Limestone calcined clay cement (LC3) offers a promising binder for reducing clinker in concrete; however, its compressive strength is influenced by both binder chemistry and mix proportions. Although many studies have investigated LC3, an integrated approach that combines machine learning prediction, optimization, and experimental validation for mix design is still limited. This study proposes a metaheuristic-assisted machine learning based framework to predict the compressive strength of LC3 concrete, and to identify an optimal mix design. The optimized mix was then subjected to preliminary experimental validation. A literature database of 172 LC3 concrete mixtures compiled from 42 published studies was used, with 19 input variables describing oxide compositions of Ordinary Portland cement (OPC), calcined clay (CC), and limestone powder (LSP), together with key mix parameters. Four ensemble learners (CatBoost, XGBoost, Random Forest, and LightGBM) were trained using an 80/20 train–test split. Five-fold cross-validation was applied to ensure model reliability. CatBoost provided the best generalization on the test set compared to other models studied. SHAP results revealed that the water-to-binder ratio (W/B) was the most important factor in determining strength, followed by the content of coarse aggregate (CA) content, sand-to-binder ratio (S/B), and LSP content. The trained CatBoost model was coupled with a Grey Wolf Optimizer (GWO) to obtain a feasible optimal combination. The strength was predicted to be 57.21MPa. The average strength of 100mm cubes was 51.54MPa with standard deviation of 0.21MPa. The proposed framework has the potential to be used for data-driven design of LC3 concretes.
The precast concrete (PC) pile reinforced with cemented soil (PCCS) is a novel composite pile system, formed by installing a PC pile into the centre of a deep mixing (DM) column. This technology has been extensively applied to support highways, railways and buildings constructed on soft soil foundation. However, PCCSs with short cores often struggle to penetrate deep enough to reach stronger bearing strata within thick soft subsoil layers, leading to inadequate reinforcement and poor settlement control. To address these limitations, this study proposes the use of a PCCS with long-core as a promising solution for reinforcing deep soft soil subgrades. Based on the field tests results, the bearing mechanism and performance of the long-core PCCS composite foundation under embankment loads were investigated through numerical analysis. Additionally, the soil arching effect in embankments supported by the PCCS with long-core, along with variations in vertical stress and horizontal soil pressure coefficients along the height of the embankment were elucidated. The results indicate that the stabilized stresses at the pile top and in the surrounding soil are 266.2 kPa and 33 kPa, respectively, yielding a stabilized pile-to-soil stress ratio of 8.1. The critical height of the embankment corresponds to 1.15 times the net pile spacing. Maximum settlements observed at the pile tops and the surrounding soil were 15.2mm and 47.5mm, respectively. The tensile stress within the geocell exhibited a symmetric, repetitive pattern along the horizontal direction, with the peak tensile force occurring near the embankment shoulder. These findings underscore the effectiveness of long-core PCCSs in enhancing load-bearing capacity and controlling settlement over soft soil foundations.
This study investigates the effects of high temperature and different cooling methods on the dynamic mechanical properties of basalt fiber‑reinforced concrete (BFRC). Concrete specimens with different basalt fiber contents such as 0%, 0.1%, and 0.2% by volume were first heat‑treated at elevated temperatures including 200°C, 400°C, 600°C, and 800°C and then cooled either naturally in air or by water immersion. Dynamic compression tests were subsequently carried out on using a split Hopkinson pressure bar apparatus. Combined with microstructural characterization, the deterioration mechanism of concrete performance caused by high temperature was analyzed. The results show that high temperature degrades the macroscopic appearance and internal structure of concrete, leading to decomposition of hydration products, generation of cracks and pores, and thus a reduction in peak stress. Quantitatively, the peak stress of naturally‑cooled specimens decreases by approximately 6.7%-8.0% per 100 °C rise within the range of 25°C-800 °C; while water‑cooled specimens exhibit a more severe reduction of about 7.5%-8.1% per 100 °C. The thermal stress induced during water cooling causes more severe damage to concrete. The decrease in peak stress and the fractal dimension of post‑impact fragments are higher for water‑cooled specimens than for naturally-cooled specimens. Higher temperature and higher impact velocity lead to a greater reduction in peak stress for water‑cooled specimens. The addition of basalt fibers effectively mitigates this deterioration, with 0.2% fiber content showing the better performance. However, when the temperature exceeds 600°C, the effect of fibers gradually weakens. The findings can provide technical support for evaluating the dynamic mechanical performance of concrete under different post‑fire treatment regimes.
