Search Results (486)

Freeze–thaw resistance is a key durability concern for cementitious materials intended for use in cold climates, especially when alternative binders are introduced into extrusion-–thaw resistance is a key durability concern for cementitious materials intended for use in cold climates, especially when alternative binders are introduced into extrusion-based 3D concrete printing (3DCP). This study examines the effect of oil shale ash (OSA), a by-product of oil shale combustion, on the fresh and hardened performance of 3D-printable cementitious mixtures, with particular focus on durability under freeze–thaw exposure. Four mixtures were prepared with 0%, 10%, 20%, and 40% replacement of ordinary Portland cement by OSA. Fresh-state properties, including flowability, density, and buildability, were evaluated alongside hardened properties such as density, water absorption, mechanical properties, microstructure (SEM) and crystalline phase composition (XRD), and ultrasonic pulse velocity. Freeze–thaw resistance was assessed using NaCl-solution cycling with mass loss measurements. The results indicate that moderate OSA replacement (10–20%) contributes to a denser microstructure, resulting in higher compressive strength and reduced permeability. At 28 days, the OSA-10 and OSA-20 mixtures achieved compressive strengths of approximately 54 MPa, compared with 50 MPa for the reference mixture. The OSA-20 mixture also exhibited the best freeze–thaw performance, with mass loss after 56 cycles reduced from 35 g/m² to 26 g/m², corresponding to an improvement of approximately 26%. In addition, 3D-printed specimens exhibited 20–30% lower compressive strength than corresponding cast specimens. These mixtures also showed improved or comparable resistance to freeze–thaw action compared to the reference mix. In contrast, higher replacement levels (40%) increase porosity, weaken the microstructure, and significantly reduce durability. At 40% replacement, freeze–thaw mass loss increased to 77 g/m² after 56 cycles. The findings suggest that controlled incorporation of OSA can improve the sustainability and durability of 3D-printed cementitious materials for cold-region applications. Full article

This study investigates the thermo-mechanical and microstructural performance of concrete incorporating waste tire rubber (WR) and recycled steel fibers (WS) under elevated temperatures. Four mixtures were prepared: plain concrete (PL), rubber-modified concrete (WR5), and hybrid mixtures containing 0.4% and 0.8% steel fibers (WS0.4WR5 and WS0.8WR5). Specimens were exposed to temperatures of 400 °C, 600 °C, and 800 °C to simulate fire conditions. The results indicate that the incorporation of rubber reduces compressive strength at ambient temperature due to its lower stiffness and weak interfacial bonding. However, the addition of recycled steel fibers significantly improves crack resistance and enhances thermal stability. At 400 °C, the WS0.8WR5 mixture showed a retention rate of 92.9% (absolute strength: 44.32 MPa), compared to 72.2% for plain concrete (absolute strength: 44.11 MPa). Although the hybrid mixture has a lower ambient strength (47.68 MPa vs. 61.07 MPa), its superior retention makes it competitive in fire scenarios. Ultrasonic pulse velocity (UPV) measurements revealed a strong correlation with compressive strength degradation, confirming its effectiveness as a non-destructive indicator of internal damage. Microstructural analyses (SEM, XRD, and TGA-DTA) demonstrated that elevated temperatures lead to dehydration, phase transformation, and increased porosity, while steel fibers help maintain matrix integrity through crack-bridging mechanisms. The findings highlight a synergistic interaction between waste rubber and steel fibers, offering a sustainable and effective approach for improving the fire resistance of concrete. Full article

Nowadays, for energy-based targets, investigations on the thermal characteristics of building materials are becoming increasingly common. Foam concrete is one of them. Foam concrete, which is already a very popular building material in terms of thermal insulation, needs to simultaneously improve its mechanical and thermal characteristics. Therefore, in the present study, we address the effects on foam mortars of blended cements containing zeolites. The replacement ratios of blended cements containing two different zeolites were 0, 10, 30, and 50%. This study aims to encourage the use of alternative additives to achieve objectives such as sustainability, energy efficiency and lower carbon emissions and to obtain optimum design data for the foam concrete market. The parameters examined in 28-day-old samples were basic physical characteristics, water absorption, ultrasonic pulse velocity (UPV), compressive strength, thermal characteristics and microstructure analysis. Based on the test results, for foam mortars containing blended cement with analcime and clinoptilolite, a 10% replacement ratio is optimal in terms of strength, whereas a 30% ratio is required for a significant improvement in thermal insulation. The foam mortars with a 10% analcime replacement ratio demonstrated the highest specific heat capacity. Full article

