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Magnesium silicate hydrate (M─ S─ H) cement has many excellent properties, but its resistance to corrosion by SO42− and Cl− has not been investigated. In this study, M─ S─ H cement was prepared from light burned magnesia powder obtained from magnesite tailings, and its erosion resistance for SO42− and Cl− was investigated. X-ray diffraction (XRD) and flight test instrumentation requirements (FTIR) showed a signal characteristic of M─ S─ H gel in M─ S─ H cement. The pH value of the M─ S─ H cement was in the range of 8–9, first increasing and then decreasing as hydration time increased. The 28-day compressive strength of the M─ S─ H cement reached 46.7 MPa. In water bath curing, the porosity was 8.3304%, and the average pore diameter was 8.526 m2/g. The retention coefficients of the M─ S─ H cement were 0.84 and 0.93 in Cl− and SO42− solutions, showing good resistance to sulfate and chloride corrosion. [ABSTRACT FROM AUTHOR]

Magnesium oxysulfate (MOS) cement features potential advantages, including light weight, green and environmental protection, low thermal conductivity, and high frost- and fire-resistance, but its poor mechanical strength limits the extensive utilization in the architectural engineering. In this study, low-cost quartz (Q) was used as a mineral admixture to increase the mechanical strength of MOS pastes. The impact of the filler Q on the early and later mechanical strength of MOS cement was investigated, in which also had an impact on fluidity, setting times, volume stability, hydration processes, phase transformations, and microstructure. The results show that hydration of periclase to form 5Mg(OH)2·MgSO4·7H2O (phase 5-1-7) in this system was a multi-stage reaction process. 3Mg(OH)2·MgSO4·8H2O was the first sediment in this system and was converted into phase 5-1-7. The dilution and dispersion effects of the filler Q increased the early hydration rate, shortened the setting time, and increased the content and crystallite size of phase 5-1-7, increasing the early mechanical strength of MOS cement, while the volume-filling effect of the filler Q reduced the content of large pore and total pore volume, and improved the pore structure of the MOS cement, improving the later mechanical strength of MOS cement. MOS cement containing 15 wt.% of filler Q exhibited the highest early and later mechanical strength, and the lowest volume shrinkage, which is more suitable for application in architectural engineering. Based on these results, filler Q can be used as an enhancer in MOS cement, however its enhancement mechanisms are effective only when the content of filler Q is no more than 20 wt.%. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of coral sand powder (CSP) and corrosion inhibitors (SBT®‐ZX(V), SBT®‐RMA(II)) on reinforcement corrosion in coral aggregate seawater concrete (CASC) in a marine environment. A reasonable time‐variation model for reinforcement corrosion in CASC is proposed and verified. Based on the time‐variation model and chloride diffusion model, the cracking time and service life of CASC are predicted. The results show that the replacement of cementitious materials by 5% CSP can improve the corrosion resistance of steel bar in CASC. Both SBT®‐ZX(V) and SBT®‐RMA(II) can reduce the corrosion rate of steel bar in CASC, and this effect of SBT®‐RMA(II) is more effective than that of SBT®‐ZX(V). Among all CASC, CASC containing 5% CSP and SBT®‐RMA(II) possesses the best corrosion resistance. The results also reveal that the corrosion current density of steel bar in CASC increases firstly and then decreases over time. The ascending segment of the fitting curves for reinforcement corrosion in CASC conforms to the logarithmic‐type time‐variation model, and the descending segment of the fitting curves for reinforcement corrosion in CASC conforms to the exponential‐type time‐variation model. The cracking time and service life of CASC containing 5% CSP and SBT®‐RMA(II) will reach more than 10 years when the thickness of protective layer is 30 mm. [ABSTRACT FROM AUTHOR]

• Successfully established a predictive model for the compressive strength of magnesium silicate hydrate cement (MSHC) using machine learning methods. • Through sensitivity analysis, it was discovered that the compressive strength of MSHC is positively correlated with factors such as age, MgO content (C-Mg), and SiO 2 content (C-Si). Conversely, it is negatively correlated with the water-cement ratio (W/C). • The non-linear relationship between the compressive strength of MSHC and parameters such as the specific surface area of MgO (S-Mg) and the Mg/Si ratio has been revealed. • The optimal parameters for preparing MSHC have been proposed, including an optimal S-Mg value of approximately 22 m2/g and an optimal Mg/Si ratio of 1:1. Additionally, the optimal dosage range for using potassium dihydrogen phosphate (K) or sodium hexametaphosphate (S) as dispersants has been determined. In this study, a machine learning approach was employed to establish a predictive model for the compressive strength of magnesium silicate hydrate cement (MSHC). Sensitivity analysis of the input parameters was conducted using Shapley Additive Explanations (SHAP). The results indicated that the Gradient Boosting Regression (GBR) and Extreme Gradient Boosting (XGB) models exhibited enhanced precision in forecasting the compressive strength of MSHC, with the XGB model showcasing superior prowess in generalization. Among the various feature parameters, the curing age (Age) was identified as the most significant factors influencing the compressive strength of MSHC. The compressive strength of MSHC was positively correlated with the content of Age, MgO (C-Mg), and SiO 2 (C-Si), and negatively correlated with the water-cement ratio (W/C). It also had a nonlinear relationship with parameters such as the specific surface area of MgO (S-Mg) and the Mg/Si ratio. Finally, the optimal parameters for preparing MSHC were proposed, including an optimal S-Mg value of approximately 22 m2/g and an optimal Mg/Si ratio of 1:1. When potassium dihydrogen phosphate (K) was used as a dispersant, the optimal dosage was around 4.5%. On the other hand, when sodium hexametaphosphate (S) was used as a dispersant, a dosage greater than 2.5% resulted in a certain improvement in strength. [ABSTRACT FROM AUTHOR]