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Published by Mohammad Qasqas, 2019-12-14 09:23:31

Underwater Concreting

Underwater Concreting


Done by
Mohammad Qasqas
Abdallah Haymour


Introduction i

1 Underwater Concrete 1
1.1 Introduction 3-4
1.2 Design of underwater concrete mixtures
1.3 Selection of materials and proportions 5
1.3.1 Choice of slump 6
1.3.2 Choice of maximum aggregate size 7
1.3.3 Determination of mixing water and air content 8
1.3.4 Selection of water/cement ratio 9
1.3.5 Calculation of cement content
1.3.6 Selection of admixtures

2 Placement Methods

2.1 Introduction
2.2 Bagwork (bagged concrete)
2.3 Tremie Method
2.4 Pump Method
2.5 Bucket Placing Method
2.6 Hydro Valve Method


3 Tests 11
3.1 Introduction 13
3.2 Flow/spread test 14
3.3 The washout-resistance test
3.4 The Orimet test 16



Concrete is the second most widely used material in the world; indeed, of all
materials. In many ways, concrete literally forms the basis of our modern
society. Almost every aspect of our daily lives depends, directly or indirectly, on
concrete. We need only consider the obvious examples: roads, bridges, runways,
dams, water conduits, buildings of all types. All these examples are familiar to
all of us, but how about when these dams, buildings, bridges have to be
-partially of fully- built underwater? This is called underwater concreting



Underwater Concrete

1.1 Introduction

Underwater concrete “UWC” is one special type of high performance
concrete used in the past, present, and future as long as there is need to
construct bridges, with foundations in soil with high water levels, and on-
shore structures. The term high performance concrete refers to concrete that
performs particularly well in at least three key performance indicators:
strength, workability, and durability. Therefore, underwater concrete should
meet these performance criteria and it remains a viable and economic choice
for consultants and contractors. UWC requires special and careful monitoring
during all stages of construction; special considerations for selecting the right
materials, specialized apparatus for the quality control, design, and methods of
construction. Underwater concrete was specially designed to enhance
constructability and performance in water environments. Using the
underwater concrete technique may avoid engineers using the “old-style” of
construction by isolating the water.

“UWC” is a highly flowable concrete that can spread into place under its
own weight and achieve good compaction in the absence of vibration, without
exhibiting defects due to segregation and bleeding. Underwater concrete
technology has developed dramatically in recent years, so that the mix can be
proportioned to ensure high resistance of washout and segregation.

The construction of a wide range of structures including bridge piers,
harbors, sea and river defenses over many decades, and the development of
offshore oilfields, has required placement of concrete underwater. This
process can be successfully carried out and sound, high-quality concrete can
be produced if sufficient attention is paid to the concrete mix design and the
production method applied.

The stability of fresh concrete depends on the rheological properties and
placement conditions. It can be characterized by the concrete resistance to
washout, segregation and bleeding and is affected by the mix proportioning,
aggregate shape and grading, admixtures, vibration and placement conditions.


1.2 Design of UWC mixtures

UWC mixtures were designed using a Portland cement, and coarse aggregate
consisting of round natural quartz and sandstone particles with a nominal
aggregate size of 20 mm. Well-graded quartzite sand with a finesse modulus of
2.74 was also employed. The relative density values of the coarse aggregate and
sand were 2.50 and 2.56, and their absorption rates were 1.7% and 1%. A new
generation copolymer-based SP* was used which has a solid content and specific
gravity of 30% and 1.11. This SP was developed for self-compacting concrete.
The SP was used at 0.2 to 2.1 per cent, by mass of cement.

All mixes were prepared in 25-liter batches and mixed in a drum mixer. The
mixing sequence consisted of homogenizing the sand and coarse aggregate for
30 s, then adding 50% of the mixing water in 15 s. After mixing for 2–3 min, the
mixer was stopped for 5 min while the contents were covered. The cement was
then added along with the remaining solution of water and SP. The concrete was
then mixed for a further 3 min.