This study investigates the combined use of fly ash (FA) and plastic waste (PW) as partial replacements for cement and coarse aggregates in the production of paver blocks. Experimental mixes were developed with a substitution level of FA (10% to 30%) and PW (3% to 15%). The performance of the modified concrete block was evaluated in terms of compressive strength (CS), flexural strength (FS), ultrasonic pulse velocity (UPV), water absorption (WA), Cantabro abrasion resistance (CAR), and rapid chloride permeability test (RCPT). Experimental results revealed that the optimal mixture, containing 25% FA and 12% PW (M4), exhibited superior performance. Compared with the control mix, the 56-day compressive and flexural strengths increased by 14.1% and 15.3%, respectively. The UPV value increased to 5.1 km/s, indicating improved concrete quality and matrix densification. Durability performance was significantly enhanced, with water absorption reduced by 25.4%, Cantabro abrasion mass loss decreased by 23.7%, and chloride ion penetrability reduced by 50.0% at 56 days. Statistical analysis using two-way ANOVA confirmed that FA and PW contents significantly influenced paver block performance (p < 0.05). The economic assessment further demonstrated cost savings of up to 3.0% compared with conventional concrete paver blocks. The study demonstrates that FA and PW can be effectively valorized in paver block production, offering both economic and environmental benefits. This green approach supports sustainable construction practices and promotes efficient waste management. Full article

This study evaluates the feasibility of utilizing wood ash (WA), derived from grilled-fish barbecue waste, as a supplementary cementitious material, in combination with crushed clay blocks (CCB) as partial or full replacements for natural coarse aggregate, to improve the sustainability of concrete. A total of twelve concrete mixtures were produced using WA replacement levels of 0%, 10%, 20%, and 30% and CCB replacement levels of 0%, 50%, and 100%. The concrete specimens were evaluated in terms of workability, compressive strength, splitting tensile strength, flexural strength, density, water absorption, ultrasonic pulse velocity (UPV), thermal conductivity, and microstructural characteristics using scanning electron microscopy (SEM). The results show that replacing cement with 10% WA achieved the highest mechanical performance at 56 days, with compressive, splitting tensile, and flexural strengths of 50.58 MPa, 5.54 MPa, and 6.07 MPa, respectively. These results represent an improvement of 11% in concrete properties compared with the control mixture. However, the use of 20% of WA enhanced microstructural densification through pozzolanic reactions, whereas higher replacement levels resulted in increased porosity, the presence of unreacted particles, and reductions in strength and UPV values. In contrast, increasing the WA and CCB contents reduced density and workability while significantly increasing water absorption. Among the investigated mixtures, the combination of 10% WA and 50% CCB provided the most favorable balance between mechanical performance, thermal efficiency, and sustainability. Further studies are recommended to evaluate the long-term durability and economic feasibility of the proposed replacement levels for sustainable concrete production. Full article

This study investigates the use of mussel shells (MSs), a biogenic by-product of the food industry, as a partial replacement for ground granulated blast furnace slag (GBFS) in alkali-activated mortars. Given their high CaCO₃ content, MSs represent a sustainable secondary raw material that reduces both waste disposal burden and reliance on natural resources, while offering a low-carbon alternative to conventional cement-based binders. Alkali-activated mussel shell/slag mortars (AAMSs) were produced with MS replacement ratios of 0%, 5%, 10%, 15%, and 20% by mass of GBFS. Sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) were used as alkaline activators. Fresh specimens were cured at 60 °C for 48 h. The experimental program included workability, compressive and flexural strength, water absorption, porosity, density, capillarity, ultrasonic pulse velocity (UPV), and freeze–thaw (F-T) resistance tests. Increasing MS content slightly reduced flowability and mechanical strength, while increasing water absorption, porosity, and capillarity. The M0 series achieved the highest 28-day compressive strength (54.06 MPa), while M15 exhibited the highest flexural strength (5.23 MPa). Following F-T cycling, the 5% and 10% MS series demonstrated the best compressive strength (30 MPa). The 10% MS exhibits a relatively balanced overall performance, providing the best balance between mechanical performance, F-T resistance, and microstructural stability, as confirmed by scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) analyses showing elevated Ca/Si ratios and the formation of Ca-rich crystalline phases. Full article

