Binders Lab

Dynamic Contact Angle (DCA) Analyzer in Dr.O'Rear's lab is used to measure the angle of contact between the asphalt binder film and a probe liquid. The DCA analyzer uses a WINDCA software to precisely record the change in mass of the sample while immersing it into and withdrawing from the probe liquid. The results are processed to determine the contact angle: advancing contact angle during advancing and receding contact angle during withdrawing. Advancing contact angle, as per Young-Dupre postulate, can be used to calculate the Surface Free Energy (SFE) components of the asphalt binder, namely acid SFE, base SFE, Lifshitz-van der Waals SFE, acid-based SFE, and total SFE. The SFE components are further used to quantify the wettability, adhesion and debonding of the asphalt binder from aggregates.

For sample preparation, a 25 mm x 50 mm standard glass plate is dipped in the liquefied asphalt binder preheated to a certain temperature such as 145°C. The plate is kept vertically in the oven to get a thin-film of the asphalt binder. Finally, the plate is placed in a desiccator overnight. Usually, DCA with three probe liquids such as water, glycerin, and formamide is required to determine the SFE components. 

Bending Beam Rheometer (BBR) is used to measure the mechanical properties, namely stiffness and creep relaxation, of PAV-aged asphalt binders at low-temperatures such as -10°C. The BBR consists of a methanol fluid bath unit with a magnetic stir and an external temperature controller to maintain a constant temperature of the sample while testing. Aluminum molds are used to prepared beam samples of 127 mm x 12.7 mm x 6.35 mm dimensions. For testing, a constant load of 980 ± 50 mN is applied at mid-span of the beam for 240 seconds. The measured stiffness and creep relaxation after 60 seconds of load application are used to determine the Superpave^® PG and cracking potential at low-temperatures.

The Rotational Viscometer (RV) is used to measure the dynamic viscosity of asphalt binders at different temperatures. The RV data are used to determine the appropriate temperatures for mixing and production of asphalt mixes. Since production compaction temperatures of asphalt mixes are quite high, the test is usually conducted at elevated temperatures such as 135°C. The RV consists of an environmental chamber maintaining the temperature to a specified level. The viscosity is determined from the developed torque in the asphalt binder due to spindle rotation (generally 20 rotation/minute).

The Rolling Thin-Film Oven (RTFO) simulates the short-term aging condition of the asphalt binder during the production of asphalt mixes. The RTFO consists of a rotating carriage which helps to create a thin-film (as the name says) of asphalt binder for fast oxidation. Asphalt binders (generally 35 ± 0.5 gm in a bottle) are generally oxidized at 163°C for 85 minutes under an air flow of 4 liters/minute. The RTFO employs a moisture-indicator to ensure absence of water during the oxidation process. The RTFO also provides a quantitative measure of the volatiles lost due to the aging of the asphalt binder.

The Pressure Aging Vessel (PAV) simulates the long-term aging of asphalt binders over a period of 7 to 10 years of service life of a pavement. To perform aging using PAV, RTFO-aged asphalt binder (about 50 ± 0.5 gm) is poured in the PAV plate and then placed in the PAV oven preheated to a certain temperature such as 100°C. After securing the PAV oven lid, the oven is pressurized to 2.10 MPa (305 psi) for 20 hours. 

The Aggregate Imaging Measuring System (AIMS)takes digital images and analyzes them to determine aggregate shape and texture characteristics. The AIMS setup uses two separate lighting schemes and a camera to capture images of aggregates at varying resolutions. The camera unit has an optem zoom 160 video microscope that operates in the y and z directions over the aggregate measurement tray while travelling in the x direction. The movement of the camera and aggregate tray is controlled by a closed loop direct current servo, which helps to achieve highly consistent focus.

Aggregate particles are placed on the measurement tray at marked locations, and the camera captures black and white, and gray images of each aggregate using separate lighting schemes. The AIMS software analyzes the captured images and produces index properties related to the shape (angularity) and texture.

The Universal Sorption Device (USD) is used to determine the Surface Free Energy (SFE) components of aggregates. The USD is a gravimetric sorption device which works on the vapor sorption isotherm, i.e., the amount of vapor adsorbed, or desorbed, on the solid surface at a fixed temperature and partial pressure. The range of relative pressure (RP) can be selected from 0.02 to 0.98 and temperature from 5° to 60°C. At each relative humidity (RH) or pressure step, the system monitors sample weight until equilibrium condition. Sample weight, temperature, and RH or RP are recorded by the equipment in a data file. Identical conditions of temperature and humidity for a sample and a reference are achieved by using a symmetrical two-chamber aluminum block.

For this test, three different prove vapors such as water, n-hexane, and methyl propyl ketone (MPK) are required to determine the adsorption isotherms which can be used to calculate the SFE components of aggregates, and the work of adhesion and work of debonding the asphalt binder-aggregate system. To prepare aggregate samples for testing, aggregates passing No.4 and retaining No. 8 sieves are selected and washed several times with distilled water to obtain a dust-free and clean surface. Then, the aggregates are oven dried at 120°C for 12 hours and allowed to cool to room temperature in a desiccator sealed with silica gel. About 20 grams of aggregate are used to conduct one USD test.

The Dynamic Shear Rheometer (DSR) is basically used to measure the rheological properties ( e.g., complex modulus and phase angle) of the asphalt binders at different temperatures. 25 mm diameter plates with 1 mm gap are used to conduct the test at high temperatures such as 58˚C and 82˚C on unaged and RTFO-aged asphalt binders. 8 mm diameter plates with 1.5 mm gap are used to conduct the test at intermediate temperatures such as 16˚C and 31˚C on PAV-aged asphalt binders. The DSR employs advanced Peltier technology to control temperature during the test. The results are used to determine the rutting potential, Superpave^® PG at high-temperatures, and fatigue cracking resistance of asphalt binders. The DSR is also used to perform Multiple Creep Stress Recovery (MSCR) test using a 25 mm diameter plate on RTFO-aged asphalt binder. A MSCR test measures the percentage recovery of a binder at different stress levels. The DSR can also be used to measure other flow characteristics such as viscosity at different temperatures, frequencies, and stress or strain levels.