Search Results (1,465)

Natural fiber-reinforced geopolymer and alkali-activated composites have emerged as promising alternatives for reducing the environmental impact of cement-based materials; however, their long-term durability remains insufficiently understood. This systematic review evaluates the durability behaviour of natural fiber-reinforced geopolymer and alkali-activated composites based on 42 studies published between 2017 and 2025, identified from 356 records retrieved from Scopus and Web of Science following the PRISMA methodology. The literature analysis reveals a significant increase in research activity in recent years, with 12 studies published in 2025 alone, indicating a growing transition from mechanical-performance evaluation toward durability-oriented design. The reviewed studies investigated multiple degradation environments, including moisture cycling, freeze–thaw exposure, chemical attack, carbonation, and thermal ageing. Across the evidence base, durability performance was mainly governed by the interaction among binder chemistry, pore structure, curing conditions, fiber characteristics, surface treatments, and exposure severity. Notably, the intrinsic surface properties of different natural fibers, including hydrophilic character, surface chemistry, and surface roughness, were found to strongly influence moisture absorption, fiber–matrix adhesion, and susceptibility to alkaline degradation, thereby contributing to distinct durability outcomes among fiber types. Fiber modification strategies and optimized matrix designs were frequently associated with improved interfacial stability and mechanical retention after ageing, whereas excessive fiber contents and poorly controlled moisture transport were recurrent factors contributing to degradation. Despite these advances, the review identified significant methodological limitations, particularly the lack of standardized durability protocols and long-term exposure assessments. Future research should prioritize harmonized testing approaches and integrated durability-based design frameworks to enable reliable prediction of service performance in natural fiber-reinforced alkali-activated composites. Full article

Early-age cracking severely limits concrete durability in hot, arid environments due to rapid plastic and drying shrinkage. This study evaluates the cracking sensitivity of cement-based materials incorporating four local supplementary cementitious materials (SCMs): limestone filler from Djebel Béchar, natural pozzolan, silica fume, and gypsum under simulated arid conditions (55 °C, 12% relative humidity, 10 km/h wind). Using a custom climatic chamber, prismatic cement-grout specimens with internal restraints were tested. SCMs were evaluated at substitution rates of 2% to 8%. Limestone was further tested at higher rates (up to 40%) and in binary combinations. Findings were validated using micro-concrete with limestone substitutions (0–35%) combined with 4% natural pozzolan. Cracking sensitivity was assessed using maximum crack width and a cracking index, along with setting times and mechanical strengths. Results indicate that limestone filler demonstrated the most favourable performance. A 4% limestone substitution yielded a single crack with a maximum width of 0.1 mm, while an 8% substitution resulted in five cracks of about 0.2 mm. The optimal cracking index was achieved at a 35% limestone substitution rate, which also successfully extended initial and final setting times. While binary SCM combinations significantly reduced cracking compared to the unsubstituted reference, they did not outperform the optimal 35% single limestone substitution. Furthermore, the 28-day compressive and flexural tensile strengths of the micro-concrete were effectively maintained at up to 35% limestone combined with 4% pozzolan. Overall, these preliminary findings demonstrate that crushed limestone fines from Djebel Béchar are highly promising as partial cement replacements to improve concrete durability in arid climates. Further durability assessments and statistical validation are recommended to confirm these benefits for practical field applications. Full article