Prismatic mortar specimens with dimensions of 40 × 40 × 160 mm were produced in accordance with TS EN 196-1:2016 using rice husk ash (RHA) as a partial cement replacement at levels ranging from 0% to 15%. The specimens were exposed to aggressive seawater and 7% NaCl environments and evaluated through compressive strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, carbonation, capillary water absorption, and thermal conductivity tests. The highest compressive strength values were generally obtained at RHA replacement levels of 8–10%, depending on the exposure condition and curing period. In the 7% NaCl environment, most RHA-incorporated mixtures exhibited higher flexural strength than the control mixture, with the highest values generally observed at replacement levels between 6% and 10%. UPV results indicated that the incorporation of RHA did not significantly impair the internal quality of the mortars. Water absorption, capillary water absorption, and carbonation depth generally increased with increasing RHA content, particularly at replacement levels of 10–15%. No carbonation depth was observed in the control specimens, whereas the highest carbonation depths were measured in the 15% RHA mixtures. Thermal conductivity decreased with increasing RHA content, with the lowest values obtained at the highest replacement levels. Overall, the results indicate that RHA replacement levels of approximately 8–10% provide a favorable balance between mechanical performance, durability-related properties, and thermal insulation performance under aggressive chloride-rich exposure conditions. Full article

Seasonal freeze–thaw cycling progressively rearranges pores and propagates microcracks in silty clay, reducing the reliability of cold-region earthworks. This study evaluated a bio–polymer stabilization strategy combining microbially induced carbonate precipitation (MICP) with anionic polyacrylamide (APAM) to improve mechanical performance and freeze–thaw durability. Six groups were prepared at identical moisture and compaction conditions: water, APAM, and four MICP–APAM groups with bacterial optical densities (OD600) of 0.8, 1.0, 1.2, and 1.4. Unconfined compressive strength, unconsolidated-undrained triaxial compression, ultrasonic pulse velocity, and SEM, TG/DTG, XRD, and FTIR analyses were conducted before and after freeze–thaw cycling. The M1.0-APAM group showed the best overall performance, with UCS values of 1.35 MPa before cycling and 0.89 MPa after nine cycles, together with high shear resistance and ultrasonic velocity. Lower bacterial concentration provided insufficient cementation, whereas higher concentrations promoted non-uniform carbonate deposition, pore heterogeneity, and local stress concentration. Microstructural evidence indicated that OD600 ≈ 1.0 produced a relatively homogeneous network of fine carbonate clusters and polymer-associated films, with calcite formation supported by TG/DTG and XRD. The results show that MICP–APAM treatment enhances silty clay primarily through coordinated mineralization uniformity, pore refinement, and polymer bridging, providing a sustainable stabilization option for seasonally frozen soils. Full article

The increasing generation of waste toner from printers and photocopiers presents significant environmental and disposal challenges. This study investigates the feasibility of utilizing waste toner as a modifier in asphalt binder to enhance performance and sustainability. Bitumen with a penetration grade of 60/70 was modified with waste toner at varying contents (0–30%). The modified binders were evaluated using penetration, ductility, and softening-point tests to assess their physical behavior. Results indicate that increasing toner content reduces penetration and ductility while improving the softening point, indicating enhanced temperature resistance. Furthermore, asphalt mixtures were evaluated using both destructive (Marshall stability) and non-destructive testing (ultrasonic pulse velocity) methods to provide a comprehensive performance assessment. In addition, an artificial neural network (ANN) model was developed to predict and evaluate the performance of toner-modified mixtures. The findings demonstrate that waste toner can be effectively used as a sustainable modifier in asphalt mixtures, thereby improving material performance and reducing environmental impact. Full article

