Concrete Mix Designs for O’Hare Modernization Plan

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Concrete Mix Designs for OHare Modernization Plan
University of Illinois Department of Civil and
Environmental Engineering
October 28, 2004
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Overview

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

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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

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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

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Airfield Concrete Mixes

• Past experience
• Future performance
• What do we expect out of the concrete mix?
• Short-term
• Long-term

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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

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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

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Airfield Concrete Integrated Materials and
Design Concepts

• Crack-free concrete (random)
• Increased slab size
• Optimal joint type
• Saw-cut timing guide
• Cost effective!

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Concrete Volume Stability Issues

• Early-age shrinkage
• Long-term shrinkage
• Tensile creep properties
• Effects of heat of hydration / environment

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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

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Early-Age Performance
Shen et al.
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Standard Concrete Shrinkage
Concrete shrinkage prism ASTM C157
Mortar Bar shrinkage ASTM C596
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Restrained shrinkage and creep test
Restrained Sample
Free Shrinkage Sample
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Typical Restrained Test Data
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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
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Measuring Internal RH

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

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Fracture vs. Strength Properties
MOR
Gf

• Peak flexural strength (MOR) same but fracture
  energy (Gf) is different
• Avoid brittle mixes

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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
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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)

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Joint Type Selection

• Are dowels necessary at every contraction joint?

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Aggregate Interlock Joint

• Dummy contraction joint
• No man-made load transfer devices
• Shear transfer through aggregate/concrete surface
  
• aggregate type and size joint opening

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Aggregate Interlock Joints

• Reduce number of dowels
• High load transfer efficiency if
• Minimize crack / joint opening
• Design concrete surface roughness

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Variation in Concrete Surface Roughness
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Concrete Fracture Energy Roughness
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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

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Saw-cut Timing and Depth

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

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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

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

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Other Brief Studies

• Fiber-Reinforced Concrete Pavements
• Shrinkage-Reducing Admixtures
• Others
• Concrete fatigue resistance
• ?

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Fiber-Reinforced Concrete Pavements

• Application of low volume, structural fibers

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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 (?)

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FRC Slab Testing
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Monotonic Load-Deflection Plot
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Load-Deflection Plot
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• Questions