The valorization of industrial textile waste as reinforcement in cementitious materials offers a promising approach for reducing polymer waste while improving the performance of cement-based composites. This study investigates recycled polypropylene (PP) fibers recovered from Moroccan pre-consumer textile waste for application in mortar and concrete. Thirteen fiber types were initially screened based on their geometrical and morphological characteristics, and four representative fibers were selected for detailed characterization and experimental evaluation. Fiber-reinforced mortars were first investigated to assess the influence of fiber type and dosage, followed by concrete-scale evaluation through mechanical, shrinkage, transport-related, and microstructural tests. The results showed that fiber characteristics and dosage influenced composite performance, with the magnitude and direction of the mechanical response depending on the fiber formulation. Statistical analysis confirmed that compressive strength was significantly affected by fiber type, dosage, and their interaction, whereas no statistically significant effect was detected for flexural strength at the 95% confidence level. The F8 mixture containing 0.10% fibers exhibited the highest compressive strength among the investigated concrete formulations, reaching 28.75 MPa compared with 26.25 MPa for the reference concrete. Flexural strength showed numerical increases of up to 8.2% for selected formulations, although these differences were not statistically significant. Early-age shrinkage was reduced by up to 75% compared with the reference mixtures, representing the most pronounced effect observed in the study. Increasing fiber content reduced workability and promoted fiber agglomeration, highlighting the importance of controlled dosage and dispersion. Among the investigated dosage levels, 0.10% by mass of cement was selected for subsequent durability and microstructural investigations because it provided a favorable overall balance among the evaluated properties for the selected formulations; this dosage should not be interpreted as a universal optimum. The F8 formulation exhibited favorable transport-related properties after 90 days of water curing, while SEM observations indicated a generally homogeneous fiber distribution within the investigated regions. Overall, the results demonstrate the potential of heterogeneous recycled PP textile fibers as reinforcement for cementitious composites under the investigated conditions and provide a systematic multi-scale experimental workflow for their screening and evaluation. Full article

Stress corrosion cracking (SCC) of prestressing steel threatens prestressed concrete structures with sudden, brittle failure and minimal visible warning. While mechanical stress, localized corrosion, and hydrogen uptake are recognized drivers, the mechanisms connecting sulfide exposure in cementitious materials to hydrogen uptake and crack initiation at the steel–concrete interface remain poorly understood. This review synthesizes the coupled electrochemical, mechanical, metallurgical, and environmental processes governing SCC, with particular emphasis on the interactions of sulfide species with chloride ingress, carbonation, pitting, and hydrogen-assisted cracking under sustained tensile stress. Evidence indicates that sulfides weaken passive-film protectiveness and facilitate hydrogen entry, while localized corrosion and acidification create favorable conditions for crack initiation and propagation. Because SCC susceptibility emerges from the combined effects of environmental exposure, steel microstructure, and mechanical loading, isolated environmental parameters cannot adequately predict risk. Accelerated laboratory tests offer comparative insight but have limited representativeness of the complex conditions of prestressed concrete. A critical gap persists: no quantitative relationship has yet been established between cement sulfide content, sulfide availability at the steel surface, hydrogen uptake, and actual SCC susceptibility. Bridging this gap requires service-representative experiments on stressed prestressing steel embedded in mortar or concrete to develop reliable durability criteria and move beyond precautionary regulatory limits. Full article

A sustainable controlled low-strength material (CLSM) was developed using ground granulated blast-furnace slag, steel slag, and flue gas desulfurization gypsum in combination with cement to synergistically utilize engineering excavated soil and industrial solid wastes for stabilizing low liquid limit clay. However, the long-term durability evolution of this material under harsh and coupled environmental conditions—particularly freeze–thaw cycles, wet–dry cycles, and prolonged drying—has not been systematically investigated. In this study, systematic freeze–thaw cycling (up to 11 cycles), wet–dry cycling (up to 11 cycles), and natural drying (until mass stabilization) tests were conducted on specimens with binder contents ranging from 8% to 16%. The evolution of mechanical performance was evaluated via unconfined compressive strength (UCS) tests, while microstructural changes were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed a distinctive “S-shaped” fluctuation in UCS under freeze–thaw cycles. High-binder (16%) specimens maintained strengths of 1783–2395 kPa with intact surfaces and no visible cracking—significantly outperforming low-binder specimens. Under wet–dry cycles, strength initially increased after the first cycle and then declined progressively, with the lowest strength loss observed at 10% binder content. During drying, both water loss rate and drying shrinkage strain decreased with increasing binder content: from 8% to 16% binder, the water loss rate dropped from 34.16% to 29.03%. Microstructural analysis revealed that higher binder content promoted the formation of a dense, interwoven network of C–S–H gel and ettringite, which effectively filled intergranular pores and encapsulated soil particles, thereby enhancing macroscopic durability. This study provides a sustainable material solution for utilizing industrial solid wastes in the stabilization of low liquid limit clay for CLSM applications under severe environmental conditions, supporting the broader adoption of waste-to-resource strategies in construction engineering. Full article

