The global industrial challenges of massive phosphogypsum (PG) stockpiles, persistent under-utilization, and inferior water resistance of conventional gypsum-based materials necessite innovative recycling strategies. Herein, we engineered a phosphogypsum-based composite binders (PBCB) by coupling ground-granulated blast furnace slag (GGBS) and carbide slag (CS) with anhydrous PG (APG) and (3-hemihydrate PG ((3-HPG). The compressive strength and water resistance of PBCB under air curing and water curing were investigated at 180d. Its phase composition, hydration process, pore structure, and microstructure were explored, followed by an evaluation of its environmental and economic benefits. Results showed that the combination of APG and (3-HPG can significantly shortened the setting time of PBCB. Under the synergistic effect of hydration products, the mixture of 70 % APG/10 % (3-HPG and 18 % GGBS/2 % CS shows the best performance. After 180d of air curing and water curing, the compressive strength and softening coefficient are 44.5 MPa, 0.83 and 41.9 MPa, 0.89, respectively. Notably, under water curing, the compressive strength decreases by only 4.17 %-10.32 %, while the softening coefficient increases by 6.74 %-12.64 %. In addition, the carbon emissions per unit strength and cost per unit strength are only 21.0 % and 35.7 % of those of ordinary Portland cement, respectively. This work establishes a viable technical pathway for transforming hazardous PG stockpiles (>80 million tons/year globally) into low-carbon sustainable binders.

This study decouples the Joule heating and non-thermal effects of alternating-current (AC) direct electric curing (DEC) on cement pastes under isothermal conditions. Cement pastes were precured for 1 h and then subjected to AC electric field of 1-2 V/cm. Isothermal calorimetry reveals that DEC markedly amplifies peak rates of heat flow and elevates the 72-h cumulative heat by 46.8-66.3% at 1 V/cm and to 228.5-260.0% at 2 V/cm. DEC-induced heat accumulates preferentially at early ages and then attenuates as resistivity increases. After excluding electric heating, results from solid phases, solution chemistry, porosity and micro-mechanical properties reveal negligible differences between DEC and reference samples, indicating an insignificant non-thermal effect under AC electric field. In addition, a hydration-based electrothermal model was developed that accurately describes the Joule effect of cement pastes, providing a quantitative basis for optimizing DEC protocols.

Phosphogypsum-based cold bonded aggregates (PCBAs) provide a large-scale application method for phosphogypsum. However, the soluble sulfates in the aggregates can induce internal sulfate attack (ISA) in concrete, which severely limits their engineering applications. In this study, carbonation treatment was employed to modify the surface of PCBAs, with two carbonation regimens designed: carbonation immediately after forming aggregates (CPCAs-1d) and carbonation after 7 days of curing aggregates (CPCAs-7d). The microstructural characteristics of the carbonated aggregates and the Interfacial Transition Zone (ITZ) of the lightweight aggregate concrete were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), scanning electron microscopy- energy dispersive spectrometer (SEM-EDS), nitrogen adsorption (NAD), ion leaching tests, backscatter electron (BSE) analysis and microhardness testing. The results indicate that carbonation treatment can reduce the sulfate leaching concentration in the aggregate by approximately 25%. Specifically, CPCAs-7d forms a dense and continuous CaCO3 shell on the surface, effectively enclosing open pores and blocking interconnected channels, thereby inhibiting the migration of internal sulfates to the external environment. In contrast, in CPCAs-1d, CO2 inhibits the formation of hydration products by disrupting the alkaline environment of the system, resulting in a loose structure, and its cylinder compressive strength decreased by up to 58.36% compared to that of uncarbonated aggregates. In addition, the compressive strength of carbonated aggregate concrete was 7.0% higher than that of uncarbonated aggregate concrete. Its ITZ was more compact and harder, and the sulfur content at the interface was significantly reduced, which to some extent suppressed the formation of ISA at the interface. This study provides an effective surface modification strategy for the safe utilization of high-sulfur gypsum-based aggregates.

