1. CHAPTER 9
UNDERWATER REPAIRS

2. INTRODUCTION
Many of the techniques available for above water
repair can be used underwater with only minor
modifications. The materials specified for use in
air, however, are often completely unsuitable for
underwater use.
The major effects that underwater working has
on repair operations are summarized as follows:
The cost & difficulty of underwater working
requires that operations to be carried out at
the repair site be minimized & made as simple
as possible. The method of repair must be
tailored to suit the available methods of
access.

5. INTRODUCTION
Preparation of the damaged area requires
specially adapted techniques. Care must be taken
to ensure that the area is not contaminated prior
to application of the repair material.
The material selected for the repair must be
compatible with underwater use both during
placing & curing. Many resin-based repair
materials are not suitable for use underwater;
cementitious systems are however in an ideal
medium.
Placement methods & formwork must be adopted
that minimize mixing between repair material &
water.

6. INTRODUCTION
Checking during the repair operation and regular
inspection on completion is difficult and costly to
achieve underwater.
The cost of underwater repair is far greater than
for similar repairs carried out in the dry. The cost
of failed repairs is also therefore high. Hence it is
important that laboratory trials on both repair
methods and materials be carried out to identify
possible problem areas and ensure smooth site
operations.

7. PREPARATION OF DAMAGED AREA
SURFACE CLEANING
All marine encrustations to be removed.
Necessary to determine extent of damage and
to ensure bond.
Small areas: Hand held tools, mechanical wire
brushes, needle guns or scabbing tools.
Large areas: High pressure jets;
Encrustations – Abrasive slurry
Oil contamination – Detergent.
After cleaning determine extent & type of
damage.

8. PREPARATION OF DAMAGED AREA
REMOVAL OF DAMAGED CONCRETE
HIGH PRESSURE WATER JETTING
• Most common for underwater work.
• A thin high pressure jet of water directed
on the concrete surface removes mortar
from between the aggregates
• The reinforcement is itself cleaned but not
cut by the water jet.

9. PREPARATION OF DAMAGED AREA
SPLITTING TECHNIQUES
• Hydraulic or Pneumatic expansive devices
can be used to split concrete.
• Hydraulic expanding cylinders are inserted
into predrilled holes & pressurized until
splitting occurs.
• Expansive cements are also effective.
Cement mixed into a paste & poured into
plastic bags, which are put into predrilled
holes. In 24 hours it expands and splits
concrete.

10. PREPARATION OF DAMAGED AREA
MECHANICAL CUTTING
Underwater cutting using hydraulically
powered diamond tipped saws & drills have
been used extensively for minor works for
many years.
THE CARDOX SYSTEM
Holes are drilled into concrete.
Into these cartridges of pressurized CO2 are
placed.
The pressure is then released by electrically
detonating a small initiating charge in each
cartridge, producing a comparatively gentle
explosion which bursts the concrete apart.

11. PREPARATION OF DAMAGED AREA
THERMIC LANCE
Comprises long steel tube packed with steel
rods.
O2 is passed down centre of the tube & lance is
ignited by external heat source.
Temperature goes up to 3500 deg C, enabling
the tip of the lance to quickly melt through
concrete or steel.
EXPLOSIVE CUTTING
Explosives using contact demolition charges
have been used for many years.
The size & placing of charge is matter of
experience. The resulting cut/tear in concrete is
irregular.
Shaped charges provide precise cut.

12. CUTTING OF REINFORCEMENT
OXY-FUEL GAS CUTTING
As Acetylene becomes unstable with risk of
explosion, Oxy-hydrogen flame is used for
underwater steel cutting.
OXY-ARC CUTTING
Same as above, only that an electric arc
instead of a flame is used.
MECHANICAL CUTTING
Diamond tipped saws can be used for small
works.
FINAL PEPARATION
Replace reinforcement rods surface flushed
with clean water to remove bacterial or
microbiological growth.

13. PATCH REPAIRS
Minor damages can be repaired by special
cementitious or resin based materials.
CEMENTITIOUS MORTARS
Conventional mortar when immersed in water,
washout of the top surface will occur.
Special admixtures can be added to resist
washout of cement.
Self-leveling, Self-compacting mortars to be
used.

14. PATCH REPAIRS
RESIN MORTARS
Normal epoxy or polyester resin mortars
unsuited for underwater works.
By careful formulation of the base resin & the
curing agent, special epoxy & polyester resin
mortars have been developed which can be
used underwater.

15. INJECTION INTO CRACKS
General procedure for underwater crack repair
same as for dry workings.
Drill 50 mm deep injection points along the
crack
Line of crack thoroughly cleaned by high
pressure water jetting.
Line of crack is sealed using epoxy putty.
Injection pipes sealed into injection points.
Width > 3mm Cementitious grout
< 3mm Epoxy grout (low viscosity,
solvent free, underwater grade)
Injection achieved by pressure pot.

16. INJECTION INTO CRACKS
Start with lowest
point till resin
flows out of the
next highest
injection point.
Lock lower
injection point and
injection is
transferred to the
next point.

17. LARGE SCALE PLACEMENT
Where large volumes of material are required,
consideration must be given to bulk placement
under water.
Precast high density concrete mats for renewing
ballast can be obtained in various sizes & offer
many advantages over wet cast systems.

18. FORMWORK
Should be simple to
erect under water
Should be tolerant to
variations.
Figure shows steel
formwork fitted to
damaged surface.
Flexible seals ensure
leak-tight fit.
Formwork is complete
with inlet pipes,
external vibrators, etc.