Crumb Rubber Content Research Articles

Pavement FRFs and noise: A theoretical and experimental investigation

Traffic and tyre/road noise affect human health. In order to mitigate the tyre/road noise, the knowledge of the frequency-based mechanics of pavements (e.g., pavement Frequency Response Functions, FRF) could be a crucial factor, because the remaining factors have been investigated in depth. Consequently, the main objective of this study was to investigate the relationships between road acoustic response (herein called RAR) and FRFs in case of bituminous mixtures added with different percentages of crumb rubber (CR). Laboratory tests and analyses were carried out. In particular, during preliminary tests, the system (i.e., impact hammer, microphone, analog-to-digital converter cards, and software) was set up using both cylindrical specimens and rectangular slabs, and a new testing procedure for both sample types (based on the standards EN29052-1 and ISO 7626–5) was defined. Subsequently, the new procedure was applied to four sets of cylindrical samples consisting of dense asphalt concretes (i.e., AC6d), where different percentages of crumb rubber (CR; i.e., 5%, 29%, and 100%) were added (dry method). Results demonstrate that even if many parameters affect the FRF estimates, FRFs and RAR are related especially in the range 0.4–3.2 kHz, and that CR content can contribute to lowering the mechanical impedance, the dynamic stiffness, and the acoustic response of the asphalt concrete mixtures used in this study. By referring to RAR-based versus Close Proximity method (CPX)-based inferences and analogies, the relationship between the RAR herein defined and measured and the on-road CPX emerges as mainly unknown and probably quite complex. Further investigations are required to have a higher accuracy of the results and to better understand CR actual impact on tyre/road noise and remaining properties.

Laboratory investigation of crumb rubber in dense graded asphalt by wet and dry processes

This article presents the perspective of the use of crumb rubber (CR) from the end-of-life tyres in dense-graded asphalt mixtures by the wet process high viscosity and a dry process in which the purpose of CR was to substitute aggregates. For the wet process CR modified binder was produced by adding 25% of rubber by the mass of the neat bitumen. Added CR content in the dry process was 41% by the mass of neat bitumen. The mixture made by dry process showed a weak internal cohesion and consequently poorer mechanical properties as reference mixtures. On the other hand, the mixture made by the wet process showed significantly better low-temperature and fatigue properties as reference mixtures.

Mechanical Properties and Durability of Rubberized and Glass Powder Modified Rubberized Concrete for Whitetopping Structures.

This paper analyzes concrete fine aggregate (sand) modification by scrap tire rubber particles-fine crumb rubber (FCR) and coarse crumb rubber (CCR) of fraction 0/1 mm. Such rubberized concrete to get better bonding properties were modified by car-boxylated styrene butadiene rubber (SBR) latex and to gain the strength were modified by glass waste. The following tests—slump test, fresh concrete density, fresh concrete air content, compressive strength, flexural strength, fracture energy, freezing-thawing, porosity parameter, and scanning electron microscope—were conducted for rubberized concretes. From experiments, we can see that fresh concrete properties decreased when crumb rubber content has increased. Mostly it is related to crumb rubber (CR) lower specific gravity nature and higher fineness compared with changed fine aggregate-sand. In this research, we obtained a slight loss of compressive strength when CR was used in concrete However, these rubberized concretes with a small amount of rubber provided sufficient compressive strength results (greater than 50 MPa). Due to the pozzolanic reaction, we see that compressive strength results after 56 days in glass powder modified samples increased by 11–13% than 28 days com-pressive strengths, while at the same period control samples increased its compressive strength about 2.5%. Experiments have shown that the flexural strength of rubberized concrete with small amounts of CR increased by 3.4–15.8% compared to control mix, due the fact that rubber is an elastic material and it will absorb high energy and perform positive bending toughness. The test results indicated that CR can intercept the tensile stress in concrete and make the deformation more plastic. Fracturing of such conglomerate concrete is not brittle, there is no abrupt post-peak load drop and gradually continues after the maximum load is exceeded. Such concrete requires much higher fracture energy. It was obtained that FCR particles (lower than A300) will entrap more micropores content than coarse rubbers because due to their high specific area. Freezing-thawing results have confirmed that Kf values can be conveniently used to predict freeze-thaw resistance and durability of concrete. The test has shown that modification of concrete with 10 kg fine rubber waste will lead to similar mechanical and durability properties of concrete as was obtained in control concrete with 2 kg of prefabricated air bubbles.

