Crumb Rubber Content Research Articles

Properties of Crumb Rubber Concrete Paving Blocks with SBR Latex

ABSTRACT The objective of this research is to investigate the potential of using crumb rubber as a partial substitute for coarse sand in the production of concrete paving block (CPB). Laboratory trials were conducted to investigate the effect of crumb rubber particle size. A comparison was also made between CPB mixtures containing various percentages of crumb rubber to determine the optimum crumb rubber content and water-cement (w/c) ratio. Styrene-butadiene rubber (SBR) latex was added to the mixtures of crumb rubber CPB and mechanical properties were evaluated. A total of 276 CPB were fabricated and tested in laboratory to determine the density, skid resistance and the compressive strength. The design strength level ranging from 31 to 43 MPa was achieved using w/c ratios of 0.45 to 0.55. The test results indicated that there was a systematic reduction in the strength with the increase in rubber content. Scanning electron micrograph showed that inclusion of SBR latex into the matrix did not improve the mechanical properties of the CPB. Results also revealed that a w/c ratio of as high as 0.55 without any SBR latex at 15% rubber content by total sand volume might be practically used to produce crumb rubber CPB which achieve the target compressive strength of 30 MPa.

Development of an empirical model for determining G*/sin δ in crumb rubber modified binders

This paper describes the development of an empirical model which may be used for predicting the G*/sin δ for neat and crumb rubber modified (CRM) binders. The model was developed using 36 unique CRM binder combinations, crumb rubber concentrations were varied at 5% intervals between 5% and 20%. The effects of crumb rubber particle size on model accuracy were also studied, ultimately a model was produced with the capability of predicting G*/sin δ values over a range of temperatures and crumb rubber concentrations. By definition, the upper limit of the performance grade is dependent on the G*/sin δ value; therefore, the relationship was also considered in terms of high end failure temperature. The rubber coefficient for G*/sin δ ( R cg) was identified as an important parameter in the estimation of G*/sin δ in addition to the CRM. This term is a quantitative representation of the increase typically witnessed in G*/sin δ values with the addition of CRM. Ambient ground CRM exhibited higher R cg values than cryogenically ground particles. Additionally, 95% confidence intervals were generated for the predictive model, thus providing a range of accuracy for the model. The resulting confidence intervals were approximately ±1300 Pa, these confidence intervals were seen to capture 92.6% of the 462 data points used. Findings from this research suggest that the differences between cryogenic and ambient CRM binder are accurately described using the R cg, furthermore binder properties may be predicted using an empirical equation.

Development of an Empirical Model for Predicting Crumb Rubber Modified Binder Viscous Properties

ABSTRACT This study presents an empirical model for estimating asphalt viscosity as a function of crumb rubber concentration, temperature, rubber viscosity coefficient, and virgin binder properties. Asphalt binders, modified and virgin alike are highly temperature sensitive materials, and to date not many research projects have been conducted establishing a relationship between rubber content and binder property changes due to temperature change. For this study relationships were established from a number of studies, where data was obtained from 28 binder types using 5 binder grades and 11 sources. The rubber coefficient was found to be of particular importance and was seen to be dependent on the nature of the rubber as well as the grinding procedure used to render it to crumb rubber. Rubber viscosity coefficient values are presented for each asphalt crumb-rubber combination. While all Crumb Rubber Modified (CRM) binder blends are unique, this study shows that they all exhibit similar trends when crumb rubber concentration, virgin properties, and temperature are varied.

Influence of Crumb Rubber and Digestion Time on the Asphalt Rubber Binders

ABSTRACT The behavior of asphalt binders modified with recycled crumb rubber depends on several factors, such as: rubber content and type, temperature and time employed during the digestion process. Some of these aspects are investigated in this paper by means of a series of tests performed on asphalt-rubber produced via the wet process. Crumb rubber manufactured by ambient grinding and cryogenic processes were used in this work. Reduction of penetration and sharp increase of viscosity, softening point and resilience were observed for increasing rubber contents. The results show that the Brookfield viscosity limits the crumb rubber content incorporated into straight binder, once it tends to become too high above a certain critical amount of incorporated rubber. The effect of digestion time on the viscosity of the modified binders depended in this research on the rubber content. For high rubber contents, there seems to exist a critical time after which viscosity tends to decrease for continuing digestion process. A rubber-binder interaction model, which could explain such results, is proposed. The influence of rubber type occurred especially in terms of Brookfield viscosity and softening point. It was observed a decrease in these properties for the asphalt-rubber binders produced with crumb rubber obtained by cryogenic process in relation to those produced by the grinding process.