This study develops a three-dimensional Gaussian mixture model (3D-GMM) framework and corresponding nanoindentation loading protocols for gel-phase creep characterization in fly ash-based geopolymers. The optimal cluster number of 3D-GMM was found to be 4, enabling the identification of the gel phase, which is characterized by an by an elastic modulus (E) of 14-19 GPa, hardness (H) of 0.6-0.7 GPa, and creep modulus (C) of 140-230 GPa in this study. A clear correlation among E, H, and C is revealed by the correlation analysis, indicating coupled elastic, plastic, and viscoelastic responses that likely originate from a common microstructural mechanism. Backscattered electron imaging analysis confirms the accuracy of the 3D-GMM phase identification, with gel-phase fractions showing good agreement with image-based estimates . Further analysis reveals that a holding duration of 180 s provides a balance between stable results and minimized environmental noise. A holding load of 10 mN offers a suitable compromise between bulk representativeness and substrate effects, whereas 2 mN is more appropriate for probing isolated gel phases. Based on these findings, a standardized nanoindentation workflow is proposed, integrating parameter selection, data quality control, 3D-GMM deconvolution, statistical analysis, and microstructural validation. This framework improves the robustness of nanoindentation data and provides a systematic methodology for characterizing heterogeneous geopolymer systems.

To enhance the service stability of concrete suffering from a low vacuum environment, the effects of silica fume (SF), redispersible latex powder (RDP), and polyethylene fibers (PEF) on concrete strength and permeability were investigated, and the potential mechanisms were analyzed. Results indicated that SF-enhanced concrete demonstrated a higher strength compared to reference concrete. However, the enhancements from SF may be diminished under prolonged low vacuum conditioning, potentially due to the more significant shrinkage induced by such environments. Although the addition of RDP reduced the compressive strength of concrete, it enhanced the flexural strength and reduced gas permeability. Particularly after low vacuum treatment, the flexural strength increased by 27.4% due to accelerated polymer film formation caused by rapid water loss. The addition of PEF enhanced both the compressive and flexural strength of concrete. However, after low vacuum treatment, a notable reduction in the toughness of PEF-reinforced concrete was observed, primarily attributed to the low vacuum environment diminishing the strain-hardening behaviors. The effectiveness of conventional methods for enhancing concrete performance would be altered in a low vacuum environment. Therefore, it is essential to consider these alterations when developing enhancement techniques for concrete under such conditions.

Micro-steel fiber reinforced ultra high strength concrete (MSFRHSC) has been extensively utilized in protective structural engineering due to its enhanced mechanical properties. The addition of steel fibers effectively alleviates the intrinsic brittleness of concrete while simultaneously improving compressive strength and fracture energy. This study investigates the anti-penetration performance of MSFRHSC through experimental and numerical approaches. MSFRHSC specimens with optimized mix ratios were prepared, achieving compressive strengths of up to 150 MPa. A series of penetration tests were conducted using W18Cr4V high-speed steel projectiles launched via a gas gun at three typical design impact velocities of 480 m/s, 650 m/s, and 770 m/s. The morphological characteristics of the penetration trajectory, the damage characteristics and the relationship between projectile velocity and target penetration depth was obtained and analyzed. Then, finite element simulations were conducted with Holmquist-Johnson-Cook (HJC) constitutive model representing the MSFRHSC material. The simulated penetration depths and damage morphologies showed good agreement with the experimental results. The high-speed penetration process and penetration mechanism of MSFRHSC were obtained and analyzed. In addition, a comparative analysis was conducted on the penetration resistance of MSFRHSC with different fiber content and the same strength plain concrete, revealing the influence pattern by which the addition of steel fibers enhances the toughness of concrete and thereby improves its penetration resistance. Finally, parametrical analysis were conducted, an empirical function relating penetration depth to impact velocities (300 similar to 800 m/s) was derived. The findings provide valuable insights for the application of MSFRHSC in impact-resistant structures and offer a reliable reference for finite element modeling of projectile penetration.