An experimental study on the fatigue properties of Alccofine-based crumb rubber concrete

The disposal of rubber tyres is one of the common causes of environmental pollution. This problem may be solved using crumb rubber (CR) as a construction material without side effects. Therefore, an attempt has been initiated in the present experimental study to prepare green concrete by replacing various sustainable materials in multiple percentages. This study continues with fatigue and mechanical properties, crack patterns, load–displacement behaviours under cyclic load and failure modes of normal concrete, CR concrete (CRC) and Alccofine-based CRC. Nineteen different mixes are taken into account with 5 and 7% replacements of CR (10, 12 and 20 mesh) with sand and different proportions of silica fume, fly ash and Alccofine. The compressive strength and splitting tensile strength are reduced with the increase in CR content and inversely increase with the rise in CR size. Therefore, Alccofine and silica fume have been used to resolve the problems of strength reduction. The results indicate that the failure manner of CRC beams is gradual, which means enhancement of structural ductility. Finally, this study proposes the application of Alccofine- and silica-fume-based CRC for magnifying structural ductility.

Assessment of various fatigue life indicators and fatigue properties of rock asphalt composite

Rock asphalt which is a natural asphalt, along with other modifiers, can be used to improve the performance of asphalt binder from crude oil. In this research, a systematic study was conducted to investigate the fatigue failure evolution behaviors of rock asphalt composite modified asphalt (RACMA). The fatigue performance of the modified asphalt subjected to rolling thin film oven (RTFO) and pressurized aging vessel (PAV) was explored to determine and assess various fatigue life indices. The applicability of various fatigue life indexes (Nf50, Nfm, Nδ, NR, and Np20) which are determined according to five different fatigue failure criteria were evaluated through statistical analysis and geometric position method. The results indicated that the Nf50 and Nfm in the stress-controlled mode and the Nf50 and NR in the strain-controlled mode of time sweep test exhibited comparable fatigue lives, respectively. The index Nf50 was recommended to estimate the fatigue performance in both stress and strain-controlled modes of time sweep test. Further, it was found that the optimal dosage of rock asphalt (RA) and styrene-butadiene-styrene (SBS) was 5% and 2% respectively in the composite modified asphalt (RA/SBS) in stress-controlled mode, while the content of RA and crumb rubber (CR) in the composite modified asphalt (RA/CR) was 5% and 18% respectively in strain-controlled mode to achieve maximum fatigue lives. The reduction of RA content and the increment of CR content can significantly improve the fatigue resistance of the RA/CR and extend its fatigue life by >5 times. The RACMA generally exhibits good fatigue resistance after RTFO aging.

Characterization of Modified Crumb rubber Interlocking Paver

Interlocking pavers, otherwise called paving blocks, brick pavers or concrete paver blocks are produced from bricks or concrete blocks and are used for paving the exteriors of buildings and surfacing of driveways, floors, paths, patios, pool decks and walkways. Interlocking paving units have been successfully used worldwide for the surface of roadways and have adequately carried traffic loads without failure or deterioration. This study investigated the impacts of 2, 4 and 6 % replacement of sand with crumb rubber on the engineering properties of the interlocking pavers in order to produce a sustainable and environmental friendly interlocking paver. For the control sample the mix ratio was 1:1.38: 2.73 for cement, sand and coarse aggregate, respectively. The mixes had a water cement ratio of 0.4. The experiments conducted on cement were chemical composition, standard consistency and setting time. The tests carried out on the aggregates included chemical composition, sieve analysis, humidity content and specific gravity. The test conducted on the interlocking paver blocks were slump, bulk density and compressive strength. The study revealed that the cement had a standard consistency of 25%, initial setting and final setting time of 28 and 246 minutes, respectively. The major oxide compositions of cement were Calcium Oxide (CaO) and Silicon Dioxide (SiO2) with 60.38 and 20.8% constituent, respectively. The fineness modulus of the sand, crumb rubber and granite samples was 2.54, 1.50 and 2.35, respectively. The density and compressive strength decreased at each of the ages of curing (3, 7, 28 and 56 days), as the crumb rubber content in the interlocking pavers increased. Though the mechanical properties of the modified crumb-rubber interlocking pavers reduced, the interlocking pavers can still be used for low trafficked roads and as kerbs on the highway.

