Crumb Rubber Aggregate Research Articles

Economic and Environmental Benefit Analysis between Crumb Rubber Concrete and Ordinary Portland Cement Concrete

Although manifold empirical studies have identified the mechanical properties of crumb rubber concrete (CRC), a comparative analysis of economic and environmental benefits between CRC and ordinary Portland cement concrete (OPCC) is not explored. In this paper, a quantitative meta-analysis between CRC and OPCC is conducted to explore optimized design strength, and a comparative analysis of the economic and environmental benefits of the two materials is undertaken. Considering cost price as the economic index and CO2 emissions per cubic meter of concrete as the environmental index in the materialization stage, CRC and OPCC were compared with different mix designs to achieve grades of similar strengths. Upon replacing less than 20% of natural fine aggregates in concrete with crumb rubber, while retaining the cement content, an increase of 6% in the cost price was achieved for CRC with 30–40 MPa strength grade. Apart from the aspect of mining and transportation of natural aggregates, the reduction of CO2 emissions by means of CRC adoption was verified in the treatment process of waste tire incineration. The results show that CO2 emissions from CRC decreased by 15–17% when compared with OPCC for 30~40 MPa grade concrete. The research conclusion can serve as a theoretical basis for the engineering application of CRC with the same strength, and make certain contributions to the industrial application of crumb rubber aggregates and the sustainable treatment of waste tires.

Durability Evaluation of Polyurethane-Bound Porous Rubber Pavement for Sustainable Urban Infrastructure

Permeable pavements are vital in sustainable urban water management, addressing critical challenges while enhancing environmental resilience. This study focuses on the innovative polyurethane-bound Porous Rubber Pavement (PRP), which possesses high permeability and elasticity due to its unique composition of stone and crumb rubber aggregates with polyurethane binders. PRP’s useful benefits, such as noise reduction, efficient snow/ice management, and others, enhance its appeal, emphasizing the necessity for a thorough investigation into its performance and characteristics, especially in North America. To address these gaps, this paper comprehensively analyzes PRP’s durability and performance, including its strength range, failure criteria, and susceptibility to moisture-induced damage. Various testing methods are utilized, such as evaluating the abrasion loss of the stone aggregate, rutting, stripping due to moisture susceptibility, resistance to degradation from impact and abrasion, and permeability tests. This study evaluates five distinct mix compositions with varied proportions of aggregates and binders. Further, it investigates the effects of different binder types on PRP performance, such as aromatic and aliphatic binders obtained from various sources. Upon the analysis of the comprehensive test results, it was found that the mix characterized by increased rubber aggregates and a high binder content demonstrated a superior performance across various tests for PRP applications. This mix exhibited an enhanced resistance to abrasion, raveling, rutting, and permanent deformation, showcasing its durability and functionality. Additionally, when combined with an aliphatic binder, it displayed an optimal performance even in challenging freeze–thaw conditions, making it a recommended choice for long-term pavement solutions.

Ultra-High-Performance Alkali-Activated Concrete: Effect of Waste Crumb Rubber Aggregate Proportions on Tensile and Flexural Properties

The declining availability of natural sand resources and the significant carbon footprint associated with the extensive use of cement are posing severe limitations on the advancement and application of ultra-high-performance concrete (UHPC). In this study, waste tyre-derived recycled crumb rubber particles (CR) were employed to replace quartz sand, and an alkali-activated cementitious material was used to produce waste tyre-alkali-activated UHPC (T-UHPAC). The influence of different CR replacement ratios (0%, 5%, 20%, 35%, 50%) on the tensile and flexural performance of T-UHPAC was investigated, and a predictive model for the stress–strain response considering the CR replacement ratio was established. An optimization method for improving the tensile and flexural performance of T-UHPAC was proposed. The results indicate that the effect of rough-surfaced CR on the interfacial properties of concrete differs from that of smooth quartz sand. A CR replacement ratio exceeding 35% led to a reduction in both the tensile and flexural strengths of UHPAC, while a replacement ratio at or below 20% resulted in a superior tensile and flexural performance of T-UHPAC. The established predictive model for tensile performance accurately forecasts the stress–strain behaviour of T-UHPAC under varying CR replacement ratios, with the accuracy improving as the CR replacement ratio increases. By utilizing CR to replace quartz sand in proportions not exceeding 20%, the production of low-carbon UHPC with exceptional comprehensive mechanical properties is achievable. Moreover, the development of T-UHPAC through the comprehensive utilization of waste tyres presents a promising and innovative approach for the low-carbon and cost-effective production of UHPC, thereby facilitating the sustainable development of natural resources. This research represents a significant step towards the widespread adoption and application of UHPC and thus holds substantial importance.

