Crumb Rubber Modified Research Articles

Discrete element modelling of mechanical response of crumb rubber-modified asphalt pavements under traffic loads

ABSTRACT This study aims to predict the mechanical response of crumb rubber-modified (CRM) asphalt pavements under traffic loads using three-dimensional (3D) discrete element method (DEM). First, irregular-shaped aggregates were generated in Python language, and discrete element models of six different asphalt layers, which considered the temperature gradient and fatigue damage, were established using 3D DEM. Then, model parameters were obtained through the uniaxial creep test for asphalt mastics at different temperatures. The fatigue damage was implemented by introducing a damage factor into the Burgers model. Finally, three mechanical response parameters (namely, permanent deformation, shear stress and transverse strain) of the six asphalt layers under traffic loads were analysed and compared. Results show that the mechanical response of CRM asphalt layers under traffic loads is significantly influenced by number of repeated loads, temperature, and asphalt layer materials. The shear stress and transverse strain at the wheel centre vary along the depth of asphalt layers, and the middle layer is the principal area of shear stresses in asphalt pavements.

Preparation and Temperature Susceptibility Evaluation of Crumb Rubber Modified Asphalt Applied in Alpine Regions

In alpine regions, the durability of asphalt pavement is worse due to the harsh climate. However, crumb rubber modified asphalt has the potential to improve the durability of pavement. Based on matrix asphalt, crumb rubber, Trans-Polyoctenamer Rubber Reactive Modifier (TOR), and an orthogonal test, the preparation scheme of crumb rubber modified asphalt suitable for alpine regions was obtained. The crumb rubber was selected 30 mesh, and the content of crumb rubber was 24% of the quality of matrix asphalt. Shearing time was 60 min, and preparation temperature was 205 °C. Shearing rate was 5000 r/min, and optimum TOR content was set as 4.5% of the quality of crumb rubber. The temperature susceptibility of matrix asphalt (JZ), crumb rubber modified asphalt (AR), crumb rubber modified asphalt mixed with TOR (TAR) was investigated. The high temperature performance indexes, including phase angle, the complex modulus index, and rutting factor, and the low temperature performance indexes including creep rate and stiffness modulus, the ratio of creep rate and stiffness modulus, Burgers model parameters, dissipated energy ratio, and the derivative of creep compliance were analyzed in depth with multiple parameters. Meanwhile, the mechanisms of prepared AR and TAR were explored. The results indicate that the PG grading is PG64-22 of JZ, PG70-34 of AR, and PG82-28 of TAR. The deformation resistance of TAR at high temperature is superior to AR. The addition of crumb rubber not only improves the temperature susceptibility, but also enhances its viscoelasticity at low temperatures. After the crumb rubber swell in the asphalt system, the network structures are crosslinked and the physical and chemical effects are produced, such as cracking and repolymerization in the asphalt system. TOR can further enhance the swelling and network crosslinking effects of rubber-asphalt. The TAR has the strongest weather resistance. The study provides guidance for AR and TAR to be used in alpine regions.

Bond Strength in Dry Condition of Reclaimed Asphalt Modified by Crumb Rubber Modified Binder

ABSTRACT Reclaimed asphalt modified by crumb rubber-modified binder aroused great interest due to its advantage of using two waste materials without compromising the mechanical performance. Apart from the economic and environmental benefits, many studies revealed that excellent mechanical characteristics could be obtained at some particular rubber and reclaimed asphalt percents. In this study, a binder bond test was performed to evaluate the binder bond strength of reclaimed asphalt modified by rubber modified binder in dry condition. Twenty-four binders with various rubber and reclaimed asphalt contents were prepared and tested. The 24 binders can be divided into four binder categories: virgin binder, reclaimed asphalt modified by a virgin binder, rubber modified binder, and reclaimed asphalt modified by rubber modified binder. Three aggregate types, limestone, basalt, and granite, were fostered. The results showed a fair correlation between binder viscosity and bond strength, indicating that higher bond strength can be achieved by increasing the reclaimed asphalt content in the reclaimed asphalt modified by rubberized binder. Even more, for binder # 70, reclaimed asphalt modified by rubberized binder with 40% reclaimed asphalt content has bond strength similar to the virgin binder, irrespective of the aggregate type.

