rebuild volume6 no 4

8/10/2019 Rebuild Volume6 No 4

1/15

In continuation of our efforts to create awareness onwaterproofing for the durabili ty of concrete structures,this issue of ReBuild is devoted to waterproofing of

water retaining structures. Achieving a high durabilityof reinforced concrete in water retaining structures isnot often planned and designed properly. This issuecovers various aspects of durability in constructionof water retaining structures pertaining to water andsewage treatment.

Water retaining structures can be below or above gradestructures. In case of below grade water retainingstructures, the raft and vertical members are subjectedto different kinds of stresses with hydrostatic pressurefrom inside and earth / ground water pressure fromoutside when the tank is in full, half-full or in empty

condition. Comparatively, in case of above grade waterretaining structures, the members are subjected tointernal pressure only. Based on functional requirements,the members are made as watertight structures andwaterproofing is done for additional protection fordurability of the structures.

When it comes to the waterproofing of water retainingstructures, constant hydrostatic pressure combined withthe rigid and porous structure of concrete pose seriouschallenges for an effective and durable waterproofingsystem. The Indian code, which is referred to for thispurpose is IS : 6494-1988, R-2010, Code of Practice forWaterproofing of Underground Water Reservoirs andSwimming Pools, but it has not yet been updated withpresent materials and systems.

The first step for achieving a watertight structureis good design along with the selection of suitableconstituents of concrete mix with a superplasticizer. Inaddition, it is important to take care of all expansion,contraction, construction joints with suitable materialsand treatment at fixtures like pipes and conduitswith waterbars etc. Thereafter, waterproofing of thestructure should be done with an integral waterproofingcompound and protection with a film-formingmembrane or a preformed membrane. The modern

system of crystalline is most suitable in any kind ofwater retaining structure for various purposes suchas integral water proofing compound, injection groutsand surface applied coating materials. While choosinga preformed membrane on PCC below a raft slab oron the external surface of a retaining wall in case of

below grade structures, preformed membranes suchas APP (Atactic Poly Propylene) / SBS (StyreneButadine Styrene) or EPDM (Ethylene Propylene

Diene Monomer) membrane will be more suitable, butrequires skilled application. Cementitious coatings aremore suitable for waterproofing of internal surfacesof water retaining structures of below or above grade.Surface preparation is one of the most importantfactors for any durable coating system along with agood quality of primer and application. Wherever tilingworks need to be carried out, the tiles should be laidwith tile adhesives and tile joints need to be filled withtile grouts. For protection of internal areas of sewagetanks; water-based thixotropic epoxy-based coating ismore suitable and care should be taken to ensure thatno infiltration takes place from the sewage tank to the

adjoining soil and ground water.

All the waterproofing materials to be used insidewater tanks, reservoirs and swimming pools need tobe tested and certified by Central Food TechnologicalResearch Institute (CFTRI) for safety purposes.

Sometimes remedial treatment of water retainingstructures may be difficult and needs to be carefullyplanned and executed at the site so that it can bein operational condition at the earliest. The usualremedial treatment of corrosion, cracks and spallingcan be made with polymer repair materials. Whereverinjection is needed on the positive side, micro-finecementitious material, with or without the addition ofadmixtures, can be used to produce injection groutsfor crack filling. If the injection is needed on thenegative side with water inside to stop the dampnessand leakages, then PU Plain or PU Foam materialsmay be injected depending on the severity of waterleakages. Where spalling of concrete has taken placein larger areas, a ferrocement concrete lining ormicro concreting can be adopted after completing allcorrosion treatments.

Apart from the broad aspects of waterproofing,this issue of ReBuild also covers some case studies

on remedial treatment. We hope it will be beneficialfor our readers for designing, waterproofing andremedial treatment of different kinds of waterretaining structures. We shall focus on water proofingof internal wet areas of buildings in the next issue ofReBuild.

From theEditors Desk

2


2/15

Waterproofing of Water RetainingStructures[Excerpts from Dr. Fixit Healthy Construction Booklet ConstructYour Ideas, 2012, pp. 14-15, 35]

1.0 Introduction

During the construction of any water retaining structuressuch as underground water reservoirs or concreteswimming pools, etc., it is essential to ensure the water-tightness of the resulting structures so that the flowof water from inside the structure to outside, and theinfiltration of water from the surrounding soil into thestructure are effectively prevented. Watertight concreteis achieved by a combination of selective materials,good workmanship and full attention to details both in

design office and on site to ensure all water containingand water retaining structures should meet the strictestspecifications from the conception to the design andfinally the materialization of the project.

There are so many materials available for waterproofingtreatment, which are more efficient for water-tightness.When it comes to the waterproofing of swimming pools,constant hydrostatic pressure combined with rigid andporous structure of concrete pose serious challenges foran effective and lasting job. Indian standards are not up todate with latest technology and material for waterproofingof swimming pools & reservoirs.

A water retaining structure may be defined as a hydraulicstructure designed to hold back, restrain, or obstruct theflow of water. The treatment of a surface or structureto prevent passage of water under hydrostatic pressureis known as waterproofing of such water retainingstructures. The different water retaining structures maybe of following types:

Swimming Pools

Reservoirs / Water Treatment Structures

Underground Water Tanks

Overhead Water Tanks

Ponds, Water Features and Fountains

Sewage Treatment Structures

2.0 Design Consideration & Precautions

Suitable precautions should be taken to avoid cracksand leakages in water retaining structures resultingfrom the following:

Movements due to shrinkage and creep

Movements due to variation of temperature and humidity

Movements due to dissipation of heat generated by theconcrete in the process of hydration

Damage to the concrete by the percolation of chemicallyaggressive liquids from outside

3

Damage due to uneven settlement of foundations

Cracking of concrete caused by rusting of bars

Hydrostatic uplift force

To avoid temperature changes as far as possible, thewater tank should be built partly into the ground sothat the soil is available to cover the roof, if necessary,and to form embankments on the outside so as toenclose the water tank completely in a covering ofearth. Special precautions should be taken to guardagainst evaporation and the movements arising fromextremes of temperature before the covering is made.

