Determination of Creep Compliance and Tensile Strength of Hot-Mix ...

IDT TestingEquipmentTesting for this project was performed using a Tinius-Olsen (T-O) Super L loadframe calibrated up to 120,000 lbf. The system is non-dynamic, closed-loop servohydraulicand is computer controlled using the software program MTestWindows byAdmet. In addition to the T-O’s standard load measurement device (pressuretransducer), a new electronic 25,000 lbf, fatigue-rated Tovey load cell (Model FR20-25K) was mounted in-line between the loading table of the T-O and the pistonconnected to the lower IDT loading platen/strip, as specified in T 322-07. The Toveyload cell was cross-calibrated up to 19,000 lbf using the T-O which had beencalibrated by a certified T-O technician approximately 10 months earlier. Just daysbefore IDT testing began, the same T-O technician again calibrated the T-O andnoted that no adjustments to the previous calibration were necessary thus verifyingthe cross-calibration of the Tovey load cell. The T-O load data output is used by theMTestWindows program for control purposes. However, for purposes of calculatingcreep compliance and tensile strength, the Tovey load data was used because ofthe load cell’s faster response and higher resolution relative to the pressuretransducer used in the T-O. Because all data was acquired at a rate of 10 Hz, afaster load cell response was necessary to determine with greater accuracy the timeat which maximum loads occurred.Specimen deformations were measured using new, MTS strain-gauge typeextensometers (Model OSDME). The extensometers were factory calibrated for twodifferent full-scale displacement ranges: vertical, 2.000 and 0.2000 mm compressiononly (utilized during strength and creep testing, respectively); horizontal, ±0.500 and±0.0500 mm compression and tension (utilized during strength and creep testing,respectively). During creep compliance testing, the smaller range was used forincreased resolution.Data acquisition was accomplished using LabView 8.0 by National Instruments.Inputs to data acquisition were the T-O load output and table position, the Toveyload cell, and the four MTS extensometers.The temperature chamber is MTS model 651.34. The temperature is controllablefrom -30 to +100°C, ±0.2°C. Figure 1 shows the equipment configuration.5