The durability of prestressed spun-cast concrete poles is typically assessed on the basis of the nominal mix design parameters and the assumption of material homogeneity. However, the centrifugal spinning of fresh concrete mix results in an uneven distribution of its components throughout the wall thickness, which may affect the actual cement content in individual layers and consequently, the durability. As part of this study, the distribution of cement content in spun concrete poles was analysed using an experimental approach based on the analysis of hardened concrete composition. Samples were taken from various locations along the height of the pole and divided into layers across wall thickness. Cement content, aggregate distribution, porosity, and water absorption were determined using a combination of chemical and physical methods. The results indicate that although the average cement content meets the design requirements (minimum amount of cement exceeds 300 kg/m³), there are significant local variations, particularly in the inner and outer layers of the cross section. The inner layer is characterized by increased cement content and porosity, while the outer layer is characterized by a higher coarse aggregate content and reduced cement content. It was also observed that the spinning program used in the production of the poles resulted in a homogeneous concrete structure at the top of the pole, where the spinning radius is smallest, with no signs of delamination. However, delamination of the concrete structure was observed at lower sections of the pole. These results highlight the limitations of assuming homogeneous material properties in durability design and suggest that the actual performance of spun concrete elements may deviate from predictions based on the standards. The results have direct implications for assessing the durability of spun concrete poles used in exposure classes such as XC4 and XD1. Full article

The use of industrial waste materials as partial cement replacement has become a popular topic for research to effectively reduce cement consumption, lower CO2 emissions and improve the sustainability of concrete production. In addition to environmental benefits, these materials have been shown to modify the mechanical and durability performance of concrete positively when used at appropriate amounts. In this study, an investigation was carried out to evaluate the effects of cement kiln dust (CKD) and ground granulated blast-furnace slag (GGBFS) as partial cement replacement at ratios ranging from 0% to 50% on the physical, mechanical, and durability behavior of the modified pervious concrete compared to the control one. The analysis proves that CKD reaches its optimum performance at relatively low replacement rates (from 5 to 10%), which results in increased early compressive strength up to 14.28 MPa (+19.3%) and tensile strength to 2.90 MPa (+55.9%). This is due to a greater particle packing and rapid hydration of cementitious materials. Oppositely, despite the decrease in compressive and flexural strength of concrete at 50% replacement ratio of cement by CKD (6.24 MPa and 1.45 MPa), GGBFS significantly increases the long-term durability. At a replacement ratio equal to 50%, GGBFS leads to permeability of 18.01 mm/s (−57.0%), water absorption of 2.53% (−56.0%), and freeze–thaw weight loss of 5.58%. Overall, low ratios (≤20%) of CKD and GGBFS are preferable for non-structural applications, as they provide performable permeability with enough mechanical and durability capacity. Full article