Glass fiber-reinforced polymer (GFRP) composites are increasingly utilized in marine infrastructure due to their high strength-to-weight ratio and corrosion resistance. A prominent application is the concrete-filled GFRP tubes (CFFTs). However, their long-term durability under prolonged seawater immersion remains insufficiently understood. This study investigates the long-term mechanical performance and service life of CFFTs in simulated seawater environments. An experimental program was conducted on 80 CFFT specimens, considering effects of matrix type (epoxy vs. vinyl ester), fiber winding angle (±60° and ±80°), immersion temperature (25 °C, 40 °C, and 60 °C) and duration (up to 540 days). Axial compression tests were also performed on CFFTs and hollow GFRP tubes, supplemented by multi-scale characterization using SEM, FTIR, and DSC. The results indicate that immersion duration and temperature significantly affect the deterioration of mechanical properties of GFRP tubes and CFFTs, with the former exerting a more pronounced influence. The Arrhenius theory was employed to develop a service-life prediction model for GFRP tubes, which was incorporated into Jiang and Teng’s model to predict the long-term mechanical performance of CFFTs. These findings provide urgently needed data, facilitating the widespread adoption of CFFTs in harsh marine engineering applications.
Thermoelectric cement-based composites (TECCs) can recover electricity from building waste heat and may help mitigate the urban heat island effect. Ten groups were investigated, including TECCs with 1.0-7.0wt.% Fe2O3 and hybrid systems containing Fe2O3 and 0.5wt.% carbon fiber. Thermoelectric, mechanical, and microstructural properties were evaluated. The Seebeck coefficient reached 0.416mV·K-1 at 5.0wt.% Fe2O3. Carbon fiber reduced electrical resistivity by over 90% and increased flexural strength by nearly 20%. Hybrid incorporation produced complementary effects, with CF0.5Fe3.0 showing the best overall performance. The ZT value reached 1.32 × 10-4, approximately 53 times higher than that of Fe3.0 with the same Fe2O3 content, while its flexural strength was 24% higher. These results demonstrate that combining Fe2O3 with carbon fiber effectively enhances both thermoelectric and mechanical performance.
Red mud (RM) has limited its application as an auxiliary cementitious material due to its high alkalinity and low pozzolanic activity. To overcome these limitations, this study investigated the modification of the RM-cement composite binder system by nano-silica (NS). The mechanical properties, microstructure, and hydration kinetics of the NS-modified RM-cement composite binder system were systematically investigated using compressive strength testing, XRD, TG, LF-NMR, BSE-SEM/EDS, and isothermal calorimetry. At a 20% RM substitution rate, the addition of 3% NS (R20N3) increased the 3-day and 28-day compressive strength by 18.06% and 12.27%, respectively, compared to the NS-free system (R20N0), while reducing the calcium hydroxide content by 1.61% and 1.98%, respectively. At 28 days, the harmless pore volume fraction increased by 5.70%. Consistent with the role of NS as a heterogeneous nucleation site, hydration kinetic analysis indicated accelerated reaction rates during the nucleation and growth and phase-boundary reaction stages. Under the adopted reference scenario, replacing 20% of PC with RM lowered the direct binder cost by 10.5% after RM transportation and milling were included, whereas the cost of R20N3 was governed mainly by the adopted price of NS. These findings indicate that NS partially offsets the strength loss caused by RM dilution and is associated with progressive microstructural refinement, revealing the hydration modification mechanism of NS-blended RM-cement binders and providing a theoretical reference for the performance optimization of RM-containing composite pastes.