Study on properties and improving mechanism of OGFC-13 asphalt mixtures modified by novel rubber pellets

Wetting modification of asphalt with single crumb rubber modifier (CRM) can no longer meet the performance requirements of porous asphalt mixtures. The purpose of this research is to investigate the influence of novel rubber-modified pellets (RMP) on the performance of open-grade friction courses (OGFC) asphalt mixtures and its improving mechanism. The RMP were employed with and without high viscosity asphalt (HVA) and SBS as references. Firstly, OGFC-13 asphalt mixtures with the optimum content of RMP were prepared. Then its road performance was evaluated using UTM-25, Hamburg wheel tracker and Marshall tester. Meanwhile, the maximum drainage volume was determined by a self-made device. Additionally, Fourier-Transform Infrared Spectroscopy, Fluorescence Microscopy and Dynamic Shear Rheometer were used to investigate the improving mechanism. The results show that the OGFC-13 with 2% RMP possess fracture energy with the maximum increment of 23.1%, creep slope and spalling slope with the maximum decrease of 49.1% and 32.3%, respectively. Meanwhile, they still possess excellent drainage capacity with a 160 mL/min rainfall intensity emission. The improved performance is caused by a denser network structure detected in the asphalt, which is related to a physical cross-linking reaction between modifiers and RMP. In conclusion, the traditional composite modified asphalt was substituted with RMP and the application of RMP is potential to extend longer service life of OGFC-13 asphalt pavement.

Effects of tetraethyl orthosilicate on rheological behaviors of crumb rubber modified asphalt

The purpose of this work is to study the rheology, fatigue properties and physical changes of crumb rubber modified asphalt (CRMA) after pretreatment of rubber crumbs with tetraethyl orthosilicate (TEOS). Six weight ratios of TEOS to crumb rubber, 0%, 15%, 20%, 25%, 35%, and 50%, were chosen to prepare modified crumb rubber (CR) and use it to prepare CRMA. The effects of TEOS on the physical properties of CRMA were analyzed through softening point, penetration and ductility tests. Mechanical tests including multiple stress creep and recovery (MSCR) test, temperature sweep test, and linear amplitude sweep (LAS) test were conducted to evaluate rheological properties and fatigue resistance. The results show that TEOS addition can effectively improve the physical properties, rheological properties and high temperature stability of CRMA. However, the excessive addition of TEOS can decrease rheological properties and fatigue life of rubber-modified asphalt. The results of temperature scanning test and MSCR test show that CRMA has the best G* and δ under the condition that TEOS content is 25% of CR mass; and it has optimal non-recoverable creep compliance (J(nr)) and percentage of recovery (R%). LAS test results indicate that CRMA has better fatigue life when TEOS content is 25% of CR.

Structural and mechanical evolution of the multiphase asphalt rubber during aging based on micromechanical back-calculation and experimental methods

Asphalt rubber (AR) is a sustainable paving material composed of bitumen and crumb rubber modifier (CRM) recycled from waste tires. The interaction between bitumen and CRM re-distributes the bitumen fractions and creates a multiphase internal structure of AR. Although the superior aging resistance of AR has been acknowledged, the aging mechanism of AR remains unclear due to the limited understanding on the behaviors of different phases of AR during aging. This study aims to investigate the structural and mechanical evolution of AR binder during aging through micromechanical back-calculation and experimental tests. A series of separation methods were used to disintegrate the multiphase system of AR at four aging conditions. The mechanical properties of different phases obtained from frequency sweep tests and their volumetric fractions were used as the input for the micromechanical back-calculation, which yielded accurate prediction for the complex modulus of swelling rubber but failed for that of undissolved rubber, so further chemical characterization was conducted to estimate its mechanical evolution. The results indicated that the aging of AR is a process in which internal multiphase structures changed simultaneously with mechanical properties. All subphases became stiffer but their influences on the overall mechanical property of AR variated after aging.

