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This study aims to evaluate the physical, mechanical, permeability, and durability characteristics of pervious geopolymer concrete (PGC) made with recycled concrete aggregates (RCA), blast furnace slag (GGBS), and fly ash (FA). PGC mixes were formulated to attain two design porosities, 10 and 15%, using two binder combinations of GGBS:FA at ratios of 1:0 and 1:1. Natural coarse aggregates (NCA) were substituted with up to 100% RCA. Hardened density, porosity, compressive, splitting tensile, and flexural strengths, permeability, and abrasion resistance were determined. Results showed that PGC mixes had superior or comparable performance to the control mix made with cement and NCA. The incorporation of RCA or FA into the PGC mix reduced the hardened density, strengths, and abrasion resistance, while increasing porosity and permeability. The combined effect of FA inclusion and higher design porosity of 15% intensified the reduction in performance. The clogging and permeability restoration potential were evaluated after a simulated 20-year exposure to clogging materials. Despite permeability losses reaching 71% due to clogging, nearly 94% of the initial permeability could be restored through pressurised water washing. Research findings highlight the ability to valorise GGBS, FA, and RCA in the production of a cement-free PGC for use in pavement applications.

The exit exam is a comprehensive assessment tool that provides direct evidence of student learning and the level of achievement of program learning outcomes (PLOs). Initial offerings of exit exams showed poor student performance and little correlation to their coursework grades. Accordingly, a continuous improvement process was prompted, including planning, implementing, monitoring, responding, and reporting. In this context, four remedial actions were applied to the exit exam over five semesters, including distributing practice questions, followed by rescheduling exams, simplifying and distributing questions, and increasing the exit exam’s weight contribution. This study explores the effectiveness of these remedial actions to assess and improve student learning and the attainment of PLOs. The performance data indicated significant improvements in exit exam scores, with the average exit exam score increasing from 47% to 78%. Students’ exit exam performances aligned with their grade point averages (GPAs, %), evidenced by a reduction in the variation between the two parameters from 39.2% to 0.6%. Furthermore, the study confirmed that the exit exam, through continuous improvement and targeted remedial strategies, improved the attainment level of PLOs to achieve the target of 70%. The study highlights how strategic interventions can lead to significant enhancements in individual and cohort performances, providing a model for other engineering programs aiming to boost student outcomes and align with accreditation standards and student needs.

This study examines the combined effect of geopolymeric binder and recycled coarse aggregates (RCA) on the properties of concrete masonry units (CMU). A target 1-day compressive strength of at least 13.8 MPa was attained for all mixes to satisfy the load-bearing strength requirements. Geopolymer mixes made with RCA at replacement rates of up to 100 % were evaluated and compared to a cementitious control mix made with natural coarse aggregates. The environmental and economic impacts were then integrated with the quantity of waste valorized and compressive strength in a multifunctional performance index. Experimental results showed that the utilization of geopolymers as a substitute for Portland cement in the production of CMU did not impact the oven-dry density but reduced the water absorption capacity by up to 26 %. Although the incorporation of RCA negatively impacted these two properties, their values remained within the acceptable range stated by the standards. The geopolymer CMU mix made without RCA had 9 and 25 % lower 28-day compressive and splitting tensile strengths compared to the cement control mix, respectively. Subsequent RCA replacement further reduced these mechanical properties. While the linear drying shrinkage was reduced upon substituting the cementitious binder with the geopolymeric counterpart, RCA replacement of up to 100 % increased the linear drying shrinkage to reach 0.091 %, exceeding the limit set by the standard. Overall, the CMU mix made with geopolymer binder and 75–100 % RCA was found to be optimal for load-bearing applications.

This study focuses on a novel technique to improve the resistance of cement-based concrete to chloride ion penetration by incorporating NH2-MIL-125(Ti) metal-organic frameworks (MOF) into the mix. The MOF was produced and assessed against its chloride adsorption capacity. Subsequently, it was added to cement-based concrete in proportions of 1 %, 3 %, and 5 %, by cement mass. The effect of incorporating MOF on the concrete resistance to chloride penetration, reaction kinetics, and compressive strength was investigated. The experimental results revealed that the NH2-MIL-125 (Ti) MOF effectively removed/adsorbed the chloride ions from sodium chloride solutions, with a maximum removal capacity of 31.5 % after 7 days of exposure. Furthermore, the depth and rate of chloride ion penetration into the concrete were reduced as the mass of MOF incorporated into the concrete mix increased. Yet, the efficiency of the MOF to reduce chloride penetration decreased over time, owing to its saturation by continuous exposure to chloride ions. Furthermore, the addition of up to 5 % MOF, by cement mass, had a limited impact (