The design consideration should be made forserviceability, loads, design, durability and joints.In case of durability, the following points such asmaterials requirement, cementitious component,

strength and W/C ratio, additives, embedementsand curing components should be considered.Comparatively, in case of joints, the points need tobe considered are types of joints, joint spacing, jointmaterials (water bars, fillers, sealants, bond breaker,reinforcement and dowels), joint design and jointconstruction considerations.

3.0 Construction Details

3.1 Concreting

The first successful step in construction of waterretaining structures is to make a structurally integralprotection system comprises of only the reinforced

concrete structure that is designed to minimize waterpenetration by the structure itself. The permeability ofthe concrete is reduced by introducing water-reducingagents, high performance PCE (Polycarboxylate ether)superplasticizers, and pozzolanic products such asSilica-fume or Aluminosilicate, organic binders or poreblocking additives. A good quality superplasticizer inthe concrete mix is a solution of super plasticizingagent & additive in water. It helps in achievingincreased workability in all grades of concrete. Thewater/cement ratio should between 0.40-0.45 with aPCE based superplasticizer. This would reduce size,number and continuity of pores. Pore blockers such as

silica fume acts as hydrophobic materials to line theconcrete pores and thus reduce capillary absorptionby altering the intermolecular forces in the system;concrete air water. The minimum and maximumcementitious contents in the mix should be 360 kg/m3and 400 kg/m3respectively. In case of water retainingstructures in aggressive environment Fly ash shouldbe added by replacing 15-30% of OPC cement and insuch cases 28-days compressive strength should beminimum 40 MPa and in normal environment minimumM30 grade of concrete is desirable. Maximum dryingshrinkage at 28 days of in-situ concrete should be420 microstrain. Apparent volume of permeable voids

of hardened concrete should be less than 14%.


3/15

4

Internal vibrators should invariably be used, whereverpossible. Vibrators should not be used for displacingconcrete. Overloading the vibrators by placing too

much concrete per vibrator is not good. Over vibratingby using too many vibrators relative to quantity ofconcrete also is not good. Segregation by excessivevibration or excessive water content should be strictlyavoided. Vibrator shall be withdrawn gradually andsmoothly, and in a manner which shall not causesuction, voids or air entrapment.

Concrete cover is very important factor in all waterretaining structures. In such structures, the nominalcover to meet the durability requirement as per IS 456-2000 should not be less than 75 mm.

Concrete should be properly cured. Curing has an

important influence on the permeability of concrete and itis necessary to keep the concrete moist, particularly duringthe first few days. Concrete synthesis, placement as well ascuring practices should conform to the local regulations ofconcrete technology for water resisting concrete.

Cracks number and width is controlled from sufficientand properly placed steel reinforcement. In long walls,it is recommended that the walls should be divided intosections not more than 15 m long with a gap of about30 cm left between sections so that the shrinkage inthe long sections may occur as far as possible beforethe gaps are concreted, and the longer this can be

deferred, the better. The use of carefully rebated jointsis imperative at these construction joints.

Lapping of reinforcement in circular tanks should be soarranged that not more than 25%of the bars are jointedat any one vertical section. To reduce shrinkage stressesas far as possible, there should not be less than 0.3% ofsteel in any direction.

Depending on the smoothness of concrete substrate,a levelling mortar layer should be used. Usually theselevelling mortars are quite thin (less than 6 mm thick).To reinforce them and increase their adhesion, an SBRlatex should be used in the mix. For this purpose, a

commonly used mix can be adopted such as Portlandcement: Moist sharp sand: SBR latex in the proportionof 1 part: 3 parts: 0.2 0.25 parts with clean water asrequired for achieving a desirable consistency.

3.2 Expansion and Contraction Joints

In water retaining structures, free contraction joints dealwith early age thermal movements and irreversible dryingshrinkage where no load transfer or equalising of deflectionin the plane of joint is required.

In concrete swimming pools and reservoirs of small andmedium capacities, it is not economical to provide expansion

joints and it is not a practice also. In large reservoirs,

expansion joints shall be provided at predeterminedpositions limiting their spacing to not more than 35 min the case of underground structures or those with fully

covered sides, and not more than 28 m in the case ofpartly exposed structures.

3.3 Polysulphides (PS) Sealant at Expansion and

Contraction Joints

Polysulphide sealants, based on mercaptan terminatedpolymers, are high-performance elastomeric jointsealants and are very well-suited for such expansionand construction joints. They have excellent chemicalresistance and weathering properties. Polysulphidesealants provide a durable, flexible, watertight seal forall traditional sealant applications in addition to moreaggressive immersion application. They have excellent

chemical resistance for which they are very well-suitedin case of large water reservoir and sewage treatmentstructures. They should not be exposed to hightemperature and they will not adhere to substrates withcontamination and traces of bitumen. Use of shalitexboard as a backup material should be avoided. Pouringgrade version must only be applied in horizontal joints.Application should be started only after 30 minutes ofpriming the substrate for Gun & Pouring Grade sealant.

3.4 Construction Joints

Construction joints should be set at right angles to thegeneral direction of the member. As far as possible,

vertical joints should be avoided. This can be done bycompleting a layer of concrete not more than 60 cmhigh in a continuous operation working around thecircumference in both directions from the starting pointand repeating the process for the days operation. Beforeclosing days operation, a rebate should be formed in theconcrete on the top surface of the wall forming key toget construction joints as shown in Fig. 1 for the nextdays operation. Before the next operation is started, alltimber spoils, laitance, scum or loose concrete shouldbe removed by hacking the surface and then scrubbingoff with a wire brush to remove all loose mortar oraggregates. Thereafter, before resuming the concreting

operation, the surface should be thoroughly washedand wetted with water, and then a thin coat of cementsand grout of cement mix, as that in concrete, shouldbe applied. As an additional precaution, water bars maybe used at such joints. But sufficient care should betaken when PVC water strips are being used. Otherwise,while pouring concrete from a height, these strips mayget bent and thereby restrict the passage of concrete,causing large size pores and honeycomb concrete.

All non movable joints e.g. new-to-aged concrete, floor-to-wall joints and casting interruption joints should bepreventively sealed with water bars. The same is valid forall through-wall penetrations.


