Construction Materials

Basalt-fiber-reinforced recycled aggregate concrete (BFRAC) produced with 100% recycled coarse aggregate is still constrained by the inferior quality of recycled aggregate and the difficulty of optimizing fiber reinforcement parameters. This study investigated the effects of basalt fiber length configuration and dosage on the mechanical performance and pore structure of recycled aggregate concrete incorporating recycled coarse aggregate subjected to two-step pretreatment with nano-silica and cement slurry. Four fiber length configurations, namely 6, 12, and 24 mm and a mixed-length system, were evaluated at volume fractions of 0.1, 0.2, and 0.3%. The reinforcing effect was assessed through compressive strength, splitting tensile strength, scanning electron microscopy, mercury intrusion porosimetry, and statistical analysis. The pretreatment improved recycled aggregate quality, reducing water absorption from 4.97% to 3.11% and crushing index from 20.5% to 13.4%. Basalt fiber incorporation generally enhanced mechanical performance, although the response depended on fiber length and dosage. At 28 days, BF24V1 achieved the highest compressive strength, whereas BFmixV1 exhibited the best overall performance by combining high compressive strength with the highest splitting tensile strength. Relative to the average performance of the corresponding single-length mixtures at the same dosage, the mixed-length system showed a positive synergistic effect. Microstructural observations indicated that this behavior was associated with more effective crack bridging and refinement of the pore-size distribution. The results demonstrate that a low-dosage mixed-length basalt fiber system provides an effective route for upgrading pretreated waste-derived aggregate into higher-performance recycled aggregate concrete. Full article

This study investigates the effect of nano-zeolite and lime on the resistance of reconstituted soil using an integrated experimental and explainable machine learning framework. Soil samples were prepared with varying proportions of nano-zeolite, lime, and fines, and cured under controlled temperature and time conditions. Soil resistance (q) was measured to evaluate the mechanical performance of each mixture. Eight machine learning models, including artificial neural networks (ANN), random forest (RF), random tree (RT), random committee–random tree (RC-RT), M5Rules, KStar, RBFS, and additive regression–decision stump (AR-DS), were developed using Weka 3.8.6 to predict soil resistance based on the input parameters. Model performance was assessed using SSE, MAE, MSE, RMSE, Error %, Accuracy %, R², correlation coefficient, Willmott Index, Nash–Sutcliffe Efficiency, Kling–Gupta Efficiency, and SMAPE. ANN and RF achieved superior accuracy (R² ≥ 0.98) with minimal prediction error, effectively capturing the nonlinear interactions between stabilizer content, curing time, and environmental conditions. Sensitivity analyses using the analysis index and SHAP values revealed that nano-zeolite, lime, and curing time were the dominant factors influencing soil resistance, while fines content and curing temperature had secondary effects. The results demonstrate that nano-zeolite and lime significantly enhance soil resistance and that explainable machine learning models can reliably predict and interpret soil performance, providing a data-driven framework for optimized soil stabilization in geotechnical engineering applications. Full article

This study experimentally investigates the structural behavior of hexagonal- and square-shaped composite specimens subjected to vertical compression, vertical tension, and diagonal tension loading. The specimens were fabricated using four- and six-layer alkali-resistant (AR) glass textile reinforcements embedded in a modified cementitious mortar via pull, pour, and roll manufacturing techniques. The mechanical performance of polyvinyl alcohol (PVA) fiber-reinforced composite connectors and steel clamp-type elements was also evaluated at the joints of hexagonal specimens under vertical tension and lateral shear loading. The results show that increasing the number of textile layers significantly enhances structural performance. A 50% increase in textile layers improved load-carrying capacity by up to 56% in compression, 104% in tension, and 216% in diagonal tension. Corresponding increases of approximately 20–42% in ductility and up to 266% in energy dissipation capacity were observed. No failure occurred in the connecting elements, confirming their adequate stiffness, strength, and ductility. In addition, validated three-dimensional finite element models were developed to simulate the response of the hexagonal specimens. Overall, the proposed system demonstrates strong potential for applications such as infill walls, cladding, and sandwich panels due to its favorable strength, ductility, and energy absorption capacity. Full article

