Crumb Rubber Content Research Articles

An experimental study on the shear behaviour of recycled concrete aggregate incorporating recycled tyre waste

Very limited research has been conducted to examine the shear behaviour of blended recycled waste materials using the large direct shear testing apparatus. In this study, a series of large-scale direct shear test (LDST) was undertaken to evaluate the effect of different sizes and different amounts of recycled tyre waste on the shear strength properties of recycled concrete aggregate (RCA) mixed with crumb rubber as pavement base/subbase application. The results of LDST indicated that RCA mixed with two different sizes (i.e., fine and coarse rubber) and three different percentages (i.e., 0.5%, 1% and 2%) of crumb rubber satisfied the shear strength requirements for use in pavement base/subbase applications. The introduction of both fine and coarse crumb rubber led to an increase in the apparent cohesion of RCA/rubber blends. However, beyond 0.5%, increasing the content of crumb rubber resulted in a decrease in the apparent cohesion. Based on the results of the laboratory testing undertaken in this research, a rational and useful model was proposed to estimate the shear strength parameters of RCA incorporating crumb rubber.

High-Temperature Performance and Workability of Crumb Rubber–Modified Warm-Mix Asphalt

Abstract Crumb rubber produced from scrap tires has been widely applied in asphalt mixtures to improve the pavement performance. Warm-mix technology has also been employed to lower the production temperature of asphalt mixtures. The objective of this article is to investigate the effects of warm-mix additive types and crumb rubber concentration on the resistance to deformation of crumb rubber–modified (CRM) binders through the repeated creep and recovery test (RCRT), dynamic shear rheometer (DSR), and rotational viscosity test. The CRM binders with crumb rubber concentrations of 10 %, 15 %, 20 %, and 25 % were prepared first as the control binders. Then, three types of warm-mix additives, Sasobit, RH, and Advera, were added into the CRM asphalt to produce CRM warm-mix asphalt (WMA) binder. Generally, the workability of CRM asphalt can be improved with the addition of warm-mix additives. The effect of warm-mix additive on the high-temperature performance is highly dependent on the crumb rubber dosage. The RCRT results overall showed that the warm-mix additives can improve the high-temperature performance of asphalt when the crumb rubber concentration is low. However, according to the DSR test, Sasobit improved the rutting resistance of CRM asphalt, while the RH and Advera sacrificed the rutting resistance. The inconsistency between the RCRT and DSR results suggests that it may be necessary to conduct both the tests when investigating the high-temperature performance of CRM asphalt with warm-mix additives.

Review and comparison of methods to assess the storage stability of terminal blend rubberized asphalt binders

Terminal Blend (TB) rubberized asphalt binders exhibit excellent storage stability compared with conventional rubberized asphalt binders, but there is still a phase separation in TB rubberized asphalt binders. Previous studies have developed different assessment methods to examine the phase separation of polymer modified asphalt binders, but it is still unclear whether these methods are suitable for TB rubberized asphalt binders. In this study, current commonly used assessment methods of storage stability were examined with TB rubberized asphalt binders that were prepared with two types of crumb rubber in various particle sizes and contents. After storage stability tests, non-dissolved crumb rubber particles were extracted from TB rubberized asphalt binders. The relationships between non-dissolved crumb rubber particles and different assessment methods were then examined with the help of Spearman’s rank correlation coefficient. It was found that crumb rubber content has a positive effect on the storage stability of TB rubberized asphalt binders and the effect of particle size on the storage stability is highly dependent on rubber source. Additionally, softening point difference, separation index, separation and degradation ratios at intermediate temperatures are not reliable indicators for assessing the storage stability of TB rubberized asphalt binders. Conversely, separation and degradation ratios at high temperatures and low frequencies are better indexes to characterize the storage stability compared with the other indexes, followed by percentage of separation.

