This study investigated the effect of reclaimed asphalt pavement (RAP) on the rheological properties of a hybrid binder and the fracture properties and cracking performance of resultant mixtures. Fracture properties of the same mixtures containing up to 40% RAP with a standard polymer-modified asphalt (PMA) binder were used as benchmarks. RAP mixtures with hybrid binder exhibited lower resilient modulus, higher failure strain and higher fracture energy density than PMA RAP mixtures. Results indicated that rubber particles might not dissolve in the base binder; therefore, hybrid binder had more “free” soft binder to blend with the RAP whereas the more integrated polymer network present in PMA binder resulted in stiffer mixtures. Furthermore, PMA RAP mixtures exhibited lower damage accumulation rate than hybrid RAP mixtures. Eventually, hybrid and PMA RAP mixtures yielded comparable energy ratio values, which indicate both binder types can be interchangeably used in mixtures with up to 40% RAP for satisfactory cracking performance.

The need for continuous recording rain gauges makes it difficult to determine the rainfall erosivity factor (Rfactor) of the Universal Soil Loss Equation in regions without good spatial and temporal data coverage. In particular, the R-factor is only known at 16 rain gauge stations in the Madrid Region (Spain). The objectives of this study were to identify a readily available estimate of the R-factor for the Madrid Region and to evaluate the effect of rainfall record length on estimate precision and accuracy. Five estimators based on monthly precipitation were considered: total annual rainfall (P), Fournier index (F), modified Fournier index (MFI), precipitation concentration index (PCI) and a regression equation provided by the Spanish Nature Conservation Institute (R_ICONA). Regression results from 8 calibration stations showed that MFI was the best estimator in terms of coefficient of determination and root mean squared error, closely followed by P. Analysis of the effect of record length indicated that little improvement was obtained for MFI and P over 5- year intervals. Finally, validation in 8 additional stations supported that the equation R = 1.05·MFI computed for a record length of 5 years provided a simple, precise and accurate estimate of the R-factor in the Madrid Region.

Pavement distress leads to frequent rehabilitation that increases the global cost of pavement sections. A clear understanding of distress mechanisms is the cornerstone for extending pavement service life. The overall objective of this study was to provide guidance for the design of semi-rigid long-life pavements. The potential distress mechanisms in semi-rigid pavements were revisited in order to synthesize the primary factors affecting performance. One key observation from the literature was that, while thickness primarily controls fatigue cracking, material requirements are the primary factor governing other distress mechanisms. Semi-rigid sections proposed for the heaviest traffic conditions in Spain were analytically evaluated from the long-life perspective. Results showed that only some sections met the structural requirements to be considered long-life pavements; however, two of them were clearly overdesigned. In addition, thick asphalt lifts are used to delay the onset of reflective cracking, which is not a cost-effective approach. Findings from linear elastic analysis of alternative sections and observations on potential distress mechanisms led to establishment of guidelines for a more efficient design of semi-rigid long-life pavements. The established design concept integrated both layer thickness and material requirements

Load-induced fatigue cracking is one of the primary distress modes in asphalt pavements at intermediate temperatures. The asphalt community is still searching for a reliable methodology to obtain relevant properties of asphalt binder to assess relative cracking performance. This study proposed an enhanced binder fracture energy (BFE) test to determine the fracture tolerance of asphalt binders. The BFE test successfully differentiated unmodified and modified binders based on the characteristics of the true stress–true strain curve. More importantly, binder fracture energy density (FED) quantitatively distinguished rubber-modified, hybrid, and polymer-modified binders. Finally, fracture properties translated well from binder to mixture such that binders with higher FED resulted in higher mixture FED values. Mixture cracking performance was evaluated by using the energy ratio (ER) parameter that is governed by both failure limit (FED) and rate of damage of asphalt mixtures. An excellent correlation was found between binder FED and mixture ER, given binders containing SBS polymer typically lead to a low mixture rate of damage. Therefore, it appears that binder FED obtained from the BFE test can be used to assess relative cracking performance. Future research on binder rate of damage may be necessary to account for new binder modifications.