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Traditional asphalt mixture design practices recognize the need for laboratory parameters, which relate to field performance throughout the life of the pavement. However, many design methodologies consider volumetric proportions and strength characteristics of the mixtures, which may not provide adequate insight into mixture performance. Laboratory testing that can ascertain an asphalt mixture's capability to resist common distresses is needed to complement current design methodologies. Distresses commonly associated with flexible pavement failure are fatigue cracking and permanent deformation (rutting). The Louisiana Department of Transportation and Development proposed specification modifications for 2013 to address the need for balanced mixtures (i.e., mechanistic laboratory evaluation to complement volumetric criteria). This paper presents Louisiana's experience with specification modifications to develop a balanced mixture as evaluated through the use of the Hamburg loaded wheel tester (HLWT) and semicircular bend (SCB) tests. Laboratory performance of 11 mixtures produced with the 2013 proposed specification modifications was compared with that of 40 mixtures produced under the 2006 specifications. Laboratory tests included HLWT and SCB to evaluate rutting and intermediate temperature cracking, respectively. The research showed that specification modifications did not adversely affect rutting or fatigue cracking resistance of the mixtures.

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The use of biobinder as a replacement for petroleum-based asphalt binders has received considerable attention in recent years. The objective of the study reported in this paper was to conduct a comprehensive laboratory evaluation of asphalt mixtures that contained biobinder technology at a content of 20%, 25.5%, 30%, and 50%. To achieve this objective, Superpave® performance grade (PG) of the modified blends was compared with the unmodified binder. In addition, laboratory tests were conducted to capture the mechanistic behavior of the mixtures against major distresses. Laboratory testing evaluated the rutting performance, moisture resistance, and fracture resistance of the produced mixtures with the use of the Hamburg loaded-wheel tester, the modified Lottman test, the semicircular bending test, and the thermal stress restrained specimen test. Results of the experimental program showed that the use of biobinder did not influence the final PG of the binder with the exception of one blend, which dropped one grade at low temperature. Mixtures modified with biobinder had rutting performances that were similar to, or improved, compared with those of the conventional mixes. With respect to moisture susceptibility, all mixtures, except the mixes prepared with PG 67-22, exceeded the 80% tensile strength ratio. However, when an antistripping agent was added, the tensile strength ratio of the mix with 50% biobinder exceeded 80%. At intermediate temperatures, the mixes that contained biobinder exhibited less fracture resistance than the conventional mixes did. Biobinder modification improved the low-temperature fracture performance of the mixtures compared with that of the conventional mixtures of similar PG.

The use of bio-binder as a replacement to petroleum-based asphalt binders has received considerable attention in recent years. The objective of this study was to conduct a comprehensive laboratory evaluation of asphalt mixtures containing bio-binder technology at a content of 20, 25.5, 30, and 50%. To achieve this objective, a suite of laboratory tests was conducted to capture the mechanistic behavior of the mixtures against major distresses. Laboratory testing evaluated the rutting performance, moisture resistance, and fracture resistance of the produced mixtures using the Hamburg loaded-wheel tester, the modified Lottman test, the semi-circular bending (SCB) test, and the thermal stress restrained specimen (TSRST) test. Results of the experimental program showed that mixtures modified with bio-binder had similar or improved rutting performance when compared to the conventional mixes. With respect to moisture susceptibility, all mixtures, except the mixes prepared with PG 67-22, exceeded the 80% tensile strength ratio. Mixtures containing bio-binder exhibited reduced fracture resistance as compared to conventional mixes. Bio-binder modification improved the low temperature fracture performance of the mixtures when compared to conventional mixtures of similar performance grade.

Blending ground crumb rubber (CR) with the asphalt binder is an economical and sustainable method of binder modification. The objective of this paper was to evaluate the interaction between the asphalt binder and the three CR types at 170 and 190 °C. The three CR types, ambiently ground, cryogenically ground, and Ecorphalt (E-rubber), were blended with a Louisiana conventional PG 67-22 asphalt at two temperatures, 170 and 190 °C. The composition of the CR before and after treatment with asphalt was studied using thermogravimetric analysis. Gel permeation chromatography was used to study the molecular weight changes to the asphalt before and after rubber treatment. Fourier transform infrared spectroscopy was used to study the aging characteristics of the CR-modified asphalt binder prepared at the two temperatures. Scanning electron microscopy (SEM) shows the morphology of the rubbers before and after dispersion in the asphalt binder. Performance-grade tests of the CR/asphalt binder blends were used to characterize the rheological properties. E-rubber additive did allow for better dispersion of particles in the asphalt binder at a lower temperature than the other additives evaluated. Ground CR particles were comprised of favorable polyisoprene contents (minimum natural rubber content was 50%) for blending with the asphalt binder. An increase in the blending temperature from 170 to 190 °C resulted in a minimal increase in the favorable polyisoprene contents of CR/asphalt binder blends containing 5 and 10% E-rubber, which is likely to influence performance. Favorable polyisoprene contents of the CR/asphalt blends containing 10% ambiently ground CR did not change with the blending temperature, whereas that of the CR/asphalt blend containing 10% cryogenically ground increased with the blending temperature. The CR particles isolated from asphalt blends prepared at 190 °C were more swollen than those separated from asphalt blends prepared at 170 °C, as measured by SEM. Approximetely 73–87% of the E-rubber particles dissolved in the asphalt binder during blending, confirming that E-rubber had great compatibility with the binder chemistry and, hence, can improve performance.