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• Permeability is investigated on unloaded or preloaded during the heating process. • Axial permeability of concrete decreases with increasing radial confining pressure. • Axial permeability increases with increasing preheating under uniaxial loading. • Radial permeability of concrete decreases with increasing uniaxial compressive loading. • Permeability strongly depends on crack width and orientation, both influenced by axial compression or radial confinement. Concrete permeability is related to pore connectivity and measures the flow rate of gases and liquids through the concrete under a pressure gradient. Information about concrete permeability - both in ordinary environmental conditions and after the exposure to high temperature - is, therefore, badly needed to better understand fluid transport in concrete, with specific reference to high temperature. In fact, permeability influences concrete spalling in fire by favoring pore-pressure build-ups during the heating process. In this research project, two different procedures are adopted to carry out permeability tests on concrete specimens either unloaded or preloaded during the heating process. The results show that concrete permeability strongly depends on crack width and orientation, both are affected by the axial compression or radial confinement. [ABSTRACT FROM AUTHOR]

• Mortar with varying dosages and lengths of amorphous metallic fiber (AMF) were studied. • Flexural performance was enhanced by adding a higher dosage and length of AMFs. • Voids and water absorption increased with the dosage and length of AMFs. • Flexural properties of beams were higher for cured in water than CO 2 -curing. • 0.50% AMF with 20 mm is recommended for producing fiber-reinforced mortar. The present study aims to scrutinize the flexural behavior and engineering properties of beams reinforced with amorphous metallic fiber (AMF) at varying dosages (0%, 0.25%, 0.50%, and 0.75% AMF according to the volume of mortar) and lengths (5 mm, 10 mm, 15 mm, and 20 mm). A total of fourteen mortar mixes, i.e., seven mixes for water curing (immersed in fresh tap water) and seven mixes for carbonation curing (60% relative humidity, 20 °C, and 10% CO 2 concentration) were considered. The load–deflection behavior, flexural strength, pore structures, voids, and water absorption of the beams were investigated. The outcomes were justified with the mix containing 0.5% steel fiber (SF) and a length of approximately 20 mm. The results reveal that the load–deflection behavior and flexural strength were dramatically augmented for the beams with AMF as compared to the control beam (fiber-free beam), and the difference was more pronounced with an increase in both the dosage and the length of the AMF. Greater flexural strength with a lower deflection at failure was registered for the beam with AMF compared to that with SF. The voids and water absorption increased with an increase in the dosage and length of the AMF compared to the control specimen. It was also revealed that the carbonation-cured beams exhibited lower load–deflection behavior and lower flexural strength than those cured in water due to the substantially increased number of voids and greater water absorption driven by the better-connected pores. This study demonstrates that 0.50% AMF with a length of 20 mm can be used in cement-based materials due to the outstanding performance among all mixes. [ABSTRACT FROM AUTHOR]

• Fire spalling and pore pressure of concrete were investigated under different levels of biaxial compressive stress. • The specimens are more prone to spalling when externally loaded than the unloaded specimens. • Fire spalling of concrete occurs due to thermal stress and external biaxial compressive stress, and tensile stresses derived from the vapor pore pressure. • Pore pressure tends to increase with external biaxial compressive stress. • Fire spalling tests should be carried out in loaded conditions. Explosive spalling of concrete exposed to fire consists in the expulsion of shards from the heated face during rapid heating. The phenomenon can seriously jeopardize the integrity of reinforced concrete structures due to the reduction of the cross-sectional area of the structural elements and even lead to the direct exposure of reinforcing bars to flames. The literature shows that various parameters influence the occurrence of fire spalling, such as heating rate, specimen geometry and boundary conditions, concrete grade, and external loads. In this regard, the present study aims at highlighting the role of external loading in combination with the effects of pore pressure and thermo-mechanical stresses in triggering spalling in normal-strength concrete (fc 28days ≈ 45 MPa). Unreinforced concrete slabs (size: 800 × 800 × 100 mm3) were subjected to a standard (ISO 834–1) fire curve under seven different levels of external membrane biaxial compressive load. The experimental results clearly show that compressive loading significantly increases spalling propensity and severity. [ABSTRACT FROM AUTHOR]