The construction industry contributes significantly to global CO₂ emissions, primarily due to the production of ordinary Portland cement (OPC). As a sustainable alternative, geopolymer concrete, utilizing industrial by-products, such as ground granulated blast furnace slag (GGBFS) and fly ash (FA), has attracted increasing attention. However, studies on the post-fire behavior of high-strength slag–fly ash-based geopolymer concrete (HSSFGC) remain limited. In this study, two HSSFGC mixtures with FA contents of 10% and 30% were prepared and exposed to elevated temperatures of 100 °C, 300 °C, 450 °C, and 600 °C. After natural cooling, mass loss, ultrasonic pulse velocity (UPV), residual compressive strength, and microstructural evolution were investigated using XRD, FTIR, TGA, SEM, and EDS techniques. The results show that as temperature increases, mass loss and internal defects also increase, accompanied by deterioration of the interfacial transition zone (ITZ). At 100–300 °C, specimens with higher FA content exhibited improved residual compressive strength due to secondary geopolymerization of unreacted FA. However, above 300 °C, all specimens experienced significant strength degradation, with residual compressive strength at 600 °C reduced to 57% for FA-10 and 49% for FA-30 of their respective room-temperature values. This mix-specific difference, attributed to higher pore connectivity and more severe dehydroxylation in FA-30. These findings reveal the temperature-dependent degradation mechanisms of HSSFGC and provide a theoretical basis for post-fire assessment and sustainable engineering applications. Full article

In this study, the effect of substituting waste glass aggregate and recycled concrete aggregate (RCA) at different ratios (20%, 40%, 60%, 80%, 100%) on the compressive strength performance of geopolymer concretes reinforced with tire-derived textile fibers (TDTF) was investigated. A total of 22 different mixtures were prepared, and their 7-day and 28-day compressive strengths, water absorption rates, and ultrasonic pulse velocity (UPV) were determined. The results showed that TDTF improved compressive strength in both waste aggregate series, with a more pronounced contribution at 28 days. Increasing the waste glass aggregate content reduced 28-day compressive strength by 16–31% compared with the control mixture, whereas RCA mixtures showed only 1–4% strength loss up to 60% replacement and 17–19% loss at higher replacement levels. Glass aggregate mixtures generally exhibited higher early-age strength, while RCA mixtures performed better at 28 days. TDTF addition increased the 28-day compressive strength by approximately 25–30%, depending on aggregate type and replacement level. The lowest water absorption value was obtained in the fiber-reinforced glass aggregate series, whereas the highest value was measured in the RCA series, mainly due to the porous adhered mortar on RCA particles. Based on the compressive strength, water absorption, and UPV results, RCA replacement levels up to 60% and glass aggregate replacement levels of 40–60% may be considered suitable for the mixtures examined in this study. Full article

Mining and industrial activities generate large volumes of waste, up to 99% of the extracted material, forming a major global residue source. In this context, the valorization of mining sludge for sustainable construction materials gains relevance. This study examines the fabrication of ceramic bricks incorporating mining sludge from the Panasqueira mine, evaluating sludge incorporation levels and sintering temperatures to optimize resource use and reduce environmental impacts. Bricks were produced by blending residual clays from Víznar (Granada, Spain) with Panasqueira sludge at substitution rates of 10, 25 and 50%, and fired at 800, 950 and 1100 °C. Granulometry was determined for the Víznar clay and mining sludge, while bulk density was measured for the fired bricks. The raw materials were analyzed by XRF and XRD, whereas the ceramic samples were characterized by water absorption, porosimetry, ultrasound pulse velocity, compressive strength testing, ESEM, leaching and colorimetry, to assess their chemical, physical and mechanical behaviour. Both clays and sludge are rich in SiO₂ and Al₂O₃, suitable for ceramic processing, while fluxing oxides promote vitrification and densification. Incorporating 25 and 50% sludge reduces porosity, increases ultrasonic velocity and improves mechanical strength, achieving optimal performance at 1100 °C. Moreover, firing immobilizes toxic metals and allows controlled colour development, confirming their technical performance and suggesting their potential suitability from an environmental perspective. Their microstructure and stability depend on sludge content and firing temperature, essential factors for sustainable construction and architectural rehabilitation. Full article

