Basic Constructin

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3. BASIC MATERIALS FOR CONSTRUCTION AND PUMPS

3.0 Introduction

1. In addition to the pond soil itself, you might use a range of dierent materials forthe sh farm, for example for foundations, water supply and water control devices.

The choice ranges from locally available materials such as bamboo and wood tobricks, cement blocks, concrete and plastics for pipes!, for which you may have togo to speciali"ed dealers.

Selecting materials

#. The choice of construction materials essentially depends on their suitabiit!,their oca a"aiabiit! and the amount of #on$! you are prepared to invest.

$. If you are a beginner sh farmer and your farm is very small, it is best to usesimple structures and not to spend too much on materials. %s you gain experienceand wish to expand, your investments may increase, and more permanent, betterstructures may be built.

&. It you plan to build a large sh farm, you should select the most suitable

permanent structures from the start.

Weight per unit volume of materials


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'. The materials generally have to be transported to the construction site. To planthis properly and help estimate the cost of transport and handling, use Tab$ %,which gives the weight per unit volume kg(m$! of common basic materials.

TABLE %

S&$ci'c #ass o( "arious construction #at$rias

Mat$riaS&$ci'c #ass)*+,#3-

)amboo*ood

$++'++'++11++

)ricks-ement blocks

-rushed bricks for foundation!

1'++1++1'++#+++

/'+1#'+

)uilding stone, dry loose0arth, dry loose0arth, moist rammedravel2and, dry to wet-ement-lay, dry compacted

1&++13++1$++1'++14'+1'+1$++1'++1&'+#+++1#'+1&++1&++1'++

-ement concrete-ement mortar5einforced concrete '6 steel!

#1++#&++#+++##++#3++#4++

R$in(orc$#$nt st$$

bars)s$$ aso -hart in 2ection$.'-

Dia#$t$r)##-

$i+/t)*+,#-

3 +.###

+.$/'

1+ +.314

1# +.

Not$7 for granular materials, these gures are bulk densities, i.e. including thepore space between the particles. The actual density is higher

3. Ba#boo and 1ood

Special characteristics of bamboo

1. )amboo is a wooden perennial grass that lives foran indenite number of years. It grows fast, occurringnaturally throughout the world, but particularly intropical %sia. The -hinese bamboo or 8yellowbamboo8 )ambusa vulgaris! has been introduced inseveral %frican and 9atin %merican countries where itis now found widely at altitudes between sea level

2ro1in+ ba#boo

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and 1'++ m.

#. 9engths of bamboo wood, or culms, are cylindricaland divided at intervals by raised nodes from whichthe branches grow. %t each node there is a partition

wall that completely separates the cavity of oneinternode from the next. -ulms are covered outsideand inside by hard waxy cuticles that oerconsiderable resistance to the absorption of water,particularly when properly dried out. )amboo isstrongest at the age of three to four years. )ecauseof its versatile characteristics, bamboo has numeroususes, for example as a construction material, forwater pipes and for erosion control.

Producing good bamboo pipes

$. *hen harvesting fresh bamboo, avoid letting them dry for too long: they shrinkas they dry, and small cracks develop, which can weaken the bamboo for later useas a water pipe.

&. To produce good ;uality bamboo pipes7

a! -ut mature bamboo and carry them out of the forest.

b! If necessary store bamboo in the shade, covering them with branches or largeleaves.c!


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of the pipes.f! %fter desapping, remove all remaining parts of the partition walls in the bamboopipe.g! The bamboo pipe is ready for use.

Not$7 if you harvest bamboo during the dry season or at the beginning of the rainyseason, desapping will be easier, and the ;uality of the pipes will be better.

Removing the partition walls of bamboo

'. There are two simple ways of removing the partition walls of bamboo7 drillingthem or cutting them out. If the walls are tough, they might be too hard to drill.

3. =rill the partition walls manually with a circular bit, which you can easily makeyourself.

a!B$ out one end of a short length

of steel pipe to increase the diameter.

b!S/ar&$n the edge with a le.


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c!Pus/ a length of bamboo ofsu>ciently small diameter into thepipe to act as a /and$.

d! 2ecure this bamboo to the pipeby driin+ a s#a /o$ through theassembly and ins$rtin+ a nai in thehole.

e! B$nd t/$ nai to x it into place,making sure it does not stick out toofar and cause the drill to ?am.

f! @or each bamboo, 'rst us$ t/$s#a$st dia#$t$r bit and bore a holethrough each partition wall.

g! 9ater, for example after desappingthe pipes, &ro+r$ssi"$!$nar+$ these holes with largerdiameter bits.

Not$7 you may need several bits forvarious si"es of bamboo. To drill throughor break partition walls, you may need thehelp of other people.

4. To cut out the partition walls, proceed as follows.

a! @ix the bamboo culm on the ground,for example between strong stakes, to

b! Asing a saw, cut a thin slit on eachside of the rst node where the partition


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keep it from rotating .

wall is known to be.

c! Asing a sharp wood chisel, cut out asmall s;uare piece from the top part ofthe bamboo culm. -ut it as cleanly aspossible.

d! Beep all the s;uares that you cutout. Cou will need them later.

e! Through the hole, cut out t/$&artition 1a with the wood chisel.

f!


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g! *hen you have removed the lastpartition wall, place the bamboovertically and take out all the loosepieces from inside the bamboo.

h!


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/. *herever possible use lashings orties to connect the pieces, as nails andscrews will cause splitting and will

weaken the structure.