4/15

5

3.6 Waterbar

The construction joints as well as movement jointsif provided should be laid watertight, preferably with

the provision of PVC water bars. A water bar looks likea rope, which should be compressible or swellable toone of the different sizes in case of water retainingstructures. They are made of different materials likehydrocarbon-based polymers, hydrophilic rubber,bentonite-based butyl rubber and other materials suchas pigments and fillers, adhesion promoters and manyadditives. The preformed construction joint sealant isavailable in non-swellable (SW20X20)) or swellable of5 x 10 mm or 5 x 20 mm sizes. It is used to seal coldconstruction joints in swimming pools and reservoirs,which are in constant touch with water. Such jointsare susceptible to water leakages in horizontal,

vertical, inclined and curved profiles and can be takencare by water bars since they are highly adhesive,flexible and swellable having controlled expansionand withstanding ability to hydrostatic and hydraulicwater pressure. The typical step-by-step method ofwater bar installation is shown in Fig.3 and the detailsof application in horizontal and vertical sections areshown in Fig. 4 and Fig. 5 respectively.

1. Plain cement concrete

2. Flexible waterproofing coating/membrane

3. Protective screed

4. RCC raft

5. Protective method on vertical surface

C1. First construction joint minimum at 300 mm above raft top

C2. Subsequent construction joint (As minimum as possible)

3.5 Treatment at Fixtures like Pipes & Conduits

The pipes and special fixtures should be fixed in positionbefore concreting operation so that these are built in at

the time of construction. These special fixtures should beprovided with puddle collars for proper grip with concreteand also to act as a water bar around the periphery ofsuch fixtures.

Preferably, pipe inlets will be formed in-situ during thecasting of the concrete and sealed using expandingwaterbar (Fig. 2).

Where it is necessary to install pipes after the casting of theconcrete, these can be sealed using a PU sealant.

Holes or cut outs in concrete done for fittings of underwaterlights, pipe openings for the filtration plant etc. must begrouted with non-shrink cementitious grouts before the

waterproofing coating is taken up for application.

3 1 2

22

5

5

4

C1

C2

200mm

Fig. 1: Construction joints

a. Clean the surface b. Apply primer 20 mm wide

c. Uncoil Waterbar d. Place in position

e. Pour concrete f. Finished waterproof joint

Fig. 3: Installation of Waterbar

Fig. 2: Waterbar around pipe joints


5/15


6/15

The thickness of polymer-modified bitumen membraneor self-adhesive SBS-modified bitumen membrane andEPDM (Ethylene propylene Diene Monomer) membrane

varies from 1.2 to 2 mm whereas torch-appliedmembrane thickness varies from 3 4 mm. Whenever,the membrane is used in large reservoir, it should resista minimum hydrostatic water pressure head of 8-10 Bar.

However, while selecting any waterproofing materialfor underground reservoirs or swimming pools, onehas to check the major functional properties requiredsuch as hydrostatic pressure head to resist, presenceof aggressive chemicals if any, and service life of thewaterproofing system. The thickness of the coating/membrane and other properties need to be selectedbased upon their required performances of thewaterproofing systems.

In general, the various properties of the membranesuch as water absorption should be 0.10 g/m 2 /24 h,water vapour transmission rate should be less than0.05 g/m2 /24h. The membrane should have betterchemical resistance properties, crack bridging abilityof 0.5 mm, elongation between 100-200%, punctureresistance of more than 900 N and adhesion strengthfrom 1.5 to 2 N/mm when used in reservoirs or swimmingpools. In case of water tanks the coating should haveanti-microbial/anti-fungal/anti-algae properties andeffectively prevent the growth of harmful elementsthat are hazardous to human beings. Such coatings

should be non-toxic and eco-friendly that is 100% safefor potable water contact and tested and certified bycompetent authority.

4.3 Application on Raft Slab and External Walls

4.3.1 Surface Preparation

The surface should be cleaned thoroughly of allcontaminants like dust, traces of curing compound,oil and grease. All surface imperfections, protrusions,structurally unsound and loose concrete must beremoved and repaired with polymer-modified mortarusing SBR latex commonly used waterproofing andrepair material.

4.3.2 Priming

All over the blinding concrete or PCC that is properlylevelled, polymer-modified elastomeric bituminouscoating diluted with water in 1:1 proportion or a solventbased bitumen primer should be applied with a roller orbrush over a dried surface. Allow the primer to dry for 8to 10 hours prior to the application of coating.

4.3.3 Application on PCC Below Raft Slab

APP (Atactic Poly Propylene) / SBS (Styrene ButadineStyrene) modified bitumen-based preformed membraneshould be laid by providing an overlap of at least 100

mm. APP / SBS modified bitumen-based membraneshould be extended to maximum extend of the fullarea of the blinding concrete. A geotextile membrane

of 120 gsm should be laid as a protection layer overAPP / SBS modified bitumen membrane. A screedof 50 mm must be overlaid in M 20 concrete grade,which will facilitate the reinforcement cage to beassembled for the RCC raft to be cast over it.

4.3.4 Application on Retaining Wall

Concrete joints in retaining walls and at raft levelshould be provided with flexible adhesive stripspopularly known as water bars either of a swellablestrip of 5 mm X 20 mm size or of a compressible stripof 20 mm X 20 mm size, which shall be placed in jointswhile concreting of raft slab and retaining walls.

40 mm X 40 mm sized angle fillets must be providedat the corners all around the floor and walls from theexternal side.

The retaining wall should be prepared by cleaningthe surface and priming it with primer to receive thewaterproofing system.

APP / SBS modified bitumen should be appliedstarting from the bottom of external wall right upto ground level. It has to be ensured that APP / SBSmodified bitumen is applied up to at least 300 mmabove ground level.

After completion of application, a 4 mm thickbituminous protection board should be placed or a12 mm thick dimpled HDPE drainage board should beapplied for protection. The application details on raftslab and external wall is given in Fig. 6.

