Due to the rapid development of industrialization, the recycling and utilization of industrial by-products have received extensive attention. In this paper, binary, ternary, and quaternary composite cementitious materials were prepared using steel slag, blast furnace slag, and fly ash, and the effects of different cementitious materials on concrete properties were explored. A variety of solid wastes were mixed, and batches of concrete with high mechanical properties and durability were prepared by adjusting the type and amount of cementitious materials used. A total of 15 batches of concrete were prepared and tested for compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, and drying shrinkage. The test results show that a fly ash, blast furnace slag powder, and steel slag powder ratio of 1:1:2 produces a concrete with the best mechanical properties. Among them, the cube compressive strength can reach 62.9 MPa, the splitting tensile strength is 5.7 MPa, the axial compressive strength and elastic modulus are increased, the early shrinkage is small, the growth rate is slow, and the 28d concrete shrinkage rate is 4.87 × 10⁻⁴. This new type of green mixed concrete can not only control production costs, but can also reduce environmental impact and decrease carbon dioxide emissions.

In order to promote the high-quality utilization of solid waste—steel slag—this study prepared ground steel slag powder with specific surface areas of 400 m²/kg, 500 m²/kg and 600 m²/kg respectively. Different fineness levels of steel slag powder were used to replace cement to prepare ultra-high performance concrete (UHPC), with replacement rates of 20%, 30% and 40% respectively. The effects of fineness and dosage of steel slag powder on the workability, mechanical properties and microstructure of UHPC were further investigated. The results show that the incorporation of steel slag powder can significantly reduce the yield stress and plastic viscosity of UHPC, thereby increasing its fluidity, but also decreasing its thixotropy. The tensile properties of UHPC mixed with steel slag powder were all superior to those of the reference group. The compressive strength of UHPC prepared by using steel slag powder with a specific surface area of 400 m²/kg or 600 m²/kg instead of 20% cement was higher than that of the reference group. The compressive strength of UHPC mixed with 600 m²/kg specific surface area steel slag powder was generally stronger at the same dosage. At the same fineness, the mechanical properties of UHPC decreased gradually with the increase in steel slag powder content. The recommended dosage for the steel slag powder with a specific surface area of 400 m²/kg is 20%, which results in the best comprehensive properties in UHPC. At this time, compared with the reference group, the compressive strength increased by 3.35%, and the tensile strength increased by 20.73%. Moreover, adequate fineness of the steel slag powder can be achieved without excessive grinding energy, which contributes to sustainability.

Terraced fields and the Gully Land Reclamation Project (GLRP) are important soil and water conservation measures, widely constructed in China's Loess Plateau and other ecologically fragile areas in the world. However, under large‐scale governance scenarios, the impacts of the “terraced fields‐GLRP” cascade system on water and sediment processes in watersheds constitute a critical scientific issue that needs to be addressed for optimizing governance strategies under the context of high‐quality development of the Loess Plateau. To address this issue, this study developed a novel watershed solid‐scale physical model based on 3D scene reappearance. The spatial pattern of “terraced fields‐GLRP” significantly affected watershed runoff and sediment production. The study defined the coefficient (watershed erosion modulus reduction per unit area of terraced fields and GLRP) as their spatial layout control index, and proposed three deployment modes: series, parallel, and mixed. Under the series mode, the maximum watershed erosion reduction (86.25%) occurred when the relative layout area of terraced fields was 40%–50% and relative height 0.5 ~ 0.9; under the parallel mode, the maximum reduction (91.22%) was achieved at 40% relative terrace area; under the mixed mode, the maximum reduction (95.33%) was observed at 40% relative terrace area and 0.6–0.8 relative height. Watershed erosion remained stable when was 0.4–0.5, with an erosion growth inflection point at ≈ 0.5. The results of this study have important practical significance for the water and sediment source of Yellow River and optimization of soil and water conservation measures in highly managed small watershed in the world.

Concretes incorporating moderate-heat Portland cement (MHC) and Portland–slag cement (PSC) are widely used in hydraulic engineering due to their low temperature rise and excellent long-term strength. However, understanding of the hydration and carbonation behaviours of these cements is incomplete. In this investigation, long-term calorimetry was combined with thermodynamic modelling to quantify hydration degrees, pore-solution evolution and phase transformations. A predictive model for the hydration degree of MHC was established, giving a stable-state value of 87.9%. Thermodynamic simulations revealed that the saturation indices (SIs) of different calcium silicate hydrate end-members correlate positively with the portlandite SI and with the concentrations of OH− and silicon, but negatively with calcium concentration. The addition of slag led mainly to the consumption of portlandite, which was completely depleted at a slag content of 60%. Lower slag contents promoted calcium silicate hydrate (C-S-H) with a higher calcium/silicon ratio (CSR), whereas higher slag contents reduced the C-S-H content, the CSR and the pH of the pore solution. Carbonation directly lowered the paste alkalinity and caused decalcification of portlandite, C-S-H gel and ettringite to form calcium carbonate, amorphous silica and microcrystalline aluminium hydroxide. Although PSC offers considerable potential for low carbon dioxide and mass concrete applications, its lower alkalinity may impair carbonation resistance. When the pH of the paste pH was reduced to 9, MHC exhibited 31.8% superior carbonation buffering capacity compared with PSC.