Crumb Rubber Content Research Articles

Experimental Study on the Influence of Crumb Rubber on Temperature Susceptibility of Asphalt for Railway Application in the Tropics

The granular sub-ballast in conventional ballasted trackbed structure, though cheap and easy to construct, requires frequent maintenance, and cannot protect the subgrade against water infiltration. However, asphaltic sub-ballast in asphalt-ballast trackbed can reduce stress on the subgrade and provide a waterproofing layer against water infiltration. Asphalt binder is however, susceptible to temperature fluctuations. The aim of this study therefore is to investigate whether the addition of crumb rubber to asphalt binder could reduce the susceptibility of asphalt to temperature, and thus, improve its performance. The main objective of this research is the addition of four different ratios of crumb rubber; 1, 2, 3, and 4%, of size 0.3 mm to bitumen or asphalt 60/70 grade. The results showed that penetration of the asphalt binder reduced from 66.70 to 59.20 mm at 4% rubber content, implying that the modified asphalt became harder with addition of crumb rubber and thus, can withstand temperatures variations in asphaltic pavements. Softening point, used to test temperature susceptibility of bitumen, increased from 49.10°C to 52.80°C at 4% crumb rubber content, implying that crumb rubber modified asphalt can withstand elevated temperatures in asphaltic pavements, in the tropics. Flashpoint increased from 295.20 to 296.12°C, fire point also increased from 306.50°C to 308.28°C, Specific gravity of the unmodified and crumb rubber-modified asphalt did not change significantly because crumb rubber is not very flammable, Viscosity at 135°C increased from 338.00 to 360.00 cSt at crumb rubber content of 4%, Ductility at 25°C reduced from 122.40 cm to 79.40 cm at 4% crumb rubber content, implying that crumb rubber made asphalt stiffer. This study concludes that crumb rubber can reduce the susceptibility of asphalt to temperature changes.

Study on high-temperature emission behaviors of crumb rubber modified asphalt: Experimental analysis and molecular simulation approach

The harmful emissions produced during the manufacturing and construction processes of crumb rubber modified asphalt (CRMA) significantly hinder its widespread application. Addressing this issue hinges on a thorough investigation into the mechanism governing its high-temperature emissions. This study employed microscale testing methods to analyze the microstructure and chemical property disparities between CRMA and base asphalt (BA). Subsequently, the impacts of varying crumb rubber (CR) content, experimental temperature, and sulfur stabilizer dosage on the high-temperature emissions of CRMA were investigated. Furthermore, comparative analyses of the molecular weight distribution, emission species, and CR crosslink density in asphalt after the fume experiment were conducted to further elucidate the high-temperature emission mechanisms. Finally, molecular simulation techniques were employed to analyze the interactions between CR and the four fraction molecules of asphalt at the microscale. The results indicated that the fume release volume of CRMA initially decreased and then increased with the addition of CR, while both the experimental temperature and sulfur stabilizer content exhibited a positive correlation with emission volume. CR reduced the volatilization of some small molecular hydrocarbons in the BA by absorbing light fractions. Meanwhile, excessive swelling caused the crosslinking density of CR to decrease by 77 %, which led to the release of toxic substances. At 20% CR content, the overall emissions of CRMA achieve their lowest level; however, the emission of toxic gases does not diminish. Molecular simulations have also confirmed the above results, showing that there is a strong interaction between CR and the light fractions. Compared with asphaltene molecules, rubber molecules had higher molecular polarity and stronger adsorption behavior for light fraction molecules.

Emission Risk and Inhibition Technology of Asphalt Fume from Crumb Rubber Modified Asphalt

