Search Results (1,165)

Calcium leaching increases the hydraulic concrete material’s porosity and the diffusion coefficient, thereby jeopardizing engineering safety. Fly ash and silica fume are commonly used mineral admixtures in hydraulic concrete, and their effects on the material’s leaching characteristics, especially its microstructural and transport properties, require further investigation. In this study, calcium leaching tests were conducted on cement paste (CP), silica fume–cement paste (SF), and fly ash–cement paste (FA) using a 6 mol/L ammonium chloride solution to accelerate the leaching process. Subsequently, a series of quantitative and qualitative analyses was performed on the deteriorated specimens, including phenolphthalein indicator spraying, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). Additionally, the diffusion coefficients of the material at different locations were calculated and analyzed. The results show that partially replacing cement with silica fume or fly ash increases the initial porosity, gel pore content, and initial diffusion coefficients. After 28 days of leaching, compared to the initial values, the porosity increases in the 0–4 mm layer from the leached surface were 83.6% for CP, 11.0% for SF, and 39.0% for FA. The diffusion coefficients increased by factors of 14.3 (CP), 6.1 (SF), and 13.6 (FA), indicating enhanced resistance to leaching. The primary reason for this is that the reactive silica in the admixtures undergoes a pozzolanic reaction with the calcium hydroxide generated by cement hydration, producing additional calcium silicate hydrate (C-S-H) gel, which reduces the capillary pores that would otherwise result from calcium hydroxide decomposition. Full article

To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital image correlation (DIC), and scanning electron microscopy (SEM), the “heterogeneous” evolution mechanism of macro-micro damage was revealed. The results indicate that disturbance level and frequency exert distinctly different driving effects on the deterioration of CTB, rather than a simple linear superposition. Specifically, low-frequency disturbance produces a compaction strengthening effect, microscopically promoting the generation of Ca(OH)₂ and ettringite (increased Ca/Si ratio). In contrast, the combination of high disturbance and high frequency induces free water extrusion and inhibits hydration, leading to an advanced damage threshold based on energy evolution and the accelerated coalescence of microcracks, which favors the formation of C-S-H gel (decreased Ca/Si ratio). Within this heterogeneous mechanism, the disturbance level acts as the dominant controlling factor. This study clarifies the nonlinear mechanical and chemical evolution paths under composite disturbances, providing theoretical support for the dynamic stability control of backfill in deep multi-step mining. Full article

Magnesium–rich environments are frequently encountered in cementitious systems, including the use of high–Mg raw materials in clinker production, cement–clay interfaces relevant to nuclear waste disposal, and exposure of cement–based materials to seawater, where progressive decalcification can substantially alter the structure and durability of calcium aluminosilicate hydrate (C–A–S–H) phases. In this study, density functional theory (DFT) calculations were employed to investigate the combined effects of interlayer and intralayer partial decalcification, Mg²⁺ substitution, and reinforcement with epoxy– and hydroxyl–functionalized reduced graphene oxide (rGO) on the structural stability and elastic properties of alkali charge–balanced C–A–S–H under dry and hydrated conditions. Adsorption–energy calculations reveal thermodynamically favorable interactions between functionalized rGO and silicate hydrate species in the presence of Mg²⁺, with hydroxyl/rGO promoting stronger interfacial stabilization and epoxy/rGO preserving greater graphene lattice integrity. The results demonstrate that Mg²⁺ substitution together with rGO intercalation generally enhances the mechanical response of partially decalcified structures through structural densification and interfacial cohesion. Relative to dry systems, hydration further improves elastic performance, increasing Young’s modulus and bulk modulus by 1–11% and 4–19%, respectively, for interlayer decalcified nanocomposites, while intralayer configurations exhibit stronger but model–dependent enhancements of up to ≈22% and ≈33%. Compared with untreated systems, rGO–treated nan–composites exhibit enhanced stiffness, with Young’s modulus and bulk modulus increasing by up to ≈22% and ≈15%, respectively. Overall, these findings provide atomistic insights into stabilization mechanisms in partially decalcified alkali charge–balanced C–A–S–H systems and identify Mg²⁺–rGO incorporation as a promising strategy for mitigating decalcification–induced degradation in durable low–carbon cementitious nanocomposites. Full article

