Macro-synthetic Fibers Research Articles

Effect of shrinkage-mitigating materials, fiber type, and repair thickness on flexural behavior of beams repaired with fiber-reinforced self-consolidating concrete

While self-consolidating concrete (SCC) has emerged as a highly effective approach for the repair of concrete structures, there have been few investigations regarding the effect of the combination of different fiber and shrinkage-mitigating material types (shrinkage-reducing admixture, SRA; superabsorbent polymer, SAP; and expansive agent, EA) on the flexural behavior of repaired structures. This study aims to explore the influence of three different shrinkage-mitigating materials (1.25%–2.5 % SRA, 4%–8% EA, and 0.2%–0.4 % SAP), four fiber types (two macro synthetic fibers, MSFA and MSFB; 5D hooked steel fibers, 5D; a combination of 80 % 3D hooked steel +20 % short steel fibers STST) on fresh and hardened properties, cement hydration, and drying shrinkage of fiber-reinforced self-consolidating concrete (FR-SCC). Specifically, the effect of different shrinkage-mitigating materials, fiber types, and two repair thicknesses corresponding to 1/3 and 2/3 of the total height of prismatic element on the flexural performance of composite specimens repaired using FR-SCC was studied. The bond strength between existing concrete and FR-SCC was also investigated to reveal the flexural behavior of the composite beams. The results indicate that prismatic specimens repaired with FR-SCC made with 1.25 % SRA showed excellent flexural performance compared to those repaired using FR-SCC made with 4%–8% EA and 0.2%-0.4%SAP. The adverse effect of the incorporation of 4%–8% EA and 0.2%–0.4 % SAP on flexural behavior of repair specimens can be attributed to a lower existing concrete-FR-SCC interfacial and fiber-matrix bond strengths. Using SRA, EA, or SAP in FR-SCC improved bond strength with substrate by 10%–60 % compared to FR-SCC without any shrinkage-mitigating materials. The use of 1.25 % SRA showed the highest bond strength, which increased by 10%–37 % and 33%–44 %, respectively, compared to that made with SAP and EA. As the increase in the repair thickness of specimens, the incorporation of SRA, EA, or SAP had different efficiencies to enhance the flexural toughness and residual strength of the repair specimens. Furthermore, the incorporation of 5D fiber and 1.25 % SRA in SCC showed excellent flexural performance, followed by MSFA, STST, and MSFB fibers. The increase in the repair thickness from 1/3 to 2/3 of the total height of the composite beam enhanced the flexural toughness and residual strength by a maximum of 133 % and 160 %, respectively, attributing to fiber type and the increase in fiber volume at the cross-section of specimens.

Flexural post-cracking performance of macro synthetic fiber reinforced super workable concrete influenced by shrinkage-reducing admixture

Most literature has focused on the effect of shrinkage-reducing admixture (SRA) in shrinkage mitigation resistance of concrete. This study aims to examine the impact of SRA on the efficiency of macro synthetic fibers (MSF) in enhancing the flexural post-cracking behavior of fiber-reinforced super workable concrete (FR-SWC). A comparative analysis of the influence of fiber combinations on the flexural post-cracking behavior of beams is also included. Results showed that a higher dosage of SRA, particularly at 5 % by mass of binder, had a noticeable negative impact on flexural post-cracking performance of beams while exhibiting positive effect on workability and shrinkage reduction. However, incorporating low dosages of SRA (1.25 % by mass of binder) did not have a significant impact on the ability of MSF. This was attributed to the reduction of the MSF-matrix bond strength caused by a significant delay in cement hydration. The characteristics of selected MSF type, including length and surface roughness had a positive effect on the post-cracking performance of FR-SWC, regardless of SRA dosage. The notched beams made with 100 % MSFA outperformed those made with fiber combination of 25 % MSFA and 75 % MSFB. Beams made with 100 % MSFA showed 55 % higher residual flexural tensile strength, 49 % higher equivalent flexural tensile strength, 50 % higher fracture energy, and 35 % higher equivalent flexural strength ratio compared to beams made with fiber combination of 25 % MSFA and 75 % MSFB. Therefore, the negative effect of SRA on the flexural-post cracking behavior can be partial compensated by adjusting MSF content and combinations.