% @loorframing) 2addle

?oint- Insetblocksupport=

)ranchnodesupport

Diverse characteristics of wood

1+. The characteristics of wood, in particular d$nsit!4 /ardn$ss and naturadurabiit!, vary greatly. It is best to select the wood variety according to itsuse see Table 3!7

• "$r! durab$ 1ood can be permanently exposed to humidity and kept incontact with the soil. It is usually very resistant to rot, termites andwoodborers:

• durab$ 1ood resists air humidity well but should not be in permanentcontact with the soil without treatment for preservation:

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• non5durab$ 1ood should preferably not be used under humid conditions orin contact with soil.


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Iroko -hlorophora! $

Gakore, douka Tieghemella! $

Gukulungu %utranella! $

Goabi )aillonella! $

=oussie, af"elia %f"elia!

+.++./'heavy

3/hard

$

Tali 0rythrophloeum! #

Hiov 2taudtia! #$

%"ob, ekki, bongossi9ophira!

JK+./'veryheavy

/#+veryhard

$

L 1 K nondurable: # K durable: $ K very durable

Using and treating wood

11. *ood used as a permanent construction material should be free from bark woodand should not have any large holes or too many knots. It should be well dried and

should not be twisted or split. It should be stored Mat in a dry place with good aircirculation.


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1#. @or temporary use, e.g. to make casting forms for concrete see 2ection $.&!,use light, cheap wood. If you are reusing it, make sure that the surfaces facing theconcrete are even and are free from nails or splinters. To build water controlstructures, use heavier, preferably very durable wood, such as iroko or makore.

1$. To increase durability, especially of wood in permanent contact with the soil, youcan treat its surface.

a! )urn the surface of the wood e.g.the bottom part of poles!.

b! Ase tar e.g. on the bottom part ofpoles or the outside of a structure nearsoil!. If you can, it is better to apply hottar.

c! Ase waste motor oil diluted with asolvent such as para>n which, whenapplied, will penetrate the wood and willhelp to force moisture out.

d! Ase special wood preservatives. These are more expensive and areusually copper, lead, "inc, or tincompounds in a solvent. %s these arepoisonous materials they should behandled very carefully.



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Not$8 for the best results with tar, oil or other preservatives, apply the preservativegenerously and allow plenty of time to let it get into the wood.


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&. )ricks are used together with cement mortar see 2ection $.$!. They should bestored and handled carefully to avoid excessive breakage. They should be wellsoaked in water for at least $+ minutes before use.

Cement or concrete blocks

'. -ement or concrete blocks are made of a mix which is cast and pressed into aspecial form. -oncrete blocks can be made on site if needed, but care should betaken to make sure they are properly cast see 2ection $.&, paragraph '4!. )locksshould be at least # days old before they are used for construction.

3. )oth hollow and solid cement blocks are produced. They are available in severalstandard si"es, usually with a length of from &+ to '+ cm, a height of #+ cm and a

thickness of from ' to #+ cm. The following are examples of various standard si"es7' x #+ x &+ cm,1+ x #+ x &+ cm and #+ x #+ x &+ cm. )locks are sometimesavailable in dierent weights7 generally the heavier the block, the stronger. )locksare used together with cement mortar see 2ection $.$!. They should be properlystored and handled. They should be well wetted with water before use.

4. 2tandard clay bricks and cement blocks have a low resistance to humidity. Theyshould, therefore, preferably not be used for foundations or undergroundconstructions. In the presence of water, they should be well protected byimpervious surfacing made of rich mortar see 2ection $.$!.

;inds o( boc*s


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Stones

. 2tones are used in some areas for construction, usually for walls and for liningwater canals, dikes and spillways. Their characteristics depend on the type of rockthey come from7

• s$di#$ntar! 7 sandstones, siltstones, shales, limestone. These are even,regular, often ;uite soft with rounded corners, and can often be split or cut tomake regularshaped blocks:

• i+n$ous 7 granite, basalt, pitchstone, pumice. These have various properties

and are often very hard and strong and of an irregular structure. It is di>cultto make blocks from them. 2oft lava rocks are very light and weak:

• #$ta#or&/ic7 marble, ;uart"ite. These are often irregular, hard, very toughand di>cult to shape. 2lates can be split to make Mat pieces and can beuseful for stopping movement of water.

/. 2tones are used either :dr!:, without any mortar or ?ointing material, by carefullyselecting and tting them together or, more commonly :1$t:, by setting them inmortar.

1+. @or walls, unless you have cut stones, it is usually important to have a range of

si"es, using smaller stones to ll in the gaps and secure the larger stones in place.

11. Cou will also need larger stones at the corners, at intervals along the wall andacross the width of the wall, to give the wall strength and stability.

1#. Asually, stones with irregular, rough edges make stronger walls. @or liningcanals, small, smooth, rounded stones are best as they let water Mow past moreeasily.


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3.3 C$#$nt #ortars

1. % cement mortar is a wellproportioned mixture of sand, cementand water. It is mainly used for ?oiningtogether and surfacing materials suchas stones, bricks and cement blocks. %good mortar is homogeneous, soft andshiny. It has a smooth appearance anda plastic consistency.

#. To prepare a good mortar, it is veryimportant to use the properingredients and to mix themthoroughly in the right proportions.

Mi>in+ c$#$nt #ortar

Selecting the sand


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$. It is best to use a clean, wellgradedmixture of coarse to ne sand, withparticle si"es varying from +.# to ' mm.If possible, you should avoid using seabeach sand or sand deposits

contaminated with salts. If you have touse these materials, you should washthe sand well.

