Ferrocement Water Storage Tanks forRain Water Harvesting in

Hills & Islands

P.C. Sharma Retd. Head, Material Sciences & Project Leader NDWM Projects, Structural Engg. Research Centre Ghaziabad (India)

Consultant, Rain Water Harvesting & Concrete TechnologyEditor New Building Materials & Construction World

165 Jullena, Adjacent Escorts Heart Institute, New Delhi-25, E-mail: nbmcw@vsnl.com

Rain water harvesting has a specialimportance for hill areas andislands as it can solve the

drinking water problem of populationliving there. Since water recharging intoground is difficult and an immediateexisting need for drinking water can bemet by storing it in suitable and safestorage structures during rain. Thisstored water is consumed during dryspells. Families residing in these areas(mostly in scattered locations) canharvest Rain water using their roof topsand court yards, easily and successfully.

As an active participating researchinstitution in the National Drinking waterMission (RGNDWM now) programme ofGovt. of India, Structural Engg. ResearchCentre Ghaziabad developed anddemonstrated several types ofFerrocement Structures like tanks upto25000 ltr. Cap, filters, checkdams,underground water barriers, etc. for RainWater harvesting schemes. Simple, easyto learn and Practice techniques forcasting and installing F.C. Tanks andfilters were developed and demonstratedin many NDWM, unicef and 35 pointaction plan projects in H.P., U.P. hills,Assam, Nagaland, Manipur, Meghalaya,M.P., Rajasthan, A.P., Andamans &Lakshdeep etc.

The paper presents details forconstruction techniques for F.C. Tanksupto 10000 litre capacity, F.C. Filterssuitable for Roof top R.W.H. Systems forindividual households, schools,community Bldgs. etc. for solvingDrinking water problem in hills andislands.

Water storage Tank and Filters are thetwo major cost components of a Roofwater harvesting and storage system.The other requirement are Roof, Gutters,Inflow Pipe, bypass. Tanks can beconstructed in Rectangular, Cylindricalor Spherical shapes using steel,Reinforced cement concrete, FiberReinforced plastics. Brick/stonemasonary, Ferrocement etc. Studiescarried out during NDWM, Unicef and35 point action plan projects haveconfirmed that Ferrocement Tanks are thelowest cost options in urban and ruralsites. Apart from cost the fastconstruction speed is an addedadvantage.

What is Ferrocement?Ferrocement is a durable long lastingcement based composite material -modified form of reinforced cementconcrete in which the reinforcement isfinely subdivided and dispersed in thematrix in order to achieve a closely

spaced crack regime coupled withexcellent corrosion resistance and highimpermeability to ingress of water. Thematrix of the composite is modifiedcement based microconcrete/mortarprepared using ordinary portland cement(33 & 43 gd), well graded medium silt freecoarse sand, specially formulatedadmixtures containing bonding agents +plasticizer + poresealent and water.Techniques and equipment for vibratingthe thin ferrocement layers (including anorbital vibrator and a medium frequencysurface vibration device) have beendeveloped by author for use inferrocement jobs. The orbital vibratordeveloped is suitable for working oververtical and horizontal surfaces. Fig. 1 (a)& 1 (b) shows cross section of twoferrocement units.

Developed in 1847- First Patent in Nameof Fericement by JF Lambot 1853 - usedby Italian Arch P.L. Nervi for constructionof Roofs, Swimming Pools & large sizeboats in Italy & European countries in1940–49 Period. Lot of R&D work hasbeen taken up at various ResearchInstitutes and Universities to understandthe properties and behaviour of thismaterial in countries like India, Poland,USSR, USA, Thailand, New Zealand andSingapore, China etc. and the material iswell accepted as an efficient low costappropriate construction material.

SERC (R/G) was actively engaged in R&Dwork and dissemination of thistechnology in India and other Asiancountries from 1966 to 2000 anddeveloped large number of applicationsfor housing, water & sanitation and repair& rehab of structures.