Effect of age and waste crumb rubber aggregate proportions on flexural characteristics of self‐compacting rubberized concrete

AbstractGeneration of waste has been a significant problem in recent decades in many engineering fields. Self‐compacting rubberized concrete (SCRC) is a new type of SCC, which replaces part of natural aggregates by rubber aggregates in SCC to increase the application range of waste tyre rubber. This study investigates the effect of age and crumb rubber aggregate ratio on fresh and mechanical performance. Eight different SCRC mixtures using 2–5 mm rubber aggregates to replace 10%, 20%, 30%, and 40% natural aggregates by volume respectively, and 5–10 mm rubber aggregates to replace 10%, 20%, 30%, and 40% natural aggregates by volume respectively, are tested after 7, 28, 56, and 91 days for their mechanical properties. Results show that both the compressive and the tensile strength increase with the aging time, both of these properties drop with the amount and size of the crumb rubber content. Similar to compressive and tensile properties, flexural toughness and the modulus of rupture showed increased with the aging time. Small addition of crumb rubber has shown improvements in both rupture and fracture toughness properties, which diminishes when the crumb rubber content becomes significantly large.

Evaluation of Micro-Mechanism and High- and Low-Temperature Rheological Properties of Disintegrated High Volume Crumb Rubber Asphalt (DHVRA).

The aims of this paper are to prepare disintegrated high volume crumb rubber asphalt (DHVRA) with low viscosity, good workability and low-temperature performance by adding disintegrating agent (DA) in the preparation process, and to further analyze the disintegrating mechanism and evaluated high-temperature and low-temperature rheological properties. To obtain DHVRA with excellent comprehensive performance, the optimum DA dosage was determined. Based on long-term disintegrating tests and the Fluorescence Microscopy (FM) method, the correlations between key indexes and crumb rubber (CR) particle diameter was analyzed, and the evaluation indicator and disintegrating stage division standard were put forward. Furthermore, Fourier transform infrared spectroscopy (FT-IR) and Gel Permeation Chromatography (GPC) was used to reveal the reaction mechanism, and the contact angle test method was adopted to evaluate the surface free energy (SFE). In addition, the high-temperature and low-temperature rheological properties were measured, and the optimum CR content was proposed. Results indicated that the optimum DA dosage was 7.5‰, and the addition of DA promoted the melt decomposition of CR, reduced the viscosity and improved the storage stability. The 135 °C rotational viscosity (RV) of DHVRA from mixing for 3 h could be reduced to 1.475 Pa·s, and the softening point difference was even less than 2 °C. The linear correlation between 135 °C RV and the diameter of CR particle in rubber asphalt system was as high as 0.968, and the viscosity decay rate (VDR) was used as the standard to divide the disintegrating process into a fast disintegrating stage, stable disintegrating stage and slight disintegrating stage. Compared to common rubber asphalt (CRA), DHVRA has an absorption peak at 960 cm−1 caused by trans olefin = C-H, and higher molecular weight and polar component of surface energy. Compared with CRA, although the high-temperature performance of DHVRA decreases slightly, the low-temperature relaxation ability can be greatly improved.

