Mod-03 Lec-08 Material sin repair and rehabilitation

Mod-03 Lec-08 Material sin repair and rehabilitation


Ocean structures and materials. In the first
module and the second module we have seen different types of ocean structural systems
off shore structures, their applications and different kinds of dredging equipments, which
have been used and deployed commonly for coastal protection systems and maintenance. In the
third module we have been looking at different kinds of materials, which can be used for
construction of ocean structural systems. In this lecture we will closely see some of
the repair methodologies which can be used, which is commonly employe for maintaining
and repairing ocean structures. So, we look for materials especially for repair and rehabilitation
of ocean structures. The moment we talk about material for repair
and rehabilitation. Ladies and gentlemen please underline that there are no standard procedures
in international codes, which will suggest and recommend certain classification of material
which can be used for repair and rehabilitation. There are various reasons for this, the foremost
reason is that this material can be applied for repair only as case specific, because
choice of material to be used for repair and rehabilitation depends on the decision taken
by the construction managers and engineer in maintenance in charge of these kind of
structural systems. Therefore, in this lecture we will see some of the important techniques,
which are generally used for repair and rehabilitation. And of course recent advancements of different
material, which are suggested and been commonly used for repair and rehabilitation will also
be discussed in detail in the next module. If you look at ocean structures, many types
of ocean structural system are generally constructed for various functional requirements, we have
seen them in detail. In the previous modules they are generally designed to sustain critical
loads, but there are some special issues related to their existence of survivability of service
life of this kind of structures. Although, the service life is exceeded, they are expected
to serve, which is very critical issue as far as these structural systems are concerned.
They become functionally very important and therefore, they cannot be dismantled or reconstructing
them. Once again causes a lot of shut down time,
which is not acceptable by the service sector. So, very importantly ladies and gentlemen
even though ocean structural systems have exceeded the design service life, they are
still put to constant use on different functional requirements is very important. I can quote
a very simple example, for example offshore jetties are functionally important. Therefore,
shut down time for the new construction of the jetty is very difficult and therefore,
existing jetties are generally put to use after suitable repair and rehabilitation.
So, therefore ladies and gentlemen it becomes very important to understand the repair methodologies
and techniques to strengthen them. While they are in service, probably ocean structural
systems who are one amongst the structural systems, which are generally put to repair
and rehabilitation. When they are also in service, interestingly no standard coral regulations
specify or recommend any specific type of special repairs applicable to ocean systems. The photograph what you see here is actually
a ship dock yard in Pennsylvania. The underwater inspection conducted on this dock yard indicated
extensive repair rehabilitation has got to be done while keeping the crude oil dock in
service, which is a very important criteria imposed on the maintenance engineer at this
juncture. The construction involved actually a new approach when the pile is supported,
while the loading is taking place the rehabilitation was done for this job during 2007-2008. The other example what you see here, is up
gradation of the Cap may in New Jersey to enhance the ferry capacity. New construction
with board walks is proposed by the designer, pre stress concrete is used as a new material
for enhancing the ferry capacity of this jetty. Bulk heads have state of art composite fender
systems, which have been installed all along the surface special feature is a monopole
supported fender clusters it, which acting as an energy absorbing piers and dolphins. The photograph what you see here is an Exelon
power corporation, Philadelphia at the bottom what you see here is an intake system at Eddy
stone, Pennsylvania. In case of Exelon power corporation steel auxiliary piles are installed
to replace the front and efficient piles as you see in this photograph here. They reinforce
concrete encasements of interior steel pipes are also done. They have been replaced whereas,
in Eddy stone Pennsylvania intake well. The steel sheet piles, which have been used
are extensively damaged the underwater steel structural members are also found to be extensively
damaged. Structural repair was designed to associate with the mechanical piping system,
which in an integral part of the intake well. Therefore, ladies and gentlemen rehabilitation
is not simply a repair system it is actually a state of art design procedure as well. Another classical example is a bulk material
export jetty located in South Iran. The photograph what you see here, is the photograph of the
jetty. The berthing structure has jetty to import alumina, a dolphin jetty is also parallelly
constructed to export LPG. They are access from the land through breakwaters and bridges
as you see in this photograph. Design is special because it has to avoid the impact of two
jetties due to lateral loads, the expansion joint is designed in such a manner so that
this moment is allowed under the service loads also. Under strong lateral loads, impact energy
is dissipated by cylindrical fenders, which have been provided as one of the repair methodology
for this kind of jetty at South Iran. Now, the fundamental question which is being
asked in such kind of repair mechanisms is that, what is done before the start of the
repair? Before the actual repair has to be carried out, following factors are necessarily
to be established; one what is the existing strength of the structure, two what is the
magnitude of the proposed repair? In terms of the volume of work the matrix of work to
be carried out and of course, the cost involvement and the shutdown time of the proposed structural
system. What could be the important cost factor associated
with the repair work and what will be the shutdown time of the service of the structure,
which are most important to be considered much before attempting a repair to kind of
ocean structural system? Above all interestingly one also looks at what is the feasibility
to undergo this kind of repair. And ladies and gentlemen all of them together all under
one hat or a single process system this, what we call as integrity analysis of ocean system. What are the challenges which are generally
posted, while you attempt a repair on ocean structure? Unlike land based structures, ocean
structures need to be repaired in coastal environment because these kinds of structures
mostly have less or remote access to land. It also requires specialized equipments, chemicals
and construction expertise to carry out repair with these kinds of structural systems.
