Built-in negative temperature gradients from hot weather construction have the effect of shifting the entire temperature gradient distribution such that the slab is predominantly upward curled. This condition in turn greatly increases loss of slab support, which was the major factor promoting premature top-down midslab transverse cracking for a jointed plain concrete pavement (JPCP) Interstate project in southeastern Michigan. Finite element analysis predicts that loss of slab support, maximum at the joints, shifts the maximum stress during truck loading at the joints toward midslab in JPCP, coinciding with maximum curling stresses. A built-in upward-curled slab condition was quantified from joint corner deflections and slab temperature measurements. Slab surface elevation profiling using the dipstick device verifies that these slabs are permanently upward curled and that loss of joint support is a function of daily changes in slab surface temperature. Detailed falling-weight deflectometer slab deflection profiles show that loss of slab support along the outer edge for this project exceeds 800 microns at the joint during morning temperature conditions typical for summer and fall in Michigan, corresponding to a nearly fivefold increase in outer edge joint deflection as measured during the afternoon, during which time the slab is in full contact with the base. The loss of slab support extends inward toward the slab middle, creating a "rocking chair" condition typical for short slab behavior, which allows the slab to rock if loaded only at one joint. This condition is underscored by field observations. During morning and evening testing, when the pavement surface was cooler, there was a noticeable rocking sensation at the joints when loaded trucks passed in the adjacent lane. Later in the afternoon, after the pavement temperature rose, the movement stopped.
Abstract