Low Pavement Temperatures Research Articles

Rheological and Morphological Characterization of Modified Bitumen with Cup Lump Rubber

Pure bitumen is not suitable for heavy traffic loads; hence modifiers are used to improve the bitumen performance. Recently, cup lump rubber (CLR) has become a preferred modifier due to its outstanding performance and less cost. However, little is known about the interactions between CLR and bitumen. Thus, this study investigates the behavior of bitumen with CLR. Four percentages of CLR (2.5%, 5.0%, 7.5%, and 10.0% by weight of bitumen) were used to modify conventional 60/70 penetration grade bitumen. The modified bitumen was evaluated through different laboratory testing such as dynamic shear rheometer, rotational viscosity, softening point, bending beam rheometer, ductility, and elastic recovery. The testing results show that the addition of CLR increased the bitumen’s rutting resistance by 3 PG grades at high temperatures. At low pavement temperatures, the cup lump rubber modified bitumen (CMB) can withstand up to −34°C. Fourier Transform Infrared (FTIR) analysis shows that the Aromaticity index at 1600 cm-1 rose as the CLR percentage increased, indicating the formation of a binder with a compact structure. This is expected to improve the elasticity of bitumen through π – π interactions. Atomic Force Microscopy (AFM) results showed the Catana phase increased in size and quantity at 5.0% and 7.5% CLR content. While contact angle measurement revealed that the binders are hydrophobic and tend to repel the dropped water on the bitumen surface.

Use of performance-based testing for high RAP mix design and production monitoring

In 2014 the Wisconsin Department of Transportation and industry developed a pilot programme for hot mix asphalt with higher recycled asphalt content that required use of performance tests during mix design and production. Following the balanced mix design concept mixture tests were selected to address rutting resistance after short-term ageing and durability after long-term ageing. The tests selected were the Hamburg Wheel Tracking test, the Semi-Circular Bend (SCB) test at intermediate temperature, and the Disc-Shaped Compact Tension test at low pavement temperatures. Asphalt binder extraction and grading from aged mix was also required. The focus of this paper is to summarise the mixture performance test and recovered binder data gathered during the pilot project on State Highway 77 in Ashland County, WI, suggest modifications to the SCB test procedure, and to present accelerated ageing protocols for continued use of performance testing in practice. SCB test results collected during the project at 25°C did not relate well to values published in the literature or show adequate sensitivity to changes in mix properties. The effects of test temperature and an alternative analysis method are presented. Based on the results, recommendations include use of a climate-based approach for test temperature selection and inclusion of post-peak analysis to better discriminate between mix composition and ageing conditions. Accelerated long-term-ageing protocols involving loose mix ageing at 135°C for 12 and 24 h are compared to American Association of State Highway and Transportation Officials (AASHTO) R30 compacted mix ageing using recovered binder and mixture fracture properties. Results found that 12 h loose mix ageing produced similar recovered binder grading to AASHTO R30, whereas the effect of ageing on mixture fracture tests was inconclusive. The relationship between laboratory and field ageing is investigated through comparison of field cores to laboratory-aged plant-produced mix from a project constructed in SE Minnesota in 2006. Lastly, the laboratory performance of the high recycled and conventional mix designs are compared on the basis of mixture cracking resistance and recovered asphalt binder properties after extended ageing. The high recycle mix exhibited equal or better performance relative to the conventional mix across all selected performance tests. This comparative analysis also provides an example of how the inclusion of performance testing can influence the material selection process and produce test results indicative of improved overall performance of the mix.