4.4 Application on Internal area

4.4.1 Surface Preparation

The internal surface areas (horizontal and vertical)

should be cleaned thoroughly of all contaminants

7

PCC

Primer

APP/ SBSmodified bitumenbased membrane

Geotextile fabric

Screed

Flexible adhesivewaterstop strip

Protective Board

Fig. 6: Raft slab and external wall waterproofing details


7/15

like dust, traces of curing compound, oil and grease.All surface imperfections, protrusions, structurallyunsound and loose concrete must be removed and

repaired with polymer-modified mortar using SBR latexfor waterproofing and repairs. At internal side wallsand raft junction, cast 40 mm X 40 mm sized anglefillets all around floor (Fig 7).

4.4.2 Application

After complete curing of the raft slab and retainingwalls a 1st coat of high performance polymer modifiedcementitious coating should be applied by maintainingthe saturated surface dry condition. While the coatis still wet, a glass fibre mesh of 2.5mm x 2.5 mm of50 GSM should be embedded over the angle filletsas a reinforcing strip and should be allowed to soakcompletely. Thereafter one additional coat should

be applied for sandwiching the glass fibre meshimmediately. Then a 2nd coat of high performancepolymer modified cementitious coating should beapplied. After the 2ndcoat is completely dried, a 3rdcoatof high performance polymer modified cementitiouscoating should be applied and coarse sand shouldbe sprinkled while the same is still in wet condition.This will provide the key for subsequent tile adhesivematerials in case of swimming pools. The schematicdiagram of typical waterproofing detailing of a waterretaining structure is given in Fig. 8.

4.4.3 Pipe Inserts

Pipe inserts should be wrapped around with leak-proofsealing tape for pipe wrapping to ensure a water-tight fitting. Light fitting casings, pipes, inserts, etc.,provided in the concrete raft floor and walls shouldbe grouted with a non-shrink grout. Non-shrink groutfor pipe fitting of high-performance polymer-modifiedcementitious coating should be liberally appliedaround the insert pipes and the around the lightfittings sandwiched with an open woven mesh for extraprecautions.

8

Waterproofing Coating

Angular Fillet

Fig. 7: View of fillet at raft and retaining wall

5.0 Waterproofing in Internal Areas of Swimming

Pools

Swimming pools (Fig. 9) offer an excellent wayto relax, exercise and provide enjoyment to anindividual. They come in different shapes and sizes.To effectively and safely manage a swimming pool,one should have a pump, basin, water filter, chemicalfeeder, drains, return and the proper plumbing totransport the water.

The primary function of swimming pools needs tobe considered while designing any kind of swimmingpool. Whether kids will be playing water sports allsummer long or anybody wants to swim laps. It can bebuilt to any size or shape or style as per the budget.There are two major types of swimming pools suchas elevated swimming pools generally on rooftop orground level swimming pools which may be flat orslopped. A flat swimming pool typically is not deeperthan five feet. Play pools generally are built forcooling off and relaxing in, playing volleyball, other

Fig. 9: View of a Swimming Pool

1

2

4

3

5

6

7

8

9

10

11

1 B nd ng Concrete (PCC)

2 Primer

3 APP/SBS modifiedbitumen based membrane

4 Geotextile

5 Concrete Screed

6 Concrete raft slab

7 H gh Per ormance polymer mod edcementitious coating (2 coats)

8 High Performance polymer modifiedcementitious coating (3rd coat with sand)

9 Epoxy based tile joint filler10 Light fixture with Non-shrink grout

11 Pipe opening with Non-shrink grout

Fig. 8: Typical waterproofing detailing of waterretaining structure


8/15

water sports, as well as for swimming laps. Sloppingswimming pools are generally gradually deeper witha diving board or platform. They have a slope at the

bottom as they start from 1 m to about 15 m.

5.1 Waterproofing in Swimming Pools

There are many stressing factors that need to beconsidered while doing waterproofing in case of swimmingpools such as alkaline substrates, water pressure, variouschemicals, mechanical abuse, solar radiation, UVs etc. Thepaint, if any, should be waterproofed, resistant to mildewand discoloration and, if possible, water vapour permeable.It should be both functional and aesthetically appealing.

For internal surface waterproofing, EPDM Membranebelow the raft slab and high performance cementitiousliquid applied coating on internal surfaces should be usedin case of swimming pool before the tiling.

5.1.1 Cementitious Waterproofing Coating

Two-component cementitious coating, composed ofhigh quality cement, properly selected and gradedfillers, additives and liquid polymer should be usedas a cementitious coating. It is suitable for achievingwaterproofing in swimming pools because it providesstrong bonding, good waterproofing and provides excellentresistance to hydrostatic water pressure by forming ahighly elastic seamless coating over the applied concrete ormasonry surfaces. The water proofing detailing in internalsurfaces of an elevated swimming pool is given in Fig. 10.

5.1.2 EPDM Membrane

EPDM rubber-based prefabricated membrane is moresuitable in deep swimming pools and under raft ofground level swimming pool. It is used for waterproofingand lining of underground concrete structures ofswimming pools because it exhibits a high degree ofresistance to water, ozone, UV, weathering, abrasion,extreme temperatures, acids, alkalis and oxygenatedsolvents. The water proofing detailing in internal surfacesof an ground level swimming pool is given in Fig. 11.

5.2 Tiling in Case of Swimming Pool

Tiles should be applied using tile adhesives of 23 mmthick depending upon whether they are glass mosaics orceramics. After the tile fixing, fill the grooves / tile jointswith epoxy-based tile joint filler grouts.

5.2.1 Tile Adhesives

It should comprise ordinary Portland cement properlyselected and graded aggregates, polymer, rheologymodifier and additives. It is generally used for fixingof tiles internally and externally over walls and floorsin swimming pools with an added application of tile ontile because it gives excellent bonds on cementitioussurfaces like concrete, plaster, etc. It forms a waterproof

9

barrier between two surfaces and has excellent grabproperties of tiles to the substrate.

5.2.2 Waterproof of Tile Joint Fillers

The tile joint filler material should be a fine powderconsisting of Portland cement, specially selectedpolymer, properly selected and graded fine fillers,additives and inorganic chemicals. It is used forgrouting of tiles because it has water repellantproperties, excellent adhesion (high bondingstrength), soft consistency, workability and seals

joints permanently. It is non-shrinking, non-toxic andodourless grout used for sealing of swimming pooland water tank joints as well.

