Batching Effects on Properties of Recycled Aggregate Concretes for

Airfield Rigid Pavements

Dr. Andres Salas

Prof. David Lange

Prof. Jeff Roesler

2010 FAA Technology Transfer Conference and ExpositionApril 22, 2010

O’Hare Modernization Program (OMP)

The purpose is to reconfigure the intersecting runways at O’Hare International Airport into a more modern parallel layout.

Prior to this O’Hare had not added a new runway since 1971.

Project budget of $6.6 billion.

O’Hare Modernization Program (OMP)

Sustainable practices are desirableReuse and conserve natural resourcesCost savings over traditional methodsUse of RA in concrete and asphalt

showed comparable performance over virgin aggregates.

Why Recycle?

Resistance to changeLack of experience Inadequate codes, specifications

and standards Inconsistent aggregate gradingLower and variable quality

Challenges for using Recycled Challenges for using Recycled Concrete AggregatesConcrete Aggregates

Recycled Concrete Aggregates at Recycled Concrete Aggregates at AirportsAirports

Commonly used for base and subbaseNot used on airport concrete surface before in

U.S.?Technical issues for surface applications

Durability, shrinkage, premature cracking

Two-Stage Mixing Approach, TSMA Two-Stage Mixing Approach, TSMA (Tam et al. 2005):

Mixing process divided into two parts with required water proportionally split and added at different timing.

Initial water used for the formation of thin layer of cement slurry on the surface of RA.Permeate into old porous cement mortar, filling up

the old cracks and voids. Do the aggregates have to be dry, partially-saturated, or

saturated+surface moisture?

A new idea about mixing with RCAA new idea about mixing with RCA

Mixture Procedure Mixture Procedure (Two-Stage Mixing Approach)(Two-Stage Mixing Approach)

Recycled coarse + cementing material 1 min 50% water 1 min Virgin coarse + sand+ 50%water 2 min

mix mix mix

* Control concrete (VAC) was mixed following the commonly used mixing procedure

O’Hare Aggregate Physical O’Hare Aggregate Physical PropertiesProperties

Aggregate BSG Absorption Capacity

Sand 2.57 2.43%

CA-16 2.68 2.73%

CA-7 2.67 1.90%

Recycled Agg. 2.41 5.51%

Mixture DesignMixture Design

Virgin (CA-7) 43% 1429 30% 997 21% 713 21% 712 0% 0 0% 0 0% 0Virgin

(CA-16) 12% 400 9% 283 6% 202 6% 201 0% 0 0% 0 0% 0

Recycled 0 0 17% 495 28% 825 28% 823 55% 1649 55% 1647 55% 164945% 1439 45% 1439 45% 1439 45% 1437 45% 1439 45% 1437 45% 1439

VAC

217414103

0Silica Fume

Coarse Aggregate

WaterType I CementClass C Fly ash

0

217414103

0 16

21739810316

217414103

0

217414103

0

0Synthetic MacrofibersFine aggregate

0 00

100% RACFRC

217398103

3

MaterialContent (lb/yd3)

0

217414103

0

70-30Blend

50-50Blend

50-50Blend+SF

100% RAC100% RAC+

SF

w/cm = 0.42The recycled aggregates sprayed to approximately fill 80% of the total absorption capacity.

Fresh PropertiesFresh Properties

Slump for 100% RA was higher than expected. Nearly saturated aggregates reduces effects of RA absorption

MIXSLUMP

(in)

AIR CONTENT

(%)

UNIT WEIGHT (lb/ft3)

UNIT WEIGHT (kg/m3)

VAC 5 3.2 146.4 2345

70-30 BLEND 6.5 3.2 147.2 2358

50-50 BLEND 4.5 3.2 145.8 2335

50-50 BLEND + SF 2.5 2.5 146.2 2342

100% RA 7 3.4 149.2 2390

100% RA+ SF 3 2.5 142.8 2287

100% RA + FIBERS 2.2 2.5 145 2323

1 day

7 days28 days

90 days0

1000

2000

3000

4000

5000

6000

7000

0 30 5050+SF 100

100+SF100 + FIBERS

Compressive Strength of Recycled Aggregate Concrete (psi)

1 day

7 days28 days

90 days0

1000

2000

3000

4000

5000

6000

7000

0 30 5050+SF 100

100+SF100 + FIBERS

Compressive Strength of Recycled Aggregate Concrete (psi)

