Carolina Rodezno

Effect of rubber characteristics on asphalt binder properties

The use of scrap tyres in ground tyre rubber (GTR)-modified binders has continued to evolve since its introduction in the early 1960s. Currently, many states have developed recipe specifications requiring contractors to blend GTR with asphalt binders using specified rubber sizes, percentages, and grinding methods. While these specifications were developed based on early research, the GTR industry has developed new methods and techniques which might improve the quality of GTR in asphalt binders. The objective of this research was to assess how rubber properties affect the properties of an asphalt binder. This objective was completed by blending 12 unique GTR samples with a singular asphalt binder at a loading of 10% rubber. Two of the selected rubbers were additionally tested at 15% loading. These 14 GTR-modified asphalt binders were then tested using the performance grade (PG), multiple stress creep recovery, cigar tube separation test, and softening point methodologies. Statistical analyses were conducted to determine how particle size, grinding temperature, rubber chemistry, and surface area affected the four test results. GTR particle size was the most influential parameter on the majority of the test results. The smaller particle sizes improved the high- and low-temperature PG and particle separation as tested by cigar separation tubes and the softening point.

Performance-Based Mix Design for Porous Friction Courses

.......................................................................................................................................... ii List of Tables ................................................................................................................................. ix List of Figures .............................................................................................................................. xiv Chapter 1 – Introduction ................................................................................................................. 1 Background ................................................................................................................................. 1 Objective and Scope ................................................................................................................... 3 Chapter 2 – Literature Review ........................................................................................................ 4 Introduction ................................................................................................................................. 4 Benefits of Porous Mixtures ....................................................................................................... 4 Reduced Hydroplaning and Improved Friction ...................................................................... 5 Backsplash, Spray and Glare Reduction ................................................................................. 6 Pavement Noise Reduction ..................................................................................................... 7 Mix Designs ................................................................................................................................ 9 Suitable Materials ................................................................................................................... 9 Design Gradation Selection .................................................................................................. 12 Determining the Optimum Asphalt Binder Content ............................................................. 15

Improving cohesiveness of porous friction course asphalt mixtures

The use of porous friction course (PFC) provides numerous safety benefits and improves the noise quality of surrounding areas. Many agencies once used PFC for these reasons, but have since stopped using PFC due to performance issues. PFC pavements have reportedly been prone to ravelling and cracking, which leads to reduced service life. In addition, PFC is also typically more expensive than a dense-graded mix due to its use of high-quality aggregates, modified asphalt binder, and higher asphalt binder contents. Research is needed to extend the service life of PFC pavements in order to encourage agencies to start, or continue, use of PFC for its safety benefits. The objective of this research is to address the ravelling and cracking distresses commonly seen by adjusting the asphalt and dust content of PFC mixes to improve durability. This was accomplished by using an array of performance tests to evaluate the effect of additional fine aggregate passing the 0.075 mm (P−0.075) sieve on two PFC mixtures: one that had good field performance (up to 18 years) and one that had poor field performance (less than 8 years). It was found that the Cantabro test was a good indicator of mix performance and a maximum loss of 20% is recommended. The study revealed the importance of increased percent passing the 0.075 mm sieve to provide more durable PFC mix designs. An increased P−0.075 content had a positive effect on almost all of the results; thus, it is recommended that the current P−0.075 gradation band be expanded.

Improving accuracy of asphalt content determination by ignition test

Accurate determination of asphalt content and aggregate gradation is critical for controlling quality of asphalt mixtures during construction. Most state specifications require quantitative evaluation of the asphalt content of mixes as a criterion for acceptance. The ignition oven test procedure specified in AASHTO T 308 (Standard method of test for determining the asphalt binder content of Hot Mix Asphalt [HMA] by the ignition method) is required or allowed by most state DOTs for determining the asphalt content and aggregate gradation of asphalt mixtures. The ignition oven test specified in AASHTO T 308 procedure requires the determination of asphalt content correction factors for each asphalt mix and for each ignition oven used. However, in some instances when numerous asphalt mix designs and several ignition ovens are available, correction factors (CFs) are shared between ignition units, even when that practice is not allowed by the standard. There is a need to identify the consequences of sharing correction factors between units/mixes and also to identify testing parameters that affect the measured CFs. By identifying possible causes of variation, the test procedure could be adjusted to make the CFs more consistent between ignition ovens. Also, it should be possible to reduce the amount of difference in CFs between all types of equipment. A study was conducted to assess the variability of ignition oven CFs for different ignition oven unit brands and mixes to better understand the implications of sharing CFs. Twenty-three laboratories used various brands of ovens to test four mixes containing aggregates with varying CFs. The results indicated that CFs were significantly different for the different mixes even when the same unit brand was used. The within-lab and between-lab precision developed in this study suggests that different precision statements are necessary for aggregates with high breakdown potential and that the current precision included in AASHTO T 308 was likely developed for low weight loss aggregate making it unacceptable to use for aggregates with higher CFs. It was also found that the addition of lime caused no significant difference in the measured asphalt content when the CF was correctly measured. However, it was cautioned that a change in amount of lime during mixture production would affect the measured asphalt content. In addition, ways to minimise variability in asphalt CF were evaluated. It was determined that ignition tests conducted at lower temperature (427°C) proved to be effective in reducing the variability in measured asphalt content since the lower temperature reduced the asphalt correction factors for asphalt mixes.