&. Hatural sand deposits can sometimesbe found not too far from theconstruction site, for example in streambeds, driedup lake or stream areas or;uarries, but wellgraded sands seldomoccur naturally. In many cases, you willhave to sift the sand through a +.# mm

mesh screen to eliminate the nestparticles. If there are particles largerthan ' mm, you should also eliminatethem, using a 'mm mesh screen.

Checking the cleanliness of the

sand

'. The sand should be free from silt,clay and organic materials.

3. % simple test to check the cleanliness of the sand is as follows7a! Fbtain a clear, widemouthed glass ?ar.b! @ill the bottom of the ?ar with sand ' cm deep.c! %dd clean water until the ?ar is three;uarters full.d! %dd, if available, two teaspoons of common table salt per litre of water.e! -lose the ?ar and shake it vigorously for one minute.f! 9et it stand for three hours.g! -heck the sand surface. If there is silt present, it will form a layer on top of thesand.h! If there are more than $ mm of silt, the sand must be washed.


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4. %nother simple test to check the cleanliness of sand is as follows7

a! Take a handful of sand and s;uee"eit.

b! Throw it away.

c! It your hand is clean and free ofsticky dust, the sand is clean.

d! If your hand is dirty and sticky, thesand is dirty.

Washing the sand

. If there is too much silt, you will have to wash the sand before using it. 5epeatthe following procedure until all your sand is clean.

a!


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c! 2tir vigorously.d! 9et it stand for a few minutes.

e!


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Selecting the cement to use

1+. Cou should use ordinar! Portand c$#$nt F


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properly.e! N$"$r use hardened cement, but throw it away.

Selecting the water to use

13. The water should be clean and neutral or slightly alkaline pD 4 to .'!. It should

be free from organic matter, oil, alkali or acid. %void using saltwater or a water toorich in sulphates more than #'+ ppm!.

14. If you have to use brackish water or dirty water, add a tablespoon of soappowder for every sack of cement used. =issolve the soap into a small amount ofwater and add it to the mix.

Selecting the mortar to prepare

1. There are three basic types of mortar which you can prepare yourself, asshown in Table 4, according to their use. 5emember that the richer a mortar is in

cement, the more it will shrink, and the more it will be inclined to crack.

TABLE @ Basic t!&$s o( c$#$nt #ortars

T!&$ o( #ortar

Portand c$#$ntSand)-

Utii=ation

uait! *+

9ean #'+ $'+ 1+++ Hormal brickwork, pipe ?oints

Frdinary #'+ &'+ 1+++ 2urfaces exposed to the air

5ich $#'LL 3++ 1+++*aterproof surfacing, re?ointing ofbrickwork

L Nuantity of the material to prepare 1 m$ of mortar with the addition of about #++l of waterLL If available

1/. In acid sulphate soils, the


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• ric/ #ortar8 one part cement preferably $#' grade! and two parts sand.

#1.Cou will need about #++ l of water per m$ of mix about one part water for veparts mix!.

Measuring the mortar components

##. To produce a good mortar, it is essential that you measure accurately theamounts of cement and sand to be mixed, according to the proportions re;uired.

#$. If you know the weight of one sack of cement, it is easy to calculate how manysacks you will need to use seeTab$ @!.

#&. If you plan to use the above proportions by volume, it is best to use a containerof known volume, such as a 1+litre bucket or a '+litre wheelbarrow. @or larger;uantities, you can easily build yourself a 1++litre bottomles wooden box withhandles as shown.

#'. % shovel may also be used for sand and cement, but you should take care toload the same amount each time. 0ven then this method is not very accurate.

Con"$ni$nt contain$rs (or #$asurin+sand and c$#$nt

Preparing a good mortar

#3. To prepare a good mortar, carefully proceed as follows7

a! Pr$&ar$ a c$an #i>in+ ar$a, forexample a metal sheet or a watertightwooden platform. %s a rough guide, a 1

b! M$asur$ the ;uantity of sandre;uired. If it is very dry, wet it a littlebefore measuring.


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m# area is enough for '+ kg of mix.

c! S&r$ad t/$ sand over the mixingarea.

d! M$asur$ the ;uantity of cementre;uired.

e! S&r$ad t/$ c$#$nt on top of thesand.

f! Mi> t/$ sand and c$#$ntto+$t/$r t/orou+/!, until the mixhas a homogeneous colour. )e sure tomix in the bottom and side materials.


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g! For# a /oo1 in the middle, slowlyadd a little water in the hollow andmoisten part of the mix. *ork the waterin by carefully moving the dry mix intoward the hollow. )e careful not to let

water run away.

h! 5epeat adding water little by littleuntil the whole mix is moistened.-ontinue mixing thoroughly, adding ?ustenough water to obtain a plasticconsistency. The mortar should have arm, smooth appearance. Cou should be

able to make a clean slice into it with atrowel or shovel. It should sit on a trowelcleanly and rmly without loss of waterand should spread smoothly.

#4. R$#$#b$r8 do not add too much

water.

Using a cement mortar

#. The mortar should be used immediately after its preparation. % mortar shouldnever be used after it has started to set, which you can tell is happening if the mixstarts to become sti and breaks up when spread. %void using mortar which hasdropped from the working area.

#/. The surfaces to come in contact with the mortar should be clean and rough. It isessential to wet them well before applying the mortar, for example by soakingbricks in water for $+ minutes and wetting cement blocks, so that they do notabsorb the water from the mortar and reduce its strength. If you are working in dryconditions, be careful to keep the bricks or blocks wet.


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$+.


