Removing Obstacles for Pavement Cost Reduction by Examining Early Age Opening Requirements: Material Properties

The risk of cracking in a concrete pavement that is opened to traffic at early ages is related to the maximum tensile stress that develops in the pavement and its relationship to the measured, age dependent, flexural strength of a beam. The stress that develops in the pavement is due to several factors including traffic loading and restrained volume change caused by thermal or hygral variations. The stress that develops is also dependent on the time-dependent mechanical properties, pavement thickness, and subgrade stiffness. There is a strong incentive to open many pavements to traffic as early as possible to allow construction traffic or traffic from the traveling public to use the pavement. However, if the pavement is opened to traffic too early, cracking may occur that may compromise the service life of the pavement. The purpose of this report is two-fold: 1) to examine the current opening strength requirements for concrete pavements (typically a flexural strength from beams, and 2) to propose a criterion based on the time-dependent changes of ratio of the tensile stress to the flexural strength, which accounts for pavement thickness and subgrade stiffness without adding unnecessary risk for premature cracking. An Accelerated Pavement Testing, APT, facility was used to test concrete pavements that are opened to traffic at an early age to provide data that can be compared with an analytical model to determine the effective ratio of the tensile stress to the flexural strength based on the relevant features of the concrete pavement, the subgrade, and the traffic load. It is anticipated that this type of opening criteria can help the decision makers in two ways: 1) it can open pavement sections earlier thereby reducing construction time and 2) it may help to minimize the use of materials with overly accelerated strength gain that are suspected to be more susceptible to develop damage at early ages than materials that gain strength more slowly