• Areca nut husk fiber (AHF) has been added as reinforcement in cement-based mortar. • Workability, mechanical strength, shrinkage, and porosity of mortar were investigated. • Including AHF in mortar mixes enhanced the mechanical strength, mitigated shrinkage, and increased the porosity of mortar mixes. • Reinforcement of AHF withstands the crack propagation and shows gradual failure. • 0.5% AHF is recommended for the production of cement-based mortar. Cement-based materials perform well in compression but poorly in tension due to their brittleness. They also exhibit shrinkage cracking over time, which can be mitigated by incorporating fibers. Areca nut husk fiber (AHF) is agricultural waste, which is eco-friendly, light in weight, renewable, offers higher corrosion protection, and is a sustainable construction material. A novel application of AHF in a cement-based material has been undertaken. The effect of incorporating AHF (0%, 0.25%, 0.50%, 0.75%, and 1.0% by volume of mortar) on the properties of mortar was investigated. Workability, mechanical strength (compressive, tensile, and flexural), shrinkage, and porosity tests were performed. The results were compared to those obtained with jute and coir fiber mortars, as no data on mortar/concrete containing AHF have been reported. The mechanical strength of the mortar was increased at an AHF content of 0.5%. Beyond this level, the strength declined but was not lower than that of the control mix (0% AHF). Furthermore, significant shrinkage mitigation was observed with an increase in the AHF percentage. The porosity of the mortar increased with an increase in the content of AHF. This study reveals that 0.5% AHF can be used in mortar, given its excellent performance among all mixes. [ABSTRACT FROM AUTHOR]

• Waste rubber tire aggregate (WRTA) derived from end-of-life tires replaced clay brick aggregate (CBA) in concrete. • The flexural performance of reinforced concrete beams, mechanical properties, and shrinkage of concrete with untreated and chemically treated (bleaching powder-BP and NaOH) were assessed. • Concrete made with WRTA treated with NaOH and BP has significantly enhanced the mechanical properties and mitigated shrinkage. • WRTA treatment with BP exhibited more promising performance than NaOH. • 15 % WRTA treated with BP solution for 72 h was recommended for structural concrete production. The disposal of waste end-of-life vehicle tires has become a major environmental issue around the globe, as it is not completely biodegradable and can be a massive threat to the environment. Several researchers have attempted to use tires as aggregate with and without chemical treatment. However, to the best of the authors' knowledge, no research has investigated the performance of clay brick aggregate (CBA) concrete by replacing the CBA with bleached powder-treated waste rubber tire aggregate (WRTA) at different treatment times. Within this context, this study examines the mechanical strength, shrinkage, and flexural performance of reinforced concrete (RC) beams made with seven replacement percentages (0, 5, 10, 15, 20, 30, and 50 % by volume) of CBA by WRTA treated with H 2 O, NaOH, and bleaching powder (BP) for 2 h and 72 h. The experimental outcomes reveal that as the percentage of untreated WRTA increases, the slump, dry density, and mechanical strength decrease. Furthermore, concrete shrinkage increases with the increasing content of untreated WRTA in the mix. Likewise, the flexural load of RC beams declines with an increased percentage of untreated WRTA. It has been observed that the concrete made with WRTA treated with NaOH and BP has significantly higher mechanical strength, a flexural load carrying capacity of RC beams, and lower shrinkage compared to the untreated WRTA. The improvement in all properties was more remarkable for the treatment with BP than NaOH and treatment of 72 h than 2 h. The findings reveal that 15 % WRTA treated with BP solution for 72 h can be used as a CBA replacement whose design strength is not significantly high (f c a t 28 d a y s ≈ 20 MPa). [ABSTRACT FROM AUTHOR]

