As a solid waste generated in the alumina industry, red mud poses a significant environmental hazard and a storage problem. In this study, red mud was added to road cement clinker in order to utilize it. The sintering red mud was first de-alkalized, and then mixed with fly ash, clay, limestone, and sandstone, among other materials, to make Portland cement for road clinker. The effect of the addition of red mud on the thermal decomposition characteristics of Portland cement for roads was studied. The existent states of alkali and radioactive elements in Portland cement for road clinker were investigated by XRD and SEM analysis. The research results showed that the addition of red mud in Portland cement for road raw material significantly promoted the decomposition of carbonates in raw material. The major mineral phases of Portland cement for road clinker were C₃S with a polyhedral morphology, quasi-spherical C₂S, and tubular C₄AF. A small part of the alkali combined with the silicate phase to form a solid solution, and most of the alkali combined with S to form vermiform sulfate in the intermediate phase. The radionuclide ²²⁶Ra was mainly distributed in the silicate phase. ²³²Th was mainly distributed in interstitial phases and then silicate phases, while ⁴⁰K was mainly distributed in the interstitial phases.

The application of large amounts of red mud in the field of building materials is one of the main ways to reuse this material, but the high alkali content of red mud limits its application. In this paper, the washable alkali, removable alkali, and lattice alkali contents of Bayer red mud were studied, and the occurrence states of potassium and sodium in red mud were studied using XRD, IR, XPS, and NMR. On this basis, the removal mechanism for potassium and sodium in red mud was analyzed. The results showed that the Na in the red mud was mainly deposited in the shelf silicon voids of hydroxy sodalite (Na₈(AlSiO₄)₆(OH)₂(H₂O)₂) in the form of Si-O-Na or Al-O-Na. K is deposited in the shelf silico-oxygen void of potassium feldspar (KAlSi₃O₈) in the form of Si-O-K or Al-O-K. The washable Na and K contents of the mud were 13.7% and 4.47%; the alkali removal agent CaO removed 83.1% and 50.8% of Na and K in the red mud; and the lattice alkali Na and K contents were 3.20% and 44.8%, respectively. In the process of red mud dealkalization, Ca²⁺ ions can enter the internal voids of the hydroxyl sodalite and potassium feldspar silica skeleton and then replace Al³⁺ in the Si-O skeleton and Na⁺ and K⁺ in the skeleton voids. The replacement reaction changes the silica tetrahedron network structure, resulting in the disintegration of the frame-like silica tetrahedron in the hydroxyl sodalite and potassium feldspar, forming an isolated, island-like silica tetrahedron in hydrated garnet.

The utilization of waste rubber in concrete will reduce pollution and improve the efficiency of resource utilization. The effects of rubber particles and basalt fibers on the compressive strength and splitting tensile strength of concrete were investigated. In addition, the influence of basalt fibers on the mechanical properties and micropore structure of rubber concrete (RC) were analyzed using scanning electron microscopy (SEM) and X-ray computed tomography (CT). The distribution of rubber particles in concrete was also studied. The results indicate that the effects of basalts fibers on the mechanical properties of rubber concrete were significant. The rubber particles were evenly distributed in the concrete. Compared with normal concrete (NC), rubber concrete with 10% rubber particles had lower compressive strength and splitting tensile strength. Compared with rubber concrete, basalt fiber rubber concrete (BFRC) with 2% basalt fibers had no obvious effect on the compressive strength, while significantly improving the splitting tensile strength, refining the pores of rubber concrete, and reducing the porosity of the matrix. The effects of basalt fiber on the properties and pore distribution of RC should be considered in future applications.

As one of the main raw materials of engineered cementitious composite (ECC), fly ash exerts the “ball effect” and “pozzolanic effect” in concrete, which improves the working performance of concrete and enhances the strength of the concrete matrix. Polyvinyl alcohol (PVA) fiber has been widely used in the preparation of ECC, while ground fly ash can be used to enhance the performance of ECC as a kind of high-activity admixture. In this paper, the compressive strength, flexural strength and flexural toughness of ECC prepared from different types of fly ash (raw fly ash, sorted fly ash and ground fly ash) are compared, and the rheological properties of the ECC are analyzed by studying the two parameters of yield stress and plastic viscosity. The results show that the smaller the particle size of fly ash is, the more sufficient it reacts with Ca(OH)₂ produced by cement hydration, and the more it can improve the compressive strength and flexural strength of the matrix. In addition, the smaller the particle size of fly ash, the higher the yield stress and plastic viscosity of ECC; therefore, the distribution of PVA fiber in ECC is more uniform, thereby improving the flexural toughness and ductility of ECC.

To enhance the effectiveness and precision of design and to produce more low-carbon and high-performance Engineered Cementitious Composites (ECCs), novel hybrid fiber-reinforced high-ductility cementitious composites developed by incorporating a combination of ultra-high-molecular-weight polyethylene fibers (UHMWPE) and basalt fibers (BFs) into the cementitious matrix. Building upon the Box–Behnken design model from Response Surface Methodology (RSM), this study investigates the effects of different water-to-binder ratios and fiber contents on the mechanical properties of hybrid fiber-reinforced ECC. Analysis of variance (ANOVA) was used to validate the regression models. Furthermore, multi-objective optimization of the ECC mix proportion was achieved by employing the NSGA-II algorithm in conjunction with the TOPSIS comprehensive evaluation method. The results indicate that UHMWPE and BFs exhibited a significant positive hybrid effect. The order of factor significance was as follows: The content of ultra-high-molecular-weight polyethylene is greater than that of basalt fiber, and the content of basalt fiber is greater than that of the water–binder ratio. The results of variance analysis show that the regression model has high fitting accuracy. Furthermore, the algorithmic optimization yielded an optimal mix proportion: a water-to-binder ratio of 0.21, UHMWPE fiber content of 1.51%, and BF content of 0.85%. This study provides a valuable reference for the multi-objective optimization design of ECC mix proportions targeting diverse strength and toughness requirements.