BESIKTAS FISH MARKET

AIDA SALÁN SIERRA

INDEX

PROJECT INFO

INTRODUCTION

CAUSES

PREVENTIONS

SOLUTIONS

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PROJECT INFO

Project Name: BESIKTAS FISH MARKETProject Location: Turkiye/Istanbul/Besiktas

Collaborator: Besiktas MunicipalityArchitectural Project: Gokhan Avcioglu & GAD

Project Architect: Gokhan AvciogluProject Team: Ozan Ertug, Serkan Cedetas, Tahsin İnanici

Photographs: Özlem Avcioglu, Ozan ErtugProject Date: 2007-2008

Construction Date: 2008-2009Owner: Besiktas Municipality

Construction type: SteelSite Area: 320 m2

Total Construction Area: 320 m2Project Cost: 500.000$

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INTRODUCTION: BESIKTAS FISH MARKET

Besiktas Fish Market is one of the most attractive and important architecture pieces in Besiktas neighbourhood and maybe in all Istanbul. Located in one of Istanbul’s most populated and diver-se neighborhoods, Besiktas is an eclectic area with a village-like atmosphere that is in the process of urban renewal. The Besiktas Fish Market is located on a triangular site.

It is an iconic venue where many locals and visitors buy fresh fish daily. The construction of the old fish market was in very poor shape and needed to be replaced. The studio in charge of the restoration was GAD Architects, who solve the problem of the old fish market designing a triangular shaped concrete shell covering the entire site with large openings at street level. The design solution was to maintain its iconic neighborhood presence, while also reaffirming its welcoming feeling. The con-crete shell provides a column-free interior space, optimizing the project’s programmatic needs. The new design injects a con-temporary and pragmatic solution, at once preserving the fish market’s history.

Nowadays, six years after its construction, the fish market doesn’t need a structure restoration. But it has a problem that it is of common interest now in concrete buildings: efflorescences.

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This work talks about why efflorescence can damage concrete, not only it aspect but its quality too. Also it is going to describe all the types of restoration the fish market can be evolve in to not only solve the efflorescences but to prevent more in a fu-ture. One purpose of architecture is to study the material and show it the way you want it to show. Any transformation or malformation of the material can damage the last aspect of the material, so that of the whole building. That is why is so impor-tant to prevent this type of malformations and much more in a material so strong as concrete. The essay it is going to be divided in two big parts: first one will describe the methods of preventing efflorescence in concre-te; while the second one will describe the solutions when this efflorescence have appeared and how we are going to prevent they appear again.

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WHAT CAUSES EFFLORESCENCES?

The easy explanation is: As concrete cures, the moisture slowly migrates to the surface of the block where it evaporates into the air. Like a candle wick, the water brings dissolved salts and minerals from within the concrete mixture. As the water evapo-rates, those minerals are left on the surface of your block, giving it a whitish, hazy or streaky stain.In most cases, this problem is temporary – eventually the salts will all be removed from the concrete, and the efflorescence will stop. How long this takes depends on the ingredients with which the concrete was made, and how long it takes for the concrete to cure and dry out completely.

An example of extreme efflorescence. The concrete was placed, coloured, and stamped shortly before winter. The extended pe-riod of water movement through the concrete to the surface brought chemicals to the surface where they combined with carbon dioxide from the air to produce calcium carbonate.

Efflorescence occurs with all concrete and is the most frequent problem that concrete contractors face with coloured concrete. Owners don’t care about “plain” concrete, but coloured concre-te is another matter.

Efflorescence is caused when soluble salts and other water dis-persible materials come to the surface of concrete and mortars. It’s induced by low temperatures, moist conditions, condensa-tion, rain, dew, and water added to the surface of fresh concre-te to assist troweling. It can occur very soon after exposure to moist or cool conditions or gradually, especially when it comes from within the concrete or from the sub-grade.