Thermosetting post-consumer plastics like polyethylene terephthalate (PET) raise serious recycling challenges, leading frequently to disposal through incineration or landfilling. This study assesses the feasibility of cementitious materials containing PET additions including the influence of cement content, water-to-cement ratio (w/c), styrene-butadiene rubber (SBR) polymer additions, and PET volume on the fresh and hardened properties. The mixture proportioning followed the Taguchi methodology, which entailed the utilization of four factors, each possessing three different levels to create an L9 orthogonal matrix. The assessment included diverse performance indicators such as flow, compressive strength, flexural strength, bond strength, water absorption, and resistance to carbonation. Test results revealed that the incorporation of SBR and PET degraded the compressive strength, albeit this can be restored by increasing the cement content and/or reducing w/c. The addition of SBR significantly improved the flexural and bond strengths yet curtailed the water absorption and resistance to carbonation due to increased closed porosity that facilitated the transport properties. The multi-criteria optimization approach (TOPSIS) indicated that superior performance can be achieved using a cement content of 525 kg/m3, w/c of 0.55, SBR of 3.5 %, and PET incorporation of 4.5 %. These parameters were subsequently employed in the development of multivariate regression models, allowing for the prediction of fresh and hardened properties in SBR-PET mortar.

This study examines the properties of cementitious composites incorporating volcanic ash (VA) and dune sand. The effect of five mix design parameters was studied using the Taguchi method. The fresh, mechanical, and durability properties of sixteen mixes were evaluated. To convert the evaluation from single criterion to multi-criteria, a hybrid Taguchi-TOPSIS was employed. Results showed that the optimum composite mix was made with a binder content of 500 kg/m3, a water-to-binder ratio of 0.5, VA replacement of 20%, dune sand replacement of 20%, and SP content of 0.75%. The optimum mix had a flow, final setting time, 28-day compressive strength, volume of permeable voids, and calcium leaching strength retention of 175 mm, 440 min, 50.5 MPa, 11.3%, and 78.8%, respectively. Portlandite, tobermorite, and gismondine were characterized as hydration products, while calcite and dolomite were also detected. This work provides an advanced understanding of the impact of mix design parameters on various properties while optimizing their levels for superior performance.

This research examines the performance of concrete reinforced with different sizes and combinations of basalt fibers (BF). Test parameters comprised the base concrete grade [normal-strength concrete (NSC) and high-strength concrete (HSC)] and BF configuration (short with length of 20 mm, long with length of 50 mm, and hybrid combination at ratio of 1:1). The BF volume fraction (νf) was 1.0%. The tests included slump, compression, splitting, flexure, bulk resistivity, and ultrasonic pulse velocity (UPV). The base concrete grade had no effect on the slump reduction, splitting and flexural strength gains caused by BF when short BF were used. The slump reduction caused by BF was aggravated when long or hybrid BF were used. The use of BF slightly reduced the compressive strength by up to 13%. Short BF resulted in a minor increase of up to 8% in the splitting and flexural strengths, irrespective of the base concrete grade. Hybrid BF resulted in similar or higher splitting and flexural strength gains, except in one case where long BF were more effective. The splitting tensile strength gain caused by long BF was more pronounced for NSC (25%) than HSC (14%). NSC mixtures exhibited higher flexural strength gains (18–20%) than those of their HSC counterparts (10–16%), when long or hybrid BF were used. The use of BF improved the bulk resistivity but had no effect on UPV. Simulation models were developed for the tested concrete prisms. A new tensile softening law was established for BF-reinforced concrete based on inverse analysis of test data.

The properties of pervious concrete made with coarse recycled concrete aggregates (RCA), recycled fine glass (RFG), and ground granulated blast furnace slag (GGBS) were examined. Pervious concrete was produced by substituting coarse aggregates with 0–40% RCA, fine aggregates with 0–100% RFG, and cement with 50% GGBS. Results revealed that incorporating RCA and RFG decreased slump and density but increased porosity and permeability. RCA replacement had a more noticeable negative effect on compressive strength, while RFG replacement was more impactful on splitting tensile and flexural strengths. Abrasion resistance decreased upon RCA inclusion and slightly increased with RFG incorporation. The performance of pervious concrete enhanced with GGBS addition. Its clogging potential was evaluated over a 30-year simulated lifespan. Permeability could be restored to half the original level. While RCA led to lower restoration rates, RFG and GGBS inclusions improved it. Analytical models were developed to correlate and predict the properties of pervious concrete.