Hybrid Fiber Reinforcement in HDPE–Concrete: Predictive Analysis of Fresh and Hardened Properties Using Response Surface Methodology

Plastic waste accumulation has driven research into recycling solutions, such as using plastics as partial aggregate substitutes in concrete to meet construction needs, conserve resources, and reduce environmental impact. However, studies reveal that plastic aggregates weaken concrete strength, creating the need for reinforcement methods in plastic-containing concrete. This study used experimental data from 225 tested specimens to develop prediction models for the properties of concrete containing macro-synthetic fibers (MSFs), steel fibers (SFs), and high-density polyethylene (HDPE) plastic as a partial substitute for natural coarse aggregate (NCA) by volume utilizing response surface methodology (RSM). HDPE plastics were used as a partial substitute for NCA by volume at levels of 10%, 30%, and 50%. MSFs were added at levels of 0, 0.25%, 0.5%, and 1% by volume of concrete, while SFs were added at levels of 0, 0.5%, 1%, 1.5%, and 2% by volume of concrete. The input parameters for the models are the ratio of HDPE, the dose of MSF, and the dose of SF. The responses are the slump value, the compressive strength (CS), the splitting tensile strength (TS), and the flexural strength (FS) of concrete. The significance and suitability of the developed models were assessed and validated, and the parameters’ contribution was investigated using analysis of variance (ANOVA) and other statistical tests. Numerical optimization was used to determine the best HDPE, MSF, and SF ratios for optimizing the mechanical properties of concrete. The results demonstrated that replacing NCA with HDPE plastics increased the workability and decreased the strength of concrete. The results demonstrated the applicability of the developed models for predicting the properties of HDPE–concrete containing MSFs and SFs, which agreed well with the data from experiments. The created models have R2 values more than 0.92, adequate precision more than 4, and p-values less than 0.05, showing high correlation levels for prediction. The RSM modeling results indicate that the inclusion of MSFs and SFs improved the mechanical properties of HDPE–concrete. The optimum doses of MSFs and SFs were 0.73% and 0.74%, respectively, of volume of concrete, leading to improvement in the mechanical properties of HDPE–concrete. This approach reduces plastic waste and its detrimental environmental impact. Further development of models is needed to simulate the combined effects of different fiber types, shapes, and dosages on the performance and durability of plastic-containing concrete.

Effect of long-term ageing by temperatures on mechanical behaviour of Fibre Reinforced Concretes

This study examines the effect of ageing by operating temperatures on the mechanical properties of Fibre Reinforced Concretes (FRCs) when exposed during long-term periods (180 days of conditioning). There is little information in the literature about long-term mechanical performance of steel (SFRC), and especially, macro synthetic fibre reinforced concretes (MSFRCs), which may be affected due to this exposure. One type of steel fibre and three types of macro synthetic fibres were selected to reinforce an ordinary concrete in this work. An extensive experimental campaign (with a total of 260 specimens) which includes compression and flexural tests performed at temperatures, was carried out to investigate the influence of a range of temperature from −15 to 60 °C. Additionally, the interaction between cracking conditions (up to 0.5 mm) and temperature was analyzed for both type of FRC beams. The compression results obtained show higher strengths at low temperatures (25–30 %) and a decrease on the strengths at higher temperatures (15–20 %), but these variations are not crucial on the ageing of FRCs. Similar effects were detected for the strength at the peak load, and to a minor extent, for the residual flexural strengths, for all the FRCs. Specimens with a pre-existing crack (cracked condition) exposed to the studied temperature had the same results as uncracked specimens. Thus, both FRCs have the potential to obtain appropriate results for structural applications when exposed to the studied temperatures.