The durability deterioration of concrete under the coupled action of freeze–thaw cycles and corrosive media is a critical technical challenge for engineering structures in cold regions and salt corrosive environments. This paper systematically reviews the research progress on the mechanical properties of concrete subjected to coupled freeze–thaw and corrosion effects. Starting from the mechanisms of freeze–thaw damage and corrosion damage, it analyzes the material degradation laws under individual factors and the synergistic failure mechanism of the coupled freeze–thaw–corrosion condition. The coupling effect is revealed: freeze–thaw-induced microcracks accelerate the penetration of corrosive media, while the expansion of corrosion products in turn aggravates freeze–thaw damage. Building on this, from the perspective of factors influencing concrete failure, this paper systematically summarizes the key factors governing concrete damage under single-factor and coupled-factor conditions as well as their nonlinear response characteristics. The review indicates that the damage degree under the coupled action is far greater than the simple superposition of damage caused by individual factors and presents complex patterns, including the concentration threshold effect, the time-sequence effect, and sensitivity to a low water–cement ratio. Existing reviews predominantly focus on qualitative descriptions of single-factor deterioration mechanisms, while systematic comparative analyses of threshold behaviors under multi-factor coupling and quantitative consolidation of mechanical degradation metrics remain limited. Furthermore, targeted durability design guidance tailored to cold saline environments is rarely summarized in the prior literature, which motivates the present comprehensive review. Although existing studies are relatively well-established for single damage mechanisms, further efforts are still needed to deepen the understanding of multi-factor interaction thresholds and dynamic evolution processes. The findings of this review can provide theoretical support and engineering reference for the durability design and service life prediction of concrete structures in cold regions and salt corrosive environments. The summarized threshold laws and quantitative mechanical degradation data can provide targeted parameter guidance for the durability design of hydraulic structures, bridge substructures, and port engineering in northwest saline soil, northern severe cold, and eastern coastal salt fog areas. Full article

This study focuses on the mechanical properties and durability performance of polypropylene (PP) fiber incorporated into M25-grade concrete using sustainable waste materials such as microsilica (MS) and grounded e-waste (EW). Cement is partly replaced with varying proportions of MS starting from 0 to 15% in the concrete mix. Ground waste printed circuit board (PCB) is utilized as the partial replacement for fine aggregate with varying content from 0 to 45%, addressing a major environmental issue related to EW disposal. Additionally, PP fiber content is varied from 0 to 0.6% to improve the strength and toughness characteristics of concrete. The mechanical properties and durability analysis of the samples are conducted to assess the performance of concrete containing MS, EW, and fibers. Optimization of these ingredients was carried out through design of experiments (DoE). The experimental validation mix (MEV) achieved a 28-day compressive strength of 33.66 MPa comparable to the control mix (M0) (35.76 MPa), exceeding the target design strength. The MEV mix exhibited enhanced durability, with the reduction in RCPT value attributed to the low chloride ion penetrability. Meanwhile, sulphate-induced compressive strength loss was diminished by 38% for MEV compared to the control mix, indicating improved stability against acid attacks. This work sheds light on the inclusion of these sustainable materials as a potential pathway to achieve superior mechanical and durability properties for concrete, providing a sustainable solution to the recycling of PCB e-waste. Full article

Cement-stabilized crushed stone is widely used in semi-rigid pavement bases, but fatigue cracking can reduce pavement durability. Supersulfated cement-stabilized crushed stone is a promising low-carbon alternative, yet its fatigue behavior under the micro-expansion induced by ettringite (AFt)-seeded hydration has rarely been clarified. This study investigated the fatigue performance of AFt-seeded SSC-stabilized crushed stone with explicit consideration of the resulting self-stress, through paste expansion tests, splitting fatigue experiments, and a coupled finite element–discrete element analysis. The seeded paste developed a stable free expansion of approximately 400 με, which was converted to an equivalent expansion of 18.5 με and an estimated compressive self-stress of 0.283 MPa at the crushed-stone scale. The material reached a 90-day indirect tensile strength of 1.45 MPa, approximately 57.6% higher than that of the OPC-stabilized reference. Under comparable normalized stress levels of 0.45 and 0.49, the SSC-stabilized crushed stone achieved 17,441 fatigue cycles, exceeding the reference by 28%, with slower stiffness degradation and lower permanent deformation accumulation. Numerical simulation further showed that the self-stress delayed bond breakage and crack penetration, with simulated base fatigue failure at approximately 5.3 × 10⁵ cycles. These findings clarify the role of micro-expansion-induced self-stress in fatigue resistance. They also indicate its potential for durable, low-carbon pavement bases. Full article