The workability of the concrete was evaluated using the slump test. Because
of the viscous nature of concrete containing an AWA*, the readings of the
measurement were delayed for one minute following the removal of the slump
cone. The test consisted of determining the mass loss of a fresh concrete sample
weighing 2.0  0.2 kg which was placed in a perforated basket and allowed to
freely fall three times through a 1.7 m-high column of water.

The improvement of the properties of underwater concrete is related to the
enhancement in washout resistance. A SP is used to ensure high fluidity and
reduce the water/cement ratio (W/C). An anti-washout admixture (AWA) is
incorporated to enhance the yield value and viscosity of the mix and hence the
washout resistance and segregation resistance. The majority of AWAs are water-
soluble polymers that increase the yield value and viscosity of cement paste and


SP: Superplastisizer
AWA: Antiwashout admixtures
Welan gum was selected as the AWA. Welan gum is a high molecular-weight, water-
soluble polysaccharide obtained through a controlled microbial fermentation.

1.3 Selection of materials and proportions

The principles underlying the ACI recommended practice can adapted for
determining the proportions of concrete mixtures for most underwater structures,
the following illustrations show how this can be done.

1.3.1 Choice of slump

Concrete mixtures should have a consistency that permits through
homogenization on mixing, and ease of transportation, placement, and
consolidation without segregation placed n. Note that superplasticized concrete
for heavily reinforced sea structures to be placed by pumping generally requires
150-200 mm slump.

1.3.2 Choice of maximum aggregate size

Owing to narrow spacing between bars in heavily reinforced structural elements
and form the stand point of keeping the permeability of concrete low, it would
desirable to limit the maximum aggregate size to 10mm. concrete mixtures with
25 to 37 mm maximum aggregate size can be used for unreinforced structures.

1.3.3 Determination of mixing water and air content

With well-graded normal aggregates the amount of mixing water depends on the
maximum aggregate size, the desired consistency and the air content of the
concrete, assuming the no air entrainment is needed, it can be determined from
the ACI specifications that approximately 210 kg/m3 mixing water will be
needed to produce 150-175 mm slump in concrete mixture containing 19 mm
maximum aggregate size. A 25% water reduction by the mandatory use of
superplasticizing admixtures should bring down the water requirement to
160 kg/m3.

1.3.4 Selection of water/cement ratio

For structures exposed to seawater, the ACI recommends a maximum
permissible water/cement ratio of 0.40, even when a higher water/cement may
be acceptable from consideration of the concrete strength.


ACI: American Concrete Institute

1.3.5 Calculation of cement content

From the water content and the water/cement ratio, the calculated cement
content is 160 ÷ 0.4=400 kg/m3.

1.3.6 Selection of admixtures

In addition to the high rang water reducers -superplasticizer- , a high quality
pozzolan should be used to improve workability and reduced permeability.
Approximately 5 to 15 liter/m3 of a naphthalene or melamine sulfonate type
superplasticizer may be needed to obtain the desired consistency. Either
condensed silica fume (7-10% by weight of cement) or a high quality fly ash
(15-20% by weight of cement) should be considered for use as a pozzolanic
additive to the concrete mixture.
Concrete mix specifications for offshore structures:



Placement Methods

2.1 Introduction

When a limited amount of water is needed for cement hydration and for
concrete workability, additional water will damage the mix. As the ratio of water
to cement increases, the permeability of concrete increases, and the strength

If conventional concrete is dumped in water without confinement as it falls
through the water, it will lose fine particle and become segregated or it will
disperse, depending on the distance of fall and the velocity of the water current.

Saltwater mixed with the concrete may affect the reinforcement of the
concrete (steel bars). Special techniques are needed to protect the concrete as it
placed underwater.

The method of placing concrete will be governed to a great extent by the
location and the volume of material to be placed.

When devising a technique of placing concrete under water, the quality of the
concrete must be ensured. However, the critical factors in concrete placing
underwater are avoiding segregation and minimizing the contact between the
surface of the concrete and the water.

