Post on 21-Jul-2015
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