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Any material containing portland cement results in efflores-cence. The most usual reaction occurs when calcium hydroxide (lime) formed in the hydration reaction of portland cement is transported by water to the surface through capillaries in the concrete. There it combines with carbon dioxide from the air to produce calcium carbonate (an insoluble material) and water. But efflorescence can also be caused by hydroxides and sulpha-tes of either sodium or potassium, which are much more soluble in water than calcium. And they form efflorescence more rapi-dly than calcium hydroxide. These salts can come from cement, aggregates, water, or admixtures.

Efflorescence is normally white and shows up more on darker colours than white or light grey because of the contrast. Some forms are very difficult to remove, while others are easy—espe-cially if they are removed right after they form.

In the Besiktas Fish Market this problem occurs because of the rainwater in Istanbul. The chemical disposition of the water is a big problem in all types of materials, but even more in the ones that are sensitive to stains and damage in their surface. Further more, another explanation of this damage is the high level of salt in the water of the Bosphorus, salt and lime. That, as it has been explained before, affects directly to this stains problems of the surface. A high concentration of salt in water always cause a damage in the building surrounding the coast line. So that when the salt water condense into clouds and then it precipitates into all these buildings, they can show the stains that are the rests of the salt in the rainwater.

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HOW TO PREVENT EFFLORESCENCE

Prevention is better than cure, both in cost terms and in those situations where repeated remedial treatment is needed for new appearances of efflorescence.

The only way to completely and permanently prevent (both pri-mary and secondary) efflorescence in cementitious materials is by using special admixtures that chemically react with and bind the salt-based impurities in the concrete when hydrogen (H) is present. The chemical reaction in these special additives fuses the sodium chloride on a nanomolecular level, converting it into non-sodium chemicals and other harmless matter that will not leach out or migrate to the surface.

It is also possible to protect porous concrete against efflores-cence by treating the material with an impregnating, hydro-pho-bic sealer. This is a sealer that repels water and will penetrate deeply enough into the material to keep water and dissolved salts well away from the surface. Prevention is better than cure, both in cost terms and in those situations where repeated reme-dial treatment is needed for new appearances of efflorescence. In order to prevent efflorescence the transport of water through the structure should be hindered, so that calcium hydroxide and other salts cannot gravitate towards the exposed surfaces. This can be achieved by increasing the hydrophobicity with water-proofing admixtures and/or by lowering the permeability. For lowering the permeability in cementitious structures, the water/cement ratio should he kept as low as possible commensurate with good workability by using super-plasticisers in the mix. In addition, extenders ground granulated in allowing additional calcium silicate hydrate to form the internal permeability of the

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hardened structures is lowered thus hindering internal trans-port. These extenders have a good record in preventing or at least minimising the extent of efflorescence.A very effective method for preventing efflorescence is to treat the structure with an appropriate polymeric system that effecti-vely covers it in a film and so stopping the transport of dissolved salts to the exposed surfaces by a blocking effect. This can apply to cementitious systems like concrete as well as to clay brick-based systems.

The surfaces should be clean and free from oil, algae, dust and any existing efflorescence and the substrate must be dry. Any efflorescence can be removed by cleaning off with an appropria-te proprietary efflorescence removal fluid prior to sealing, so that the white patches can be removed from both the surfaces and the upper layers of the blocks as well.

Concluding remarksPrevention is better than cure. Special polyurethane membranes can stop efflorescence from forming in the first instance in both concrete materials and in brickwork, by effectively cutting off the water flow to the surfaces. Blended cements containing pfa, ggbs, metakaolin or microsilica are very useful for dealing with efflorescence by lowering the permeability in cement-based structures. Waterproofing agents can be applied to concretes.

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HOW TO REMOVE EFFLORESCENCES

Despite all efforts, efflorescence may sometimes occur. A detail may have been omitted. Materials may have been in-correctly specified or may not have been used as specified. Sometimes conditions just naturally conspire to generate efflorescence on a wall. The materials may not have been covered or stored on pallets off the ground. Unknown salts could infiltrate masonry materials during a wind storm or sim-ply through ignorance and misuse of the materials. Salt laden soils could be backfilled against a wall where the salts could be absorbed and cause efflorescence. Whatever the reason, when efflorescence does appear, it has to be removed.