Crumb rubber-modified asphalt mixtures have been proven to have extensive utilization value in road engineering. However, the rubber releases more fumes during the construction period, which causes severe harm to human health and the environment. This research focused on the emission risk of asphalt fume from crumb rubber-modified asphalt, and then the inhibition technology was also optimized. Firstly, the emission behavior and the hazardous evaluation of the asphalt fume from crumb rubber-modified asphalt were investigated. Then, the characteristics of the inhibition materials were evaluated. Finally, the reduction in the emission of inhibited crumb rubber-modified asphalt fume was identified, and the optimized formula was determined based on the inhibition effect, rheological properties, and cost. The results indicate that crumb rubber-modified asphalts release more fume components with an increment in the temperature and crumb rubber content. Desulfurized rubber reduces the release of H2S and NO. Benzene compounds, including paraxylene, toluene, and benzene, are the most released pollutants that harm human health, especially DS CRA 20% and CRA 50%. Kaolin powder and expanded graphite have a sufficient pore structure and volume, the addition of which reduces the release of pollutants while possibly promoting the release of NO and H2S. Their addition also has a significant control effect on the release of particulate matter at 170 °C and 185 °C. With the consideration of emissions, rheological properties, and cost, CRA 40%-EG2%-KL2% was determined as the optimization formula. This research is helpful to the application of crumb rubber-modified asphalt in road construction and maintenance.

Rheological and adhesive improvements of terminal blend rubberized asphalt via fumed silica nanoparticle modification

Due to the high degree of desulfurization and depolymerization of crumb rubber (CR) particles in terminal blend rubberized asphalt (TBRA), their elasticity and adhesive performance are insufficient. To address this, the study utilized low-cost fume silica nanoparticles (FSNPs) to enhance the elasticity and adhesive properties. TBRA binders with varying CR contents (30 %, 40 %, 50 %) were modified using different dosages of FSNPs (2 %, 4 %, 6 %). The microstructure of FSNPs was examined through TEM and SEM. Using a dynamic shear rheometer (DSR) test, contact angle test, and atomic force microscope (AFM) test, the effects of FSNPs on the rheological properties, surface energy, and adhesive properties of TBRA binders were evaluated. The results showed significant improvements in the deformation resistance and elasticity of the TBRA binders modified with FSNPs. This is attributed to the branched network structure of FSNPs, which notably enhances the binder's cohesion, thereby strengthening its resistance to shear deformation and improving elasticity. FSNPs effectively reduce the moisture sensitivity of TBRA, due to the hydrophilic hydroxyl groups on FSNPs being replaced by hydrophobic methyl groups (-CH3). The inadequate bonding performance of TBRA can be attributed to the high levels of extensively depolymerized and desulfurized CR particles, which reduce the cohesiveness of the binder. The addition of FSNPs, although it lowers the surface energy of TBRA binders, significantly enhances their cohesiveness due to the branched network structure, thereby improving their bond performance. AFM results indicate that FSNPs enhance the adhesive strength of the TBRA binder surface due to their high specific surface area, which provides more van der Waals forces and electrostatic interactions. For economic efficiency, an addition of 4 % is recommended for TB30, and 2 % for TB40 and TB50. At these specified concentrations, the bond strength of the TBRA binder can be increased by 45–55 %.

Effects of palm oil fuel ash and crumb rubber on mechanical and thermal properties of sustainable engineered cementitious composites

The construction sector using natural sand causes rapid depletion and environmental harm, including erosion, biodiversity loss, and aquatic habitat destruction. To address these challenges and advance sustainability, this study systematically investigated the behaviour of engineered cementitious composites (ECC) incorporating 10–30 % ground palm oil fuel ash (GPOFA) and crumb rubber (CR) as a fine aggregate substitution. Two different sizes of GPOFA, P600 (in the range of 300 μm–600 μm) and P300 (less than 300 μm), were utilized to substitute the fine aggregate in the mix. Dry density, workability, thermal conductivity, modulus of elasticity, tensile strength and strain, compressive strength, flexural strength, and ultrasonic pulse velocity (UPV) were investigated. Furthermore, the microstructures and mineralogical compositions of the selected ECC samples were also examined. The results indicate that increasing GPOFA and CR content reduced ECC's flowability and density. Incorporating GPOFA reduced the compressive strength by 23 % for P600, 12 % for P300, and 74 % for CR, for 30 % substitution at 28 days. Both substitutions reduced the modulus of elasticity and UPV of ECC due to reduced packing efficiency and increased porosity. Increasing GPOFA improved the first cracking load slightly but decreased ultimate flexural strength, whereas CR significantly reduced both. In addition, tensile strain and strength dropped more significantly for ECC with CR compared to ECC with GPOFA. ECC with CR recorded the highest shrinkage and the lowest thermal conductivity (0.66W/mK). Overall, P600 outperformed P300, and CR showed the lowest performance in ECC across all parameters studied. This study highlights that partial replacement of silica sand with GPOFA could produce greener ECC with acceptable mechanical properties, while CR effectively reduces the thermal conductivity of ECC. Integrating GPOFA and CR adds significant value to these wastes while simultaneously providing a sustainable solution for waste disposal.