Amid growing research interest in 3D printed concrete, its further development remains constrained by limitations in reinforcement strategies. While fiber reinforcement has emerged as a promising approach, single-fiber systems often yield limited mechanical improvements. This study proposes a hybrid fiber reinforcement approach that combines polypropylene fibers (PF) and steel fibers (SF) to synergistically leverage their respective advantages, thereby achieving multi-directional mechanical enhancement of 3D printed concrete. Firstly, a systematic investigation was conducted to evaluate the compressive and flexural properties of 3D printed concrete reinforced with single fiber types (either PF or SF) in multiple directions, thereby determining the optimal content for each single fiber type. Subsequently, based on these findings, the compressive and flexural performance of hybrid fiber reinforced concrete was examined. Finally, X-ray computed tomography (X-ray CT) was employed to characterize the microstructure of the fiber-reinforced 3D printed concrete, aiming to elucidate the reinforcement mechanisms of the two types of fibers. The results demonstrate that the incorporation of hybrid fibers exhibits a more pronounced enhancement effect on the compressive and flexural strength of concrete compared to single fiber reinforced 3D printed concrete. SF effectively enhance the mechanical properties along the printing direction, while PF significantly improve the weak interfacial performance between printed layers. This hybrid system achieves complementary advantages through synergistic reinforcement mechanisms.
Steel slag is a promising carbonatable cementitious material, but its heterogeneous mineral composition makes conventional full-slag grinding energy-intensive and inefficient. This study proposes a component-separation strategy that selectively isolates the easily pulverizable fraction from basic oxygen furnace (BOF) steel slag through light ball milling, and systematically compares its physicochemical properties and carbonation performance with the hard-to-grind fraction. Particle size distribution, mineral composition, pore structure, and iron valence states were characterized using laser diffraction, XRD, TG-DTG, SEM-EDS, MIP, and XPS, while carbonation reactivity was evaluated through compressive strength and CO2 uptake measurements. Results show that approximately 30wt% of steel slag is selectively converted into ultrafine powder (<75 μm) under a single low-energy milling cycle. Despite containing fewer calcium silicate minerals, the pulverizable fraction achieves a carbonation strength of 73.9MPa—1.5 times that of the hard fraction. These findings demonstrate that targeted utilization of the pulverizable component, instead of energy‑intensive grinding of the entire slag mass, has the potential to reduce grinding energy and facilitate the selective high‑value utilization of steel slag for carbonated building materials.
This study investigated the incorporation of municipal solid waste incineration bottom ash (MSWIBA) into magnesium potassium phosphate cement (MKPC) composites and evaluated the effect of expanded perlite on their properties and heavy metal immobilization. MSWIBA was added at 10–20wt.%, while expanded perlite was incorporated into selected mixtures as a lightweight porous additive. The addition of MSWIBA refined the pore structure, reduced open porosity to 9.5%, and increased compressive strength to approximately 48MPa. However, arsenic concentrations in the leachates reached 0.148–0.175mg·L⁻¹ and exceeded the regulatory limit. Expanded perlite increased open porosity to 21.9% and reduced compressive strength to 20–26MPa but substantially improved arsenic immobilization. The arsenic concentration decreased to 0.039–0.043mg·L⁻¹, thus meeting the applicable legislative requirement. The results demonstrate that expanded perlite can improve the environmental safety of MKPC composites containing MSWIBA, although at the expense of density and mechanical strength.
