Concrete Mix Designs for O’Hare Modernization Plan

1. Concrete Mix Designs for O’Hare Modernization Plan University of Illinois Department of Civil and Environmental Engineering October 28, 2004

2. Overview • Concrete Mix Design Team • Concrete Mix Design Objectives • Work Plan • Concrete mixes • Mechanical tests • Modeling • Other studies • Technical Notes

3. Concrete Mix Design Team • Prof. David Lange • Concrete materials / volume stability • High performance concrete • Prof. Jeff Roesler • Concrete pavement design issues • Concrete materials and testing

4. Graduate Research Assistants • Cristian Gaedicke • Concrete mix design / fracture testing • Sal Villalobos • Concrete mix design and saw-cut timing • Rob Rodden • testing, instrumentation, shrinkage • Zach Grasley • Concrete volume stability • C.J. Lee • FE modeling

5. Airfield Concrete Mixes • Past experience • Future performance • What do we expect out of the concrete mix? • Short-term • Long-term

6. Concrete Mix Objectives • Durable Concrete (Prof. Struble) • Early-age crack resistance • environment / materials / slab geometry • Long-term crack resistance & joint performance • environment / materials / slab geometry • aircraft repetitive loading

7. Concrete Mix Design Variables • Mix proportions • Strength Criteria • Modulus of rupture*, fracture properties • Shrinkage Criteria • Cement, aggregate effect • Aggregate • Type, size, and gradation • Admixtures • Chemical and mineral • FRC

8. Airfield Concrete Integrated Materials and Design Concepts • Crack-free concrete (random) • Increased slab size • Optimal joint type • Saw-cut timing guide • Cost effective!

9. Concrete Volume Stability Issues • Early-age shrinkage • Long-term shrinkage • Tensile creep properties • Effects of heat of hydration / environment

10. Early-Age Shrinkage • Early age cracking is a growing concern • Shrinkage drives cracking • Creep relaxes stress and delays cracking • Modeling of early age concrete in tension is needed to predict cracking • Effects of mix constituents & proportions

11. Early-Age Performance Strength Temperature Total (Temp+Shrinkage) 500 Shrinkage & Creep 400 Strength or Stress (psi) 300 200 100 0 -100 0 1 2 3 4 5 6 7 Time (days) Shen et al.

12. Standard Concrete Shrinkage Concrete shrinkage prism ASTM C157 Mortar Bar shrinkage ASTM C596

13. Restrained shrinkage and creep test Restrained Sample Free Shrinkage Sample

14. Typical Restrained Test Data Creep Cumulative Shrinkage + Creep

15. Curling of Concrete Slabs PCC slab subgrade High drying shrinkage Low drying shrinkage Ttop < Tbottom sh,top < sh,bottom Dry Trapped water High moisture Ttop > Tbottom RHtop < RHbottom

16. Measuring Internal RH • A new embedded relative humidity measurement system has been developed at UIUC

17. Fracture vs. Strength Properties Brittle s Tough / ductile Deflection MOR • Peak flexural strength (MOR) same but fracture energy (Gf) is different • Avoid brittle mixes Gf

18. Increased Slab Size 25 ft x 25 ft slabs = 6 paving lanes • Benefits • Less saw-cutting and dowels • Increased construction productivity • Less future maintenance 18.75 ft x 20 ft slabs = 8 paving lanes

19. Requirements for Slab Size • Pavement Analysis • Curling stresses  moisture and temperature • Airfield load effects • Base friction • Joint opening • Concrete Mix Needs • Minimize concrete volume contraction • Larger max. size aggregates • Concrete strength and toughness (fibers)

20. Joint Type Selection h • Are dowels necessary at every contraction joint?

21. Aggregate Interlock Joint • Dummy contraction joint • No man-made load transfer devices • Shear transfer through aggregate/concrete surface • aggregate type and size; joint opening

22. Aggregate Interlock Joints • Reduce number of dowels • High load transfer efficiency if… • Minimize crack / joint opening • Design concrete surface roughness

23. Variation in Concrete Surface Roughness

24. Concrete Fracture Energy & Roughness

25. Concrete Surface Roughness • Promote high shear stiffness at joint • High LTE • Larger and stronger aggregates • Increase cyclic loading performance • Predict crack or joint width accurately

26. Saw-cut Timing and Depth a d • Notch depth (a) depends on stress, strength, and slab thickness (d) • Stress = f(coarse aggregate,T, RH)

27. Requirements for Saw-cut Timing Stress Strength s • Stress = f(thermal/moisture gradients, slab geometry, friction) • Strength (MOR,E) and fracture parameters (Gf or KIC) with time Time

28. Common Strength Tests Compressive strength and Concrete elastic modulus 3rd Point Loading (MOR)

29. Concrete Mix Design • Minimum strength criteria (MORmin) • Minimum fracture energy (Gf) • Max. concrete shrinkage criteria (sh) • Aggregate top size (Dmax) • Strong coarse aggregate (LA Abrasion) • Slow down hydration rates and temperature

30. Other Brief Studies • Fiber-Reinforced Concrete Pavements • Shrinkage-Reducing Admixtures • Others • Concrete fatigue resistance • ?

31. Fiber-Reinforced Concrete Pavements • Application of low volume, structural fibers

32. Benefits of FRC Pavements • Increased flexural strength and toughness • Thinner slabs • Increased slab sizes • Limited impact on construction productivity • Limits crack width • Promotes load transfer across cracks (?)

33. FRC Slab Testing

34. Monotonic Load-Deflection Plot

35. Load-Deflection Plot

36. Questions