3D Cementitious composites printing with pretreated recycled crumb rubber: mechanical and acoustic insulation properties

ABSTRACT Cementitious materials incorporating recycled crumb rubber have become a common sustainable resolution in diverse building environments to achieve various functions in terms of lightweight, ductility, as well as energy absorption. This study explored the 3D printed rubberised cementitious composites (3DPRC) in two aspects: examining the effects of crumb rubber pretreatment conditions on compressive properties; conducting experimental and numerical analysis on the acoustic dissipation characteristics of 3DPRC. Fine crumb rubber granules (3-5 mm) replaced 10%, 20%, and 30% of river sand in the composites. Uniaxial compression tests indicated that the compressive strength of 3DPRC decreased with the increase of crumb rubber content and introduced anisotropic behaviour. Impedance tube tests were conducted to evaluate the sound absorption and insulation capabilities of 3DPRC. An optimal Noise Reduction Coefficient (NRC) of 0.35 was achieved with 30% crumb rubber. The sound insulation properties depend strongly on the mass density and porosity of the 3DPRC. Additionally, it is proved that the volume of built-in air gap has positive effects on both sound absorption and insulation properties. The results from Finite Element Method (FEM) numerical simulations correlated well with experimental data, proving the efficiency of the simulation and validating the experimental results.

Study on the synergistic regeneration effect of tall oil and crumb rubber on aged SBS modified asphalt

The thermo-oxidative aging of Styrene-Butadiene-Styrene (SBS) modified asphalt (SMA) includes the aging of base asphalt and the degradation of SBS modifiers. With the aim of restoring the performance of base asphalt and making up for the loss of performance advantage caused by the degradation of SBS modifier, tall oil and crumb rubber (CR) were applied to synergistically regenerate aged SBS modified asphalt (ASMA). The effect of the particle size and content of CR, as well as the degree of microwave-activated CR on the properties and storage stability of the reclaimed ASMA were discussed in details. The regeneration mechanism of ASMA by CR was studied from the surface properties, morphology and thermal behavior, respectively. The results show that tall oil can restore the low-temperature properties of ASMA significantly, but it seriously detrimental to the high-temperature properties. CR play the role of secondary modification on the reclaimed ASMA, which can improve the high-temperature properties of the reclaimed ASMA at the cost of low-temperature properties and storage stability, and the modification effect is related to the particle size and content of CR. Microwave activation of CR can improve the storage stability of the reclaimed ASMA with CR, which is because that microwave activation modification disrupts the cross-linking structure of the CR and improves the surface properties, which are conducive to the diffusion migration of molecular chains and multiphase material exchange between the CR and the reclaimed ASMA. Thus, the interaction between the multiphases can be enhanced in the reclaimed ASMA with CR. This work provides an effective regeneration method for aged SBS modified asphalt, and also achieves the reuse of non-renewable resources.

Analysis of crumb rubber content influence on damage evolution and pattern recognition of rubberised epoxy asphalt mixture using acoustic emission techniques

ABSTRACT The application of coarse crumb rubber (CR) to toughen the epoxy asphalt mixture has emerged as a viable choice. However, the evolution rule of strength and damage modes of mixtures with different crumb rubber contents remains elusive. The objective of this study is to clarify the failure mechanisms in rubberized epoxy asphalt mixture combined acoustic emission (AE) data and k-means clustering theory. Four types of epoxy asphalt mixture samples are tested with the monitor of AE sensors. Based on the temporal and frequential features of AE signals, damage evolution is evaluated by the Weibull function, b-value, and the relationship between the raise angle and average frequency at the peak loading. Moreover, the k-means algorithm is conducted to cluster the AE events and damage characteristics after pre-processing the data. The test results indicate that CR particles enhance the toughness of epoxy asphalt mixtures and the mixtures with fewer CR are susceptible to occur sudden fracture due to brittle coarse aggregates. The k-means method effectively identifies AE events into four types of damaged behaviours. The findings offer valuable insights into the strength attenuation, modification characteristics, damage evolution and damage modes of rubberized epoxy asphalt mixtures, contributing to the development of more durable and resilient asphalt materials.

