Methodology for determining the timing of saw cutting in concrete pavements

Stresses develop in portland cement concrete pavements (PCCP) shortly after placement when the volume changes associated with temperature change, moisture loss, or chemical reaction are restrained. These stresses may become large enough to cause microcracking around the aggregates or random cracking through the depth of the pavement. To reduce the potential for microcracking and to control crack formation, saw cuts are placed in PCCP shortly after placement. Although the idea of saw cutting is relatively straightforward, determining the timing of the saw cut can be complicated. Sawing too early can result in raveling, whereas sawing too late can result in microcracking or random cracking. Even though saw cutting is done on a daily basis in practice, the timing of saw cut placement is often determined based only on the saw cutting operator's experience. Opportunities exist to provide construction crews with more reliable methods to determine when the cut should be placed. This study introduces a method to determine the timing of saw cutting based on the concrete strength and the stress that develop. Toward this end, a strength reduction factor was introduced. A finite element model was used to determine the influence of a variety of factors, including material properties (e.g., strength, elastic modulus, moisture migration, heat capacity), environmental conditions (relative humidity and wind speed), and geometric factors (pavement thickness and crack depth), on the behavior of concrete pavements. The introduction of the saw cut and the development of a localized crack are discussed. The implications of construction variability are also discussed.