It also requires state of art electronic systems to map under water conditions of the existing
system because the existing system should be thoroughly examined. And the states of
art electronic system should be deployed to understand the asis varies basis of the system.
If you really want to propose the appropriate repair methodology for underwater structural
members, it also requires state of art electronic surveillance that includes hydrographic survey
equipment side scan and sonar imaging while the repair is also in process.
It also requires ultrasonic thickness measurements of steel members because it is very important
to assess, the actual thickness of existing members if you want to propose an appropriate
repair methodology for these members. Therefore, underwater videography, photography and marine
borer assessment technologies are very commonly deployed, when you want really think about
repair of ocean structural system. Therefore, ladies and gentlemen even to attempt the repair
in ocean structures is a complex task. it is not an as easy and an as simple as we do
for land based structural systems. What are the unique challenges, which can
be posted on when you attempt to do a repair of ocean structural system? Structure has
to remain in service while you are carrying out the repair it is a very interesting task,
which is assigned to maintenance or a construction or a rehabilitation engineer who attempts
to do a repair on existing structural system. The structure should remain in service when
the repair is being carried out. Therefore, the load carrying capacity should not be challenged
when you are attempting a repair. Hence, specialized equipments are generally used because of two
reasons; one you cannot damage the existing structural system to a greater extent, which
affects the load carrying capacity, two the shutdown time to which you are going to carry
out the repair is always available to you in a limited point of time.
Therefore, specialized equipments are to be used to carry out urgent repair process and
of course, the repair process suggested by you should be cost effective. It should remain
as a long term solution because these are two important factors, which are generally
demanded by the client, so that they need not have to put the repair very often. Therefore,
the shutdown time during the repair of a foreseen system is also limited. Hence, the client
is always interested to limit the long term solution of this problem attempted as well
as the solution suggested by the consultant or the designer should also be cost effective.
The repair processes as I said are not generally available in the standard literature and are
not generally recommended by international codal provisions because the chemical admixtures,
which are generally used for repairs are case specific. Therefore, on any emergency situation
one should be aware of understanding the repair methodology, which is generally recommended
for this kind of repair. Hence, one should have a standard of understanding
of various repair methodologies and chemicals available to do repair on emergency situation.
Enough time is generally not available for the maintenance engineer to carry out repair.
Therefore, detailed studies and verifications cannot be carried out at a longer time duration
because generally repairs are attempted, when there is an emergency call. When you talk about damage of reinforced concrete
ocean structural systems. There are very interesting points to be understood as far as concrete
as a construction material is concerned. Concrete structures can be damaged as a result of either
deterioration of concrete due to chemical reactions or physical phenomenon within the
material. The second major issue is that the reinforcement, which is embedded in concrete
also receives a corrosive attack, because of the marine environment. If you look at this chart, which indicates
me what are the general causes for deterioration of concrete as studied in Queensland University,
North Ireland UK. The majority of people and researchers has spoke as saying the reason
for deterioration of concrete is from external chlorides. Followed by which put together
is an internal or inbuilt chloride system and of course, temperature variation in terms
of freezing and thawing also contributes to the deterioration of concrete structures in
terms of ocean structural systems. Carbonation and alkali aggregates also contribute about
one fourth or 25 percent in total about the deterioration process in together. If you also look at the reasons for failure
of concrete structures as attempted in ocean structural systems as seen from this chart
as occurred to see with Queensland University at U K, poor quality concrete contribute only
for about 2 percent. As you see here because enough quality control methods are exercised
in terms of construction of ocean structural systems. The majority actually comes mainly
from wrong specification, wrong material selection and in sufficient water proofing and very
poor cover in terms of design or in terms of construction aspects.