This study examines the effect of using ceramic waste (CW) and granulated blast furnace slag (GBFS) as a blended binder on the mechanical and durability characteristics of geopolymer concrete. The experimental design was carried out following the Taguchi approach for five factors, each having four levels, to produce an L16 orthogonal array. The factors included the binder content, CW replacement by GBFS (CW:GBFS), ratio of alkaline solution to binder (AS:B), ratio of sodium silicate solution to sodium hydroxide solution (S:H), and sodium hydroxide (NaOH) solution concentration. The quality criteria were compressive strength, elastic modulus, splitting tensile strength, flexural strength, abrasion resistance, water absorption, sorptivity, ultrasonic pulse velocity, and bulk resistivity. The proportions of CW-GBFS geopolymer concrete mixes were optimized using the best-worst method and TOPSIS approach considering 9, 5, and 2 quality criteria in three scenarios. Experimental test results revealed that the optimum mix was the same for both optimization techniques irrespective of the number of quality criteria considered. The optimum mix comprised a binder content of 450 kg/m3, CW:GBFS ratio of 2:3, AS:B ratio of 1:2, S:H ratio of 3:2, and NaOH solution concentration of 10 M. The anticipated results of the optimum mix were validated through experimental testing. Its experimental test results included compressive, flexural, and splitting tensile strengths of 58.9, 5.72, and 3.81 MPa, respectively. Meanwhile, it had a water absorption of 3.45%, elastic modulus of 27.4 GPa, sorptivity of 0.025 mm/s0.5, bulk resistivity of 4652 Ω•cm, abrasion resistance of 8.98%, and UPV of 6745 m/s.

This study investigates the potential use of geopolymer (GP) composites for screed applications complying with BS 8204 requirements. Different cementitious (CM) and GP screed mixtures were prepared with varying the liquid-to-binder ratio, binder-to-sand ratio, and type of sand. The fresh and mechanical properties were evaluated by testing the flowability, flow retention, density, setting time, compressive and flexural strengths, drop impact resistance, and pull-off and slant shear bond strengths. Test results showed that the fresh properties of GP screeds were relatively inferior to those of CM counterparts; however, the strength development rates and resistance against the impact of GP screeds were higher, reflecting their capability to accelerate operation works without the use of moist curing that is normally required for cement-based materials. The sand content was increased in GP screeds without compromising the superior mechanical and bond properties. Screed mixes made with crushed sand at a binder-to-sand ratio of 1:7, and the solution-to-binder ratio of 0.60 complied with Category B, while screed mixes made with dune sand at a binder-to-sand ratio of 1:2 and the solution-to-binder ratio of 0.55 complied with Category A of BS 8204. An increase in the binder-to-dune sand ratio to 1:3 did not affect the classification of the screed composites, while decreasing the solution-to-binder ratio shifted the material to Category B. Such data can be of interest to contractors and engineers aiming to replace Portland cement and crushed sand with GP-based mixtures containing dune sand for screed applications, leading to an enhanced sustainability of the construction industry.

The shear performance of recycled aggregates beams reinforced with basalt fiber-reinforced polymer (BFRP) bars is evaluated and compared with that of similar beams made with natural aggregates (NA). Six beams with a shear span-to-effective depth ratio (a/d) of 3.0 were tested to failure. Test variables consisted of the recycled concrete aggregate (RCA) replacement percentage (60 and 100%) and the presence of BFRP stirrups in the shear span. Experimental results showed that a RCA replacement of 60% marginally reduced (5%) the shear capacity. However, the reduction in the shear capacity was more pronounced (17%) for the specimen made with 100% RCA. The contribution of BFRP stirrups to the shear capacity decreased with an increase in the RCA replacement percentage. The width of the major shear crack at a given value of load was higher for the beams with RCA. The deflection values at the ultimate load were greater for beams made with RCA. A codified analytical approach as well as a model published in the literature were employed to predict the shear capacity of the tested beams. Predictions of the codified analytical approach were very conservative. The analytical model published in the literature provided a more reasonable prediction for the shear capacity of the tested beams than that of the codified analytical approach.

