Haldia Institute of TechnologyDepartment of CIVIL Engineering

A presentation of Seminar Report inUNDERWATER CONCRETING

by

Sanjan Banerjee

Introduction

• We are quite familiar with the concrete placed in air, but what if the concrete has to place in water, that contain at several warnings like cement washout, Segregation, laitance, cold joints, water entrapment etc and the placement which is totally invisible to us, and no other option without depending on high skilled divers.

• It is clear that the concrete should posses some extraordinary and special properties, obviously in underwater it cant be compacted, so it must compact by its self weight(named SCC- self compacted concrete) along with high workability, self levelling power(Self levelling Concrete).

Underwater concrete construction Technology

Mix proportions Underwater concrete Construction

1.Workbility & Rheology Placement Planning2.Strength Development Concrete production/Transportation(High Strength/Performance) Placement ProceduresFinish & ProtectionInspection & Quality Control

Mass Tremie Concrete Properties1.Thermal behavior2. Segregation, Bleeding & Laitance

LAITANCE :- Lack of adequate Cement & Aggregates at a particular place i.e. lean mix.

Performance Requirements for Underwater Concrete in Structural Applications

• Flow ability and Self-Compaction• Workability Retention within Work Window• Cohesion Against Washout, Segregation, Laitance form• Low Bleeding• Low Heat of Hydration• Controlled Set Time• Compressive Strength• Adequate Bond PRINCIPLE PARAMETERS IN MIX

DESIGNParticle Packing Characteristics- Sand content, gradation, Size & ShapeWater to Fines Ratio - 0.85-1 for good cohesiveness & WorkabilityCementittious Material Content- High Volume Fly ash plus Silica Fume

Dispersion Characteristics- Proper Use of Admixtures, HRWR, Set retarders

Water Cement Ratio – Not more than 0.6N.B.-Anti Washout Admixtures is used here

METHODS OF PLACEMENT

1. Tremie Method, 2. Pump, 3. Hydro valve Method, 4. Bucket & Skip method, 5. Preplaced Aggregates Method

• Tremie Method Its basically a rigid pipe suspended vertically to

water and a hopper fixed on top of pipe to receive concrete & it places concrete underwater by means of gravity.

Most Reliable method to place underwater concrete as concrete flow in a continious way. The tremie pipe should embedded in fresh concrete up to 0.7 m or 2 ft.

Two method to start placement, Dry method & Wet method. In dry method utilizes end cap to seal off tremie from water. Wet method utilizes a moving plug fitted inside pipe to prevent concrete from underwater i.e. acts like a piston.Spacing of TREMIE PIPE- 3-5 times depth of tremie pours

Flow of Concrete Underwater in a Tremie Pipe

Bulged Flow PatternConcrete is Highly flow able & Cohesive.

• Newly placed concrete pushes previously placed sideways, forming a successive series of bulges .

Layered Flow PatternLess flow able Concrete.• Newly placed concrete flows upward

around the placement pipe, and over the top of the previously placed concrete which is dangerous.

Quality Control fig: Removal of Laitance

• After the concrete hardens the core should be taken to verify the quality of in-place Concrete. Use suitable precautions to avoid formation of Cold Joints.

• Conduct frequent testing of concrete from batch to batch and within a batch. Important tests such as Slump ,slump flow, Unit weight, temperature, and concrete compressive strength test.

• Careful monitoring of all concreting operations including any restart and completion of concrete placement. Therefore well skilled divers are needed and Tremie pipe has to embedded with the underground soil.

• 5 critical items has to be checked, i) Rate of Placement, ii) Depth of Concrete at various locations, iii) Vol. of concrete produce vs. Vol. of in place concrete measured by sounding, iv) Concrete Delivery system, v) Embedment depth of tremie.

Conclusion

• Underwater Concreting has historically evolved largely through a trial & error process. The concrete should technically posses some extraordinary properties followed by mix design, concrete production, admixtures, and proper placement method. Self Compacted, Self leveling concrete are used here as it is impractical to compact concrete underwater. Obviously there is a continouoas supply of concrete to avoid formation of Cold joints. A lots of critical parameters are there that is to be taken care of by Engineer.

APPLICATIONS IN INDIA

1.Bandra Worli Sea Link, Mumbai 2. Pamban Setu, Rameswaram, 3. Sardar Sarobar Dam, 3. Salem Hydro project, Salem, Andhra Pradesh.

Acknowledgements

• I take this opportunity to express my profound gratitude and deep regards to Prof. Dr. Bisaka Madam, Associate Professor of Civil Engineering Department, for her exemplary guidance, and constant encouragement throughout the seminar report.

• I would like to thank all the Teachers and Technical Assistants of Civil Engineering Department, Haldia Institute Of Technology for share their valuable knowledge with us.

• Above all I would like to thank God for completion of this.

THANK YOU