Effects of Crumb Rubber at Different Sizes in Asphalt Mixtures on Mechanical Properties

High vehicles loads due to increasing the road users are one of the main issues affecting the asphalt pavement surface and its performance by resulting various problems such as fatigue cracking and other deformations due to road overloading caused by vehicles loads. The use of crumb rubber in asphalt pavements has attracted increasingly growing attention and become one of the factors that increase the strength of the pavement. Crumb rubber is used to improve asphalt binder properties and pavement performance since it contributes as an additive material in the structural applications and reducing the environmental problem. The main contribution and purpose of this research is to investigate the effectiveness of adding crumb rubber into the asphalt by using the wet method. There were two different amounts of crumb rubber content used in this study (2.5 % and 3.5 % of the overall asphalt mixture weight) and two different crumb rubber sizes (0.6 mm and 0.3 mm) that were examined in this study. In addition to this study, asphalt grade 60/70 penetration grade. The performance of the modified binder is comparatively evaluated with an unmodified binder to find the best modifier. The evaluation is done through conducting the comparison between results obtained from modified and unmodified asphalt samples using Marshall stability, flow and resilience modulus test. The results from this study shows crumb rubber is an efficient material to be used as an additive to asphalt binder since it contributes in better performance by increasing the strength and stiffness of pavement and can be used for future development.

Water permeability, strength and freeze-thaw resistance of crumb rubber-modified permeable concrete brick based on orthogonal test

Permeable concrete brick (PCB), as a new type of pavement material, is commonly used in sidewalks and parks owing to its environmental benefits. Crumb rubber, as an excellent pavement materials modifier, has many advantages in improving freeze-thaw durability of PCB. In this paper, a kind of rubber-modified permeable concrete brick (RMPCB) was prepared. The effects of water-binder ratio, designed porosity and crumb rubber content on compressive strength, split tensile strength, permeability coefficient and freeze-thaw durability of RMPCB were studied. Nine groups of tests were carried out by orthogonal design; range analysis and variance analysis were used to investigate the effect of three factors (water binder ratio, designed porosity and crumb rubber content) on the test results of RMPCB. The results show that porosity is the dominant factor in the properties of permeable bricks. Higher porosity can significantly increase the permeability coefficient of RMPCB, but weaken its strength and freeze-thaw durability. The split tensile strength and freeze-thaw durability of RMPCB are positively affected when crumb rubber content is 4% of the weight of cement. With the increase of water-binder ratio, the compressive strength of RMPCB first increases and then decreases, but the effect of water-binder ratio on other properties is not significant. The optimal water-binder ratio, design porosity and crumb rubber content for RMPCB are 0.30, 15% and 4%, respectively.

Pavement and Noise Reduction Performance of Open‐Graded Asphalt Friction Course Improved by Waste Tire Crumb Rubber

To further reveal the road performance and noise reduction performance of open‐graded friction course (OGFC), the crumb rubber prepared by adding waste tires were considered, and the performance requirements of the material were put forward. To avoid the influence of rubber particle swelling on aggregate, the special gradation and mix proportion of OGFC mixture were designed, and the particle size of 4.75 mm was proposed as the control size. The test results show that the aggregate forms a good embedded structure. The resilient modulus, deformation performance, and fatigue performance of R‐OGFC asphalt mixture with different crumb rubber contents were studied. According to the test results, the rubber particle content under the best road performance and noise reduction effect was proposed. The results show that, after adding a certain amount of crumb rubber, the performance of asphalt mixture has been greatly improved, especially the dynamic stability has been improved by 84%. Although the resilient modulus has decreased by 10%, the creep performance has decreased by 37%, and the fatigue life has decreased by 31% (2% rubber content), the noise reduction can reach 3.6–8.6 dB, and the noise reduction performance is significant. This shows that the best content of rubber particles is between 1.5% and 2%, and the R‐OGFC mixture modified by rubber has a good application prospect.

