{"id":12827,"key":"Rural_Water_Supply_in_Nepal","title":"Rural Water Supply in Nepal","latest":{"id":1211501,"timestamp":"2025-11-28T13:55:31Z"},"content_model":"wikitext","license":{"url":"https://www.appropedia.org/Appropedia:Copyrights","title":"CC-BY-SA-4.0"},"source":"[[File:NEWAH WASH water project in Puware Shikhar, Udayapur District, Nepal. (10710586734).jpg|thumb]]\n\n== Rural Water Supply in Nepal: Concrete Course ==\n\nTechnical Training Manual No. 3\n
\n\nPublished by:
\nLocal Development Department, Ministry of Home\nand Panchayat, Government of Nepal/
\nSwiss Association for Technical Assistance/
\nUnited Nations Children's Fund
\nKathmandu, Nepal
\n
\nAvailable from:
\nUnited Nations Children's Fund
\nLazimpat
\nP.O. Box 1187
\nKathmandu
\nNepal
\n
\n
\nReproduced by permission of UNICEF/Nepal.
\nReproduction of this microfiche document in any\nform is subject to the same restrictions as those\nof the original document.
\n\nTRAINING MANUAL no. 3
\nCONCRETE COURSE;
\nPrepared and Published by
\nLocal Development Department, Ministry of Home and Panchayat
\nSATA - Swiss Associationn for Technical Assistance
\nUNICEF - United Nations Children's Fund
\nKathmandu 1977
\n\n== CONCRETE COURSE ==\n\n'''1. General'''\n
\n
\n\n'''1.1 Definition'''
\n\n----\n\nConcrete is a mixture of:\n
\n- aggregates ( sand, gravel)
\n- adhesive ( cement )
\n- water
\n
\n
\n\n'''1.2 Types of concrete'''
\n\n----\n\nThere are many types of concrete which can be grouped,\nfor example, according to the raw materials or to the\nquality.\nFor our purpose we can seperate three different types\nof concrete, according to their use:\n
\n- lean concrete
\n- non-reinforced concrete
\n- reinforced concrete
\n\nAs non-reinforced and reinforced concrete have the same\nmixture of aggregates, cement and water, the difference\nis explained as follows:
\nConcrete alone has a very high compression strength\nbut a low tensile strength. So concrete which is\nexposed to tensile stresses has to be strengthened\nwith steelbars, These have a very high tensile\nstrength.
\n\nTake for example a slab of a spring collection chamber-\n
\n[[Image: Nepal1.jpg]]\n\nDue to dead load and additional loads such as people,\nearthfill, snow etc. the slab will get tensile stresses\nat the bottom. So in this place we must put some steelbars\ninto the concrete.\n
\nThe number, diameter, length and position of the bars\nis a matter for the design engineer or the engineer -\nin - charge of the project.
\n
\n\n'''1.3 Application of concrete'''\n----\n\nI. Lean concrete: To make a clean and completely\nhorizontal base for concrete and\nmasonry constructions.
\n1. Example : Storage tank wall - foundation.
\n[[Image:Nepal2.jpg]]\n2. Example: Foundation of a ,spring collection chamber.
\n
\n[[Image:Nepal3.jpg]]\nII. Non-reinforced concrete: ,- To make foundations, floors\nsmall staircases, walls etc.\nAll concrete constructions\nwhich are not exposed to\nhigh tensile stresses.\n
\n\nExample: Floor of a storage tank\n[[Image:Nepal4.jpg]]\n
\n\nIII. Reinforced concrete: To make all kind of concrete\nconstructions such as slabs,\nwalls, bridges, etc.
\n\nExample: Slab of a spring collection chamber\n
\n[[Image:Nepal5.jpg]]\nNote: The decision to use reinforced or non-reinforced\nconcrete is a matter for the engineer,and it should\nbe shown on the site drawings.\n\n== 2. Materials ==\n\n'''2.1 The aggregates'''\n----\n\n2.1.1 Origin and extraction
\n
\n\nNatural materials
\nRubble sediments in rivers and lakes. Due to long\ntransport in the rivers, gravel and sand are\nground round,and bad materials have already been\neliminated. They are also washed’s0 that in many\ncases they are ready to be used \n
\nCrushed materials
\n\nPieces of rocks, and big stones broken in stone\nbreakers or by hand.
\nThis material must be washed and sorted out. It\nis important to remove all the dust which arises\nby crushing; stone with cracks should be eliminated.\nTo obtain a high strength the crushed material\nshould be mixed with river sand.
\n
\n\n2.1.2 The form of grains\n
\nThe compressive strength of each grain must be\nhigher than the strength of the finished concrete.\nThe ideal form of gravel is round for river gravel\nand cubic for crushed gravel. Do not use weatherworn\nstones,slate and flat stones.
