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Evaluation of Long-term Strength and Durability Properties of Pre-stressed Concrete Girders with Microcracking

The presence of unexplained surface microcracks in several in-service prestressed girders across Texas led to concerns of reduced service life due to loss in long-term strength and durability. This project was designed to estimate both this potential loss in service life and the likelihood of long-term strength and durability issues that might arise due to the presence of these microcracks. Measurements of crack width, strain, stiffness and resistivity were taken from full-scale in-service and overcast or rejected girders over two years. Cores were collected from the overcast girders for further laboratory investigation of cracking, strength, stiffness, and durability properties. While the girders exhibited an increase in cracking and shrinkage, they have not shown a significant loss in strength, stiffness, and durability due to the presence and temporal growth of the microcracks. Exposure to environment and presence of pre-existing cracks were major factors affecting the rate of increase in cracking, while external loading was not. This temporal data was used to generate an empirical model to estimate the remaining service life of the girders using non-destructive test measurements as input variables. The model had a regression coefficient and reliability index in the “Good” range, and an error of 359 days. Laboratory specimens were cast to determine a critical cracking index value of 18 mm/m (0.5755 in./yd). The empirical model under-predicted service life by 4–10 years for all girders when compared to Life-365®. As these girders are designed for a service life of 75 years, the present rate of growth in microcracking can reduce the service life of the in-service girders from 2 to 13 years depending on the girder and nature of cracking. Further reduction in service life is also possible under fatigue loading as the girders age. Thus, continuous monitoring of the girders, especially in the last two decades of the girders’ lives, is recommended. In addition, the behavior of these girders with surface microcracks under marine exposure was observed to determine the effect of the microcracks on chloride-induced corrosion. Exposure to the simulated marine environment led to the formation of microcracks in the low water-cement ratio concrete specimens. However, the presence of microcracks did not significantly impact corrosion potential in the timeframe of the study. A novel approach using guided ultrasonic waves and acoustic emission to monitor corrosion process in prestressing strands was explored, with encouraging results. Further research should explore the key parameters that can influence corrosion monitoring using guided ultrasonic waves and to determine the efficacy of using the guided wave ultrasonic method as part of the maintenance program.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 259p

Subject/Index Terms

Filing Info

  • Accession Number: 01755269
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/TX-20/0-6922-1, 0-6922-1
  • Contract Numbers: 0-6922
  • Files: NTL, TRIS, ATRI, USDOT, STATEDOT
  • Created Date: Oct 23 2020 5:36PM