5.3 Grouting Steel Rods by Anchorfix Grouts

The railings, handle and all steel rods or pipes need to befixed with polyester resin anchor fix grouts.

6.0 Waterproofing in Internal Areas of Reservoirs

and Water Treatment Structures

In addition to imparting waterproofing properties,products designed for protecting water-retainingstructures such as reservoirs (Fig. 12) or watertreatment for drinking water applications need tomeet additional requirements. These include:

Safe for use in contact with drinking water

High resistance to leaching

Protection from infection

Water bar

Polysulphidesealant

Tile adhesivesand tile grouts

High performancecementitiouswaterproofingcoating

..

.

.

.

.

.

.

..

...

.

.

.

..

..

..

.

.

.

.

.

.

..

...

.

.

.

..

..

..

.

.

.

.

.

.

..

...

.

.

.

..

..

...

.

.

.

..

..

..

.

.

.

....

.

Protection screed

Fig. 10: Waterproofing detailing of an elevated swimmingpool

Fig. 11: Detailing of waterproofing of ground level

swimming pool

High performance cementitiouswaterproofing coating

Ground level

Polysulphide sealant

Ground level

EPDM membrane with protection board

Blinding concrete

Waterbar

..

.

.

.

.

.

.

. .

...

.

.

.

. .

. .

...

.

.

.

...

.

...

.

.

.

. .

. .

...

.

.

....

.

...

.

.

.

. .

. .

...

.

.

.

. .

. .

...

.

.

.....

Tile adhesivesand tile grouts

Protectionscreed


9/15

Resistant to attack from condensate

Smooth, easily cleaned surface

First a fillet is formed around the inside-perimeter of thepond using polymer mortar. Once the mortar has cured,two coats of cementitious water proofing coating are to beapplied to the sides and floor of the pond. If a tiled finishis required, a render of 3: 1 sand: cement should be appliedover the second coat of cementitious coating whilst it isstill green. This will provide a suitable base for tiles to befixed using a suitable waterproof tile grout. In common withall cementitious coatings, will cause the water in the pondto have a high pH (typically between 12 and 13) when firstfilled. To bring the pH down to a more neutral level, thepond will have to be emptied and filled several times untilthe correct pH is reached.

7.0 Waterproofing in Internal Areas of Underground

and Overhead Water Tanks

Overhead water tank should be designed in such a waythat the structure itself should be made watertight. Incase of underground water tanks the structure shouldbe made watertight additionally at bottom raft and atexternal surface of the wall. While considering internalsurface waterproofing of smaller water tanks like inhousing societies, a two component cementit ious coatingcan be used where as for larger water tanks crystallinewater proofing would be more suitable. A two-componentepoxy resin based coating specially formulated forinternal applications for the waterproofing of watertanks can also be used.

Crystalline or equivalent (injection grouting admixture)should be mixed with dry cement @ 5 kg per 50 kgof cement. Sufficient water should be added to thismix to obtain slurry and grouted under pressureusing a pressure grouting pump of 2-10 bar capacity.

The concrete surface should be saturated well withwater and a crystallization waterproofing compoundshould be applied on the clean and saturated surfaceof the walls and raft slab in 2 coats at 1 kg per m2. The

coating should be protected with a layer of cement

mortar mixed with waterproofing compound withneat finish. The curing should be done after 24hof application of 2nd coat for atleast 5 days. The

application detail inside a water tank is given in Fig. 13.

8.0 Waterproofing in Internal areas of Ponds, Water

Features and FountainsThe decorative artificial ponds, water features, fountains,fish breading ponds or fish tanks are constantly exposedto pressing water. They need to withstand a constantbattering from the elements and leaking is common aftera few years. Liquid-applied Polyurethane waterproofingsystems is more suitable for waterproofing or lining insuch structures. Polyurethane resin coating has excellentmechanical, chemical, thermal, UV and natural elementresistance properties and safe for uses on surfaces indirect contact with potable (drinking) water. It cures byreaction (cross linking) of the two components. Howeverfor longer service life EPDM rubber based preformed

membrane is more suitable.

9.0 Protective Coating in Internal Areas of Sewage

Tanks

Sewage treatment structures are subjected to severechemical attack and physical stress. While designing andtaking protection measures of RCC structures one hasto ensure that no seepage into the earth and groundtakes place from sewage tanks. Concrete waterproofingand chemical resistance products for use in sewers andsewage treatment plants need to be specifically designedto cope with the following stresses caused by:

Continuously changing degree of contamination

10

Fig. 12: Inside view of water reservoirs

Fig. 13: Typical internal area waterproofing details

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

Ang e Fi e

Waterbar

Screed

Polymer modified cementitious coating (2 coats)

Coating with sprinkled sand

Plaster

Leak-proof sealing tape & non-shrink grout

8 Intake Pipe


10/15

Environmental effects

Fluctuating liquid level

Formation of aggressive microclimates in sealed holding

tanks To provide additional protection to the hydrogen sulphide

corrosive atmospheres encountered in enclosed sewage tanks.

To provide protection against aqueous sulphate solutions andliquid manure

Waterproofing

Re-profiling and

Protection of concrete against

Increasing surface resistance

Protection for extreme loads

Epoxy is the best material against chemical resistance.In case of sewage treatment tanks, a two parts, water

based, thixotropic, high performance, epoxy based,waterproofing coating is most suitable. Coal tar epoxycoating is also suitable. PU (Polyurethane) coatings aremore suitable for sewage water tanks due to their excellentchemical resistance properties.

10.0 Testing after Construction

It is detrimental to keep the water retaining structuresdry for a longer period than 4 weeks, as it may lead toformation of cracks. So it is imperative that before the lastcasting is completed, water arrangement for testing thetank is ready at site. Immediately after the removal of formwork, the tank should be tested. All preliminaries should be

completed in advance.

