Recycled tire rubber (RTR) from waste tires has been used in asphalt by the paving industry since the 1960’s. The rubber has been used as asphalt binder modifier and asphalt mixture additive in gap-graded and open-graded asphalt mixtures and surface treatments. The routine use of RTR in pavements has been limited to a few states. While performance is generally good, RTR cost has been high when compared to conventional practices. Local, State, and Federal regulations have also created an increase in the availability of RTR. This has driven a renewed interest in RTR as an asphalt binder modifier and mixture additive – with the goal of providing a long-life, cost competitive, environmentally-responsible pavement system. In 1991, Section §1038(d) of the ISTEA required states to use a minimum amount of crumb rubber from recycled tires in asphalt surfacing placed each year beginning with the 1994 paving season. Although the mandate was lifted in 1995, a significant number of RTR asphalt sections were placed and national research was fostered. Many States discontinued use of RTR after the mandate was lifted. However Agencies such as Florida, Texas, and Rhode Island continued their use of RTR. In 2005, the State of California Public Resource Code Section §42700-42703 legislated the use of RTR. The application of RTR modified asphalt binder has evolved with the development of terminal blended AR binders. This development was driven to reduce the need for asphalt mixture production plant modification (needed to incorporate RTR) and to address some performance concerns. A few RTR pavement failures had been linked to poor quality control with field blending practices. In the Unites States, the predominate use of RTR asphalt pavements has been in warm climates. This has led some to believe that RTR modified materials will not perform well in cold climates. There have been issues with compaction and raveling of mixes in cold climates, but this has typically been a construction issue with unfamiliarity when working with high viscosity binders and trying to pave in cooler climates. In recent years RTR has been in cold climates. One significant property for pavement performance is achieving sufficient compaction on the roadway. Slightly higher binder contents in the RTR modified mixtures may help to achieve sufficient compaction. WMA technologies combined with RTR modified AR mixtures may help reduce production temperatures and also improve workability and compaction. This also could potentially reduce the exposure of workers to fumes that would otherwise be produced in greater concentration with higher mixture temperatures.

This study is examining the potential benefits of routing in hot mix asphalt pavement prior to installing crack sealant. (1) Definition. Crack sealing and crack filling are two separate activities. While both crack sealing and crack filling involve placing sealants in pavement cracks, they differ in process. Generally, crack sealing is defined as using a router or saw to create a reservoir in a crack which is then filled with a sealant material. Crack filling is defined as minor crack preparation, such as using an air gun to blow debris out of cracks, prior to installation of the sealant. There is no pavement removed with crack filling. Additionally, crack sealing is performed on working cracks, whereas crack filling is generally the term used to refer to the treatment of nonworking cracks. (2) Implementation. Crack sealing should be carried out on structurally sound pavement which has low pavement distress. The pavement selection consideration should be based on pavement age, pavement and geometric design, pavement selection boundaries, traffic, type and extent of previous maintenance treatments and condition rating. The best candidates for crack sealing are newer pavements which are in the range of 1 to 3 years, and the majority of pavement distress can be found in terms of longitudinal or transverse having slight to moderate crack density. (3) Evaluation. The performance life of a treatment mostly depends on the preparation of crack and the type of the material used. One inspection should be made each year to chart the rate of failure and plan for subsequent maintenance. A mid winter evaluation is highly recommended as it will indicate treatment effectiveness when there is maximum pavement contraction and the crack is near the maximum opening. A small representative sample of the pavement, minimum of 150 m length should be selected for the evaluation. The first step in determining a treatment’s effectiveness is establishing how much of the treatment has failed in relation to the total length of treatment applied: Percent failure = (failed length after treatment / total length of treatment) × 100 After that the treatment’s effectiveness can be determined by subtracting the percentage of treatment failure from 100 percent: Effectiveness = 100 - Percent failure After a number of inspections a graph of effectiveness versus time can be developed. (4) Cost. Crack treatments can be considered as effective if it delays pavement deterioration and extends the pavement service life. Generally, the effective treatment extends the pavement life by two to five years. The effectiveness of rout and seal maintenance depends upon three points: (a) Performance of the sealant materials and appropriate rout width and depth; (b) restraining of crack development and delaying the existing pavement distress; and (c) crack treatment implication period. Chip seal treatment cost 3-14 times more than crack sealing and an overlay cost 8-26 times as much as crack sealing. The cost of crack sealing varies depending on state, materials, whether or not routing is required, and unit being priced.

Since warm mix asphalt (WMA) was introduced in early 2000, many of these pavements were built more than 10 years ago. Therefore, the WMA recycling research is important and necessary. However, the recycling issue of WMA has lagged behind other researches such as moisture sensitivity and long-term performance of WMA. If the aged WMA is incorporated into the asphalt mixes, the mixing and compaction temperatures of the mixtures are expected to decrease by the warm additives. The effect of warm additive after in-service period needs to be evaluated to see if the aged WMA can be used in asphalt pavements. The main objective of this study was to evaluate the properties of recycled asphalt binders containing long-term aged (LTA) WMA binders through Superpave asphalt binder tests. The WMA binders were manufactured with two wax additives, LEADCAP and Sasobit, and artificially aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. The aged WMA binders were recycled at 15% and 30%. The viscosity properties for the binders in the original state, the rutting properties in the original state and after RTFO aging, the fatigue cracking properties at intermediate temperature after RTFO+PAV aging methods, and the low temperature cracking properties after RTFO+PAV procedures were evaluated. The following conclusions were drawn for the materials used in this study: (1) Although the addition of LTA into virgin binder increased the binder’s viscosity, the binders containing wax additives had significantly lower viscosities compared with the unmodified binders at all recycling content (0, 15, and 30%). (2) Even though the binder with wax experienced the aging processes, the wax additive within recycled binder was effective to decrease the binder viscosity at almost the same degree, provided with the actual amount of wax in recycled binders. (3) The binders containing wax additive had higher G*/sin δvalues than control binders at each recycling content. It means that the wax additive still plays an important role in increasing rutting resistance, even though the additive was aged within asphalt binder. (4) From the DSR test at intermediate temperature, it appears that the higher recycling content seemed to have negative effects on resistance to fatigue cracking, regardless of the wax additive. (5) The recycled WMA binders at 30% recycling content were observed to have significantly lower resistance on low temperature cracking (measured by the BBR test). It is recommended that the WMA be recycled in a lower contents in cold regions.