• Overburnt distorted brick aggregate (ODBA) replaced coarse aggregate (regular brick aggregate-RBA) in concrete. • Mechanical strength and porosity before and after high temperatures were investigated. • Incorporating ODBA enhanced the mechanical properties and porosity of concrete. • Concrete with ODBA performed better at elevated temperatures than the RBA. • 75% ODBA was recommended for the production of structural concrete. This study examines the mechanical and durability properties of five concrete mixes made with different replacement percentages (0 %, 25 %, 50 %, 75 %, and 100 % by volume of regular brick aggregates-RBA) of RBA by overburnt distorted brick aggregate (ODBA) before and following exposure to elevated temperatures (250, 400, and 600 °C). The compressive, splitting tensile strength and the flexural load of the beams increased by 17 %, 23 %, and 18 %, respectively, at 28 days, when 75 % RBA was replaced with ODBA. The porosity decreased for the concrete containing up to 75 % ODBA. Conversely, the compressive strength decreased as the temperature increased, which agrees with the increased porosity with the increasing temperature. [ABSTRACT FROM AUTHOR]

This study developed microbial fuel cell (MFC)-based hybrid constructed wetland systems using different filter media, i.e., organic (biochar), construction (sand), and rejected (iron particle, concrete particle, and stone dust) materials, and evaluated the performance of the developed systems for treating landfill leachate. The mean ammonium nitrogen (NH 4 –N), total nitrogen (TN), total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD) removal percentages within the hybrid systems ranged between 91 and 98%, 90 and 98%, 97 and 99%, 88 and 93%, 93 and 97%, respectively, despite higher pollutants concentration in leachate wastewater. The aerobic environment in the cathode compartment (due to intermittent load) and free-draining of wastewater (from cathode to anode compartment) supported electrochemically inactive, active pollutants removal in the electrodes integrated first stage vertical flow (VF) wetlands. The second stage electrodes integrated horizontal flow (HF) wetlands supported electrochemical-based organic removal and nitrification because of efficient organic removal in the previous VF wetland stages. Nitrogen, phosphorus accumulation percentages in plant tissues ranged between 0.3 and 7%, 0.4 and 14%, respectively. Nutrient removal was achieved through chemical and microbial routes. The biochar-packed VF wetland produced a maximum power density of 20.6 mW/m2. The coexistence of unsaturated, saturated media in the partially saturated HF wetland maintained the required environmental gradient between the electrodes and improved operational performance. [Display omitted] • Electrodes integrated hybrid wetlands treated landfill leachate. • Free-draining improved pollutant removal of the VF wetlands. • Filter media influenced bioenergy production in VF wetlands. • Media saturation controlled the operational performance in HF systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Free-draining waste media packed, two-stage MFC-based wetlands were designed. • Biomass, construction, industrial waste can be used as filter media. • Stable pollutant removal was observed regardless of input loads increment. • Nutrient accumulation in plants varied between the MFC-based wetlands. • Input organic load increment decreased voltage production. This study reports organic, nutrient, and coliform removal performances in free-draining, three parallel two-stage microbial fuel cell (MFC)-based wetlands that were filled with organic, construction, industrial waste materials and planted with Canna indica. Two hydraulic load rates, i.e., 260 (Phase I) and 520 mm/d (Phase II), were employed. Mean ammoniacal nitrogen (NH 4 -N), total nitrogen (TN), total phosphorus (TP), coliform removal percentages of the organic, construction, industrial waste materials packed two-stage MFC-based wetland systems ranged between 88 and 96%, 83 and 94%, 59 and 78%, 72 and 100%, respectively, throughout the two operational periods. Chemical oxygen demand (COD) removal percentage in construction, industrial waste materials packed systems ranged between 66 and 79%. The organic waste media packed system achieved low COD removal (33%) during the first operational period that improved substantially (84%) during the last phase. Wastewater organic, nutrient removals were achieved by plant uptake, media-based adsorption, and microbial transformation. Nitrogen, phosphorus accumulation percentages in the plants tissue (with respect to total removal) ranged between 0.3 and 64%, 0.2 and 6%, respectively. Nitrogen, phosphorus concentration in the used media ranged between 0.4 and 13.5 g/kg, 0.7 and 1.1 g/kg, respectively. Maximum voltage and power density production across the construction waste jhama brick packed MFC-based wetland (i.e., 119 mV and 86 mW/m2, respectively) exceeded the bioenergy production of organic, industrial waste materials packed wetlands. Input organic load increment adversely impacted voltage production across all MFC-based wetlands. The carbon composition of the waste media partially supported electrochemical removal mechanisms. This study demonstrates a relatively stable pollutant removal performance of the free-draining construction, industrial waste media packed two-stage MFC-based wetlands despite input pollutant load increment. [ABSTRACT FROM AUTHOR]