The abrupt failure of shear-deficient RC beams may lead to harmful consequences under dynamic loading. The use of Carbon Fiber Reinforced Polymers (CFRP) aims to convert this brittle fracture into a ductile one. However, the complexity of the multiple damage mechanisms makes it difficult to assess their condition using conventional testing methods. In this study, the damage evolution of a shear-critical reference beam and its CFRP-strengthened counterpart was monitored using the acoustic emission (AE) technique. After correcting attenuated AE amplitudes, damage analysis was performed using the Shannon entropy approach based on true source amplitudes. The entropy analysis performed with these corrected data clearly revealed the shear failure in the reference beam through abrupt drops in entropy, indicating damage homogenization. In contrast, the entropy remaining high and dynamically varying over a much longer deflection range in the CFRP-strengthened beam demonstrated that CFRP distributes damage over a wider region and that different damage mechanisms, such as debonding and fiber breakage, in addition to concrete cracking, were simultaneously active. Full article

The performance and durability of asphalt pavements are strongly influenced by the rheological properties of asphalt binders, particularly under severe climatic and traffic conditions. This study investigates the synergistic effects of incorporating multi-walled carbon nanotubes (CNTs) at dosages ranging from 0.25% to 1% into AC 40-50 asphalt binders modified with 4% Styrene–Butadiene–Styrene (SBS). A comprehensive experimental program involving physical, rheological, and chemical characterization tests was conducted, including penetration, softening point, viscosity, storage stability, a Dynamic Shear Rheometer (DSR), Multiple Stress Creep Recovery (MSCR), Linear Amplitude Sweep (LAS), Fourier Transform Infrared Spectroscopy (FTIR), and Glover-Rowe (G-R) analysis. Statistical inference using one-way ANOVA was also conducted to evaluate the significance of differences among the binder formulations investigated. The results showed a continuous increase in binder stiffness with increasing CNT content, as indicated by decreasing penetration values, higher softening points, and increased viscosity. Incorporating 1% CNT reduced the softening-point difference from 3.1 °C to 1.6 °C in SBS-modified binders, indicating improved storage stability. Rheological evaluations showed that 0.75% CNT increased the high-temperature performance grade from 82 °C to 88 °C and provided the best rutting resistance, as indicated by MSCR results. In contrast, the 0.5% CNT formulation exhibited superior fatigue resistance and the lowest Glover-Rowe index, indicating improved cracking resistance and durability. Overall, the findings demonstrate that CNTs can effectively enhance the performance of SBS-modified asphalt binders, with 0.75% CNT being optimal for hot-climate applications, while 0.5% CNT exhibited improved fatigue and cracking resistance under moderate-temperature conditions. Full article

The integration of advanced additive manufacturing technologies, particularly 3D printing (3DP), also known as Additive Construction (AC), could influence a shift in the construction industry towards improved efficiency and automation. This research evaluated the effect on hardened properties of two different concrete mixes for use in 3DP based on the presence or absence of alkaline-resistant (AR) glass fibers. Furthermore, three different curing methods were evaluated: air-curing, plastic-covered curing, and spray-curing. Concrete beams were printed for flexural testing, and cores were taken from other depositions to evaluate compressive strength and split-tensile strength. An analysis of the size and location of cracks on the beams after curing was performed for the different mixes and curing methods. For beams without fibers, plastic-covered curing produced the highest flexural modulus values, and air-curing produced the lowest flexural modulus values. Plastic-cured beams with fibers had higher flexural modulus values than the air-cured beams with fibers. However, the spray-cured beams with fibers produced somewhat anomalous results, with one flexural modulus value being larger than those of the plastic-cured beams, and the other flexural modulus value being less than those of the air-cured beams. All 28-day compressive strengths and split-tensile strengths across mixes and curing conditions fell within a small band ranging between ~19.3–22.1 MPa and ~1.7–2.0 MPa (~2800–3200 psi, and 240–290 psi), respectively. There was a large amount of scatter in some of the tests. It appears that neither the presence of the AR-glass fibers, nor the type of curing had a large influence on compressive strength or split-tensile strength. Results showed that the addition of fibers and the use of the plastic during curing significantly reduced the occurrence, the width, and the depth of cracks as a result resulting from the curing process. Plastic-curing was the most effective curing method for minimizing the occurrence of cracks. Any cracks that formed during plastic-curing were extremely fine and had little or no effect on mechanical properties. Full article

