- Sponsor
- Department of Civil and Environmental Engineering
Development and Validation of Economical, Resilient, and Sustainable Stone-Mastic Asphalt
Advisor: Professor Imad L. Al-Qadi
Abstract
Stone-mastic asphalt (SMA) is widely recognized for its durability compared with conventional dense-graded hot-mix asphalt (HMA). Despite this advantage, the use of SMA in Illinois has been limited due to higher initial construction costs associated with the reliance on imported, high-quality aggregates and the long transportation distances required to obtain them. Consequently, there is a need to develop resilient SMAs that incorporate local aggregates while maintaining performance.
An integrated research approach was developed and implemented combining laboratory mixture design and performance testing, full-scale pavement construction and accelerated loading, and life-cycle environmental and economic analyses. SMAs were designed using both imported control aggregates and local aggregates. To mitigate aggregate degradation during compaction, mixture designs employed reduced compaction effort. Laboratory evaluation included volumetric characterization and performance tests assessing rutting and cracking potential, moisture susceptibility, complex modulus, and aggregate degradation.
Aggregate breakage was quantified at multiple stages to evaluate the influence of mixture design and compaction on aggregate integrity preservation. Laboratory results showed that SMAs designed with reduced compaction effort maintained required volumetric characteristics and stone-on-stone contact while reducing aggregate degradation. Aggregate degradation occurred primarily during mixing and compaction rather than during loading.
To validate laboratory findings, six SMAs were produced at an asphalt plant and constructed as full-scale pavement overlays. The SMA overlays were placed over a dense-graded HMA leveling course on continuously reinforced concrete pavement and were instrumented with strain gauges, pressure cells, and thermocouples. The SMA sections were evaluated using the Illinois Accelerated Pavement Tester (I-APT). Each section was subjected to 120,000 passes of a heavily loaded tandem axle, while pavement responses such as stresses, strains, viscoelastic recovery behavior, and surface rutting were continuously monitored.
SMA behavior, as a viscoelastic material, demonstrated that the trailing axle always resulted in greater stresses and transverse strains. Transverse strain revealed the critical impact of trailing loads occurred before full pavement recovery and was stable throughout the APT continuous loading. Pavement recovery behavior was controlled by temperature and mixture characteristics. The recovery of SMAs was stable throughout the APT continuous loading.
Full-scale accelerated pavement testing confirmed that all SMA sections demonstrated excellent resiliency. SMAs incorporating local aggregates exhibited slightly higher early-stage densification and modestly greater damage rates than SMAs with imported aggregate. Results also showed strong agreement between laboratory Hamburg wheel-tracking test trends and full-scale rutting behavior.
Based on observed pavement responses and SMA properties, a rutting prediction model was developed incorporating SMA viscoelastic properties and aggregate quality. The model uses axle load and inverse of complex modulus as a surrogate representation of shear-induced flow responsible for permanent deformation. In addition, a parameter based on aggregate soundness test results captures mixture susceptibility to rutting.
Life-cycle assessment and life-cycle cost analysis conducted over a 50-year period indicated that aggregate transportation distance was a dominant contributor to environmental impacts. SMA incorporating locally sourced aggregates reduced several environmental impact indicators and achieved comparable life-cycle economic performance despite potential increased rehabilitation needs.