Physical, rheological and morphological characterization of modified asphalt binder with differing crumb rubber contents

Waste crumb rubber (CR) which is obtained from scrap tires can be successfully used as an asphalt binder modifier for the purpose of attaining the economic benefits with a desirable performance. The wet process was used in this study to investigate the rheological, morphological, and physical changes that would occurred to asphalt binder as a result of the interaction with different rubber contents, that is, 5%, 7%, 10%, 12% and 25%. The penetration, viscosity, softening point, ductility, Superpave performance grades, multiple stress creep recovery (MSCR) of the prepared modified binders were measured under different ageing conditions and temperature ranges. Furthermore, atomic force microscopy (AFM) scanning technique was also conducted in tapping mode to characterize the microstructure of these binders. The obtained results showed that as the rubber content increased, the viscosity and softening point values increased with a reduction in the penetration and ductility values. Rubber content of 10% was ranked as the higher percentage of rubber in terms of bumping the performance grade by at least two grades at high testing temperatures. The grading performance tests based on rutting index (G*/sin δ°) and non-recoverable creep compliance index (Jnr) showed a comparable result for ranking the stiffer binder with a greater resistance to rutting. However, most of crumb rubber modified binders failed to meet the stress sensitivity criteria of MSCR test. AFM images can be considered as a new effective and suitable tool that should be adopted for further microstructural analysis.

Investigation of aging behavior of terminal blend rubberized asphalt with SBS polymer

The influence of aging properties of terminal blend rubberized asphalt (TBRA) with styrene-butadiene-styrene (SBS) polymer was investigated. 3% content of SBS was added into TBRA, which was made of base asphalt and crumb rubbers with different contents (0, 5, 10, 15, 20%) to prepare TB hybrid asphalt. The functional groups of TB hybrid asphalt were monitored by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). All the samples of TB hybrid asphalt were tested with rolling thin film oven test (RTFOT) and pressure aging vessel (PAV), respectively. Physical and rheological properties were tested on all samples of TB hybrid asphalt, and chemical structures were analyzed by ATR-FTIR. FTIR test result shows that TB hybrid asphalt can inhibit the degradation of SBS polymer, and degradation of SBS in TB hybrid asphalt may occur mainly in the short-term aging, while the oxidation of bitumen mainly occurs in the long-term aging process. Compared with SBS modified asphalt, TB hybrid asphalt offer better anti-aging performance than SBS modified asphalt, and 3S_5TB (3 wt% SBS and 5 wt% crumb rubber) and 3S_20TB (3 wt% SBS and 20 wt% crumb rubber) exhibit the best short-term anti-aging properties and long-term anti-aging properties respectively. Furthermore, TB hybrid asphalt is softer than SBS modified asphalt, has better low temperature performance, and higher viscosity, but its high temperature performance is reduced. After RTFOT and PAV aging, the temperature sensitivity of TB asphalt is improved. With the increase of the content of crumb rubber, the influence of temperature sensitivity is better, and 3S_20TB (3 wt% SBS and 20 wt% crumb rubber) showed the best temperature sensitivity performance. Moreover, based on correlation analysis, the complex modulus aging index could be used as an index to evaluate the aging degree of TB hybrid asphalt.

Investigating the rheological properties of asphalt binder incorporating different crumb rubber contents based on a response surface methodology

The effects of different crumb rubber (CR) contents and their interactions with high temperature ranges on the rheological behavior of asphalt binder were investigated in this study using the response surface methodology (RSM). A temperature sweep test was performed using a dynamic shear rheometer (DSR) on modified binders with 5%, 7%, 10%, 12%, and 15% crumb rubber content at temperatures ranging from 46 °C to 82 °C. RSM statistical analysis was conducted based on central composite design (CCD) and assuming the rheological parameters complex modulus (G*) and phase angle (δ°) as response variables. Results from analysis of variance (ANOVA) test indicated that temperature and rubber content affect rheological parameters significantly (p < 0.05). A value of p < 0.0001 indicated a good agreement between the predictions of quadratic models and experimental results with a mean error <5% for all responses. The separate effects of temperature and rubber contents were analyzed, and the results revealed that all responses were influenced by the interaction of both independent variables but were more strongly influenced by rubber content than temperature. Consequently, it can be concluded that RSM is an effective approach for investigating rheological properties.

Laboratory Investigation of Rubberized Asphalt Using High-Content Rubber Powder.

