Engineering Materials Characterization Research Facility
The Engineering Materials Characterization and Research Facility (EMCRF) at LTRC conducts basic and applied research that is related to characterization and performance of transportation materials. In addition, EMCRF provides the necessary support for characterization of materials utilized in accelerated loading experiments.
EMCRF is equipped with state-of-the-art equipment to fundamentally characterize transportation materials. This includes two MTS materials test system and Superpave binder and mixture equipment.
EMCRF is equipped to undertake a full range of standard and specialized tests used in fundamental characterization of transportation materials. This include a sophisticated materials research equipment such as two MTS Model 810 materials test systems that is fully automated to perform dynamic testing. The systems are rated for 22 Kip and 55 Kip, respectively. Both systems have digital controller operated under IBM OS/2 and MTS tester software for dat a acquisition and equipment control. Several user friendly menu driven software were developed to conduct test on asphaltic concrete samples such as indirect tensile strength and strain, indirect tensile and axial creep test, resilient modulus test, fati gue test, and other specified tests. In addition, software to conduct resilient modulus on subgrade soil is also available. Two environmental chambers are also available at the facility to provide testing capability at a range of temperature representi ng in-service pavement temperature. The temperature inside these chambers are controlled by microprocessor based controller for processing heating/cooling application. The operating range of the chamber is -100 F (-73 C) 600 F (356 C).
Louisiana Modified Indirect Tension Test Device
The EMCRF staff developed the Louisiana Modified Indirect Tension Test (LMITT) that is currently used to conduct fundamental testing on transportation materials in the indirect tension mode. Displacement measurement to dynamic loadin g is a critical factor in determining the fundamental properties of transportation materials. A typical range of the deformation along the horizontal diameter during the dynamic load application is 4-100 micro-inches. Thus, the measurement device must have the sensitivity in this range so that it can respond and capture the change in sample deformation resulting from the application of dynamic loads.
Superpave Performance Based Binder and Mixture Equipment
From October 1987, through March 1993, the Strategic Highway Research Program (SHRP) conducted a $50 million research effort to develop new ways to specify, test, and design asphalt materials. The final product of the SHRP asphalt re search program is a new system referred to as Superpave TM ,which stands for Superior Performing Asphalt Pavements. It represents an improved system for specifying the components of asphalt concrete, asphalt mixture design and analysis, and asphalt pavement performance prediction.
EMCRF and the asphalt Laboratory at LTRC is equipped with the new SHRP Superpave asphalt binder and mixture tests equipment. Superpave binder equipment include the dynamic shear rheometer, bending beam rheometer, the direct tension a pparatus, the pressure age vessel, and Brookfield rotational Viscometer. The mixture equipment at EMCRF include the Superpave Gyratory Compactor and the Simple Shear tester.
Resilient Modulus Testing of Subgrade Soil
The resilient modulus is very sensitive, among other things, to the testing equipment and the testing procedure. Misalignment, seating errors, bedding errors, and end friction can cause erroneous axial measurements and thereby affect the resilient modulus calculations. The end friction between the sample and platens induces stress/strain concentrations at the ends and this results in a non-uniform strain distribution down the axis of the specimen. Measurements inside the cell are found to reduce the bedding, seating and system compliance problems. It is also reported that the use of inside measurements has been found to be important for granular materials whose resilient modulus is greater than 105 MPa (15000 psi). EMCRF conducts resilient modulus testing using a MTS model 810 servo-hydraulic material testing system with a 100 kN (22 kip) axial load actuator capacity. The experimental setup consists of pressure panel, MTS 810 load system, analo g controller, triaxial cell and accessories, signal conditioning module, high speed personal computer equipped with data acquisition hardware and software, and MTS micro-controller.
Deformations and load are measured inside the triaxial cell. The triaxial cell is custom made with connectors for two deformation measurement systems and an internal load cell with a capacity of 1.36 kN (300 lbs). The pressure trans ducer, used in measuring the confining stress, has a full scale of 700 kPa (100 psi) with a combined repeatability and non-linearity of ±2.31 kPa (0.33 psi). Two independent measurement systems can be used simultaneously to monitor the axial deformation. The first system is used to measure specimen deformation with LVDTs clamped at one-third points in from each end of the specimen. The clamps which are made of plexiglas material, do not provide any rigid confinement to the sample since they are in cont act with sample at four point-locations. This system measures displacements between two points on each side of the sample. The second system is used to monitor the deformation with LVDTs mounted at the end plates. The second system has external adjusta ble knobs in the triaxial cell allows to externally re-zero the LVDTs without opening the cell chamber. Both measurement systems have two diametrically placed internal LVDTs. The deformation in each system is measured with two LVDTs mounted 180 degrees a part from each other. The output from each LVDT is monitored independently and compared with the output of the other LVDT of the same system. If the difference between the axial deformations was not within the assigned tolerance, then the tests will be discarded. This ensures good seating and uniform loading on the specimen.
In order to minimize errors in data collection, all outputs from the instrumentation devices, described in previous sections, were conditioned prior to digitizing by the analog/digital (A/D) board and stored in the high speed personal computer. A 16-bit data acquisition board, along with a signal conditioning unit capable of providing 8 active channels was used for data collection. The minimum values that could be read for end system LVDTs, middle system LVDTs, load cell and cell pr essure transducers were 0.00309 mm, 0.0014 mm, 3.3 N and 0.35 kPa, respectively. A fully automated test software for equipment control, data acquisition and data reduction was developed.