The incorporation of nanoparticles is one of the effective approaches for enhancing the stability of preformed foams. However, there is still no unified understanding of how hydrophilic/hydrophobic nanoparticles affect foam stability, and relevant studies have drawn conflicting conclusions. In this study, an amphoteric surfactant was employed as the foaming agent to systematically explore the influences exerted by hydrophilic and hydrophobic nano-silica on bubble properties and foamed concrete performance. The results indicate that hydrophilic nano-silica promotes thicker bubble films, a narrower bubble size distribution, and enhanced foam stability. Furthermore, ultrasonic dispersion is more conducive to the uniform dispersion of nano-silica, effectively inhibiting particle agglomeration and enhancing its interfacial activity, thereby further improving foam stability. Foamed concrete prepared with ultrasonically dispersed hydrophilic nano-silica-modified foam exhibits higher compressive strength, lower water absorption, and a more homogeneous pore structure. Hydrophilic and hydrophobic nano-silica possess average contact angles of 33.7° and 159.6°, respectively. The theoretical desorption energy of hydrophilic nano-silica is nearly nine times greater than that of hydrophobic nano-silica. The hydrophilic nano-silica with higher theoretical desorption energy promotes more uniform and stable particle adsorption on bubble interfaces, consequently boosting foam stability. Hydrophobic nano-silica mainly contributes to foam stabilization by physically restricting liquid drainage and bubble coalescence through particle accumulation at Plateau borders. Furthermore, with the increase of hydrophilic nano-silica doping, the Ca/Si ratio of the hydration products decreases from 3.67 to 2.02, indicating enhanced pozzolanic reaction and the formation of silica-rich C-S-H gel. However, excessive hydrophilic nano-silica addition increases the Ca/Si ratio to 3.37 due to nanoparticle agglomeration, which weakens the pozzolanic reaction and deteriorates the mechanical performance.
In this work, MgO-incorporated mayenite (C12A7) was synthesized to explore how curing temperature governs its hydration behavior. Hydration tests at ambient temperature, 50 °C and 80 °C were conducted, with XRD, FT-IR, TG-DTG and SEM-EDS used to characterize hydration phases and microstructural evolution. Temperature strongly dictates product assemblages: metastable C2AH8 prevails at room temperature, with minor CAH10 only emerging at 28 d, while CAH10 vanishes at 50/80 °C and stable C3AH6 forms from early hydration and converts to hydrotalcite; MgO is nearly fully consumed after 14 d at 80 °C. Higher temperatures strengthen FTIR and thermogravimetric signatures of hydrotalcite, and boost Mg2+ leaching to corrode C3AH6, producing Ca–Mg–Al ternary hydrates and low-calcium rose-petal hydrotalcite aggregates. The hydration sequence is: C12A7 hydrates into metastable CAH10/C2AH8, which transform to C3AH6; dissolved Mg2+ then forms hydrotalcite. Elevated temperatures speed up both metastable phase conversion and Mg2+ erosion. This work reveals the coupled regulating effect of temperature and Mg2+ on aluminate hydrate evolution, offering theoretical support for tuning hydration of quick-setting aluminate minerals.
The internal curing performance of superabsorbent polymers (SAPs) in cement-based materials is strongly governed by their chemical composition and water-regulation behavior. Hydrophilic monomers determine the type and interactions of hydrophilic groups in SAPs, thereby regulating their water absorption, ion sensitivity, and water desorption. In this study, a series of starch-based SAPs were synthesized using varying proportions of acrylic acid, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as monomers to elucidate how hydrophilic monomer composition influences SAP performance and internal curing efficiency. The results show that acrylic-acid-derived carboxyl groups enhance the water absorption of SAPs in deionized water, but their complexation with Ca2+ leads to a significant decrease in water absorption in cement slurry filtrate. Acrylamide-derived amide groups help improve the absorption stability of SAPs under ionic interference, whereas AMPS-derived grafted units provide sulfonate-dominated ionic swelling. The carboxyl group exhibits the highest sensitivity to variations in water-to-cement ratio (w/c) or solution alkalinity, followed by sulfonate and amide groups. Under sealed conditions and at the same entrained w/c, the starch-based SAP synthesized from 70wt% acrylamide and 30wt% AMPS mitigated the autogenous shrinkage of cement paste by 95.1% relative to the reference paste at 7 days, while retaining 96.3% of the reference paste compressive strength at 28 days.