Rubberized asphalt (RA) has been successfully applied in road engineering due to its excellent performance; however, the most widely used rubber content is about 20%.To improve the content of waste rubber and ensure its performance, seven rubberized asphalts with different powder content were prepared by high-speed shearing. Firstly, penetration, softening point, and ductility tests were carried out to investigate the conventional physical features of high-content rubberized asphalt (HCRA). Then, the dynamic shear rheometer test (DSR) was conducted to estimate the high-temperature rheological properties. The bending beam rheometer test (BBR) was carried out to evaluate the low-temperature rheological performance. Finally, combined with the macroscopic performance test, the modification mechanism was revealed by the Fourier transform infrared reflection (FTIR) test, and scanning electron microscope (SEM) analysis was used to observe the microscopic appearance before and after aging. The results show that rubberized asphalt has excellent properties in high- and low-temperature conditions, and fatigue resistance is also outstanding compared with neat asphalt. As the crumb rubber content increases, it is evident that the 40% RA performance is the best. The low-temperature properties of HCRA are better than the traditional 20% rubberized asphalt. This study provides a full test foundation for the efficient utilization of HCRA in road engineering.

Low-Temperature Rheological Properties and Microscopic Characterization of Asphalt Rubbers Containing Heterogeneous Crumb Rubbers.

Asphalt rubbers mixed with untreated and plasticized crumb rubbers and a compounding coupling agent were investigated in this study. The low-temperature rheological properties of asphalt rubbers at different aging levels were tested using a dynamic shear rheometer (DSR). An interconversion between linear viscoelastic material functions was used to obtain converted evaluation indexes for the asphalt rubbers at low temperatures. Lastly, the physicochemical characteristics and the microscopic morphology of the asphalt rubbers were evaluated using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. In conclusion, the storage moduli of the asphalt rubbers containing heterogeneous crumb rubbers increased with the plasticized crumb rubber content and the aging level. The converted relaxation moduli were consistent with the change trend of the storage moduli, and the relaxation rate decreased as the plasticized crumb rubber content and the aging level increased. The process of mixing the base asphalt with crumb and plasticized crumb rubbers was physical blending, and the effect of aging on the absorption peak change of asphalt rubber with plasticized crumb rubbers was less than that of asphalt rubber with ordinary crumb rubbers. Aging deteriorated the blending between the crumb rubber and the base asphalt, and a distinct interface appeared between the crumb rubber and the base asphalt. The particle cores of the plasticized crumb rubber in the asphalt rubber were difficult to maintain. Furthermore, as the plasticized crumb rubber content increased, more fine particles stripped off the plasticized crumb rubber after aging.

Engineering properties and sustainability assessment of recycled fibre reinforced rubberised cementitious composite

To provide an eco-friendly disposal way of increasingly accumulated waste tyres and reduce the environmental impact caused by the production of industrial fibres, this study explores the feasibility of using recycled tyre materials as substitutes for natural fine aggregates and manufactured fibres in cementitious mortar. The effects of crumb rubber (CR) replacement ratio (5%–15% by volume of fine aggregates), recycled tyre steel (RTS) fibre content (0.5–1.5 vol%) and recycled tyre polymer (RTP) fibre content (0.5–1.0 vol%) on the engineering properties of fibre reinforced cementitious composite (FRRC) were experimentally investigated. Results indicate that the pre-treated CR using NaOH solution is feasible to combine with a high dosage of recycled fibres without considerably weakening the workability, bulk density, ultrasonic pulse velocity and compressive strength of FRRC. The incorporation of CR, RTS fibre and RTP fibre together can reduce the drying shrinkage by up to 41.6% and enhance the flexural strength by at most 174% as compared to the plain mortar. The production cost, embodied carbon and embodied energy of FRRC are decreased by 13.3%–68.2% when replacing the manufactured fibres with recycled tyre fibres. The optimal content of CR and RTS fibre and RTP fibre is 5%–10%, 1.0 vol% and 0.5 vol%, respectively, considering the engineering properties, cost and environmental impact.