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graded so that when mixed they ttogether with minimum pore spacebetween them. These small remainingpores are lled up by the cement,which will then strongly bind the

aggregates after its reaction withwater.

#. The most important factors inmaking strong concrete are therefore7

• use of &ro&$r! +rad$da++r$+at$s with the right si"eand the right shape:

• addition of the ri+/t a#ount o(

1at$r:• a"oidanc$ o( "$r! 'n$

&artic$s as these will ll thesmall pores which should belled with cement.

$. There are two to three dierentgrades of a++r$+at$s, depending onthe type of concrete re;uired7

• 'n$ a++r$+at$s, sand and rock

screenings, si"e +.# to ' mm.2ometimes termed 8sharp8sands, these are usually coarserthan sands used for mortar:

• coars$ a++r$+at$s,gravel(pebbles, broken bricks,si"e ' to #' mm:

• "$r! coars$ a++r$+at$s,broken stones or bricks, si"e #'

to 3+ mm.

Di$r$nt +rad$s o( a++r$+at$s


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inding good sources of materials

&. ood natural sources of aggregate materials, sand and gravel for constructionpurposes )Tab$ - are relatively infre;uent. *ellgraded soils that have the rightrange of particle si"es are particularly hard to nd. If the soils contain some silt,they are only moderately suitable.

'. 2oils where silt and clay predominate are poor natural sources of aggregates.

Ansuitable soils are all those belonging to the other Anied 2oil -lassicationA2-! groups see 2ection 11.1,Soi4 6!.

TABLE Suitabiit! o( sois as sourc$s o( a++r$+at$s (or +$n$ra construction

2oodsourc$s

Mod$rat$suitabiit!

Poorsuitabiit!

Unsuitab$ sois

2* 2*2G 2G G9

2< 2


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plasticity(compressibility

L 2oils are dened according to the Anied 2ystem of -lassicationA2-!, see 2ection 11.1, Soi46LL These suitability classes apply for use in concretes and in dry

aggregates e.g. for mending roads, etc.!3. ood concrete is a homogeneous mix without excess water. It is smooth andplastic. It is neither too wet and runny, nor too dry and crumbling.

4. To prepare good concrete, you should use the proper ingredients and mix themthoroughly in the right proportions. Cou have already learned which kinds of sand,cement and water to use see 2ection $.$!. In the following sections, you will nowlearn about coarse aggregates and concreting.

Selecting the kind of gravel and broken materials to use

. Cour concrete is only as strong as the strength of its coarse aggregates. Thereforeyou should look for hard, dense and durable gravel and stones. These aggregatesshould never be lateritic see 2ection 1., 2oil,6!.

/. If you have doubts about the strength of the coarse materials to be used, you canuse the following test.

a! )reak some stones with a hammer. b! )reak similar si"es of concretepieces, and compare how di>cult theseare to break.

c! The stones are hard enough if they are more di>cult to break than the concrete.

1+. These coarse aggregates should preferably be neither Mat in shape nor havesharp edges. The best materials have round or cubical shapes such as gravel from astream bed or beach.

ftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e11.htm#138pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e11.htm#138pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6708e/x6708e03.htm#41'aftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6708e/x6708e03.htm#41'aftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm#139pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm#139pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e11.htm#138pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e11.htm#138pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6708e/x6708e03.htm#41'aftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6708e/x6708e03.htm#41'aftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm#139pftp://ftp.fao.org/fi/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm#139p


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11. The aggregates should be c$an and free from dirt and organic material. %s withsand, you should wash them if necessary see 2ection $.$, paragraph !.

as/ a++r$+at$s i( n$c$ssar!

1#. ravel and broken stones usually range in si"e from +.' to 3 cm across. @orparticular construction works, such as relatively thin concrete walls and slabs, youwill have to use smaller broken stones.

Not$7 the si"es of the largest aggregate particles should never exceed one;uarter

of the concrete thickness.

A++r$+at$s s/oud n$"$r $>c$$d , o( t/$ concr$t$ t/ic*n$ss

1$. @or heavier concrete work, particularly base slabs and heavy foundations, largeboulders and rocks may be thrown in, provided the concrete can be packed aroundand over them.

1&. In areas where rock aggregate is unavailable, broken brick is fre;uently used. Itdoes not make strong concrete but can be acceptable for simple foundations and

lightly loaded walls. -are should be taken in preparing, placing and curing theconcrete to make it as strong as possible.

Lar+$ roc*s #a! b$ us$d (or bas$sabs i( t/$!do not $>c$$d , o( t/$ sabt/ic*n$ss

ou can us$ bro*$n bric*s (orsi#&$ (oundations



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Selecting the concrete to prepare

1'. @or generalpurpose concrete work, there are three basic ways to determine thecorrect proportions of aggregates and cement7

• simple rules of thumb, based on the kind of construction and dening

the 1$i+/t o( c$#$nt &$r cubic #$tr$ o( concr$t$:

• simple rules of thumb, based on the kind of construction and deningthe ratios b! "ou#$:

• the more accurate method, based on the (r$$5&or$ "ou#$ inside theconcrete.

13. @or small concreting ?obs and for repairs, use one of the rst two methods. @orlarger concreting ?obs, it is safest to use the third method.

14. The simple rules of thumb are given as guidelines for the preparation of fourbasic types of concrete, from a lean to a very rich mix.

1.Tab$ provides guidelines based on the weight of the cement for concretescontaining from 1'+ to &++ kg cement per m$ . The ;uantity of water to be useddepends greatly on the moisture content of the sand and gravel and must be ?udgedwhen mixing the concrete.

