TABLE OF CONTENTS List of figures. 1 1. Introduction. 1 2. Factors effecting durability of concrete in marine environment. 2 3.
Methods to repair the concrete deteriorated in marine environment. 2 4. Protecting concrete from corrosion in marine environment. 9 4.
1. Experiments for quality improvement of concrete. 9 4.2. Experiment results and discussion. 10 5. Summary and Conclusions: 12 LIST OF FIGURESFigure1.
A severely damaged pile which wasrepaired earlier with fiberglass jacket. 4Figure2. Integral pile jacket system using fiber glass jacket with mesh anode. 6Figure3. Galvanic system where thin layer of zinc is attached to cleaned steel andadjacent concrete. 6Figure4.
Conductive rubber pile jacket system protecting tidal and splash zones of abridge pile. 6Figure5. Embedded galvanic anodes installation. 8Figure6. Repairing the spalls.
8Figure7. Compressive strength variation. 10Figure8. Flexural strength variation.
10Figure9. Sorptivity variation. 11 1. IntroductionConcretein marine environment is directly affected by severe exposure conditions. Corrosionis the main problem for concrete in marine environment which can be caused dueto chloride ion penetration, sulfate attack, alkali-silica reaction, carbonationetc. Concrete acts as protectivematerial towards steel reinforcement at normal exposure conditions. Theprotection is due to higher levels of pH in concrete and formation of aprotective film around the steel. However presence of excess chloride ions inconcrete-steel interface destroys the protective film and initiate the steelcorrosion.
Chloride ions which are present abundantly in marine water permeatesthrough concrete to the steel. The pH decrease or carbonation in concrete causesthe steel to corrode. The deteriorated concrete in marine exposure need to berepaired. To prevent the concrete from corrosion and increase its life span,appropriate concrete which is resistant to chloride need to be used in thestructures.2. Factors effecting durability of concrete inmarine environmentToprotect the concrete structures from corrosion it is important to use a goodchloride ingress resistant concrete.
The durability of concrete in marineconditions is dependent on quality of it. High strength concrete is requiredfor longer life of structures in marine conditions. Concrete having minimumcompressive strength of 60MPa is typically used in marine conditions. Theperformance of concrete is influenced by its permeability, mix compositions andbinder material. For better performance of concrete in marine conditions, itmust possess lower permeability and by using proper mixed proportions. Usingpozzolanic materials with blended cements is known to reduce the permeability. Also,high strength concrete is known to withstand extreme environments due to thepresence of relatively high binder material, strong aggregate-cementinterfacial zone, superplasticizer and absence of large capillary spaces.
Theycan achieve a capillary pore structure which is very discontinuous within fewdays of cement hydration that helps to lower the permeability.3. Methods to repair the concrete deteriorated in marineenvironment Severeexposure of structures to marine environment leads to corrosion due to chlorideion penetration etc. The structural components deteriorated due to corrosionneed to be repaired. The repair procedure opted is dependent on type ofexposure the structure has undergone.
There are two categories of marineexposure for structures. Direct exposure where structures are partially ortotally submerged and indirect exposure where structures exist along coastlineand do not come directly in contact with ocean water. The important part of apartially submerged structures are tidal and splash zones. Continuous cycles ofwetting and drying lead to high chloride ion concentration and sufficientoxygen quantities. The electrical conductivity is also high in this region. Thefirst approach to repair the corroded region is by repairing damaged areasonly.
Many materials and techniques had been used for the repair. Initiallysand/cement mortars were used for repairing the spalled regions. Later,shotcrete became popular technique as it is more economical and convenient touse especially in larger projects. With advancement of material technology,many specialty materials like silica fume concrete, latex modified concrete,polymer modified concrete were used for repairs. The effectiveness of therepair material is attributed to its electrical conductivity and lowerpermeability. To get a better bond between repair material and sound concrete,surface preparation techniques were improved.
However, the removal of thedamaged part of concrete and replacing it with other material does notcompletely resolve the problem of chloride ions, moisture and oxygen. Higherconcentration of chloride are still present in the remaining concrete andcontinue to corrode. The repair material itself also causes problem as thecorrosion cells keep developing in the steel embedded repair material and steelembedded concrete. This leads to corrosion of the periphery of the patch andeventual failure of the repair material itself. This phenomenon is called “Holoeffect”. This process may actually increase the damage due to corrosion in the surroundingconcrete which is not suitable for marine environment where structures areexposed to chloride from all sides.