Hardened properties of concrete with different proportion of crumb rubber and fly ash

The utilisation of waste materials in concrete is one of the sustainable construction approaches introduced in the industry that can indirectly reduce the environmental issues arisen from the disposal problem of the wastes. The aim of this study is to investigate the hardened properties of rubberised pozzolanic concrete (RuPC) with different proportion of crumb rubber and fly ash as partial fine aggregate and ordinary Portland cement (OPC) replacement, respectively. The crumb rubber content replacing fine aggregate is in the range of 0% to 20% while fly ash replacing cement ranges from 0% to 30%. Testing of RuPC with different percentage of crumb rubber and fly ash were performed at the age of 28 days for density, compressive, splitting tensile and flexural strength, and were compared with properties of control specimens. Results showed that the density of RuPC decrease with increase in crumb rubber and fly ash content. The overall strength of RuPC decrease as crumb rubber content increase in which 5% crumb rubber show the least reduction in strength. Replacing 10% cement with fly ash shows improvement in the strength of RuPC when compared to specimens without fly ash, however still lower than strength of control specimen. The optimum crumb rubber replacement is 5% while fly ash is 10% to avoid significant reduction in strength.

Rendering mortars with crumb rubber: Mechanical strength, thermal and fire properties and durability behaviour

The difficulties related to waste tire disposal encourage the use of crumb rubber in civil construction as a component of cement composites. In this study, crumb rubber is evaluated as a partial replacement of the aggregate in rendering mortars, in quantities of 0%, 2%, 4% and 6%, using a systemic approach. A wide range of characteristics were analyzed, related to the fresh and hardened mortar, thermal and fire properties, along with the durability of the composites used as rendering mortar. Crumb rubber mortars require a higher water content to achieve the same workability of the control mixture, decrease the bulk density and increase the water retention and air content of the mortar. The flexural strength is maintained for hardened mortars with up to 4% crumb rubber, the compressive strength and dynamic modulus of elasticity are maintained only up to 2% rubber, with the decrease of these properties at higher contents of the residue. Generally, water absorption raises with the increment of rubber, but capillary water absorption decreases. The mortars do not propagate flame and they are non-combustible. The addition of crumb rubber leads to a reduction in thermal conductivity of up to 32% for the mortar with 6% of crumb rubber, which enhances their behaviour as a thermal insulator. The durability of rendering mortars with crumb rubber is increased, reducing cracking and maintaining their tensile bond strength at the same level of the reference mortar, even after thermal cycles of accelerated aging. The rendering mortars with 2% and 4% of crumb rubber content presented the best set of properties related to deformation capacity, thermal insulation and lower cracking, with tensile bond strength above the minimum required at standards.

The Evaluation of Mechanical Rheology on Rubber Asphalt Modification

Scientifically natural rubber can be used as an asphalt modifier. Natural rubber production in Indonesia is dominated by crumb rubber products. Based on the technology developed by the addition of natural rubber can improve the rheology properties of asphalt. Therefore, this research used SIR 20 crumb rubber by evaluating the mechanistic rheological properties of asphalt mixtures. The purpose of this research to analyze of effect adding crumb rubber to asphalt Pen 60/70 toward the mechanistic rheology parameters to analyze the bitumen stiffness modulus (E *) that occurs with rubber modified asphalt.In order to obtain optimum levels of addition of rubber into asphalt pen 60/70. The method of this research was carried out in two stages, the first was to make a mixture of Pen 60/70 asphalt and crumb rubber on a variation of crumb rubber content, namely 0%, 4%, 6%, 7%, 8%, 9%, 10%, and 20 % while the second is to test the mechanical rheological properties performed with a Dynamic Shear Rheometer (DSR). The results of this study indicate that the value of Bitumen Stiffness Modulus (E *) has decreased in line with the addition of SIR 20 Crumb Rubber content. The optimum level of addition of SIR 20 crumb rubber is on adding 9% of SIR 20 crumb rubber content to asphalt pen 60/70.