Seawater and sea sand as constituents in concrete are valuable alternatives to freshwater and river sand. Further, the use of seawater and sea sand in projects located in the proximity of a sea/ocean can reduce the overall project cost and lower the carbon footprint. Nevertheless, seawater contains high concentrations of chloride (Cl⁻), sulphate (SO₄²⁻) and magnesium (Mg²⁺), which can react with tricalcium aluminate (C₃A) in cement and the byproduct calcium hydroxide (Ca(OH)₂), and form Friedel’s salt, delayed ettringite and brucite, respectively. These chemical compounds are aggressive and can degrade the strength and durability of the concrete. Differences in the physical properties of sea sand compared to river sand can also lead to weak and porous concrete. In reinforced concrete, steel bars are susceptible to corrosion due to the formation of corrosion products as a result of high concentrations of Cl⁻. Whilst mitigation strategies such as the use of supplementary cementitious materials (SCMs) and fibre-reinforced polymer (FRP) reinforcements have been investigated in the literature, no validated method that enables the use of concrete with seawater and sea sand has been established. Based on research reported in the literature, the present study investigates the chemistry, strength and microstructure of concrete mixed with seawater and sea sand as a means of establishing their use in concrete without compromising the properties of the concrete. The study shows that the compressive strength of seawater–sea sand mixed concrete (SWSSC) is increased in the short term (up to 28 days) due to the formation of additional chemical compounds in the former. However, the long-term (i.e., beyond 28 days) compressive strength of concrete reduces by up to 20% after one year due to the weakening of the microstructure (more flaws/expansions), which further reduces the durability of the reinforced concrete. Although the long-term degradation of SWSSC has been noticed, the underlying causes are not fully understood. The present critical review study provides chemical and microstructural insight into the degradation of concrete with seawater and sea sand, and the current developing understanding is used to develop a mitigation strategy towards the use of seawater and sea sand in real-world concrete applications. Full article

This study investigates the effect of mass-based replacement of natural coarse aggregate with electric arc furnace (EAF) slag on the performance of ordinary Portland cement (OPC) concrete. Replacement levels of 0%, 30%, 50%, and 100% were examined, with particular attention to the volumetric changes induced by the higher density of EAF slag, which leads to an increase in paste volume. Fresh, mechanical, durability-related, and microstructural properties were evaluated. Results show a continuous reduction in workability with increasing slag content, despite the increase in paste volume, indicating the dominant influence of aggregate morphology on rheological behavior. Mechanical performance exhibited a non-linear response. Within the tested series, the 50% replacement mixture showed the highest mean compressive and splitting tensile strengths; however, the compressive strength difference relative to the control mixture remained small and within typical experimental scatter. In contrast, water absorption decreased progressively, reflecting improved matrix densification. However, this densification did not translate into enhanced mechanical performance, highlighting a decoupling between durability-related indicators and strength. A screening-level CO₂ assessment further showed that reductions in aggregate-related emissions were offset by increased cement content associated with mass-based replacement. The results emphasize the importance of considering volumetric effects when interpreting the behavior and sustainability of slag-based concrete. Note: all strength comparisons are based on mean values from three-specimen sets without formal statistical testing and should be regarded as exploratory observations. Full article