The transition from face-to-face classes to fully online learning (OL) during the spring semester of 2020 occurred almost globally because of the imposed COVID-19 lockdown. The present study investigated the perception and experiences of undergraduate students and faculty members of the Civil Engineering program at the United Arab Emirates University concerning switching to OL during COVID-19. Quantitative questionnaires were distributed to faculty members and students following the end of the spring semester of 2020. Students and faculty members identified student engagement and online exams as major areas that require improvement. Online exams were challenging for students and difficult to prepare, control, and administer for faculty. Providing technical support is critical for the successful streaming of online courses. Initially, half of the surveyed students began the transition with a positive attitude toward OL, and this percentage increased during the transition. The capacity to continue learning during the COVID-19 crisis and the availability of recorded materials were perceived by the students as the main advantages of OL while challenging online examinations and the lack of social interaction were the main disadvantages.

The temperature rise in mass concrete usually leads to premature distresses and early-age cracking. This paper correlates the time-temperature profiles to the mechanical properties and durability of high-performance mass concrete (HPMC). Five types of cement having different specific surface areas (SSA) and granulated blast furnace slag (GBFS) replacement rates are tested. Thirteen thermocouples were inserted at various locations inside a 1-m3 formwork to record the rate of concrete temperature rise, maximum temperature (Tmax), and time needed to attain Tmax. The mechanical properties were characterized by the compressive and flexural strengths, while the durability was evaluated using the drying shrinkage, water permeability, and chloride migration. Experimental results showed that concrete containing fine cement exhibited better strength and durability, yet increased tendency to thermal cracks and drying shrinkage. The partial cement replacement by GBFS reduced the concrete rate of temperature rise and Tmax, which led to reduced shrinkage. Analytical correlations and multivariable linear regression models were developed to predict the effect of SSA, GBFS replacement rate, and 28-day heat of cement hydration on the time-temperature characteristics and durability of HPMC.

The performance of hybrid basalt fiber (BF)-reinforced concrete made with recycled concrete aggregates (RCAs) and dune sand as an eco-friendly construction material is examined. Test variables comprised the base concrete grade (normal- and high-strength concrete (NSC and HSC)), the hybrid BF volume fraction (νf = 1.0 and 1.5%), and the RCA replacement percentage (30, 60, and 100%). The workability of the concrete mixtures was evaluated via the slump test. The mechanical properties were assessed using compression, splitting tensile, and four-point flexural tests. The durability characteristics were examined using bulk resistivity and ultrasonic pulse velocity (UPV) tests. The addition of hybrid BFs was detrimental to the slump and compressive strength of the concrete mixtures. In contrast, improvements of up to 32 and 40% were recorded in the splitting and flexural strengths of NSC mixtures made with 30–100% RCA. The HSC mixtures exhibited respective improvements of up to 26 and 34% at RCA replacement percentages of 30–60%. The bulk resistivity and UPV values of NSC and HSC mixtures remained almost unaltered with the addition of hybrid BFs. New idealized tensile softening laws were developed for RCA–based concrete reinforced with hybrid BFs. The tensile softening laws were implemented into numerical models that simulated the flexural behavior of the tested concrete prisms with good accuracy.

The construction industry has seen a growing emphasis on the use of sustainable materials in recent years. This is driven by various factors, including a desire to reduce environmental impact, improve indoor air quality, and promote the health and well-being of building occupants. One sustainable material that is being increasingly utilized in construction is natural fibers. Phragmites australis fibers, in particular, are renewable, biodegradable, and have a low carbon footprint. The present study aims to evaluate the impact of Phragmites australis fibers on the behavior of reinforced concrete beams. Five concrete mixes were utilized in the experiment, with the control mix having a 1:1.5:3 ratio of cement to sand to coarse aggregate by weight. The other four mixes incorporated Phragmites australis fibers at 0%, 0.5%, 1%, and 1.5% of the volume of the mix, with cement replaced by 10% glass by weight. The water-to-cement ratio was set at 0.4 for all mixes. Concrete cubes, cylinders, and prisms were prepared to determine mechanical and physical properties, while reinforced concrete beams were used to assess structural performance. The results of the experiment showed that the addition of Phragmites australis fibers slightly decreased the compressive and tensile strength of the concrete compared to the control mix. However, the inclusion of 0.5% Phragmites australis fibers enhanced the split tensile and flexural strength of the concrete. In terms of reinforced concrete beams, the maximum load-bearing capacity was realized for the mix with 10% glass and 0% Phragmites australis fibers. However, the highest ductility index and deflection were achieved for the mix with 10% glass and 0.5% Phragmites australis fibers. Therefore, the use of Phragmites australis fibers can improve the structural performance of concrete.

