Concrete Mix Designs for O

1
Concrete Mix Designs for OHare 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
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
15
Curling of Concrete Slabs
PCC slab
subgrade
High drying shrinkage
Low drying shrinkage
Ttop lt Tbottom
?sh,top lt ?sh,bottom
Dry
Trapped water
High moisture
Ttop gt Tbottom
RHtop lt RHbottom
16
Measuring Internal RH

• A new embedded relative humidity measurement
  system has been developed at UIUC

17
Fracture vs. Strength Properties
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

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?

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)

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