The failure of this kind of structural system generally gets focused upon wrong selection
of material as a majority. Therefore, ladies and gentlemen is very important for us to
understand selection of material plays a very important role when you want to apply this
as a construction material for ocean structural systems. If you look at the process of deterioration
of concrete due to chemical reaction, which is a very important task as far as repair
is attempted in ocean structural system. Leaching and sulphate attack are considered to be a
serious problems as far as concrete under chemical reactions are consist. Calcium hydroxide
is dissolved and reacts with carbon dioxide which forms as a deposit, which is white calcium
carbonate within the concrete and also on the surface of concrete. Extensive leaching
could decrease the strength of concrete and also facilitate ingression of aggressive agents
into the concrete, which then further reacts with rebar embedded concrete and causes corrosion.
If you look at the sulphate attack as one of the reasons for chemical reaction, which
deteriorates strength of concrete sulphates reacts with calcium hydroxide to form a compound
called gypsum. Gypsum in turn reacts with hydrated compounds to form Ettringite this
results in expansion of concrete in manifold volume, which results ultimately in cracking
of concrete. Once concrete surface gets cracked it gets exposed to weather and therefore,
penetration of chlorides and weather environment then attacks the reinforcement, which results
in corrosion. In addition attack by magnesium sulphate is
more damaging because magnesium hydroxide that is formed the reaction between CSH replaces
the calcium irons with magnesium irons, which destroys the so called cementing effect in
concrete. Also, if you look at the alkali silica reaction as one the important reason
for deterioration of concrete. Hydroxides of sodium and potassium that are
present in cement can react with fine grained porous silica aggregates a product what is
called is a silica gel is formed is absorbs water and as a result this expands. When all
the pores all filled further expansion causes cracking of concrete dehydration of the gel
leads the cracks open. When the silica has high surface area as in case of silica fume,
which is commonly used or concentration of alkalis is low, then non swelling gels are
formed which of course results no damage. If you look at the alkali carbonate reaction
present in concrete which is subjected to marine environment, the dolomitic lime stone
aggregates can react with alkaline. This results in the loss of bond strength and develops
what we call micro cracking in the concrete structure. The steps in alkali reaction can
be seen as follows; as a first step release of alkali from cement during hydration increases
concentration of hydroxide ions in the pore solution.
In the second step initial hydrolysis of siliceous fraction of aggregate in highly alkaline solution
destroys the aggregate integrity completely, followed by which swelling of alkali silicate
gel by inhibition of water cost local swelling, increases internal pressure and this result
in cracking of concrete. As a last step liquefaction of alkali silicate gel takes place the further
inhibition of water this results in the expulsion liquid gel through cracks. As you understand sometimes ocean structures
are also subjected to reversal of time in terms of temperature like Freeze Thaw cycles,
what we call as Frost attack in literature. When the temperature of concrete drops below
0 degrees, water actually immediately does not freeze, water in smaller pores needs a
lower temperature below 0 to get frozen. So, water in 10 nanometer pores will not freeze
until minus 5 degrees is reached and pores of 3 point 5 nanometer will not freeze until
minus 20 degree is reached. So, gel water will not freeze until minus 78 degrees Celsius
is reached. So, water does not freeze immediately as soon
as temperature drops down to 0 as the water freezes it dilutes and compresses the remaining
water. Pressure is relieved if the water diffuses to open the voids, if voids are not available
then pressure may build up and it causes rupture in concrete. If the air entrained concrete,
bubbles relieve the pressure and prevent damages from occurring instead of dilation there is
contraction on freezing. Ladies and gentlemen it is a very interesting
picture showing the damage in piers beams and socket of the slab, which are primarily
due to the chlorine attack which is a port in Indonesia. You can see the socket of the
beams, which are extensively corroded even the surface of the columns which are corroded
and spoiling of concrete takes places, which exposes the reinforcement not only on the
side faces of the beam as well as the main reinforcement in the bottom face of the beam
as well. If you look at the damage picture of the jetty
due to sea water exposure, again you can see here the bottom surface of the slab is also
getting exposed, whereas the reinforcement is getting exposed to a severe attack of chemical
environment in marine sea state. Also the jetty fenders get deteriorated due
to chloride attack and mechanical action. You can see here the deteriorated jetty fenders,
where the steel is getting exposed thoroughly and some repairs being attempted using a specific
specification of the chemical and the concrete, which will be discussed in the next part. Now, as we understand looking at these examples
we see that role of admixtures play a very important role in inculcating corrosion resistance
to the reinforcement embedded in concrete. As I said, these admixtures have different
roles to play as case specific. Therefore, no international codes clearly recommend certain
set of chemicals it all depends on experience site engineers and maintenance engineers to
recommend certain admixtures and chemical treatment to protect ocean structures or systems
from further corrosion. This is the process what we call repair and
rehabilitation. You can use plasticizers or water reducers, which will help to limit the
water cement ratio. This can yield concrete with low permeability better contraction and
good quality top layer. The top layer will remain dense and will free from bleeding waters.