Fracture Resistance of Rubber-modified Asphaltic Mixtures Exposed to High-Temperature Cyclic Aging

The fracture resistance of rubber-modified asphaltic mixture exposed to different durations of high-temperature thermal cycling is investigated using the J-Integral approach. Crumb rubber content of 15%, as a percentage of the binder was adapted. Semicircular core specimens (76 mm radius and 57 mm thickness) were used for fracture resistance tests. A cyclic thermal aging program was performed in an environmental chamber between 20 and 50 C for four different periods (0, 8, 28, and 56 days). The effect of thermal cycling on the fracture resistance of the rubber-modified mixture, as determined by the critical energy release rate ( J1c), was studied and compared with samples of unmodified asphalt concrete mixture (0% rubber content). A relationship between the number of thermal cycles and the critical energy release rate was established. The current investigation revealed that the fracture resistance of the studied mixtures decreased as the number of thermal cycles increased. However, rubber modifier managed to improve the fracture resistance of the modified mixture over the entire range of the thermal cyclic program as compared to the unmodified mixture. The fracture resistance analysis of the studied mixture predicted from the J-integral concept is consistent with the prediction made based on the conventional indirect tensile strength test. Thus, fracture resistance can be correlated to indirect tensile strength. No significant improvement was found in the unconfined compressive strength of the modified mixture, when compared to the unmodified mixture when a rubber modifier was used at a higher number of thermal cycles.

Influence of Crumb Rubber Concentration on the Rheological Behavior of a Crumb Rubber Modified Bitumen

Bitumen is widely used in construction. Its applications go from binder for road asphalts to built-up roofing membranes and other waterproofing uses. The use of crumb tire rubber as a binder modifier may contribute to solving a waste disposal problem and to improving the quality of road pavements. This paper deals with the effect that rubber concentration exerts on the thermorheological properties of rubber-modified bitumens. The results obtained confirm that the rheology and storage stability of these modified binders are largely dependent on rubber concentration. The linear viscoelastic measurements carried out revealed an improvement of both low and high in-service properties of the binder. The viscous flow measurements showed an important increase in viscosity and a noticeable reduction in temperature susceptibility. A swelling process of the crumb rubber by light components of the maltenic fraction was confirmed by modulated differential scanning calorimetry (MDSC). The stability tests, performed on samples stored at 180°C, demonstrated that the storage stability of rubber-modified bitumen was improved as rubber concentration increased.

Crumb Rubber–Bitumen Interactions: Cold-Stage Optical Microscopy

The problem of waste rubber tires is a global issue. One method of reusing tires is to process them into crumb-sized particles for use in flexible pavement applications by incorporating crumb rubber (known as crumb rubber modifier, CRM) into asphalt mixes. An understanding of the interaction between rubber and bitumen is therefore of vital importance. A review of the existing techniques and equipment used for the investigation of the microstructure of polymer-modified bitumens has revealed the high cost of the equipment and complexity of the techniques, and that it is not possible to employ such methods in the case of crumb-rubber-modified bitumens because of the sample size limitation. In the present work a new technique to obtain images of microstructures has been developed for use as an alternative standard procedure. Cold-stage optical microscopy uniquely provides a new method of observing the physical characteristics of crumb rubber particles in bituminous binders and can be useful when the particle shapes and binder properties are correlated. A 100-pen binder from Kuwait was modified with crumb rubber from truck tires of 600 μm nominal maximum size (30 mesh) at concentrations of 3% and 10% by weight of the binder. Data obtained from storage stability tests and extensive particle swelling (growth in size) studies were used to assess and illustrate the applicability and ability of the technique to obtain reproducible and clear images for any combination of crumb rubber type, size, content, bitumen type, mixing time, and temperature.

Fatigue Life Of Asphalt Concrete With Rubber Grains

This paper presents some results achieved in a wide research carried out in the road material laboratory of the Rome University La Sapienza to assess the suitability of a new hot mix asphalt (HMA), containing crumb rubber (particle size 2-5 mm), as sub-ballast in railways or base layer in road pavements. This material could be effective in the reduction of vehicular traffic vibrations; however, crumb rubber is responsible for reducing mechanical characteristics of the asphalt concrete. The aim of this step of the program here discussed is to evaluate the influence of kind and content of crumb rubber on bituminous mixes, regarding fatigue life. The experimental analysis was directed to detect .the initial modulus value, above which this bituminous material will remain structurally serviceable for a considerable period. The tests were conducted on cylindrical specimens, using a servo-hydraulic loading system and operating in a loaded-controlled fashion (tension-compression), at a frequency of 10 Hz and a temperature of 20 C. The adopted failure criterion, considering an assigned constant stress amplitude, was the number of load repetition that causes a decrease in modulus to half the initial value or, depending on the progress of the test, the fracture of the specimen due to macro-cracking. The tests were performed with various stress levels, related to the stiffness of the mix. This study documents the relationship between stiffness, as characterized by dynamic (complex) modulus, and fatigue life. Four mixes, different in kind and content of rubber, were checked and compared with a traditional WMA. The interpretation of experimental results demonstrates that mixes, containing a certain kind and a weight content up to 3% of crumb rubber, show a fatigue life comparable with traditional HMA. Transactions on Engineering Sciences vol 40, © 2003 WIT Press, www.witpress.com, ISSN 1743-3533