This research investigates the flexural and durability performances of reinforced concrete (RC) beams made with induction furnace steel slag aggregate (IFSSA) as a replacement for fired clay brick aggregate (FCBA). To achieve this, 27 RC beams (length: 750 mm, width: 125 mm, height: 200 mm) were made with FCBA replaced by IFSSA at nine replacement levels of 0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% (by volume). Flexural tests of RC beams were conducted by a four-point loading test, where the deflection behavior of the beams was monitored through three linear variable displacement transducers (LVDT). The compressive strength and durability properties (i.e., porosity, resistance to chloride ion penetration, and capillary water absorption) were assessed using the same batch of concrete mix used to cast RC beams. The experimental results have shown that the flexural load of RC beams made with IFSSA was significantly higher than the control beam (100% FCBA). The increment of the flexural load was proportional to the content of IFSSA, with an increase of 27% for the beam made with 80% IFSSA than the control beam. The compressive strength of concrete increased by 56% and 61% for the concrete made with 80% and 100% IFSSA, respectively, than the control concrete, which is in good agreement with the flexural load of RC beams. Furthermore, the porosity, resistance to chloride ion penetration, and capillary water absorption were inversely proportional to the increase in the content of IFSSA. For instance, porosity, chloride penetration, and water absorption decreased by 43%, 54%, and 68%, respectively, when IFSSA entirely replaced FCBA. This decreasing percentage of durability properties is in agreement with the flexural load of RC beams. A good linear relationship of porosity with chloride penetration resistance and capillary water absorption was observed. [ABSTRACT FROM AUTHOR]

The use of waste streams for the production of sustainable cement-based materials cannot be overemphasized. This study investigates the feasibility of reusing waste steel slag (WSS) and waste clay brick (WCB) as a replacement for natural sand (NS) in mortar. Numerous studies have reported mainly the compressive strength of concrete/mortar, while limited research is available that focuses on the tensile and flexural strength of mortar, and especially the performance at elevated temperature. Hence, this study investigates the tensile and flexural strength of mortar with three different replacement percentages (0, 50 and 100% by volume of NS) of NS by WSS and WCB at normal temperature (without thermal treatment) and after exposure to elevated temperatures (250, 400 and 600 °C). At ambient condition, both tensile and flexural strength were enhanced as the WSS content increased (76 and 68%, respectively, at 100% WSS). In comparison, the strength increased at 50% WCB (25 and 37%, accordingly) and decreased at 100% WCB (23 and 20%, respectively) compared to 100% NS. At elevated temperatures, both the tensile and flexural strength of mortar mixes decreased significantly at 600 °C. [ABSTRACT FROM AUTHOR]

Landfill leachate treatment is challenging because of complex chemical composition. This study identifies the factors associated with organics and nutrients removal performance improvement in construction or organic materials based four hybrid wetland systems dosed with landfill leachate. The imbalanced pollutant composition ratio of leachate influenced removal pathways in the hybrid wetlands; effluent recirculation (50 and 25% ratios) adjusted leachate composition and improved removal performances. Mean nitrogen (N), phosphorus (P), biochemical oxygen demand (BOD), and chemical oxygen demand (COD) removal percentages in the hybrid wetlands during without, with recirculation periods ranged between 50 and 93, 69–100, 34–89, and 55–76%, respectively. Pollutant removals were achieved through adsorption, microbial (heterotrophic organic removal, ammonia assimilation, nitrification, denitrification) degradation, and plant uptake. Removal rates did not vary substantially among organic or construction materials based first stage VF (vertical flow) wetlands because of leachate composition. Constant water saturation depth variation influenced pollutant removal rates among the second stage wetlands. Shallow water depth HF (horizontal flow) wetlands appeared to be a promising wastewater treatment technology due to the coexistence of unsaturated, saturated bed matrix that supported diverse removal pathways. Image 1 • Effluent recirculation improved the leachate biodegradation ratio. • Ammonia assimilation, ammonification, nitrification, denitrification removed N. • Media supported nutrient adsorption. • Shallow water depth HF wetlands supported concurrent aerobic-anaerobic removals. [ABSTRACT FROM AUTHOR]