The formation of blisters in reactive resin coatings on concrete is a widely known phenomenon that is also a subject of debate in the literature. In particular, blisters forming after curing of the coating can lead to extensive damage. This study was focused on the investigation of blistering between the concrete substrate and the resin coating. The hypothesis is that the cementitious material and the overlying reactive resin coating form a system that leads to damage under certain boundary conditions regarding material composition, as well as moisture and mass transport. Systematic investigations were carried out in an extensive testing program with various substrate mortars that differ in cement type, water–cement ratio, and aggregate. As coating systems, two different EP primers were used with a transparent EP topcoat. The long-term testing was conducted on potential blistering of composite test specimens stored under various (practically relevant) conditions prior and after the coating. It was found that a higher moisture content of the substrate reduces blistering of the EP coating system. EP systems containing benzyl alcohol do not automatically tend to blister. Furthermore, condensation in the substrate provides sufficient amounts of water to cause blistering and ASR can contribute to blister formation. Full article

Recycled aggregates (RAs) from construction and demolition waste (CDW) provide substantial circular-economy benefits, yet their elevated porosity, adhered mortar, and heterogeneity typically impair the mechanical performance and durability of recycled aggregate concrete (RAC). This PRISMA 2020-compliant systematic review synthesises 2180 records (2015–2026) to evaluate advanced strategies for enhancing RA quality prior to structural use. This paper critically compares removal-based treatments (mechanical, thermal, acid cleaning) with strengthening and densification approaches, including accelerated carbonation, pozzolanic and nano-silica coatings, polymer impregnation, microbial-induced calcium carbonate precipitation (MICP), and modified mixing methods such as triple-stage mixing (TSMA). Evidence shows that while all RA types (including recycled fine aggregate (RFA), recycled coarse aggregate (RCA), and their combination (RFCA)) can slightly reduce compressive strength and 30% replacement serves as a critical threshold, beyond this, strength loss accelerates, particularly in RCA and RFCA mixes. However, accelerated carbonation and TSMA consistently refine the interfacial transition zone, reduce water absorption by 17–30%, and recover 85–94% of natural aggregate concrete strength. Bio-deposition reduces water absorption by 13–21%, while acid/silica fume treatments improve late-age strength but carry environmental trade-offs. This review formulates a practice-oriented implementation framework for structural-grade RAC. Sustainability analyses indicate that carbonated RA can achieve net-positive CO₂ abatement when under low-carbon energy supply. A mechanistic schematic is presented to synthesise treatment-to-pore-structure/durability pathways across the four principal treatment routes, and a quantitative synthesis plot compares water absorption reductions across all treatment types using 13 data points drawn from included studies. A structured treatment comparison evaluates the energy intensity, industrial scalability, CO₂ footprint, and technology readiness level for each strategy. The remaining challenges include a lack of hybrid treatment studies, limited real-scale durability data, and insufficient mechanistic models linking treatment to pore structure evolution. This review recommends harmonised durability-based criteria and updates to standards (e.g., BS 8500, EN 12620) to support the scalable deployment of treated RA. Full article

Drying shrinkage is a critical durability issue in concrete structures, particularly in high-strength concrete (HSC), which is more susceptible to early-age cracking due to its low water–cement ratio and dense microstructure. This study experimentally evaluates the restrained drying shrinkage behavior of fiber-reinforced concretes with compressive strengths ranging from 23 to 84 MPa, employing a total of 84 ASTM C1581 ring specimens exposed to three exposure conditions: outdoor climate, indoor laboratory conditions (25 °C, 50% RH), and a controlled chamber (50 °C, 30% RH). Plain concretes exhibited increasing shrinkage with both strength and environmental severity. Under indoor exposure, 90-day shrinkage reached approximately 660 × 10⁻⁶ (23 MPa), 291 × 10⁻⁶ (40 MPa), 753 × 10⁻⁶ (60 MPa), and 338 × 10⁻⁶ (84 MPa), with high-strength mixes showing greater cracking susceptibility. Fiber incorporation significantly mitigated both strain and cracking in a dosage-dependent manner. Steel fibers at 1.0–1.5% reduced shrinkage by up to 75% in 40–60 MPa concretes, while polypropylene fibers at 0.25–0.5% achieved reductions up to 66% and eliminated cracking in several cases. Results demonstrate that concrete strength, exposure condition, fiber type, and dosage collectively govern shrinkage and cracking resistance. Full article