Axial Compression Damage Model and Damage Evolution of Crumb Rubber Concrete Based on the Energy Method

The current constitutive model and damage evolution law of crumb rubber concrete (CRC) were obtained by fitting and changing parameters based on the normal concrete model. However, this model does not accurately reflect the characteristics of the material. In this paper, we studied the energy dissipation in the failure process of CRC to derive the constitutive model and damage evolution law of CRC based on the energy method. Four substitution rates of 5%, 10%, 15%, and 20% were selected, and the rubber concrete prism was prepared by replacing the natural fine aggregate with the same volume of crumb rubber aggregate. After that, uniaxial compressive tests were conducted. The energy lost due to the damage was calculated and analyzed, and the energy method was used to establish the damage evolution law and damage model of the crumb rubber concrete. The results demonstrated that the Guo Zhenhai damage model, which is based on the energy method, can more effectively explain the crumb rubber concrete stress–strain full curve, and the energy consumed as a result of the damage exhibits a growing and then reducing pattern with the increase in rubber doses. When the energy-based method is used, the Guo Zhenhai damage evolution model is similar to the damage evolution law calculated using the SIR damage evolution model. During uniaxial compression damage, rubber concrete with various rubber dosages demonstrated varying energy absorption in different deformation phases. When the rubber particle content was 10%, the energy absorption capacity of the specimen was 6.9% higher than that of normal concrete.

Designand Properties of Crumb Rubber Aggregates Additive in Hot Mixture Asphalt Concrete

Abstract: This research aims to establish the design and properties of crumb rubber aggregates additive in hot mixture asphalt concrete. Rubber crumb is rubber waste which is processed through mechanical grinding or tire milling into small splinters. The objective of this research is to have high durability of flexible pavement with different percentages of crumb rubber. The experiment was done respectively through several phases as follows: preparation, quality examination of materials such as aggregate and asphalt, mixed-planning, and specimen testing implementation with Marshall Test. Properties of crumb rubberlike type stability and flow of durability can affect the different stability and flexibility of pavement. The data collected from the laboratory experiments were presented in different forms like tables, charts, diagrams, etc. The results from the crumb rubber asphalt mixture show that there is an increase in the amount of crumb rubber in a mixture of hot mix concrete asphalt. This mixture can increase the Marshall stability by 2.5 % crumb rubber higher than the other mixtures with crumb rubber.

PVA fiber-reinforced geopolymer mortar made with hybrid recycled aggregates: Toward thermal insulation, lightweight and improved durability

Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar minimizes the shortcomings of large drying shrinkage and high brittleness of conventional geopolymer mortar made with natural sand. Replacing natural sand with crushed glass (CG) and crumb rubber (CR) aggregates is a sustainable alternative. However, their collaborative role in the performance of PVA fiber-reinforced geopolymer mortar remains unclear. To fill this gap, this research investigated the performance of a novel geopolymer mortar reinforced with 0–0.6 vol% PVA fibers and made with CG and CR aggregates with a mix ratio of 10:0–0:10. Due to different physical properties, CG and CR aggregates worked together to control their respective disadvantages. Compared to 100% CG, incorporating 30%–100% CR reduced the hardened density by 8.33%–27.13% and the thermal conductivity coefficient by 44.37%–82.17%. For 0.6 vol% PVA fibers, the 28-d drying shrinkage and 364-d alkali-silica reaction expansion decreased by 10.24%–35.20% and 60.71%–72.50%, respectively.

