Enhancing CO₂-Cured cementitious binder with Mg-doped γ-C₂S from high-Mg limestone

This study explores the use of Mg-doped γ-C2S, an alternative to conventional Portland cement, to address the environmental impact of the cement industry. γ-C2S, known for low hydration activity, shows promise as a CO2-cured binder. The research investigates Mg substitution in γ-C2S synthesis, utilizing high-Mg limestone resources. Varying Mg/Ca ratios in γ-C2S synthesis promoted bredigite and merwinite phases during calcination, enhancing specific surface area by over 40%. Optimal Mg doping significantly increased carbonation reactivity, resulting in a 20% strength boost (115 MPa) after 24h of CO2 curing. This improvement is attributed to enhanced crystallinity in carbonation products, namely hydromagnesite, nesquehonite, aragonite, and magnesite, leading to microstructure densification. The findings highlight Mg-doping as a promising strategy to enhance the carbonation performance of γ-C2S from high-Mg limestone, offering prospects for sustainable construction materials with reduced CO2 emissions.</p

Enhancing CO₂-Cured cementitious binder with Mg-doped γ-C₂S from high-Mg limestone

This study explores the use of Mg-doped γ-C2S, an alternative to conventional Portland cement, to address the environmental impact of the cement industry. γ-C2S, known for low hydration activity, shows promise as a CO2-cured binder. The research investigates Mg substitution in γ-C2S synthesis, utilizing high-Mg limestone resources. Varying Mg/Ca ratios in γ-C2S synthesis promoted bredigite and merwinite phases during calcination, enhancing specific surface area by over 40%. Optimal Mg doping significantly increased carbonation reactivity, resulting in a 20% strength boost (115 MPa) after 24h of CO2 curing. This improvement is attributed to enhanced crystallinity in carbonation products, namely hydromagnesite, nesquehonite, aragonite, and magnesite, leading to microstructure densification. The findings highlight Mg-doping as a promising strategy to enhance the carbonation performance of γ-C2S from high-Mg limestone, offering prospects for sustainable construction materials with reduced CO2 emissions.</p

Research and application of inorganic and organic composite grouting reinforcement materials in deep weak rock

In response to the problems of large deformation, fracture closure and poor permeability of the surrounding rocks in the weak rock roadways of the 1 000 m or deeper coal mines, it is required that the grouting material has good injectability, fast solidification speed, high early strength, and strong bonding performance. A new method of synergistic preparation of inorganic grouting materials was designed using “component optimization + ultra-fine + nano-reinforcement + organic modification”. An inorganic grouting material with an optimum composition ratio of 50∶40∶10 for the ternary cementing system of calcium sulphate aluminate, gypsum and lime was developed. After ultra grinding, the compressive strength of the concretion increased by 163.0% within 4 hours, achieving initial early strength and rapid solidification. A nano-lithium-aluminium hydrotalcite reinforcement material with synergistic effects of nano-nucleation-induced crystallization and lithium ion promotion was developed, resulting in a 183.7% increase in the 2 h strength of the ultra grinding grouting material. The organic modifier with directional coupling effect at the coal-rock interface was synthesized, which formed a bridge through bonding with the grout and coal interface, significantly improving the bonding between the slurry concretion and the coal rock interface. The synergistically prodeuced inorganic-organic composite grouting reinforcement materials has small particle size (D95<10 μm), fast setting (<8 min), high early strength (2 h strength 11.5 MPa), and strong bonding performance (sandstone bonding strength 3.12 MPa). The inorganic-organic composite grouting reinforcement materials with “high early strength, high injectability and high bonding” properties for weak rocks in deep mines have been developed. The field application test adopted high-pressure grouting method, and the grout can be injected into large and micro cracks of the coal sample, connecting isolated cracks to achieve high-pressure splitting, and the loose coal mass was compacted. Microscopic observation showed that the grout under high pressure injection can increase the fissure opening and inject more grout into microfissures. Finally, the development direction of grouting materials in the future is proposed

Effects of Aluminum Sulfate and Quicklime/Fluorgypsum Ratio on the Properties of Calcium Sulfoaluminate (CSA) Cement-Based Double Liquid Grouting Materials

Grouting materials are used frequently in grouting reinforcement projects, such as mining and coastal engineering. Double liquid grouting materials are mostly used because of the fast setting and high early strength properties when the two slurries are mixed together but high fluidity when the two slurries are separated. In our study, double liquid grouting materials were developed from CSA cement (slurry A), quicklime and fluorgypsum (slurry B). Aluminum sulfate was added in slurry B in order to counteract any adverse effects caused by the fluorgypsum, such as the decreased early compressive strength and the prolonged setting time. The effects of aluminum sulfate content and the quicklime/fluorgypsum ratio on the setting time, hydration heat, and compressive strength of the double liquid grouting materials were investigated, and the hydration products were characterized through thermogravimetry-differential thermal analysis (TG-DTA), X-ray Diffraction (XRD), and Scanning Electron Microscope (SEM) tests. The results show that the addition of aluminum sulfate can shorten the setting time and increase compressive strength at both early and later ages. Considering the setting time and compressive strength of double liquid grouting material at the same time, the optimum content of aluminum sulfate was found to be 2%, and the optimum ratio of quicklime/fluorgypsum was found to be 2:8. The values of the optimum content of aluminum sulfate and ratio of quicklime/fluorgypsum were verified from theoretical analysis

Improving the Mechanical Properties of Sulfoaluminate Cement-Based Grouting Material by Incorporating Limestone Powder for a Double Fluid System

