The preparation of high-performance green cementitious material from industrial solid waste is a feasible large-scale utilization approach for industrial solid waste. This work investigates the feasibility of using industrial solid wastes in a sulphoaluminate–magnesium–potassium–phosphate cementitious composite material (SAC-MKPC) clinker preparation and the influence of the calcination temperature and clinker ingredients on the hydration behavior and mechanisms of the SAC-MKPC with a Mg/P ratio of 5. The results show that the novel SAC-MKPC that was prepared from aluminum slag, carbide slag, coal gangue, and magnesium desulfurization slag was composed mainly of mineral MgO, ${\mathrm{C}}_4{\mathrm{A}}_3\overline{\mathrm{S}}$, and C₂S and the calcination temperature of the main mineral phases was 1250–1350 °C. The solid-waste-based SAC-MKPC had better mechanical properties and excellent water resistance compared with the MKPC. The optimal compressive strength reached 35.2, 70.9, 84.1, 87.7, and 101.6 MPa at 2 h, 1 d, 3 d, 7 d, and 28 d of hydration, respectively. The X-ray diffraction spectra and scanning electron micrographs of the hydration products of the SAC-MKPC clinker showed that AFt and K-struvite crystals coexisted and adhered to form a dense structure. This work provides an innovative idea to produce green cementitious material using industrial solid wastes and may promote the sustainable development of the power and mining industries.

Underwater concrete 3D printing (3DPC) technology, as a pioneering construction process, has demonstrated significant potential in various fields, such as marine engineering, underwater restoration projects, and ecological construction. However, the complexity and variability of the underwater environment pose stricter quality standards for the printed structures. To address this, this study employed a self-developed framed concrete 3D printer and utilized response surface methodology to optimize the structural dimensions of the printing nozzle. Through in-depth analysis of the internal flow field of printing nozzles with various size combinations using ANSYS Fluent 2022R1 software, an optimal parameter configuration was determined, including a nozzle diameter (D) of 55 mm, an inclination angle (θ) of 20°, and a length (L) of 34 mm, ensuring uniform extrusion of the concrete material. Furthermore, this study applied an orthogonal experimental design to systematically investigate the combined effects of screw speed, printing speed, and nozzle height on the print quality and mechanical properties (compressive strength and flexural strength) of underwater concrete 3D printing. The experimental results, presented based on direct observation and analysis, identified the optimal combination of process parameters: a printing speed of 16 mm/s, a nozzle height of 10 mm, and a screw speed of 50 r/min. This combination ensures efficient printing while maintaining the mechanical properties of the printed samples. This study not only provides solid scientific and practical guidance for optimizing the nozzle structure and process parameters of underwater concrete 3D printing technology but also offers innovative solutions to underwater construction challenges in the field of marine resource development and utilization.

The effects of ash and slag from a biomass power plant on the compressive strength, setting time and fluidity of the pastes of Portland cement (P.O) and sulfoaluminate cement (SAC) were studied, and the hydration products and microstructure at the age of 7 days were analyzed via XRD, SEM and other test methods. The results show that the compressive strength of the composite cementitious material decreases, the setting time prolongs and the fluidity increases with the increase in the ash and slag content in the power plant. The microscopic analysis shows that the ash and slag of the biomass power plant can promote the hydration of Portland cement and sulfoaluminate cement paste, and increase the generation of hydration products. The results showed that replacing SAC clinker with 20–30% biomass power plant ash (BPPA) decreased the cement strength, and that an appropriate amount of BPPA (10–15%) could significantly improve the mechanical strength of SAC blended cement. The compressive strength of blended BPPA composite cementitious material in 28 days could reach 60 MPa. This study provided solutions to utilizing the BPPA as a building material admixture to minimize the consumption of energy-intensive cement and to meet the growing needs of the construction industry.

In order to solve the dietary problems of patients with dysphagia, a mathematical model for predicting extrusion pressure is established. The predictive model parameters are determined with the aid of the finite element method, and a 3D printing nozzle capable of printing nutrient-rich sandwich food is designed according to the predictive model. Pumpkin puree and minced pork are verified according to IDDSI standards. Finally, the accuracy of the predictive model and the printing effect of the design nozzle are verified by extrusion and printing experiments, respectively. The results show that four groups of simulation experiments reveal that the extrusion pressure increases by 15.6%, 13.5%, 12.7% and 12.4%, respectively, with a 1 cm increase in nozzle length. When the nozzle length is in the range of 1–5 cm, the extrusion pressure increases with the increase of the volume flow rate in the extrusion cylinder. The extrusion speed has little correlation with the length of the nozzle outlet, but for every 1 cm³/s increase in the inlet volume flow rate, the extrusion speed increases by about 1.5%. The finite element simulation experiment determines that the parameters of the prediction model are σ₀ = 0.6, α = 1.1, m = 0.21, τ₀ = 0, β = 0.52 and n = 0.2; the error between the predictive value and the experimental value is 15%, and the printed sandwich food has smooth lines, good molding and complies with IDDSI standards.

Concrete 3D printing technology is emerging as a new way to transform the construction industry in the future. However, the existing concrete 3D printing technology still has different degrees of defects in the print molding process. The existing concrete 3D nozzles need to undergo a long motion trajectory when printing complex curved components, which leads to lower geometric accuracy of curved structures, as well as poorer overall molding quality of the printed components. The aim of this study is to design a reducer nozzle to effectively shorten the printing stroke and thus improve the printing accuracy. A reducing nozzle is proposed with multi-gear internal meshing and a rotating blade structure nozzle with an adjustable outlet caliber. The mechanical strength of the rotating blade of the nozzle and the distribution characteristics of the flow field inside the nozzle are verified through fluid–solid coupling analysis. Experimental comparison shows that compared with the existing concrete 3D printing nozzle, the variable-caliber nozzle significantly improves the surface quality of the specimen, which strongly promotes the practical application and development of concrete 3D printing technology in the engineering field.