The increasing adoption of additive manufacturing in the construction sector has intensified the demand for lightweight, recyclable cement-based composites with low environmental impact, suitable for automated 3D printing. Foamed concrete reinforced with dispersed fibers and incorporating recycled constituents represents a promising class of multifunctional materials. However, its environmental performance remains insufficiently characterized. This study provides a comprehensive evaluation of thermal stability, leaching behavior, and microbial resistance of 3D-printable fiber-reinforced foamed cement composites produced with recycled components. Thermogravimetric–Fourier transform infrared (TG–FTIR) analysis confirmed a characteristic three-stage thermal decomposition pathway typical of hydrated cementitious systems. All composites exhibited high thermal stability, with residual masses of 88.56–90.17% at 900 °C. The binder type exerted a stronger influence on decomposition behavior than atmospheric exposure or freeze–thaw conditioning. Leaching tests revealed strongly alkaline eluates (pH 11.0–11.4), low total organic carbon (<0.6 wt.%), and only trace concentrations of BTEX (35–41 μg/kg), PAHs, and PCBs. Alkali activation increased the release of chromium (3.6–4.0 mg/kg), arsenic (1.2 mg/kg), copper (4.5 mg/kg), antimony (0.26 mg/kg), and sulfates (2700–4700 mg/kg), accompanied by elevated total dissolved solids (~18,000 mg/kg). Nevertheless, all environmentally relevant constituents remained well below the waste acceptance criteria (WAC), confirming effective immobilization of hazardous species within the hardened matrix. The results provide new insights into the relationships among material composition, porous microstructure, and environmental safety, demonstrating that the developed 3D-printable foamed composites exhibit robust performance, suitability for safe and durable applications, and favorable environmental performance. Full article

Grouting materials used in water-rich and chloride-exposed environments require adequate workability, mechanical performance, and durability. To optimize the formulation, a series of orthogonal tests was conducted to assess how fly ash (10–30%), rust inhibitor (1–3%), and anti-corrosion agent (2–6%) affect the fresh and hardened properties of cement grouts at a constant water-to-binder ratio of 0.5. Setting behaviour, mechanical properties, chloride ion penetration resistance, pore structure, and hydration products were investigated. Fly ash and the anti-corrosion admixture prolonged the setting time. The highest 28-day compressive and flexural strengths were obtained at 20% fly ash. At 30%, the dilution effect outweighed the later-age pozzolanic contribution and slowed strength development. Within the investigated range, 6% anti-corrosion admixture provided the greatest improvement in strength and chloride ion penetration resistance, whereas the rust inhibitor had a smaller effect on the charge passed. Mixtures containing 20% fly ash and 4–6% anti-corrosion admixture exhibited lower porosity and a refined pore-size distribution. By contrast, 30% fly ash resulted in a less favourable pore structure. SEM and XRD results indicated a denser matrix at 28 days, consistent with continued cement hydration and the later-age pozzolanic reaction of fly ash. Previous studies have mainly focused on individual mineral or chemical admixtures, whereas the combined effects of fly ash, rust inhibitors, and anti-corrosion admixtures under fixed workability conditions remain insufficiently understood. This study reveals their distinct and complementary roles, providing a basis for the multi-objective optimisation of grouting materials in chloride-rich and water-saturated environments. Overall, 20% fly ash, 4–6% anti-corrosion admixture, and 1–2% rust inhibitor provided the best performance balance under the investigated conditions. Full article