To improve the hardening performance of sulfoaluminate cement-based grouting material (SCGM) and reduce its cost, limestone powder was adopted to replace anhydrite in the control SCGM. The influence of the replacement rate of limestone powder on the hydration, hardening strength, expansion, and microstructure evolution of the SCGM was systematically researched. The results indicated that replacing anhydrite with limestone powder in SCGM can improve the flowability, shorten the setting time, and enhance the compressive strength at early and late stages. When the replacement rate of limestone powder was 20%, the compressive strength of SCGM for 6 h and 28 days increased by 146.41% and 22.33%, respectively. These enhancements were attributed to the fact that fine limestone powder can accelerate the early hydration reaction rate and promote the formation of ettringite due to its nucleation effect. Moreover, due to the presence of limestone powder, mono-carbonate (Mc) can be formed, which would densify the microstructure and refine the pore structure of the hardened SCGM

Revealing the Microstructure Evolution and Carbonation Hardening Mechanism of β-C₂S Pastes by Backscattered Electron Images

&#946;-dicalcium silicate (&#946;-C2S) minerals were prepared. The compositions, microstructures, and distributions of the carbonation products of hardened &#946;-C2S paste were revealed by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and backscattered electron (BSE) image analysis. The results show that a dense hardened paste of &#946;-C2S can be obtained after 24 h of carbonation curing. The hardened pastes are composed of pores, silica gel, calcium carbonate, and unreacted dicalcium silicate, with relative volume fractions of 1.3%, 42.1%, 44.9%, and 11.7%, respectively. The unreacted dicalcium silicate is encapsulated with a silica gel rim, and the pores between the original dicalcium silicate particles are filled with calcium carbonate. The sufficient carbonation products that rapidly formed during the carbonation curing process, forming a dense microstructure, are responsible for the carbonation hardening of the &#946;-C2S mineral

Unveiling the Carbonation Behavior and Microstructural Changes of Magnesium Slag at 0 ℃

Magnesium slag (MS) is an industrial byproduct with high CO2 sequestration potential. This study investigates the carbonation behavior and microstructural changes of MS during wet carbonation at 0 °C. XRD, TG, FTIR, SEM, and BET techniques were used to characterize the phase composition, microstructure, and porosity of MS samples carbonated for different durations. The results showed that the main carbonation products were calcite, vaterite, and highly polymerized silica gel, with particle sizes around 1 μm. The low-temperature environment retarded the carbonation reaction rate and affected the morphology and crystallization of calcium carbonate. After 480 min of carbonation, the specific surface area and porosity of MS increased substantially by 740% and 144.6%, respectively, indicating improved reactivity. The microstructure of carbonated MS became denser with calcite particles surrounded by silica gel. This study demonstrates that wet carbonation of MS at 0 °C significantly enhances its properties, creating an ultrafine supplementary cementitious material with considerable CO2 sequestration capacity

Synthesis of Aragonite Whiskers by Co-Carbonation of Waste Magnesia Slag and Magnesium Sulfate: Enhancing Microstructure and Mechanical Properties of Portland Cement Paste

This study focused on the synthesis of aragonite whiskers through a synergistic wet carbonation technology utilizing waste magnesia slag (MS) and magnesium sulfate (MgSO4), aiming to improve the microstructure and mechanical properties of ordinary Portland cement (OPC) paste. The influence of MgSO4 concentration on the wet carbonation process, phase composition, and microstructure of MS was investigated. Furthermore, the effect of incorporating carbonated MS (C-MS) on the mechanical properties and microstructure of Portland cement paste was evaluated. Results showed that appropriate MgSO4 concentrations favored aragonite whisker formation. A concentration of 0.075 M MgSO4 yielded 86.6% aragonite with high aspect ratio nanofibers. Incorporating 5% of this C-MS into OPC increased the seven-day compressive strength by 37.5% compared to the control OPC paste. The improvement was attributed to accelerated hydration and reduced porosity by the filling effect and microfiber reinforcement of aragonite whiskers. MS demonstrated good CO2 sequestration capacity during carbonation. This study provides an effective method to synthesize aragonite whiskers from waste MS and use it to enhance cementitious materials while reducing CO2 emissions, which is valuable for the development of a sustainable cement industry

Effect of Nano-Si3N4 on the Mechanical Properties of Cement-Based Materials

In this paper, in order to improve the wear resistance of road cement, nano-Si3N4 (NSN) was incorporated into cement, and the effect of NSN on compressive strength and wear resistance of road cement was investigated. The main variable of the experimental investigation was the dosage of NSN. The experimental results showed that the addition of NSN could significantly improve the compressive strength and wear resistance of cement paste. Compared with the reference group, the wear resistance can be improved by 46.5% and the compressive strength of cement paste can be improved by 12.3% when the addition of NSN is 0.16% by weight. In addition, the improvement mechanisms of NSN on cement paste were revealed by hydration heat, XRD, DTA-TG, nanoindentation, nitrogen adsorption, and SEM for microscopic phase tests. Through the microscopic analysis, the addition of NSN can accelerate the hydration reaction and promote the hydration degree, optimize the pore structure, and make the cement paste more compact. Additionally, NSN can improve the performance of the interface transition zone (ITZ) and increase the content of HD C-S-H gel. The action mechanism of NSN is mainly dominated by the surface effect, filling effect, and larger surface energy of NSN thereby improving the mechanical properties of cement-based materials. These research results have guiding significance for the design of the high wear resistance and high compressive strength of cement-based materials