This study examines the fresh and hardened properties of normal- and high-strength concrete (NSC and HSC) reinforced with basalt macro-fibers (BMF) at a volume fraction (νf) of 0.5–1.5%. Workability tests were conducted on the fresh concrete to evaluate the slump, compacting factor, and vebe time. Mechanical tests were performed on the hardened concrete to examine the compressive strength, tensile properties, and flexural performance. Different durability characteristic tests were carried out to evaluate the water/chloride penetrability, bulk resistivity, and abrasion resistance of the hardened concrete. The addition of BMF reduced the concrete workability of both NSC and HSC at almost the same rate. A maximum slump reduction of 78%, on average, was recorded at νf of 1.5%. The compressive strength of the NSC slightly increased by 1–5% due to the addition BMF, whereas that of the HSC with BMF was, on average, 6% lower than that of their plain counterparts. The NSC with BMF exhibited significant improvements of 10–52% in the splitting tensile strength, 18–56% in the flexural strength, and 17–27% in the abrasion resistance. The enhancement caused by the addition of BMF was less pronounced for the HSC, where maximum respective improvements of 22, 25, and 4% were recorded. The NSC and HSC with BMF exhibited a similar reduction in the water absorption (max. of 12%), chloride penetrability (max. of 19%), and a comparable improvement in the bulk resistivity (max. of 21%), relative to those of their plain counterparts. The flexural test results along with an inverse analysis were employed to develop new tensile softening laws of concrete with different BMF volume fractions.

Geopolymer concrete is typically characterized by a brittle behavior and limited crack resistance. This study evaluates the performance of ambient-cured slag-fly ash blended geopolymer concrete reinforced with glass fibers. Two types of glass fibers were used exclusively or as a hybrid combination. The workability of glass fiber-reinforced geopolymer concrete was assessed using the slump, compaction factor, and vebe time. The compressive strength, splitting tensile strength, and modulus of elasticity were used to characterize the mechanical properties, while water absorption, sorptivity, abrasion resistance, and ultrasonic pulse velocity were employed in evaluating the durability. Experimental results showed that the slump and compaction factor decreased by up to 75% and 18%, respectively, with glass fiber addition but less significantly in mixes reinforced with hybrid fiber combinations. Meanwhile, the vebe time increased by up to 43%. Hybrid glass fibers led to superior mechanical and durability properties compared to plain mixes and those reinforced with a single type of glass fiber, even at higher volume fractions. The compressive strength, splitting tensile strength, and modulus of elasticity increased by up to 77%, 60%, and 85%, respectively. While the water absorption decreased by up to 42%, the sorptivity, abrasion resistance, and ultrasonic pulse velocity increased by up to 67%, 38%, and 280%, respectively. Analytical regression models were established to predict the mechanical and durability characteristics of glass fiber-reinforced slag-fly ash blended geopolymer concrete and were compared to those of design codes.

A bilinear tensile softening law that can describe the post-cracking behavior of concrete made with recycled concrete aggregates (RCAs) and steel fibers was developed based on an inverse analysis of characterization test data. Numerical simulation models were developed for large-scale concrete deep beams. The tensile softening laws along with characterization test results were used as input data in the analysis. The numerical deep beam models were validated through a comparative analysis with published experimental results. A parametric study was conducted to investigate the effect of varying the shear span-to-depth (a/h) ratio, steel fiber volume fraction (vf), and the presence of a web opening on the shear response. Results of the parametric study indicated that the shear strength gain caused by the addition of steel fibers at vf of 1 and 2% was higher in the deep beam models with a lower a/h of 0.8, relative to that of their counterparts with a/h of 1.6. The effect of a/h on the shear strength gain of the solid deep beam models diminished at the higher vf of 3%. The solid deep beam models with a/h of 0.8 exhibited a shear strength gain of 78 to 108% due to the addition of steel fibers, whereas their counterparts with the web opening experienced a reduced shear strength gain of 45 to 70%.