\n\n2.1.3 Impurities
\n\nIf aggregates are dirty and contain grass leaves,\nwood, humus, silt, clay etc, they have to be\nwashed, but particular attention should be paid\nnot to wash away the fine sand aggregates. Gravel\nand sand containing impurities cause heavy loss of\nstrength in the finished concrete.
\nSimple methods for field tests:
\n'''Fist test''':\nThe hand filled with the aggregates to be tested\nis to clench and then to open again. If the\nmaterial is clean it should not stick together\nin a lump. When the material is rubbed between\nthe hands, they should remain almost clean.\n
\n\n'''Bottle test''':\nA clear bottle filled up to 2/3 with material and\nthe remaining space with water is to be shaked\nvigorously. After about 30 minutes of settlement,\nthere should be no dirt or silt on top of the material.
\n
\n\n2.1.4 Grading or gradation
\n\nIn properly made concrete, each particle of aggregate\nis completely surrounded by cement paste. The better\nthe distribution of the particle\"sizes, the better all\nspaces will be filled and the denser and stronger the\nfinished concrete will be.
\n[[Image:Nepal6.jpg]]\nThe most common composition is 3 parts gravel and\n2 parts sand.
\nTo find out the proper composition, it is recommended\nto make testing mixtures on site. The following table\nshould give an idea of a good gradation.
\n\nTable of gradation:\n\n{| style=\"width:50%; height:50px\" border=\"1\"\n|\n|\n! Range of grains\n|-\n|\n! mm\n! 0-8\n! 0-15\n! 0-30\n! 0-60\n|-\n! Dust\n| 0.0-0.1\n| 8-14\n| 5-10\n| 3-7\n| 2-5\n|-\n! Fine Sand\n| 0.1-1\n| 15-21\n| 16-15\n| 7-11\n| 5-7\n|-\n! Medium Sand\n| 1-4\n| 38-37\n| 23-26\n| 13-18\n| 9-14\n|-\n! Coarse sand\n| 4-8\n| 39-28\n| 24-21\n| 16-15\n| 9-10\n|-\n! Fine gravel\n| 8-15\n|\n| 37-28\n| 21-19\n| 13-14\n|-\n! Medium gravel\n| 15-30\n|\n|\n| 40-30\n| 22-20\n|-\n! Coarse gravel\n| 30-60\n|\n|\n|\n| 40-30\n|}\n\n
\n
\n
\n
\n\n'''2.2 Cement'''\n----\n\n2.2.1 Introduction
\n\nCement is a product of minerals which are burnt\nand then pulverized. If water is added it becomes\na binding paste which first sets (becomes firm)\nard then hardens for an indefinite period. The\nsetting and hardening are brought about by chemical\nreaction between the cement and the water. This\nprocess is called hydration.
\nOn the world market there are a lot of different\nadhesives available. But in Nepal, and also in\nother countries, only portland cement is used\nto date. Therefore the following chapters give\na brief description of this portland cement.
\n
\n\n2.2.2 Manufacture
\nThe raw materials, limestone and clay, are extracted\nfrom quarries and crushed into pieces\nof the size of a fist. After this, the raw\nmaterials are mixed with hydraulic compound,\ngranulated and burnt at a temperature of 15OOOC.\nThis burning produces a clinker which is cooled\nand pulverized into fine powder with a small\namount of gypsum added to regulate the setting\ntime. This powder is the finished portland\ncement.
\n
\n\n2.2.3 Hydration
\n\nHydration of the cement is divided into two\nprocesses: The setting stage and the hardening\nstage.
\n\n'''Setting''':\nThis chemical process which radiates heat, starts\nat a certain time after the water has been added\nand it lasts till the mass is solid. The time of\nbeginning and the duration of this process\nvaries mainly according to the temperature. At\na temperature of 180C the setting starts after\nabout 2.5 hours and lasts 7 hours. If the temperature\nfalls to O°C, no setting process takes\nplace. In the tropics, where temperatures of\n30°C often occur, the same cement may change to\na quick setting one.\n
\nDuring the setting time the material must not be\ndisturbed, 2s this would diminish its strength\nconsiderably.
\nThe setting time can be checked on site, by a very\nsimple method :
\nThe concrete is scratched with a\nfingernail or 2 piece of soft wood.
\nIf it flows together again, the setting has not\nyet started, if the scratch remains, the setting\nis in process, if no scratch can be seen on the\nconcrete, the setting stage has finished and the\nhardening stage has already started.
\n
\n'''Hardening''':\nTheoretically portland cement never stops hardening\nand therefore the end of the process cannot really\nbe determined.
