Junan Shen

The influence of crumb rubber modifier (CRM) microstructures on the high temperature properties of CRM binders

Many physical and chemical factors affect the rheological properties of crumb rubber modifier (CRM) binders. This study is aimed at understanding the influence of CRM microstructure on one of the rheological properties, the high temperature properties of the CRM binders. To this end, the high temperature properties of the binders that were modified by two types of CRM with different microstructures, three different sizes, two percentages as well as three different mixing times, were evaluated by dynamic shear rheometer (DSR) test on samples before and after RTFO aging. A series of scanning electron microscope (SEM) were taken on the two types of CRM of three different mesh sizes. Results from this study showed that: (1) ambient CRM has porous surfaces and cryogenic CRM has angular with smooth cracked surfaces; (2) an addition of 10–15% of CRM in the binder can increase one and two PG grades at high temperature for either ambient or cryogenic CRM regardless of the microstructure of CRM; (3) when a high percentage and coarser CRM is mixed, the microstructures of CRM have significant influence on the high failure temperature and (4) change in mixing time from 15 to 45 min did not alter much in the failure temperature, suggesting that a mixing time of 15 min interact completely for 15% CRM with the binder.

The effects of rejuvenating agents on recycled aged CRM binders

The recycling of asphalt pavements containing crumb rubber modifier (CRM) modified binders is increasing in areas having these types of asphalt pavements more than 10 or 15 years old. The performance and physical and rheological properties of the blends of aged CRM binders containing rejuvenating agents due to the presence of CRM have not been considered in detail. In this study, two CRM binders and one control binder of PG76-22 were artificially aged and then used as recycled materials by adding different rejuvenating agents, i.e. a rejuvenator and a softer binder. The properties of the blends of the three aged binders containing various percentages of the rejuvenating agents were evaluated using Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) as well as viscosity tests. The test involved three different aging states of the blends: original, RTFO residual and RTFO+PAV residual. Results from this study show that: (1) the aged CRM binders can be rejuvenated back to a targeted PG grade; (2) the rejuvenating agents investigated are effective in changing the properties when used with the aged CRM binders; (3) the presence of crumb rubber in the modified binders enhances their aging resistance; (4) the target grade is more easily reached by adding the rejuvenating agents to the aged CRM binders rather than the aged control PG76-22.

Effects of Various Long-Term Aging Procedures on the Rheological Properties of Laboratory Prepared Rubberized Asphalt Binders

Rubberized asphalt has been used to improve the mechanical characteristics (e.g., rutting resistance, fatigue life, friction, and skid resistance) of hot mix asphalt mixtures. The objective of this research was to investigate the rheological characteristics of the rubberized asphalt binders after various long-term aging procedures, using the penetration index, the dynamic shear rheometer, the bending beam rheometer, and high pressure-gel permeation chromatographic testing. The experimental design included the use of three binder sources, three binder grades (PG 64-22, PG 64-22+10 %-40 ambient rubber, and PG 76-22) and three aging states, i.e., virgin, rolling thin film oven, and pressurized aged vessel [four test temperatures (65, 80, 100, and 110°C) and five aging durations (15, 20, 40, 80, and 144 h) under the pressure of 2070 kPa]. The test results show that, as expected, the use of crumb rubber can effectively improve the PG grade and aging resistance of the virgin asphalt binder. A series of rheological properties (e.g., penetration, stiffness, m-value, and percentages of large and small molecular sizes) illustrate that the PG 64-22 binder, mixed with 10 %-40 ambient rubber, yields similar or improved rheological properties in comparison with PG 76-22 using 3 % styrene-butadiene-styrene polymer after various long-term aging procedures.

Surface area of crumb rubber modifier and its influence on high-temperature viscosity of CRM binders

In general, crumb rubber modifier-modified binders (CRM binders) have better performance properties than base binders and thus, are becoming more widely used in pavements in a few states. However, the mechanism by which the interaction between the asphalt base binder and the CRM blends added takes place has not been fully characterised. In this study, the surface areas of CRM were at first measured using the Brunauer, Emmett and Teller (BET) tester. Second, 108 CRM binders were produced using different combinations of CRM blend variables and mixing conditions and consequently tested for their viscosity at 135°C. The influence of the surface area and the average size of the CRM blends on the viscosity of the CRM binders was statistically investigated. Results from this study indicated that: (1) the surface area of the ambient CRM is almost twice as large as that of the cryogenic CRM, leading to an increase in the viscosity up to 16–58% over cryogenic CRM binders and (2) the viscosity of the CRM binders has a moderate correlation with both the surface area and the average size of the CRM blends, but is prevailingly influenced by the average size of the CRM blends.

Laboratory Investigation of the Effect of Warm Mix Asphalt (WMA) Additives on the Properties of WMA used in China

To investigate and compare the influence of various commonly used warm mix asphalt (WMA) additives on the physical, mechanical, and performance properties of WMA, a series of laboratory testing programs such as air void, voids in mineral aggregate, freeze-thaw splitting, wheel tracking test, and bending beam tests were performed. The experimental design of WMA mixtures included the use of three WMA additives of Sasobit, Evotherm and Rediset, two asphalt binders of SK-70 base asphalt, and a styrene-butadiene-styrene (SBS)-modified one. The testing results of WMA were also compared to that hot mix asphalt (HMA) as controls. Results from this study showed that: (1) volumetric properties (air voids and VMA) of WMAs did not have significant difference from the controls; (2) WMA with Sasobit had the greatest Marshall stability, followed by the WMA with Rediset, whereas all WMAs with Evotherm had the least, regardless of the types of asphalt; and (3) for WMA with modified asphalt, the dynamic stability of WMA with Rediset was a slightly greater than other two WMAs. For WMAs with base asphalt, the dynamic stability with Evotherm and Sasobit was similar to the control and greater than that with Rediset: (4) The WMAs with Sasobit have slightly greater indirect tensile strength (ITS) and tensile strength ratio (TSR) than the other two, regardless of the types of asphalt. (5) WMAs with Rediset had the greatest bending failure strain, regardless of the types of asphalt. Among all asphalt mixtures, most of WMAs had lower bending failure strain than the controls.

Empirical Rutting Models of Recycled Mixtures Containing CRM

Recycling of Reclaimed Asphalt Pavement (RAP) is now a normal practice because it saves aggregate resources and reduces environmental pollutants. The performance properties of asphalt mixture containing RAP could be improved by adding additives such as crumb rubber modifier (CRM). This study was conducted to investigate the contribution of CRM to the reduction of the rut depth in asphalt mixtures containing RAP through the establishment of rutting models. Lab tests including ten Superpave mix designs and rutting tests using Asphalt Pavement Analyzer (APA) were performed. Two types CRM, four percentages of rubber, and three percentages of RAP were used in this study. Results from the study include: 1) a logarithmic function fitted well with the curves showed the relationships between the rut depth and the repetitive loading times; 2) several good rutting models, which indicated that the CRM and the RAP were effective to reduce the rut depth, were determined between the rut depth with the percentages and types of CRM, and with percentages of RAP.