This study investigates the chemo-mechanical effects of untreated and nitric acid-treated biochar on the compressive strength and cesium immobilization of ordinary Portland cement matrices. Untreated biochar contributed to pore refinement and enhanced the 28-day compressive strength up to 52.22MPa, corresponding to a 24.3% increase. Conversely, acid functionalization amplified the biochar's negative surface charge without altering its crystalline structure. This surface modification increased the negative surface charge of the biochar, which may have promoted interactions with mobile cesium ions. Consequently, the 4% acid-treated biochar mixture exhibited the lowest 90-day cumulative fraction leached, representing a 6.1% reduction compared with the reference. Overall, this study reveals a distinct chemo-mechanical trade-off in biochar-blended cementitious systems. Untreated biochar predominantly contributed to matrix refinement and mechanical integrity, whereas acid functionalization increased the negative surface charge and promoted interactions with mobile Cs+. These findings suggest that targeted surface modification of biochar can be utilized to balance structural stability and radionuclide retention in cementitious waste forms, with the 4% acid-treated biochar demonstrating the lowest CFL within the tested dosage range.
Cemented tailings backfill (CTB) is widely used in underground mining; however, its fracture behavior under complex stress conditions remains a critical issue for structural stability. Incorporating waste rubber particles can improve deformation tolerance and energy dissipation, but the mixed mode I/III fracture mechanism of rubber-modified CTB remains unclear. In this study, Edge-Notched Disc Bend (ENDB) tests were conducted to investigate the mixed mode I/III fracture behavior of rubber-cemented tailings backfill (R-CTB). Rubber particles with different sizes (20–100 mesh) were introduced by replacing 10% of tailings, and specimens with loading angles of 0°–62.5° were tested. Mechanical testing, three-dimensional fracture morphology analysis, fractal characterization, and scanning electron microscopy (SEM) were combined to reveal the fracture mechanisms. The results demonstrate that loading angle is the dominant factor controlling the fracture response of R-CTB. The peak load continuously increases with increasing mode III contribution, whereas effective fracture toughness reaches a maximum at approximately 10° and then decreases due to fracture mode transition. Coarse rubber particles enhance fracture resistance by promoting crack deflection and energy dissipation, while fine particles introduce more rubber–matrix interfaces and weak interfacial transition zones, facilitating crack initiation. Increasing mode III tearing increases fracture surface roughness, fractal dimension, and fracture work, indicating more complex crack propagation involving deflection, branching, and out-of-plane tearing. This study establishes the relationship between rubber particle size, mixed mode I/III fracture behavior, fracture morphology, and interfacial evolution, providing new insights into the optimization of rubber-modified CTB for underground mining applications.