Using Crumb Rubber to Improve the Bituminous Mixes: Experimental Investigation of Rutting Behavior of Flexible Asphalt Mix for Road Construction

Tires that are simply thrown away are a serious environmental problem and safe disposal is a difficult problem. Using the crumb rubber (CR) obtained from shredding of those scrap tires in roads is an alternative solution to their safe disposal. On the other side, excessive rutting in the bituminous layer is a structural defect associated with functional implications. Wheel loads and high pavement temperatures are environmental factors which the main cause of premature rutting. Modified binders and rut resistant mixes especially gradations can reduce premature rutting. The object of the paper to solve two main problems: firstly, the solution to the problem of the tires waste to safe disposal and; secondly, to study the rutting behaviour in bituminous mixes modified by tires waste in CR form. In this paper, two types of bituminous mixes, stone matrix asphalt and bituminous concrete those are used to carry wheel tracking test. The results are shown by using Marshall Test that 6% of CR content by weight if normal binder 60/70 content and optimum binder content for the binder in bituminous mixes is 5.1% & 5.5% by weight of mix is have improved the bituminous mixes. In addition, results indicated that the mixes prepared with a modified binder by CR are good in forming rut resisting mixes. The benefit of this study is the tires waste disposal in an environment-friendly way and better road to withstand rutting.

Effects of Modifiers and Binder Properties on the Performance of Asphalt Mixtures in the Hamburg Wheel-Tracking Device Test

The Hamburg Wheel Tracking Device (HWTD) test has been widely used in practice and reported to be successful in identifying hot mix asphalt (HMA) mixes that are prone to rutting and/or susceptible to moisture damage. This paper presents a comprehensive study aiming to offer informative references for pavement engineers to select modified asphalt materials with good moisture and rutting resistance. First, the impacts of these modifiers on the HWTD test results were investigated. Based on the degree of their improvement in the HWTD results, additives were classified into the following three grades: (1) the first grade including branched styrene–butadiene–styrene (SBS) and Gilsonite; (2) the second grade including linear SBS, high-density polyethylene, and polyphosphoric acid; and (3) the third grade including asphalt rubber (AR) and terminal blend (TB) asphalt rubber. In addition, the effects of modifier content on the Hamburg performance of the asphalt mixes were studied. It was found that higher modifier dosages do not necessarily result in the improvement of Hamburg performance. The results show that an optimal content existed for most additives, whereas a poor-performance dosage range (10.0 % - 18.0 %) existed for crumb rubber content in the AR. Finally, based on the results of the various test materials, the roles of different properties of modified asphalt binders on the Hamburg performance were also investigated. The healing, adhesive, viscosity, and elastic properties (HAVE) of modified binders were found to play different roles: the healing property of modified asphalt binder is a necessary factor; the adhesive property is a fundamental factor; the viscosity has a maximum limitation (3.5 Pa∙s at 135°C); and the elastic property due to the modification is the determining factor in achieving good Hamburg performance of modified asphalt mixtures.

Quantification of recycled rubber content of end-of-life tyres in asphalt bitumen by total-reflection X-ray fluorescence spectrometry

This article presents a new methodology developed to quantify the amount of crumb rubber used in asphalt bitumen by Total-reflection X-Ray Fluorescence (TXRF) spectrometry. For the evaluation of the crumb rubber content in rubberized binders, the samples were completely digested by microwave-assisted acid digestion in a mixture of HNO3:HF acids. TXRF spectrometry has proven to be a powerful analytical technique capable to detect up to 12 elements in these matrixes with detection limits of only a few ppb's (μg/L). From those elements, Zn was elected as indicator of recycled crumb rubber and used for its quantitative correlation. The results obtained show that the proposed methodology is capable of quantifying the content of recycled crumb rubber in asphalt bitumen in a robust, accurate and reproducible way.

Effect of crumb rubber aggregate on the performance of cementitious composites: A review

The increasing use of cementitious composites for different infrastructure constructions has led to an increase in the consumption of raw materials such as aggregate which is a major component in cementitious components. In order to reduce the huge strain posed on the natural sources of aggregate, and continually meet the increasing demand of aggregates to produce cementitious composites; the use of recycled products such as crumb rubber as aggregate in these composites is a viable alternative. However, as the properties of crumb rubber differ from those of conventional aggregate, it is paramount to understand how the incorporation of crumb rubber affects the performance of the cementitious composites. Therefore, this paper presents an overview of how the use of crumb rubber as aggregate affects the performance of cementitious composites in terms of its mechanical, durability, thermal and insulation properties. Conclusions from this paper showed that crumb rubber content in cementitious composites can be optimized to achieve desired properties. Also, the use of crumb rubber as aggregates in cementitious composites reduce significantly the embodied carbon and cost of the composite.