This paper investigates the possibility of utilizing steel slags produced in the steelmaking industry as an alternative to burnt clay brick aggregate (BA) in concrete. Within this context, physical, mechanical (i.e., compressive and splitting tensile strength), length change, and durability (porosity) tests were conducted on concrete made with nine different percentage replacements (0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% by volume of BA) of BA by induction of furnace steel slag aggregate (SSA). In addition, the chemical composition of aggregate through X-ray fluorescence (XRF) analysis and microstructural analysis through scanning electron microscopy (SEM) of aggregates and concrete were performed. The experimental results show that the physical and mechanical properties of concrete made with SSA were significantly higher than that of concrete made with BA. The compressive and tensile strength increased by 73% when SSA fully replaced BA. The expansion of concrete made with SSA was a bit higher than the concrete made with BA. Furthermore, a significant lower porosity was observed for concrete made with SSA than BA, which decreased by 40% for 100% SSA concrete than 100% BA concrete. The relation between compressive and tensile strength with the porosity of concrete mixes are in agreement with the relationships presented in the literature. This study demonstrates that SSA can be used as a full replacement of BA, which is economical, conserves the natural aggregate, and is sustainable building material since burning brick produces a lot of CO2. [ABSTRACT FROM AUTHOR]

This study evaluates the mechanical, durability, and residual compressive strength (after being exposed to 20, 120, 250, 400 and 600 °C) of mortar that uses recycled iron powder (RIP) as a fine aggregate. Within this context, mechanical strength, shrinkage, durability, and residual strength tests were performed on mortar made with seven different percentages (0%, 5%, 10%, 15%, 20%, 30% and 50%) of replacement of natural sand (NS) by RIP. It was found that the mechanical strength of mortar increased when replaced with up to 30% NS by RIP. In addition, the increase was 30% for compressive, 18% for tensile, and 47% for flexural strength at 28 days, respectively, compared to the reference mortar (mortar made with 100% NS). Shrinkage was observed for the mortar made with 100% NS, while both shrinkage and expansion occurred in the mortar made with RIP, especially for RIP higher than 5%. Furthermore, significantly lower porosity and capillary water absorption were observed for mortar made with up to 30% RIP, compared to that made with 100% NS, which decreased by 36% for porosity and 48% for water absorption. As the temperature increased, the strength decreased for all mixes, and the drop was more pronounced for the temperatures above 250 °C and 50% RIP. This study demonstrates that up to 30% RIP can be utilized as a fine aggregate in mortar due to its better mechanical and durability performances. [ABSTRACT FROM AUTHOR]

• Media supported physico-chemical and microbial removal routes. • Nutrient accumulation percentage in plants was low. • N removal was higher in partially saturated coal based TFCW. • Contact period duration influenced pollutant removal in TFCWs. • Combination of feeding sub-cycles and alternative media improved removal. Six partially saturated and unsaturated tidal flow constructed wetlands (TFCWs) were studied for the removal of nitrogen, phosphorus and organics from municipal wastewater. The TFCWs were packed with organic (biochar, coal, coco-peat), waste (slag), construction (gravel, concrete block) materials and planted with Phragmites or Vetiver. Daily wastewater feeding cycle was divided into sub-cycles across all TFCWs. Experimental analyses illustrated higher nitrogen and organics removals in organic media based TFCWs (71–85% and 84–96%, respectively), when compared with those of waste, construction material based units (49–69% and 74–95%, respectively); carbon availability from organic materials increased denitrification that was also supported by energy dispersive spectroscopy (EDS) analyses. Construction and waste material based TFCWs achieved better P removals (≥93%); Ca/Al/Fe ingredients of such materials allowed P removal via adsorption. Increment of wastewater contact period inside the media triggered physico-chemical and microbial removal routes. Partially saturated coal packed TFCW was the most efficient unit in terms of N removal percentage; presence of stationary water volume created anoxic environment and reduced input load, thereby improving removal performances. In terms of removal rates (g/m2 d), unsaturated TFCWs showed higher removal (over partially saturated units), which could be linked with greater input load. Mass balance analyses indicated ≤3% N removal through plant uptake; variation of plant species did not influence N removal. Therefore, observed removal kinetics was governed by adsorption and microbial routes. The results of this study suggest that, feeding sub-cycles could improve pollutant removals in TFCWs when packed with specific media. [ABSTRACT FROM AUTHOR]

