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.

The growing demand for more sustainable construction materials has driven the development of composites incorporating industrial and agricultural residues, contributing to the reduction in virgin raw material consumption and the valorisation of by-products. In this context, the present study investigated the influence of incorporating rice husk subjected to different chemical treatments and the partial replacement of commercial gypsum with recycled gypsum on the flexural strength, compressive strength and microstructural characteristics of gypsum-based composites. Initially, formulations containing 5 wt.% and 10 wt.% rice husk in three different conditions, untreated, treated with calcium hydroxide, and treated with acetic acid, were produced and evaluated in terms of compressive strength and flexural strength. The formulation containing 5 wt.% rice husk treated with acetic acid exhibited the best overall performance and was therefore selected for the subsequent stage of the study. In the second phase, mixtures incorporating 20 wt.%, 30 wt.% and 40 wt.% recycled gypsum, with and without the addition of 5 wt.% treated rice husk, were investigated. Furthermore, particle size distribution, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analyses were performed. The results demonstrated that the acetic acid treatment resulted in higher flexural and compressive strength compared with the other treatment conditions evaluated. Partial replacement with recycled gypsum also yielded promising results, with the formulation containing 70 wt.% commercial gypsum and 30 wt.% recycled gypsum exhibiting the highest mechanical strength among the composites without lignocellulosic reinforcement. Microstructural characterisation revealed the preservation of the principal mineralogical phases following the recycling process, and SEM micrographs showed the incorporation of rice husk within the gypsum matrix. Overall, the combination of 30 wt.% recycled gypsum and 5 wt.% rice husk treated with acetic acid represents a technically viable alternative for the development of gypsum composites intended for non-structural applications in the construction industry, while promoting the beneficial utilisation of waste materials.

Plant fiber-reinforced fiber–cement composites are promising sustainable products, but their durability under alkaline and moisture-variable conditions remains a key limitation. This systematic review critically examines accelerated aging methodologies applied to plant fiber-reinforced fiber–cement/mortar composites. It links protocol severity to degradation mechanisms and performance evolution. Following PRISMA guidelines, 518 records were retrieved from SciFinder, Scopus and Web of Science. After screening, 41 experimental studies (2013–2023) were included. Wetting–drying (W/D) cycles dominate the evidence base (36 studies), whereas freeze–thaw (F/T) protocols are scarce (five studies) and other methods (immersion, induced reactions, biological agents) appear only once each, representing clear research gaps. Methodological appraisal showed that 87.5% of the aging studies adequately described the exposure protocol, whereas only 32.5% used multiple aging checkpoints and 26.8% included complementary microstructural or chemical validation. Mechanistically, durability losses are mainly governed by coupled matrix transport/alkalinity effects and fiber–matrix interface degradation, while matrix densification may mask deterioration if flexural strength is used alone. Quantitatively, severe W/D protocols at 70 °C produced post-cracking strength losses of up to 87–90% and toughness losses of 95–99% within 10–30 cycles, whereas under moderate or EN-type protocols MOR could remain stable or increase despite reductions of approximately 50–90% in toughness-related metrics. Matrix composition modification (SCMs/low-alkalinity binders) is identified as the predominant and most transferable durability strategy compared with fiber treatments or hybrid reinforcements. Based on evidence consistency, a reference W/D protocol is proposed (200 cycles; wetting at ~20–25 °C; drying at 60 °C; balanced phase durations with intermediate checkpoints), together with recommended durability tests prioritizing post-cracking metrics and multi-scale validation.