Subzero curing severely restricts the hydration and early performance development of cement-based repair materials. This study compares the age-dependent effects of NaNO₂, Li₂CO₃, and Ca(HCOO)₂ on the setting time, mechanical properties, interfacial properties, hydration behavior, and microstructure of CSA–PC repair mortars at -10 °C. Based on the overall performance, Na-2, Li-0.15, and Ca-1 were identified as the preferred mixtures. At 6 h, Li-0.15 increased the interfacial flexural and tensile bond strengths by 174.5% and 147.6%, respectively, and exhibited the highest engineering performance. Na-2 showed the most sustained strength development and slightly surpassed Li-0.15 at 28 d, whereas Ca-1 exhibited limited subsequent strength growth. XRD and TG/DTG results showed that all three salts promoted hydrate formation without altering the principal crystalline phase assemblage. Li-0.15 exhibited the highest chemically bound water contents at 6 h and 7 d, reaching 17.6% and 19.3%, respectively, whereas Na-2 showed the greatest increase over this period. SEM and N₂ adsorption–desorption results showed that Li-0.15 developed the densest AFt network and the lowest cumulative pore volume by 6 h. Na-2 exhibited the greatest pore refinement and microstructural densification from 6 h to 7 d, while Ca-1 showed limited further densification. These findings provide a basis for selecting inorganic salt admixtures to balance rapid hardening and sustained performance development in CSA–PC repair materials under subzero conditions.

In this study, the two critical aspects of nanoindentation techniques-deconvolution methods and loading parameters-for characterizing sodium aluminosilicate hydrate (N-A-S-H) in fly ash based geopolymers were experimentally investigated. Three prevailing deconvolution methods, i.e., Gaussian Mixture Models (GMM), Probability Density Functions (PDF), and Cumulative Distribution Functions (CDF), are employed to separate the gel phase and capture its micromechanical properties and proportions. Meanwhile, novel indicators were introduced to assess the effectiveness of deconvolution models. The optimal number of phases (K) was determined using information-theoretic and clustering quality metrics, including the Bayesian Information Criterion, silhouette coefficient, and Calinski-Harabasz index. Furthermore, the Bin Size Index was utilized to optimize the bin size for PDF models, ensuring robust histogram representation. Results indicate that the GMM demonstrates superior fitting quality when the optimal K is 6. The PDF model demonstrated optimal performance under K = 4, with bin sizes of 2.0 GPa and 0.15 GPa for elastic modulus and hardness, respectively. The CDF model achieved an optimal balance between model complexity and fitting accuracy at K = 4. Furthermore, comparative analysis reveals that GMM is superior in clustering capability among the other two deconvolution methods. By utilizing this method, the influences of loading parameters on test results were further studied. It was found that the increase in the holding load leads to a decrease in elastic modulus and hardness with a more concentrated distribution and an increased gel phase proportion, but overlooks local microstructural characteristics. Extended holding times induce creep deformation, creating larger indentation areas that underestimate hardness and affect unloading analyses. A power function relationship exists between mechanical properties and indentation depth, with holding load exerting significantly greater influence than holding time on penetration depth. Based on a comprehensive evaluation of indentation depth, model accuracy, and microstructural preservation, a loading regime of 5 mN for 10 s was identified as optimal for N-A-S-H gel characterization.

The low-vacuum, pressure-cycling, and strong magnetic field environment of vacuum-tube maglev systems presents considerable challenges for structural material design. This study develops a class of low-vacuum tube concrete (LVTC) featuring high strength, high toughness, and low magnetic susceptibility, based on dense particle packing, polymer modification, and fiber reinforcement principles. The effects of atmospheric drying (AD), continuous low-vacuum drying (VD), and cyclic low-vacuum/atmospheric drying (CD) on the macro-micro properties of LVTC were systematically investigated. The results show that low-vacuum conditions increase the brittleness and shrinkage of concrete. The addition of redispersible latex powder and modified emulsified asphalt was effective in mitigating brittleness, reducing shrinkage, and decreasing impermeability. Among the tested fibers, polyethylene fibers significantly outperformed basalt and glass fibers in enhancing mechanical performance under vacuum exposure. CD exhibited intermediate effects on strength, moisture migration, and pore structure compared to AD and VD, primarily influenced by vacuum exposure duration. SEM analysis revealed that the viscoelastic fiber-flexible film-matrix network plays a key role in suppressing vacuum-induced shrinkage cracking. Magnetic induction tests confirmed that all constituent materials are weakly magnetic (<30 nT), and the incorporation of silica fume and polymers further reduces magnetic susceptibility. These findings provide a scientific basis for the design of LVTC, supporting the development of next-generation high-speed vacuum maglev infrastructure.