Properties of sustainable self-compacted concrete with recycled concrete and waste tire crumb rubber aggregates

The concrete building industry has to adhere to stringent sustainability standards. In previous investigations, the utilization of recycled concrete aggregates (RCA) from construction and demolition waste (CDW) or crumb rubber (CR) from waste tires in producing sustainable self-compacted concrete (SCC) was well studied; however, the combined effect of RCA and CR on the performance of SCC is scarce. Therefore, the main purpose of this study is to evaluate the feasibility of developing SCC mixtures containing both RCA and CR and their influence on the performance of SCC. Three distinct series of SCC mixes were designed so that the water-to-binder ratio and total binder content were kept at 0.32 and 505 kg/m3. In the first series, the effect of RCA content (0%, 50%, and 100%) in place of natural coarse aggregate (NCA) on the performance of SCC mixtures was studied. Moreover, the effect of various CR contents (0%, 10%, 20%, 30%, and 40%) as a sand substitution and 50% RCA was investigated in the second series. In the third series, the influence of CR inclusion and 100% RCA was utilized to promote the sustainability of SCC. The fresh behavior of the mixtures was assessed by measuring followability, viscosity, and segregation resistance. Density, water absorption, and apparent porosity for all mixes were also examined. The mechanical properties were assessed for compressive, splitting tensile, and flexural strengths. The findings show that the inclusion of RCA and CR has an adverse impact on the fresh, physical, and mechanical properties of SCC, excluding segregation resistance. However, it is possible to produce a SCC using 100% RCA and 40% CR with a slump flow diameter of 605 (SF1 class) and a compressive strength of greater than 31 MPa, which is applicable for structural applications. Moreover, the ACI and Euro code CEB-FIP proposed models can predict the mechanical properties of the developed SCC made with recycled materials. This research could contribute to a more sustainable SCC by substituting recycled materials for natural aggregates.

Natural Rubber Latex-Modified Concrete with PET and Crumb Rubber Aggregate Replacements for Sustainable Rigid Pavements

There are ongoing research challenges for the addition of the blend of PET and crumb rubber in polymer-modified concretes, which aims to leverage the benefits of both materials. In this study, various percentage combinations of waste aggregates, such as PET and crumb rubber, were used to replace coarse and fine aggregates in natural rubber latex (NRL)-modified concrete. Engineering properties such as compressive and flexural strengths, modulus of elasticity, and toughness obtained from compressive- and flexural stress-strain curves were investigated. Scanning electron microscopy (SEM) analysis was performed to examine the microstructural properties and study the strength development of the studied concretes. The results revealed that the compressive and flexural strengths of NRL-modified concretes with PET and crumb rubber aggregate replacements decreased with increasing replacement ratios. SEM analysis indicated that PET and crumb rubber (hydrophobic and non-polar materials) can affect the microstructure of the studied concrete by creating a weak interface between the aggregate and cement pastes, leading to reduced strength development. With the addition of the NRL additive, the film formation was found to act as a bridge and improve the bond strength of aggregates and hydration products in NRL-modified concrete. Furthermore, the integration of PET and crumb rubber aggregate can enhance the ability of the concrete to absorb energy and improve ductility. It was found that 10% of PET and crumb rubber aggregate replacement can be used for NRL-modified concrete as a rigid pavement, as its mechanical strengths satisfy the requirements set by the Department of Highways (DOH) in Thailand. This research helps repurpose waste materials and reduce the environmental footprint of concrete production.

