Binder Laboratory

Binder Rheology Laboratory

NCHRP 90-07: "Understanding the Performance of Modified Asphalt Binders in Mixes"

The purpose of the Binder Rheology Laboratory is to conduct Superpave performance-based binder (asphalt) specification testing, research, and development, and advanced rheological research in asphalts, modified asphalts, and mastics. This laboratory is equipped with state-of-the-art rheology instrumentation. The purpose of such research is to improve the performance, i.e., the durability, longevity, quality, and life-cycle cost, of asphalt pavements from the point of view of their most expensive raw material, the asphalt binder. The research conducted in the Binder Rheology Laboratory is of two types: staff research projects conducted within the binder lab and research support for other research groups within the Asphalt Pavement Team.

Short descriptions of three of the most important staff studies currently underway are given below:

• Development of Asphalt Mastic Test to Predict Pavement Performance - "Asphalt mastics" is the term used to designate asphalts containing suspended fillers. The word 'filler' in this context refers to that fraction of mineral dust passing the 200-mesh sieve or particles smaller than 75 µm. The objective of this study is to determine whether rheological tests performed on the mastics will provide better prediction of the mixture performance than those performed on binders. Measurements are done of the rheology of asphalt-filler systems using the binders that are being studied under the NCHRP 90-07 program described elsewhere. The idea is to compare the predictions from the binder tests with those from mastic tests and see whether any relationship exists that could help in better prediction of mixture and pavement performance.

• Fatigue Testing of Binders - Asphalt pavements are known to exhibit fatigue distress or deterioration of binder stiffness under repeated traffic load in the intermediate temperature range from about 10°C to 30°C. The objective of this study is to establish the proper procedure for testing of binders for their resistance to fatigue damage e.g. cracking, using the dynamic shear rheometer (DSR) and to provide a specification parameter that could be used for binders in order to rank their fatigue resistance. The method involves the measurement of the deterioration of binder stiffness during a strain sweep and a time sweep at the intermediate temperatures. Since fatigue would be dependent on the applied strain, frequency and temperature of measurements, various combinations of these variables have to be tested before finding the right window for carrying out fatigue experiments using the DSR and to propose new intermediate temperature specification.

• Unification of Rheological Data - The rheological response of a material is dependent on variables such as the frequency of oscillations, strain levels and temperature. The generated information is often limited to the ranges of the tested variables. Unification provides a method of coalescing sets of |G*|, G", and |G*|/sinδ versus frequency ω curves, and this then expands the information available through the time-temperature superposition principle and goes beyond the limited range of the tested variables. When the normalizing parameter for unification is chosen to be a simple and easily determinable parameter, then the entire rheological information becomes available through this parameter. In this study, the Material's Volumetric-flow Rate (MVR) determined on a Flow Measurement Device (FMD) is seen to unify high temperature rheological data of unaged and aged, unmodified and modified asphalt binders. The unification technique is a simpler, easier, faster, much less expensive method for getting the high temperature rheological specification parameter |G*|/sinδ or its refinement |G*|/(1-(1/tanδsinδ)) and the Superpave Specification Temperature.

The research support activities involve such areas as use of chemically modified crumb rubber in asphalt, the causes and cures of moisture sensitivity (stripping) in asphalt pavements, NCHRP 90-07 concerning the use of polymer modified asphalts, and the validation of the Laboratory Asphalt Stability Test (LAST). Details of these activities are reviewed in the write-ups of other laboratories.