The stacking voidage of coarse aggregate is a key parameter influencing the performance of concrete. However, its governing mechanisms related to particle morphology, gradation, and the sidewall effect remain unclear. This study aims to clarify how these three factors affect stacking voidage and to identify pathways for its reduction. Real aggregate models were reconstructed using image analysis techniques (AIMS and laser scanning), and the packing process of coarse aggregates in a cubic mold was simulated using the Discrete Element Method (DEM). In addition, a three-graded mixing experiment with real coarse aggregates was conducted to investigate the effect of gradation on the stacking voidage. The results show that stacking voidage consists of a basic component (PS) and two additional components (PW, PG). PS is primarily determined by aggregate morphology, with sphericity and angularity as the main influencing factors. PW represents the increased voidage caused by the container sidewall effect, while PG denotes the reduction in voidage due to aggregate gradation. The greater the particle size difference between aggregates, the larger the decrease in PG. In concrete columns up to 1000 mm, the contributions of morphology, gradation, and the sidewall effect to overall voidage were 57.17

To address the issues such as poor cementitious properties, insufficient water resistance, and brittle fracture behavior encountered when using phosphogypsum in building materials, as well as to fill the gap concerning the interaction mechanism between polypropylene fibers and the phosphogypsum-slag system, this study prepared polypropylene fiber-reinforced phosphogypsum slag concrete (PF-PSC) in an alkaline environment. The performance and hydration mechanism of PF-PSC were then evaluated through macroscopic property tests and microscopic characterization. The results indicated that when GBFS content was 40% and PF content ranged from 0.1% to 0.3%, the cubic compressive strength at 28 d reached 78.9 MPa, meeting the C60 strength grade. Compared with the reference group, the splitting tensile strength and flexural strength increased by 27.1% and 66.7%, respectively. The softening coefficient rose to 0.93, the gas permeability coefficient decreased to as low as 1.53 & times; 10(-18 )m(2) (close to UHPC), and the chloride migration coefficient significantly decreased. The established chloride diffusion model showed good accuracy. Microscopically, the C-S-H and ettringite formed by the hydration reaction of GBFS, combined with the bridging effect of PF, a dense 'gel bonding-fiber crack resistance' microstructure was formed. The proportion of harmless pores (<10 nm) reached 19.1%, and the total porosity decreased to 6.06%. Environmental-economic assessments demonstrated that the carbon emission per cubic meter of PF-PSC was reduced by over 31% compared with traditional C60 OPC concrete, while the cost was lowered by 42%. This study could provide theoretical support for the high-value utilization of phosphogypsum and the development of green concrete.

Turning electrolytic manganese residue (EMR) into circular construction materials kills two birds with one stone: sustainable EMR valorization and alleviating construction resource scarcity. Herein, we fabricate a green concrete synergizing EMR with fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBFS), focusing on strength and gas permeability under low vacuum. Results indicate that GGBFS-EMR synergy achieves a performance index of 4.71 kg CO2-eq/MPa & sdot;m3, balancing strength, low-carbon efficiency, and costeffectiveness. Strength of EMR-compounded concrete increases initially before declining over the duration of low vacuum. A standard curing (SC) followed by low-vacuum curing (LVC) treatment reduces per unit strength carbon emissions and gas permeability coefficient by 33.3-76.9 % versus 56d SC, while SF enhances strength across all EMR ratios of 10-30 %. GGBFS supplementation further amplifies strength gains over equivalent EMR proportions. The gas permeability coefficient evolves with time and correlates linearly with mass loss rate, enabling permeability prediction based on mass loss behavior. Combined standard and low vacuum curing ensures Mn and NH3-N compliance with regulatory limits. This approach combines EMR's cost efficiency with GGBFS reactivity to mitigate regional FA scarcity, creating a sustainable circular system balancing ecological, mechanical, and economic criteria. Though demonstrating industrial viability and waste valorization potential, this preliminary study highlights remaining limitations in the engineering complexities of scaling low-vacuum treatment with precise cost accounting-fundamental barriers requiring resolution before commercial scaling.