The first step in removing efflorescence should be an attempt to identify the salts. If the salts are water soluble, the best removal method is with a dry brush. Rinsing with water or natural weathering process may also be effective. Alternately, if the efflorescence is in small patches or limited areas, hand washing with a mild detergent and a stiff bristle brush will often prove sufficient.

Several methods are suggested. One is to use water under pressure or one of a number of products available from stone dealers; another is washing the concrete with an appropriate dilute acid like hydrochloric acid HCl with subse quent flus-hing with water. Several mild individual applications are bet-ter than one overpowering dose. Again, care must be taken to thoroughly presoak the wall with clean water and to tho-roughly flush the wall of all remaining acids with clean water. Most chemical cleaning agents are proprietary and must be used according to the manufacturer’s directions.

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Generally, thorough presoaking and post washing with clean potable water is required. Presoaking is done to saturate the wall, reducing its natural porous tendencies and limiting the depth of penetration of the cleaning solution. After the cleaning solution has been used, the wall must be thoroughly washed with clean water to remove any of the cleaning che-micals. This is very important since most cleaning agents are acidic in nature and cannot be permitted to remain in the wall where they will continue to react with and erode the masonry itself.

The use of light sandblasting for removal of stubborn efflo-rescence (after many months). Allowing the surface to dry thoroughly and then using a stiff brush, prior to wash ing with water, has helped prevent re-penetration of the surface by the salt. Incorporating waterproofing admixtures/polymeric membranes into blocks, bricks and cladding panels to main-tain their original condition upon prolonged exposure to the weather.

These salts would then reappear on the surface as the structu-re redried. It was learned accordingly, that the best way to re-move these soluble salts was to brush the surface thoroughly with a stiff brush. Water, however, has been satisfactory for removing efflorescence from the face of concrete structu-res, since concrete is fairly well saturated with water. In fact, efflorescence in the form of alkali salts will be washed from the surface of concrete structures, if exposed to rain, over some period of time. If the coating is largely calcium carbona-te or calcium sulfate, it adheres rather strongly and is difficult to remove by brushing.

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The practice developed in this case for masonry surfaces, has been to saturate the structure as thoroughly as possible with water, and then wash with diluted muriatic acid, followed im-mediately with an alkaline wash, then washed with water.

The last method but also used by experts is the reliance upon natural weathering - Here the calcite crusts either fall off by wind erosion, or by their progressive reaction with moist at-mospheric carbon dioxide to form calcium hydrogen carbona-te, a very soluble material, which can easily be washed away by rain. It is essential that remedial treatments for removing efflorescence be always carried out by experts, so that any risk of damage to the structure can be avoided.

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Cleaning efflorescence from masonry walls does not cure the problem; it only removes the symptoms. After cleaning, the efflorescence will reappear unless the natural efflorescent chain is broken. Due to the added water used when pre- soa-king and post-flushing the walls when using chemical or acid cleaners, the efflorescence will sometimes reappear, often stronger than before. The efflorescence already indicates that soluble alkali sulfates may exist in the wall and that the sulphates have migratory paths to the surface. All we can pre-vent now is the moisture from entering the masonry and ren-dering the sulphates into solution.

South and West facing walls are normally less prone to efflo-rescence since the sun exposure moves the point of evapora-tion further into the wall. The point of evaporation is where efflorescence occurs. On the other hand, North and East fa-cing walls are normally cooler and the point of evaporation remains on the surface of the wall where the efflorescence occurs. It is not a cure-all to simply seal a wall when efflo-rescence already exists. The presence of efflorescence shows that the salts are already in the wall, have sufficient water to be made soluble, and that migratory paths exist for the salt solution to travel through to the surface. It would be better, if possible, to wait until the efflorescence problem has been reduced to a minimum before sealing the wall. Efflorescence is a controllable condition that should not be a problem in modern masonry. Breaking the chain of conditions necessary for efflorescence can be done with good details, the correct materials and quality construction.

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