Few strategies have been developed to mimic and control the supramolecular degradations induced by spontaneous fermentation in sour cassava starch, which are partly responsible for its characteristic expansion capacity in breadmaking, and their effectiveness has remained limited. In this context, the objective of this study was to evaluate the effect of adding α-amylase on the functional and nutritional properties of cassava starch used in breadmaking. Cassava starch from the INIAP 651 variety was modified with different α-amylase dosages (0, 2, 4, 6, 8, and 9 U/g α-amylase for 20 min), followed by hydration and pre-gelatinization before baking. Determinations of the specific volume of the bread (SV), dough characterization by Mixolab, pasting properties using a rheometer, and nutritional properties were performed. The treatment with 6 U/g α-amylase showed the best functional properties, achieving the highest SV (4.28 mL/g), C3 (1.67 Nm), C4 (1.11 Nm), and peak viscosity (6550 mPa·s), as well as the lowest setback (1526 mPa·s). In contrast, the treatment with 9 U/g α-amylase exhibited the most favorable nutritional profile, with the lowest estimated glycemic index (51.25) and rapidly digestible starch (15.85 g/100 g). These results confirm that controlled α-amylase dosing modulates cassava starch functionality for breadmaking and glycemic control. Full article

In this study, the rapidly setting and hardening high-belite sulfoaluminate cement (HBSAC) is used as the cementitious material, with natural river sand as the fine aggregate, and a high-performance repair mortar is prepared through the synergistic use of different polymers and admixtures. The influences of two polymers (VAE and HPMC) on the working performance, mechanical properties, and hydration characteristics of HBSAC mortars are systematically studied. The results showed that the two polymers had a significant improvement effect on the setting time, mortar flowability, and water retention rate of HBSAC mortar. Among them, VAE had a significant effect on the mortar flowability, and a 5% content could increase the flowability of HBSAC mortar by 29.8%. HPMC has a significant improvement effect on setting time and water retention rate; at 0.1% content, it can delay the initial setting time by 6.5 min and achieve a water retention rate of over 90%. As the polymer to binder ratio increases, both polymers, except for 2.5% VAE, which can slightly improve the flexural strength of mortar, will reduce the flexural and compressive strength of mortar, with VAE causing greater damage to strength. On the contrary, the polymer significantly enhanced the bond strength of the mortar. Compared with the cement control group, the 28 d bond strength of 5% VAE and 0.1% HPMC groups increased by 56.7% and 15.1%, respectively. Moreover, the addition of polymers delayed the occurrence of the exothermic peaks of HBSAC dissolution and ettringite formation, but the total amount of hydration heat released within 48 h was higher than that of pure cement. The diffraction peaks of AFt in the hydration products of VAE-HBSAC paste at 3d and 28d showed significant enhancement, and the peak intensity increased with higher doping levels, while the diffraction peak intensity of C₂S showed a certain decrease. The polymer significantly increased the weight loss peak intensity and mass loss after heating of AFt, AH₃, AFm, and C-S-H gel. The SEM images indicate that VAE can form a mesh on the surface of hydration products and refine the crystal size of AFt; HPMC wraps more flocculent substances around the hydration products, thereby improving the compactness of paste. This study can provide scientific reference for improving the performance and promoting the practical application of high-performance rapid repair mortar for concrete structure damage. Full article

This study aims to explore the preparation process and properties of unburned lightweight aggregate using red mud synergistically with fly ash, granulated blast-furnace slag, and other multi-source solid wastes. Curing regimes and alkali-activated systems were controlled. Their effects on physical properties and environmental safety of lightweight aggregate were systematically evaluated. Results show that curing temperature and alkali activator exert significant synergistic effects on physical properties of lightweight aggregates. Steam curing performs better than standard curing. Performance improves with increasing steam temperature. Sodium silicate solution with a modulus of 1.0 is determined as the optimal activator. Under 90 °C steam curing, Sample D2 achieves the best overall performance. Its cylinder compressive strength reaches 6.92 MPa. 1 h water absorption is 14.8%. Softening coefficient is 0.93. Porosity is as low as 31.07%. Microscopic analysis reveals that higher curing temperature significantly accelerates the hydration reaction of the RMLWA system. It promotes the formation of abundant cementitious products such as C-S-H gel. These products fully fill internal pores and microcracks of the aggregate. A dense three-dimensional network skeleton structure is finally formed. For environmental safety, heavy metal leaching concentrations of steam-cured samples are generally lower than those of standard-cured samples. This study realizes high-value resource utilization of industrial solid wastes. It also provides a new technical route for the development of green building lightweight aggregate. Full article

