Progress Report on O’Hare Modernization Plan February 8, 2004 University of Illinois Department of Civil and Environmental Engineering Concrete Mix Designs

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

Overview of Project Objectives Mix Design Minimize cracking potential  Short and long-term Minimize Shrinkage Joint Enhancement Aggregate Interlock Targeted dowel placement GroupObjectives 1Mechanical Properties Max. G f (Crack resistance) Max. l ch (ductility) 2Volume StabilityMin. Shrinkage 3Load TransferMax. Aggregate Interlock

Completed Activities Survey of Existing Concrete Mixes Initial Mix and Testing Methods Evaluation Technote: Shrinkage Reducing Admixtures in Concrete Pavements Technote: Fiber-Reinforced Concrete Pavements

Survey of Existing Mixes

Initial Mix Evaluation Mix used in previous projects at O’Hare Revised Mix #1905 (2000)

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

Standard Concrete Shrinkage Mortar Bar shrinkage ASTM C596 Concrete shrinkage prism ASTM C157

Initial Mix Evaluation Compressive strength  days Modulus of Rupture  380 7days Drying shrinkage  440  m Autogenous shinkage  170  m Instrumented cube (measurement of RH and Temp.)

Fracture vs. Strength Properties Peak flexural strength (MOR) same but fracture energy (G F ) is different Avoid brittle mixes Deflection  Tough / ductile Brittle GFGF MOR

Fracture Test Setup Wedge Split Test Notched Beam Test

Wedge Split Test Result The concept of G F Wedge split G f and l ch =EG f /f t 2 ftft G F = Area under the Curve Cracking Area

Effect of Aggregate Type on G F

Benefits of SRA in Pavements Reduced Shrinkage and Cracking Potential Near 50 –60% reduction Increased Joint spacing Brooks et al. (2000)

Problems of SRA in Pavements Technical Early age strength loss Delay in set time Interaction with air entrainment admixture Potentially washout with water Economic Cost

Fiber-Reinforced Concrete Pavements Application of low volume, structural fibers

Benefits of FRC Pavements Increased flexural capacity and toughness Thinner slabs Increased slab sizes Limited impact on construction productivity Limits crack width Promotes load transfer across cracks (?)

Use of FRC in Pavements Fiber-reinforced concrete Final cost: reduction of 6% to an increase of 11%

Testing Program Variables- Phase I Proposed Variables- Phase II

Testing Factorial Where:  fc’7 = compressive strength at 7 days  E 7 = modulus of elasticity at 7 days  G f 7 = energy release rate at 7 days   fl 7 = flexural strength at 7 days   sp 7 = splitting strength at 7 days   sh = drying shrinkage   as = autogenous shrinkage 28-day properties Fracture Energy

Joint 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 Joint

Joint Design Saw-cut timing Aggregate Interlock Targeted Dowels

Joint Design Promote high shear stiffness at joint High LTE Larger and stronger aggregates Increase cyclic loading performance Predict crack or joint width accurately

Effect of Concrete Mix on G F Mix ID G F (N/m) at 12 hours G F (N/m) at 28 days 38GTR GRG DTR GRG DRG DLS mm Limestone 25mm Gravel 25mm Trap Rock 38mm Trap Rock 38 mm Gravel 25mm Gravel

G F and Shear Load Transfer Shear load transfer depends on G F at 28 days. Concrete with high G F at 28 days provides good shear load transfer across cracks/joints.

AGGREGATE TYPE TRAP ROCK > RIVER GRAVEL > LIMESTONE

AGGREGATE GRADATION Gradation doesn’t have much impact.

AGGREGATE SIZE LARGE BETTER THAN SMALL (38MM) (25MM)

Other significance of G F G F better characterize the effect of CA on concrete performance. w/c = 0.49  fc’ (12 hrs) = 3.80 – 4.20 MPa  fc’ (28 days) = 31.7 – 38.1 MPa  G F (12 hrs) = 52.7 – N/m  G F (28 days) = 93.7 – N/m

Saw-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 Timing Stress = f(thermal/moisture gradients, slab geometry, friction) Strength (MOR,E) and fracture parameters (G f or K IC ) with time Time  Strength Stress

Project Goals Crack-free concrete (Random) Specification for shrinkage Specification for G F Specifiction for MOR Optimal joint type Aggregate Specification Stabilized base Saw-cut timing Cost effective! Minimum Quantity of Cement Improvement of Aggregate Interlock

Concrete Mix Design Minimum strength criteria (MOR min ) Minimum fracture energy (G F ) Max. concrete shrinkage criteria (  sh ) Aggregate top size (D max ) Strong coarse aggregate (LA Abrasion max ) Saw-cut timing table Slow down hydration rates and temperature

Summary of Progress Concrete Mix Survey Technote FRC Technote SRA Technote Initial Mix Evaluation Phase I - Testing Program Saw-Cut Timing

Questions