Constituents ofFerrocementCement - sand - water -mesh reinforcement -skeletal reinforcement -chemical admixturesThe thickness of ferrocement elementsgenerally varies from 10 mm to 50 mmwhereas for water proofing, rehabilitation

& retrofitting it varies from 16 mm to 50mm depending upon type of structuresand site specific requirements. Inferrocement construction the minimummesh reinforcement provided is 0.3% byvolume. This may change dependingupon the nature of job. 2 to 6 layers ofhot dip annealed galvanized meshreinforcement has been found to beadequate in most of the cases, Minimumcover to outermost layer of wire meshesis usually 4 to 5 mm which has been foundto be enough due to use of fine grainpolymer modified matrix.

ApplicationsRoofing units - wall panels - waterstorage tanks - septic tanks - bins -manholes and covers - boats / barragespontoons - sinage items - undergroundwater barriers - check dams - biogasplants - complete housing units - drainage/ irrigation units - precast culverts / pipes- canal lining - wood substitute items likedoors / windows frames and shutters -furniture -fins waterproofing /strengthening / retrofitting of structuresetc.

Merits of Ferrocementas Structural

ConstructionMaterialFerrocement has proved tobe an ideal Construction /Rehabilitation / Liningmaterial due to its followingproperties-

♦ High Compressive,Tensile, Shear strength andability to resist shocks &vibrations. ♦ Excellentimpermeability to ingress ofwater even in high water headposition. ♦ Excellentresistance to cracking. ♦Capability of improving someof the mechanical propertiessuch as tensile, shear, impact& fatigue of materials usedfor construction ofstructures due to developing

an excellent bond with the substrate -practically acts as a monolithiccombination to the surface over whichapplied. ♦ Excellent corrosion resistancein wet and low temperature conditions.♦ Flexibility for further modifications orrepair of ferrocement is easy in case needarise. ♦ Imposition of its little additionaldead load, requiring no adjustments inthe supporting structure. The dead loadin case of an existing over head RCCwater reservoir will be almost equal tothe thick finishing (plaster) applied insidewhich is removed for applying lining.♦ Ability to withstand thermal changesvery efficiently. ♦ Readily availableconstituent materials. ♦ No need forheavy equipment like concrete mixer /vibrators. ♦ Cost effective and longlasting life ♦ Environment friendly - donot use fuels, lubricants and does notrelease or generate toxic fumes / gassesor solid waste ♦ Can be adopted forcommunity projects as beneficiaries canbe trained in its construction easily andquickly and they can provide solid inputin the developmental activity.

DurabilityMany Structures constructed or treatedwith ferrocement in India in 1973–74period are still in excellent performingcondition. The development wasencouraged by the fact that there weremany very old ferrocement boats (Nowmore than 120 year old) placed inEuropean museums. These cases can beconsidered as examples of durability offerrocement construction.

Many large F.C. Dome structuresconstructed in 1976 at B.M. Instt.Ahmedabad by SERC & SarabhaiTechnology Dev. Syndicate faced theGujarat Earthquake without showingeven a single crack. A SHANKH of verylarge size and large number of domes havebeen constructed at Manan DhamGhaziabad using Ferrocement. Very largenumber of structures have been treatedfor Waterproofing 10 to 20 years ago andare without any problem. Large numberof these are basements and water bodies.

Fig.1: Cross Section of Ferrocement

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Fig. 2: Semi Mechanised Process for ProducingCylidrical F.C. Units (Patented Revised)

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Ferrocement TanksFerrocement, a cement based compositeconstruction material - modified form ofreinforced cement concrete has beenfound to be an effective & durableconstruction materials. It has been verywidely used for construction of waterretaining structure such as tanks. Thetechnique is very suitable for use inconstruction of Storage Tanks in RainWater Harvesting schemes in Hills, Plains& Islands as it involves simple procedurefor construction and easy to findmaterials.

Ferrocement tanks are being used all overthe world for domestic / industrial &commercial purposes, In India SERC(R/G) developed designs andconstruction Techniques for Tanks of upto 25000 litre capacities for NDWM,Unicef, CSTE Shimla, CSTE Shillongwhich could be constructed using localmasons after short span training. Designpackages were prepared and handed overto these organisations and thetechnology provided has beenextensively used.