An eco-friendly crack sealant approach for asphalt pavement by using laboratory tests and molecular dynamic simulation

Waste engine oil (WEO) is detrimental to the environment and challenging to recycle on a large scale. Fortunately, the utilization of WEO as an additive in asphalt pavement crack sealant offers both economic benefits and engineering feasibility. In this study, an eco-friendly crack sealant was prepared using WEO and crumb rubber (CR) modified asphalt (WCRA). The viscoelasticity, storage stability, adhesion, and water resistance properties of the sealant were tested to evaluate its suitability for crack repair. In addition, molecular dynamic (MD) simulation was employed to elucidate the interface adhesion mechanism of the sealant-crack wall interface. The test results demonstrated that the viscosity of the sealant is primarily proportional to the content of CR and inversely proportional to WEO. Furthermore, the storage stability is satisfactory after the addition of moderate WEO. The medium and high temperature flexibility of the sealant is between base asphalt and SBS-modified asphalt. Based on the laboratory tests, 35% (by weight of base asphalt) microwave-treated CR and 25% (by weight of CR) WEO are the optimal proportions for preparing the sealant. MD simulation demonstrated that CR inhibits the diffusion of asphalt components and aggregates asphaltenes in close proximity to the crack wall surface. WEO not only stimulates molecular activity but also maintains the equilibrium of the asphalt colloid system, which is conducive to the penetration and water resistance of the sealant. The study will provide a reference for the utilization of waste materials and the cost-effective repair of asphalt pavements.

Modeling and design optimization of dense graded modified crumb rubber asphalt mixtures using response surface methodology

Modification of asphalt pavement materials by using recycled waste tires in form of crumb rubber (CRM) is getting significant importance for saving resources as well as protecting ecosystem. So, in this study the crumb rubber size and percentage content effect on the performance properties of binder and mixtures were evaluated. A detailed experimental program has been performed using design expert software considering the variables like rubber size and content and their responses which were viscosity, Indirect Tensile strength (ITS), Tensile strength ratio (TSR) durability and Resilient Modulus (Mr). The viscosity of control binder with the addition of crumb rubber at high temperatures showed good improvement. The performance properties viz., ITS, TSR and Mr showed similar behavior as the size and content of crumb rubber increased under different loading conditions. The statistical models prepared using the analysis tool were found significant and well fitted based on high R2 (>0.80), high adequate precision value (>4), insignificant lack of fit and low p-value. Analysis of variance (ANOVA) model theoretical results generated by the response surface methodology (RSM) analysis were further validated by the experiments with <5 % of error showing good agreement between theoretical and experimental results. Study results showed that modified binder with 10 % crumb rubber passing sieve No. 40 in mixtures showed good improvement of mechanical properties indicating the potential source of recycled waste material usage in the pavement construction.

Mechanical and Environmental Analysis of Granular Subbase with Fine Crumb Rubber

The increasing manufacturing of tires, driven by the automotive sector, has led to various sustainability and waste management issues. Consequently, it is necessary to explore alternatives for the reuse of these wastes. Rubber has demonstrated properties that could make it an attractive material for use as a granular aggregate. The aim of this study is to evaluate the influence of crumb rubber (CR) on the mechanical behavior of a granular subbase (GSB) by replacing fine CR at 10% and 15%. An environmental analysis of the proposal was conducted using the SimaPro tool, and a series of laboratory tests were performed to assess physical and mechanical characteristics. The strength results indicate a decreasing trend as the CR content in the GSB increases. Specifically, in abrasion tests, the natural material showed an average result of 30.86%, while the mixes with 10% and 15% CR exceeded the maximum limit (50%), achieving results of 59.24% and 53.98%, respectively. In terms of the California Bearing Ratio (CBR), only the natural samples compacted at maximum energy exceeded the minimum requirements for low and medium traffic levels (30%). The highest CBR value for samples containing CR was 5%, whereas the natural GSB reached a maximum CBR of 33%. A similar trend is observed in environmental outcomes, with increases of up to 17% in abiotic depletion for the sample with 15% CR. Overall, the environmental analysis suggests that incorporating CR into the GSB could lead to an increase in various environmental impacts.