Low Temperature Properties of Crumb Rubber Modified Binders

ABSTRACT This paper presents a study to evaluate low temperature rheological properties of crumb rubber modified binders and the impact of the rubber particle size and content on such properties. Three sizes of the crumb rubber (0.18 mm, 0.425 mm and 2.0 mm), a control (0 percent) and two levels of crumb rubber content (12 percent and 24 percent) were used with four asphalt binders. The measured rheological properties consisted of creep stiffness (St) and logarithmic creep rate (m). Results showed that: increasing the crumb rubber content decreased the creep stiffness which improves thermal cracking resistance. The impact of crumb rubber content on the m-value was very highly inconsistent. The crumb rubber size did not have a significant effect on the low temperature properties. Any effect of the size of the crumb rubber on the resistance to thermal cracking was dependent on the asphalt binder type. The analysis of the data generated in this experiment showed that some combinations of crumb rubber size and content can either improve or jeopardize the PG low temperature grade of the asphalt binder.

Low Temperature Properties of Crumb Rubber Modified Binders

ABSTRACT This paper presents a study to evaluate low temperature rheological properties of crumb rubber modified binders and the impact of the rubber particle size and content on such properties. Three sizes of the crumb rubber (0.18 mm, 0.425 mm and 2.0 mm), a control (0 percent) and two levels of crumb rubber content (12 percent and 24 percent) were used with four asphalt binders. The measured rheological properties consisted of creep stiffness (St) and logarithmic creep rate (m). Results showed that: increasing the crumb rubber content decreased the creep stiffness which improves thermal cracking resistance. The impact of crumb rubber content on the m-value was very highly inconsistent. The crumb rubber size did not have a significant effect on the low temperature properties. Any effect of the size of the crumb rubber on the resistance to thermal cracking was dependent on the asphalt binder type. The analysis of the data generated in this experiment showed that some combinations of crumb rubber size and content can either improve or jeopardize the PG low temperature grade of the asphalt binder.

Potential of scrap tire rubber as lightweight aggregate in flowable fill

Flowable fill is a self-leveling and self-compacting material that is rapidly gaining acceptance and application in construction, particularly in transportation and utility earthworks. When mixed with concrete sand, standard flowable fill produces a mass density ranging from 1.8 to 2.3 g/cm 3 (115–145 pcf). Scrap tires can be granulated to produce crumb rubber, which has a granular texture and ranges in size from very fine powder to coarse sand-sized particles. Due to its low specific gravity, crumb rubber can be considered a lightweight aggregate. This paper describes an experimental study on replacing sand with crumb rubber in flowable fill to produce a lightweight material. To assess the technical feasibility of using crumb rubber, the fluid- and hardened-state properties of nine flowable fill mixtures were measured. Mixture proportions were varied to investigate the effects of water-to-cement ratio and crumb rubber content on fill properties. Experimental results indicate that crumb rubber can be successfully used to produce a lightweight flowable fill (1.2–1.6 g/cm 3 [73–98 pcf]) with excavatable 28-day compressive strengths ranging from 269 to 1194 kPa (39–173 psi). Using a lightweight fill reduces the applied stress on underlying soils, thereby reducing the potential for bearing capacity failure and minimizing soil settlement. Based on these results, a crumb rubber-based flowable fill can be used in a substantial number of construction applications, such as bridge abutment fills, trench fills, and foundation support fills.

Characteristics of crumb rubber modified (CRM) asphalt concrete

The mix design for CRM asphalt concrete with the Marshall method and laboratory tests to evaluate low temperature behaviors and temperature susceptibilities of CRM asphalt concrete are presented. The mix design was performed using one asphalt cement (120/150 penetration grade), five aggregate gradations for three rubber contents (0, 3, and 5% by weight of aggregate) and both pretreated and untreated crumb rubber (passenger tire). All mixtures satisfied the Marshall mix design criteria. For laboratory tests, two asphalt cements (85/100 and 120/150 penetration grade), three aggregate gradations for three rubber contents (0, 3, and 5% by weight of aggregate) and two types of pretreated crumb rubber (passenger and industrial tires) were used. The addition of crumb rubber did not significantly affect the overall temperature susceptibility of the mixtures. It did, however, substantially decrease the mixture modulus at any given temperature. The decrease in modulus was accentuated as the content of crumb rubber increased. The potential for thermal cracking decreased with the amount of crumb rubber. This demonstrated that a CRM asphalt mixture could relieve stress build up by its ability to strain.