SOLUTIONS FOR THE BUILT WORLD · Thermal Modeling Recommendations Severe early-age transverse...
Transcript of SOLUTIONS FOR THE BUILT WORLD · Thermal Modeling Recommendations Severe early-age transverse...
Click to edit Master title style
www.wje.com
SOLUTIONS FOR THE BUILT WORLD
Early-Age Bridge Deck Cracking: Case Study
Todd Nelson, Elizabeth Nadelman, Paul Krauss
October 15, 2017
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 2
Early-Age Bridge Deck Cracking: Case Study
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Severe early-age transverse cracking noted on a large number of bridge decks in Montana
▪ Early-age transverse cracking led to deck penetrations in three bridge decks
▪ Decks were only 1 to 9 years old
Solutions for the Built World Page 3
Early-Age Bridge Deck Cracking: Case Study
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 4
Bridge Locations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 5
Bridge Locations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 6
Typical Distress
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 7
Typical Distress
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 8
Typical Distress
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Performed investigation to determine cause of cracking and to make recommendations for mitigation and prevention
Solutions for the Built World Page 9
Early-Age Bridge Deck Cracking: Case Study
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Field Investigations
▪ Detailed investigation of four bridges
▪ Comparative investigations of eight additional bridges
– Crack mapping
– Delamination survey
– Concrete coring
– Impulse response
– Infrared thermography
– Drone
Solutions for the Built World Page 10
Early-Age Bridge Deck Cracking: Case Study
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Laboratory Evaluations
▪ Petrography
▪ Mechanical property evaluation
▪ Thermal property evaluation (COTE)
▪ Chloride ion content
▪ X-ray diffraction of efflorescence
▪ Modeling – Sensitivity Analysis
Solutions for the Built World Page 11
Early-Age Bridge Deck Cracking: Case Study
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 12
Characteristic Cracking
Map cracking
Transverse
cracking
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 13
Characteristic Cracking
Transverse cracking
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 14
Characteristic Cracking
“Jump” cracking
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Crack progression:1. Transverse cracks develop early2. Cracks progress over time3. Closely-spaced transverse cracks can
“jump”4. Holes may develop at jumps
Solutions for the Built World Page 15
Characteristic Cracking
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Modeling ▪ Temperature model: ConcreteWorks
▪ Stress model: Mathcad tool based on Zuk (1961)1
Solutions for the Built World Page 16
Early-Age Bridge Deck Cracking: Case Study
1Zuk, W. “Thermal and Shrinkage Stresses in Composite Beams,” Journal of the
American Concrete Institute, (1961): 327-340.
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Used ConcreteWorks to simulate peak temperature-time histories for 3 bridge decks▪ Deck geometry based on drawings
▪ Heat generation simulated based on mix designs and cement compositions
▪ Ambient temperature, wind speed, solar radiation based on historic records (NCDC)
▪ Assumed placement temperature of 65 degrees F based on available batch ticket information
Solutions for the Built World Page 17
Temperature Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
0
20
40
60
80
100
120
6/7 6/8 6/9 6/10 6/11 6/12 6/13 6/14
Max.
Deck T
em
pera
ture
( F
)
Date/Time
Bridge 6
6:00 AM 12:00 PM (noon)
6:00 PM
7:00 AM (Actual) Ambient
Solutions for the Built World Page 18
Temperature Model
35 oF difference!
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 19
Temperature Model
0
20
40
60
80
100
120
7/25 7/26 7/27 7/28 7/29 7/30 7/31 8/1
Max.
De
ck T
em
pera
ture
( F
)
Date/Time
Bridge 1
6:00 AM 12:00 PM (noon)
6:00 PM
2:00 AM (Actual) Ambient
0
20
40
60
80
100
120
7/7 7/8 7/9 7/10 7/11 7/12 7/13 7/14
Max.
Deck T
em
pera
ture
( F
)
Date/Time
Bridge 2
6:00 AM 12:00 PM (noon)
6:00 PM
4:00 AM (Actual) Ambient
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
0
20
40
60
80
100
120
6/7 6/8 6/9 6/10 6/11 6/12 6/13 6/14
Max.
