking ettringite framework within the pore walls. This densification significantly reinforces the mechanical skeleton and reduces phosphorus leaching by 64.2%. However, excessive seed dosages at or above 5% may promote local AFt accumulation and rheological slurry-bubble mismatch which could contribute to microstructural defects and strength regression. The findings are expected to provide a scientific basis for the engineering application of high-volume phosphogypsum in foam concrete, particularly as lightweight fillers and non-load-bearing construction materials for sustainable construction.

As a highly active mineral admixture, metakaolin is often used as an efficient performance-enhancing material for concrete, but its performance in long-term complex service environments still needs to be verified. This article presents a composite green concrete with a substitution rate of 30% for recycled coarse aggregates (RCAs) and iron tailings (IOTs) and a waste polypropylene fiber (WPF) content of 0.6%. Concrete with different mixing conditions of metakaolin was prepared, and its carbonization resistance was studied with macro- and micro-experimental methods. The results indicated that when the content of metakaolin was less than 10%, its mechanical and deformation properties gradually improved, resulting in a maximum increase of 70% in its cubic compressive strength. Overall, carbonization improved the corresponding mechanical properties. For example, when carbonized for 14 days, the compressive strength growth rate increased by nearly 30%, and the elastic modulus did not change significantly. Through microscopic testing, it could be seen that when the content of metakaolin reached 10%, an appropriate amount of metakaolin (10%) promoted the hydration of cement, with the least number of pores and the best compaction performance, resulting in the best overall performance. But when added excessively, the coupling effect of secondary hydration and carbonization reactions could lead to the emergence of new harmful pores in the matrix structure. In future engineering applications of metakaolin, it is recommended that its mixing ratio be less than 10% to achieve better concrete performance.