\nFor practical work it is sufficient to know how\nlong it takes a structural part to attain the\nrequired strength.
\n
\n\n2.2.4 Shrinkage
\nAll adhesives, including portland cement, are subject\nto shrinking during the setting and the hardening\nprocess.
\nThe shrinkage must be counteracted by keeping the\nmortar or the concrete wet.
\n
\n\n2.2.5 Storage of cement
\nCement should not be stored longer than three months.\nOtherwise the strength will be reduced to approximately\n75% of the original value. If cement is\nallowed to absorb any moisture, it will set more\nslowly and the strength will be drastically in\ndecreased.
\nIn storing cement, especially sacked cement, the\nwarehouse or shed should be as airtight as possible.\nAll cracks in the roof and walls must be closed.\nThe floor should be above ground to protect cement\nagainst dampness. Sacks should be stored close\ntogether to reduce the circulation of air, but at\nleast 50 cm away from walls, and with not more than\n10 bags per pile.
\n\nOn smaller sites, where there is no shed or other\nbuilding available, the sacks may be placed on\na raised wood platform. A waterproof tarpauline\nshould be placed over the pile to protect the cement\nagainst rain. The tarpaulin should extend over\nthe edges of the platform. If the cement is hard\ndue to moisture, it can not be used.
\n
\n
\n
\n
\n\n'''2.3 Water'''\n----\n\nThe water must b:e clean. Drinking water is always suitable\nfor making concrete. If it is not possible. to use drinking\nwater it must be certain that the water is not polluted by:\n
\n- soil particles
\n- mud
\n- dirt
\n- oil
\n- soap, etc
\nIt is important to use only clean water for making concrete\nand mortar.
\n
\n
\n
\n\n== 3. Making and handling of concrete ==\n\n'''3.1 Mixture'''\n----\n\n3.1.1 The amount of aggregates
\n\nExperiments have shown that the portion of gravel\nand sand which is used in mixing 1 m3 finished\nconcrete is not always the same. Normally 1400\nliters of aggregates are needed to make 1 m3 of\nfinished concrete.
\n
\n3.1.2 The amount of cement.
\n\nThe amount of cement for a certain mixture is\ngiven in liters or kilograms.
\n1 bag of cement = 50 kg - 40 liters
\nFor the different types of concrete we need the\nfollowing amount of cement per m3:
\nlean concrete : 150 kg = 120 liters
\nnon -reinf arced >
\nreinforced > concrete : 3@0 kg.= 240 liters\n
\n
\nThe quantity has to be increased if the\naggregates do not correspond to the requirements\ndescribed in chapter 2.1.4.
\n
\n\n3.1.3 Amount of water used in concrete\n\nThe amount of water to be used depends on:\nthe aggregates; on the consistency of concrete\nwanted; and on the amount of cement.
\nIt should be noted that the total amount bf water\nin a mixture is equal to the added.water and the\nnatural moisture of the aggregates.
\nThe proportion of water to cement is called:\n
\nwater-cement ratio =water (in kg)/\ncement(in kg)
\nThe water-cement ratio has a direct influence on:
\n\n- workability\n
\n- density
\n- strength
\nThe best results for density and strength are\nachieved by using a mixture with a water-cement\nratio of:
\n0.4 for lean concrete
\n0.5 for non-reinforced and\nreinforced concrete
\nNote: Each litre of extra water used demolishes\nthe effect of 2 to 3 kg cement.
\nNatural moisture of aggregates:\n\n{| style=\"width:50%; height:50px\" border=\"1\"\n|\n! Sand (liters/m3)\n! Gravel (liters/m3)\n|-\n! Dry Season\n| 25-20\n| 5-10\n|-\n! Rain and sun mixed\n| 70-80\n| 25-35\n|-\n! Rainy Season\n| 150-170\n| 70-80\n|}\n\n
\n\n3.1.4 Measuring the ingredients for hand mixing\n\nThe following table shows volume ratios.
\n\n{| style=\"width:50%; height:50px\" border=\"1\"\n|\n! Type of concrete\n|-\n|\n! Lean Concrete\n! Non-reinforced and reinforced concrete\n |-\n| Cement : sand : gravel\n| 1 : 4 : 7\n| 1 : 2 : 3\n|-\n| Cement : sand + gravel\n| 1: 25\n| 1 : 12\n|}\n\n
\n
\n\n'''3.2 Mixing'''\n----\n\n3.2.1 Equipment
\nHand mixing does not need much equipment but a\nlot-of manpower.
\nA batch to be hand mixed should not be larger\nthan about 0.5 m3. Concrete should never be\nmixed on soil. A platform has to be built, with\nboards, metal sheets, stones or concrete. It\nshould be level to prevent water or fluid material\nfrom flowing off the platform.