TABLE A#ount o( #at$rias r$Guir$d to &r$&ar$ #3 o( concr$t$

Concr$t$Guait!

Portandc$#$nt)*+-

Sand0.95%##)-

2ra"$ %59%##)-

Bro* $nston$s9%560##

A&&ro>.1at$r)-

E>a#&$so(constructions


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)-

9ean-4-1+L

a!

1'+LL &++ ++ 1++2ubfoundation

b!

14'LL $4' 1+++ 2ubfoundation, forms

c!

#++LL &++ 3++ $++ 1'+ @orms

Frdinary-1'

-#+

a!

#'+LL $++ 1+++ @oundationwatercontrol

structure,Moor slabsb! #'+LL &++ 3++ $++ 14+

5ich-#'-$'

$'+LL &'+ ++ #++

Anderwaterfoundation,reinforcedconcretemonk,shing pit,spillway,etc.!

Peryrich-&+-3+

&++LLL '++ 4'+ *ater pipes,canals

L 8-8 refers to approximate concrete strength in newtons(mm# LL Nuality #'+LLL Nuality $#', if available

1/.Tab$ 0 provides guidelines for similar types of concrete based on ratios byvolume. The water ;uantity to be used is about +.4' l per litre of cement. Thisshould be checked while mixing.


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TABLE 0Pro&ortions o( concr$t$ #at$rias b! "ou#$

Concr$t$

Guait!

Pro&ortion b! "ou#$

c$#$nt 8 sand

8 +ra"$

9ean

1 7 & 7 3

1 7 $ 7 '

Frdinary

1 7 # 7 &

1 7 # 7 $

5ich 1 7 # 7 #

Pery rich 1 7 1.' 7 #.'

Not$8 these gures e.g. 17#7&! are commonly used to describe concrete mixes: theweight mixes in Table /, however, give more accurate specications

Preparing concrete by the free!pore volume method

#+. The freepore volume method is based on the fact that the cement should llthe pore spaces left free in the aggregates.

#1. The volume of these freepore spaces and the amount of cement paste re;uiredcan be determined as follows.

a! Take a sample of the ungradedaggregates you will be using to prepareyour concrete.

b! 2ift this sample through a 'mmscreen to divide it into coarse aggregateslarger than 'mm diameter! and neaggregates smaller than 'mmdiameter!.



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c! @ill a small container of volume


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h! %dd 1+ percent to this volume to obtain the corrected volume


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#$. To measure accurately the amounts of cement, sand and gravel or stonesre;uired to prepare good concrete, you can use one of the methods describedearlier see 2ection $.$!.

#&. If your sand is very dry, moisten it a

little before measuring the amountre;uired.

#'. @or the measurement of volumes of

ungraded aggregates to be based on acement volume, it is useful to use ahomemade box containing &+ l, theapproximate volume of one '+kgcement bag.

Storing concrete components

#3. Cou can store aggregates in piles or bins, but be careful not to let the separatesi"es mix in with each other. 2tore them in separate areas, or use a wooden dividerbetween each grade. 5emember also that after some time, the bigger si"es tend to

be at the bottom and sides of the pile, so be careful when selecting material for use.



35/81

Preparing good concrete by hand

#4. To prepare concrete by hand, you need a clean, watertight mixing area. 2mall

amounts of concrete may be mixed on level ground using7

• a #$ta s/$$t 1 x # m!:

• a 1ood$n &at(or# 1 x # m! carefully built to be watertight:

• a &ortab$ #i>in+ &at(or# made from galvani"ed sheet metal about 1 x# m! nailed on two planks ' x $+ x 1+ cm!. The curved ends are nailedvertically to be watertight.

For #i>in+ s#a a#ounts o(

concr$t$

#. 9arger amounts of about '+ kg of cement may be mixed using7

• a wooden platform # x $ m! carefully built to be watertight:

• a concrete mixing Moor7 if the Moor is 'cm thick with a diameter of #'+ cmand a 1+cm raised edge, you will need about #++ l of lean concrete to build


36/81

it. @or example, mix '+ kg of cement, 1#+ l of sand, $++ l of gravel ' to 1#mm diameter! and about $+ l of water.

For #i>in+ ar+$r a#ounts o(concr$t$

#/. =etermine how much of each ingredient you will re;uire to prepare a certainamount of concrete and then proceed as follows.

a! Pour t/$ sand on to the mixingarea and s&r$ad it evenly.

b! S&r$ad t/$ c$#$nt evenly over thesand.

c! Mi> the cement and sand well,

stirring with a shovel, until you obtaina uniform colour: s&r$adthis mixtureevenly over the mixing area.

d! $t t/$ +ra"$ and s&r$ad it evenly

over the mixture.


37/81

e! Mi> t/orou+/! together toobtain a homogeneous mixture.

f! Ra*$ into a &i$ and (or# a /oo1 inthe middle of the mixture.

g! @rom the previously measuredvolume, so1! add 1at$r in thecentre and progressively moisten themixture.

h! S/o"$ bac* and (ort/, mixingthoroughly until you obtain concrete ofuniform plastic consistency.


38/81

i! If the concrete is either too wet or too dry, correct its consistency see paragraph$.# of this section!.

Preparing good concrete mechanically

$+. If a concrete mixer is available, it will be much easier to prepare concrete. The;uality of the concrete is also likely to be better. %s the capacity of concrete mixersmay vary from 1'+ l to '++ l or more, it is important to select a machine adapted toyour needs. Cou should know the capacity of your mixer and plan the concretemixing accordingly.