The vibration reduction performance of metaconcrete is primarily attributed to the bandgap characteristics of its cells. The width and number of bandgaps determine the operational frequency range and the effectiveness of vibration reduction in metaconcrete. To address this, a dual-resonant metaconcrete is proposed in this paper. Specifically, a metal shell and a flexible soft coating are added to the exterior of the original soft coating of the resonant aggregate, transforming the resonant aggregate from a single-degree-of-freedom system into a two-degree-of-freedom system. This design further broadens the operational frequency range of metaconcrete and enhances its vibration reduction performance. In this study, an analytical model of a metaconcrete cell containing dual-resonant aggregates was established. Subsequently, the finite-element method was used to analyze the band structure, vibration modes, and energy distribution characteristics, with a focus on the bandgap characteristics of dual-resonant metaconcrete cell. To further refine the analysis, bandgap influencing factors were selected using the equivalent model method, and the influence of design parameters on the bandgap was investigated. Building upon this, an analytical model of a dual-resonant metaconcrete, composed of 12 longitudinally arranged cells, was developed. Finally, the frequency response function, time-domain characteristics, and energy flow properties of the dual-resonant metaconcrete were analyzed. The results showed that the proposed dual-resonant metaconcrete cell can generate two bandgaps, with the starting and cutoff frequencies of these bandgaps determined by the vibration modes of Resonator I, Resonator II, and the matrix. Furthermore, the elastic modulus, Poisson's ratio, and thickness of the soft coating were identified as the key factors influencing the bandgap characteristics. The vibration reduction performance of the dual-resonant metaconcrete was demonstrated within both bandgaps. When the excitation frequency was within the bandgap, the vibration directions of the resonators and the matrix were opposite, and the superposition of these reverse vibrations resulted in a reduction of vibration at the output end. Energy was continuously converted between the kinetic energy of the resonator and the elastic strain energy of the soft coating. Under these conditions, the dual-resonant metaconcrete was shown to behave similarly to a filter, exhibiting significant filtering characteristics and energy localization. As a result, the propagation of elastic waves was shielded, achieving effective attenuation.

To enhance the service performance of concrete materials used in low vacuum pipeline engineering, two types of polymer fibers (polyethylene and polypropylene) were employed to design high-performance concrete. A comparative analysis was conducted on their flexural performance and moisture loss behavior under atmospheric drying (AD) and low vacuum drying (VD) conditions. The results indicate that while the strain hardening behavior of polyethylene fiber-reinforced concrete improves under VD, its flexural toughness decreases. In contrast, polypropylene fiber-reinforced concrete exhibits increased brittleness and reduced flexural capacity. Increasing fiber content can enhance the concrete’s flexural behavior; however, using coarse aggregates positively affects polyethylene fiber-reinforced concrete but adversely impacts polypropylene fiber-reinforced concrete. Mass loss tests reveal that the mass loss rate and the area of the drying region on fracture surfaces under VD can exceed 1.6 times and 1.4 times that under AD, respectively. For polyethylene fiber-reinforced concrete, simultaneous increases in fiber content and the use of coarse aggregates can mitigate moisture loss. Conversely, in polypropylene fiber-reinforced concrete, fibers significantly aid in moisture retention, while coarse aggregates lead to increased moisture loss rates. Overall, polyethylene fiber-reinforced concrete outperforms polypropylene fiber-reinforced concrete in terms of flexural capacity and moisture retention, making it a potential candidate for designing high-stability concrete for low vacuum pipelines, though enhancements in the fiber-aggregate network structure are necessary.

