Analysis and Estimation of Effective Built-In Temperature Difference for North Tangent Slabs: Data Analysis from the Palmdale, California Rigid Pavement Test Site

As part of the California Department of Transportation (Caltrans) Long Life Pavement Rehabilitation Strategies (LLPRS), a high early strength hydraulic cement was field tested using the Heavy Vehicle Simulator (HVS). This fast-setting hydraulic cement concrete (FSHCC) was designed to gain enough strength to allow it to be opened to traffic within 4 hours of placement. The objective of the HVS tests was to evaluate the performance of this concrete under the influence of simulated loads along with pavement design features such as dowels, tied concrete shoulder, and a wide truck lane that had not previously been implemented in California.Two full-scale test pavements, each approximately 700 ft. (215 m) in length, were constructed on State Route 14 about 5 miles (8 km) south of Palmdale, California using FSHCC. The South Tangent was constructed along State Route 14 southbound and was used to conduct a fatigue evaluation of the FSHCC with three thicknesses of PCC [4, 6, and 8 in. (100, 150, and 200 mm)]. The North Tangent test sections, constructed on State Route 14 northbound, were 8-in. (200-mm) nominal thickness PCC over a 4-in. (100-mm) nominal thickness cement-treated base and included several design features: asphalt concrete shoulders, PCC shoulders with dowels, and widened lanes with dowels). Design details of these sections are outlined in Roesler et al. and in du Plessis.(1, 2) These sections were constructed and evaluated using the HVS over a 2-year period.Prior to fatigue testing of these slabs, many of them were monitored over 24-hour cycles without any applied load (with and without a temperature control box). The slabs were also monitored over 24-hour cycles under the influence of 9,000-lb. (40-kN) dual-wheel rolling load (with and without a temperature control box). These sections were also loaded from 4,500 lb. to 18,000 lb. (20-80 kN), in increments of 2,250 lb. (10 kN) using the HVS dual-wheel rolling load within 1 to 2 hours and with the temperature control box. All loads were applied bi-directionally at low speeds [approximately 6 MPH (10 km/h)].This report presents analyses of the daily movement of the slabs observed over 24-hour cycles, particularly corner and edge deflections under the loaded and unloaded condition, with and without the temperature control box, and uses them to evaluate curling in the slab and estimate the effective built-in temperature difference in the slab. For analysis purposes, particularly in estimation of stresses, damage, and cracking, this effective built-in temperature difference in the slab can be used to represent the combined effects of nonlinear built-in temperature gradients, irreversible shrinkage, and creep.