Compressive performance of steel fiber-reinforced rubberized concrete core detached from heated CFST

In this study, the compressive behavior of concrete cores detached from the high-strength concrete-filled steel tube (CFST) members reinforced with steel fibers and containing crumb tire rubber was investigated experimentally after exposure to elevated temperatures. The test variables included the diameter-to-thickness ratio of the steel tube, volume content of crumb rubber replacing natural sand, volume fraction of steel fibers, and temperature. After the exposure of the CFST specimens to the elevated temperatures and subsequently removing the steel tubes, the detached concrete core was subjected to the axial compression test, and the parameters of compressive strength, modulus of elasticity, strain at peak stress, and weight loss, stress-strain relationship together with the ultrasonic pulse velocity, visual appearance, and failure mode were evaluated. Using the experimental results, expressions were developed to predict the mechanical properties of the concrete core at elevated temperatures taking into account the steel tube wall thickness. The findings indicated that increasing the thickness of the steel tube had a greater damaging effect on the heated concrete core, while in the fiber-reinforced specimens, this damaging effect was lower. Moreover, the addition of crumb rubber to the concrete mix as the natural sand replacement degraded the mechanical properties of the heated and unheated concrete core.

Rheological and chemical characterization of plasma-treated rubberized asphalt using customized extraction method

The storage instability issue of rubberized asphalt caused by the inherent incompatibility significantly affects its engineering performances. In this study, cold plasma was utilized to activate the inert surface of Crumb Rubber (CR) particles to further improve the compatibility in rubberized binder. Using a customized extraction method and a developed model, the mechanism of Cold Plasma Effect (CPE) was investigated by rheological and chemical methods, respectively. In terms of the rheological characterization by Dynamic Shear Rheometer (DSR) testing, the CPE on rheology was identified as the primary Particle Effect (PE) and the secondary Interaction Effect (IE). In addition, CPE together with its PE and IE portion constantly increased with an increase in CR content, while no significant tendency was found with the varying size. With respect to the chemical characterization by Gel Permeation Chromatography (GPC) testing, the results indicated the cold plasma treatment significantly resulted in an increase in the Large Molecular Size (LMS) fraction of binder, and this effect was more evident as the CR content increased and the size reduced. However, the Fourier Transform Infrared Spectroscopy (FTIR) testing failed to characterize the effect of cold plasma treatment. Furthermore, the statistical analyses reported a strong correlation between the above corresponding changes in rheology and chemistry. Above all, the mechanism of CPE on binder properties could thus primarily be seen as the promotion in diffusion of lighter fractions of asphalt binder into the plasma-treated CR particles.

UTILIZATION OF CRUMB RUBBER AS AGGREGATE IN HIGH CALCIUM FLY ASH GEOPOLYMER MORTARS

This research was carried out to find out the possibility of utilizing tire crumb rubber waste as fine aggregate in fly ash-based geopolymer mortars (GPMs). The effect of replacement of river sand with crumb rubber at the levels of 0, 25, 50, 75, and 100% by volume on the geopolymer mortar properties including workability, dry density, compressive strength, flexural strength, thermal conductivity, ultrasonic pulse velocity (UPV), water absorption, and porosity were studied. The results were compared to those of the Portland cement-based mortars (PCMs). The test results demonstrated that the higher crumb rubber content resulted in the less dense matrix of mortar. However, GPMs with crumb rubber resulted in a significant improvement in flexural strength. The average ratio of flexural to compressive strengths of GPMs was 25% compared to 15% of PCMs. Also, the lower dry density and thermal conductivity of GPMs indicated better insulating properties than those of PCMs.

