Paper by Somayeh Nassiri and Julie M. Vandenbossche from 10th ICCP Quebec 2012
Jointed plain concrete pavements curl due to temperature gradients and warp in the presence of drying shrinkage gradients. Since this deformation is restrained by factors, such as the slab self-weight, tensile stresses are generated. Slabs do not remain flat in the absence of daily gradients. This is due to the presence of permanent gradients in the slab. A portion of the permanent gradients is the temperature gradient that exists in the slab at the zero-stress time. The gradient present at the zero-stress time, known as built-in, locks into the slab, shifting the curling due to transient gradients up or down. The other component included in the built-in gradient is the permanent warp that develops due to irreversible drying shrinkage. The built in gradient is reduced over time due to creep. A procedure is established in the study for defining the built-in gradient in the slab. First, the zero-stress time is established, so that the built in temperature gradient can be identified. This is performed using the data from four instrumented pavement sections in Western Pennsylvania. A temperature/hydration model is used to predict the temperature and degree of hydration within the pavement structure based on the ambient temperature and concrete mixture design. Next, the component of the built-in gradient attributed to irreversible drying shrinkage is determined. This is achieved by using long-term strain measurements in an instrumented pavement section in Pennsylvania, as well as two instrumented sections at the Minnesota Road Research Facility (MnROAD). The unrestrained drying shrinkage is then predicted using a numerical relative humidity model. The difference between the predicted and measured drying shrinkage is attributed to the effects of creep and base restraints. The temperature gradient at the zero-stress time is then added to the irreversible drying shrinkage component to obtain the total built-in gradient. Demonstration for ISCP Board only.