Waste tire rubber is one of the most concerning environmental pollution issues. With the increasing demand for automobile production, the rate of waste tire generation has also increased. However, these tires often end up stockpiled and not properly disposed of. This non-biodegradable waste poses severe fire, environmental, and health risks. Due to the progressively severe environmental problems caused by the disposal of waste tires, the feasibility of using such elastic waste materials as an alternative to natural aggregates has become a research topic. The main objective of this research is to investigate the changes in the mechanical and durability properties of concrete with the inclusion of waste tire rubber at specific contents. A total of 80 cylinders measuring 100 mm × 200 mm were cast with waste tire aggregate as a partial replacement for natural coarse aggregate (5% and 10% by weight of natural coarse aggregate). A surface treatment of tire aggregate using a cement coating was performed to study its effect on concrete properties. This research indicates a noticeable reduction in the compressive and split tensile strength of concrete containing untreated waste tire rubber compared to normal concrete made with natural aggregates. However, an improvement was observed when the surface of tire aggregates was coated with cement grout. Additionally, it was noted that the slump value, water absorption, and porosity increased as the percentage of rubber increased. Nevertheless, unlike normal concrete, the failure pattern in tire-mixed concrete occurs gently and uniformly, indicating ductile behavior. [ABSTRACT FROM AUTHOR]

• The effect of sillimanite sand on the properties of AAS mortar at elevated temperatures was investigated. • The strength properties of AAS mortar improved by substituting the silicious normal sand with sillimanite sand. • The compressive strength of AAS mortar prepared using sillimanite sand improved up to the 250 °C exposure. • Sillimanite sand significantly reduced the cracks on the surface of AAS mortar after being exposed to elevated temperatures. The change in the properties of fine aggregate has significant potential in altering the efficacy of alkali-activated slag. Therefore, this study investigated the influence of sillimanite sand on the mechanical and microstructural properties of alkali-activated slag (AAS) mortar at ambient temperature, and after exposure to elevated temperatures (250, 500, 750, and 1050 °C). In addition, the effect of the concentration of sodium hydroxide solution (6, 8, 10, and 12 M) was evaluated. The silicious normal sand was replaced with sillimanite sand at 25, 50, 75, and 100 % by volume. The results show that the superior physical properties of sillimanite sand improved the strength of the AAS mortar, compared with silicious normal sand. After heating at 250 °C, all AAS mortar mixes showed a significantly higher increase in compressive strength compared to unheated samples. Utilization of the largest concentration of sodium hydroxide solution (12 M) as well as sillimanite sand resulted in a residual compressive strength equivalent to the control sample after 500 °C temperature exposure. A significant drop in residual compressive strength was observed for all mixes at 750 °C. Visual observation of the heated samples revealed that casting the mortar samples with sillimanite sand limited the number, width and extent of thermal cracks. XRD analysis revealed the decomposition of C-S-H and the formation of silica oxide at 750 °C. The results of this study suggest that replacing silicious normal sand with sillimanite sand can help the modification of the engineering properties of AAS mortar at ambient temperature, and after exposure to elevated temperatures. [ABSTRACT FROM AUTHOR]