Flexural response of fiber reinforced concrete beams with waste tires rubber and recycled aggregate

The increasing amount of waste tires and construction wastes mounting up on the landfills create a huge concern to environmental stability. Researchers and policymakers are searching for ways to reduce and reuse these waste materials to promote a sustainable construction practice. Thus, incorporating crumb rubber (CR) derived from the waste tire and recycled coarse aggregate (RCA) in concrete production pertains to a sustainable future of the construction industry. This paper investigates the combined influence of RCA, CR, and polypropylene (PP) fiber on the physical and mechanical properties of Fiber Reinforced Rubberized Recycled Concrete (FR3C). Furthermore, the flexural response of reinforced concrete (RC) FR3C beams is investigated. A series of fourteen RC beam specimens measuring 150 mm × 200 mm x 1500 mm (w x d x L) are prepared and tested. Several combinations are designed where the variables are CR content (5% and 10%) and steel ratio (0.59% and 1.60%) with contents of RCA and fiber fixed at 30% and 0.5%, respectively. The results of the experimental study suggest an improvement in the concrete short-term and long-term mechanical properties following the introduction of CR and PP fiber. Concrete beams with 30% RCA, 5% CR and 0.5% PP fiber showed improved flexural capacity, ductility, and toughness. Additionally, analysis demonstrates that the existing codes and design guidelines are inadequate for quantifying the flexural capacity of FR3C beams with different reinforcement ratios. Overall, this research demonstrates a new pathway towards the cleaner production of sustainable concrete.

Analysis of the Influence of Production Method, Crumb Rubber Content and Stabilizer on the Performance of Asphalt Rubber

Asphalt rubber (AR) is often described as an environmentally friendly material due to the incorporation of recycled rubber from used tires and its improved service life. Its field application is influenced by many factors. In order to evaluate the impact of different factors such as crumb rubber (CR) content, stabilizer and the production method on the performance of rubber powder modified asphalt, two different matrix asphalts were prepared, the basic experiments, control variable methods and several related tests were thereafter conducted. The results showed that a moderate amount of CR could enhance the pavement performance. The suitable CR content was 20–25% for 90# matrix asphalt and 22–26% for 70# matrix asphalt. The stabilizer had a positive impact on the AR’s high temperature behavior and was beneficial to the storage of AR, but it did not make a significant influence on low temperature behavior. In addition, different methods brought certain performance differences. Though AR produced with the heat fusion method had better high-temperature performance, the rubber particles would easily disperse and melt in the asphalt during the shearing process, which gave AR more balanced physical performance. This study identifies the shearing method as the optimal choice for site construction and provides a wider application range for asphalt rubber in the road construction field. The selection of parameters depends on the construction areas and performance requirements.

Viability of producing sustainable asphalt mixtures with crumb rubber bitumen at reduced temperatures

The construction and maintenance of road pavements need to be undertaken to ensure proper economic and social growth. Considering the high environmental impact that the production of asphalt mixtures for road pavements entails, in terms of energy consumption and greenhouse gas (GHG) emissions, these operations must follow the global transition towards more sustainable development practices. In response to this, previous research has been focused on the development of manufacturing low temperature asphalt mixtures and the use of recycled modifiers such as tire crumb rubber to improve their durability. However, the use of high dosages of the latter reduces mixture workability, thus requiring high manufacturing temperatures to reduce the viscosity of the binder, and therefore limiting the advancement towards more sustainable mixtures. In this regard, further knowledge is needed on this topic to promote the combination of such techniques to maximise their advantages. This study aims to check the viability of producing asphalt mixtures with high crumb rubber contents at reduced temperatures, testing their workability, stiffness, cohesion, resistance to permanent deformations and resistance to moisture damage. Results show that it is possible to manufacture viable, warm, rubberised asphalt mixtures at 150 °C using a high penetration bitumen and reduce this temperature to 130 °C (45 °C less than conventional rubberised asphalt mixtures) by including warm additives, without compromising their mechanical performance.