Effect of Crumb Rubber Modifier Dissolution on Storage Stability of Crumb Rubber–Modified Asphalt

Abstract

Crumb rubber–modified asphalt (CRMA) extensively suffers from high-temperature storage instability. Because of the higher density of the crumb rubber modifier (CRM) particles, they settle down to the bottom of storage tanks and cause variation between physical properties of the top and bottom samples. The storage stability of the CRMA changes under different interaction parameters and consequently different mechanisms of interaction. In this research the mechanism of separation under different levels of CRM dissolution was investigated by using Stokes’ law. The extent and mechanism of CRM dissolution in asphalt was controlled through regulating interaction temperature and inter action mixing speed. A standard storage stability test was conducted on CRMA samples to measure the corresponding storage stability index. Viscosity of the liquid phase of CRMA was measured at the same temperature as that of the storage stability test (163°C), with the use of a rotational viscometer, to study the effect of viscosity development of the liquid phase on the storage stability of CRMA. Composition analysis was conducted by using thermogravimetric analysis to investigate the effect of changes in CRM composition on the storage stability of CRMA. Results reveal that, in addition to the CRM particle size reduction resulting from CRM dissolution, the viscosity development of the liquid phase affects the storage stability of CRMA with the interaction temperature of 190°C. But increasing the interaction temperature to 220°C changes the mechanism of dissolution and the nature of the residual CRM particles and consequently leads to a different mechanism of separation.

Influence of Guayule Resin as a Bio-Based Additive on Asphalt–Rubber Binder at Elevated Temperatures

“…Different sizes of CRM were obtained. However, it was sieved, and the selected gradation was the so-called CRM 30-40 (passing sieve #30 and remaining on sieve #40) according to the US standard system [11,21,22]. Guayule resin was provided by Bridgestone Americas, Mesa, AZ, USA (abbreviated to "BGR") and produced from a mix of three different batches (2016-7-1-RES-12, - 13, and -14).…”

“…A Q50 thermo-gravimetric analyzer, from TA Instruments, was utilized for the compositional analysis of the guayule resin in order to analyze moisture and multi-components included, in addition to the as-received and extracted CRM in order to show the released constituents of the CRM into the binder liquid phase, as utilized by previous researchers in this regard [19,20,22,23,41]. Two methods were employed according to material nature [22]. The first and most common one is the ramp method, which is used to analyze materials containing a distant thermal decomposition of its components.…”

“…That is why it was used for the TGA of the as-received CRM and the extracted CRM from the selected asphalt-rubber-guayule binders. The other method is called the stepwise isothermal thermo-gravimetric (SITG) method, which is a better TGA approach in the case of the closeness of the decomposition temperatures of a multi-component material [15,22,42]. In this method, the sample is subjected to a programmed heating method to ensure that the distinction of material's decomposition will take place with no overlap.…”

“…Each component has its range of decomposition temperatures. The first region corresponds to the oily components and is from 25 to 300 • C, the second region corresponds to natural rubber and is from 300 • C to the temperature corresponding to the minimum point between the two peaks in the derivative thermo-gravimetric (DTG) curve, and the last region is the filler components at 500 • C [15,22].…”

The Influence of Crumb Rubber on Modified Bitumen Properties

“…Modification of bitumen is a very common these days' practice in order to improve its physical properties and performance. Modification of bitumen decreases its temperature susceptibility and this enables asphalt to withstand more load and more severe environments (Ghavibazoo et al 2013). However, modification of bitumen is relatively expensive procedure.…”