The retarding and plasticizing admixtures will help, when concreting is done at higher
temperatures in their absence there could be rapid work ability loss and it will result
in quick setting, which is not desirable as far as ocean structural construction is concerned.
Corrosion inhibiting admixtures increases corrosion threshold of steel by providing
additional resistance to rebar can also add admixtures, which improve abrasion resistance.
This can be increased by using higher strength super plasticized concrete. Water resisting
admixtures can also be used with hydrophobic properties which may help liquid penetration
at the surface. If you look at the action of corrosion inhibitor
in detail, it provides a second line of defense to prevent corrosion of steel reinforcement
which is embedded in concrete. This supports a protection providedby alkaline nature of
concrete, most commonly used corrosion inhibitors are nitrite based compounds. I can give an
example calcium nitrite is a compound, which is being used as a common corrosion inhibitor.
They give a second line of defense to prevent corrosion to the steel reinforcement. They
act by interfering in the corrosion reaction to the formation of protective ferric oxide
layer on steel or by reducing access to steel, which is less Chemisorption or dissolution,
corrosion resistance is better off course at lower water cement ratio. If you look at the typical case example of
the caisson gate group of a dock yard, which we examined. The picture shows you the dock
yard gate the caisson gate which is damaged, the vertical edges of the groove as you see
here. These are the vertical edges of the caisson gate groove, which are extensively
damaged because of the impact caused by the caisson gate. The vertical edges of the groove
are abetting the caisson gate are seemed to be structurally damaged, cracks are seen at
many places you can see on the surface as well as here along the grooves water therefore,
enters through the crack the peep at the groove at the emergency stop as you see from here. There is a damage caused therefore, waters
enters through these the gates does not remain water tight. So, what would be the method
to attempt a repair for this kind of treatments, If you look at the preparation action for
repair the concrete has to be completely chipped of in stages and the steel has got to be completely
exposed. As you see in this photograph during repair
you got to do a proper water proof shuttering, and keep on doing a micro plating whose specifications
are discussed in the next slide. So, the problem what you just now saw is existing
grooves are severely damaged and they seems to be structurally unsafe because they cannot
withstand the impact loads, which are posed by the gate when the gate is being under operation.
Hence, new set of reinforced concrete columns are propose in the design and the design to
withstand the said impact loads caused by the gates. What is the repair methodology? Damage caused
at the edges allows the seawater to enter the die dock position, which is hampering
the repair operation of the dock. The caisson gate grooves can be repaired only in the dry
condition. Therefore, you have got to shutdown the dock for service ability for some time.
