Concrete Mix Designs for O’Hare Modernization Plan October 28, 2004 University of Illinois...
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Transcript of Concrete Mix Designs for O’Hare Modernization Plan October 28, 2004 University of Illinois...
Concrete Mix Designs for Concrete Mix Designs for O’Hare Modernization PlanO’Hare Modernization Plan
October 28, 2004
University of Illinois
Department of Civil and Environmental Engineering
Concrete Mix Design Team
Concrete Mix Design Objectives
Work Plan
•Concrete mixes
•Mechanical tests
•Modeling
•Other studies
Technical Notes
OverviewOverview
Concrete Mix Design TeamConcrete Mix Design Team
Prof. David LangeConcrete materials / volume stability
High performance concrete
Prof. Jeff RoeslerConcrete pavement design issues
Concrete materials and testing
Graduate Research AssistantsGraduate Research Assistants
Cristian GaedickeConcrete mix design / fracture testing
Sal VillalobosConcrete mix design and saw-cut timing
Rob Roddentesting, instrumentation, shrinkage
Zach GrasleyConcrete volume stability
C.J. Lee FE modeling
Airfield Concrete MixesAirfield Concrete Mixes
Past experience
Future performance
What do we expect out of the concrete mix?Short-term
Long-term
Concrete Mix ObjectivesConcrete Mix Objectives
Durable Concrete (Prof. Struble)
Early-age crack resistanceenvironment / materials / slab geometry
Long-term crack resistance & joint performanceenvironment / materials / slab geometry
aircraft repetitive loading
Concrete Mix Design VariablesConcrete Mix Design Variables
Mix proportions
Strength CriteriaModulus of rupture*, fracture properties
Shrinkage CriteriaCement, aggregate effect
Aggregate Type, size, and gradation
AdmixturesChemical and mineral
FRC
Airfield Concrete Integrated Airfield Concrete Integrated Materials and Design ConceptsMaterials and Design Concepts
Crack-free concrete (random)
Increased slab size
Optimal joint type
Saw-cut timing guide
Cost effective!
Concrete Volume Stability IssuesConcrete Volume Stability Issues
Early-age shrinkage
Long-term shrinkage
Tensile creep properties
Effects of heat of hydration / environment
Early-Age ShrinkageEarly-Age Shrinkage
Early age cracking is a growing concern Shrinkage drives crackingCreep relaxes stress and delays cracking
Modeling of early age concrete in tension is needed to predict cracking
Effects of mix constituents & proportions
Early-Age PerformanceEarly-Age Performance
-100
0
100
200
300
400
500
0 1 2 3 4 5 6 7
Strength
TemperatureShrinkage & Creep
Total (Temp+Shrinkage)S
tren
gth
or
Str
ess
(psi
)
Time (days)
Shen et al.
Standard Concrete ShrinkageStandard Concrete Shrinkage
Mortar Bar shrinkage
ASTM C596
Concrete shrinkage
prism
ASTM C157
Restrained Sample Free Shrinkage Sample
Restrained shrinkage and creep test
-300
-250
-200
-150
-100
-50
0
50
100
150
200
0 1 2 3 4 5 6 7Time (days)
Str
ain
( )
0
1
2
3
4
5
6
7
8
9
10
Applied Load (kN
)
Restrained Specimen
Free Specimen
Load (kN)
Typical Restrained Test DataTypical Restrained Test Data
Creep
Cumulative Shrinkage + Creep
High drying shrinkage
Low drying shrinkage
Dry
Trapped water High moisture
PCC slab
subgrade
Ttop < Tbottom
Ttop > Tbottom
sh,top < sh,bottom
RHtop < RHbottom
Curling of Concrete SlabsCurling of Concrete Slabs
Measuring Internal RHMeasuring Internal RH
A new embedded relative humidity measurement system has been developed at UIUC
Fracture vs. Strength PropertiesFracture vs. Strength Properties
Peak flexural strength (MOR) same but fracture energy (Gf) is different
Avoid brittle mixes
Deflection
Tough / ductile
Brittle
Gf
MOR
Increased Slab SizeIncreased Slab Size
BenefitsLess 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 SizeRequirements for Slab Size
Pavement AnalysisCurling stresses moisture and temperature
Airfield load effects
Base friction
Joint opening
Concrete Mix NeedsMinimize concrete volume contraction
Larger max. size aggregates
Concrete strength and toughness (fibers)
Joint Type SelectionJoint Type Selection
Are dowels necessary at every contraction joint?
h
Dummy contraction joint
No man-made load transfer devices
Shear transfer through aggregate/concrete surface
aggregate type and size; joint opening
Aggregate Interlock JointAggregate Interlock Joint
Reduce number of dowels
High load transfer efficiency if…Minimize crack / joint opening
Design concrete surface roughness
Aggregate Interlock JointsAggregate Interlock Joints
Variation in Concrete Variation in Concrete Surface RoughnessSurface Roughness
Concrete Fracture Energy & RoughnessConcrete Fracture Energy & Roughness
0
200
400
600
800
1000
1200
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Opening Deflection (mm)
Lo
ad
(N
)
Concrete Surface RoughnessConcrete Surface Roughness
Promote high shear stiffness at jointHigh LTE
Larger and stronger aggregatesIncrease cyclic loading performance
Predict crack or joint width accurately
Saw-cut Timing and DepthSaw-cut Timing and Depth
Notch depth (a) depends on stress, strength, and slab thickness (d)
Stress = f(coarse aggregate,T, RH)
d
a
Requirements for Saw-cut TimingRequirements for Saw-cut Timing
Stress = f(thermal/moisture gradients, slab geometry, friction)
Strength (MOR,E) and fracture parameters (Gf or KIC) with time
Time
StrengthStress
Common Strength TestsCommon Strength Tests
3rd Point Loading (MOR) Compressive strength and Concrete elastic modulus
Concrete Mix DesignConcrete 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
Other Brief StudiesOther Brief Studies
Fiber-Reinforced Concrete Pavements
Shrinkage-Reducing Admixtures
OthersConcrete fatigue resistance
?
Fiber-Reinforced Concrete PavementsFiber-Reinforced Concrete Pavements
Application of low volume, structural fibers
Benefits of FRC PavementsBenefits of FRC Pavements
Increased flexural strength and toughnessThinner slabs
Increased slab sizes
Limited impact on construction productivity
Limits crack width
Promotes load transfer across cracks (?)
FRC Slab TestingFRC Slab Testing
Monotonic Load-Deflection PlotMonotonic Load-Deflection Plot
0
25
50
75
100
125
150
175
200
225
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Average Interior Maximum Surface Deflection (mm)
Lo
ad
(k
N)
Plain
0.48% Synthetic Macro Fiber
0.32% Synthetic Macro Fiber
Load-Deflection PlotLoad-Deflection Plot
0
25
50
75
100
125
150
175
200
225
250
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Maximum Surface Deflection at Center Slab (mm)
Lo
ad (k
N)
1st Flexural CrackRegion
Secondary Flexural CrackRegion
Ultimate Strength Region
0.35% Hooked End Steel 0.50% Hooked End Steel
0.48% Synthetic Fiber
0.32% Synthetic Fiber
Plain
Questions