Durability of rubberized concrete with recycled steel fibers from tyre recycling in aggresive enviroments

An assessment of the chemical and physical behavior of rubberized concrete (RuC) during natural carbonation exposure, freeze–thaw degradation and acid degradation (sulfuric and acetic acid (C2H4O2)) with two types of crumb rubber aggregates, is presented: crumb rubber (CR) containing only rubber; and fibers partially coated with crumb rubber (FCR). The mixtures studied with rubberized concrete reach the point of total substitution of stone aggregate (0/20/40/60/80/100 vol%). To analyze and understand the behavior of concrete, physical and mechanical properties have been also studied and related. Weight loss and ultrasonic pulse test were done throughout 3 months in rubberized concrete under accelerated attack, and strength variation recorded after the tests. As well, Scanning Electron Microscope images have been studied after the degradation processes tested. The use of CR and FCR reduces mechanical strength and increases porosity, but rubberized concrete with CR aggregates presents lower carbonation when volume is over 80% and strength reductions stability improves when FCR are used in freeze–thaw attack and under acid corrosion environments, as fibers improve matrix cohesion. Moreover, effectiveness of Ultrasonic Pulse Velocity (UPV) as a method to assess the stages of the attack and final resistance estimation is also indicated after the research results.

Application of recycled aggregates generated from waste materials towards improvement in acoustical and thermal conductivity of concrete

The construction sector, in addition to being very important for the economy of several countries, also creates a large amount of construction waste which has a significant impact on the environment. Usage of alternative coarse aggregates (ACA) materials for partial replacement or complete replacement of coarse aggregates can be identified from multiple sustainable sources including solid waste generated on a regular basis. There are limited studies that have explored the utility of waste materials for coarse aggregate (WMCA) in improving concrete qualities like compressive strength, thermal conductivity, and acoustic properties. Previous researchers have conducted several feasibility studies of using construction-and-demolition-waste (CDW) in engineering works, which lead economic and environmental sustainability in the construction sector. Studies show that the thermal transmittance (U-Value) of concrete, which varies between 0.62 to 3.33 W/m2K, is affected by the type of aggregates being used. It has also been demonstrated that concrete to be a good sound insulator due to its high density, but a poor sound absorber with a reflection of up to 99% of sound energy. Opportunities for usage of waste materials like coconut shells, crumb rubber aggregate (CRA) from scrap tyres, glass, plastic wastes. e-waste, construction and demolition waste (CDW), polystyrene, styrofoam and polystyrene as partial replacement of CA need investigation in depth. Some previous studies, that examined the utility of alternate materials like scarp tyres, broken bricks, CDW etc. used as partial replacement of CA, have shown promising results. This article presents a literature review on the production and utilization of waste materials for coarse aggregate in concrete for improving the acoustical and thermal properties. Summarily, this review may help in alleviating concerns of consumers and further promote the use of recycled aggregate on a larger scale in civil engineering.

Improving the Performance of Lightweight Crumb Rubber Mortar Using Synthetic, Natural, and Hybrid Fiber Reinforcements

The global market for tires is ever-growing, and partially replacing sand with crumb rubber (CR) as fine aggregates in concrete could reduce environmental pollution. However, the main barrier to the complete usage of recycled tire crumbs in construction is the deterioration effect of CR on the mechanical properties of cement-based composites. Therefore, this paper attempts to improve the fresh and hardened properties of crumb rubber mortar (CRM) by incorporating polypropylene-polyethylene synthetic fibers with coconut and kenaf natural fibers as reinforcements. A total of 18 mix designs were developed with varying fiber combinations and rubber crumb replacement. Subsequently, parametric studies with chemical admixture were conducted at 3, 7, and 28 days to improve the flowability and resulting mechanical properties of the fiber-reinforced CRM. According to the results, the single and hybrid fibers positively improved the mechanical properties of cement mortar at 5–15% CR replacement. It can be concluded that adding single and hybrid fibers enhanced the performance of cement mortar modified with tire crumb rubber aggregates by providing varying degrees of improvement.