Landfill leachate treatment employing normal and electrode-integrated constructed wetlands is difficult due to the presence of significant amounts of organic compounds, which frequently impede the progression of microbial-based aerobic pollutant removal pathways. As a result, this study examines the effect of supplementary air availability via intermittent and continuous aeration strategies in improving organic, nutrient, and coliform removals of the unplanted, planted (normal and electrode-integrated) two-stage tidal flow constructed wetlands designed to treat landfill leachate. The constructed wetlands were filled with coal and biochar media and planted with Canna indica. Mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages of the externally aerated two-stage unplanted, only planted, planted-microbial fuel cell integrated constructed wetland systems ranged between 96 and 99%, 82 and 93%, 91 and 98%, 86 and 96%, respectively, throughout the experimental campaign. External aeration inhibited the development of a dominant anaerobic environment within the media of the wetland systems and improved overall pollutant removal. The electrode-integrated planted tidal flow wetlands produced better effluent quality than the unplanted or only planted tidal flow systems without electrode assistance. The first stages of the three wetland systems achieved an additional 5–7% COD, 7–12% TN, and 15–22% coliform removal during the continuous aeration period compared to the corresponding performance of the intermittent aeration phase. The pollutant removal performance of the second-stage wetlands decreased during the continuous aeration phase. The media composition supported electrochemically active and inactive microbial-based pollutant removal routes and the chemical adsorption of pollutants. Nitrogen and phosphorus accumulation percentage in plant tissues was low, i.e., 0.4–2.2% and 0.04–0.8%, respectively. During the continuous aeration period, the electrode-integrated tidal flow constructed wetlands achieved higher power density production, i.e., between 859 and 1432 mW (mW)/meter3(m3). This study demonstrates that external aeration might improve pollutant removal performance of the normal, electrodes integrated tidal flow-based constructed wetlands when employed for high organic-strength wastewater treatment such as landfill leachate. [Display omitted] • Normal and electrode-assisted aerated tidal flow wetlands treated leachate. • Plants, electrodes, and aeration have a positive synergistic effect on performance. • 96–99% COD, 82–94% TN, 91–98% TP, and 86–96% coliform removals were achieved. • The nutrient accumulation percentage in plant tissues ranged between 0.02 and 2.2%. • A maximum power density production of 1572 mW/m3 was recorded. [ABSTRACT FROM AUTHOR]

• Palmyra fibre (PF) has been added as reinforcement in concrete mixes. • Rheological and mechanical properties, as well as sustainability assessment, were investigated. • The mechanical strength enhanced dramatically for mix with PF than the fibre-free mix. • Adding PF enhanced ductility and reduced fabrication cost and CO 2 emission. • 1% PF is recommended for the production of fibre-reinforced green concrete. Concrete's poor tensile strength has led to the extensive use of artificial fibre reinforcements throughout history. However, the environmental impacts associated with the production of these fibres have raised concerns, spurring interest in sustainable alternatives, including natural fibres. The untreated fibre extracted from the mesocarp region of full-grown palmyra fruit is a promising natural substitute. This study investigates the effects of adding palmyra fibre (PF) into concrete as a partial replacement for cement. Four fibre concentration levels of 0.5%, 1%, 1.5%, and 2% were considered without any fibre treatment. The addition of PF decreased the workability of fresh concrete mixtures, but it improved compressive strength by 10% and split tensile strength by 21% at an optimal PF concentration of 1%. Higher fibre concentrations led to lower mechanical strength but increased ductility as the compression-to-tension ratio was increased by 35% with incorporation of 2% fibre. Furthermore, fibre-reinforced concrete mixtures had lower production costs and carbon dioxide emissions than conventional concrete mixtures. Overall, this study suggests that palmyra fibre has significant potential for producing sustainable concrete structures. [ABSTRACT FROM AUTHOR]

This study investigates the efficacy of post-fire curing using carbonation with a 20% carbon dioxide concentration and a relative humidity cycle set between 40% and 90% for restoring the mechanical properties of thermally damaged high-performance concrete (HPC) specimens containing 0%–40% silica fume. The HPC specimens were exposed to temperatures of 600, 800, and 1000 °C for 1 h, and the compressive strength recovery was measured. The microstructure, porosity, pore size distribution, and chemical composition of the HPC specimens were analyzed to explore the strength recovery mechanism. After exposure to elevated temperatures, the average compressive strength of samples without silica fume decreased by 49.2 MPa. Subsequent carbonation recuring resulted in a significant recovery of 73.9 MPa in the average compressive strength. This recovery surpassed the original strength for the samples heated to 600 and 800 °C, attributable to the filling and coalescing effects of calcium carbonate polymorphs formed through the carbonation of residual cement particles and β-C 2 S. The samples containing 20% silica fume exhibited the second highest average strength recovery of 34.1 MPa. However, the strength recovery for the samples with 40% silica fume exposed to 800 and 1000 °C was negligible, as the microcracks exceeding 1 μm in width had barely been restored by the carbonation of the low-calcium calcium silicates with low reactivity. Overall, this study presents an exciting future prospect for the labor and cost-effective restoration of thermally damaged concrete structures through the use of carbonation curing. [ABSTRACT FROM AUTHOR]