Vocs Emission Characteristics of Crumb Rubber Modified Bitumen and its Inhibition by Using Montmorillonite Nanoclay

Vocs Emission Characteristics of Crumb Rubber Modified Bitumen and its Inhibition by Using Montmorillonite Nanoclay

Investigating the High- and Low-Temperature Performance of Warm Crumb Rubber–Modified Bituminous Binders Using Rheological Tests

Rubberized asphaltic materials have been frequently combined with warm-mix asphalt technologies to tackle the issues of high energy consumptions and emissions during construction. Effective and accurate characterization of binder properties is conducive to the improvement of long-term pavement performance. The current study aims to quantify the effects of rubber content and warm-mix additives on rutting and thermal cracking performance of crumb rubber-modified bitumen (CRMB), and explore the rubber and additives modification mechanisms and their impacts on the binder performance. CRMBs containing different rubber contents and warm-mix additives after long-term aging were subject to multiple stress creep and recovery (MSCR) tests and low-temperature frequency sweep tests using a dynamic shear rheometer (DSR) with 4-mm loading plate to investigate the high- and low-temperature performance, respectively. Rheological tests were also conducted on the bitumen and rubber phases of CRMB to understand the rubber modification mechanism. Results show that CRMB binders have superior rutting and thermal cracking resistance due to rubber modification. The improvement of high- or low-temperature performance is more prominent at higher rubber concentrations. The effects of warm-mix additives on the rutting and thermal cracking performance are different. Generally, the wax-based additive improves the rutting resistance but negatively affects the low-temperature performance. In contrast, the chemical-based additive has an opposite effect except for the high-temperature performance of neat bitumen. The stiffening of the bitumen phase and the contribution of swollen rubber particles in the bitumen matrix together contribute to the peculiar viscoelastic response of CRMB, i.e., stiffer/softer and more elastic at high/low temperatures. This modification mechanism explains the superior rutting and thermal cracking performance of CRMB.

Crack propagation characterization of crumb rubber modified asphalt concrete using J-R curves

J-Resistance curves serve as a robust tool in characterizing the entire crack propagation trend of materials. Nevertheless, thus far, investigations on J-R curves of hot mix asphalt (HMA) have been very limited leading to scarce knowledge of post-peak fracture of the mixtures. In this research, mode I single-edge notched beam (SE(B)) fracture testing of unmodified and crumb rubber (CR) modified asphalt concrete mixtures was conducted with continuous monitoring of crack extension during the tests at 0 °C, −10 °C, and −20 °C. Modified HMA beams were fabricated incorporating 10% and 20% CR with 3% warm-mix additive. The CMOD-based elastic–plastic J-integral was computed incrementally during the tests and the J-R curve of each mixture could be determined. The results indicated that reducing the temperature increases the crack blunting energy from 0 °C to −10 °C while reducing the extents of the transition zone within blunting to unstable crack propagation of the unmodified mixtures. The unmodified mixtures undergo an unstable crack propagation as early as the macro crack initiates in −20 °C. At the same time, the incorporation of CR, could increase the blunting fraction of the R-curves at each temperature. Of vital importance, it could be detected that a 20% crumb rubber modification resulted in a more significant stable crack growth zone in the mixtures while developing a progressively rising R-curve in the post-peak region than the flat state in the unmodified mixtures at severely low temperatures.