Temperature Zoning of Libya Desert for Asphalt Mix Design

The current asphalt binder specifications in Libya are based on the Penetration Grade: penetration test is performed at 25°C. Penetration is an empirical measure of the consistency that is used as an empirical indicator of the rutting and fatigue susceptibility of asphalt binder, and is not related to pavement performance. The new mix design methodology developed under the Strategic Highway Research Program (SHRP), called the SUPERPAVE is a performance-based approach. The first step in the implementation of SUPERPAVE methodology is to establish high and low pavement temperatures for a location. The temperatures define the required Performance Grade (PG) of asphalt binder. This paper documents the initial ground work towards implementation of SUPERPAVE mix design for establishing high and low geographical temperature zones. The temperature zoning of Libya was carried out by using temperature data obtained from 8 weather stations. The SHRP and LTPP prediction models were utilized for predicting pavement temperatures. A significant difference was observed between the predicted pavement temperatures from both the models. The SHRP model gives higher, high temperature PG grade providing additional protection against rutting. Since rutting is the most common distress on flexible pavements in Libya , the SHRP models at 50% level of reliability is recommended. The PG of roads that located in Libyan desert are classified to three zones (PG70-10, PG76-10 and PG82-10.PG 76-10 binder seems to be the most common grade that encompasses more than 70% area of Libya desert .However, currently none of the two local refineries produce the bitumen under penetration grade 60-70,that grade equivalent to PG 82-10 binder, thus it should be a concern for highway or the project location. The polymer modified asphalt binder are not produced by Libya refineries.

Laboratory evaluation of antioxidants for asphalt binders

A laboratory study was carried to investigate whether certain antioxidants could be used to reduce age-hardening in asphalt binders. Several additives including: Vitamin E, Irganox 1010, Irgafos P-EPQ, carbon black, hydrated lime, and DLTDP/furfural, were evaluated. The modified asphalt binders were subjected to two accelerated oxidative aging regimes in the laboratory. Short-term oxidative aging of the binders was simulated using a rolling thin film oven while long-term aging was performed using a pressure aging vessel. The effects of aging on the binders were evaluated based on changes in rheological properties of asphalt binders undergoing oxidative aging. Binders modified with a combination of furfural and DLTDP was found to posses the lowest aging index. The antioxidant-treated binders exhibited improved performance at both high and low pavement temperatures.

Comparative Study of Rheological Behavior of Modified Binders for High-Temperature Areas

The failures of the bituminous pavements are not only due to increase in traffic but also due to extreme climatic conditions prevailing in the country. There are very high and very low pavement temperatures that exist during different seasons of the year. Thus, climatic conditions play an important role in selecting the type of materials to be used in road construction. In order to increase the life of bituminous pavement, quality of bitumen needs to be enhanced. To achieve the improvement of binder, it is necessary to add the polymers to bitumen. In this study, two types of polymer — ethylene vinyle acetate (EVA), a plastomer, and linear styrene-butadiene-styrene (SBS), an elastomer — and crumb rubber (CR) were used. The changes of rheological properties of 60/70 grades bitumen modified with different percentages of CR, EVA, and SBS (3–9%) were studied. The rheological properties of the bituminous binders in terms of their complex modulus (G∗), stiffness and overall resistance to deformation, storage modulus (G′), binder elasticity, loss modulus (G″), viscous behavior and phase angle (δ), and viscoelastic behavior were measured by using dynamic shear rheometer (SR5 asphalt rheometer). Testing was performed at higher temperatures ranging from 46 to 82°C in increments of 6°C at a frequency of 10 rad/s in the range from 0.1 to 100 rad/s before and after aging. It was observed that the rheological properties of bituminous binders had changed after modification. There is an improvement in rheological properties of the neat bitumen after mixing with modifiers.

Development of asphalt binder performance grades for Omani climate

Asphalt pavements form an integral part of any transportation system. Temperature is a significant factor that affects the performance and life span of a pavement. This paper presents the research undertaken to develop models to predict high and low asphalt pavement temperatures in Oman using data from an installed monitoring station at the Sultan Qaboos University (SQU) campus. The models were compared with SHRP and LTPP models. Ten weather stations covering various regions of Oman were selected. The air temperature data for the selected stations were analyzed. The data was used together with the developed models to propose asphalt binder performance grades (PG) for the various regions of Oman. The developed models resulted in four high temperature grades: PG 52, 58, 64, and 70. The predicted low pavement temperatures were well above the available PG grades according to AASHTO M 320, and therefore, the grades were restricted to PG-10 and PG-16.