This paper examines the effectiveness of using carbon fabric-reinforced matrix (C-FRM) composites to improve the shear response of reinforced concrete (RC) deep beams. Ten RC deep beams were tested. Test variables included the presence of internal steel stirrups, number of C-FRM layers, angle of inclination of the second layer of C-FRM, and type of matrix. In the absence of minimum steel stirrups, the use of one layer of C-FRM with cementitious and geopolymeric matrices resulted in 95% and 77% shear strength gains, respectively. Increasing the number of C-FRM composites to two layers insignificantly increased the shear strength gain. Positioning the second layer of C-FRM in the vertical direction tended to be more effective than placing it in the horizontal direction. The gain in the shear capacity was less pronounced in the presence of steel stirrups, where a maximum shear strength gain of 18% was recorded. Numerical models were developed to predict the shear response of the tested beams. Outcomes of the numerical modeling were in good agreement with those obtained from the tests. The inclusion of a bond–slip law at the fabric–matrix interface insignificantly reduced the predicted shear strength. The ratios of the predicted-to-measured shear capacity of the models with and without the bond–slip law were, on average, 0.90 and 0.95, with corresponding standard deviations of 0.09 and 0.11, respectively.

In recent years, pervious concrete (PC) has gained much attention as one of the strategies for low-impact development (LID) in pavements due to its structural, economic, and road-user benefits. This study sought to review and evaluate changes in the mechanical, hydraulic, and durability performance of PC produced with cement and aggregate replacements. A meta-analysis was conducted to elucidate the feasible range of the replacement percentage and the number of materials that could be used to replace cement and aggregates; single or binary replacements were considered. Results indicated that cement-replacing materials, industrial wastes (IWA), and recycled aggregates (RA) met the minimum requirement for the mechanical, hydraulic, and durability properties of PC. The use of a single cement replacement material provided PC with better performance than when cement was replaced with two or more materials or when cement alone was used. Industrial waste was found to be a better replacement to aggregates than RA. The combined replacement of cement and aggregates with IWA and other cement-replacing materials was the most effective method for improving the mechanical, hydraulic, and durability performance of PC. Replacements of up to 40% was considered viable for cement replacement, while up to 50% replacement was considered practical for aggregate and combined replacement. PC incorporating different cement-replacing materials exhibited equivalent or improved mechanical properties and maintained hydraulic performance compared to cement-based PC. Nonetheless, limited studies are available on the durability performance of PC made with cement and/or replacements. Thus, the durability of PC coupled with the applicability of replacement materials acquired from different locations need to be evaluated to address the viability of producing more durable PC with the use of replacements.

Results of an experimental investigation aimed at studying the effect of steel fibers on the shear behavior of concrete deep beams made with a 100% recycled concrete aggregate (RCA) are presented in this paper. The study comprised testing of seven concrete deep beam specimens with a shear span-to-depth ratio (a/h) of 1.6. Two beams were made of natural aggregates (NAs) without steel fibers, two beams were made of a 100% RCA without steel fibers, and three beams were made of RCA-based concrete with steel fibers at volume fractions (vf) of 1, 2, and 3%. Two of the beams without steel fibers included a minimum shear reinforcement. Test results showed that the beam with a 100% RCA without steel fibers exhibited a lower post-cracking stiffness, reduced shear cracking load, and lower shear capacity than those of the NA-based control beam. The detrimental effect of the RCA on the shear response was less pronounced in the presence of the minimum shear reinforcement. The addition of steel fibers significantly improved the shear response of the RCA-based beams. The post-cracking stiffness of the RCA-based concrete beams with steel fibers coincided with that of a similar beam without fibers containing the minimum shear reinforcement. The use of steel fibers in RCA beams at vf of 1 and 2% restored 80 and 90% of the shear capacity, respectively, of a similar beam with the minimum shear reinforcement. The response of the RCA specimen with vf of 3% outperformed that of the NA-based control beam with the minimum shear reinforcement, indicating that steel fibers can be used in RCA deep beams as a substitution to the minimum shear reinforcement. The shear capacities obtained from the tests were compared with predictions of published analytical models.

