Performance evaluation and strain behavior of stabilized and unstabilized asphalt pavements

Abstract: Stabilized and unstabilized foundation pavements differ in how their base and subbase layers are treated. Stabilized foundation pavements involve adding cement and lime to the foundation layers, which stiffens the foundation. These two types of foundations respond differently to loading. Stabilized pavements result in a more rigid foundation and cause the loads to be distributed more widely across the foundation, which reduces deformation under loading, whereas unstabilized pavements are more prone to strain and deformation, as the lack of binding material allows more movement within the layers under loading. Accurate modeling of stabilized and unstabilized pavements in design and analysis is essential to optimize pavement structures. This research aims to evaluate the accuracy of software tools, such as WESLEA for strain prediction and AASHTOWare Pavement M-E Design software, in predicting the performance of stabilized pavements.
The objective can be achieved by monitoring and evaluating the structural response and condition of full-scale pavement sections at the NCAT Test Track and a site in Mississippi (SR76). Strain data collected over 2-7 years based on the construction dates of each section were analyzed using weekly measurements of strain and corresponding temperatures at the time of loading. Falling Weight Deflectometer (FWD) deflections were used in backcalculation to derive in-situ layer properties. These properties were then fed into WESLEA for Windows to conduct mechanistic simulations, with results compared to field data from the Test Track. The measured inflection and peak strains were compared to simulation results to understand the correlation between strain, temperature, and pavement behavior. Additionally, the study evaluated the relationship between field performance, including rutting, cracking, and smoothness, for a stabilized section and the AASHTOWare Pavement M-E Design software's predictions.
Initial findings indicate that pavements with cement-treated bases show different structural responses compared to conventional flexible pavements. These findings are consistent with previous studies, showing compressive peak strains and strain reversals in stabilized pavements at higher temperatures, suggesting the maximum strain may occur at a location other than the bottom of the asphalt concrete (AC) layer under these conditions. Notably, typical flexible pavements show tensile peaks and compressive inflection points, while stabilized sections exhibit tensile inflection and compressive peaks at higher temperatures when the asphalt concrete softens. WESLEA simulations generally mirrored the strain behavior seen in field results for unstabilized sections. For the stabilized section, field data indicated excellent performance through 20 million ESALs, with regards to IRI, rutting, and cracking. However, the AASHTOWare Pavement M-E Design software tended to overestimate pavement distress in comparison to actual field performance.
In the next phase of the study, further analysis of SR76's FWD and strain data will be used to develop a more fundamental understanding of middle-up cracking and identify the reasons behind the different behaviors of stabilized pavements. This analysis can help to confirm the strain reversal theory during warmer weather and pinpoint the location of maximum tensile strain in the AC layer. Uncovering the root causes of mid-level cracking could reduce its impact on crack initiation, thereby extending the pavement's lifespan.