Testing harvested logs is a critical step in the wood products supply chain. Non-destructive evaluation (NDE) methods are essential for grading and sorting logs, especially given variations associated with tree age. In this study, plantation-grown Eucalyptus nitens from two age groups were sourced from two Tasmanian harvesting sites for NDE and comparison with destructive stiffness testing. The key finding is that the correlation between dynamic modulus of elasticity (DMOE) and static modulus of elasticity (MOE) weakens with increasing age, particularly at the whole-log level. For further analysis, the radial location of recovered small clear samples (from pith to bark) was examined. Core samples (near the pith) showed the strongest correlation between DMOE and static MOE (R² = 0.51), followed by middle (R² = 0.46) and outer samples (R² = 0.25). This study demonstrates that considering the radial location of recovered samples is a more effective approach for improving grading accuracy. Age is a key factor for initial segregation of logs before applying NDE for property analysis of both logs and recovered samples. Full article

Chloride and sulfate ion attacks are among the leading causes of deterioration in reinforced concrete structures, leading to the corrosion of steel reinforcement, expansion, cracking, and premature structural failure. Early detection of these ion-induced deteriorations is essential not only for maintaining safety but also for supporting sustainability objectives by extending service life, reducing material consumption, and minimizing carbon-intensive repairs. This review synthesizes current advances in non-destructive testing (NDT) techniques used to identify and quantify the impacts of chloride and sulfate ions in reinforced concrete. The mechanisms of ion ingress and their associated degradation processes are examined together with the operating principles, strengths, and limitations of key NDT methods, including electrical resistivity, acoustic emission, infrared thermography, ground penetrating radar, and ultrasonic pulse velocity. By enabling timely maintenance decisions and reducing unnecessary demolition or intrusive testing, these NDT methods contribute directly to sustainable infrastructure management. Through comparative analysis and real-world case studies, the paper highlights the most effective NDT applications for deterioration scenarios and outlines emerging innovations that enhance accuracy, data interpretation, and long-term monitoring capabilities. The findings demonstrate how advancements in NDT support the development and preservation of durable and sustainable concrete structures. Full article

Cement is widely used worldwide but contributes to environmental issues due to its reliance on non-renewable resources and high CO₂ emissions. Incorporating waste materials, such as eggshell ash (ESA) and granite waste powder (GWP), as partial cement replacements offers a sustainable approach to reducing the environmental impact of mortar production. This study investigated the effects of replacing cement with a blended eggshell ash–granite waste powder (ESAGWP) mixture at 0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight. Experimental tests evaluated fresh, hardened, and microstructural properties, including workability, compressive strength, bulk density, water absorption, porosity, ultrasonic pulse velocity (UPV), and resistance to sulfate attack at curing ages of 3, 7, 28, 56, and 91 days. The results showed that a 15% replacement of cement with ESAGWP provided optimal performance, maximizing compressive strength, bulk density, and UPV, particularly at later curing ages. At this optimal level, compressive strength reached 35.00 MPa, 36.77 MPa, and 37.58 MPa at 28, 56, and 91 days, respectively, representing improvements of approximately 28.0%, 28.8%, and 26.6% over the plain cement control mix at the corresponding ages. Replacements beyond 15% led to reduced strength, increased porosity, and higher water absorption due to unreacted particles. Microstructural analysis revealed that the ESAGWP15 mix achieved a dense and well-packed matrix, correlating with improved mechanical and durability properties. Overall, the study demonstrates that ESAGWP can serve as an effective supplementary cementitious material (SCM), with 15% replacement recommended for balanced performance and sustainability in mortar production. Full article