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Standing Committee on Concrete Technology Annual Concrete Seminar 2007
High Workability Concrete for Bored Pile Construction
CC Wai, Alan Wan Gammon Construction Limited
iRl lA . det
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G 6 002©
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Week 2
Week 3
Week 1
Sequence of Work in Bored Pile Construction
Sun Mon Tue Wed Thu Fri Sat
Excavation
Excavation Rock Drilling
Rock Drilling Airlifting Concrete Cage
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Presentation Scope
• Method of Concreting Bored Pile
• Problems and Defects
• Deficiencies in Current Practice
• Proactive Approach
• The Way Forward
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Concreting of Bored Pile
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General Setup ©
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Ramp
Skip
Tremie Pipe
Concreting Platform
Concrete Truck
Concrete
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Stages in Bored Pile Concreting
(1) (2) (3) (4)
Extract Tremie Pipe Extract Temporary Casing
Concrete Overbreak
Drop in Concrete
Head
Tremie Pipe
Temporary Casing
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Cement Grout
Concrete
QA / QC
• Slump tests / Flow table
• Check temperature ( 32o)
• Cube samples to determine concrete strength
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©
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Concreting Takes Many Hours
12:00 14:00
18:00 21:00
30
25
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(h 15
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Tim
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0 0 20 40 60 80 100
Pile Length (m)
Concreting Time Varies With Pile Length ©
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©
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Slump Varies With Time
Time
Slu
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Common Problems Encountered
• Temporary casing cannot be withdrawn
• Tremie pipe cannot be withdrawn
• Blocked tremie pipe
• Reinforcement cage rides up with temporary casing
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Defects
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Honeycomb
• Reduced workability affects self compaction
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Air Voids
Entrapped Air Inside Concrete During Pouring ©
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Air Voids
(1) (2) (3) 18
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Segregated Concrete
• Additive quantity needs fine-tuning
Remedial Actions
• Grouting
• High pressure water jet to remove “weak” concrete, followed by pressure grouting
• Stitched pile
• Additional pile
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Deficiencies in Current Practice
First In …. Last Out ©
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1 *
2
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First few truckloads need to remain workable throughout concreting
* Indicate order of truckload
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Deficiencies in Current Practice ©
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• Large piles / deep piles mean large concrete volume
• Specification / Contract Document – Single slump value specified on drawing – Workability vs time not considered – Lack of flexibility in interpretation
• Quality control – Need to control consistency in material
properties
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The Proactive Approach ©
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• Need to Consider …..
– Specification
– Concrete volume (related to pile size
and depth)
– Site constraints (physical or
environmental restrictions)
– Site location (travel time to site from
batching plant)
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Pile Acceptance
Time
Concrete Performance
Material Consistency
Concrete Site Construction Volume Constraints Procedure
Route to Pile Acceptance ©
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Delivery ~ 3 hours
Grade 45/20 •Designed slump 200mm
•Workability 5 hours
SUCCESS STORY ©
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Hong Kong – Shenzhen Western Corridor
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SUCCESS STORY Hong Kong – Shenzhen Western Corridor
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• Supplier formulated a special concrete mix with enhanced workability
• Engineer relaxed concreting time to 5 hours
• Contractor checked workability prior to pouring
• Side-effect : minor segregation, need to pour additional concrete to avoid undercasting
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Way Forward
Concrete Triangle ©
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Designer
Contractor Concrete Supplier
Concrete Quality / Performance
Constructability
Slump Retention Consistency
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The End