Structures Congress 09

1
Shear Strength of ASR/DEF Affected Bridge Bent
Caps

• Structures Congress 09

• Dean Deschenes
• Oguzhan Bayrak
• Kevin Folliard

• April 30, 2009

2
Shear Strength of ASR/DEF Bents

• Motivation
• Background
• Objectives
• Research Program
• Test Specimens
• Structural Testing
• Conclusions

Deschenes
3
Motivation

• Signs of premature concrete deterioration due to
  alkali-silica reaction and/or delayed ettringite
  formation identified on several bridge bent caps
  in Houston, Texas.

US 59 I-10 Interchange
US 59 I-10 Interchange
Deschenes
4
Motivation

• Signs of premature concrete deterioration due to
  alkali-silica reaction and/or delayed ettringite
  formation identified on several bridge bent caps
  in Houston, Texas.

What are the structural consequences of this
deterioration?
US 59 I-10 Interchange
US 59 I-10 Interchange
Deschenes
5
Background
PCD Premature Concrete Deterioration
Deschenes
6
Background
PCD Premature Concrete Deterioration
Well Documented Loss of Strength and Stiffness
Deterioration of Structural Safety
Plain Concrete Materials
Reinforced Concrete Structures
?
7
Background

• Loss of material strength has led to a number of
  structural tests, but

• Very few tests designed to
• evaluate the loss of shear strength
• Results typically obtained from
• small scale specimens (d lt 12)
• Results highly variable/inconclusive

Deschenes
8
Experimental Program
Fabrication 4 Reactive Specimens 2
Non-Reactive Specimens

• Conditioning
• Short Term (12 Months)
• Long Term (24 Months)

• Shear Testing
• 6 Shear Spans Tested

R1
R1
R2
R2
R3
nR1
R4
nR1
nR2
Deschenes
9
Test Specimens

• Design, Fabrication and Conditioning

10
Test Specimen Details

• Design Objectives
• Ensure Shear Failure
• Use the Least Conservative Details Found in
  Practice

• Maximize Beam Size
• Evaluate Sectional and Deep Beam Shear Transfer
  Mechanisms

Sectional Load
Deep Beam Load
42
a 1.85d
38
a 3d
38
332
11
Fabrication

• Concrete Mixture

soduim hydroxide
hot mixing water
reactive sand
high alkali cement
Deschenes
12
Fabrication

• High Temperature Curing

Deschenes
13
Conditioning

• Moisture and Sustained Load

Simulate the Most Severe Exposure Conditions
Found in Practice
Investigate the Impact of Externally Applied
Loads on Surface Cracking
Deschenes
14
Conditioning

• Expansion Monitoring Technique

Deschenes
15
Conditioning

• Expansion Monitoring Sample Results

R2 Deep Beam Shear
5.4
3.7
eyt
0.7
16
Conditioning

• Expansion Monitoring Sample Results

R2 Sectional Shear
6.5
5.5
eyt
0.8
0.2
17
Conditioning

• Expansion Monitoring - Summary

Deschenes
18
Structural Testing
19
Structural Testing
Tested summer 2008.
Deschenes
20
Structural Testing

• Sectional Shear Test

Deschenes
21
Structural Testing

• Deep Beam Shear Test

Deschenes
22
Structural Testing

• Strength Results

Deep Beam Shear
Sectional Shear
Deschenes
23
Conclusions
24
Conclusions

• Minimum shear reinforcement insufficient to
  restrain ASR/DEF expansion

R3 Deep Beam Shear ?v,min 0.003
4.8
3.8
25
Conclusions

• Delayed obscured cracking in deteriorated
  specimens

vs.
Deschenes
26
Conclusions

• Minimum shear reinforcement insufficient to
  restrain ASR/DEF expansion
• Delayed obscured cracking in deteriorated
  specimens
• No loss of strength despite transverse expansions
  in excess of stirrup yield strains
• Structures safe when compared to ACI and AASHTO
  code equations

Deschenes
27
Future Work
?
28
Questions?