Effects of paving conditions on built-in curling and pavement performance

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Abstract
The effective temperature difference between the slab's top and bottom at time of final set is an important input parameter for the recently developed mechanistic-empirical pavement design guide (M-EPDG). However, very limited guidelines are available for the selection of this parameter. The major focus of this work is to quantify built-in curl from field temperature measurements for Michigan pavements. The results of this study show that built-in curl can be substantial for hot weather paving conditions. Early morning paving on a sunny summer day allows a maximum positive (i.e. top warmer than bottom) temperature difference at time of final set due to maximum heat of hydration and added solar radiation effects. The temperature difference between the slab's top and bottom was found to be 10–12°C. Consequently, the slab stays flat and in full contact with the base from this time only if this range is maintained. Unfortunately, this only occurs for a short time-period near mid-day, so the slab is mostly in a permanently upward curled condition. For late fall temperature conditions, the difference was slightly negative (about − 2°C) at time of set. Late fall construction therefore is favorable for maintaining slab–base contact. Despite combined built-in curl and daily curling changes, slab stress predictions using finite element analysis (ISLAB2000) for multi-axle loading at joints found the total stresses for a typical summertime 24 h period to be below the tensile stress necessary to initiate fatigue failure (i.e. below 45% of the flexure strength). This suggests that additional slab uplift from moisture warping is a factor for top–down cracking to develop.

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