- 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 opinion without depending on high skilled divers.
- It is clear that the concrete should posses some extraordinary and special properties, obviously in underwater it can be compacted, so it must compact by its self weight (names SCC- self compacted concrete) along with high workability, self levelling power (self levelling concrete).
Underwater concrete construction technology
- Mix proportions
- Workability & rheology
- Strength development
- Mass Tremie Concrete Properties
- Thermal behavior
- Segregation, Bleeding & Laitance
- Underwater Concrete Construction
- Placement planning
- Concrete production/transportation
- Placement procedures
- Finish & Protection
- Inspection & Quality Control
Performance requirements for underwater concrete in structural application
- 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 design
- Particle packing characteristics- Sand content, gradation, size & shape.
- Water to fines ratio- 0.85-1 for good cohesiveness & workability.
- Cementations material content- High volume fly ash silica fume.
- Dispersion characteristics- Proper use of admixture, HRWR, set retarders.
- Water cement ratio- Not more than 0.6
Methods of placement
- Tremie method
- Hydro valve method
- Bucket & skip method
- Preplaced Aggregates Method
It’s basically a rigid pipe suspended vertically to water and a Hooper 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 continuous way. The Tremie pipe should emended in fresh concrete up to 0.7m to 2ft.
- 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 drivers are needed and Tremie pipe has to embedded with the underground soil.
Application in India
- Bandra Worli Sea Link, Mumbai
- Pamban Setu, Rameswaram
- Sardar Sarovar Dam
- Salem Hydro project, Salem, Andhra Pradesh.