Texas Tech University

Project 0-5893

Laboratory Evaluation of Constructability Issues with Surface Treatment Binder


TxDOT depends greatly on sprayed seals for new road construction (surface treatment) and on preventive maintenance (seal coat). It is very important for TxDOT to have emulsified asphalt (EA) as a key binder type at its disposal to reduce costs. However, EA brings its own set of challenges. Compared to other binder types, EAs are more complex in composition, have a much shorter shelf life, and their behavior under different construction scenarios is difficult to predict. TxDOT field personnel can effectively use EAs if tools are available to test binder quality as received at the site and to predict their behavior. It is useful for the designers to rank the most effective binder-aggregate combinations and to predict the rate at which EA will achieve stiffness and bond strength with aggregate to be able to open the road for traffic. This research project was launched by TxDOT to address these issues and find solutions that are of benefit to field personnel. A field evaluation of selected seal coat projects was conducted to help design laboratory experiments for this study. For each field project, extensive construction-related data was collected. The same aggregate-binder combinations used in these field projects were also included in the laboratory test programs at TechMRT and CTR. The CTR team conducted additional weather-rack related tests using a wider range of binders available from the TxDOT Cedar Park lab. Laboratory test data clearly showed that some binder-aggregate combinations become ready for opening to traffic and/or brooming sooner than others. This delay also depends on the climatic conditions. The ASTM D7000 Sweep Test, used in other states to determine the effectiveness of binder-aggregate combinations for seal coats, was also conducted. A statistics-based curing model that incorporates the amount of water lost to evaporation is proposed. The experimental data was used to develop a second statistical model to predict the rate of setting of binder when in contact with different aggregates under different climatic
conditions. Two field tests were developed to assess the quality of the emulsion received at the job site. The first is a simple field test that determines mass loss and calculates the dilution ratio in EA. This test showed commendable repeatability of results. The second field test used Shell cups to determine the Saybolt-Furol Viscosity (SFV) of the binder. The repeatability of the test improved drastically when a water bath was introduced to control specimen temperature. Finally, six construction projects were used for field evaluation of the new field tests and to calibrate the statistical models that were developed. For the prediction models to be ready for widespread use, additional tests are needed to increase the model reliability.

ASTM D7000 Sweep Test Apparatus