Sustainable innovation in self-compacted concrete: Integrating by-products and waste rubber for green construction practices

Due to increasing concern about global climate change and its negative influence on societies, there is a specific focus on the construction sector as the greatest contributor to greenhouse gas emissions. About 8–10% of global CO2 emissions come from cement production, which releases almost a ton of CO2 for every ton of cement. Growing demand for cement and concrete is attributed to rapid urbanization, industrialization, and economic growth, which also substantially impacts the depletion of natural resources. To address these challenges, a feasible approach is to utilize by-product materials and waste rubber as alternatives to cement and natural fine aggregates in producing self-compacted concrete (SCC). The utilization of various percentages of fly ash (FA), ground granulate blast furnace slag (GGBFS) as cement replacement, and crumb rubber (CR) from waste tires as a partial substitution of fine aggregate offers a suitable choice for the development of sustainable SCC. In addition, compressive strength (CS) is a vital property when considering other characteristics of concrete. Therefore, it is vital to develop reliable models for predicting the CS of SCC to achieve cost, time, and energy savings. Therefore, this research examines the impact of various contents of FA and GGBFS as cement (C) alternatives and CR as a sand replacement on the CS of SCC. To predict the CS of rubberized SCC mixtures, four different models were employed: linear regression (LR), multi-linear regression (MLR), full quadratic (FQ), and M5P-tree. To accomplish this, a comprehensive set of data comprising approximately 436 samples was analyzed to develop the models; as input variables, various mixture proportions, and curing ages were considered. To ensure the accuracy and reliability of the predictive models, several statistical assessments were performed. Based on the statistical assessment tools conducted in this study, the FQ model is considered the most effective model for forecasting the CS of SCC. Based on the statistical assessment tools, the FQ model was also implemented to forecast the splitting tensile and flexural strengths of SCC. The sensitivity analysis indicates that CR and GGBFS content are the best criteria for forecasting the CS of SCC utilizing this data set.

Rheology of Crumb Rubber-Modified Warm Mix Asphalt (WMA).

This study explores the impact of adding waste vehicular crumb rubber to the commercially available warm mix additives Sasobit® and Zycotherm® on modified asphalt binders' physical and rheological properties. Various concentrations of crumb rubber (0%, 10%, 15%, and 20%) were introduced to asphalt binder samples with 2% and 4% Sasobit and 1.5% and 3% Zycotherm. The investigation employed conventional tests (penetration and softening point) and advanced mechanical characterization tests, including Superpave rotational viscosity (RV), Dynamic Shear Rheometer (DSR), DSR multi-stress creep recovery (MSCR), DSR linear amplitude sweep (LAS), and Bending Beam Rheometer (BBR). Traditional tests measured the asphalt consistency, while workability was assessed through the RV test. The results showed that the Zycotherm binders experienced a more significant penetration reduction than the Sasobit binders. Additionally, an increased crumb rubber content consistently elevated the softening point and rotational viscosity, enhancing the complex shear modulus (G*) values. Rubberized binders exhibited an improved rutting performance and low-temperature PG grades. Increasing the crumb rubber content enhanced fatigue life, with Z1.5CR20 and S2CR20 demonstrating the longest fatigue lives among the Zycotherm and Sasobit binders, respectively. Overall, Z1.5CR20 is recommended for colder climates, while S2CR20 is suitable for hot-climate applications based on extensive analysis.

Impact Resistance of Rubberized Alkali-Activated Concrete Incorporating Recycled Aggregate and Recycled Steel Fiber