Water should be supplied to the reservoir slowly at therate of 300 to 450 mm depth of reservoir per day and theresult closely observed, both from the angle of structuralstability whether any crack is being noticed anywhere inthe structure at any time and from the point of view ofwater tightness At the end of the operation, that is, whenfull supply level is reached, all valves shall be closed tightly.The water level in the reservoir should be properly markedon the wall. Leakage through the valves should have beenchecked and there should not be any drop due to the same.After 24, 48 and 72 h, the levels should be checked and thedrops in level will be a measure of water-tightness.

The permissible standard usually adopted is 6 mm dropin 24 h in case of covered reservoir and 12 mm in caseof open reservoirs. Necessary adjustment should bemade depending on the relative humidity and otherlocal conditions.

If there is no drop, but dampness is observed in the outersurface such dampness may vanish in course of time as thefree lime ejected out of cement will be plugging the minorpores causing such dampness. If the intensity of leakage isslightly more, then lime may be added to the testing water.

In case of leakages, the points should be marked and

11

separately treated after dewatering.

It is sometimes difficult to locate the source of leakagesin case of underground reservoirs. If it is from the

floor, it is hardly possible to locate unless clear cracksare noticed and hence complete floor will have to betreated. So in such case of underground reservoir, thedrop in level should be recorded for every 300 mm afterkeeping the water for 24 h. If at some stage, there is nodrop, then it is presumed that floor is in order and thewall above that height is only responsible for leakage.If drops are noticed all through, it may be only the floorwhich is responsible for the leakage or both floor and thewall. With the presumption that the floor is not in orderand the wall is in order, the floor may be set right leavingthe treatment of the wall for the future, if necessary.

For all these uncertainties, it is recommended that someadditional aids or precautions be taken for underground

reservoirs, especially to prevent outside sub soil water tofind its way inside when the reservoir is empty.

All the water proofing products should be approved foruse in contact with drinking water. Nevertheless, wherefish are to be kept in the pond, it is important to takeprecautions to ensure that the water quality is suitablefor the species of fish to be kept.

After the new construction of fish pond and sufficientcuring it should be filled with water without any fish. Thepond needs to be set for five days and then water to bedrained out and washed down all the surfaces with freshwater. Again the pond should be refilled and water to be

allowed to stabilize over night before adding a test fish(feeder fish) to assure that the water is now safe for thefishes before adding more expensive decorative fish. Ifthe test fish is still alive after 3 days next step shouldbe followed; but if the fish does not survive then drainthe pond and wash down all surfaces with fresh water.Refill the pond and allow the water to stabilize over nightagain before adding another test fish. Once the pond hasproven safe for the feeder fish then decorative fishes areput inside the fish pond.

11.0 Conclusion

Water proofing of any water retaining structures is oneof the toughest job. A better understanding of material

and proper selection of water proofing material fordifferent water retaining structures will ensure durablewaterproof system. Nevertheless the joints and pipeopenings are most vulnerable which need to be detailedand waterproofed properly.

References

Design and Construction of Joints in Concrete Structures,CIRIA Report 146,1995

Joints & Sealants, Healthy Construction Manual-1, Dr. FixitInstitute of Structural Protection & Rehabilitation,2010

IS : 6494-1988,R-2000, Code of Practice forWaterproofing of Underground Water Reservoirs and

Swimming Pools


11/15

12

infrared thermal imaging can be carried out to identifythe exact source of leakage.

The water retaining structures in distress have tobe investigated in details. The detailed physicalobservation, assimilation of data, non destructivetests will help in arriving at the reasons for distressand their extent. Based on these, appropriaterestoration measures have to be worked out.

3.0 Surface Preparations

Before doing any repair the existing surface of the oldconcrete walls and the floor of the reservoir shouldthoroughly be cleaned using a wire brush and anylaitance on the surface is removed by chipping. Finedust is removed using a fine bristled brush. In caseof swimming pools all the tiles need to be removedand repair work should be carried out on originalconcrete surface. Wherever the growth of algaeand fungi has taken place, those places need to beremoved physically followed by treatment with anantimicrobial solution to eradicate any spores and toinhibit further growth. After treatment leave for 2-3hrs and then wash down thoroughly with clean waterand allow the surface to dry completely before doingany waterproofing work.

4.0 Repair Techniques

The selection of repair scheme depends on manyfactors such as type and extent of damage,environmental conditions, load intensity, accessibility,time constraints, availability of experienced agency,etc. The repairs techniques generally adopted for therestoration of water tanks are:

Patching techniques

Substitution of members

Strengthening of existing members by

Shotcreting

Wrapping / bonding techniques

Encasement with concrete / free flow micro concrete

Chloride extraction / passivating technique

Electro chemical remedies Pressure grouting

Providing waterproof barriers

Surface protection

5.0 Repair Materials

Cement based materials such as polymers concrete /mortar composites (polymer concrete (PC), polymermodified concrete (PMC), polymer impregnatedconcrete (PIC), etc. can be used as repair material.Due to the very high strength and durabilitycharacteristics, the polymer mortar / concretecomposites are being increasingly employed in

Remedial Treatment of Water

Retaining Structures

[Excerpts from Rehabilitation and Repair of Structures, Vol.2,CE& CR, pp.7-8 and Dr. Fixit Healthy Construction BookletConstruct Your Ideas, 2012, pp. 40-41]

1.0 Introduction

Generally repairs are carried out to meet one or moreof the objectives, like restoration of structure integrity,restoration of original profile and appearance, to arrestdeterioration, to seal cracks and arrest the leakages.The remedial treatment of the structure is dependentupon amount of leakage experienced by the structure.

The gravity loads are the major loads, which act on thestructure constantly. The structure is in contact with

water continuously and is prone to ingress of moistureand other related problems. Adequate care needs tobe exercised during construction phase, especiallywith regard to quality of materials and constructionprocedures. The shortfall in any of these, leads todistress in these structures.

2.0 Causes and Symptoms of Distress

The water retaining structures undergo distress due toone or more of the following reasons such as deficiencyin structural designs, deficiency in construction,deficiency in material of construction, atmosphericpollution / hazards, natural hazards and inadequate

maintenance. The symptoms of distress can be resultantof a single or a combined symptoms such as dampnessand leakage (Fig. 1), active / passive cracks, sagging ofmembers, swelling of concrete, discolouration, white/brown patches, spalling of concrete, exposure of barsand erosion of surface.