\n
\n3.2.2 Procedure of mixing
\nMeasure the amount of aggregates used for the\nbatch, put it onto the platform in a layer,and\nspread the cement over it. Mix together until\nit is uniform in colour .
\nFor addition of water, the material is sprinkled\ngradually while it is turned over another 3 times,\nthat is, until it is uniform in consistancy.
\n
\n
\n\n'''3.3 Transporting concrete'''\n----\n\nIf mixed concrete is transported there is a tendency for\nthe larger aggregate particles to segregate by settling\nto the bottom. To avoid this, ready mixed concrete should\nnot be transported over long distances and if it has to be,\nthe transport container should be adequate. There should s\nbe no leakage, so that none of the cement milk is able to\nflow off.
\n
\n
\n
\n'''3.4 Casting concrete'''\n----\n\n3.4.1 Preparation of the formwork
\nBefore any concrete is placed, the forms must be\ncleaned of all rubbish and carefully checked for\nstrength, tightness and proper alignment. The forms\nshould be wet the day before casting and again before\nthe work starts, If this is not done, the boards\nwill absorb 2 high amount of the cement,milk,which\nis necessary to bond the aggregates.
\n
\n3.4.2 Placing of concrete
\nConcrete has to be placed in layers or strips of\nmaximum 15 - 20 cm width.
\n[[Image:Nepal7.jpg]]\nEach layer has to be cast before the former layer\nhas started setting.
\n\n3.4.3 Casting concrete inside standing water
\n\nThe depth of the water should not exceed 20 cm,\nas this would demand a pump and a water tight\nformwork.
\nThe amount of cement has to be increased by at\nleast 50 kg/m3 finished concrete.\nThe concrete has to be consolidated immediately\nafter placing.
\nIt is not possible to cast concrete inside flowing\nwater.
\n
\n
\n
\n
\n'''3.5 Consolidating concrete'''\n----\n\n3.5.1 Why consolidating ?
\n\nIf concrete is simply poured into a form and left\nto harden without further treatment, the product\nwill contain a number of defects:
\n- Large number of bubbles entrapped in the\nmaterial.
\n- Inadequate coverage of coarse aggregates.\n- Small or intricate form spaces are not\ncompletely filled.
\n- Reinforcing steel is not solidly bonded to\nthe concrete.
\n\n3.5.2 Hand - vibrated concrete
\nThe concrete layers 'should -not be thicker than\n15 to 20 centimeters. Those layers have to be\nstamped vigorously especially at the edges and\nthe corners until the water rises up to the\nsurface.
\nIf the work is interrupted for more than 2 hours,\nthe last layer has to be roughened before new\ncasting can go on.
\n
\n\n3.5.3 Consolidating with vibrator
\nProper consolidating is only possible with vibrators.
\nBut these engines are heavy and\nexpensive. From the transportation point of view\ntherefore, it is not practical to use vibrators\nin the hilly regions of Nepal.
\n
\n
\n\n'''3.6 Curing concrete'''\n----\n\n3.6.1 Drying out
\n\nAs mentioned in the chapter on cement, concrete\nhardens as a result of the hydration of the\ncement by water. Fresh concrete contains more\nthan enough water to hydrate the cement completely,\nbut if the concrete is not protected against\ndrying out, the water, especially near the surface,\nwill drop below the amount required for complete\nhydration.
\n
\n3.6.2 Shrinkage
\nRapid drying-out causes a decrease in volume,\nwhich starts at the surface of the concrete\nmass while the centre of the mass is still\nwet. This causes a surface tension which the\nfresh concrete is not able to absorb, The\nresults are reticular cracks all over the surface.\nThe more water and cement are used the more the\nconcrete shrinks.
\n\n3.6.3 Curing
\nThe procedure called curing is designed to prevent\nsurface evaporation of water during setting and\nhardening stages.
\nCuring starts as soon as possible without damaging\nthe surface. Curing is brought about\nby keeping the concrete surface continuously\nwet. Depending upon the structure and the means\navailable this may be done by:
\n- Sprinkling or flooding
\n- Covering with jute bags, grass and leaves\nwhich should be wet continuously. Min.\ncoverage 5 cm.
\nHighly strained concrete should be kept moist for\nat least 14 days.
\n
\n
\n\n'''3.7 Removal of forms'''\n----\n \nForms should be left in place until the concrete has\nhardened enough to hold its own weight and any other\nweight it may be carrying.
\nThe surface must be hard enough to remain uninjured and\nunmarked when care is used in stripping the forms. The\nengineer in charge of the project should tell how long\nthe formwork should remain in place.\n\n{{Page data\n| license = CC-BY-SA-3.0\n}}\n\n[[Category:Construction and materials]]"}