PERFORMANCE EVALUATION OF CONCRETE PAVEMENT OVERLAYS. FINAL REPORT

Two 7-in. reinforced, unbonded, and dowelled concrete overlays were constructed in 1984. One is located on US 23 at Dundee and one on I-96 at Portland. Both overlays are separated from the underlying pavement by a 3/4-in. sand-asphalt layer, and both have reinforced concrete shoulders. The original pavement on US 23 is a reinforced jointed pavement placed in 1959-61. It was in relatively poor condition when overlaid. Portions of the I-96 pavement, placed in 1958, are continuously reinforced and were sawed into 100-ft slabs to reduce the movement at previously placed repairs. The conventionally reinforced portions of the pavement were in reasonably good condition prior to overlaying. Four-inch edge drains with filter-sock were installed on both projects. Observations, measurements, examination of cores, and load tests indicate that the overall performance of the 1984 overlays to date has been satisfactory. Substantial variation in joint movements indicate that the bituminous debonding layer does not allow total independent movement in the two concrete layers. Coring through cracks in the overlay, coupled with location measurements of cracks or joints in the two concrete layers, shows that the cracks in the overlay are likely to be located near or at cracks or joints in the original pavement beneath. Cores removed from joints in the overlay revealed no deterioration where the concrete is in contact with the impermeable bituminous layer. Load testing with a Falling Weight Deflectometer showed a 29% increase in load transfer efficiency at joints and a 25% decrease in mid-slab deflection in the overlays as compared to an adjacent 9-in. recycled pavement placed on a 4-in. open graded drainage base. It is estimated that using an overlay instead of recycling will result in at least a $35,000 savings per mile of two-lane pavement. Field and laboratory data indicate that overlays will have a favorable life cycle cost compared to recycled pavements.