It is important to observe the leakage by loading partiallyan observing the decrease in level of water and identifyingthe spots form outside wherever it is possible, but in caseof underground structure identifying the leakage spotsfrom external side will not be possible. In such cases thefully filled water retaining structures need to be drainedout and after some times the wet spots on the surfaces

need to be marked. The non-destructive test method of

Fig. 1: Leakage in a roof terrace water tank


12/15

13

repairs and rehabilitation jobs. The PMC and PMM areincreasingly used for rehabilitation because they arecement based and therefore, give homogeneity to the

system and the repair materials, and due to the alkalinenature of the repair material restore the alkalinity ofdeteriorated concrete and arrest further corrosion.

A variety of micro-fine cementitious material with orwithout addition of admixtures can be used to produceinjection grouts for cracks filling. In case of severewater leakages polyurethane plain or polyurethanefoam injection can be carried out to arrest the cracksand leakages.

6.0 Patching Techniques

The cleaned surface should be inspected for cracks. Anycracks on the surface are chased into a v-groove and are

thoroughly cleaned with air blower and water jet. Thecracks are then filled with SBR based polymer modifiedmortar in the ratio Cement: Sand (1:4) and 5% by weightof cement of polymer. In case of leakage occurringthrough the horizontal construction joints, the same

joint should be cut-off by a saw cutter into a V shapedgroove and filled with polymer modified mortar. Theopenings around the rain water pipes should be packedwith cementitious grouts.

The junction of the walls and the slabs should berounded using cement mortar of 1:4 mix admixed withan integral waterproofing compound confirming to IS2645 or equivalent integral waterproofing compound@ 200 ml per 50 kg of cement by laying the fillet withsame polymer modified mortar.

The repair of a deteriorated concrete structure mayinvolve injection grouting of the cracks, patching upof the deteriorated spalled concrete surfaces andlocations, coating of reinforcing bars and concretesurfaces and replacement of deteriorated concrete andreinforcing bars in combination with repair materials.The major problem is corrosion on account of leakage.To prevent the leakage, polymer modified mortar maybe used inside the tank. For concrete member withongoing reinforcement corrosion, impregnation with

silane produces a significant reduction in the rate ofcorrosion of reinforcement. Commonly used repairtechniques are guniting using non-shrink cementmortar, jacketing with micro concrete, resin mortarpatching and cement mortar patching. Jacketing themembers of the staging is the best method for achievinggood results. In the case of patching required for largeareas, guniting has to -be resorted to for coveringthe entire surface with sufficient thickness of mortarstrengthened with mesh reinforcement.

7.0 Pressure Grouting

7.1 Preliminary Preparation

Assess the problem area & suitably mark the spots for

drilling grouting holes. If the intensity of runningwater is high & cannot be controlled, then divert theflow of water using a PVC pipe at the spot of leak.

For heavy dripping, mark the spots in a grid pattern150 mm centre-centre or in case of spot dripping dri ll

at the point of leakage at an angle of 45oto the planeof grouting.

Drill diameter for a hole should be corresponding tothe packers in use (generally 16 mm - 20 mm) & depthof the hole drilled to be 100 mm deep or generallyhalf the thickness of the substrate. Fix alloy packers(non-return type) of dimension 14 mm x 80 mm with asuitable putty. Allow the putty to cure for 24 hrs priorto commencing the injection grouting process.

7.2 ApplicationMix the base and hardener in the specified proportionsof PU Foam Injection in 10 parts of base: 1 part ofhardener. The mixing should be carried out in acompletely dry container using a mechanical stirrer.After rinsing the pump using a PU Cleaner, fill thePU mixture into the pumping container and initiatethe pumping (Fig. 2) on a low pressure and graduallybuild up the pumping pressure suitably. Stop pumpingif back pressure is sensed or if the grout has oozedout of the adjoining hole. PU foam injection oozes out(Fig. 3) of the grouting hole and hardens primarily in10-15 minutes.

Complete curing of the PU foam will happen over aperiod of 24 hours. A secondary injection shouldbe carried out with PU plain injection. Mix base andhardener in the specified proportions of PU plain

Fig. 2: PU injection in a water retaining structure

Fig. 3: PU forming foam after the injection


13/15

14

injection in 2 parts of base: 1 part of hardener. PU plaininjection, resin injection to be pumped once the PU foamhas to set in a similar manner as that of foam. This will

act as a secondary injection thus completely sealingthe leaking cavity. Cut off the extended portion of thepacker and seal the surface with suitable putty. Choiceof PU injection grout, such as foam/plain, depends onthe condition of the substrate and severity of leakage.Incase of severe dampness injection grouting can bemade using micro-fine cementitious materials. In thiscase drill grouting holes at an angle of 45 on the walladjacent to the area of dampness at a spacing of 500mm centre to centre or less in a grid pattern.

Fix PVC or MS nozzles (packers) in the grouting holes usingepoxy putty and allow the nozzle to set for 24 h. Add waterat a ratio of 0.35-0.45 to prepacked cementitious groutmix to a uniform consistency using a mixing paddle. Usinga grouting pump, inject cementitious grout through thenozzle at required pressure. Grouting should commencefrom the lowest possible level & proceed upwards alongthe grid with the pumping pressure increased gradually.Continue pumping until the grout flows out from adjacentnozzle. Detach the pump & nozzle and seal the groutinghole with epoxy putty.

8.0 Surface Protection

After reinstating of spalling plaster in floor/wall andsealing construction joint, a brush application of two

coats of cementitious crystalline coating over theplastered surface should be made. The time durationbetween two coats should be 4 hours and air cure for24 hours prior to loading of water. Depending on thefunctional requirement of water retaining structures,suitable protective coating should be applied.

The final waterproof membrane from inside must bedone using a nontoxic coating. For this purpose, anepoxystearate system (water seal), which is non-toxicand watertight, may be utilized as waterproof coatingfor the internal surface.

