AASHTO TP 141-20 pdf free download

AASHTO TP 141-20 pdf free download.Determining the Indirect Tensile Ntlex Factor to Assess the Cracking Resistance of Asphalt Mixtures.
3. TERMINOLOGY
Definitions:
3.1 .1. linear variable displacement transducei L VDT—sensor device for measuring linear displacement.
3.1.2. vertical displacement, Y—total displacement of the specimen during testing measured in the direction of the load application.
3.1 .3. brittleness slope, in—slope of the equation fitted to the stress-estimated strain data at the first inflection point following the peak stress.
3.1.4. roughness, T—area under a stress-estimated strain plot to a particular point of interest. In this method, Toughness is determined from the initiation of load through the first inflection point following the peak stress.
3.1.5. Nnjctor—index property of an asphalt mixture, which has been correlated to cracking resistance (West et al., 2017). Nriex factor is calculated by dividing toughness by the brittleness slope.
SUMMARY OF METHOD
An asphalt mixture compacted in the Superpave Gyratory Compactor (SGC) to the number of gyrations specified for mix design (Ndesjgn) is cut to obtain specimens 50 mm in thickness. After conditioning to the test temperature (i.e., 25°C), the specimen is positioned in the indirect tension fixture and a load is applied along the vertical diameter of the specimen. The load is applied such that a constant vertical deformation rate of 50 mm/mm is maintained for the duration of the test. The load and vertical displacement are measured during the entire duration of the test. A minimum of three specimens are tested to determine the average results for a mixture. The test fixture and specimen geometry are shown in Figure 1.
4.2. Toughness (7’) and brittleness slope (m) are determined from an equation fitted to the stressestimated strain data at the first inflection point past the peak stress. Toughness divided by the brittleness slope is referred to as the Nti factor.
5.2. The IDT test is used to measure loads and displacements from which parameters related to toughness and brittleness of asphalt mixture at 25°C. Specimen dimensions, load, and displacement data are used to calculate the tensile stress and estimated horizontal strain at the center of the specimens through the duration of the test.
5.3. A fifth or sixth order polynomial equation is fitted through the estimated strain versus stress (x vs. y) data and verified to have an acceptable fit to the data points. The second derivative of the polynomial equation is used to determine the location of the first inflection point (change in curvature) past the peak stress. The first derivative of the initial polynomial equation at the inflection point is the slope (m) of that equation. That slope is the brittleness slope. The toughness is determined by integrating the initial polynomial equation from zero strain to the inflection point previously determined. The Nex factor for each specimen is determined by dividing the toughness by the slope (in) at the inflection point.
5.4. This test method is being investigated as a simple method to evaluate the cracking resistance of asphalt mixtures containing virgin and recycled materials, and possibly containing different asphalt contents and/or grades, or other mix additives.
APPARATUS
Saw—Laboratory saw capable of cutting through a 150-mm diameter SGC specimen and producing test specimens with smooth, parallel faces.
6.2. Water Bath—A water bath for conditioning the specimens to the test temperature. The water bath shall be capable of uniformly maintaining a temperature of 25 ± 0.5°C throughout the bath. An environmental chamber may be used in lieu of a water bath provided that the same temperature requirements are satisfied.AASHTO TP 141-20  pdf download.