This study developed a composite solidification system for silt from the Yellow River Basin, utilizing calcium carbide slag, ground granulated blast-furnace slag, and desulfurized gypsum, in conjunction with the xanthan gum biopolymer. A Box–Behnken Design and Response Surface Methodology were employed, and the 14-day unconfined compressive strength was set as the focus of this investigation, with four variables examined: the content of the soil stabilizer, the xanthan gum-to-soil stabilizer ratio, the calcium carbide slag-to-soil stabilizer ratio, and the ratio of desulfurized gypsum to the soil stabilizer. The regression model demonstrated high significance (R² = 0.9798), with the xanthan gum ratio exerting the most substantial influence on the soil strength. The optimal proportions were determined to be 4.01% soil stabilizer content, 0.080 xanthan gum ratio, 0.143 calcium carbide slag ratio, and 0.110 desulfurized gypsum ratio. Microstructural analysis revealed that xanthan gum maintained hydration humidity through hydrogen bonding, facilitating the formation of C-(A)-S-H gels and ettringite crystals. This organic–inorganic structure effectively reduces porosity, although excess xanthan gum can impede hydration. This approach advances the sustainable utilization of industrial waste and environmentally friendly stabilization of the Yellow River silt. Full article

Energetic materials face dual challenges of enhancing detonation performance and replacing toxic lead-based formulations. Triazole-based energetic potassium salts typically struggle to achieve simultaneous high-density and excellent detonation properties. Herein, a novel gem-dinitro-functionalized 1,2,3-triazole energetic salt, tripotassium 4,5-bis(gem-dinitromethyl)-2H-1,2,3-triazolate (3K₃BNOT·4H₂O), was rationally designed and synthesized via a six-step mild route using diaminomaleonitrile as the starting material. The structure was fully characterized by IR, NMR, elemental analysis, and single-crystal X-ray diffraction (SC-XRD). 3K₃BNOT·4H₂O crystallizes in the triclinic system (space group P-1) and forms a three-dimensional K-O/K-N ionic coordination network, delivering an ultra-high anhydrous crystal density of 2.077 g·cm⁻³ at 193K. It exhibits a peak decomposition temperature of 183.8 °C (10 °C·min⁻¹), impact sensitivity of 5 J, and friction sensitivity of 60 N (standard BAM methods). The calculated detonation velocity and pressure reach 8836 m·s⁻¹ and 28.6 GPa, respectively, outperforming the classical explosive RDX. This work provides a structural analysis of triazole-based energetic potassium salt hydrates, and 3K₃BNOT·4H₂O shows structural potential as a high-energy energetic material; its initiating performance needs further experimental verification. Full article

Rural road construction in the loess region of Gansu Province is constrained by aggregate shortage, high material transportation costs, and the limited early performance of cement-stabilized soil. In this study, KDJ-II stabilizer and cement were used to prepare KDJ-II–cement composite-stabilized soil for potential use as a base-course material. Compared with cement-stabilized soil, the addition of 0.02% KDJ-II increased the 7-day unconfined compressive strength, splitting tensile strength, and resilient modulus by 16.7%, 17.6%, and 12.1%, respectively. Leaching-based ion concentration analysis, XRD, FTIR, and SEM were used to interpret the early strength development mechanism. The results suggest that KDJ-II influenced the leachable ion release and retention behavior of the cement-stabilized soil and helped form a sulfate-rich, alkaline, and soluble-silica-bearing reaction environment under the tested conditions. This environment may favor the development of sulfate-bearing hydration products, the activation of primary aluminosilicate minerals, and the formation of C–S–H-like gels. The coupled variations in leachable Ca²⁺, SO₄²⁻, and Na⁺, together with the increase in calcite, decrease in albite, broadening of the absorption band at approximately 1018 cm⁻¹, and the SEM-observed needle/fibrous products, flocculent gels, and reduced visible pores, collectively support the interpretation that KDJ-II promotes particle cementation, pore filling, and microstructural densification. Overall, this study indicates that, under the selected mixture proportion and curing condition, KDJ-II can improve the early strength and stiffness of cement-stabilized loess by modifying the early reaction environment and promoting the coordinated development of hydration-related products and a denser microstructure. Full article