Explosive spalling consists in the sudden separation of concrete layers or pieces from the surface exposed to fire, due to (a) stress caused by thermal gradients and external loads and (b) pore pressure rise induced by water vaporization. As regards the material properties, the phenomenon is affected by some meso- and micro-structural aspects mainly concerning the interaction during heating among cement paste, aggregate and fibre, thus influencing porosity and permeability variation at high temperature. Focusing on the effect of pore pressure in fracture behaviour of Normal-Strength and High-Performance Concretes, an experimental campaign has been planned, aimed at investigating the role played by the mix design. Nine concrete mixes have been studied considering three grades (f c ≥ 40, 60 and 90 MPa), three aggregate types (silico-calcareous, basalt and calcareous aggregates) and different fibre types and contents (monofilament or fibrillated polypropylene fibres). The experimental study, based on indirect tension tests performed under different levels of sustained pore pressure, clearly shows that the influence of pressure on concrete fracture response during heating strongly depends on mix design. [ABSTRACT FROM AUTHOR]

This study aims to improve the web crippling performance of pultruded glass fibre-reinforced polymer (GFRP) C sections using fibre-reinforced epoxy composite (FEC). The strengthened GFRP C sections were subjected to two loading conditions: interior-two-flange (ITF) and exterior two-flange (ETF). The parameters considered were bearing lengths, FEC strengthening length and thicknesses. Two failure modes, namely web-flange junction failure and web buckling failure were observed for the pultruded GFRP C sections under ETF loading conditions as the bearing length changed. While the combination of the web-flange junction and FEC crushing failures were observed under ITF loading conditions at 20 mm and 50 mm bearing lengths. Furthermore, the average web crippling capacity of strengthened GFRP C sections improved by up to 426 % and 488 %, in comparison to control samples under ETF and ITF loading conditions, respectively. The average web crippling capacity of pultruded GFRP C sections increased up to 45 % when the bearing length increased from 20 mm to 50 mm. The finite element (FE) outcomes showed an agreement with experimental results in the context of failure patterns, load-displacement profiles and web crippling capacities. Finally, equations were proposed to estimate the web crippling capacity of pultruded GFRP C sections strengthened with FEC. [ABSTRACT FROM AUTHOR]

This paper investigated the static behaviour of glass fibre reinforced polymer (GFRP) built-up hollow and concrete filled built-up beams tested under four-point bending with a span-to-depth ratio of 1.67, therefore focusing their shear performance. Two parameters considered for hollow sections were longitudinal web stiffener and strengthening at the web–flange junction. The experimental results indicated that the GFRP hollow beams failed by web crushing at supports; therefore, the longitudinal web stiffener has an insignificant effect on improving the maximum load. Strengthening web–flange junctions using rectangular hollow sections increased the maximum load by 47%. Concrete infill could effectively prevent the web crushing, and it demonstrated the highest load increment of 162%. The concrete filled GFRP composite beam failed by diagonal tension in the lightweight concrete core. The finite element models adopting Hashin damage criteria yielded are in good agreement with the experimental results in terms of maximum load and failure mode. Based on the numerical study, the longitudinal web stiffener could prevent the web buckling of the slender GFRP beam and improved the maximum load by 136%. The maximum load may be further improved by increasing the thickness of the GFRP section and the size of rectangular hollow sections used for strengthening. It was found that the bond–slip at the concrete–GFRP interface affected the shear resistance of concrete–GFRP composite beam. [ABSTRACT FROM AUTHOR]