The underwater concreting techniques designed mostly to prevent cement
washout. These methods did not obtain the full purpose of avoiding cement
wash out at early stages of using under water concreting apart from cases where
large masses of concreting were employed.

2.2 Bagwork (bagged concrete)

 A construction of retaining walls acts as formwork for the mass
concrete pours, the type of bags used here are normally made from an
open-weave material such as hessian (fabric bags).

 It can be used to repair damaged portions of concrete or masonry
substructure elements underwater.


 The bags should be half-filled or more specifically pre filled with dry
concrete mix (often only sand or cement are used) and anchored
together to form the exterior of the repair,

 Partial filling of the bags allows them to be molded into shape and
gives them good contact areas with adjacent bags.

 This process is often used when the water is so shallow that special
underwater equipment is not required.

 Bagged concrete application was expanded when it became possible to
take advantages of the durability and high strength of artificial fibers to
produce forms for casting concrete under water.

 These bags possess sufficient durability to be used in marine
environments exposed to cyclic changes (tidal flows) and provide
abrasion resistance to floating debris and particles carried in the water

 The properties of fabric-formed concrete are essentially the same as
those expected from concrete cast in conventional rigid forms, with one
exception: the water-cement ratio of the concrete could be low at the
surface since the permeable fabric allows water to bleed throw bags.

2.3 Tremie Method

 It is one of the most common methods used to place concrete

 Tremie concrete is placed underwater by gravity flow through a pipe
called a tremie. The underwater portion of the pipe is kept full of
plastic concrete at all times during placement of the total quantity of

 Concrete placement starts at the lowest point and displaces the water as
it fills the area.

 A mound of concrete is built up at the beginning of the placement.

 To seal the tremie, the bottom of the tremie must stay embedded in this
mound throughout the placement.


 The concrete is forced into the occupied area by the force of gravity
from the weight of concrete in the tremie.

 The thickness of the placement is limited to the depth of the mound of

 Tremie concrete is best suited for larger volume repairs where the
tremie will not need to be relocated frequently or for deep placements
where it would be impractical to pump the concrete.

 The method of placing concrete with a tremie is simple, and requires
few pieces of equipment, minimizing potential malfunctions.

2.4 Pump Method

 It is placed underwater using the same equipment that is used to place
concrete above water.

 The placement process is similar of using tremie except that the end of
the pump line does not need to be in the concrete as with a tremie.

 A direct transfer of the concrete is provided, and the pump forces the
concrete through the supply line.


 The placement of concrete must start at the bottom of the area and the
hose or pipe must stay submerged in the fresh concrete during

 The pipe does not need to be lifted as much as with a tremie. A handle
on the end of the pipe or hose will help the diver position it.

2.5 Bucket Placing Method

In this method the concrete is deposited under water by a bottom opening
bucket. The buckets usually are fitted with bottom roller or drop bottom gates.
The gate opens freely outward when tripped. The bucket is filled completely
with concrete and its top covered with a canvas cloth or gunny sack and lowered
slowly to avoid backwash or disturbance to concrete as the bucket is lowered
into the water.
Some buckets are provided with a special base, which limits the disturbance to
the concrete during discharge operation and also when the empty bucket is
raised up from the freshly laid concrete. The bucket is lowered by a crane up to
the bottom surface of the concrete and then opened either by a suitable
arrangement from the top or by a diver. It is essential that the concrete be


discharged directly on the surface on which it is to be deposited. The early
discharge of bucket, by which the fresh concrete drops through water, must be

1. The concreting can be carried out at the considerable depths below water
2. Slightly stiffer concrete than tremie method can be used.
The main disadvantage of this method is the difficulty in keeping the top surface
of the placed concrete reasonably level.

2.6 Hydro Valve Method

This method of underwater concreting is developed and employed by the Dutch
in 1969. A flexible hose which hydrostatically compressed is employed to pour


As soon as concrete placed in the upper of the pipe, both friction inside the pipe
and hydrostatic pressure is overcame by concrete weight. This leads to move
concrete slowly in the pipe and avoid segregation. A rigid tubular section is used
to seal the end of the hose. This method is not costly and quite simple.




