In-Depth Evaluationof the Effects of Tensile Strength Ratios on Service Life and Pay Factors of Asphaltic Pavements

Abstract

Indirect Tensile Strength Tester is used to evaluate a mixture's moisture sensitivity. The evaluation of moisture sensitivity is performed by measuring the indirect tensile strength values of both conditioned and unconditioned mixture. For conditioning, a mixture sample is subjected to saturation and immersion in a heated water bath to simulate field conditions over time. Strength loss is then evaluated by comparing indirect tensile strengths of an unconditioned control group to those of the conditioned samples. The ratio of indirect tensile strength values of conditioned mixture to indirect tensile strength values of unconditioned mixture is termed as Tensile Strength Ratio (TSR). If the average retained strength of the conditioned group is less than eighty-five percent of the control group strength, the mix is determined to be moisture susceptible. This indicates that the combination of asphalt and aggregate would fail prematurely due to water damage.

An exclusive dependency on the TSR values may be misleading in many cases. The individual values of tensile strength of conditioned and unconditioned mixture specimens in conjunction with TSR values should be employed in assessing the effect of water damage on the performance of pavements.

In order to achieve this objective, the fatigue and rutting performance of both conditioned and unconditioned mixture specimens were evaluated with the aid of SUPERPAVE Shear Tester (SST) tests. The Castle Hayne mixture that was determined to be the lowest moisture susceptible from the TSR results showed the lowest % decrease in mixture performance (fatigue and rutting) of conditioned mix when compared to its unconditioned Castle Hayne mix. The Fountain mixture that was determined to be the highest moisture susceptible from the TSR results showed the highest % decrease in mixture performance of conditioned mix when compared to its unconditioned Fountain mix.

The methodology of development of pay adjustment factors is suggested based on rutting and fatigue performance. The critical tensile strength value of 85 psi for 0.5 inch rut depth is extrapolated from the regression relationship established between rut depths and Indirect Tensile Strength values was used as a guiding value in suggesting the methodology for the development of pay adjustment factors based on rutting performance. The regression relation was established between the indirect tensile strength and fatigue life. The relationship showed the increase of fatigue life with increase in indirect tensile strength. The fatigue life corresponding to unconditioned tensile strength, 85% of unconditioned tensile strength and conditioned strength were calculated. The methodology of pay adjustment factors was suggested based on these values. The deciding pay adjustment factor is suggested based on either fatigue performance or rutting performance depending on the mixture.