Numerical Modeling of Distributed Macro-Synthetic Fiber and Deformed Bar Reinforcement to Resist Shear

Macro-synthetic fibers are increasingly used in concrete as secondary reinforcement to control temperature and shrinkage cracks, improving durability by limiting crack widths. However, their impact on the shear strength of structural elements remains underexplored, particularly when used in combination with traditional steel reinforcement. To address this knowledge gap, this study developed and calibrated a non-linear numerical model to simulate the shear response of macro-synthetic fiber-reinforced concrete (PFRC) elements, using finite element software VecTor2. The model was calibrated with experimental data from PFRC panels subjected to pure shear loading, incorporating a custom concrete tension-softening model to capture the contribution of fibers. Validation against a broad range of PFRC beam experiments from the literature demonstrated the model’s accuracy, achieving an average predicted-to-experimental shear strength ratio of 0.99 (COV = 5.5%). Additionally, the model successfully replicated key response characteristics such as deformation patterns, crack propagation, and residual strength. The proposed modeling approach provides valuable insights into the interaction between fiber volume and transverse reinforcement. It also serves as a powerful tool for future numerical studies, addressing the existing data gap on PFRC behavior and exploring the synergistic effects of macro-synthetic fibers and steel reinforcement on shear strength.

Mechanical Properties and Chloride Penetration Resistance of Concrete Combined with Ground Granulate Blast Furnace Slag and Macro Synthetic Fiber

Concrete with good mechanical properties and durability has always been a necessity in engineering. The addition of fibers and supplementary cementitious materials to concrete can enhance its mechanical and durability performance through a series of chemical and physical interactions. This study aims to investigate the effects of key parameters on the compressive strength, splitting tensile strength, and chloride penetration resistance of concrete combined with ground granulate blast furnace slag (GGBS) and macro polypropylene synthetic fiber (MSF). Based on the Taguchi method, a total of eighteen mixtures were evaluated, considering the effects of GGBS content, MSF content, water-to-binder (w/b) ratio, and chloride solution concentration on concrete properties. The results showed that the w/b ratio has a significant impact on the properties of concrete, which are enhanced by a decrease in w/b ratio. The GGBS content had little effect on the 28-day strength of concrete, which even decreased with a large GGBS content, but GGBS had a positive effect on the long-term strength of concrete. Moreover, the chloride penetration resistance of concrete was enhanced by an increase in the GGBS content. The MSF content had no obvious effects on the compressive strength and chloride penetration resistance of concrete, but it could enhance the splitting tensile strength to some extent, and this enhancement was more obvious over time. The chloride diffusion coefficient of concrete changed with the concentration of chloride solution, and the two increased simultaneously.

Performance evaluation of indented macro synthetic polypropylene fibers in high strength self-compacting concrete (SCC)

Concrete is used worldwide as a construction material in many projects. It exhibits a brittle nature, and fibers' addition to it improves its mechanical properties. Polypropylene (PP) fibers stand out as widely employed fibers in concrete. However, conventional micro-PP fibers pose challenges due to their smooth texture, affecting bonding within concrete and their propensity to clump during mixing due to their thin and soft nature. Addressing these concerns, a novel type of PP fiber is proposed by gluing thin fibers jointly and incorporating surface indentations to enhance mechanical anchorage. This study investigates the incorporation of macro-PP fibers into high-strength concrete, examining its fresh and mechanical properties. Three different concrete strengths 40 MPa, 45 MPa, and 50 MPa, were studied with fiber content of 0–1.5% v/f. ASTM specifications were utilized to test the fresh and mechanical properties, while the RILEM specifications were adopted to test the bond of bar reinforcements in concrete. Test results indicate a decrease in workability, increased air content, and no substantial shift in fresh concrete density. Hardened concrete tests, adding macro-PP fibers, show a significant increase in splitting tensile strength, bond strength, and flexural strength with a maximum increase of 34.5%, 35%, and 100%, respectively. Concrete exhibits strain-hardening behavior with 1% and 1.5% fiber content, and the flexural toughness increases remarkably from 2.2 to 47.1. Thus, macro PP fibers can effectively improve concrete's mechanical properties and resistance against crack initiation and spread.