3.1 Introduction

Underwater concrete (UWC) continues to flow with time under its own weight
before it starts to harden, unlike ordinary fresh concrete, which usually assumes
its stable shape very rapidly. The commonly used standard tests for workability
of ordinary fresh concrete, such as the slump test or the flow (spread) test, are
inadequate. Flowing concrete usually drops to one-third or less of the original
height in the slump test, and the result is a collapsed heap, the height of which is
likely to be determined by the angle of repose of the largest particles. Therefore,
visual measurement of col-lapsed concrete, or simply the height of the slumped
concrete, does not differentiate the characteristics of two cohesive concretes.
Moreover, even if a measurable slump is obtained, the sample will continue to
settle and show increasing slump with time. The DIN flow table, which had
been developed in Germany as a workability test for ordinary concretes and
adopted as the British Standard test (BS 1881:1984), is no more satisfactory than
the slump test. The test is intended to measure a bulk property of the concrete,
but the end-point condition for the flowing concrete (510 mm spread) can only
be achieved by assuming that the concrete spreads into a disc of 21 mm
thickness, equal to the size of the largest particles, and clearly not representative
of the bulk. The test is also operator-sensitive (manual jolting of the base plate,
perfectly level position). Many other tests have thus been developed to assess
UWC, and they will be described briefly in the following section.


DIM: Deutsches Institute Fur Normung ( Germany )

73.2 Flow/spread test
0There have been several tests proposed based on this principle. The version of
the test described here was originally developed in Germany by Graf in the
1930s. The test measures the spread of a sample of fresh concrete after it has40
been molded into the shape of a truncated cone and allowed to slump following200
the removal of the mold. The slumped concrete is then subjected to a controlled
amount of jolting. The term “spread” test appears to be more appropriate than
“flow” in order to avoid confusion with other “flow” tests. The “spread”
describes much better the principle of the test in which the sample spreads in all
directions. Flow of concrete tends to imply moving or “flowing” in one
direction, restrained within a container or pipe.




The test had originally been aimed at the assessment of workability of
medium range concrete mixes and remains in use for such purposes in several
European countries. It is widely used in Germany, its country of origin. The test
can also be used for fresh mixes of high and very high workability, where
collapsed slumps are recorded. This capability has increased the use of the test
for assessment of superplasticized and other special flowing fresh mixes. The
apparatus consists of a flat, square (700 mm × 700 mm) plywood top plate,
which has its upper surface lined with a metal sheet at least 1.5 mm thick.
Center-lines at 90 degrees are engraved on to the surface of the metal lining
together with a concentric circle of 200 mm in diameter. The mass of the top
plate should be within 16 kg ± 1 kg.


The top plate is attached to a bottom plate by hinges along one side. The top
plate is fitted with a handle at the center of the edge opposite to the hinged side.
The handle is used for lifting the top plate; however, the height of the lift is
restricted to 40 mm ± 1 mm by metal retainers. The bottom plate extends
forward by at least 120 mm along the side with the handle to provide a foothold.
Spread values in the range of 450 to 600 mm (18 to 24 in.) were recommended
for underwater concrete used in drilled shaft construction and values of 550 to
650 mm (21 to 26 in.) were reported in underwater concrete repair.

3.3 The washout-resistance test

The washout-resistance test was developed at the University of Paisley,
particularly as a method for the assessment of the non-dispersability of fresh
concrete placed underwater. The test is based on the principle of evaluating
non-dispersability by direct contact of fresh concrete with water. The washout-
resistance test is applicable to fresh concrete mixes of any level of workability
conditions, to evaluate their suitability for an under-water application.
The test assembly consists of a barrel containing water (30 L) with a pipe and a
spray head connected at the bottom. The test sample is placed on a frame, which
is freely suspended on an electronic balance. The balance is supported on a
bench. The test is simple. A sample of a concrete mix is put into a mold on the
plate. The mold is removed and the plate with the sample is placed on the frame
suspended from the balance. The tap on the pipe connected to water tank is
turned on. Water from the spray head washes out the sample until the tank is
empty. A computer connected to the electronic balance records the whole
washout process.

