<p><p><h2>Project Summary/Scope:</h2>Nine low-volume flexible pavement sections were constructed at the Advanced Transportation Research and Engineering Laboratory (ATREL) at the University of Illinois, Urbana-Champaign (UIUC). The nine sections were divided into three categories based on the total thickness of the pavement system structure. The first category has 8 inches of aggregate base and 3 inches of Hot-Mix Asphalt (HMA). The three sections in that category differ in aggregate reinforcement: one control and two reinforced with geogrids having different tensile strengths. The second category has a 15-inch pavement structure. Two sections were unreinforced, while one was reinforced with geogrid. One of the unreinforced sections has 5 inches of HMA and a 10-inch aggregate base. The remaining two sections have a 12-inch aggregate base and 3 inches of HMA.</p><p>Subsurface Conditions: Illinois CA-6 granular material, a typical dense-graded unbound base layer, was used as the base. The 5-inch thick HMA consisted of a 3-inch SM-9.5 surface mix and a 2-inch BM-25.0 base mix. All HMA layers used PG 64-22 binder. Every attempt was made to maintain the subgrade California Bearing Ratio (CBR) at 4%; however, strength measurements after construction indicated a somewhat variable subgrade condition. A predetermined water volume was added to the subgrade and thoroughly mixed to achieve the target CBR prior to fine grading.</p><p>The construction materials used in this study are in accordance with Illinois Department of Transportation specifications. After completion of the subgrade construction, the layer was instrumented with vertical Linear Variable Differential Transformers (LVDTs), pressure cells were placed at the top of the subgrade, and piezometers and thermocouples were placed at different depths below the surface. Time-Domain Reflectometry (TDR) probes were placed horizontally and vertically to monitor moisture content changes. Base layer instruments were at the top of subgrade. Vertical and lateral deflections at the bottom of base layer were also measured. The rest of the instruments were placed after the aggregate layer was laid. The HMA was placed in two lifts for the 3-inch thick sections and in three lifts for the 5-inch sections.<br><h2>Performance Monitoring:</h2>Material density and moisture content were monitored regularly throughout construction using a nuclear gauge and Dynamic Cone Penetrometers (DCP). 6-inch diameter drainage pipes were installed between the cells to divert water to edge drains. Two edge drains were placed at both sides of the sections to remove water. Transverse and longitudinal drainage pipes were installed along the section edges and the transition zones. An emulsion tack coat was applied at a specific application rate after the completion of the subgrade preparation to maintain the water content of the subgrade.</p><p>Temperature, moisture, and pore water pressure were measured at regular intervals. The effects of speed, load, tire pressure, and tire type on the reinforcement effectiveness were investigated. Preliminary results from response testing suggest that these pavement sections, reinforced with geogrid and constructed on low CBRs, exhibited less tensile strain at the bottom of HMA, less vertical pressure at the top of base layers, and less vertical deflections at the subgrade layers when tested at low speed.<br><h2>Case History Author/Submitter:</h2>Imad L. Al-Qadi, PhD, PE<br>Founder Professor of Engineering<br>Department of Civil Environmental Engineering<br>University of Illinois at Urbana-Champaign<br>205N. Mathews Ave., MC-250<br>Urbana, IL 61810<br>email: alqadi@uiuc.edu<br><h2>Project Technical Paper:</h2>Al-Qadi, I.L., Tutumluer, E., and Dessouky, S. (2006). “Construction and instrumentation of full-scale geogrid-reinforced flexible pavement test sections.” Airfield and Highway Pavements Specialty Conference, Atlanta, pp. 131-142.<br><h2>Date Case History Prepared:</h2>November 2012</p></p>