This study investigates the sampling sufficiency required for accurately characterizing the morphological properties of rigid polyurethane foams across three distinct regions: core, crown, and lateral edge. A total of 200 individual cells were analyzed from 30 SEM micrographs, enabling the quantification of cell length, cell width, anisotropy index, linear cell density, and shape index. Average cell length ranged from 715 to 763 μm, while cell width varied between 386 and 531 μm depending on the region. The anisotropy index increased from 0.186 in the core to 0.289 in the lateral edge, indicating progressively more elongated cells. Linear cell density showed a marked decrease from 0.062 in the core to 0.001 in the crown, reflecting differences in cellular packing. Shape index values remained relatively stable, confirming its lower sensitivity to structural variations. Monte Carlo simulations were employed to evaluate sampling sufficiency for sample sizes ranging from 2 to 30. Results demonstrated that optimal sample sizes varied with foam region and parameter: 16 cells were sufficient for core and lateral regions, whereas up to 22 cells were required for the crown to capture higher structural heterogeneity. For anisotropy and shape indices, sufficient sampling ranged between 13 and 20 cells depending on the region. The results confirm that the core exhibits lower variability (CoV for cell length: 29.1%) compared to the crown (36.4%) and lateral edge (34.9%), supporting its more homogeneous structure. However, exclusive sampling from the core may lead to biased characterization, as crown and lateral regions display significantly higher variability in both geometry and orientation. These findings establish quantitative guidelines for sampling strategies in polyurethane foam morphology, contributing to improved reproducibility and reliability in structure–property investigations of cellular materials.

This study evaluates the performance of a rehabilitation mortar in controlling chloride ion migration in artificially contaminated ceramic masonry under controlled laboratory conditions. Coatings with thicknesses of 3 cm, 5 cm, and 7 cm were applied to ceramic brick substrates saturated with saline solution and exposed to accelerated contamination. Chloride concentration profiles were determined by potentiometric titration after 120 days of curing. The results showed that the rehabilitation mortar effectively retained soluble salts within its porous matrix, limiting their migration toward the surface. The 3 cm coating provided satisfactory salt retention and reduced the potential for surface efflorescence. Among the evaluated thicknesses, the 5 cm coating exhibited the most favorable chloride distribution, characterized by a pronounced concentration peak at the substrate–mortar interface followed by a sharp decrease toward the external surface, indicating the formation of an effective chloride retention zone. In contrast, the 7 cm coating showed a more homogeneous ion distribution but a less defined retention profile. The results demonstrate the potential of the rehabilitation mortar to act as a protective barrier under controlled laboratory conditions using artificially contaminated ceramic substrates. These findings provide experimental evidence that may support future applications in salt-contaminated historic masonry, although further validation under real field conditions is still required.

This study investigated the mechanical performance and durability of concretes produced with varying proportions of recycled coarse aggregate from construction and demolition waste (CDW), ranging from 0% to 100% replacement of natural coarse aggregate, using recycled aggregates derived from crushed concrete and mortar debris, characterized by lower density and high water absorption (~9%) compared to natural aggregates. A key contribution of this research lies in the inclusion of intermediate replacement levels (20%, 25%, 45%, 50%, and 65%), which are less explored in the literature and allow a more refined identification of performance thresholds. Fresh-state parameters (slump), axial compressive strength (7 and 28 days), total immersion water absorption, sorptivity, and chloride ion penetration depth (after 90 days of immersion in a 3.5% NaCl solution) were evaluated. The results indicate that, up to 50% CDW content, the concrete maintains slump (≥94 mm), characteristic strength (≥37.2 MPa at 28 days), and chloride penetration (≤14.1 mm) within the limits for moderate exposure conditions, in accordance with ABNT: NBR 6118. Water absorption doubled from 4.5% (0% CDW) to 9.5% (100% CDW), reflecting the higher porosity and adhered mortar on the recycled aggregate, which necessitates adjustments to the water–cement ratio and SSD pre-conditioning to preserve workability and minimize sorptivity. Concretes with more than 65% CDW exhibited chloride penetration depths exceeding 15 mm, potentially compromising durability without additional mitigation. The judicious incorporation of CDW, combined with optimized mix design practices and the use of supplementary cementitious materials (SCMs), demonstrates technical viability for reducing environmental impacts without significantly impairing the structural performance or service life of the concrete.