Crack Control in Toppings for Precast Flat Slab Bridge Deck Construction

The Florida Department of Transportation (FDOT) has experienced problems with reflective cracking in the topping of some precast flat slab bridges. The cracking usually occurs over the joint between the precast panels on which the topping is placed, hence the term reflective cracking. This research project evaluated techniques for improving crack control in these toppings. Four full-scale bridge superstructures were constructed to evaluate steel fibers, synthetic fibers, steel/synthetic fiber blend, carbon fiber reinforced composite (CFRP) grid, and shrinkage reducing admixture. Each superstructure was composed of three 4-ft x 30-ft precast flat slabs with a 6 in. concrete topping. The toppings were visually monitored for 30 weeks for crack formation. Load tests were also performed on each of the specimens. Insufficient tensile stresses from drying shrinkage were generated in the toppings to induce cracking. One possible explanation is that the placement and curing were conducted in relatively ideal conditions which contributed to the lower shrinkage strains. Another is that the slabs were constructed in the very humid summer months in which ambient humidity was at 80% or above, providing improved curing conditions over that which might occur in the dryer winter months. Yet another is that these specimens were not as wide as is generally seen in the bridges where reflective cracking has been observed. It is suspected that a wider cross-section would lead to more lateral restraint in the center of the cross-section. Modulus of elasticity and tensile strength were unaffected by the crack control treatments used in this research. In both the restrained ring and load test the all steel fiber (STL) topping provided nearly an order of magnitude reduction in crack widths. The CFRP grid (GRD) topping reduced the crack widths in the load test by a factor of two. In the restrained ring test the blended fiber (BND) and all synthetic fiber (SYN) toppings reduced crack widths by a factor of four. In the load test, BND and SYN toppings reduced the crack widths by a factor of two. The topping with shrinkage reducing admixture (SRA) reduced crack widths in the restrained shrinkage tests by a factor of seven.

• Record URL:
  https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/research/reports/fdot-bd545-09-rpt.pdf
• 
• Summary URL:
  https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/research/reports/fdot-bd545-09.pdf
• Corporate Authors:

  University of Florida, Gainesville

  Department of Civil and Coastal Engineering
  Gainesville, FL  United States  32611-6580

  Florida Department of Transportation

  Structures Research Center, 605 Suwannee Street
  Tallahassee, FL  United States  32399
• Authors:
  • Alfonso, Lazaro
  • Cook, Ronald A
  • Hamilton, H R
• Publication Date: 2006-3

Language

• English

Media Info

• Media Type: Web
• Edition: Final Report
• Features: Appendices; Figures; Photos; References; Tables;
• Pagination: 120p

Subject/Index Terms

• TRT Terms: Admixtures; Bridge decks; Bridge superstructures; Concrete; Concrete curing; Construction; Cracking; Fiber composites; Humidity; Load tests; Modulus of elasticity; Precast concrete; Reflection cracking; Shrinkage; Steel fibers; Synthetic fibers; Tensile strength
• Subject Areas: Bridges and other structures; Construction; Highways; I53: Construction of Bridges and Retaining Walls;

Filing Info

• Accession Number: 01025867
• Record Type: Publication
• Report/Paper Numbers: UF Project No. 00030907
• Contract Numbers: BD545, RPWO# 9
• Files: TRIS, STATEDOT
• Created Date: Jun 27 2006 10:26AM