Injecting epoxy for cracks was attemptedwhich was not successful. Use of jackets was another type of conventionalrepair techniques. There are two categories of jackets, “structural jackets”used for structural repairs and “non-structural jackets” used to repair thecorrosion damages. Materials like fiber glass or wood are used to manufacturethese non-structural jackets and materials like sand, cement and mortar areused as fillers. It was believed that jackets protect the structures fromfuture corrosion but it is found that they are powerless due to many reasonslike the capillary action that allowed the water from submerged part of pile toreach up the pile. And also the chloride ions were left in unrepaired regionsin high amounts. Although there jackets could delay the process of migration ofchloride ions into the pile, it could do nothing to help the corrosion. Also,these jackets were observed to be acceleration the corrosion process as it isnever allowed to dry out the concrete due to the presence of water and oxygenis always present in these jackets.
All the things the jackets could do iskeeping the corrosion out of visibility which is still more dangerous.Figure 1. Aseverely damaged pile which was repaired earlier with fiberglass jacketCathodicprotection technique has been widely increasing to protect partially submergedconcrete against long term corrosion. Cathodic protection is widely used incivil engineering industry to protect structures from corrosion. It uses directcurrent to transmit the corrosion from protected material to another location. Thusthey prevent the structure from reacting to environment and corrosion. Typically,cathodic protection can work for more than 30 years.
There are two types ofcathodic protection. Impressed cathodic protection and galvanic cathodeprotection. Galvanic which is also called sacrificial involves two metals interlinked electrically in which one metal is more susceptible to corrosion thanthe other. The galvanic anodes corrode themselves before the steel corrosionoccurs. In this method, the anodes are connected to the structure to beprotected. The anodes are charged negatively more than the structure. Whenconnected, the current passes from anode to the structure. Galvanic anodes doesnot require external power to work hence they work for a limited time.
Howeverwhen applied properly, they can last for longer periods. Examples for galvanicanodes configurations are bare metals including zinc, magnesium, aluminum etc.,backfill for underground purposes, ribbon types, rod shapes, steel straps thatcan be attached to structures etc. In many applications between galvanic anodessteel structures, the potential difference between them is not enough toproduce sufficient current required for the protection. In this case a largepotential difference is generated using a rectifier which supplies power togenerate more current to protect the structure. This procedure is called impressedcurrent cathodic protection system.Impressedcurrent cathodic protection systems are proved to be successful in protectingthe conventional reinforced concrete structures.
Galvanic cathodic protectionhas been increased to protect semi submerged structures and it is mostpreferred for prestressed components to avoid hydrogen embrittlement problems.Bridgesubstructure systems has three categories. Surface applies system, encapsulatedand non-encapsulated systems. Surface applied system involves applying anodematerials such as thermally sprayed zinc and conductive paint over the concretesurface. Application of zinc can be used both for impressed and galvaniccathode system where a thin layer of zinc will be applied to the concrete.
Ingalvanic protection, zinc can be directly applied to the steel reinforcementwhere damaged concrete can be removed. The bond between zinc and the concreteis significantly affected by the moisture present in concrete duringapplication zinc. The encapsulated system has two categories. Both thecategories use titanium anode mesh. The first category involves shotcrete foranode mesh encapsulation. The second category is developed recently and iscalled integral pile jacket system where a prefabricated fiber glass jacketincluding the mesh anode is attached to the pile using compression bands andthe spaces between concrete and jacket are grouted.
Non encapsulated system hasthree types. First type where a corrugated compressive rubber material isattached to concrete using compression bands or fiberglass panels. This systemacts as good protection to the tidal and splash regions of bridge piers inmarine conditions. Second type is similar to the conductive rubber type exceptfor recycled wood or plastic panels with cut grooves on its contact surface areused instead of fiber glass.
Third type is bulk zinc anode system. A large zincblock is submerged adjacent to concrete in marine environment which acts asgalvanic protection.Figure 2.
Integral pile jacket system using fiberglass jacket with mesh anode.Figure 3. Galvanic system where thin layer of zincis attached to cleaned steel and adjacent concreteFigure 4. Conductive rubber pile jacket systemprotecting tidal and splash zones of a bridge pileExcesschloride ion penetration to reinforced steel of concrete causes eventualcracking and spalling of the structure, requiring the concrete structure to berepaired.
The repairs performed to fix these issues often last for shortperiod. To resolve this problem U.S Navy in collaboration with A/E consultantshas set a goal to develop concrete repairs extend the service life of theirwaterfront structures which are made of reinforced concrete that includespiers, wharves and dry docks. It is challenging to repair concrete deteriorateddue to harsh marine conditions.
