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What makes durable concrete? Celik Ozyildirim, Ph.D., P.E. VCTIR, VDOT
Virginia Concrete Conference, March 8, 2012
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Outline
• Is concrete durable? • What are the distresses? • Making durable concrete depends on
– Application (loads, environment) – Structural design – Selection of materials and
proportioning – Construction practices
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Different Concretes
Low permeability High strength Self consolidating Durable Etc…
Different concretes for different applications
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Durable Concrete
• When exposed to the environment resists – weathering action – chemical attack – abrasion
while maintaining the desired properties.
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Pantheon
Roman concrete, 2,000 years old!
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Environmental Distresses
• Freezing and thawing • Alkali-aggregate reactions • Sulfate attack • Corrosion: consider both the
concrete and the reinforcement (corrosion resistant reinforcement)
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Freezing and Thawing Damage
Non-air entrained
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ASR
Water is necessary.
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Sulfate Attack
Sulfate solution penetrating.
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Cracking Drying shrinkage
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Due to loss of moisture
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Corrosion Related Cracking and Spalling
Chlorides penetrate through the concrete and/or the cracks
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Cracking and Spalling
(chlorides on surface seep in through the leaking joints)
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Durable Concrete Structures
• Require proper: – structural design and foundation – material selection and proportioning – construction practices – specifications (ERS)
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Design
• Proper foundation • Reinforcement: size, spacing, cover • Reduced skews • Fewer joints in decks • Closely spaced joints in pavements • Good drainage: Keep it dry!
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Poor Foundation?
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Material Selection and Proportioning
• Give proper attention to the selection of – cementitious material (include
supplementary cementitious material) – water – aggregates – chemical admixtures
• low water-cementitious material ratio (0.40 to 0.45 for bridge decks)
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Permeability
0
1000
2000 3000
4000
5000
6000 7000
28 Days 90 Days 1 Year
Age
Cou
lom
bs
100/0/0/0 90/5/0/0 80/0/24/0 50/0/0/50
PC/SF/FA/S
w/cm=0.45
Portland cement
Fly ash
Slag
Silica Fume
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Year 1,002,012
Cast: 2,006 Cast: 2,012
Build it right! Keep it dry!
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Freezing and Thawing
• Proper air-voids (bubbles < 0.2 mm from any point)
• Sound aggregates
• Adequate strength
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Reduced Shrinkage
• Reduced water, cement and paste contents – Combined aggregate (well graded) with
good particle shape – Large maximum size aggregate – Admixtures: SRA, WRA
• ERS do not have minimum cementitious material requirements
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CONSTRUCTION PRACTICES
• Batching • Mixing • Transportation • Placement
• Consolidation • Finishing • Curing
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Transporting - Pumping
Free fall may reduce workability and air voids
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Poor Consolidation
Unacceptable voids
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Consolidation and Finishing
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High paste content – segregation, fine material on top
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Finishing
Low slump – poor workability
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Curing
Need good coverage
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Curing
Keep it wet!
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Curing
Avoid ponding water on the fresh surface (weakens the surface)!
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Cracking Plastic Shrinkage
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Prevent evaporation!
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Thermal Cracks – Bridge Deck
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Differential deck/beam temperature for at least 24 hours under 22 F.
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Route 40
Cold weather - use external heat and insulating blankets.
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Durable Concrete
Resists weathering action, chemical attack, and abrasion through • low permeability (SCM, low w/cm) • low water, cement, and paste
content (minimal cracking) • proper air void system • sound aggregates • adequate strength to resist stresses
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Thank you.
Celik Ozyildirim, Ph.D., P.E. VCTIR, VDOT