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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

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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

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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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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• Temporary casing cannot be withdrawn

• Tremie pipe cannot be withdrawn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 ©

2006

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Designer

Contractor Concrete Supplier

Concrete Quality / Performance

Constructability

Slump Retention Consistency

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The End