Control of Early Cracking of Concrete Bridge Decks (Compaction and Durability of Concrete)

1. 29th September 2005 Control of Early Cracking of Concrete Bridge Decks (Compaction and Durability of Concrete) Presenter: Taha Ahmed, Project Engineer, Bridge Maintenance & Rehabilitation Methods RTA Bridge Technology Section Australian Small Bridges Conference 2005

2. Control of Early Cracking of Concrete Bridge Decks - A Case Study Contents • Background • Concrete cracking – causes and consequences • Early cracking – mitigation strategies • Case study – Four Mile Creek Bridge • Description of the bridge • Construction practices adopted • Instrumentation and data logging • Data analysis and deck inspections • Conclusions

3. Control of Early Cracking of Concrete Bridge Decks - A Case Study Background Bridge Over Plain Creek, 22 km NE Dubbo, Golden HWY

4. Control of Early Cracking of Concrete Bridge Decks - A Case Study Background Macksville Bridge Over Nambucca River 52.49 km N Kempsey

5. Control of Early Cracking of Concrete Bridge Decks - A Case Study Background • Cracks diminish durability & structural integrity • Cracking commences within first few days • Visible cracks in concrete decks within first year • Early cracking is the single most prevalent problem • Many RTA controlled bridges suffer deck cracking • 100,000 bridges suffer early deck cracking in USA • RTA requires deck waterproofing & surfacing

6. Control of Early Cracking of Concrete Bridge Decks - A Case Study Concrete Cracking • Main causes of cracking • Physical changes (temperature and moisture) • Structural loadings • Chemical reactions • Main components of early cracking : • Plastic settlement • Plastic shrinkage • Thermal shrinkage

7. Control of Early Cracking of Concrete Bridge Decks - A Case Study Early Cracking – Mitigation Strategies • Concrete mix design (mix engineer) • W/c and cement content/type • Aggregate type and size • Supplementary cementitious materials • Structural design (design engineer) • End restraint and support stiffness • Deck reinforcement and thickness • Bridge articulation • Construction practices (contractor/ project manager) • Compaction/ finishing/curing • Control of rates of heating/cooling & evaporation

8. Control of Early Cracking of Concrete Bridge Decks - A Case Study Description of the 4 Mile Creek Bridge

9. Control of Early Cracking of Concrete Bridge Decks - A Case Study Construction Practices - 4Mile Creek Bridge • Control concrete placement and compaction •  Prior placement and curing of shear keys • Attention to construction joints • Use of vibrating screed • Continuous steel bull floating before broom finish • Protection of fresh concrete from evaporation • Wet-cure deck by soaker hoses over hessian • Apply thermal insulation • 60 mm Glasswool Anticon roofing blanket (foil side upward) • Two 0.3 mm black polyethylene sheets

10. Control of Early Cracking of Concrete Bridge Decks - A Case Study Construction Practices - 4Mile Creek Bridge • Four Mile Creek Bridge

11. Control of Early Cracking of Concrete Bridge Decks - A Case Study Instrumentation - 4Mile Creek Bridge • Thermocouples • 22 k-type wire thermocouples (+/- 1C) • 6 locations, top & bottom reo • Two locations with temperature profile • Strain gauges • 12 Vishay EGP-120 wire resistance (+/-10ms) • 6 locations, top & bottom reo • Dataloggers • 2 Series 3 DataTakers • Instrumentation box

12. Control of Early Cracking of Concrete Bridge Decks - A Case Study Instrumentation - 4Mile Creek Bridge

13. Instrumentation - 4Mile Creek Bridge

14. Control of Early Cracking of Concrete Bridge Decks - A Case Study Data Analysis - 4Mile Creek Bridge • Temperature monitoring • Placement temp. was 11C ( 20/5.5C max/min) • RH 77%, no wind speed recorded (calm) • Following two days temps were 20/4.5 C &17/8C • Average temp over 7 days was 17/6.5C. • Max rise in deck temp 11C at 12 hrs • Max temp difference in deck 4C at 12 hrs • Deck temp almost uniform, 19C at 7 days • Max gradient in planks 14C at 12hrs, 6C at 48hrs almost zero at 7 days

15. Control of Early Cracking of Concrete Bridge Decks - A Case Study Temperature monitoring

16. Control of Early Cracking of Concrete Bridge Decks - A Case Study Temperature monitoring

17. Control of Early Cracking of Concrete Bridge Decks - A Case Study Temperature monitoring

18. Control of Early Cracking of Concrete Bridge Decks - A Case Study Temperature monitoring

19. Data Analysis - 4Mile Creek Bridge • Strain monitoring • Strains recorded at top and bottom reo only • Strains were negative, i.e. shrinkage • Strains peaked to 150 ms at 24 hrs • Successive peaks at noon gradually decreasing • Max strain of 80 ms at 7days • Strain gradient, top and bottom, 30 ms at 48hrs • Strain gradient insignificant at 7 days

20. Control of Early Cracking of Concrete Bridge Decks - A Case Study Strain monitoring

21. Control of Early Cracking of Concrete Bridge Decks - A Case Study Strain monitoring

22. Control of Early Cracking of Concrete Bridge Decks - A Case Study Strain monitoring

23. Control of Early Cracking of Concrete Bridge Decks - A Case Study Strain monitoring

24. Data Analysis - 4Mile Creek Bridge • Crack monitoring • No visible cracks at 7 days • No visible cracks at “28” days • Link slab cracks of 0.12 mm at 4 months • <0.025 cracks in deck outside link slabs

25. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 7 Days

26. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 28 Days

27. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 28 Days

28. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 28 Days

29. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 4 Months Crazing in Span 1 < 0.025 mm Longitudinal crack 0.05 – 0.075 mm in Span1-Span2 Infill Longitudinal Crack 0.025 mm in Span1

30. Control of Early Cracking of Concrete Bridge Decks - A Case Study Crack monitoring – 4 Months Longitudinal Crack 0.05 – 0.075 mm in Span2-Span3 Infill Longitudinal Crack <0.025 mm in Span 2 Longitudinal Crack 0.1 – 0.12 mm in Span2 –Span 3 Infill

31. Control of Early Cracking of Concrete Bridge Decks - A Case Study Conclusions • Bridge Technology’s construction practices adopted have alleviated early deck cracking. • Further refinement of construction practices is required especially the way link slabs are constructed. • Further refinement of bridge design is required