Crumb rubber modifier (CRM) binders easily suffer from instability at high temperatures, with many suggestions being developed to evaluate their storage stability. However, much uncertainty around CRM binders still exists regarding the relationship between mixing methods and experiments in order to calculate the separation index. In this study, a laboratory investigation into how CRM binders behave regarding storage stability using different mixing methods and experiments was conducted. The CRM asphalt binder in this study was prepared through a wet mixing process with the addition of 5% and 10% crumb rubber modifier (by weight) at 200 °C. The three main modification methods were method A: high-shear mixing (8000 rpm) for 2 h, method B: low mixing (300 rpm) for 8 h, and method C: high-shear mixing (8000 rpm) for 2 h + low mixing (300 rpm) for 6 h. In addition, the effect of separation index (SI) on storage stability was assessed, measuring viscosity, G*/sin δ, and percentage recovery. In general, the results of this study revealed that method C appeared to have the most prominent effect on decreasing the difference between the values of the top and bottom parts; the results for 5% CRM using method C showed that there were no differences among the values for the top, middle, and bottom parts; from the MSCR test, method C was effective in decreasing the difference between the values of the top and bottom parts. It was observed that method C improved storage stability. However, the results for percentage recovery were relatively higher than the separation index when using rotational viscosity and G*/sin δ.

In continuously reinforced concrete pavement (CRCP) research, it has been assumed that transverse crack spacing plays an important role in determining CRCP behaviour and performance. For the longitudinal reinforcement design, the 1993 American Association of State Highway and Transportation Officials (AASHTO) Design Guide recommends a minimum crack spacing of 3.5 ft. The minimum spacing of 3.5 ft is recommended to minimise the occurrence of punchouts. This concept of narrow crack spacing being more prone to punchout has been accepted. Hence, all the available CRCP design algorithms are based on this concept. However, since treated base/non-erodible base is now provided in CRCP, this theory has some discrepancies with the real CRCP performance especially in Texas. In this study, an extensive field evaluation was conducted for the number of punchouts recorded in TxDOT pavement management information system (PMIS). Out of 1472 punchouts, 232 punchouts that developed in major metropolitan Districts in TxDOT were surveyed and evaluated to determine whether punchouts have a relationship with closely spaced transverse cracks and the resulting load transfer efficiency (LTE). Field survey and testing results show that the majority of distresses in CRCP have been caused by quality issues of either materials or construction in the vicinity of transverse construction joint and repair joint.

Concrete volume changes due to temperature and moisture variations (environmental loading) are severely restrained in Continuously Reinforced Concrete Pavement (CRCP) by longitudinal reinforcement and base friction, resulting in numerous transverse cracks, which are held tight by primarily longitudinal steel. Tight transverse cracks provide good load transfer at transverse cracks, ensuring good performance of CRCP. In general, an adequate amount of longitudinal steel and base friction used in CRCP will restrain concrete volume changes to an adequate level, keeping transverse cracks tight and providing good CRCP performance. In Texas, the performance of CRCP is excellent; however, severe spalling problems have been observed in CRCP sections where a certain type of coarse aggregate was used, resulting in costly repairs and traffic delays. This study investigated the causes of severe spalling problems in CRCP in Texas. Fourteen CRCP sections with severe spalling and 10 sections with no spalling distress were identified. A minimum of two cores were taken from each section and concrete material properties, including Coefficient of Thermal Expansion (CoTE) and modulus of elasticity, were evaluated. Test results indicate a strong correlation between spalling and concrete CoTE. Concrete with a CoTE larger than 9.9 × 10^-6/℃ (5.5 × 10^-6/F) is quite prone to severe spalling. On the other hand, CRCP sections with a concrete CoTE smaller than 9.9 × 10^-6/℃ showed almost no spalling problems.