This report describes laboratory testing of laboratory-prepared specimens as part of the second phase of a warm mix asphalt study, which compares the performance of a hot mix control produced at 310°F (155°C) against the performance of warm mixes produced at 250°F (120°C) with four different technologies (Advera, Evotherm, Sasobit, and Rediset). Key findings from the study include: The laboratory test results indicate that use of the warm mix technologies assessed in this study, which were produced and compacted at lower temperatures, did not significantly influence the performance of the asphalt concrete when compared to control specimens produced and compacted at conventional hot mix asphalt temperatures. Laboratory performance in all the tests appeared to be mostly dependent on air-void content and less dependent on mix production temperature. Test results were influenced by specimen air-void content, actual stress and strain levels, and actual test temperature. Variation in these parameters needs to be taken into consideration when comparing performance between the different mixes. All mixes were sensitive to moisture content. Rutting performance, fatigue-cracking performance, and tensile strength retained all deteriorated with increasing moisture content in the specimens. All mixes performed significantly better in the Hamburg Wheel-Track Test when subjected to additional curing, indicating that hot and warm mixes are likely to have similar performance on in-service pavements after a short period of aging (e.g., 6 to 12 months). This is consistent with performance on the test track. Test results were consistent with those from earlier testing phases. The laboratory testing completed in this phase has provided no new results to suggest that warm mix technologies should not be used in dense- or open-graded mixes in California, provided that standard specified construction and performance limits for hot mix asphalt are met. It should be noted that lower production temperatures could lead to insufficient drying of aggregates, which in turn could result in moisture-related problems in the road. Moisture content in aggregates should be strictly controlled at asphalt plants and specified mix moisture contents (i.e., less than 1.0 percent by weight of the mix) should be adhered to.

This study presents an improved methodology for the mix designs of open-graded friction courses (OGFC). The methodology has been enhanced by the development of an Excel macro in order to suggest revisions to California Test 368, Standard Method for Determining Optimum Binder Content (OBC) for Open-Graded Asphalt Concrete. In addition to the development of the Excel macro, one of the primary objectives of this study was to evaluate the effect that fines content has on mix performance, which cannot be identified by the “break point sieve” concept or by volumetric properties. The proposed OGFC mix design includes two phases: Phase I: Volumetric OGFC Mix Design and Phase II: Performance Testing. The tasks required to perform Phase I include the determination of material volumetric properties such as specific gravities, voids in coarse aggregate in dry-rodded condition (VCADRC), and asphalt absorption. These must be performed so it becomes possible to select three trial binder contents for fabricating specimens for performance testing. The main purpose of Phase II is to decide the optimum binder range (OBR) according to the results of draindown, Cantabro, and Hamburg Wheel-Track Device (HWTD) tests. Two aggregates (Watsonville and Sacramento), three binders (PG 76-22 PM, PG 64-28 TR, and PG 64-10), two gradations (Coarse and Fine) designed to verify the fines content, and three trial binder contents obtained from Phase I were used in the Phase II testing. It was found that an increase of fines content is significant in reducing Cantabro loss, preventing draindown, minimizing the variation of Superpave gyratory compaction curves, and producing more consistent HWTD test results. Hence, it is suggested that the fines content should be part of the OGFC performance specifications. This study also demonstrated the accuracy of the measured air-void contents of Superpave gyratory-compacted specimens that were fabricated with height control rather than gyration control and with binder contents calculated based on the volumetric equation, VCADRC. A preliminary comparison indicated that the proposed mix design produces similar binder contents for conventional and asphalt rubber binders with similar gradations, and that unreasonably low binder contents it may produce indicate a fines content that is too high. This improved OGFC mix design together with the Excel macro developed provides a rational, accurate, and convenient methodology for determining OBR. However, further studies are required to establish the proper performance specifications that relate to field performance.

This report is one of a series detailing the results of the CAL/APT program, a research effort being performed jointly by the University of California, Berkeley Pavement Research Center and the California Department of Transportation (Caltrans). It contains an evaluation of the performance of asphalt treated permeable base (ATPB) in asphalt concrete pavements based on observation, laboratory testing of ATPB, and computer simulation of representative pavement structures. The evaluation includes: 1) a summary of Caltrans experience with ATPB and drainage systems relative to their development and implementation, together with observations of field performance with respect to maintainability and stripping of asphalt treated materials; 2) a summary of the characteristics and performance of ATPB materials and drainage systems used by two other highway agencies; 3) results of laboratory investigation of the stiffness and permanent deformation characteristics of ATPB mixes, including the effects of soaking and loading while saturated on these parameters; and 4) the results of analyses of representative pavement structures to quantify the expected effects of as-compacted and soaked ATPB on pavement performance.

This study presents efforts to further inspect the variability of California Test Method CT 371—“Method of Test for Resistance of Compacted Bituminous Mixture to Moisture-Induced Damage”—through the collection of field data. The purposes of this study are (1) to inspect the factors that affect the wet and dry indirect tensile strengths and their ratio (CT 371-TSR); (2) to identify the between- and within-variations of CT 371-TSR; and (3) to evaluate the factors that affect the stabilometer value (S-value). Trellis graphs and tree-based models were used to qualitatively and quantitatively characterize the data structure. Analyses revealed that (1) there is considerable within-variation and noticeable between-variation among CT 371-TSR values, (2) the effect of lime treatment on the CT 371-TSR value is prominent while the effect of liquid anti-strip (LAS) on the CT 371-TSR is far more limited, and (3) the ratio of percent passing at #200 sieve to percent asphalt content (#200/AC) is the most critical factor that affects S-value.