Combined effect of silica fume and various fibers on fresh and hardened properties of concrete incorporating HDPE aggregates

Recycling of waste plastics has become essential to mitigate their detrimental impact on the environment. However, it can be used in the construction sector to fulfill construction needs and conserve natural resources. Previous research has demonstrated that incorporating plastic aggregate reduces the strength properties of concrete; hence, there is a need to improve its strength properties. In this study, high-density polyethylene (HDPE) plastic is incorporated in aggregate form, as a partial substitute for natural coarse aggregates (NCA) at volumetric ratios of 10 %, 30 %, and 50 %. Various strength enhancement techniques, including the addition of macro synthetic fibers (MSF), steel fibers (SF), and substituting 20 % of cement with silica fume, were employed. The results indicated that workability of concrete is improved with an increase in the content of HDPE coarse aggregates (HCA). Furthermore, concrete containing 30 % HCA performed better in terms of strength compared to concrete with 10 % and 50 % HCA. The findings demonstrate that concrete containing fibers performs better than concrete without fibers. The utilization of 0.75 % MSF and 1 % SF dosage leads to a 93 % improvement in splitting tensile strength, a 72 % improvement in flexural strength, and a 48 % improvement in compressive strength for concrete containing 30 % HCA. Using scanning electron microscopy, it was found that incorporating HCA weakens the internal matrix. However, the addition of a precise amount of fibers and pozzolanic materials resulted in improvements in microstructure. The significance of this research lies in the utilization of HDPE waste materials in concrete by simultaneous usage of different fibers.

Utilizing sugar factory lime waste and crumb rubber for sustainable Ultra-High-Performance Concrete

Ultra-High-performance Concrete (UHPC) offers significant advancements in construction due to its superior strength and durability. However, its traditional formulation demands extensive cement use, leading to high costs and adverse environmental impacts. This research explores the feasibility of repurposing lime waste, a by-product of sugar production, as a substitute for cementitious materials in UHPC, while also examining the use of crumb rubber powder as a complementary filler within the UHPC matrix. Glass, steel, and synthetic macro fibers are also added to improve the ductility of the concrete mix. A series of mechanical tests are conducted to evaluate the performance of the developed concrete. The results are compared with those of conventional cement and other cement substitutes. It is found that replacing 10 % of cement with lime waste and rubber powder produces the optimal UHPC mix, with 104 MPa compressive strength, 7.1 MPa bending strength, 5.8 MPa tensile strength, and 32.8 GPa modulus of elasticity. Moreover, steel fibers are the best reinforcement option, as they significantly improve the ductility and malleability of the concrete, achieving 13,456 J rupture energy and 17.4 MPa bending strength. However, a microstructure analysis reveals that the cement substitutes cause a slight deterioration in the concrete quality, but this is compensated by the benefits of the fibers. It is also shown that the use of lime waste and rubber powder reduces the carbon footprint and the cost of UHPC, making it a more sustainable and economical choice for construction materials. Therefore, it is concluded that the use of lime waste and rubber powder as cement substitutes in UHPC is a feasible and beneficial strategy for developing environmentally friendly UHPC with enhanced mechanical properties. This study contributes to the advancement of eco-conscious UHPC and opens new avenues for future research.

Constitutive Relations for Modelling Macro Synthetic Fiber Reinforced Concrete

Constitutive Relations for Modelling Macro Synthetic Fiber Reinforced Concrete

Effect of Graphene Oxide Surface Deposition Process on Synthetic Macrofibers and Its Results on the Microstructure of Fiber-Reinforced Concrete.

