Surface treatments are used by many highway agencies to improve the surface quality and extend service life of their pavements. While there are different types of surface treatments, the use of chip seals has created significant attention since it is considered a cost-effective treatment capable of dealing with multiple distresses. In a chip seal, an asphalt emulsion is sprayed on the surface and aggregate is placed on top, thus correcting most surface distresses. Unfortunately, the specifications used to select the emulsion are primarily based on the consistency of the residue that does not fully characterize the behavior of the material under different loading conditions or environments. This lack of adequate characterization leads to mixed results in terms of the performance and longevity of chip seals. To address the lack of proper material characterization, a number of studies have been performed. For example, in 1995 the Texas Department of Transportation (TxDOT) sponsored a research study titled: Performance-Based Seal Coat Asphalt Specifications (Report 1367-1). In 2001, TxDOT funded additional research to develop new specifications, based on PG testing equipment, to address chip seal distress. This research produced a draft specification show on table 1. In 2005, NCHRP published Synthesis 342: Chip Seal Best Practices. It provided a comprehensive review of chip seal practices and experiences. More recently, NCHRP sponsored project 14-17: Manual for the Design and Construction of Emulsion-Based Chip Seals for Pavement Preservation. This work, being conducted at Colorado State University, is in the final phases and the report should be out late 2010. Finally, NCHRP Project 09-50: Performance-Based Specification for Binders Used in Chip Seals is currently being advertised. Among its objectives are to develop an enhanced performance-based purchase specification for asphalt binders for chip seals, develop chip seal binder grade selection criteria, and validate the proposed specification with field testing. These projects, as well as the work done by others including the Federal Highway Administration¿s Pavement Preservation Expert Task Group (PPETG) have advanced the knowledge of emulsions and surface treatments in general. Particular attention has been placed on the recovery of residue using low temperature evaporative techniques (ASTM D7497-09). However, both research work and anecdotal evidence have created some doubts regarding the properties of the residue subjected from this recovery procedure (1). Specifically, it has been reported that `the properties of the emulsion residue do not reflect those of the un-aged based binders¿ (2). There are also issues regarding the preservation of the modification structure during the recovery (3). There has also been questions regarding the condition and type of the silicone pads used during the procedure, the ambient pressure and humidity during the procedure, and the time required to fully recover the residue. All of these issues have raised significant questions regarding the recovery method. A validation or ruggedness study is needed to address these concerns.

The objective of this study is to evaluate the performance of asphalt emulsions in chip seal applications. Phase I of this pooled fund study will concentrate on the validation of the recovery procedures that are needed to evaluate the performance of the emulsion residue. Many studies are been conducted to develop performance-based specifications; all of which rely on testing the residue. By validating the recovery procedures, more consistent results and better relations to the field can be expected.

The scope of this pooled fund study is to specifically concentrate on validation of the residue recovery procedures (both procedures a and b, as described in ASTM D7497). It is evident that no rational performance testing of residue can be accomplished without detailed knowledge of the ruggedness of existing residue recovery procedures. The study will be divided into regions (e.g., Rocky Mountain) based on the existing pavement preservation groups across the country. For each region, the following steps are proposed: ¿ Materials will be collected from participant state agencies and shipped to a local laboratory participating in the pooled fund study. The materials will include the base binder as well as the related emulsion. o Each laboratory will recover the residue following the procedures in ASTM D7497 along with an evaporative recovery. Variables to be studied include recovery time, silicone pad age or condition, o The laboratories will use accepted test parameters (DSR G* and , MSCR, BBR) to compare the recovered residue with the based binder under both RTFO and PAV conditioning ¿ The results from the initial testing and the performance evaluate will be collected at a central location where the variables will be summarized and analyzed by a research team. The team will interact with the PPETG to ensure proper guidance as well as the latest developments. ¿ A final report will be created with the recommendations regarding the applicability of existing protocols and specifications to more generalized conditions.

The Pooled-Fund Study Team will: ¿ Purchase and provide a moisture analyzer balance for each laboratory that will test the residue. ¿ Collect the test data generated by the regional laboratories; summarize the results and present it on regularly scheduled progress reports. ¿ Interact with the PPETG to ensure proper guidance as well as the latest developments. ¿ Write a final report with conclusions and recommendations regarding the residue recovery process