In designing tall buildings, the primary concern is ensuring an effective lateral load-resisting system in addition to the gravity load system, since it largely governs the overall design. This study investigates the influence of X-cable bracing on the structural weight of tall steel frame buildings subjected to service and wind loading. Three numerical case studies, 10-story, 20-story, and 30-story planar steel frames, were modeled and analyzed using SAP2000, then optimized using Differential Evolution (DE) and Enhanced Colliding Bodies Optimization (ECBO) algorithms. These designs were evaluated under both service and wind load conditions, considering strength and drift constraints. The results indicate that the inclusion of wind loads in addition to service loads leads to a higher total structural weight than considering service loads alone, while cable bracing effectively reduces the overall mass by up to 6%, 38%, and 20% for the 10-story, 20-story, and 30-story frames, respectively, compared to unbraced structures, by improving the internal force distribution among structural components. Strength demands, reflected by the interaction ratio, governed all design cases, while lateral displacement was always less than the maximum limit according to AISC and ASCE requirements. Overall, the results highlight the potential of cable bracing systems to deliver efficient tall building designs; however, further studies are needed to generalize these findings to a broader range of building configurations. Full article

Concrete linings are used for water containment, in particular in reservoirs and canals. When the soil underlying a concrete lining has a high permeability, seepage into the ground of water from concrete-lined reservoirs and canals is essentially governed by leakage of water through the concrete linings. Therefore, it is essential to properly evaluate the hydraulic conductivity of concrete linings. It is known that cracks generally develop in concrete linings. This article provides material data and a method for the evaluation of the hydraulic conductivity of concrete linings, in particular cracked concrete linings, through two approaches. The first approach consists of a review of selected published values of the measured hydraulic conductivity of intact and cracked concrete. The second approach consists in developing an original analytical method to determine the hydraulic conductivity of cracked concrete using the results of an experimental evaluation of the influence, on water flow, of the tortuosity and rugosity of concrete cracks. The results obtained with the two approaches are compared and numerical examples are presented. Based on these results, practical guidance is provided to design engineers for a safe evaluation of the hydraulic conductivity of concrete linings, cracked or not cracked. Full article

In this study, the characteristics of concretes made from mixed recycled aggregate—the cheapest and most common secondary raw material in construction and demolition waste—were determined. For this study, besides experimental concretes using mixed recycled aggregate, reference compositions were developed using river gravel, recycled concrete aggregate, and recycled masonry aggregate. The workability of concrete mixtures was measured as class S1, which is acceptable for use with slipform concrete pavers, and was achieved by varying the water/cement ratio, considering the different water adsorptions of the concrete fillers. The following mechanical characteristics of the concretes were defined on the 3rd and 28th days: density, compressive strength, flexural strength, water absorption, and frost resistance. The test results showed sufficiently high indicators of strength and durability for the recycled aggregate concretes. Moreover, the strength of the concrete developed from mixed recycled aggregate was comparable with that of the reference concretes. Considering the low strength requirements for the construction of the lower layers of rigid pavements, it was established that such an application of recycled aggregate concrete, including that derived from mixed recycled aggregate, could be permitted. Full article

Palm oil waste (POW) is generated during the production of palm oil, and a large quantity of this waste often travels to landfills for disposal. This review aims to provide a comprehensive understanding of the circular economy approach to sustainable engineering and environmental applications of POW, including its generation, disposal concerns, challenges, and prospects. This review provides an overview of the features, composition, and prospective applications of several POWs, including palm oil clinkers (POCs), palm oil fuel ashes (POFAs), palm oil kernel shells (POKSs), and palm oil fibres (POFs). Furthermore, this overview describes the different applications that POW has found, such as sustainable construction materials, renewable energy production, and environmental remediation. Moreover, this review discusses the leaching and risk assessment of POW. The overview also discusses the circular economy implications of using POW. The results showed that while some wastes are reused and recycled, a good quantity are still discarded in environmentally harmful ways. With this overview of a wide circular economy approach to the sustainable use of POW, there will be a rallying call to experts and researchers to identify research gaps that could contribute to the sustainable use of POW. The results of this overview of the sustainable engineering and environmental applications of POW with a circular economy approach indicate that cleaner production technologies and better environmental sustainability of the palm oil industry are feasible through proper waste management, renewable energy generation, resulting in minimal environmental impacts. Furthermore, this analysis will be very useful in providing tools to engineers, environmentalists, and other relevant stakeholders to enable the efficient and sustainable use of POW in the global circular economy. Full article