Concrete in the coastal environments suffers from coupled effects of chloride erosion, sulfate erosion, freeze-thaw deterioration, etc., resulting in a significant reduction in durability and an increase in construction and maintenance costs. Surface protection technology protects concrete from environmental erosion, serving as an important method to improve the service lifetime of coastal concrete. And it promotes the development of sustainable and low-carbon concrete materials. Therefore, the research progress on surface protection techniques for enhancing concrete durability in the coastal environment is reviewed systematically in this paper. First of all, the different erosion types and regional differences of concrete were briefly summarized. And the protection mechanisms and engineering applicability of various coatings have also been analyzed. The protection technologies can be categorized into three main types: organic protection technology, such as organic protective coatings; inorganic protective technologies, encompassing traditional inorganic protective coatings, geopolymer-based protective coatings, microbially induced protection technology, and carbonation protective coatings; organic and inorganic composite coatings, including coatings modified by nanomaterials, superhydrophobic coatings, and self-repairing coatings. Surface protection is more economical than the overall strengthening of concrete. Moreover, currently more advanced protection technologies such as protective layer reinforcement, multifunctional protective layer protection, and fiber mesh reinforcement protection have further enhanced the protective performance. Overall, surface protection technologies function by means of dense filling, obstructing function, and energy conversion. This paper provides valuable information for durability enhancement and sustainable development of coastal concrete by presenting an outlook on the development of concrete surface protection technology. Future research should focus on the multi-factor coupled environment, the development of intelligent coatings, and a standardized future research process.

Molybdenum tailings are the solid waste left from ore processing, which damages soil and water resources. To address that, molybdenum tailings (MTs) powder obtained from molybdenum tailings sands was processed as an admixture. Compared with moisture-cured conditions, the influence of MTs on the steam-cured mortar's mechanical properties, surface and internal pore characteristics, and microscopic morphology was investigated. The results show that steam-cured mortar containing appropriate MTs can still have high early strength. When the content of MTs doesn't exceed 15%, the mechanical strength of mortar steam-cured for 3 d can reach 85% of that of corresponding mortar moisture-cured for 28 d, and that of mortar steam-cured for 28 d isn't lower than 90% of that of pure cement mortar. The proportion of harmful pores (HFP) and more harmful pores (MHFP) and most probable pore diameters (MPD) on the mortar surface containing MTs steam-cured for 28 d are significantly decreased. When MTs' content is 15%, the proportion of HFP and MHFP on the surface of paste is decreased by 71.4% and 72.2%, respectively, with MPS decreasing from 12.7 nm to 10.8 nm. SEM analysis shows that the surfaces of steam-cured paste containing 15% MTs have more hydration products and dense microstructures. The effect of pozzolanic and dense filling of MTs effectively refines the pore structure, reducing the large pore-size pores.

Understanding and predicting the creep behavior of fly ash-based geopolymer pastes (FAGPs) requires a quantitative linkage between phase-specific micromechanics and macroscopic deformation. However, such a linkage remains unclear due to the complex heterogeneous microstructure and the lack of reliable multiscale characterization frameworks. In this study, a multiscale experimental-modeling approach was developed to bridge phase-level creep properties with macroscopic creep behavior in FAGPs with varying Si/Al and Na/Al ratios. Nanoindentation combined with three-dimensional Gaussian mixture model deconvolution was employed to quantify the creep modulus and volume fractions of individual phases, while microindentation tests were conducted to provide intermediate-scale validation. The results reveal that the geopolymer gel acts as the primary load-bearing phase, exhibiting creep moduli in the range of 100-160 GPa and strong sensitivity to mixture composition. In contrast to conventional homogenization models that neglect the interfacial transition zone (ITZ) and assume time-independent pore behavior, an enhanced framework is established by explicitly incorporating the interfacial transition zone and time-dependent pore compliance. Sensitivity analysis demonstrates that the ITZ exerts a dominant influence on the overall creep response, exceeding that of pore-related effects. Compared with conventional Mori-Tanaka-based homogenization models, the proposed framework significantly improves creep prediction accuracy and captures the scale-dependent discrepancy between nano/micro-indentation and macroscopic creep responses. This enhanced multiscale model provides a quantitative framework for linking phase-specific creep behavior to macroscopic deformation in FAGPs, highlighting the coupled roles of gel viscoelasticity, ITZ compliance, and pore structure in governing multiscale creep.

