Transcript Document

Concrete Mix Designs for
O’Hare Modernization Plan
University of Illinois
Department of Civil and
Environmental Engineering
October 28, 2004
Overview
 Concrete Mix Design Team
 Concrete Mix Design Objectives
 Work Plan
•Concrete mixes
•Mechanical tests
•Modeling
•Other studies
 Technical Notes
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
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
Airfield Concrete Mixes
Past experience
Future performance
What do we expect out of the concrete mix?
Short-term
Long-term
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
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
Airfield Concrete Integrated
Materials and Design Concepts
Crack-free concrete (random)
Increased slab size
Optimal joint type
Saw-cut timing guide
Cost effective!
Concrete Volume Stability Issues
Early-age shrinkage
Long-term shrinkage
Tensile creep properties
Effects of heat of hydration / environment
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
Early-Age Performance
Strength
Temperature
Shrinkage & Creep
500
Strength or Stress (psi)
Total (Temp+Shrinkage)
400
300
200
100
0
-100
0
1
2
3
4
5
6
7
Time (days)
Shen et al.
Standard Concrete Shrinkage
Mortar Bar
shrinkage
ASTM
C596
Concrete
shrinkage
prism
ASTM
C157
Restrained shrinkage and creep test
Restrained Sample
Free Shrinkage Sample
Typical Restrained Test Data
200
10
Restrained Specimen
150
8
Load (kN)
50
7
0
6
-50
5
Cumulative
Shrinkage + Creep
-100
4
-150
3
-200
2
-250
1
-300
0
0
1
2
3
4
Time (days)
5
6
7
Applied Load (kN)
Strain (me)
100
9
Creep
Free Specimen
Curling of Concrete Slabs
PCC slab
subgrade
High drying shrinkage
Low drying shrinkage
Ttop < Tbottom
esh,top < esh,bottom
Dry
Ttop > Tbottom
Trapped water
High moisture
RHtop < RHbottom
Measuring Internal RH
A new embedded
relative humidity
measurement
system has been
developed at UIUC
Fracture vs. Strength Properties
Brittle
s
MOR
Tough / ductile
Gf
Deflection
Peak flexural strength (MOR) same but
fracture energy (Gf) is different
Avoid brittle mixes
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
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)
Joint Type Selection
Are dowels necessary at every contraction joint?
h
Aggregate Interlock Joint
Dummy contraction joint
No man-made load transfer devices
Shear transfer through aggregate/concrete
surface
aggregate type and size; joint opening
Aggregate Interlock Joints
Reduce number of dowels
High load transfer efficiency if…
Minimize crack / joint opening
Design concrete surface roughness
Variation in Concrete
Surface Roughness
Concrete Fracture Energy & Roughness
1200
1000
Load (N)
800
600
400
200
0
0.00
0.10
0.20
0.30
0.40
0.50
0.60
Opening Deflection (mm)
0.70
0.80
0.90
1.00
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
Saw-cut Timing and Depth
Notch depth (a) depends on stress, strength,
and slab thickness (d)
Stress = f(coarse aggregate,T, RH)
a
d
Requirements for Saw-cut Timing
s
Stress
Strength
Time
Stress = f(thermal/moisture gradients, slab geometry,
friction)
Strength (MOR,E) and fracture parameters (Gf or
KIC) with time
Common Strength Tests
3rd Point Loading (MOR)
Compressive strength and
Concrete elastic modulus
Concrete Mix Design
Minimum strength criteria (MORmin)
Minimum fracture energy (Gf)
Max. concrete shrinkage criteria (esh)
Aggregate top size (Dmax)
Strong coarse aggregate (LA Abrasion)
Slow down hydration rates and temperature
Other Brief Studies
Fiber-Reinforced Concrete Pavements
Shrinkage-Reducing Admixtures
Others
Concrete fatigue resistance
?
Fiber-Reinforced Concrete Pavements
Application of low volume, structural fibers
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 (?)
FRC Slab Testing
Monotonic Load-Deflection Plot
225
Plain
0.48% Synthetic Macro Fiber
200
0.32% Synthetic Macro Fiber
175
Load (kN)
150
125
100
75
50
25
0
0
1
2
3
4
5
6
7
8
9
Average Interior Maximum Surface Deflection (mm)
10
11
12
13
Load-Deflection Plot
250
0.35% Hooked End Steel
225
0.50% Hooked End Steel
Secondary
Flexural Crack
Region
200
0.48% Synthetic Fiber
1st Flexural
Crack
Region
175
Load (kN)
150
0.32% Synthetic Fiber
125
Plain
100
75
50
Ultimate
Strength Region
25
0
0
1
2
3
4
5
6
7
8
9
Maximum Surface Deflection at Center Slab (mm)
10
11
12
13
Questions