Corrigendum to “Partial replacement of copper slag with treated crumb rubber aggregates in alkali-activated slag mortar” [Constr. Build. Mater. 256 (2020) 119468

Corrigendum to “Partial replacement of copper slag with treated crumb rubber aggregates in alkali-activated slag mortar” [Constr. Build. Mater. 256 (2020) 119468

Alkali-activated slag (AAS) and OPC-based composites containing crumb rubber aggregate: Physico-mechanical properties, durability and oxidation of rubber upon NaOH treatment

Value-added utilization of waste tires in cementitious materials has been studied for decades, whereas the synergy between rubber and alkali-activated cements deserves more investigations. To this end, we compared physico-mechanical and durability properties of alkali-activated slag (AAS) and OPC-based composites containing NaOH-pretreated/as-received crumb rubber (CR). It was found that the incorporation of CR had both positive and negative effects on specimens due to its special attributes. CR reduced electrical conductivity which was associated with the ion transport ability, since it worked as an electrical insulator and increased hydrophobicity of pore walls. The sulfate expansion decreased with CR content because the flow of sulfate ions was demobilized, and the flexibility of CR relieved the internal stress. CR also improved the freeze-thaw durability of composites if the total CR content was less than 30% in specimens. However, the low Young's modulus of CR impaired the compressive strength and failed to effectively control the total shrinkage upon drying. The composites with CR must avoid high temperature exposure which resulted in the pyrolysis of rubber. In addition, the NaOH pretreatment enhanced adhesion between CR and hydrated cement and improved overall performances of composites. The FTIR spectra confirmed the NaOH-induced accelerated oxidation of CR surface and the generation of polar functional groups including carbonyl and carboxyl groups, increasing the total surface energy of rubber. More importantly, the alkali-activation process for AAS could treat the CR aggregate in the meantime, which means the use of CR in alkali-activated cements does not require the pretreatment of CR before blending.

Mechanical and shrinkage performance of 3D-printed rubberised engineered cementitious composites

Taking the advantages of 3D concrete printing (3DCP) and tackling the environmental issues related to the waste tires, current paper evaluates the material behaviour of rubberised engineered cementitious composites (ECC) using waste crumb rubber (CR) aggregates and polyvinyl alcohol (PVA) fibres, manufactured through 3DCP. To elaborate on the role of PVA fibres on the material properties, two different control mix designs were prepared through conventional mould-casting method, including control mix design without PVA fibres and ECC with PVA fibres equal to 1.75 vol% of binder. Thereafter, using the control ECC mix design, four mix designs containing 5, 10, 15, and 20% CR aggregates as replacement of fly ash, were prepared to assess the effect of CR on the mechanical performance of ECC. The prepared mix designs were subjected to compressive and flexural strengths, and shrinkage tests, and the rubberised ECC containing 5% CR was selected for 3DCP as it revealed superior compressive, flexural and shrinkage behaviour. Results obtained for 3D-printed specimens confirmed the dominant role of anisotropy on the material performance, which was very pronounced for flexural behaviour of printed elements. Comparing to the samples loaded in perpendicular direction, loading in the parallel direction to the fibre orientation (X direction) led to 3 and 4% higher 7- and 28-day compressive strengths, and loading parallel to the fibre alignment along the longitudinal axis of the specimen (Z direction) resulted in 104% and 47% increase in the 7- and 28-day flexural strengths, respectively. Moreover, printed specimens in the fibre-parallel direction showed 37% less drying shrinkage comparing to those printed in the perpendicular direction. Additionally, 3D-printed elements represent superior performance in terms of compressive strength, ductile characteristics, flexural behaviour, and shrinkage performance over the mould-casted ones.

Stiffening Performance of Cold-Formed C-Section Beam Filled with Lightweight-Recycled Concrete Mixture.