Development of Asphalt Pavement Temperature Models for Oman

Asphalt pavements form an integral part of any transportation system. The structural capacity of the hot mix asphalt concrete layers depends on many factors including its temperature. Moreover, temperature can be a major contributor to several types of distresses. Therefore, temperature is a significant factor that affects the performance and life span of a pavement. The Sultanate of Oman's road network expanded at a phenomenal pace from approximately 10 km of paved roads in 1970 to 9,673 km in 2001. with the recent SHRP and LTTP research findings, it was necessary to investigate the applicability of the models developed from these research studies to Oman's environmental conditions and more generally to the Arabian Gulf climate. This paper presents the research undertaken to develop models to predict high and low asphalt pavement temperatures in Oman. A pavement monitoring station was set-up at the Sultan Qaboos University (SQU) campus to monitor air, pavement temperatures and solar radiation. Data were collected for 445 days. Daily minimum and maximum temperatures were recorded. A regression analysis was used to develop the low pavement temperature model. A stepwise regression was used to develop high temperature models using air temperature, solar radiation, and duration of solar radiation as independent variables. The developed models were compared with the SHRP and LTPP models. The SHRP and LTPP models were found to be more conservative than the developed models, which are more suitable for predicting pavement temperatures in Oman, and more generally in the Gulf region.

Analysis of Temperature Data for the National Center for Asphalt Technology Test Track

Several combinations of mix type, aggregate type, asphalt binder type, and layer thickness are in place at the National Center for Asphalt Technology (NCAT) test track. It was desirable to examine the effects these various combinations may have on temperatures within the pavement. The purpose of this study was to evaluate measured versus predicted temperatures, evaluate the effect of mix type on pavement temperature, and compare the effect of surface layer thickness on pavement temperatures. On the basis of temperature data from the NCAT test track, some of the general conclusions are that ( a) both the Strategic Highway Research Program (SHRP) and Long-Term Pavement Performance (LTPP) temperature models slightly underpredicted high pavement temperatures at 50% reliability and slightly overpredicted temperatures at 98% reliability and ( b) the low-temperature models for SHRP overpredicteded low pavement temperatures for both 50% and 98% reliability. The LTPP models were also overly conservative at 98% reliability. These results indicate that asphalt binders may not need to be as soft as specified in the Superpaver; performance grading system for low-temperature performance.

Minimum Pavement Temperature Modeling and Mapping for Alaskan Conditions

According to the Superpave design system, the selection of asphalt binder using performance-based binder specifications depends in part on the expected high and low pavement temperatures. For low-temperature cracking considerations, the binder should satisfy minimum pavement temperature requirements selected for design. In this case, knowledge of minimum pavement temperature during the design period is essential for proper binder selection. In this study, field temperature data for a number of sites were collected and analyzed. Correlations between minimum air and pavement temperature were established for different Alaskan climatic zones. Results indicate that the minimum pavement temperature could be lower or higher than minimum air temperature. However, for low temperature ranges the pavement temperature is generally warmer than air temperature by 2 to 7° C, depending on climate zone. Comparisons of minimum pavement temperature for Alaskan conditions with Superpave and the Asphalt Institute criteria for selecting minimum pavement design temperature were made. Results show that the criteria are not appropriate for Alaskan pavements. The Superpave prediction is conservative whereas the Asphalt Institute’s prediction model is unconservative. In addition, contour maps corresponding to 50 percent and 98 percent reliability were developed for minimum air and pavement temperatures. The temperature correlations and contour maps provide a simple tool for design engineers to estimate minimum design pavement temperature for selecting appropriate binder specifications.