Alkali-activated concrete (AAC) features excellent mechanical properties and sustainability. The incorporation of crumb rubber (CR), recycled concrete aggregates (RCAs), and recycled steel fibers (RSFs) can further enhance environmental sustainability. This paper mainly investigated the dynamic behaviors of a novel rubberized AAC incorporating RCAs and RSFs (RuAAC) through Split-Hopkinson Pressure Bar (SHPB) tests. The variables included three types of RSF content (1%, 2% and 3%), five types of rubber content (0%, 5%, 20%, 35% and 50%) and five impact pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa and 0.9 MPa). Dynamic stress–strain curves, dynamic strength, the dynamic increase factor (DIF), impact toughness and the synergistic effects of RSF and CR were discussed. The results show that increasing RSF and CR contents could improve the impact resistance of RuAAC under impact loading. The RuAAC exhibited significant strain rate sensitivity, and the sensitivity increased with larger contents of RSF and CR. The increase in strain rate sensitivity was more pronounced with higher CR contents, which was reflected in larger dynamic increase factor (DIF) values. Under high impact pressure, the impact toughness was obviously enhanced with higher RSF contents, while the contribution of increased CR content to impact toughness was not apparent, which may be attributed to the fact that this study only calculated the integral under the dynamic stress–strain curve before the peak stress to determine impact toughness, neglecting the potential contribution of CR particles after the peak point. The obvious strain sensitivity exhibited by the RuAAC in the SHPB tests indicated superior impact performance, making it particularly suitable for architectural structures prone to seismic or explosive impacts.

Mechanical characterization of fiber-reinforced rubberized recycled concrete

Dumping non-biodegradable wastes, such as construction and demolition waste (CDW) and scrap tires, is causing significant environmental problems. Thus, this study used recycled coarse aggregate (RCA) and crumb rubber (CR) procured from CDW and scrap tires as a partial replacement of natural aggregates. 30% natural coarse aggregate (NCA) was replaced by RCA, and 0, 5, 10 and 15% natural fine aggregate (NFA) was replaced by CR. Besides these, 0.5% polypropylene (PP) fiber was incorporated into the concrete mixtures. Different physical and mechanical properties of rubberized recycled concrete (R2C) and fiber-reinforced rubberized recycled concrete (FR2C) were investigated. Microstructural analysis, chemical analysis, failure modes, and cost-effectiveness were also evaluated. Simplified regression equations have been proposed to predict various mechanical properties of R2C and FR2C mixtures. The inclusion of RCA, CR, and fiber decreased the slump value of the fresh concrete up to 69.7%. The compressive strength decreased with an increase in CR percentage, but it increased by including fiber content. Though all the R2C and FR2C specimens exhibited lower tensile and flexural strength, a marginal reduction was found in FR2C specimens containing up to 5% CR content, which was only 3.3% and 6.8% lesser compared to the control samples. The surface resistivity test revealed that the chloride ion penetrability may be very low for all the combinations of R2C and FR2C specimens. By raising the percentage of CR, the UPV decreased, but the addition of PP fiber slightly increased the value. The cost analysis results pointed out that both the R2C and FR2C combinations saved more energy (up to 2.22 times) and decreased fuel consumption (up to 20.2%). Finally, the present study will aid in advancing sustainable fiber-reinforced rubberized recycled concrete.

Advancing sustainable hybrid bitumen systems: A compatibilization solution by functionalized polyolefins for enhanced crumb rubber content in bitumen

Polymer waste pollution has a profound effect on the environment and, consequently, on the lifestyle of humankind. The massive production and disposal of cross-linked polymers clearly exemplify the challenges of recycling. Increasing efforts are being undertaken to introduce recycled polymers, especially crumb rubber (CR), into asphalt formulations. Due to the rather poor processability and phase separation associated with CR-modified bitumen (CRMB) compositions, a broader implementation of such concept is challenging unless an efficient compatibilizer is applied. Results from the study on usage of In-Reactor-Functionalized Polyolefins viz. poly(propylene-co-hex-1-ene-co-hex-5-en-1-ol) (FPP), demonstrated excellent compatibilizing ability in CRMB, allowing incorporation of up to 10 wt% of CR. This represents a significant improvement when compared to the best-in-class solutions. The FPP-containing products exhibit superior bulk, nanomechanical and rheological properties, as well as stability during binder annealing. Furthermore, the bitumen surface morphology is significantly improved. The polar groups present in the FPP create a thermo-reversible interpenetrating cross-linked network that provides mechanical integrity and contributes to the adhesion to different components of the modified bitumen at service temperatures, enhancing its processability. The exceptional compatibility of FPP in CRMB resulted in a significant increase in the Performance Grade of the hybrid system by 5 classes (88) compared to neat bitumen (58). Moreover, the best-performing composition fulfilled the low-temperature ductility specifications, withstanding deformation without fracturing or breaking up to a 400 mm elongation.