To advance the development of sustainable buildings, this study investigates recycled cement-based materials. The core component of this material is concrete-based recycled micropowder (CRM), which is shaped and reinforced from recycled construction waste. It is then activated through high-temperature calcination to produce modified recycled micropowder (MRM), and the resulting changes in its properties are analyzed. X-ray diffraction, Brunauer–Emmett–Teller surface area, and hydration heat tests reveal that cementitious materials incorporating MRM800 contain more C-S-H and other hydration products, exhibit lower porosity, and demonstrate stronger hydration reactions. The results show that 800 °C is the optimal calcination temperature for CRM activation. For recycled silica-based mortar (RSM), the introduction of an efficiency coefficient (K_λ) allows for a quantitative, scientific, and intuitive evaluation of the contributions of three admixtures, aiding in the optimization of the mix ratio. RSM with MRM showed improved performance, with compressive strength ranging from 24.3 to 42.3 MPa. A 20% MRM addition effectively enhanced the mechanical properties of the mortar, while the mixture with 10% MRM and a 1:3 cement-to-sand ratio exhibited only 8.23% strength loss and 0.78% mass loss after 50 freeze–thaw cycles. MRM can improve the compactness of the cement matrix and thus optimize its freeze–thaw resistance, providing an eco-friendly technical solution for the engineering application of recycled mortar in cold regions. Full article

The functionality of ionomeric membranes is influenced by small changes of several parameters. Aqueous network formation by phase separation between the hydrophilic and hydrophobic parts of the polymer is one critical factor for water and ion transport. In particular, the transport of highly charged ions like ${\mathrm{V}}^{3+}$ is not well understood. The unsteady diffusion in Nafion, a sulfonic acid based cation exchange polymer, using ${\mathrm{V}}^{3+}$ profiles obtained with micro X-ray fluorescence ($0.5 \mathsf{\mu }$m spot over a $180 \mathsf{\mu }$m scan) yields a diffusion coefficient of $4\times {10}^{-13} {\mathrm{m}}^2{\mathrm{s}}^{-1}$ at ${\lambda }_{H_{2}O/S{O}_3}=12$ and at ca. $20 °$C. It is confirmed that the concentration profile can be described by an error function formalism. The diffusivity, determined from the entire profile, represents mainly the transport into a vanadium free environment with very low ionic strength as the membrane was conditioned in ultra-pure water. The macroscopic ion transport is influenced by local molecular interactions, interconnection of water pockets and long range ionic interactions. The local interactions of ${\mathrm{V}}^{3+}$ were studied using molecular dynamics (MDs) simulations. The MD simulation studies diffusion at a constant ion concentration and short length scale (ca. 30 nm). It gives insights on the effects of dissolved ${\mathrm{V}}^{3+}$ ions on the local structure. Radial distribution functions reveal that at low hydration, the vanadium ions have an ordering effect on water molecules. The diffusion coefficient of ${\mathrm{V}}^{3+}$ is determined on a molecular level from the mean-square displacement yielding $2.5\times {10}^{-10} {\mathrm{m}}^2{\mathrm{s}}^{-1}$ for ${\mathrm{V}}^{3+}$ ions at a membrane water content of ${\lambda }_{H_{2}O/S{O}_3}$ = 6. The phenomenon in which the diffusivity decreases over longer length scales was documented before for water and ${\mathrm{H}}^{+}$ in Nafion; however, this was by only about one order of magnitude. The experimental microscopic approach described by us is universally applicable, e.g., to environments of higher ionic strength, ions with different charges, and different types of ion-exchange membranes. Longer diffusion times allow us to distinguish between different concentration regimes. Full article

This study investigates the effect of mineral additives of different natures, namely blast-furnace slag, fly ash, and bentonite, on structure formation, phase composition, microstructure, and physicomechanical properties of cement matrices. The analysis included measurements of mass change and linear shrinkage during hardening, determination of density and microhardness, X-ray phase analysis, and microstructural examination by scanning electron microscopy. It was found that the introduction of mineral additives reduced linear shrinkage from 6.06 mm for the control composition to 0.25 mm for the composition with blast-furnace slag, 2.31 mm for the composition with fly ash, and 1.01 mm for the composition with bentonite. The maximum density and microhardness values were obtained for the matrix with blast-furnace slag and amounted to 1.99 ± 0.03 g/cm³ and 39.95 ± 1.12 HV1, respectively, whereas the overall range of values for the investigated compositions was 1.52–1.99 g/cm³ and 30.2–39.95 HV1. X-ray phase analysis showed that the amorphous component varied from 61 to 78%, reaching its maximum value in the composition with blast-furnace slag, which is associated with the formation of poorly crystalline C–S–H and aluminosilicate phases. According to the SEM data, the average size of visible pore-like defects was 2.4 μm for the control composition, 1.4 μm for the composition with blast-furnace slag, 1.3 μm for the composition with fly ash, and 1.7 μm for the composition with bentonite. The most favorable combination of high density, microhardness, developed amorphous component, and homogeneous microstructure was established for the composition with blast-furnace slag. The obtained results can be used as a materials-science basis for the development of cement matrices intended for further studies on the immobilization of solid radioactive waste. Full article

