MEMBRANE TECHNIQUE FOR CONTROL OF EXPANSIVE CLAYS

Much northeastern Arizona highway is built on expansive clay. Changes in the moisture content of these clay subgrades cause volume changes that in turn cause excessive pavement deterioration and thus affect safety. During initial construction, a variety of experimental sections were built to test such stabilization methods as moisture and compaction control, chemical admixtures, electro-osmosis, overexcavation, ditch widening, underdrains, and membranes, alone or combined. Some methods were relatively successful when compared to the rapid deterioration of the untreated highways. These findings led to choosing impermeable rubber membranes to control moisture in the clay subgrades. The first trial of the technique at full contract scale was an 18-km (11-mile) overlay on I-40 completed in 1975. After the slopes were flattened for safety, the roadway prism under the asphalt concrete overlay and down the shoulder slopes was covered with the asphalt-rubber membrane. The control section was an adjacent overlay of the same design but with no membrane. In 1976, a 5-km (3-mile) overlay on US-89 with asphalt-rubber membranes and shoulder and ditch paving was constructed. This report presents the data on the three full-scale overlays on the success of the membrane. /Authors/