The aim of this paper is to investigate the flexural performance of a new steel–concrete composite beam system, which is required to carry higher loads when applied in flooring systems with less self-weight and cost compared with conventional composite beams. This new composite member is prepared by filling a single cold-formed steel C-section with concrete material that has varied lightweight-recycled aggregates. In addition, varied stiffening scenarios are suggested to improve the composite behavior of this member, since these cold-formed C-sections are of a slender cross-section and more likely to buckle and twist under high bending loads than those of hot-rolled C-sections. The influence of using four different lightweight-recycled aggregates that combine together in the infill concrete material was investigated. These recycled aggregates are recycled concrete aggregate (RCA), expanded polystyrene (EPS) beads, crumb rubber aggregates (CRA) and fine glass aggregates (FGA). For this purpose, 14 samples of cold-formed galvanized steel C-purlin were filled with concrete material (containing 0 to 100% recycled aggregates) which are experimentally tested under pure bending load, and 1 additional sample was tested without the filling material. Further numerical models were prepared and analyzed using finite element analysis software to investigate the effects of additional parameters that were not experimentally examined. Generally, the results confirm that filling the C-sections with concrete material that contains varied percentages of recycled aggregates offer significantly improved the flexural stiffness, bending capacity, and ductility performances. For example, using infill concrete materials with 0% and 100% recycled aggregate replacement increased the bending capacity of hollow C-section by about 11.4 and 8.6 times, respectively. Furthermore, stiffening of the concrete-filled C-sections with steel strips or screw connectors eventually improved the composite behavior of the specimens which led to an increase in their bending capacities accordingly, and this improvement enhanced more with an increased number of these strips and connectors.

The effect of scoria, perlite and crumb rubber aggregates on the fresh and mechanical properties of geopolymer concrete

To broaden the practical applications of the geopolymer concrete (GC) at the same large-scale structural level as the conventional concrete (CC), careful assessment of the fresh and mechanical performance of the new concrete technologies based on the GC binder are essential. Lightweight concrete (LWC) is of significant importance for the seismic-resistant lightweight structures, while rubberised concrete is an innovative structural material to tackle the issues associated with the accumulation of the scrap tires in the environment. Current research makes attempt to develop and characterise the rubberised geopolymer concrete (RGC) using 10-mm recycled crumb rubber (CR) aggregates as substitution for the natural coarse aggregates by 5, 10, 15, and 20% replacement. Lightweight geopolymer concrete (LWGC) utilising lightweight scoria and perlite aggregates as replacement for the natural coarse and fine aggregates, respectively, by 25, 50, 75, and 100% proportions were prepared as well. Thereafter, the RGCs and LWGCs were subjected to the fresh and mechanical properties analysis after 3, 7, and 28 days of ambient-curing. For the RGCs, the obtained results denoted no deterioration of the flowability, improved 7-, and 28-day compressive, tensile, and flexural strengths, and enhanced strain-hardening behaviour comparing to the plain GC. For the LWGCs, the obtained results revealed severe segregation for the mixes containing 25% perlite or more, and high risk of segregation for the mixes containing more than 75% scoria. The results obtained for the mechanical properties of the LWGCs suggested that the scoria content in the range of 25–75% improved the fresh and mechanical properties of LWGC compared with GC. In addition, the RGCs represented superior load-bearing capability rather than the LWGCs.

Toward the development of sustainable concrete with Crumb Rubber: Design-oriented Models, Life-Cycle-Assessment and a site application

This study shows a comprehensive research program and practical application of concrete made from crumb rubber produced using end-of-life tyre for use in municipal concrete infrastructure. In light of a large experimental database containing 1334 datasets reported in 126 studies and covering a wide range of parameters, design-oriented models for the compressive strength of crumb rubber aggregate based concrete (CRC) is developed and a large scale life-cycle analysis (LCA) is undertaken to theoretically assess the mechanical properties and environmental performance of concrete containing crumb rubber aggregates. Using the developed models for the compressive strength of CRC and the established LCA, the allowable crumb rubber content in concrete to maintain the sustainability and mechanical properties of the concrete can be identified. Following the theoretical work, a lab-based experimental program is conducted to develop a green concrete mix containing crumb rubber aggregate and other waste-based materials including ground-granulated blast-furnace slag, manufactured sand and recycled PET fines to meet the practical and commercial requirements, field applications of these concrete as pavement materials. Finally, a site application of the developed green concrete is performed to demonstrate that the innovative “green” premix concrete has appropriate engineering properties to enable its use in concrete applications for municipal concrete infrastructure. The benefits and outcomes of this work for the concrete construction are to allow:1) an alternative to recycle end-of-life tyres, 2) for more rapid development of green concrete using waste-based materials for construction applications with high confidences and 3) a faster transition of the materials from lab technologies to real-world engineering applications.

