Longitudinal Cracking in Concrete at Bridge Deck Dams on Structural Rehabilitation Projects.

摘要

The main objective of this project was to identify the causes of longitudinal cracking in newly placed concrete deck segments adjacent to bridge deck expansion dam rehabilitations within District 3-0 of the Pennsylvania Department of Transportation (PennDOT). This objective was accomplished through three tasks. (1) A literature review of the potential causes of early-age cracking in restrained concrete elements, including bridge deck dams and concrete repair sections, was conducted. This task also included a survey of bridge engineers in other PennDOT districts and several other state DOTs and municipalities with regard to concrete bridge deck rehabilitation operations and occurrence of concrete early-age cracking. (2) A review of current PennDOT specifications related to bridge deck construction and rehabilitation was undertaken. This task compared current PennDOT requirements regarding concrete materials, structural/ reinforcement design, and construction operations with the recommendations from the literature review and survey of other transportation agencies and, when needed, suggested modifications to the current PennDOT specifications. In addition, three past and two active bridge deck rehabilitation projects within PennDOT Districts 2-0 and 3-0 were reviewed and inspected to evaluate their compliance with existing PennDOT specifications and literature recommendations to eliminate early-age cracking. (3) A comprehensive experimental evaluation of the material properties of three concrete mixtures commonly used for PennDOT bridge deck projects was performed to evaluate the early- and long-term performance and the risk of cracking of these mixtures. The three mixtures included AAA, HPC, and AAA-P. The following main conclusions were drawn from Tasks 1, 2, and 3 of the project. (a) The most likely causes of early cracking observed in deck rehabilitation projects are inadequate moist curing and failure to properly eliminate plastic shrinkage cracking during construction. In several occasions, it was found that the existing PennDOT specifications for proper water curing of concrete and monitoring of ambient conditions to minimize the evaporation rate from the surface of fresh concrete were not correctly followed. (b) The review of the three past deck rehabilitation projects show that the design of shrinkage and temperature steel reinforcement had been adequate and should not result in early-age cracking. (c) The existing PennDOT concrete mixtures AAA, HPC, and AAA-P can yield adequate performance in the field, provided that they are placed, consolidated, and cured properly. (d) A number of suggested modifications to the current PennDOT specifications are included in this report to minimize the risk of early-age cracking in concrete bridge deck construction and rehabilitation projects.