This study developed a high-iron-phase steel slag-based silicate cement system through high-temperature reconstruction and multi-source solid waste synergistic modification. The effects of reconstruction temperature and Ca/Si ratio on burnability, mineral evolution, microstructure, and hydration performance were investigated. Results showed that carbide slag and bauxite significantly improved the sintering behavior of steel slag. At 1275 °C, the f-CaO content in reconstructed steel slag decreased sharply from 1.45% to 0.11%, while overburning and liquid-phase coating occurred at 1300 °C, hindering further reaction of residual f-CaO. Reconstruction promoted the conversion of low-reactivity γ-C₂S to active α-C₂S and the formation of well-crystallized C₄AF. The decomposition of the RO phase enabled Mg²⁺ and Mn²⁺ to solid-solve into spinel phases, thus improving volume stability. The Ca/Si ratio regulated intermediate phases: higher ratios favored C₄AF, whereas lower ratios promoted spinel or olivine phases. The optimal sample (1275 °C, 65% steel slag + 25% carbide slag + 10% bauxite) achieved a 28 d compressive strength of 107.56 MPa, 18.26% higher than the reference cement, owing to synergistic hydration of α-C₂S and C₄AF. The F4 sample showed the lowest residual CH content (11.31%) and the highest hydration efficiency. Full article

This research investigates the relationship between mineralogical composition and compressive strength in alkali-activated cement–sand mortars incorporating palm oil fuel ash (POFA) as a partial replacement of Portland cement. POFA was introduced at 5 wt.% and 10 wt.% of the binder, and activation was achieved using a NaOH–Na₂SiO₃ solution (3:1 mass ratio). Compressive strength and bulk density were evaluated at 7 and 28 days, while phase evolution was analyzed by X-ray diffraction (XRD) coupled with Rietveld refinement. The results demonstrate that POFA incorporation significantly modified the CaO–SiO₂–Al₂O₃ balance of the system, promoting the consumption of portlandite and the formation of Na- and K-rich aluminosilicate phases such as albite and muscovite. The control mixture exhibited the highest compressive strength values, whereas increasing POFA content reduced both strength and density due to calcium dilution, lower gel compactness, and increased porosity. Nevertheless, all mixtures exhibited progressive strength development over time, indicating continued hydration and geopolymerization reactions associated with the formation of hybrid C–(N,K)–A–S–H gels. These findings demonstrate that POFA can effectively participate in alkali-activated hybrid binders when applied at controlled replacement levels, highlighting its potential as a sustainable supplementary material for lower-carbon cementitious systems. Full article

The use of iron tailing powder (ITP) and granulated blast-furnace slag (GBFS) offers a feasible route for preparing low-cement mortar while recycling industrial by-products. In this study, seven cement mortar mixtures were designed to investigate the influence of the ITP–GBFS ratio on mechanical properties, microstructure, hydration products, and chloride ion penetration resistance. The mixtures included plain cement mortar (A0), mortar with 50% ITP (A1), mortar with 50% GBFS (A2), and four composite mixtures (A3–A6) in which ITP and GBFS jointly replaced 50% of cement at different ratios. The results showed that the mixture containing 20% ITP and 30% GBFS (A4) exhibited the best overall performance among the composite mixtures. At 28 d, A4 reached a compressive strength of 51.3 MPa and a flexural strength of 11.0 MPa, exceeding those of the plain cement control. SEM and XRD analyses suggested that the optimized ITP–GBFS combination promoted the formation of poorly crystalline hydration products, such as C–S–H/C–A–S–H gels, and refined the pore structure, resulting in a denser hardened matrix. The rapid chloride migration test showed that the chloride migration coefficient of A4 was 15.47 × 10⁻¹² m²/s, only slightly higher than that of A0, indicating that the optimized composite binder maintained chloride penetration resistance close to that of plain cement mortar while replacing 50% of cement. The results indicate that a properly proportioned ITP–GBFS binder can maintain acceptable strength and chloride resistance while reducing cement consumption. Full article