The repaired marine structures often requirefurther repair for every 5 to 10 years. So, U.S Navy has set goal to developrepair of concrete that can extend its life for 15 years without disruptionfrom subsequent repairs. They studied and investigated one of the piers inlocated in Pearl Harbour, Hawaii with design level inspection. Concreterehabilitation specifications were modified based on this research such asusing concrete that is specifically designed for marine conditions. Theresearch found that using “Marine Concrete” effectively controls corrosion andincrease the life expectancy of structures in marine environment. Hence it ispreferable to use marine concrete for repair rather than conventional concreterepair mix designs that does not account for high levels of chloride andconstant wetting in marine environment.
Repairing spalls in concrete can leadto cracks that can occur in edges of repaired area. This leads to shrinkage ofthe material and penetration of chloride ions to concrete. So, it is essentialto incorporate drying shrinkage tests and limitations into the specifications.
These tests are crucial in quality, durability and positioning of durablerepairs in confined areas. The deteriorated portion of concrete must beproperly removed, the corroded reinforcement should be properly cleaned beforethe placement of the repair material. Installing galvanic anodes protect theconcrete against corrosion and protecting the concrete that is adjacent to therepaired material. Installation of embedded galvanic anodes serve as protectivematerial that will degrade itself instead of the steel reinforcement next tothe repaired material to reduce the holo effect. Figure 5. Embedded galvanic anodes installationTherepair procedure involves identification of deteriorated areas and removing thedeteriorated concrete until sound concrete is reached. The steel reinforcementwas cleaned using a wire brush or a needle gun. If more than 20 percent of thesteel reinforcement of damaged, then it is removed and replaced.
Preparation ofsubstrate surface is done by applying high pressure water blasting that helpsin cleaning loose debris. Embedded galvanic anodes were installed to the steelreinforcement along the repair region to protect the repair area and areaadjacent to it against corrosion.Figure 6. Repairing the spallsConcretein overhead and vertical areas is repaired by installing plywood formwork.
Formand Pump method is used for the placement of repair material where the formworkincludes pumping ports with pressure gauges. The repairs were furtherconsolidated using external vibrators. Samples of repair materials werecollected at every shift and tested for compressive strength to ensure propermixing of the product. In-situ bond pull off test was also performed toevaluate the bond performance between existing substrate and bond material.Concreteis tested for slump, air entrainment and temperature and the placed in repairregion, vibrated and finished. The finished concrete is cured for 7 days andtested again for compressive strength and bond strength between existing andrepair materials. After placement of the repair, the areas were inspected forcracking. It was observed that hand trowel repairs produce defects thatincludes delamination and cracks.
Although hand trowel repairs are relativelyeasier and cheaper, it requires proper inspection and evaluations. Placedrepair tend to have more rate of failure compared to trowel, form and pumpmethods. The quality of form and pump repairs are observed to be satisfactory.The repaired areas were revisited after one year and the repair work appearedto meet the Navy’s goals.4. Protecting concrete from corrosion in marineenvironmentStructuresin marine environment can be protected by using concrete resistant to chloridepenetration. The durability of concrete in marine environment depends on itsquality. The higher quality of concrete is function of higher strength, lowerpermeability etc.
Hence efforts are made to improve the quality of cement bydifferent ways such as adding cementitious materials in it. One such materialthat improves the strength of concrete is copper slag. Properties of copperslag are similar to that of river sand. Hence, it can be used as a replacementfor sand. Studies have also shown that copper slag is nontoxic andnon-leachable. Copper slag has its benefits by using it as fine aggregate incement, but it delays the setting time. Studies have shown that using copperslag in clinker instead of lime and clay has improved the properties of cement.
Using copper slag as fine aggregate reduces the concrete shrinkage and improvesthe compressive strength, flexural strength and durability properties concreteand mortar (Ayano and Sankata2000). Also, using ground granulated blast furnaceslag is another way to improve the compressive strength of concrete. 4.1.Experiments for qualityimprovement of concrete Astudy is made by S.
Geeta et al(2017) ondeveloping corrosion resistant concrete by maxing fly ash, silica fumes andcopper slag with Portland cement. The behavior of concrete specimens wasanalyzed when mixed with silica fumes and copper slag. Experiments wereconducted on cube specimens with size 15cms, cylinders with 20cm height and10cm diameter and beams with dimensions 10cmX50cmX500cm. Combinations of silicafumes, fly ash and copper slag were used to make the specimens. Statisticallybased designed experiments are used to detect the components that have greaterinfluence on the response.
In this study, statistical analysis is performed usingResponse surface methodology to identify the optimal combination of thecomponents. The specimens were stem cured for 24 hours at 1000C.Strength and durability tests were performed on these cured specimens.