0

100

200

300

400

500

600

700

800

0 30 5050+SF 100

100+SF 100 + FIBERS

Strength (psi)

Splitting Tensile Strength (56 days)

0

100

200

300

400

500

600

700

800

0 30 5050+SF 100

100+SF 100 + FIBERS

Strength (psi)

Splitting Tensile Strength (56 days)

Drying Shrinkage ResultsDrying Shrinkage Results

Lower microstrain for 100% RA at 14 days ageRA soaked for 24 hrs while virgin aggregate in oven dry condition

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 10 20 30 40 50 60

Free Shrinkage (x 10-6 )

Age (days)

VA

30% RA

50% RA

100% RA

50% RA + SF

100% + SF

100% + FIBERS

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 10 20 30 40 50 60

Free Shrinkage (x 10-6 )

Age (days)

VA

30% RA

50% RA

100% RA

50% RA + SF

100% + SF

100% + FIBERS

Summary Properties of RACSummary Properties of RAC(Two Stage Mixing Approach)(Two Stage Mixing Approach)

Similar or higher compressive strength compared to VAC

Similar shrinkage to VAC at early agesReduced bleeding and segregationSimilar concrete workabilityLow dosages of silica fume (2 to 3%) enhances

the behavior of RAC

Minimize old mortar attached to aggregateAggregate grain size distribution and proportionsAggregate Absorption CapacityRA should be nearly-saturated conditions to

avoid loss in slump and excessive shrinkage.Two-Stage Mixing Approach (TSMA) and pre-

soaking treatment method for the production of RAC are encouraged

Issues to Consider for RACIssues to Consider for RAC

Field Testing

Pouring Gate F7B at O’HarePouring Gate F7B at O’Hare

Run #1 of RACRun #2 of VAC

2 strips of 25ft x 125ft x 17in were placed Prairie supplied the materials Rossi Construction was the contractorSAM Consultants handled material testing

Sensor InstallationSensor Installation

28 Sensors to measure RH and Temperature

7 LVDT sensors to measure lift-off of the slab

Placement and FinishingPlacement and Finishing

After placement of the RAC No bleeding was observed Finishing took place almost

immediately after placement Very little effort required to finish

Field Visits 10/29

RAC (Run #1)VAC

Field Visit 11/12

RAC (Run #1)

VAC

VAC (Run #2)

VAC

Field Visit 3/18

Contraction joints remain unchanged Some scaling observed in the test strips

VAC

RAC

24

Compare Lab to Field

Mix designs and early age results for the Recycled Aggregate Concrete Mixes. Comparison between U of I mix designs and Prairie Mix Design

Compressive Strength Design 4000psi

Prairie (RAC) Prairie (VAC) U of I (20%FA) 30% Class C FA 40% Class C FA 50% Class C FA

Water (gal) 28 ~26 ~26 ~26 ~26

Cement (lbs) 490 414 362 310 259

Fly Ash (lbs) 130 103 155 207 259

Air (%) 4.5-7.5 3% 3% 3% 3%

% WRA Variable dosage No No No No

Initial Slump (in) 3±1 4 7.5 8 8

Recycled Coarse (lbs) 1500 1688 1683 1677 1672

Extra Fines (lbs) 400 274 273 272 271

Natural Sand (lbs) 1093 1011 1007 1004 1000

Compressive strength at 3 days (psi) 3547 3581 - - - -

Compressive strength at 7 days (psi) 5190 4855 4700 3978 3830

Compressive strength at 28 days (psi) 6900/5858 5182 5751 5507 5435 5005

Flexural strength at 3 days (psi) 704.5   - - - -

Flexural strength at 7 days (psi) 760 - - - -

Flexural strength at 28 days (psi) 915/1052 826 - - - -

w/cementitious ~0.375 0.42 0.42 0.42 0.42

* Blod and blue represents testing results from SAM Consultants

Summary

• Lab test program helps us predict behavior of RAC using recycled material sources at O’Hare

• Lab test program encourages us to use high(er) volume of fly ash

• Lab test encourages lower cement than used in the field RAC

• Testing underscores importance of keeping RA supply near saturation to control shrinkage

• Field testing confirms that RAC slabs were well-constructed and not experiencing high deformations

• So far, so good!

Acknowledgements