To promote the high-value utilization of untreated phosphogypsum (PG) and improve the suitability of backfilling materials for complex underground conditions, an all-solid-waste cementitious system was prepared using PG, phosphorus slag, red mud, and quicklime. Four curing regimes, including standard curing (SC), 35 °C constant-humidity curing (HC), water-bath curing (WC), and natural curing (NC), were adopted to simulate typical service environments of mine backfill. The effects of curing condition and mixture proportion on strength development, dimensional stability, pore-structure evolution, and hazardous-element leaching were systematically evaluated through compressive-strength, mass-loss, and volume-change tests, together with XRD, FTIR, SEM-EDS, mercury intrusion porosimetry, fractal analysis, pH measurement, and leaching tests. The results showed that curing environment was the dominant factor controlling material performance. Compared with SC and NC, HC and WC more effectively reduced mass loss and volumetric shrinkage and promoted later-age strength development. Among all mixtures, A2 exhibited the best overall performance, with 28 d compressive strengths of 4.86, 5.92, 5.30, and 4.66MPa under SC, HC, WC, and NC, respectively. Microstructural analyses indicated that the continuous formation of AFt and C-(A)-S-H gel refined the pore structure and densified the matrix, with HC producing the most compact microstructure. In addition, the leaching concentrations of P, F, and heavy metals generally followed the order HC < WC < SC < NC. These findings indicate that the PG-based clinker-free system shows considerable potential for mine backfilling under simulated high-geothermal and water-rich curing conditions
Traffic tunnels present acoustic challenges because confined geometry and reflective boundaries cause severe reverberation and impair emergency public address systems. Conventional sound-absorbing materials are constrained by tunnel fire safety and durability requirements. Although coal-based porous ceramics offer fire resistance and mechanical strength, their field acoustic effectiveness remains insufficiently validated. This paper assesses coal-based porous ceramics in a 145m operational traffic tunnel (8.0m wide, 5.0m high) using impedance-tube characterization, reverberation-room measurements, field tests, and validated numerical simulations. Field measurements in the untreated tunnel revealed the spatially averaged overall speech transmission index (STI) around 0.34 (“Poor”) and the per-band modulation transfer index (MTI) as low as 0.18 at 500Hz. After treatment, the 100-5000Hz band-averaged reverberation time (RT) was reduced by approximately 5.2s. The sound pressure level at 500Hz decreased by approximately 11-14dB at 100m from the source, while the spatially averaged RT along the tunnel axis was reduced from 8-9s to about 1.2s; the spatially averaged overall STI increased to approximately 0.63 (“Good”); and the 500Hz MTI rose to approximately 0.55. Parametric simulations showed that a 20mm backing cavity suited space-constrained tunnels, whereas a 60mm cavity enhanced low-frequency absorption, achieving an approximately 58% RT reduction at 125Hz. Single-wall treatment provided a material-efficient option, while double-wall treatment was preferable for safety-critical tunnels. The findings demonstrate the acoustic feasibility of porous ceramic panels prepared from coal-based raw materials and provide design guidance for noise control in tunnel infrastructure.
Embedding PVA-ECC in critical load-bearing regions can provide structural toughening, but preforming and positioning ECC units while ensuring reliable bonding with post-cast concrete remains challenging. Liquid-nitrogen quick freezing, slow freezing, and conventional pre-hardening were compared to examine how temporary shape stabilization by freezing, relative to pre-hardening, affected the subsequent interface-forming capacity of PVA-ECC. The frozen specimens were thawed at 20, 40, or 60 °C. Splitting tensile and compressive tests, digital image correlation (DIC), mercury intrusion porosimetry (MIP), and SEM–EDS were used to assess interfacial performance and microstructure. The quick-frozen composites achieved interface-related splitting tensile strengths of 4.53-5.21MPa, 50.0%-72.5% higher than the pre-hardened control. Increasing the thawing temperature improved bonding, although gains above 40 °C were limited. DIC showed that the quick-frozen specimens maintained dispersed strain fields at high load levels. The MIP-tested quick-frozen specimens exhibited lower mercury intrusion volumes and lower fractions of mercury-accessible pore volume in the micrometer-scale range. SEM–EDS indicated fewer large defects, more continuous gel-like hydration products, and more continuous major-element signals near the interface. Their apparent ITZ widths were 3.6-5.4 μm, compared with 6.2 μm for the control and 6.1-12.9 μm for the slow-frozen specimens. Slow freezing was associated with more near-interface voids and microcracks that were not fully mitigated by elevated-temperature thawing and curing. These results indicate that quick freezing provides temporary shape stability while preserving post-thaw hydration potential, thereby supporting interface development and load transfer. The findings provide interface-scale evidence for embedding freeze-shaped PVA-ECC in critical load-bearing regions.
