Concrete Mix Designs for O Hare Modernization Plan University

Concrete Mix Designs for O’Hare Modernization Plan University of Illinois Department of Civil and Environmental Engineering October 28, 2004

Overview Ø Concrete Mix Design Team Ø Concrete Mix Design Objectives Ø Work Plan • Concrete mixes • Mechanical tests • Modeling • Other studies Ø 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 C 596 Concrete shrinkage prism ASTM C 157

Restrained shrinkage and creep test Restrained Sample Free Shrinkage Sample

Typical Restrained Test Data Creep Cumulative Shrinkage + Creep

Curling of Concrete Slabs PCC slab subgrade High drying shrinkage Ttop < Tbottom Low drying shrinkage sh, top < sh, 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

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

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

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

Load-Deflection Plot

Questions