Optimization of composite-modified asphalt ratio and performance evaluation of rich bottom layer mixes

This study focused on developing a high-toughness composite-modified asphalt (CMA), to enhance the performance of rich bottom layer mixes and its crack resistance. The content of crumb rubber (CR), epoxy resin (ER), and polyaryl polymethylene isocyanate (PMDI) were chosen as design parameters. Response surface methodology (RSM) was employed to develop models for creep strength (S), fatigue performance parameter (Nf), yield energy (YE), and Brookfield viscosity (BV) of CMA. Then, these models were used to optimize the content of modifiers. Additionally, rich bottom layer mixes were designed using SBS-modified asphalt (SMA) and the newly developed CMA as binders, and their performances were evaluated. The results demonstrated the accuracy and predictive ability of the RSM models. The composite-modified asphalt mixes (CMAM) showed superior road performance and crack resistance compared to SBS-modified asphalt mixes (SMAM). Importantly, CMAM aligned effectively with the functional requirements of the rich bottom layer. This research contributes novel materials and methods for enhancing pavement crack resistance, providing valuable insights for improving the durability and longevity of pavements.

Effects of crumb rubber and styrene-butadiene rubber additives on the properties of asphalt binder and the Marshall performance properties of asphalt mixtures

The primary aim of this study is to evaluate the impact of incorporating crumb rubber (CR) and styrene-butadiene rubber (SBR) additives, ranging from 0% to 5% by weight of bitumen, on the performance of a bituminous concrete mixture using the wet process. Laboratory experiments, including the Marshall test, were conducted to establish the optimum bitumen content (OBC) for the hot mix. The study focuses on determining the optimal proportions of CR and SBR to achieve maximum strength. The results show that increasing the proportions of both CR and SBR leads to significant improvements in strength, with the maximum stability recorded at 16.14 kN and a flow of 1.23 mm for a mix containing 5% CR and 4% SBR. The findings further suggest an inverse relationship between CR content and strength, while an increasing SBR content enhances strength. Consequently, the optimal proportions for incorporating CR and SBR additives are identified as 5% and 4%, respectively.

Experimental study and predictive modelling of damping ratio in hybrid polymer concrete

The improved damping capacity of concrete materials is crucial for many applications, especially the ones exposed to dynamic external forces. This study explores the optimal circumstances of copolymer composite binder, ratio of fine to coarse aggregate, curing time, size and content of tyre crumb rubber on enhancing damping ratio of hybrid polymer concrete. Owing to the limitation of conventional models and experimental methods in effectively handling the multiple and complicated relationship between the input parameters of the hybrid polymer concrete and its damping capacity, two robust machine leaning models including extreme gradient boosting (XGB), and artificial neural network (ANN) algorithms were developed to predict the values of damping ratio from an experimental database of 196 samples. Multiple linear regression (MLR) was employed in this study as a benchmark for comparing with the ANN and XGB methods. The results indicate that the considered algorithms yield accurate models for predicting the damping ratio of HPC composites. However, ANN and XGB outperform MLR with an impressive R-square of 0.985 and 0.981, respectively versus 0.875. Analysing the importance of input features using the XGB algorithm also reveals that the curing time has the highest impact on predicting the damping ratio. The volume fractions of resin matrix and crumb rubber are the next most important features. The crumb rubber size, within the studied range, appears to be the least impactful one.

Study of Crumb Rubber as Binder Material in Asphalt

Asphalt is a mixture of aggregates, bitumen, quarry dust, and cement. As an addition in hot mix asphalt mixtures, recycled tire rubber known as "crumb rubber" is regarded as an environmentally friendly building practice. The laboratory hot mix asphalt design tests were conducted according to Marshall method procedure. In this study, three different crumb rubber contents (10%, 15%, and 20% by weight of bitumen), and three different bitumen contents (4%, 5%, and 6%) with a penetration grade 60/70 were investigated. The Marshall stability value and durability properties were taken into account in a comparison study between the standard and modified asphalt concrete mixtures. The strength and performance of asphalt mixtures tended to improve with the addition of crumb rubber. As some of the test results were within the acceptable range, the findings indicated that crumb rubber is advised for use as an addition in asphalt mixtures. Besides, the durability of asphalt mixtures also needed to be concerned.