Performance of Aggregate Subgrade Layers in Low Volume Roads Constructed with Unconventional Recycled Aggregates

With transportation sector accounting for approximately 27% of total greenhouse gas emissions, transportation agencies all over United States have made sincere efforts to reduce such carbon footprint by incorporating more recycled materials in design mixes. In Illinois, recycled materials commonly include large sized unconventional aggregates used to stabilize weak subgrade soils that are abundantly found in wet of optimum conditions and prone to frost effects. To facilitate increased use of such “aggregate subgrade” materials, IDOT has recently introduced new gradation bands. However, performance of such recycled aggregate subgrade materials within the bounds of current design framework is largely unknown. To this end, a full scale accelerated pavement test study was undertaken to study six different aggregate subgrade materials involving construction of twelve full scale flexible pavement sections over weak engineered subgrade. Results of accelerated pavement testing on six test sections and performance of three different aggregate subgrade materials are highlighted in this paper including data from quality control tests such as nuclear density gauge, GeoGauge for composite layer modulus, and lightweight and falling weight deflectometers. Current pavement design framework was adequate when designing with two out of three aggregate subgrade materials that constituted different proportions of recycled materials. One noteworthy finding was that as-constructed hot mix asphalt thickness variation was found to be quite large due to reclaimed asphalt pavement subbase sinkage observed during paving operations