This paper discusses the potential of using steel fiber to produce self-compacting high-strength concrete. The effects of water–binder ratio and mortar and steel fiber content on the workability and mechanical properties of high-performance concrete were studied. The working performance of cementitious materials was evaluated by a slump expansion test, T₅₀₀, L-shaped instrument, U-shaped instrument, and V-shaped funnel. The mechanical properties were evaluated by compressive strength and flexural strength. The results show that when the compressive strength of self-compacting high-strength concrete with steel fiber is 90 MPa, the optimum mix ratio is a water–binder ratio of 0.22, sand ratio of 46%, and steel fiber content of 0.3%. When the steel fiber content is 0.3%, the compressive strength of the time can be increased by more than 4%, and the flexural strength can be increased by more than 5%. When the steel fiber content is 0.6% to 0.9%, the compressive strength of the specimen can be increased by more than 10%, and the flexural strength can be increased by more than 7%. However, with the increase in steel fiber content, self-compacting concrete becomes less and less dense, and the bond strength becomes lower and lower. When the water–binder ratio is 0.20, the fluidity of self-compacting concrete is poor, and the forming effect is not good. When the water–binder ratio is 0.24, the working performance of self-compacting concrete is better, but the cohesion is poor, and it can easily produce segregation. When the water–binder ratio is 0.22, the working performance of self-compacting concrete can be the best, and the strength of concrete is higher and more stable. The optimum sand ratio is 46%. At this time, the compressive strength and flexural strength of self-compacting concrete are the largest, and the working performance is also the best. When the sand ratio is lower than the optimum sand ratio, the self-compacting concrete will produce segregation. When the sand ratio is higher than the optimum sand ratio, the fluidity of self-compacting concrete is poor. This study provides insights into the potential for large-scale and high-value utilization of steel fibers and the development of cost-effective ways to reduce the carbon footprint of self-compacting concrete production.

To promote the recycling and reuse of waste concrete, this study investigated the comprehensive impact of recycled aggregate (RA) content and particle size on the mechanical properties of concrete. A novel equivalence parameter (λ_eq) of RA was developed to consider the influence of RA content and size on the mechanical properties of concrete. Empirical equations were developed using linear regression to describe the test results and predict the impact of content and size of RA on the mechanical properties of concrete. The results showed that the comprehensive impact on the mechanical strength of recycled concrete shows a certain regularity when the content and particle size of RA change simultaneously. The measured mechanical properties and regression equations provided a reference and basis for engineering applications, such as the processing of RA in a crushing plant, the design of mix proportions in concrete using RA, and the rapid assessment of mechanical properties on-site. This study provides a design method and technical path for green construction.

This paper discusses the potential of adding a self-made super-early-strength agent to produce quick-setting, quick-hardening, and high-strength concrete. A super-early-strength agent is prepared by mixing triethanolamine (TEA), aluminum sulfate (Al₂(SO₄)₃·18H₂O), formic acid (HCOOH), and sodium fluoride (NaF) with a water-reducing agent in different proportions. In this paper, the effects of super-early-strength agent ratio and dosage, water–binder ratio, silica fume content, and cementitious material content on the setting time and compressive strength of high-strength concrete were studied. The hydration characteristics were evaluated by X-ray diffraction (XRD) and TG-DSC thermal analysis. The results show that the high-strength concrete prepared by 42.5R ordinary Portland cement mixed with appropriate amount of silica fume and self-made super-early-strength agent has a compressive strength of 10 MPa in 6 h, a compressive strength of 40 MPa in 1 day, a compressive strength of not less than 80 MPa in 28 days, and a compressive strength of not shrinking in 180 days. Using conventional raw materials and general process methods, the concrete prepared according to the preparation method of this experiment can significantly shorten the setting time and improve the compressive strength. However, it is difficult to form concrete when the amount of super-early-strength agent is too large. Nevertheless, this study provides a theoretical basis for large-scale and high-value utilization of the potential of super-early-strength agents and development to improve efficiency. At the same time, it provides a reference for the application of coating technology in rapid repair engineering.