Creep deformation characteristics of rubberised structural concrete

The influence of replacement of fine mineral aggregates with crumb tyre rubber of different particle sizes (2.36, 1.18 and 0.425 mm) on creep and shrinkage of structural rubberised concrete (rubcrete) is investigated. Rubcrete specimens were made using plain Portland cement (PC), 0.60 w/b ratio, crushed andesite coarse aggregate and a 90/10 blend of, respectively, crushed fine andesite and crumb rubber aggregate. The crumb rubber sizes were not blended in the concrete, resulting in three rubcrete mixes. Drying shrinkage and creep was monitored for approximately 1 year. The results show that compared to mineral aggregate concrete (MAC) both drying shrinkage and creep of the rubcretes increased, respectively, by up to 20% and 10% with decrease in crumb rubber particle size. Minimal differences were observed between the drying shrinkage and creep of the rubcretes made with the 1.18 and 2.36 mm crumb rubber aggregates. The results also showed that the introduction of crumb tyre rubber in concrete did not alter the micro-cracking potential of the rubcretes. Ultimately, the findings clearly show that structural rubcrete has similar creep and shrinkage deformation characteristics to that of MAC of similar strength.

Bond behavior of FRP bars in CR concrete

This paper evaluated the bond behavior between recycled crumb rubber (CR) concrete and fiber reinforced polymer (FRP) bar. An experimental study consisting of fifty-seven pull-out specimens with fine recycled crumb rubber aggregate content of 0%, 5%,10% and 15% was described. The results showed that recycled crumb rubber concrete pull-out specimens exhibited similar bond stress-slip curves, which had four stages: the micro-slip, concrete internal cracking, pullout and residual stages. The use of crumb rubber in concrete reduced the bond strength. The bond strength decreased with the increase of the compressive strength of recycled crumb rubber concrete. The type and content of recycled crumb rubber also affected the bond strength. The glass fiber reinforced polymer (GFRP) bars tended to have stronger bonds than that of basalt fiber reinforced polymer (BFRP) bars.

The combined effect of crumb rubber aggregates and steel fibers on shear behavior of GFRP bar-reinforced high-strength concrete beams

To reduce reinforcement congestion in locations of high rebar concentration in a structure, fiber-reinforced polymer (FRP) rebar (replacing steel rebar) can be used in combination with steel fiber (replacing stirrups). Here, an extensive investigation was conducted for the first time in literature on the effect of steel fibers and crumb rubber (CR) aggregate on the shear behavior of high-strength concrete beams reinforced with glass FRP (GFRP) bars. Thirty beam specimens were manufactured and the effect of the key variables including the GFRP reinforcement ratio, shear span-to-depth ratio, CR content, and fiber content in volume on the shear performance of the beams was investigated. Parameters under investigation were the cracking pattern, manner of failure, load-midspan deflection performance, shear capacity, toughness, and post-cracking strength of the beams. The results indicate that when the fiber volume fraction, concrete compressive strength, and GFRP reinforcement ratio increased, the beam shear capacity increased. Conversely, increasing the shear span-to-depth ratio and CR content led to a decrease in the shear capacity. It was also found that the steel fibers were more efficient in improving the beam shear behavior at higher content of CR, such that they changed the cracking type and failure mode from shear to flexural. Finally, the analysis of variance (ANOVA) technique was used to perform statistical analysis of experimental data and calculate the contribution of different parameters to the experimental results.