Herein, this work proposes a dual-layer high-performance coating comprising a silica fume and epoxy putty primer and a topcoat of tetraethyl orthosilicate (TEOS) and silane co-modified acrylic polyurethane (APS) or polyurea (PS). We systematically examine the effects of modified components (TEOS, silane, sodium silicate, and silica sol) and the TEOS: silane ratio (10:1, 6:1, 4:1, 6:5, 6:3) on wettability, adhesion, abrasion resistance, and impermeability through rapid chloride permeability test (RCPT), TG, XRD, and N-2 adsorption analyses. Results indicate that the topcoating exhibits a contact angle >= 98 degrees, reaching 110-120 degrees for silicon-containing system. In APS system, the 4:1 TEOS: silane ratio is optimal for abrasion resistance with the ten cycles weight loss of similar to 0.04 g, capillary water uptake (approximate to 1.2 mm at 700 s(1/2), approximate to 78% lower than the control), and significantly reduced electric flux, followed by the 10:1 ratio. Higher silane ratios (6:5, 6:3) display slight deterioration. Standard curing yields lower low-temperature water loss and Ca(OH)(2) dehydroxylation peaks, a weaker 650-800 degrees C carbonates decomposition peak, a smaller cumulative pore volume, and fewer pores >50 nm compared to air curing. TEOS undergoes hydrolysis-polycondensation at the coating and interface to form a Si-O-Si network and engages in a pozzolanic reaction with Ca(OH)(2). A small amount of silane facilitates molecular bridging and surface hydrophobization. This tripartite synergy blocks fine interconnected pores, reduces surface energy, and increases diffusion tortuosity. Reducing water/binder ratio to 0.3 shifts strengths upward overall and diminishes inter-formulation differences. These findings elucidate the coupling effects among formulation, processing, curing, and performance, providing replicable material and process guidance for unifying long-term protection and architectural finish on highly exposed concrete facades.

Phosphogypsum is a bulk solid waste generated during phosphoric acid production. To address its poor water resistance and frost resistance in constructional material applications, anhydrous phosphogypsum is used as the base material to design polypropylene fiber-slag modified anhydrous phosphogypsum-based concrete (PF-SPC) by varying the content of ground granulated blast furnace slag (GBFS) from 20 to 40

Flexural properties are crucial for concrete as they determine the stability and durability of concrete structures. Understanding the influences of interfacial transition zone (ITZ) properties and aggregate strength on flexural behavior is essential, as the ITZ governs crack initiation, and aggregates affect stress distribution. In this study, a 3D mesoscale concrete model was developed, in which aggregates were efficiently generated using the Quickhull algorithm. This geometry-based approach enables the rapid construction of irregular polyhedral aggregates with morphological features that resemble those of real coarse aggregates. The Linear parallel bond model (LPBM) was employed to simulate bonding behaviors, due to its advantages in capturing crack initiation and propagation in concrete. On this basis, the effects of ITZ properties and aggregate strength on the mechanical response and failure mechanism of concrete were analyzed under four-point flexural load. The results show that increasing the ITZ strength enhances the displacement and flexural strength of concrete, shifting the weak part from the ITZ to the mortar. A higher elastic modulus of ITZ (EITZ) increases stiffness while reducing flexural strength of concrete. In contrast, aggregate strength has a limited effect on flexural strength, increasing it by only 15%, but transforms crack paths toward the ITZ. Moreover, low-strength ITZ, high EITZ, and weak aggregates induce localized stress concentrations and crack clustering beneath the loading point. Improving ITZ and aggregate strength increase the contact force volume and peak contact force of the corresponding components, while the enhanced EITZ is the opposite.