Why Ferrocement forTank ConstructionIn addition the merits of Ferrocementexplained earlier in this paper it is :-

* Free from problems of corrosion,leakage & seepage * Cost effective -lowest cost tanks for storage of drinkingwater. * Minimum Maintenance Need.* Retain Quality of drinking water * Castat Site - No Transport Problems. * Lighterthan RCC and masonary Tanks.* Reduced cement consumption whencompared to RCC & Masonary. * Occupyless space than RCC and masonaryTanks. * Easy to repair by localtechnicians - Even Accidental damagesdue to hitting of a rolling stone from hillslope can be repaired easily. * Do notneed concrete mixers or vibrators and canbe constructed in Remote areas. * Do notrequire shuttering - No Electricityneeded. * Provide employment to localtechnicians and labour. * Can be finishedand Painted to match any environment.

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Casting of Segmental Basefor Cylindrical Ferrocement

Units

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SegmentalF.C. Roof for

CylindricalUnits

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Use for Repair & Rehab of existing Masonary /Steel/ RCC TanksFerrocement has been successfully used in Repairing / leakproofing/Retrofitting ofexisting leaking / distressed tanks.

Design of F.C. TanksA Diploma holder in Civil Engg. can carrythe design of F.C. Tanks by usingdeveloped procedures. Ref - 2,12, 13 &14 provide design procedures and detailsfor Reinf, size shape & casting methodfor F.C. Tanks & Filter for RWH system.

The CastingTechnologyF.C. tanks are produced using ‘skeletalcage plastered by hand’ method in mostof the countries outside India. Thethickness for such units comes to about30 mm even for smaller capacities andcasting speed is also slow. The authorand his group at SERC (R/G) improvedthe casting system and bought theminimum thickness to 20 mm for tanksupto 2500 l. capacity. The time taken incasting was also reduced to all most half.For overcoming these problems, theauthor at SERC (G) developed threecasting techniques for fabrication of wallsfor cylindrical F.C. tanks upto 25,000 litrecapacity. Use of SERC techniques resultin reduction of wall thickness,improvement in compactness of mortar,improved performance, reduction ofconstruction time and cost whencompared to the traditional castingsystem. Two of these processes (givenon sl. 1 & 2) are covered by Indian PatentNo 145250 and have been released tomore than 75 licencees through NRDC,New Delhi.

Tanks cast with semi-mechanised processand segmental system light being thinwalled and are assembled using pre-fabricated components. Tank basegenerally cast using R.C.C. but can becast with ferrocement for capacities upto5,000 litres. Tank walls are cast usingeither of the three casting methods :

A. Semi-mechanised process forproducing F.C. cylindrical units.

B. Precast segmental shell elementscasting and assembling these intocylindrical units.

C. Tempformer method for casting wallsof ferrocement tanks.

SERC Semi-Mechanised Processfor Cylindrical TanksIn the semi-mechanised process a simplehand operated equipment (Fig. 2) is usedin which the galvanised woven wirefabric (square woven mesh) from a tightlywrapped roll is continuously wound onto a cylindrical fast openable mould madeof wooden frame body covered with G.I.sheet. Rich cement and sand mixdesigned to obtain a compressivestrength 250 kg/cm2 at 28 days is appliedon each layers of mesh continuously. TheMesh end is anchored to the mesh layerbelow by stitching. The Mould is openedafter 18 to 24 Hrs. depending upon theweather. The Roof, lid for the Tank arecast over masonary moulds and base isprecast using steel moulds placed overLevelled Floor. Inlet, outlet, scouring andoverflow sockets are cast while casting

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* Larger tanks can be cast in segmentsand transported to sites for fast erection.* Technology already demonstrated inlarge number of states hence mastermasons available. * Double wall insulatedtanks can be constructed for subzeroareas.

Precaution

* Need some care in construction &Initial training for masons & supervisors.* Painting of inside with Drinking WaterTank Paint once in 10 years.

Expected Functional Life - 35 to 40 years

the wall or the mesh area at their locations are left unplastered forfixing these at the time of assembling. Because of Mechanisedcasting the walls for tanks upto 2500 litres cap could be cast 12mm thick.

SERC Precast Segmental Shellelements casting and assemblingprocessSuitable for mass production, long distance transfers and erectionover multi storeyed bldgs or in hill areas and islands. Segments ofa cylinder with designed reinforcement meshes projecting on bothsides for subsequent field assembling, are cast (designedthickness - 10mm) over permanent or temporary moulds.