Lim,Teng et.al(2016), developed a study to produce concrete resistant to chlorideion penetration. Research was conducted to study the influence of supplementarycementitious materials on early age strength, ultimate strength, chloridepenetration resistance. Effects of using normal ground granulated blast furnaceslag and ultra-fine blast furnace slag and silica fume as cement replacementwere evaluated.
Twelve mixture proportions were used for the tests by varyingthe proportions of cement, water, normal blast furnace slag, ultra-fine blastfurnace slag, silica fume, fine aggregate and course aggregates. The specimenswere casted, cured and tested for compressive strength and rapid chloridemigration test on day 3, 7,28,56 and 90. The specimens were tested for modulusof elasticity on day 28. Also, electrical resistivity test was performed on thespecimens on day 3 and 90.
4.2.Experiment results anddiscussion From the tests performed by Geeta et al (2017), thechanges in concrete properties by using various combinations of copper slag,silica fumes and fly ash were analyzed.
The analysis from the tests arepresented below.4.2.1. Compressive strength:Compressivestrength test is performed on cube specimens at a load rate of 140kg/cm2per minute ina Universal testing machine.
Figure 7. Compressive strength variation Responsesurface was plotted from the experiments, showing the compressive strengthincrease of specimen with increase in fly ash and silica fumes. Also,compressive strength is observed to be increasing with increase in silica fumesand copper slag.4.
2.2. Flexural strength: Flexuralstrength was tested on beam specimens with load rate of 400kg/min. The resultsshowed that the flexural strength increase with increase in fly ash and silicafumes. Also, using copper slag has contributed in increasing the flexuralstrength. Figure 8. Flexural strength variation4.2.
3. Water Permeability: Waterpermeability test was performed on 28 day cured cube specimens. The specimenswere oven dried for 24 hours and cooled in desiccators. The weight of the ovendried samples were measured and then placed them in a tray with water andallowed water to penetrate. The absorption of water was measured at differentintervals of time. The test showed marginal decrease in sorptivity withincrease in fly ash and silica fumes. A drastic decrease in permeability ofwater was observed with increase in copper slag.
Figure 9. Sorptivity variationRapidchloride penetration test was performed to measure concrete’s ability to resistchloride ion penetration. Rapid chloride penetration test is important to beperformed for concrete to be used in marine environment. The results from theexperiment showed decrease in chloride ion penetrability with increase in flyash, silica fumes and copper slag.Fromthe study developed by Lim, Teng et.al(2016), it is observed that using groundgranulated blast furnace slag has shown lower chloride diffusion and higherelectrical resistivity and hence, the durability properties of the concrete canbe greatly improved. Using ultra-fine blast furnace slag increase the surfacearea for hydration reactions.
Hence, the early age strength of the concrete isimproved. In addition, the chloride diffusivity is also decreased by 78% with45% slag replacement. Using silica fumes as replacement has improved the long-termproperties of concrete and chloride diffusion better than using ultra-fineblast furnace slag.5. Conclusions: 1. Copperslag is useful for concrete in marine environment which increase thecompressive strength, flexural strength, reduce the water penetration andchloride ion penetration.
2. Addingsilica fume and fly ash improve the pozzolanic reactivity. It helps in improvingInter transition zone forming a compact microstructure that increases thestrength.3. Usingblast furnace slag as cement replacement improves the durability properties ofconcrete by resisting the chloride ion diffusion. Increasing the fineness ofthe slag increases the durability of concrete even further.4. Silicafumes used as cement replacement works better than ultra-fine blast furnaceslag in terms of durability and resistance to chloride ingress producing theconcrete durable for marine environment.
5. UsingMarine concrete is effective for repairing the concrete deteriorated in marineenvironment.6. Installingembedded galvanic anodes near the edge of the steel reinforcement protects thereinforcement by acting as sacrificial material by deteriorating itself beforedamaging the steel. 6. References: 1. Sohanghpurwala, Ali, and William T.
Scannell. “Repairand protection of concrete exposed to seawater.” Concrete Repair Bulletin (1994): 8-13.
2. Cathode protection systems by Matcor3. Robbins, Daniel B., and Linn B. Lebel. “DevelopingState-of-the-Art Marine Concrete Repair.
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Geetha, S., and Selvakumar Madhavan. “High PerformanceConcrete with Copper slag for Marine Environment.” Materials Today: Proceedings 4.2 (2017):3525-3533.
5. Lim, Tze Yang Darren, et al. “Durability ofvery-high-strength concrete with supplementary cementitious materials formarine environments.