The test produces diagrams showing the loss of mass during the test. The
measurement recorded directly from the balance at any moment during the test
is the mass of the sample and of the plate resting on it plus the mass and
pressure of water which is poured on the sample. The net amount of lost
material is the direct measurement from the balance minus the effect of the
pressure and weight of the poured water. The end result is the loss of material
expressed as the percentage loss of the original sample, accompanied by graphs
of the washout mass during the test, and visual assessment of the sample after
test. The variability of the washout results inherently increases when a greater
mass has been washed out from the original sample. However, the test is able to
recognize clearly the dosage of underwater admixtures and the suitability of
fresh concrete to be placed underwater.


The advantages of this test are:
• Good simulation of concrete-water interaction in practice
• A simple test procedure
• Highly sensitive to washout resistance
• Acceptable mass of the test samples (1 kg).
However, the apparatus is not designed for use on site. The apparatus is
expected to be used by concrete laboratories and companies producing
underwater concrete admixtures. Washout values of 1% to 6.6% are
recommended for underwater concrete.

3.4 The Orimet test

The Orimet was developed by Bartos specifically as a method for a rapid
assessment of very highly workable, flowing fresh concrete mixes on
construction sites. The test is based on the principle of an orifice rheometer
which is applied to fresh concrete. The Orimet test is applicable to fresh
concrete mixes of very high workability, preferably mixes for which the result
of the slump test is greater than 150 mm or which record a collapse slump. The
test is used for specifications of workability (mobility) of fresh concrete mixes,
for the compliance with specifications and for a rapid check of adjustments of
mix proportions/admixtures on construction sites where very high workability of
a fresh mix has to be maintained. It is particularly suitable for superplasticized
and other flowing mixes. The Orimet consists of a vertical casting pipe fitted
with an interchangeable orifice at its lower end. A quick-release trap door is
used to close the orifice. The basic Orimet is provided with an orifice having an
80 mm internal diameter which is appropriate for assessment of concrete mixes
of aggregate size not exceeding 20 mm. Depending on the composition of the


1090mix and the workability required, orifices of other sizes, usually from 70 mm to980
60090 mm in diameter can be fitted instead. The casting pipe, the orifice and the
trap door mechanism are supported by an integral tripod which folds back to
60facilitate transport. A sample of at least 7.5 liters of fresh mix is required.
The Orimet test includes two stages:
1) Go or not Go for underwater concrete mixes.
2) Recommended value of 3–5 seconds for good underwater concrete.



- Sonebi, M. “Development of high-performance, self-compacting concrete for
underwater repair applications”
- Khayat, K. H., Gerwick, B. C. and Hester, W. T. “Self-levelling and stiff
consolidated concretes for casting high-performance fl at slabs in water”.
- Yamaguchi, M., Tsuchida, T. and Toyoizumi, H. “Development of high-
viscosity underwater concrete for marine structures”
- Ghio, V. A., Monteirio, P. J. M. and Gjørv, O. E. “Effect of polysaccharide
gums on fresh concrete properties”, ACI Materials Journal
- Brown, D., Bailey, J. and Schindler, A. “The use of self-consolidating concrete
for drilled shaft construction”
- Ceza, M. and Bartos, P. J. M. “Development of an Apparatus for Testing the
Washout Resistance of Underwater Concrete Mixtures”. ACI Concrete in
Marine Environment, Proceedings Third CANMET/ACI International
Conference, Canada.
- Dr Sidney Mindess,Developments in the Formulation and Reinforcement of
Concrete 2nd Edition, Emeritus Professor of Civil Engineering at the University
of British Columbia, Canada.
- Arnon Bentur, Concrete in the Marine Environment.


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