Deck T
em
pera
ture
( F
)
Date/Time
Bridge 6
6:00 AM 12:00 PM (noon)
6:00 PM
7:00 AM (Actual) Ambient
Solutions for the Built World Page 20
Temperature Model
Placing concrete in late afternoon shifts peak temp.
difference to Day 2 or 3.
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Stress analyses were performed using Mathcad, based on first-principles model by Zuk (1961)▪ Developed for composite bridge decks
▪ Calculate free strain in each segment due to temperature change and/or shrinkage
▪ Calculate stresses generated by compatibility along interfaces
Solutions for the Built World Page 21
Stress Model
Zuk, W. “Thermal and Shrinkage Stresses in Composite Beams,” Journal of the American
Concrete Institute, (1961): 327-340.
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Modifications:
▪ Creep was implicitly modeled by reducing the elastic modulus of concrete
Solutions for the Built World Page 22
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Sensitivity Analysis
▪ Autogenous shrinkage
▪ Drying shrinkage
▪ Temperature changes in deck and girder
▪ Compressive strength of deck concrete
▪ Thickness of deck
▪ Girder spacing
Solutions for the Built World Page 23
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Sensitivity Analysis
▪ Autogenous shrinkage
▪ Drying shrinkage
▪ Temperature changes in deck and girder
▪ Compressive strength of deck concrete
▪ Thickness of deck
▪ Girder spacing
Solutions for the Built World Page 24
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Sensitivity Analysis: Key Findings
▪ High sensitivity to tensile stresses caused by early-age temperature drops
▪ Stresses due to thermal gradients (e.g., cooling of deck surfaces) are greater magnitude than stresses due to uniform temperature changes
▪ Strains due to temperature generally larger than strains due to autogenous shrinkage for bridges investigated
▪ Drying shrinkage may be significant at later ages
Solutions for the Built World Page 25
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Simulations also performed for “realistic” temperature distributions
▪ Assumed top 1/3 of deck is cooled 10 degrees F relative to interior
– Simulated tensile stresses reached up to 130 psi at 3 days (after cooling)
– Steeper substantial gradients may have existed in actual deck
Solutions for the Built World Page 26
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Simulations also performed for “realistic” temperature distributions
▪ Simulations also performed assuming uniform drying shrinkage of 500 microstrain
– Simulated tensile stresses reached up to 590 psi
Solutions for the Built World Page 27
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Simulations also performed for “realistic” temperature distributions▪ Tensile capacity of the concrete may be
exceeded by “realistic” thermal and shrinkage effects
▪ Simulated stresses generally correlated with observed crack severity
Solutions for the Built World Page 28
Stress Model
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Curing recommendations to limit thermal cracking
▪ Move pour times to later afternoon
▪ After peak hydration, apply insulation
▪ Recommendations implemented on 2 new bridge decks in late 2016 and 3 new bridge decks in 2017
▪ DOT reports little to no transverse cracking observed (typically over bents, if observed)
Page 29
Recommendations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
Solutions for the Built World Page 30
Recommendations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Additional recommendations for reducing early-age shrinkage cracking:
▪ Immediately fog mist placements until wet curing media is in place
▪ Limit cementitious material contents to 600 lb/yd3 or less
▪ Limit silica fume replacement to 5%
▪ Specify w/cm between 0.42 and 0.45
Solutions for the Built World Page 31
Recommendations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Additional recommendations for design:
▪ Increase design thickness of decks to 8 inches minimum
▪ Modify specifications to require staggering of top and bottom transverse reinforcing mats
Solutions for the Built World Page 32
Recommendations
▪ Outline
▪ Project Background
▪ Investigation
▪ Thermal Modeling
▪ Recommendations
▪ Early-age thermal effects can generate significant thermal stresses in bridge decks.
▪ Risk of cracking may be reduced by:
▪ Pouring concrete in late afternoon
▪ Applying insulation to the deck after peak hydration
Solutions for the Built World Page 33
Conclusions
Questions?Thanks for attending!
Solutions for the Built World Page 34