$rsStandard #i>$r )&$tro-

Mini5#i>$r )$$ctric- 2rindin+ #i>$r )&$troor $$ctric-

$1. )efore preparing a concrete batch, gather all the ingredients re;uired close tothe mixer. Then proceed as follows.

a!


39/81

windy days: • when mixing by hand, do notwash cement out with the water:

• rinse and clean your tools andyour mixer well at the end ofeach working session.

Correcting the consistency of concrete

$#. ood fresh concrete should have a plastic consistency. If this is not the case, itsconsistency should be corrected as follows7

• if the mix is too 1$t, add smallamounts of sand and gravel inthe right proportion until the mixbecomes plastic:

• if the mix is too dr!, add smallamounts of water and cement inthe right proportions until the mixbecomes plastic.

$$. Take note of the amounts of the materials added so that you will have thecorrected proportions for the next batch of concrete.


40/81

"esting the #uality of fresh concrete

$&. @or larger construction works or where the strength is critical, the ;uality offresh concrete should be routinely tested beforeuse. This can be simply done usingthe slump test, which provides a relative measurement of the fresh concrete

plasticity and its expected strength after setting or hardening.$'. To execute the slump test, you will need7

• a conica! s/a&$d buc*$t 1' to #+ l!:

• a 1ood$n rod about 3+ cm long and 1' to #+ mm in diameter with wellrounded ends:

• a bas$ &at$ at least $+ x $+ cm, either a thick wooden board or preferablya steel plate.

$3.


41/81

d! S#oot/ t/$ sur(ac$ of theconcrete to enable you to ll the bucketexactly to the top.

e! -arefully turn t/$ buc*$t u&sid$do1n on to the base plate.

f! -arefully i(t t/$ buc*$t o theconcrete, place it alongside andimmediately measure, in cm, thedierence between the height of theslump cone and the height of the bucketoriginal concrete cone!.

g! This dierence is called t/$ su#&.

$4. -ompare the measured slump with the range of values suggested according tothe type of construction see Tab$ !. Asually, a slump of #' to $+ percent shouldbe taken as satisfactory. Hote that with some standard mixes, the concrete mayshear. If so, repeat the test, or estimate the slump from the upper edge of theremaining sample.

TABLE Su#& t$st8 acc$&tab$ ran+$s o( su#&

T!&$ o( construction Su#& ran+$

2labs and thin reinforced structures #''+6

*ork Moors, culverts and drainage structures 1+#'6


42/81

*alls without reinforcement 1+$'6

*alls with reinforcement #+'+6

L 0xpressed as percentage of bucket height at $+S-

$. If the slump is not satisfactory,the cement ;uality has to beimproved using the sameproportions as in the original mix asfollows7

• to decrease the slump, addsand and gravel:

• to increase the slump, addwater and cement.

Preparing forms for placing concrete

$/. -oncrete is usually used in con?unction with forms shutterings!, whichdetermine the nal shape of the concrete structure to be built. In many cases theconcrete is reinforced see 2ection $.'!.

&+. The forms in which the concrete can be cast are generally made of light, cheapwooden boards and timber pieces, nailed or bolted together. @or a series of standard

shapes, steel plate is sometimes used.

&1. ood forms should have the following characteristics. They should7

• be ri+id enough not to lose their shape when full of concrete:

• be 1at$rti+/t:

• be $as! to r$#o"$ without damaging the concrete:

• be r$5usab$, in case other similar structures have to be built:

• easily accommodate reinforcement material, if used.

. @orms should be well braced so that they remain rmly in place.

A (or# (or a concr$t$ 1a /ast1o sid$s

For# r$ad! (or &acin+ concr$t$



43/81

Placing concrete

&$. -oncrete should be as fresh as possible when placed, ideally7

•

1it/in 9% #inut$s after opening the cement sack:

• 1it/in 90 #inut$s after adding water to the mix.

&&. Fnce the concrete has started to set, it cannot be used. It is therefore importantto have everything ready for use. Fnly make as much concrete in each batch as youcan place in the time available.

&'. %void placing concrete underwater, because it is very di>cult tomake good concrete in theseconditions. Ase a drainage ditch, ifnecessary, to make sure that theconcreting site is well drained. Theearth, however, should be slightlymoist. The supporting base should berm and in many cases may re;uire alayer of rock, brick rubble or otheraggregate. If the concrete is to bermly placed on rock, it should be wellcleaned and dried.

Pacin+ concr$t$

A (oundation sit$ A +$n$ra buidin+ sit$


44/81

&3. %void segregating the ingredients of the concrete during placing, as thisweakens the concrete and makes poor surfaces and poor ?oints between layers7

• never let concrete drop freelymore than 1.' m:

• never let it slide down a verysteep incline:

• do not transport it over a longdistance without remixing it.

&4. )efore placing the concrete inthe forms, you should oi or+r$as$ their inside surface to makeit easy to remove them once theconcrete has set. Cou shouldalso 1$t t/$ (or#s.

&.


45/81

&/. Ase a shovel, a wooden pole or a#cm diameter iron rod to tamp thefresh concrete rmly into place.

'+. Do not tr! to us$ :1$t: concr$t$ tomake better ?oints, as it will only separatemore and the water will wash out, leaving avery poor surface and ?oint.

'1. Cou can also hammer on theoutside of the forms to help to settlethe concrete along the sides.

'#. If the previous layer hasset, rou+/$n its u&&$r sur(ac$ tomake a good connection to the nextlayer. Cou can also brush on a coat

of li;uid cement, which is cementdissolved in water. If available, use acement bonding compound instead.