Numerical Simulation of Modified Rubberized Concrete Block Under Impact Loads

Rubberized concrete was innovated by many researchers to enhance energy absorption under impact load and by reusing scrap tires. Thus, this research was aims to develop the numerical procedure using the Finite Element Method (FEM) to simulate modified rubberized concrete under impact loads and predict its energy absorption under different impact loads. Three existing constitutive models: Concrete Damage Plasticity (CDP), Drucker-Prager (DP), and Modified Drucker-Prager Cap (MDPC) available in ABAQUS software were used to replicate the rubberized concrete with 10% of Rice Hush Ash (RHA) as cement substitution and different percentages (0%, 5%, 10%, 15%, and 20%) of crumb rubber as sand replacement. All three models produced successful FEM results with reasonable modelling assumption, and the CDP model was more effective in simulating rubberized concrete under impact to predict energy absorption than DP and MDPC models. Further, it was concluded that crumb rubber could enhance the energy absorption of concrete. Generally, the energy absorption of the concrete increased as the crumb rubber increase. However, the strength decreased as the crumb rubber increased, but 10% of RHA in concrete mix can maintain the concrete strength. Overall, this study reveals that FEM incorporated with the CDP model is able to predict the impact response of modified crumb rubber as an application of concrete road barrier.

Laboratory investigation and statistical analysis of the rutting and fatigue resistance of asphalt mixtures containing crumb-rubber and wax-based warm mix asphalt additive

Recent studies show that using crumb rubber modifier (CRM) improves the mechanical and rheological properties of asphalt samples. However, the higher viscosity of rubberized binders increases the production temperatures of resulting mixtures. Using Warm Mix Asphalt (WMA) technology in combination with rubberized binders is a practical solution to alleviate this problem. However, mechanical characteristics of rubberized warm mixtures should be further analyzed to determine the effects of warm additives on the performance of asphalt mixtures. This study was performed to investigate the effects of an organic WMA additive, Slack wax (SW) (2%, 4%, and 6% by weight of binder), upon rutting and fatigue resistance of rubberized asphalt mixtures (15% and 20% CRM by binder weight). Further, a statistical analysis was conducted to define the possible relationships between fatigue life and three mechanical factors: toughness index (TI), resilient modulus, and indirect tensile strength (ITS). The results of the dynamic creep test indicated that both CRM and SW increased the flow number of asphalt samples yielding more resistant mixtures against rutting distress. The wheel tracking test results were consistent with the dynamic creep test. According to the indirect tensile fatigue test, the addition of SW was effective in improving the fatigue life of both control and rubberized asphalt specimens under two studied stress levels. TI values derived from the ITS test showed that rubberized warm mixtures can significantly increase the flexibility and energy absorptivity of asphalt mixtures. The results of bivariate correlation analysis indicated a direct relationship between the fatigue life-Mr and fatigue life-TI parameters. The significant values of correlation demonstrate that TI value derived from a cheap, easy, and fast ITS test is a practical parameter to predict the fatigue life of rubberized warm mixtures.

Improvement the Durability of the Hot Mix Asphalt by Using Crumb Rubber

Introduction: With the rapid economy growth and continuously increased consumption, a large amount of tire waste materials is generated Objective: This study attends to test the performance of many samples of asphalt concrete mix with adding the crumb rubber modifier (CRM) of 5%, 10%, 15%, 20% and 25% as percentage of asphalt cement content (AC) to address the best content of CRM (optimum) for asphaltic mixes the hot one HMA Methods: The Marshall design was used here to examine the influence of the Optimum CRM content. The CRM is blended with AC using wet process. Subsequently, by obtaining low price and economic mixes that will reduce the optimum asphalt content OAC Results and Discussion: The laboratory tests show that optimum rubber content is 17% by the weight of the asphalt cement. This meets the ASTM Standards 2001and Jordanian MPWH requirements Conclusion: Adding the CRM to HMA will increase the consistency and viscosity of the mixes which leads to higher rutting resistance, reduce fatigue and reflecting cracking and improve durability