The improvement of the mechanical properties of concrete can be achieved with the use of synthetic macrofibers. However, this fiber-matrix interaction will be sufficiently efficient for tensile efforts only when there is a binding agent that associates the characteristics of the paste with the characteristics of the surface of the reinforcing material. As already identified, in a first phase of this research using synthetic microfibers, a better fiber-matrix interaction can be achieved with the surface treatment of synthetic fibers with graphene oxide. In this way, we sought to evaluate the surface treatment with graphene oxide on two synthetic polypropylene macrofibers (macrofiber "A" and macrofiber "B") and its contribution to the concrete transition zone. The surface deposition on the macrofiber was carried out using the ultrasonication method; then, the macrofiber with the best deposition for creating reinforced concrete mixtures was identified. To evaluate the quality of GO deposition, scanning electron microscopy (SEM-FEG) and energy-dispersive spectroscopy (EDS) tests were carried out; the same technique was used to evaluate the macrofiber-matrix transition zone. The SEM-FEG images indicated that macrofiber "B" obtained greater homogeneity in surface deposition and it presented a 13% greater deposition of C in the EDS spectra. The SEM-FEG micrographs for reinforced concrete indicated a reduction in voids in the macrofiber-matrix transition zone for concretes that used macrofibers treated with GO.

A Study on Durability and Microstructural Analysis for Macro Synthetic Fiber Reinforced Concrete with Supplementary Cementitious Materials

Background: Thermal cracking, delayed ettringite production and low tensile strength are three significant problems for high-strength concrete. Objectives: The current experimental study aims to determine the durability characteristics of concrete for application in pavements. To test how well the M40 grade of concrete absorbed chloride and water, the amounts of Supplementary Cementitious Materials (SCM) like Granulated Blast-Furnace Slag (GBFS) and fixed amounts of Fly Ash (FA) and Macro Synthetic Fiber (MSF) were optimized. Methods: One sample (S1) was made entirely of Ordinary Portland Cement (OPC) and five samples (S2, S3, S4, S5, and S6) made simply of SCMs, in which OPC was substituted with 20% FA+20% GBFS+1.5% MSF, 20% FA+25% GBFS+1.5% MSF, 20% FA+30% GBFS+1.5% MSF, 20% FA+35% GBFS+1.5% MSF, and 20% FA+40% GBFS+1.5% MSF, respectively, were cast in standard blocks with a volume of one cubic meter for this purpose. Field Emission Scanning Electron Microscopy (FESEM), Fourier-Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) investigations are used to examine the number of hydration products created at 28 days, which differ for different percentages of SCMs. Findings: Furthermore, 501, 520, 535, 565, and 590 coulombs are the measured Rapid Chloride Permeability Test (RCPT) values for the S2 to S6 samples. Similarly, the S1 sample is projected to have more than 2600 coulombs, showing a better endurance of samples based on SCMs. The microstructural characterization findings (i.e., XRD, FTIR and FESEM) suggested that GBFS and FA are promising SCMs for enhancing the strength and durability properties of the mix. Novelty and applications: This study validates the viability of using GBFS, FA, and MSF in pavement applications, yielding noteworthy environmental advantages and lowering dependency on OPC. Keywords: Durability, Microstructural investigation, Macro synthetic fiber, Fly ash, Granulated blast furnace slag, Pavements

Novel UHPC with calcium-oxide-activated materials and fibres: engineering properties and sustainability evaluation

Novel ultra-high-performance concretes (UHPCs) made with calcium-oxide-activated materials (CAM), modified synthetic macro (MSM) fibres, glass fibres and steel fibres were developed. The mechanical and durability properties of UHPC-CAM specimens made with the different fibre types were tested and compared. The microstructure of the samples was examined using scanning electron microscopy (SEM). The environmental impacts of the mix designs were assessed using the Impact 2002+ method, a life cycle assessment tool. The results showed that the UHPC-CAM made with glass or MSM fibres had a high compressive strength (>110 MPa) and improved ductility. These specimens also had low water absorption and high electrical resistance, indicating low corrosion risk. SEM analyses showed that the MSM fibres created a denser geopolymer matrix than the glass fibres. The UHPC-CAM was found to have a lower environmental impact than conventional UHPC in terms of human health, ecosystem quality, carbon dioxide footprint and use of resources. MSM fibres were determined to be the most eco-friendly fibres for UHPC-CAM production.

