Construction and Preliminary HVS Tests of Pre-Cast Concrete Pavement Slabs

This report presents the details on the construction and preliminary load tests on an experimental pavement comprised of ten pre-cast slabs of the pavement known as the Super-Slab® System, installed at the intersection of I-15 and SR210, in San Bernardino County in southern California. The construction of the test section consisted of: (a) Construction of a cement-treated base (CTB), (b) Preparation of a sand bedding layer, (c) Placement of the pre-cast slabs, (d) Application of grout materials for the bedding and for the dowel/tie bars, (e) Diamond grinding the test pads, (f) Filling the joints, and (g) Construction of an asphalt concrete shoulder. Subgrade evaluation was carried out with a dynamic cone penetrometer (DCP) and indicated a strong granular subgrade, with CBR (California Bearing Ratio) between 45 and 80. Average backcalculated elastic modulus for the CTB was about 2,200 MPa (tested on the pre-cast panels) and presented great variation. Subgrade modulus was 70 MPa (tested on CTB, consistent with results of testing on pre-cast panels). FWD testing showed deflections of 0.3 to 0.6 mm on the slabs, which after grouting were reduced to approximately 0.2 mm. The backcalculated elastic modulus of the concrete was found to be between 19,000 and 23,500 MPa (after grouting, averaging morning, and afternoon FWD data). Load Transfer Efficiency (LTE) values in the range of 5% to 40% were observed before grouting, and consistently near 100% after grouting, revealing that the grouting process mobilized the dowel bars so that they provided effective LTE. The materials used for the dowel grout and for the bedding grout showed flexural strengths at 28-days of 5.1 and 1.7 MPa, respectively. The slabs were instrumented with displacement sensors (vertical and horizontal) and with thermocouples. Thermal deformations were collected, and revealed that the slab curl reduced from a range of ±1.5 mm before grouting to ±0.5 mm after grouting. The responses to traffic load also improved greatly after grouting. The wheel-induced deflections at the transverse joint decreased to one-quarter of the initial value at the standard load of 60kN (from about 1.0 mm to 0.25 mm). Rocking of the slabs, present before grouting, was also eliminated by grouting. Two HVS tests were performed on the ungrouted slabs and indicated that the Super-Slab® System is able to withstand at least 86,500 ESALS in the ungrouted condition. This test was intended to simulate placement of the slabs without grouting during one nighttime closure, and then grouting the slabs during the next nighttime closure 24 hours later.