A New Eco-Friendly Porous Asphalt Mixture Modified by Crumb Rubber and Basalt Fiber

In this paper, the performance of environmentally friendly porous asphalt mixture was optimized by the response surface method. Taking the asphalt-aggregate ratio, crumb-rubber content, and basalt fiber content as the independent variables, the air void, Marshall stability, flow value, Marshall quotient, and Cantabro particle loss are the response values. The best model was determined by fitting the experimental data. After the influence of the independent variables on the response values was clarified, the models were used to optimize the dosage of the asphalt, crumb rubber, and basalt fiber through comprehensive analysis. The results showed that the application of the response surface method can complete the establishment of the models and the optimization of the performance of the porous asphalt mixture with sufficient accuracy. The optimum dosage of the asphalt to aggregate ratio, crumb rubber, and basalt fiber is 4.51%, 11.21%, and 0.42%, respectively. The high-temperature stability, low-temperature crack resistance, water stability, and Cantabro particle loss resistance of the optimized porous asphalt mixture were effectively improved, which provides a reference for the construction of eco-friendly pavement.

Classification of damage in self-consolidating rubberized concrete using acoustic emission intensity analysis

This article presents the results from an experimental study on the application of acoustic emission (AE) analysis to assess the damage progression of self-consolidating rubberized concrete (SCRC) mixtures under four-point flexural tests. Self-consolidating concrete (SCC) mixtures incorporating four variable replacements of crumb rubber (CR) including 0, 10, 20, and 30% were examined to study the effect of CR content on the AE damage detection and quantification capability. Normal concrete (NC) and normal rubberized concrete (NRC) mixtures, with 0 and 40% CR respectively, were also tested for the comparison. Two prism samples were tested from each mixture under monotonic loading conditions, while being constantly monitored via two attached AE sensors until failure. The acoustic emissions obtained from these sensors were related to the damage evolution of the tested prisms from all mixtures. The effects of variable mixture types and CR content on different AE parameters were highlighted. The considered AE parameters included signal characteristics (in terms of signal amplitude) as well as number of AE hits and cumulative signal strength (CSS). In addition, AE b-value and intensity analyses were further performed on the amplitude and signal strength of all AE signals to evaluate the extent of damage by means of three additional AE parameters including b-value, historic index, H (t), and severity, Sr. The outcomes of the AE analysis indicated the usefulness of the considered AE parameters in the detection of two early damage stages including micro- and macro-cracking before failure, irrespective of the CR content. Eventually, the intensity analysis parameters (H (t) and Sr) were correlated to the stages of micro- and macro-cracking in all mixtures for the purpose of damage classification via developed chart.

Mechanical properties of recycled aggregate concrete containing crumb rubber and polypropylene fiber

Scrap tire-derived crumb rubber (CR) in concrete, along with recycled coarse aggregate (RCA) and polypropylene fiber, constitute a way to reusing and recycling waste material and providing green and sustainable concrete structures. This study investigates the effect of substituting recycled constituents such as RCA and CR as a partial replacement of coarse aggregate and fine aggregate, respectively, along with polypropylene fiber addition into the concrete mixture. Fifteen different mixes are considered, with 10% and 30% RCA, 5% and 10% CR, and 1% and 2% fiber content. This study focuses on the experimental investigation of concrete combining RCA, CR, and fiber and evaluates its compressive strength, splitting tensile strength, and flexural strength at different ages. The compressive strength, splitting tensile strength, and flexural strength decrease as the CR content increases, but increase with the increasing fiber content. With regard to toughness and ductility, the effect of fiber is greater than that of RCA and CR, with each being found to increase with the incremental addition of fiber. It is also observed that the beams with fiber show failure in a more gradual manner. Finally, as a general recommendation in the interest of sustainability and environmental concern this paper suggests the use of rubberized concrete with RCA and polypropylene fiber for any structural purpose subjected to further investigations.

Graphene sandwiched crumb rubber dispersed hot mix asphalt

The crumb rubber obtained from discarded vehicle tires and graphene oxide prepared by oxidation of graphite powder in laboratory were used to modify virgin bitumen. Four different hot mix asphalt matrices prepared using virgin bitumen, crumb rubber modified bitumen, graphene oxide modified bitumen and combination of crumb rubber-graphene oxide modified bitumen are compared. The modified bitumen matrices are characterised by Fourier transform infrared spectroscopy and scanning electron microscopy for structural and morphological analysis. Marshall properties along with indirect tensile test and tensile strength ratio tests were carried out to check the resistance towards cracking and moisture susceptibility of matrices. The results show that, crumb rubber and graphene oxide are completely compatible with bitumen. 9.8% crumb rubber content in crumb rubber modified bitumen hot mix asphalt exhibits the optimum result. The performance of graphene oxide modified bitumen hot mix asphalt exhibits superior performance in comparison to control mix and crumb rubber modified bitumen hot mix asphalt samples. The enhanced properties of modified bitumen hot mix asphalt with the combining effect of graphene oxide and crumb rubber, are suitable for road construction.