Effect of post-peak flexural toughness on the residual performance of macro synthetic fibre reinforced concrete sleepers subjected to impact loading

Dynamic impact loading is one of the predominant causes of premature failure of concrete railway sleepers, demanding a fair portion of the railway budget. Therefore, macro synthetic fibre reinforced concrete (MSFRC) is suggested as an alternative owing to its improved post-peak flexural capacity, ductility and crack arresting properties. In such adaptation, the residual behaviour after dynamic impacts caused by wheel-rail irregularities governs the reusability and the life cycle of the sleepers. Correspondingly, the residual performance of impacted MSFRC sleepers was evaluated experimentally compared to conventional prestressed concrete sleepers. The residual behaviour of the sleepers was further supported by a series of material-scale flexural experiments. The fracture toughness of MSFRC increased with the crack-opening width because of the tension stiffening associated with fibre bridging. As a result, the residual capacity, stiffness, and toughness of MSFRC sleepers were higher than conventional sleepers, thereby improving their adaptability to the rail network.

Macrosynthetic fibers as replacement of conventional steel reinforcement for concrete of partition walls

AbstractConventional reinforced concrete for building partition walls has proven numerous advantages (in terms for instance of acoustic performance and robustness) with respect to other existing alternatives. However, its use leads to high material consumption and environmental footprint together with time‐consuming processes for placing steel reinforcement. To reduce time‐consuming processes and carbon footprint, the replacement of ordinary steel reinforcement by structural macrofibers is envisioned as a suitable solution due to: (1) the acceptance of fiber reinforced concrete (FRC) for structural applications in various guidelines (as Annex L of FprEN 1992‐1‐1:2023, draft for future Eurocode 2) and (2) the fact that the amounts of fibers necessary to reach the required mechanical performance of the FRC for crack control are expected to be economically competitive. Additionally, within the spectra of types of macrofibers capable of efficiently reinforce concrete, macrosynthetic fibers (MSFs) were considered in this research due to their benefits in terms of durability performance and reduced environmental impact (potential to use cements with lower clinker content and reduced thickness of elements). Aiming at confirming both the constructability, casting procedure and structural performance of macrosynthetic fiber reinforced concrete (MSFRC) partition walls, these walls were constructed in a real building in Switzerland. In this article, the design process is presented as well as the associated MSFRC material and structural experimental programmes, conducted both in laboratory and on‐site. In addition, several FEM‐modeling considerations as well as quality control and construction aspects observed during the implementation process are raised. Finally, for reference purposes, a first approach to the economic and environmental impact (CO2eq‐based) of such MSFRC walls is presented.

Numerical investigation of prestressed concrete sleepers reinforced with high-performance macro synthetic fibres

As modern railway tracks are exposed to heavier loads and higher operational speeds, the excessive cracking and premature failure of prestressed concrete sleepers are becoming more and more critical. Towards addressing these issues, this study focuses on the numerical integration of macro synthetic (polypropylene) fibres in prestressed concrete sleepers to improve the structural behaviours (i.e. residual capacity, cracking resistance & ductility) and assess the damage evolution. Moreover, the numerical investigation performed using Abaqus attempted to validate experimental results and optimised the sleeper design by partially reducing the number of prestressing wires. The analysis reveals good agreement with the experiment at critical cross-sections (i.e. rail seat & centre) and analytically allowed a ∼ 15 % reduction in prestressing steel reinforcement for the macro synthetic fibre reinforced concrete (MSFRC) sleeper. Accordingly, the optimised MSFRC sleeper performed adequately with minimum ultimate capacity reduction that meets the permissible specifications and future demands.