Improvement the Durability of the Hot Mix Asphalt by Using Crumb Rubber

Introduction: With the rapid economy growth and continuously increased consumption, a large amount of tire waste materials is generated Objective: This study attends to test the performance of many samples of asphalt concrete mix with adding the crumb rubber modifier (CRM) of 5%, 10%, 15%, 20% and 25% as percentage of asphalt cement content (AC) to address the best content of CRM (optimum) for asphaltic mixes the hot one HMA Methods: The Marshall design was used here to examine the influence of the Optimum CRM content. The CRM is blended with AC using wet process. Subsequently, by obtaining low price and economic mixes that will reduce the optimum asphalt content OAC Results and Discussion: The laboratory tests show that optimum rubber content is 17% by the weight of the asphalt cement. This meets the ASTM Standards 2001and Jordanian MPWH requirements Conclusion: Adding the CRM to HMA will increase the consistency and viscosity of the mixes which leads to higher rutting resistance, reduce fatigue and reflecting cracking and improve durability

Rheological Findings on Storage Stability for Chemically Dispersed Crumb Rubber Modified Bitumen

Elastomers and different Plastomers are most common additives used to improve the performance of binder. However, bitumen modified with these additives is known to be unstable followed by the problem of separation. The separation problem becomes worse, when bitumen is modified with CR, which can undergo a high degree of phase separation during hot storage. The incorporation of CR reclaimed from waste tyres resulted in enhanced properties of conventional bitumen but with limited constraints. Scrap tyres is taken as important product followed by its effective use with virgin bitumen in order to rectify the mechanical and performance properties of base bitumen.The changes in densities of material constituents also affected the storage stability of blends. It is also dependent on the phase separation and dispersion of CR particles for storage intervals. The improved storage stability was attributed to a good CR dispersion which was also observed during softening point and X-Ray image analysis resulting into improved performance for experimented temperatures. Besides, the involvement of DDSA imparted with the significant change in the performance of blends against storage stability. The study is based on empirical techniques to be adopted as revolutions for smart and sustainable pavement materials.

Effect of Silica Fume and Synthetic Fibre towards the Compressive Strength of Modified Crumb Rubber Cement Mortar

Cracking is very common problem in cement mortar. Many past research has explored the prospect of using crumb rubber (CR) to overcome this issue. Different sizes of CR have been tested to measure its effect on the pore structure and mechanical strengths of cement mortar. Hence, this study has further modified the crumb rubber mortar mix by adding silica fume and synthetic fiber to improve its mechanical properties. The experimental results suggested that the optimum silica fume replacement of cement content was 5%. Hence, for the subsequent experiment with a fixed 5%silica fume replacement, the highest compressive strength of 26 MPa was achieved with 5% crumb rubber replacement. Finally, additional 0.1% of synthetic fiber added the modified crumb rubber mix to reduce the mix brittleness has produced a desirable compressive strength close to the control specimen which was significantly higher than the minimum threshold required by the standard. However, the water content ratio for the modified mortar mix should be further investigated as the present modified crumb rubber mix has lower workability. It is envisaged that the modified crumb rubber mortar mix has a sound potential to mitigate shrinkage cracking in cement mortar.

Can crumb rubber modifier effectively replace the use of polymer- modified bitumen in asphalt mixture?

ABSTRACT Laboratory scale mechanical performances on six plant produced mixtures; three semi-dense surface courses and three dense binder courses modified with engineered crumb rubber (ECR) using the dry process are presented. The two types of mixtures produced and investigated fulfilled for the most part, the requirements of the Swiss and/or US standards regarding volumetric properties, water sensitivity and rutting. In advanced testing where no requirements exist, the dense ECR mixtures performed similar to the reference polymer modified mixtures and slightly worse for semi-dense mixtures in high temperature tests, where the binder becomes viscous in the rubber-binder composite and its ability to transfer loads is reduced. The ECR mixtures performed similarly or better than the reference in low temperature tests. Across the advanced testing data set, all obtained results were well within acceptable values for both ECR and reference polymer mixtures indicating that crumb rubber can effectively replace polymer in asphalt mixtures.