To alleviate the ecological pressure caused by the over exploitation of natural sand and gravel, and to address the environmental pollution resulting from industrial solid waste as well as the difficulty in utilising low-quality aeolian sand, this study employs a combination of aeolian sand and three types of solid waste. Utilising a two-step cold-bonding granulation process involving extrusion and coating, a continuous production method for multi-graded artificial coarse aggregate (ACA) has been developed to replace natural sand and gravel aggregates, thereby meeting the sustainable development needs of desert construction. This study investigates the effects of the red mud to fly ash ratio, water to binder ratio and alkali equivalent on the cylinder compressive strength, 1hour water absorption rate and apparent density of ACA. It quantitatively characterizes the pore structure and reveals the formation mechanism by analyzing microstructure and phase composition. The results indicate that the optimal ACA formulation is a red mud to fly ash ratio of 3:1, a water to binder ratio of 0.25 and an alkali equivalent of 8%. with a cylinder compressive strength of 15.63MPa, a 1-hour water absorption rate of 4.21% and an apparent density of 2323kg·m−3. A comprehensive analysis using entropy and gray correlation analysis indicated that porosity, as well as the proportions of large pores and capillaries, are key factors influencing macroscopic properties. In ACA, aeolian sand forms the skeleton, while C-(A)-S-H and N-A-S-H gels act as binders and unhydrated particles and carbonate products jointly contribute to compaction and densification. In addition, ACA demonstrates good environmental safety, with carbon emissions lower than those of cement-based artificial aggregates. The study has elucidated the mechanisms underlying the physical and mechanical properties and microstructural characteristics of ACA, thereby providing both theoretical significance and practical value for the sustainable engineering application of artificial coarse aggregates produced through the co-processing of industrial solid waste and aeolian sand.
The incorporation of carbon dioxide (CO₂) into cement-based materials has emerged as a promising approach to reduce the carbon footprint of concrete while potentially enhancing performance. This study investigates carbon incorporation through two carbonation techniques: direct addition of dry ice during mixing and accelerated carbonation curing (ACC) in a sealed CO₂ chamber. A total of eighteen concrete mixtures were prepared using three water-to-cement (w/c) ratios (0.35, 0.45, and 0.55), two cement types (Type I and Type V), and three curing regimes: conventional water curing (control), dry ice carbonation followed by water curing, and ACC. The experimental program evaluated compressive strength and key durability indicators, including rapid chloride permeability, surface electrical resistivity, and water absorption, alongside correlations between mechanical and transport properties. Results indicate that the w/c ratio governs the effectiveness of carbonation treatments. The most pronounced improvements were observed at w/c = 0.35, where enhanced performance was achieved. ACC provided the most consistent performance, with the Type V mixture achieving a 28-day strength of 53.67MPa (12.2% higher than control). Carbonation-cured specimens exhibited reduced chloride permeability, increased resistivity, and reduced water absorption. Overall, controlled carbonation enables effective CO₂ utilization without compromising concrete performance.
The application of ultra-high-performance fiber-reinforced concrete (UHPFRC) for strengthening corrosion-damaged reinforced concrete (RC) structures has demonstrated a significant potential in engineering practices. However, the influence of the post-peak stress-strain behavior of UHPFRC materials on the flexural performance of strengthened beams remains insufficiently understood. This study conducts a numerical study on the flexural behavior of RC beams retrofitted with UHPFRC after corrosion damage. Using nonlinear finite element simulations, a parametric study was performed to evaluate the effects of UHPFRC thickness, strengthening configurations, UHPFRC tensile constitutive laws, and corrosion rates on key performance indicators of strengthened beams, including the load-bearing capacity, stiffness, and ductility. The results demonstrate that the U-shape strengthening significantly enhances the cracking load, stiffness, and ultimate capacity compared with other configurations with the same thickness of UHPFRC. Furthermore, UHPFRC with a pronounced strain-hardening response provides superior structural strengthening results compared with the strain-softening UHPFRC, particularly in mitigating the corrosion-induced degradation of both the load-bearing capacity and ductility.
