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