Characterizing Compatibility of Crumb Rubber Modified Asphalt by Customized Drainage Method

Abstract The poor compatibility between crumb rubber (CR) and asphalt matrix always brought difficulties to the engineering application of CR modified (CRM) asphalt. The compatibility in CRM asphalt was universally characterized by storage stability test at a macroscale. Actually, the term “compatibility” was introduced to describe the “level of interaction” between the asphalt and polymers in polymer modified asphalt. Therefore, in this study, the compatibility in CRM asphalt (i.e., the level of asphalt-rubber interaction) was newly characterized by removing the CR particles in the CRM binder through a customized drainage process and quantifying the difference between drained asphalt and base asphalt. In practical terms, the changes in the rheological properties and chemical composition of binder relative to base asphalt were measured by dynamic shear rheometer and gel permeation chromatography, respectively. Based on this novel characterization, it was found that smaller CR particles tended to possess greater compatibility with asphalt, and the asphalt with a higher percentage of light fractions was expected to be more compatible with CR particles. On the other hand, the result of the conventional hot tube test found the storage stability mainly depended on the size and content of CR particles. Furthermore, a strong statistical correlation between the novel characterizations (i.e., changes in rheology and chemistry of binder) and the common characterization (i.e., storage stability) was found, and its essential cause was discussed. Therefore, this novel characterization could provide another reliable and simple way to evaluate the compatibility in CRM asphalt.

Secondary-Reaction Method to Improve Performance of a Compound Modified Rubber Asphalt after Short-Term Aging

AbstractAsphalt aging occurring during the mixing and transportation of a mixture will decrease the performance. In this study, a compound modified rubber asphalt containing crumb rubber modifier (...

Evaluation of an Asphalt Mixture Containing a High Content of Reclaimed Asphalt and Different Crumb Rubber Modified Binders

Abstract Recently, environmental concerns have become a primary driving force in most countries and industries dealing with natural resources. As a part of this category, asphalt pavement industry is trying to implement more green and sustainable features in its products, while maintaining the mechanical and performance-based properties of the resulting asphalt mixtures. Among potential recycled materials, vehicle tires and aged asphalt pavement have been demonstrated to show economic, ecological, and behavioral improvements in the mixtures. However, mixtures with a high content of reclaimed asphalt (RA) and crumb rubber present some limitations. Therefore, using another group of additives, i.e., a warm mix asphalt (WMA) additive, has been considered. The presented paper investigates the use of an elevated content of RA with different crumb rubber modified binders and (in some mixtures) a warm mix additive in an asphalt concrete (AC) binder mix. Regular empirical tests have been conducted and more advanced performance or functional characteristics, i.e., stiffness, thermal induced cracking, resistance to permanent deformation, complex modulus have been determined and evaluated. Selected results are presented in the paper.

Evaluation of Petroleum Resin in Rubberized Asphalt Binder

The crumb rubber modified (CRM) binder was evaluated considering the general operating temperatures of high, intermediate, and low temperatures. CRM binders were produced with four different contents (0, 5, 10, and 15%) using the base asphalt binder (PG64-22). Then, they were artificially aged by a rolling thin-film oven (RTFO) and pressure aging vessel (PAV). Superpave binder tests using a rotational viscometer (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR) was applied to characterize the performance of the original and aged binders. Multiple stress creep recovery (MSCR) tests were also performed for deeper rutting characterization. The results of this study are as follows: (1) the presence of PR increases the binder viscosity, (2) the integration of CRM greatly improved the rutting resistance of the binder, and it was found that PR also improved the rutting characteristics, and (3) it is observed that PR is detrimental to the cracking properties of CRM binders.