The total circumference of the cylinder is divided into 3, 4, 6, 8, 12or 16 segments. These units are cast separately and cured forabout 7 days and then transported to site. The precast units havereference number marked over these. The base concrete is castusing designed reinforcement and segmental units are placedvertically over the premarked wall point & held in vertical position.Wire mesh laps (as per design) for projections on both sides arefixed. M-25 grade mortar/microconcrete is impregnated into thecage and extra mesh layers are fixed over joint portion and mortarapplied over these meshes also. Fig 3(1) to 3(18) show differentstages of segmental casting process. Base and Roof for segmentaltanks can also be cast in segments and assembled jointed at siteFig. 3 (19) & 3 (20) show Tank Roof cast in segments. Fig. 4 showfinished 10000 ltr. tanks cast using segmental technique.

Tempformar TechniqueWhen large number of same capacity Tanks are required use oftempformer technique saves time in construction, ensured propershape, uniform thickness of casting. Tempformer are inside mouldsmade using light section wooden scantlings and light gage G1sheet. Fast to assemble and dismental Tempformers weredeveloped at SERC for NDWM project and were used in NE Area.As the cost of these units is low and also distributed on largenumbers of cast units these donot add much cost to tank cost.Fig. 4 show the technique.

Skeletal Cage TechniqueAlso known as Traditional Technique for FC Tank Construction -

Steps

♦ Decide the size according to capacity and follow a proper designfor the capacity selected.

♦ Select a place nearest to catchment, level and make a platform atleast 30 cm above ground level.

♦ Mark Reinf. Pattern on ground and fabricate the skeletal cage -First the base and then wall cage. Remember to provide properlaps in steel bars and wires. Join the base and wall cage properly.

♦ Fix woven wire square mesh of size given in Drg. - Provideminimum lap of 100 mm at all mesh joints number of mesh to beas per design.

Fig. 10: Dimension and Other Details for 10,000 lit.Capacity F.C. Tanks.

Fig. 11: Reinforcement Details for Wall & Base of 10,000lit. Capacity F.C. Tank.

♦ Fix, in let out, scouring and overflowsockets.

♦ Make a earthen mould for the domeshaped Roof - Cover it with polythenesheet and prepare the roof cage.

♦ Cast the base portion using 1 : 2 : 3 mixcement concrete using 8 mm and downgrade aggregate compact it properly -also make sure the cover below basereinforcement.

♦ Apply a Thin layer of microconcreteon wall Reinf - cage and cover the innermesh layer to vertical reinf. Rod.

♦ Wait for 18 to 24 hrs and apply onelayer of mortar and one layer of mortaron exterior surface making up thedesigned thickness.

♦ Finish Base wall joint and cover thecorner with microconcrete - wait for 24hrs.

♦ Lift the Reinf. cage of Roof, keep inposition connect to vertical wallsprovided in wall - Fix temp supportsbelow the Roof cage to keep it indesired shape.

♦ Apply mortar without climbing overcage. For this purpose make a temp.supporting arrangement using vertical

and cross supports on outside thetank.- Mortar may be applied in twolayer one from top and anotherfrom bottom. A 30 gage G1 sheetpiece is held against the mesh forapplying the mortar. The openingthe central manhole and openingfor filter are left unplastered.♦ Once the Roof plaster is over,the Filter body is erected and fixedat its opening.Fig. 6, 7, 8, 9 shows stages ofskeletal cage construction. Fig. 10,11 & 12 shows details ofReinforcement & dimensions for a10000 ltr. tank. Author hasdeveloped two vibrators forimproving the compactness inskeletel cage casting system. Thisreduces the mortar consumptionand thickness.

Social Aspects ofFerrocement TankTechnologyFerrocement is a labour intensive

Technology & the skills involved can belearned easily by unemployed rural youthand even by women.

This has made Community ParticipationPossible in Rural Development and waterprojects. The total unskilled manpowercan be tapped from local source byinvolving beneficiaries. Local masons,smiths are good enough to produceferrocement structure under supervisionof a Trained memberof the same group.This has beens u c c e s s f u l l ydemonstrated inremote areas of hillsin Manipur,Meghalaya &Islands likeAndamans andLakshdeep.