9.0 Conclusion

Water retaining structures need to be functional roundthe clock. Unless there is any stand by services fora continuous water supply in case of water tanks orreservoirs, repair work needs to be carried out withinthe shortest possible time and the same structuresshould be in operation. Keeping this in mind, the repairand waterproofing materials should be fast setting.Since all these water retaining structures containeither drinking water or potable water, the repair andcoating materials should be water-based and needto be certified by the Central Food TechnologicalResearch Institute (CFTRI) for safety in usage.


14/15

14

Case Studies of Remedial

Treatment of Water Retaining

Structures

1.0 Ferrocement Lining for Leak Proofing of a

Swimming Pool

Anchored ferrocement lining provides an excellenteffective leak-proof surface inside leaking masonryand concrete tanks as a cost effective rehabilitation.The present case study discusses the treatment for anold swimming pool with leakage through walls, base,

joint between wall and floor which was carried out inthe following steps.

Removing the inner finishes from affected areas tiles /mortar rendering with paint application etc.

Cleaning, roughing and washing of surface and applyingbond coat slurry over the wet surface.

Application of sealing base coat using polymer-modifiedmortar and fixing of anchors at a suitable grid.

Fixing of hot dip galvanized mesh of specified quality,diameter and spacing with specified gaps at joint.

Application of a coat of polymer cement bond slurry andapplication of polymer-modified mortar into the meshlayer using angular push technique and finish rough wait for 24 hours.

Fixing of one more layer of mesh reinforcement andapplying one more layer of polymer mortar in thesame manner as given in Fig. 1. Then repeat to providespecified no. of layers of mesh and mortar layers to buildup the designed thickness for lining.

Application of finishing surface such as tiling or epoxy /PU paint etc.

Fig. 1 provides a view of FC lining over swimming pools for new swimming pools, the continuous lining is providedin between the retaining structure and finishing surface.

(Source: NBM & CW, April 2003, Vo.8, Issue 10, pp.-42)

Fig. 1: Ferrocement treatment of the swimming pool

2.0 Treatment of Overhead RCC Water Tank with

Ferrocement Lining

A study was taken up on 12 randomly selected leaking

over head tanks in the districts of Saharanpur andMuzaffarnagar in the past which showed that:

The supporting structure in eight cases was intact andleakage was from the wall and the dome wall joint.

In six out of eight cases, there was porosity due to honeycombing at locations of leakage or the shuttering lift ringposition where a horizontal crack developed separating thebottom concrete ring from the ring above.

In four cases, the outlet pipe and inlet pipe junction withconcrete was not properly packed and there was seepagethrough these positions.

A 50,000-galllon overhead water tank was rehabilitatedusing the following steps:

Removal of internal finishes 25 mm thick cement mortarplaster.

Opening of the shuttering lift ring from inside and outside,fixing of grout nozzles and packing the same with non-shrink polymer micro concrete after applying a coat ofcement slurry added with bond improvers.

Pressure grouting of dome wall joint and shuttering of liftjoint.

Fixing of anchors in concrete over inner surface of wall andbase.

Fixing of meshes over the wall and base dome on inside

surface and application of high-strength polymer-modifiedcement mortar in layers. Each layer is properly reinforced.A special type of bond coat is used between layers offerrocement and old concrete.

Application of thin, high-strength, non-shrink mortar asinner finishing layer.

(Source: NBM & CW, April 2003, Vo.8, Issue 10, pp.-42)

3.0 Rehabilitation of a Large Leaking Below Ground

RCC Water Tank

The water tank under this case study is of basic size 17 x4.9 m having a top dome roof. The crown of the dome is

about 2 m. About 1.5 m of the tank is below the groundlevel and the rest is projected above.

3.1 Condition Assessment

3.1.1 Horizontal Construction Joints

The foundation of the water tank is of PCC (1:4:8), 75 mmthick over which RCC was laid, with M-20 concrete withminimum 330 kg/m3over for which an inclined PCC filling(1:5:10) was provided and finally the surface was finishedwith a PCC (1:2:4) to a smooth surface. The diameter ofthe 450 mm base slab was about 170 m whereas theinternal diameter of the tank was 15.2 m with a 0.25 m


15/15

15

vertical wall. The total height of the vertical wall was4.9 m having a ring beam of 0.3 m depth over it. Thevertical lift of the circular vertical wall was 1 m. Thus,

there were four horizontal construction joints in thebody of the circular vertical wall. Water stoppers wereprovided in each lift with a PVC water bar of about 150to 200 mm. The water bars have been provided insidea groove of 90 mm x 90 mm in the circular verticalwall. Thus, a possible zone of weakness was aroundthe PVC water bar, which is prone to leakage.

3.1.2 Vertical Construction Joints

The outside perimeter of the circular wall was about49.5 m. It was unlikely that a formwork of this lengthhad been used for the construction. It was most likelythat there were about 3 to 4 vertical construction

joints in every vertical lift. The length of formwork forthree such construction joints was about 16 to 17 mwhereas if there were five construction joints, thenthe length of formwork would have been about 10 m.

3.1.3 Quality of Concrete

The concrete was not properly compacted. The waterwas leaking over an area of 10 x 10 cm where waterwas coming out profusely. In different parts of thetank, reddish stains could be seen. Horizontal bandsof wetness of varying degrees on the external surfaceof the tank indicated the rusting of reinforcement.

3.2 Remedial MeasuresBased on the observation, the following remedialmeasures were recommended:

Removal of the protective plaster and the surroundingsoil up to a distance of 3 m from the face of the tank.Injection grouting at 0.5 m vertical spacing and 1 mhorizontal spacing.

The total height of the tank from the base slab level upto the bottom of the ring beam was 4.9 m; thus about11 holes were required for covering the vertical heightin one line. Thus, along the circumference for 50 suchvertical lines a total of 550 holes were drilled.

The grouting was done using polygrout / cement grout.

Weak plaster was removed and redone after applicationof bond coat of acrylic-based polymer-modifiedcementitious composite coating system.

Application of one coat of acrylic-based polymer-modified cementitious slurry followed by one coat ofbrush topping from inside.

Acrylic-based polymer-modified cementitious slurrytreatment could extend to the internal surface of thedome.

(Source: CE& CR, May 2008, pp.-76-77)

rebuild volume6 no 4

Documents