The purpose of this study was to evaluate the effect of binder type, mastic, and aggregate type on the low-temperature cracking characteristics of asphalt mixtures. Six different performance grade (PG) binders were utilized for this study: PG64-28, PG64-28 with poly phosphoric acid, PG64-34 SBS, PG76-22 SBS, a terminal blend asphalt rubber, and PG64-28 with 2 % latex. Each binder was tested to determine its low-temperature cracking resistance using the asphalt binder cracking device (ABCD) and the Superpave tests. A Superpave 9.5 mm mixture was designed using each of the six binders for this study and two sources of aggregates (crushed stone and gravel). Each mixture was then tested for low-temperature cracking resistance using the asphalt concrete cracking device (ACCD). Mastics corresponding to each mixture were tested for low-temperature cracking resistance using the ABCD. Analysis of the results showed that the AASHTO critical cracking temperature had a strong correlation with the ABCD binder and mastics results, but did not correlate well with the mixture tests. Mastic testing generally did not correlate well with the mixture test results. ABCD and ACCD tests results indicated that they were sensitive to binder type, aging time, and aggregate types.

Introduction and Research Approach -- Findings -- Interpretation, Appraisal, and Applications -- Conclusions and Recommendations -- References -- Appendixes.

The research presented in this report was conducted to identify the important factors influencing the water sensitivity of asphalt paving mixtures, and to develop a test method to evaluate water sensitivity of asphalt concrete mixtures for mix design. The test method was to be performance related. A review of current procedures revealed that no single method was suitable for evaluation and related to field performance. Based on a hypothesis that air voids in the mixture may be the major source and cause of water damage, a test system was developed to evaluate the major factors that influence water sensitivity. The Environmental Conditioning System (ECS) was used to develop a test procedure that includes specimen preparation; measurement of permeability using air, water, or both; vacuum wetting; cycling at various temperatures; and continuous repeated loading while monitoring resilient modulus after each conditioning cycle.

Ohio Department of Transportation has adopted the hot mix asphalt concrete containing polymer modifiers for use in the interstate highway pavement. Among the various reasons cited for the adoption of polymer modifiers are the favorable field experiences by ODOT, extensive literatures reporting enhanced performance, such as rutting resistance, low temperature thermal cracking resistance, and possibly fatigue endurance. However, despite these favorable findings, there are still cases involving premature failure of hot mixtures containing polymer modifiers. Concerns regarding optimum polymer content, compatibility between polymer additives and asphalt cement, proper mixing and compaction procedure remain to be resolved. Furthermore, performance based specifications to ensure production of desirable final asphalt concrete product require additional development. Questions regarding the suitability of Superpave binder testing procedures for the polymer-modified binders need to be clarified.