The technologyprovide employmentto unemployedyouth and improvetheir skills for futureuse.

F.C. Tanks are cheapest and easiest toconstruct and Maintain even in difficultareas. Amount of materials required issmall hence less problems of handlingand transport.

Effectiveness ofTechnology is CostReductionBased on field studies carried out as Partof Unicef project & CSTE project inHimachal Pradesh. Table 1 Provides costdata for a comparison.

Ferrocement FiltersFerrocement Filters are cast usingskeletal cage technique or are precastover masonry moulds. Circular filters of500 to 900 mm dia and depth of about 700mm are adopted. Fig. 10 Provides detailsof a F.C. Filter and bypass arrangement.

ConclusionFerrocement Tanks are the mosteconomical structures for storage ofdrinking & water. If constructed usingproper design & construction techniquethe life span can be upto 50 years.

SERC (G) is not available for technicalhelp now but New Building Materials &Construction World (a Civil Engg. journalpublished monthly from Delhi) isproviding technical support to agenciesinterested in construction of FerrocementStructure. Tel.: 011-26841228,Fax: 26832424

Fig. 12: Details of Roof for 10,000 lit. F.C. Tank.

References

1. P.C. Sharma and others ‘Small capacityferrocement water tanks,’ proceedingsof 8th session of IASS Committee ofPipes and Tanks, Budapost, Hungary,June 1978.

2. P.C. Sharma and V.S. Gopalaratnam‘Ferrocement Water Tanks’ - Do itYourself Book, InternationalFerrocement Information Concrete,Asian Institute of Technology,Bangkok, Thailand, 1978.

3. Watt S.B. ‘Ferrocement water tanks andtheir construction,’ IntermediateTechnology Publications Limited,London, 1978.

4. P.C. Sharma ‘Construction ofFerrocement Water Tank using SkeletalCage and Hand plastering System,’Technology package given as coursematerial in training courses conductedfor National Drinking Water Mission& Unicef on “Construction of RainWater Collection System andFerrocement Water Storage Structuresbetween January 1987 to December1991

5. P.C. Sharma ‘Ferrocement Lined BrickMasonary - Manual Prepared Tanks’at SERC, Roorkee / Ghaziabad January,1987

6. P.C. Sharma & others ‘Ferrocement

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Treatment for Repairing of 50,000gallon O.H. Water Tank,’ Journal ofFerrocement, Vol. 14, No. 3, July 1984.

7. P.C. Sharma ‘Ferrocement SegmentalShell - a Multipurpose Unit,’ AsiaPacific Symposium on FerrocementApplication for Rural Development,Roorkee (India), April 1984.

8. P.C. Sharma ‘Construction Techniquesfor Ferrocement Application,’ AsiaPacific Course on FerrocementTechnology, April 1984, Roorkee, 1984.

9. P.C. Sharma, ‘Ferrocement Water Tanksfor Safe Storage of Drinking Water,’National Workshop on Water Missionat C.S. & M.C.R.I., Bhavnagar, 10–12April, 1987.

10. P.C. Sharma, ‘Ferrocement Structuresfor Islands and Remote Areas,’ I.A.S.S.Conventional on Technology forRemote Areas, New Delhi, 2–3 May,1998.

11. P.C. Sharma & J. Swarup,‘Construction Techniques for F.C.Water Storage Tanks,’ Symposium onWater and Sanitation Services in Asiaand the Pacific, Kualalampur,Malaysia, 11–15, 1988.

12. P.C. Sharma, H.V. Krishnaswamy -Technology Package on Rain WaterHarvesting Structures forimplementation of RWHS Programmeon a large scape in Himachal Pradesh -UNICEF Delhi Project - 1996.

13. P.C. Sharma - Technical Package, RainWater Harvesting Schemes for Townsin Himachal Pradesh - includingdetailed designs - Project Sponsoredby State Council for SC. & TechnologyShimla, H.P.

14. P.C. Sharma - Ferrocement StorageUnit (Ferrocement Bhandaran Patra) Doit yourself Manual on water Jars 400 to1500 lit. capacity - ContainingProcedure suitable for Rural woven onself help basis.