Steel scaffoldings are used using vertical props and horizontal ties both for vertical
edges of each group and they are erected as straight as possible. Existing loose or damaged
edges of grooves are cleaned thoroughly, they are completely dismantled using hand held
electrical chisel and hammers to expose the reinforcement. The exposed RCC surface is then thoroughly
cleaned using water jet and the wire brush. Rust and scales from the old reinforcement
are removed by applying scarified anode, which is for example, can be a Sika Fera Zinc R
chemical compound or equivalent. Epoxy based bonding agent is then applied between the
old and new concrete for example, Sikadur 32 Lp or equivalent can be used for such kind
of applications. New reinforcement is now placed in position as per the suggested design. The slurry tide form work is then erected
to provide microcrete concrete, proper poring shall be ensured by using a suitable feed
hopper mechanism. Free flowing, non shrink high strength M45 grade was designed for this
application, which should be a fluid micro concrete with 12mm to 8mm down well graded
clean coarse aggregate is recommended for this application. For example, Sika Rep microcrete
4 or equivalent with 4 liter of water for 25kg is recommended as a mixture of micro
concrete, which can be poured in the water tight slurry for repairing this gate groove. Mixing should be done by heavy duty slow speed
electrically operated stirrer after pouring the water in the mixing vessel. Mixed material
should be poured through feed hopper system into the well position hessian cloth for 10
hours after placing the micro concrete and after sticking the shutter for at least 15
days with water. If you look at the advanced materials, which
are used for repair… Cathodic protection forms a very major role
in such kind of treatments, one of the effective methods to stop corrosion of reinforcement
bar in concrete is cathodic protection. This method uses direct current from external source
through anode that is embedded in concrete cover. When the electrons flow in between
the supplemental anode and rebar, rebar becomes cathodic and therefore, it is protected because
no corrosion takes place in the reinforcing bar. If you look at one of the examples again where
the major deterioration is caused by chloride attack on concrete. As you see here the cathodic
protection which is being prepared shows a current flow from an external supplement node,
which is acting as anode to the embedded reinforcement. So, the supplemented anode is being connected
to existing rebar, which are corroded which is becoming the cathode that is why we call
this as a cathodic protection. The ribbon anode is also used in RCC been
prior to concrete as you see in this photograph. These are all ribbon anodes which have been
used. Therefore, they are allowed to corrode whereas, the rebar inside embedded inside
does not corrode because it becomes cathodic. If you look at electro chemical protection
systems further as an advance method for protecting this kind of structural systems. Steel concrete
remains normally in a passive state, if chlorides reach steel they act to break down this passive
layer. So, corrosion becomes free to progress therefore, corrosion current flows from one
part of steel, which becomes anode through concrete into another part which becomes cathode.
So, steel corrodes at anode and produces rust, corroded steel then can expand four to five
times of its normal volume, which cracks concrete and also results in spoiling and delamination
of concrete. This in turn exposes the steel further and accelerates the corrosion process. Early detection of corrosion therefore, is
a very important stage in planning the corrosion prevention measures, the solution could be
what we call corrosion monitoring system will discuss this system in detail an as applied
to various examples in the fourth module. However, now will see very briefly what is
a corrosion monitoring system? This provides information to the rate of corrosion at which
the rebar is being corroded. Early detection of chloride contamination of concrete is also
an integral part of this corrosion monitoring system. This system is based on embedded corrosion
monitoring units in concrete itself. It detects corrosion by measuring the galvanic
current between carbon steel and stainless steel electrodes with their embedded into
concrete, it measures the corrosion rate by electro chemical polarization technique, it
measures the reinforcement potential of the embedded steel. If you look at the recent advancements available
in the literature as one of the important case study been done for improving corrosion
resistance to steel. Ladies and gentlemen so very recent advancement
had been done by using Nano layered coatings. Nano structured coatings enhance the resistance
surface against corrosion. The recent invention in Taribat Modares University in Tehran highlights
the use of Nano structured coatings, which I will discuss very briefly now in two slides.
In this method, alkoxide tetra butyl ortotitanate, which is abbreviated as TBT is used to prepare
a soluble gel solution. The advantages of this method are its simplicity, homogeneity
and high uniformity of the applied coating, which is very thin, therefore this is called
Nano layered coating. How this is done? Ethanol and ethyl acetoacetate
are mixed together at room temperature, TBT added to the solution and the solution is
stirred well. While stirring taking place some drops of distilled water is also added
during this process, for polymeric reactions the prepared reaction is then left for about
6 hours. After surface preparation is done using titanium oxide Nano coating is then
applied on the surface of steel by submerging method. It is possible to reduce the causes
of corrosion in petroleum gas and petrochemical industries by applying simply a Nano coating
on the steel surface by submerging method, which is one of the recent advancements done
in Tehran. So, ladies and gentlemen in this lecture we
discussed about quickly the repair methodologies and rehabilitation techniques, which are commonly
adopted. We also discussed few case sheets where these methods were attempted successfully
for repair and rehabilitation. So, the construction materials chemical admixtures, which are commonly
used for repair and rehabilitation are really challenging because no standard international
procedures are recommended by the codes to follow any repair schemes because these repair
schemes are generally case to case basis. We will discuss more about these schemes in
the next module. Thank you very much for listening to this lecture.

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