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This investigation attempted to analyze the environmental impact of fibers, including their effect on the cost and durability of concrete mixtures, especially given the variety of fibers that are available in the market. Five types of fibers (polypropylene [PP], glass, basalt, polyvinyl alcohol [PVA], and steel) possessing different aspect ratios were considered in this study. The concrete mechanical properties--including the resistance to sorptivity, heat, and freez-ing-and-thawing cycles--were evaluated. Test results showed that the best environmental/cost/durability indicator was achieved for concrete prepared with 0.25% PVA or PP fibers by volume. This indicator gradually degraded with the use of basalt, glass, and steel fibers because of higher cost and greenhouse gas emissions generated during the fiber manufacturing. The use of PVA fibers significantly enhanced the resistance to heat and freezing-and-thawing cycles, while the least-performing concrete contained basalt fibers with relatively reduced flexural properties and increased sorptivity. Keywords: durability; effect of heat; fibers; life-cycle assessment (LCA); mechanical properties.

ABSTRACT Latexes including polyvinyl acetate (PVA) and styrene-butadiene rubber (SBR) are widely used to improve adhesion and bond properties of cementitious-based repair materials. The main objective of this paper is to evaluate the effect of such polymers on stability of highly flowable self-consolidating concrete (SCC) during placement and until onset of hardening. Also, the bond properties to existing concrete substrate and steel bars are investigated. Two series of mixtures prepared with relatively low to high water-to-binder ratio and incorporating 5–15 % polymers were tested. Special emphasis was placed to highlight the altered stability responses including flowability, viscosity, passing ability, and segregation resistance with respect to the European Guidelines for SCC. Remarkable improvements in the concrete-bar bond stresses were noticed with PVA and SBR additions. This was attributed to improved concrete elasticity and tensile splitting strength that increased contribution of material bearing strength around the steel bars.

The development and use of geopolymers (GP) considerably increased in the construction industry. This paper assesses the suitability of metakaolin-based GP mortars for masonry plastering works, including their comparison to masonry cement (MC) mortars and compliance to relevant EN 413-1 and ASTM C91 specifications. Three classes of GP mortars prepared with different metakaolin-to-limestone ratios are tested; the sodium hydroxide and sodium silicate activators contained air-entraining molecules to secure approximately 10% ±2% air content. Test results showed that GP mortars exhibited excellent water retention and increased rheological properties, which was related to higher viscosity of alkaline solution that increases stickiness and overall cohesiveness. For given limestone concentration, the mechanical properties of GP mortars including the pulloff bond strength and sorptivity were remarkably better than MC mixtures. Almost 90% of ultimate compressive strength was achieved after 7 days for GP mortars cured at ambient temperature, while this variedfrom 55 to 80% for MC mixtures cured in moist conditions. This can be particularly advantageous in masonry applications to speed up construction operations while, at the same time, eliminate the hassle of moist curing normally required with cement-based plasters.

The use of self-consolidating concrete (SCC) containing recycled concrete aggregate (RCA) considerably increased in sustainable structural applications and civil engineering works. However, current literature and construction practices are not clear regarding the influence of RCA additions and presence of steel reinforcement on formwork pressure exerted by the plastic concrete. This paper reports experimental data obtained from 32 SCC mixtures possessing different stability levels and cast in 1.6-m high formwork containing various combinations of vertical and transverse steel bars. Test results have shown that mixtures incorporating recycled aggregates exhibited reduced initial maximum pressure, given the higher RCA surface roughness that promotes internal friction and material build-up at rest. The decrease in pressure was particularly accentuated in presence of steel bars, suggesting that the reinforcement cage confines the plastic concrete and carries part of its load. The transverse steel was around 1.5-times more influential than vertical steel in reducing the formwork pressure. The rates of pressure drop over time were not altered because of steel, implying that pressure decay is governed by the concrete intrinsic properties such as thixotropy, RCA friction, and cement hydration. Special emphasis was placed to develop regression models and examine suitability of existing ones to predict lateral pressure of RCA-modified SCC cast in formworks containing reinforcing bars.

Fibers are widely used in concrete structures to control crack propagation and widening due to sustained or impact loads. Nevertheless, the concrete’s mechanical and structural properties are strongly affected by the fibers’ spatial distribution and clumping tendency within the mass material. The main objective of this paper is to assess the efficiency of stochastic finite element modeling to predict the shear strength properties of fiber-reinforced concrete (FRC) beams without stirrups, as tested by four-point loading. Polypropylene and polyvinyl alcohol micro-filament fibers are investigated in this experimental program at relatively high rates, varying from 0.5% to 1% by volume. A stochastic sensitivity analysis is performed using both random fields and random variables to determine the effect of fiber additions on the concrete’s mechanical properties (i.e., splitting tensile strength and modulus of elasticity) including the beam cracking patterns, ductility, mid-span deflection, and ultimate load. Such data could be of interest to civil engineers and structural designers to reduce the effort and resources needed to assess the FRC strength variability and failure behaviors of structural members.