This study investigates the pullout behaviour of hooked-end superelastic shape memory alloy (SMA) fibres embedded in concrete with the aim to develop an analytical model. Single fibre pullout experiments were performed to evaluate the mechanical response of SMA fibres with various hook geometries. A mathematical model based on the friction pulley method was then developed to predict the experimental pullout load versus displacement plots. The model integrates the tensile stress–strain response and the elastic–plastic constitutive behaviour of superelastic SMA materials, while also accounting for fibre slip and superelastic deformation during the pullout process. The pullout process is modelled through staged mechanisms including elastic response and debonding, progressive mechanical anchorage, and frictional pullout. The contribution of mechanical anchorage is governed by the elastic–superelastic strain distribution within the hook bends. The proposed model reasonably reproduces the overall load-slip response, peak pullout load, slip at peak load, and pullout energy for the three different fibre geometries extracted from normal strength and high-performance concrete matrix. The proposed mathematical model offers a transferable and predictive tool for assessing the pullout performance of hooked-end SMA fibres and supports their integration into design of SMA fibre-reinforced cementitious composites. Full article

The depletion of natural aggregates and the rapid increase in construction and demolition waste have intensified the need for sustainable structural materials. Recycled aggregates (RAs) represent a promising alternative; however, their performance under elevated temperatures remains insufficiently investigated. This study examines the combined influence of recycled coarse and fine aggregates (RCFA) replacement ratios and fire exposure on the shear behavior of RC beams. Five replacement levels (0%, 25%, 50%, 75%, and 100%) were considered. A total of forty-five beams (1500 × 150 × 200 mm) were tested at 23 °C, 400 °C, and 600 °C. In addition, a finite element model was developed to validate the experimental findings. The results showed at 23 °C, increasing the RA content led to a moderate reduction in the ultimate shear capacity of approximately 6–10%. Fire exposure significantly aggravated strength degradation, with additional reductions of up to 11% at 400 °C and total losses reaching about 22% at 600 °C compared to the control beam at room temperature. Stiffness deterioration and crack propagation became more pronounced with higher temperatures and replacement ratios due to thermal damage to the cement matrix and interfacial transition zones. Nevertheless, moderate replacement levels (25–50%) maintained acceptable residual shear capacity and improved ductility and energy absorption. Numerical predictions closely matched experimental results, with load differences within 1–5%, confirming the model’s reliability. Full article

Construction materials are the primary source of embodied carbon in long-span bridge projects, particularly for steel-intensive structures. This study presents an empirical construction-stage carbon footprint assessment of the Anhsin Bridge, an asymmetric cable-stayed steel truss bridge in Taiwan. Using the emission factor method in accordance with ISO 14067 and Taiwan Environmental Protection Administration guidelines, a cradle-to-gate (A1–A5 equivalent) system boundary was applied, covering material production, transportation, and on-site construction activities. Total construction-stage emissions were estimated at 55,349 tCO₂e, dominated by structural steel (51.8%), followed by reinforcing steel, concrete, and cement. Material-related emissions accounted for over 90% of the total, highlighting the critical role of material selection in embodied carbon reduction. Three practical mitigation strategies were evaluated using verified project data, as follows: 40% cement substitution with supplementary cementitious materials, optimized steel erection methods, and enhanced reuse of formwork and temporary works. The combined scenario achieved a 7.3% reduction in construction-stage emissions without compromising constructability. The findings demonstrate the effectiveness of material-oriented, constructability-aware strategies for reducing embodied carbon in steel-intensive bridge construction. Full article