This study evaluates the performance of alkali-activated slag-fly ash blended concrete made with recycled concrete aggregates (RCA) and reinforced with steel fibers. Two blends of concrete with ground granulated blast furnace slag-to-fly ash ratios of 3:1 and 1:1 were used. Natural aggregates were substituted with RCA, while macro steel fibers with 35 mm of length and aspect ratio of 65 were incorporated in RCA-based mixtures at various volume fractions. Fine aggregates were in the form of desert dune sand. Mechanical and durability characteristics were investigated. Experimental results revealed that RCA replacement decreased the compressive strength of plain concrete mixtures with more pronounced reductions being perceived at higher replacement percentages. Mixtures made with 30%, 70%, and 100% RCA could be produced with limited loss in the design compressive strength upon incorporating 1%, 2%, and 2% steel fibers, by volume, respectively. In turn, splitting tensile strength was comparable to the NA-based control while adding at least 1% steel fiber, by volume. Moreover, higher water absorption and capillary sorptivity and lower ultrasonic pulse velocity, bulk resistivity, and abrasion resistance were reported during RCA replacement. Meanwhile, incorporation of steel fibers densified the concrete and enhanced its resistance to abrasive forces, water permeation, and water transport. Analytical regression models were developed to correlate hardened concrete properties to the 28-day cylinder compressive strength.

Fiber reinforced polymer (FRP) composites have been suggested as corrosion-resistant alternatives to traditional steel reinforcement in concrete structures. Within this family of composites, glass fiber reinforced polymers (GFRPs) have been gaining momentum as the primary selection of FRP for construction applications. Despite being advantageous, its wide adoption by the industry has been hindered due to the degradation of its performance in severe environmental conditions. As such, significant studies have been carried out to assess the mechanical properties of GFRP bars subject to different conditioning schemes. However, the inconsistencies and wide variations of results called for more in-depth microstructure evaluation. Accordingly, this paper presents a critical review of existing research on the microstructure of GFRP reinforcing bars exposed to various conditioning regimes. The review analysis revealed that sustained load limits set by codes and standards were satisfactory for nonaggressive environment conditions but should be updated to include different conditioning regimes. It was also found that conditioning in alkaline solutions was more severe than concrete and mortars, where test specimens experienced irreversible chemical degradation, more hydroxyl group formation, and more intense degradation to the microstructure. The progression of hydrolysis was reported correlatively through an increase in hydroxyl groups and a decrease in the glass transition temperature. While moisture uptake was the primary instigator of hydrolysis, restricting it to 1.6% could limit the reduction in tensile strength to 15%. Further, the paper identifies research gaps in the existing knowledge and highlights directions for future research.

This study aims to examine the potential use of a geopolymeric matrix as a sustainable alternative to commercial mortars in carbon fabric-reinforced matrix composites. Single-lap shear tests were conducted to examine the bond behavior at the fabric-matrix interface. Test parameters included the type of matrix (geopolymeric and cementitious matrices) and the bonded length (50 to 300 mm). The geopolymeric matrix was a blend of fly ash/ground granulated blast furnace slag activated by an alkaline solution of sodium silicate and sodium hydroxide. The bond behavior of the geopolymeric-matrix specimens was characterized and compared to that of similar specimens with a cementitious matrix. The specimens failed due to fabric slippage/debonding at the fabric-matrix interface or fabric rupture. The effective bond lengths of the geopolymeric- and cementitious-matrix specimens were 150 and 170 mm, respectively. The geopolymeric-matrix specimens exhibited higher fabric strains, higher ultimate loads, and a steeper strain profile along the bonded length than those of their cementitious-matrix counterparts. New bond-slip models that characterize the bond behavior at the fabric-matrix interface for geopolymeric- and cementitious-matrix specimens were developed. Both models exhibited equal maximum shear stress of 1.2 MPa. The geopolymeric-matrix model had, however, higher fracture energy and higher slip at maximum shear stress than those of the cementitious matrix model.

This study investigates the impact of eggshell particle size and solid-to-water (s/w) ratio on lead (Pb2+) removal from aqueous solution. Collected raw eggshells were washed, crushed, and sieved into two particle sizes (2+ removal experiments were conducted at different s/w ratios with initial Pb2+ concentrations of up to 70 mg/L. The contribution of precipitation to Pb2+ removal was simulated by quantifying removal using eggshell water, whereas sorbed Pb2+ was quantified by acid digestion. Results indicated that eggshell particle sizes did not affect Pb2+ removal. High removal (up to 99%) of Pb2+ was achieved for low initial Pb2+ concentrations (2+ by eggshells. Yet, this role decreased as the s/w ratio and initial concentration of Pb2+ increased. A predictive relationship that relates the normalized removal capacity of eggshells to the s/w ratio was developed to potentially facilitate the design of the reactor.