Rou+/$n t/$ sur(ac$


46/81

Coat 1it/ iGuid c$#$nt or bondin+co#&ound

Not$7 it is always best to build a structure continuously, without interrupting theplacing of the concrete. 5emember the higher the structure, the stronger the formshave to be. If this is a problem, it may be necessary to build the structure in stages,

letting each stage set before placing the new stage.

Curing concrete

'$. *ithin $ss t/an /a( an /our after adding water to the cement, the chemicalreaction between these two ingredients results in the setting and progressivehardening of the concrete. The concrete ac;uires its strength, durability andimpermeability during the curing process. To get the strongest possible concrete,curing should not be too rapid. It normally takes at least # days.

'&. If the concrete is allowed to dry out, it will stop hardening: the curing process

will not start again when the concrete is rewetted. Therefore, as soon as theconcrete is placed, you should protect it from drying too fast by following theseguidelines.

a! =o not let the concrete dry out before placing it.

b! %void placing concrete during the hot hours of the day.

c! *et the forms abundantly before placing the concrete. Beep them wet and donot remove them too ;uickly.


47/81

d!


48/81

left to dry out. Hormally, the nish is not as good as that for machinemade blocks,which are formed under pressure using a dry concrete mix.Not$7 the forms shown on this page are for blocks of #+ x #+ x &+ cm.

A si#&$ bo> (or# (or

#a*in+ a soid boc*

A t1o5&i$c$ (or# (or

#a*in+ a /oo1 boc*

Pus/5out (or#

D$tais (or buidin+ t/$ out$r (or# and t/$ inn$r #oud (or #a*in+ a/oo1 boc*

Out$r (or# Inn$r (or#

/$n t/$ c$#$nt is n$ar! dr!4 car$(u! r$#o"$ t/$ inn$r (or# andso1! &us/ t/$ boc* (ro# t/$ out$r


49/81

3.% Concr$t$ r$in(orc$#$nt

1. 5einforced concrete is made by adding reinforcement to normal concrete.5einforcement is used to keep the concrete from collapsing.

Selecting reinforcement

#. There are three main kinds of concretereinforcement7

• round steel bars, with a standarddiameter from ' mm to &+ mm:

• diamond mesh, 8expanded metal8used for reinforcement of lightconcrete sabs the longer meshdiagonal is set perpendicular to

the slab supports!:

• welded wire mesh with rectangularmesh of standard dimensions.

Round st$$ bars

E>&and$d #$ta #$s/

$. To use reinforcement, you may alsoneed7

• tie wire, soft annealed steel wirefrom +.4 to 1 mm in diameter, to

$d$d 1ir$ #$s/


50/81

connect bars and mesh together:

• spacers, in metal, wood, plastic,etc., to make sure reinforcement ispositioned correctly within the

forms.

Using reinforcement

&. The amount of reinforcement needed for a particular construction should bedetermined by an engineer, who should also specify how and where thereinforcement should be placed within the concrete to avoid collapse. 2implespecic designs are given in the second part of the manual.

'. @or your guidance only, the number of steel bars is generally calculated as a

percentage of the gross area of each section of concrete as follows7

• for foundations7 at least 1 percent:

• for slabs7 at least $ percent:

• for columns7 at least 3 percent.

Ar$a o( st$$ )in ##9- &r$s$nt in concr$t$ s$ction accordin+ to dia#$t$rand nu#b$r o( st$$ bars)+$n$ra (or#ua H 3.6 > d9 > n -

=iam

mm*eightkg(m!

-ircumf.

mm!

Humber of steel bars

1 # $ & ' 3 4 / 1+

+.+/ 1#.'4 1# #' $4 '+ 3# 4' 1++ 11 1#'

+.1'& 1'.4+ #+ $/ '/ 4 / 11 1$ 1'4 143 1/3

+.### 1.& # '3 ' 11$ 1&1 14+ 1/ ##3 #/& ##

+.$+# #1./ $ 43 11' 1'$ 1/# #$+ #3/ $+4 $&3 $&

+.$/' #'.1& '+ 1++ 1'1 #+1 #'1 $+1 $'# &+# &'# '+#

+.&// #.# 3$ 1#4 1/+ #'& $1 $1 &&' '+ '4# 3$3


51/81

+.314 $1. 4/ 1'4 #$3 $1& $/$ &41 ''+ 3# 4+3 4'

+.4&3 $&.'' /' 1/+ #' $+ &4' '4+ 3$' 43+ '' /'+

+. $4.41 11$ ##3 $$/ &'# '3' 34/ 4/# /+& 1+14 11$1

1.+ &+.+ 1$# #3' $/ '$+ 33$ 4/3 /#/ 1+31 11/& 1$#4

1.#+ &$.// 1'& $+ &3# 313 44+ /#&1+4

1#$1 1$' 1'$/

1.$4 &4.1+ 144 $'$ '$+ 4+4 &1+3

+

1#$

41&1$ 1'/+ 1434

1.'4 '+.1+ #+1 &+# 3+$ +&1++'

1#+3

1&+4

13+ 1+/ #+1+

1.4# '$.&+ ##3 &'$ 3+ /+411$&

1$31

1'

11' #+ ##3/

1.// '3.'& #'& '+/ 43$1+1

1#4#

1'#3

14+

#+$' ##/+ #'&&

#.##3 '/.4+ #$ '34 '+11$&

1&14

14+1

1/&

##3 #''1 #$'

#.&33 3#.# $1& 3# /1#'4

1'41

1&

#1//

#'1$ ##4 $1&1

$.'$ 4.3+ &/1 /#1&4$

1/3$

#&'&

#/&'

