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
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
-100
100
200
300
400
500 1 2 3 4 5 6 7
Strength
Temperature
Shrinkage & Creep
Total (Temp+Shrinkage)
Strength or Stress (psi)
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
Comprehensive program at U of I on restrained shrinkage for past 5 years.
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
Ttop < Tbottom
Low drying shrinkage
sh,top < sh,bottom
Dry
Ttop > Tbottom
Trapped water
High moisture
RHtop < RHbottom

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

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

18. Increased Slab Size Benefits Less saw-cutting and dowels
Increased construction productivity
Less future maintenance
25 ft x 25 ft slabs = 6 paving lanes
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 Are dowels necessary at every contraction joint?h

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
Notch depth (a) depends on stress, strength, and slab thickness (d)
Stress = f(coarse aggregate,T, RH) d a

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