The use of high content of fine crumb rubber in asphalt mixes using dry process

The two traditional methods to incorporate crumb rubber into asphalt mixes are the dry process and wet process. Although dry process has greater advantages including more crumb rubber usage, conservation of natural resources, and so on, there is less desire to apply dry process compared to wet process because of its poor performance. This study aims to evaluate the usage of high contents of crumb rubber powder (CRP) as filler in asphalt mixes and provide further development in the dry process method by considering the curing process effect, different CRP contents and micro-scale size of CRP filler. The conventional filler of mixes was replaced with 20, 40 and 60% CRP by weight of filler and the mechanical properties of modified mixes, including moisture susceptibility, stiffness modulus, rutting performance and fatigue life were evaluated. The results indicated that simultaneously applying curing process and very fine CRP in the asphalt mix, enhanced considerably the resistance of asphalt mixes against failures. In addition, the performance of mixes with high contents of CRP was weakened, which could be improved by curing process.

Investigation on Preparation Process and Storage Stability of Modified Asphalt Binder by Grafting Activated Crumb Rubber.

According to the theory of molecular design, crumb rubber was grafting activated with acrylamide and then used as asphalt binder modifier. An orthogonal three-factor, three-level test was designed to optimize the preparation process of modified asphalt. Softening point, viscosity, rutting factor, ductility, stiffness modulus and creep speed index were selected as evaluation indicators to study the effects of rubber content, shear time and shear temperature by variance analysis and range analysis. The results show that the rubber content had a significant impact on the performance of modified asphalt with grafting-activated crumb rubber, while the shear temperature and shear time had little effect. The grafting activated crumb rubber content of 20%, shear temperature of 170–190 °C, and shear time of 90 min was determined as the reasonable preparation process. Modified asphalt with common crumb rubber (CRMA) and modified asphalt with grafting activated crumb rubber (A-G-R) were prepared, respectively, using the reasonable process to analyze the influence of grafting activation of crumb rubber. The results indicate that A-G-R had smaller softening point difference, lower segregation index and more stable and uniform dispersed phase.

Investigation of the Mechanical Properties of Engineered Cementitious Composites with Low Fiber Content and with Crumb Rubber and High Fly Ash Content

Engineered cementitious composites (ECCs) are a type of micromechanically-designed cementitious composite reinforced with a moderate volume fraction of short fiber, typically 2% by volume. ECCs form steady-state multiple cracking that considerably improves the tensile strength and ductility of traditional concrete. In this study, the properties of matrix and the interface of ECCs were tailored through the use of crumb rubber, different types of sand, and different replacement levels of cement with fly ash. The study examined the effect of sand replacement with crumb rubber (20% by volume), two types of river sands (coarse and fine), increasing the content of class F fly ash (up to 75% cement replacement), and low fiber content (1.75%) on the mechanical properties of ECCs. Compressive strength, uniaxial tensile, and third-point bending tests were performed to characterize the properties of ECC mixes. Experimental results demonstrated that increasing fly ash content and using crumb rubber favored ductility of the composites. However, higher fly ash contents and a low water-to-binder (W/B) ratio produced lower strengths as these limited the pozzolanic reaction of fly ash making it act partially as a filler. While incorporation of crumb rubber showed adverse effects on the tensile strength of ECC materials (up to 26% decrease), the tensile ductility of ECC materials improved significantly (up to 434% improvement). Moreover, the implementation of different types of sand produced minor effects on the mechanical properties of ECCs. Overall, a tradeoff between the strength and ductility of the composites was detected, which highlights the implications of matrix/interface tailoring in the overall performance of ECC.