This study presents a physics-informed, climate-responsive model for predicting carbonation depth and compressive strength degradation in conventional and sustainable cementitious composites under real environmental exposure. The Semi-Theoretical Predictive Degradation (STPD) model couples hourly temperature, relative humidity, and CO₂ concentration data with two-dimensional diffusion–reaction equations implemented in FEniCS. The model accounts for humidity-sensitive diffusivity, temperature-activated carbonation kinetics, and CO₂ consumption via Langmuir decay. Experimental validation was performed on ordinary Portland cement (OPC) concrete specimens exposed for 30 days to climate profiles representative of Portugal (average 14.2 °C, RH 74%, CO₂ ~417 ppm) and Slovakia (average 4.7 °C, RH 80%, CO₂ ~414 ppm). Carbonation depth increased from 0 to 0.30 mm in Portugal and up to 0.15 mm in Slovakia, with corresponding predicted reductions in compressive strength relative to the corresponding uncarbonated reference of up to 25% and 14%, respectively. The STPD model accurately reproduced these trends, achieving RMSE values of 0.008 mm for carbonation depth and 1.55 MPa for compressive strength in OPC concrete. To assess the broader applicability of the framework, simulations were extended to fly ash/slag-blended, geopolymer, and biochar-containing concretes using material-specific parameters. Among the simulated systems, geopolymer concrete showed the highest predicted durability, with carbonation depths below 1 mm and strength loss below 10%. A degradation index combining carbonation depth and strength loss mapped high-risk zones near the exposed surface, particularly under warm and fluctuating climatic conditions. The model provides a transferable framework for climate-informed durability assessment, material selection, and the design of sustainable cementitious composites. Full article

The increasing generation of construction and demolition waste, along with the depletion of natural aggregates, has driven growing interest in recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) as sustainable alternatives in concrete production. However, a direct and systematic comparison between the two materials remains limited. This review addresses this gap by applying PRISMA guidelines to analyze 82 peer-reviewed studies published between 2010 and 2026. Both materials are evaluated across three key domains: physical properties, mechanical performance, and microstructural characteristics. The findings indicate that RCA can reduce compressive strength by up to 26%, mainly due to the presence of porous adhered mortar and a complex interfacial transition zone (ITZ). In contrast, RAP weakens bonding with cement paste because of its hydrophobic bituminous coating, leading to adhesive failure at the mortar asphalt interface. Despite these limitations, RCA and RAP exhibit distinct behaviors in terms of shear capacity, ductility, energy absorption, and durability. Enhancement techniques such as surface treatment, carbonation, supplementary cementitious materials, and fiber reinforcement show potential in improving performance. Additionally, life cycle and economic analyses reveal that RAP can reduce total costs and carbon emissions when efficiently processed. This study provides a unified comparative framework to support sustainable material selection and design optimization. Full article

Concrete is the most used construction material, but its long-term performance depends on durability. Although fly ash has been used as a supplementary cementitious material, the effects of its mechanical activation on the concrete durability require further investigation. This study evaluated the influence of replacing 30% of cement with natural Class F fly ash (NFA) and ground fly ash (GFA) in concrete with a water-to-binder ratio (w/b) of 0.62, using a mixture without fly ash (WFA) as reference. Mechanical activation was performed by milling the fly ash, followed by characterization through particle size analysis and X-ray diffraction. Concrete durability was assessed using electrical resistivity, ultrasonic pulse velocity (UPV), water absorption, porosity, rapid chloride permeability (RCPT), carbonation resistance, and compressive strength tests. Mechanical milling reduced and transformed the ash morphology from spherical to amorphous, while quartz and mullite remained the main crystalline phases. Compared with CNFA, CGFA exhibited up to 101% higher electrical resistivity, 39.6% greater resistance to chloride penetration, 10.8% improved carbonation resistance, 0.4% lower water absorption, and a 5.38% reduction in porosity, although compressive strength decreased by more than 20%. These results demonstrate that mechanically activated fly ash is a viable alternative for enhancing the concrete durability performance exposed to aggressive environments. Full article