Influence of macro-synthetic fibers on the flexural behavior of high strength concrete beams reinforced with GFRP bars

Influence of macro-synthetic fibers on the flexural behavior of high strength concrete beams reinforced with GFRP bars

Development of a Low-Cost IoT-based Sensor for Early-Stage Concrete Monitoring

Concrete is an essential construction component that needs to be examined carefully for an early strength assessment in order to guarantee structural integrity and long-term durability. This paper delves into the viability of utilizing low-cost sensors, interfaced with an Arduino-based microcontroller, for real-time data acquisition in concrete structures. The study focuses on their application in the early stages to investigate the thermal cycles due to hydration reaction, particularly within macro-synthetic fibre reinforced concrete. DHT22 sensors are used to measure the concrete sample’s temperature and humidity parameters. These sensors are linked to a NodeMCU microcontroller that has an integrated WiFi module to provide real-time data updates on the cloud. The programming code is created using the Arduino IDE platform and then loaded into the NodeMCU microcontroller to control sensor functions. The validation process consists of an early laboratory test and the placement of an additional DHT22 sensor outside the concrete sample to monitor the surrounding temperature and humidity to evaluate the system’s operation and sensor´s accuracy. The collected data reveal promising insights, particularly in investigating corrosion within embedded reinforced rebar for future researches.

Effect of macro-synthetic and hybrid fibres on the behaviour of square concrete columns reinforced with GFRP rebars under eccentric compression

GFRP rebars have emerged as a suitable alternative for steel rebars to tackle corrosion-related issues. However, the abrupt failure of GFRP-reinforced concrete (RC) elements due to the brittle behaviour of GFRP rebars is a significant concern. Fibre reinforced concrete (FRC) reduces brittleness by providing pseudo-ductility to GFRP RC members failing in compression. Moreover, fibre addition helps reduce crack widths by bridging them when subjected to tensile stresses. The current study aims to understand the influence of adding macro-synthetic Polyolefin (PO) and a hybrid mix of steel and PO fibres (HB) on the behaviour of GFRP-RC columns. Twenty-six square columns reinforced with GFRP rebars and discrete fibres are tested. A low-eccentricity to-width ratio (e/d of 0.2) and a high-eccentricity to-width ratio (e/d of 0.4) are chosen as loading parameters. The test matrix includes the following specimens: i) control with no fibres, ii) only PO fibres, and iii) a hybrid mix of steel and PO fibres. Test results show that specimens reinforced with hybrid fibres outperformed macro-synthetic fibres in energy absorption and strength improvement. They also had better post-peak behaviour under eccentric compression. Fibre addition increased the load resistance contribution of GFRP rebars and prevented the complete spalling of concrete cover. It also improved the deformabilty factors when compared to control columns with no fibres under eccentric compression.

Effect of Macro Polyolefin Fibers on Bond Strength of Tension Lap Splices in RC Beams

The effect of macro synthetic polyolefin fibers on the bond strength of tension lap splices in reinforced concrete (RC) beams is investigated in this study. The bond between the reinforcement and concrete plays a vital role in the strength of RC beams. The presence of polyolefin fibers in the lap splice zone confines the concrete and enhances the bond strength of the steel bars. The use of synthetic fibers is preferable to steel ones since steel suffers from corrosion over time. Tests were conducted on 12 full-scale beam specimens to determine the effect of fiber volume fraction (Vf), bar diameter (db) and concrete cover-to-bar diameter (c/db) on the response. Four volume fractions (Vf = 0, 0.5, 1 and 1.5%) of polyolefin fibers and three bar sizes (db = 16, 20 and 25 mm) with the corresponding (c/db = 2.31, 1.75 and 1.30) were considered to evaluate the bond strength. The test results demonstrated that the polyolefin fibers noticeably enhanced the bond strength and ductility of spliced tension bars. Experimental results were compared with those obtained from two theoretical methods including ACI Committee 318 design provisions. The results showed that the equation proposed by the ACI Committee overestimates the bond strength.