Fiber-reinforced high-strength grout (HSG) can secure exceptional mechanical properties; yet, case studies show that the interfacing layer to the existing substrate can be particularly vulnerable when used in specialty repair, precast, and retrofitting applications. Polymeric latex materials such as styrene-butadiene rubber (SBR) and acrylic ester (AE) are often incorporated to improve the bond properties and ensure monolithic behavior of the composite system. This paper assesses the concurrent effects of using steel fibers (SFs) and polymeric latexes on the flow and rheology of HSG, including their impact on mechanical properties and bond to existing concrete. The SF content varied from 0 to 5% by volume, while the mixing water was replaced by 10 to 20% of latex. Test results showed that the rheological properties of HSG increased with latex inclusion, given the coalescence of watersoluble polymers in the cementitious matrix that increased the viscosity of the interstitial liquid phase. The viscosity was aggravated with the addition of SF that accentuates the tendency of fiber grouping and interference between solid particles to hinder the ease of flow. The compressive strength slightly decreased when part of the mixing water was replaced by SBR or AE. Yet, in contrast, the flexural properties and pulloff bond strength were remarkably improved, which can be relevant to guarantee the integrity and monolithic behavior of the repair application. Keywords: bond strength; fibers; high-strength grout; polymers; rheology; thixotropy.

The utilization of expanded polystyrene (EPS) beads in semi-lightweight concrete (SLC) intended for repair and building applications has gained great attention in recent years. This study examines the effect of mix design parameters including binder content, water-to-binder ratio (w/b), EPS content, and silica fume (SF) additions on the mechanical properties and durability of SLC mixtures. The experimental program was carried out following the Taguchi approach for four parameters, each having three levels, to produce an L9 orthogonal array. The performance criteria under investigation were the superplasticizer demand, density, compressive strength, splitting tensile strength, ultrasonic pulse velocity, water absorption, sorptivity, and abrasion resistance. Test results showed that the w/b and EPS content were the most contributing parameters that altered the SLCs performance. The multi-response optimization method (TOPSIS) revealed that superior performance could be achieved using a binder content of 375 kg/m3, a w/b of 0.45, an EPS content of 3 kg/m3, and a SF replacement rate of 8%. The mix design parameters were utilized to create multivariate regression models to predict the SLCs mechanical and durability properties. Such data can be of particular benefit to engineers seeking the use of lightweight materials for sustainable construction with optimized durability and a reduced cement carbon footprint.

Limited investigations have evaluated the effect of expanded polystyrene (EPS) beads on the structural lightweight concrete properties. EPS offers many features compared to natural or artificial lightweight aggregates including the elimination of aggregate saturation prior to concrete batching, ability to be fabricated on site, consistency in size and quality, and reduced cost. The main objective of this paper is to assess the suitability of finite element (FE) modeling based on deterministic and stochastic approaches to predict the shear strength behavior of reinforced concrete (RC) beams containing EPS additions. Test results showed that the experimental load-deflection properties recorded at failure can be well reproduced using both FE approaches. Nevertheless, the damaged-zone distribution and crack patterns that occur during the loading stages of RC beams cannot be approximated using the deterministic FE approach. In contrast, the stochastic method was quite suitable as it accounted for the concrete heterogeneity and altered spatial mechanical properties (such as compressive strength, splitting tensile strength, and Young’s modulus) due to EPS additions. Such data can be of interest to civil engineers seeking to predict the failure patterns and performance of structural lightweight members while reducing the time and resources needed to account for the concrete’s strength variability during experimental testing.

Nowadays, the increasing demand for concrete is causing serious environmental impact including pollution and waste generation, rapid depletion of natural resources, and increased CO2 emission. Incorporating natural fibers in concrete can contribute toward environmental sustainability. This paper is concerned with the use of natural fibers obtained from the plant species Phragmites australis (PA). The plant is invasive, and rapidly grows abundantly along rivers and waterways, causing major ecological problems. This research is part of a wide range investigation on the use of natural fibers produced from the stem of PA plants in concrete. Using a machine, plant stems were crushed into fibers measuring 40 mm in length and 2 mm in width, and treated with 4% NaOH solution for 24 h. A total of four concrete mixes were prepared with varying additions of treated fibers, ranging from 0% to 1.5% (by volume) with water to cement ratio of 0.5% (by volume). Concrete specimens were tested at 3, 7, and 28 days. Testing included compressive strength, density, total water absorption, and capillary water absorption. The results show that incorporating PA natural fibers reduces the water absorption by total immersion and capillary action by up to 45%. Moreover, there is a negligible decrease in concrete density and strength when fibers were added. It is concluded that adding up to 1.5% natural PA fibers to concrete is a feasible strategy to produce an eco-friendly material which can be used in the production of sustainable building material with adequate mechanical and durability performance.

Limited investigations have evaluated the potential of using layered sections of normal-weight and lightweight concrete (NWC and LWC) mixtures in structural beams and slabs. The main objective of this paper is to assess the flexural strength properties of layered reinforced concrete (RC) beams, which help conserve natural resources and reduce construction weight. Six RC beams cast with different NWC/LWC combinations are tested to determine the damage patterns, concrete strains, ultimate load, displacements at failure, and ductility. The test results showed that the LWC cast in the tension zone (and up to the neutral axis) has a negligible effect on the beam’s stiffness and ultimate load since the overall behavior remains governed by the yielding of tensile steel reinforcement. Nevertheless, the deflection at failure and ductility seem to gradually curtail when the NWC is partially replaced by LWC at different elevations across the beam’s cross-section. A finite element analysis using ABAQUS software 6.14 is performed, and the results are compared with experimental data for model validation. Such data can be of interest to structural engineers and consultants aiming for optimized design of slabs and beams using layered concrete casting, which helps reduce the overall construction weight while maintaining the structural integrity of members.