$&$3

$/#3 &&14 &/+

'.'&/ /&.$+ 4+4 1&1& #1#1

##4

$'$&

&1

&/&

'3'& 3$31 4+3

3.$1$ 1++.'+ +& 13+#&1$

$#14

&+#1

&#3

'3$+

3&$& 4#$ +


52/81

4.''$ 11+.+1 /3# 1/#&#3

$&

&11

'44$

34$'

43/3 3'/ /3#1

/.3' 1#'.4+ 1#'3 #'1$$44+

'+#3

3#$

4'&+

4/4

1++'$

11$+/

1#'33

L @or round and smooth steel bars

E>a#&$8

% reinforced concrete column +.#+ x +.#' m is to be built. The necessaryreinforcement can be estimated as follows7

a! -alculate the gross area of the section of the column7 +.#+ m x +.#' m K +.+'

m# K '++ cm#

b! -alculate the minimum area of the steel reinforcement re;uired7 '++ cm# x +.+3K $+ cm# K $+++ mm#

If you plan to use 1+ steel bars as shown in the drawing, start with the 1+barcolumn on the righthand side of the chart above. @ollow the column down until yound an area at least e;ual to $ +++ mm# or in this case $ 1&1 mm# . How follow thisline across and you will see that this area corresponds to a steel bar diameter of #+mm. 2o, for this si"e of concrete column use reinforcement made of 1+ steel bars of#+ mm.

Preparing the steel bar reinforcement


53/81

3. The steel bars should be clean and free of oil and earth. 5ust, unless so severethat bars are weakened, does not re;uire particular attention, although any looserust should be removed with a wire brush.

4. To bend the steel bars according to design, you need a wellxed piece of steel

plate or heavy planking in which you have driven or xed four small pegs of 1+mmdiameter steel bar. If you plan to bend a lot of bars, you may prefer to build a strongworkbench.

. )uy a special clamp or make one yourself by sawing a narrow notch in a piece ofvery thick steel bar or rod.

/. Insert the steel bar to be bent between two of the rst three pegs, making surethat the bar is positioned to bend in the right place. Asing the clamp, bend the steelbar at the level of the single peg.

1+. Fnce the steel bars have been cut and bent according to design, the

reinforcement is constructed. The bars should be rmly and securely boundtogether at their intersections with tie wiresee paragraph $ above!.

Making reinforced concrete slabs



54/81

11. )y using wire mesh reinforcement, you can make simple slabs with a fairly moistconcrete mix of 17#7& to 17'7 that has aggregates smaller than 1$ mm across. Tomake a slab, place the concrete inside a simple wooden form resting on a Matsurface or level a piece of ground, cover it with a heavy plastic sheet and put thewooden form on that. %s with blocks, you should take care in curing the concrete.

Not$7 the wire mesh may be held in place within the form using strips of wood overthe top of the form and hang wires see below!. 5emember to $a"$ at $ast 9%## o( (r$$ s&ac$ a around t/$ #$s/ and b$t1$$n t/$ to& and botto# o(t/$ (or#. %lso, it is often useful to set in one or more small loops to use as handlesfor lifting or moving the nished slab.

A r$in(orc$d concr$t$ sab Co#&act concr$t$

D$tai$d s$ction t/rou+/ (or# 1it/ concr$t$ in &ac$

Not$7 the form shown is for a slab of 4 x '+ x 1++ cm. Dowever, dimensions mayvary from ' 1+ x $+ + x '+ 1#+ cm

Making reinforced concrete


55/81

1#. To reinforce concrete, proceed asfollows.

a! Fi> t/$ r$in(orc$#$nt 1$,

exactly according to the engineeringdesign, There should normally be atleast #' mm between the bars and theoutside surface. Gake sure tie wires aresound, and that the bars are nottwisted.

b! Pac$ t/$ (or#s around thereinforcement. If necessary, use spacersto hold reinforcement bars in place.

A r$in(orc$d concr$t$ cou#n

c! $t t/$ (or# and the reinforcement well.

d! Pac$ t/$ concr$t$ into the form, without disturbing the reinforcement.

e! Co#&act t/$ concr$t$ 1$, especially around the reinforcement, but do notdisturb the reinforcement or shake it.

$t (or# andr$in(orc$#$nt

Pac$ concr$t$


56/81

f! Take particular care in making +ood

Joints between layers.

g! Cur$ t/$ concr$t$ well before

removing the form.

h! R$#o"$ an! s&ac$rs if used, andnish and ll the outer surfaces. )ecareful to make sure no reinforcement isexposed to water.


57/81

3.6 Ot/$r construction #at$rias

1. There are several other materials commonly used for construction purposes,particularly where supplies for normal cement or concrete are not easily available.

These are generally not so strong or durable, but may be used if necessary. Thereare also many speciali"ed materials, but these are usually too expensive or toocomplex to use for most sh culture constructions. 2ome of the materials you mightuse are7

• i#$ #ortars which use sa*$d i#$, produced from crushed and burntlimestone, mixed 17# to 17$ with sand. Cou need about +.1' to +.# m$ of limemortar per m$ of brickwork and +.# m$ of lime mortar per m$ of stonework.

This can make a reasonably strong mortar, although the ;uality of all limemixes depends on the characteristics of the lime used. Cou should check the;uality locally before using:

• i#$ concr$t$ which can be made using i#$ instead of cement, in similarvolume proportions as in ordinary concrete for example 17#7&, 17$73, etc.!. %slime is lighter than cement, you need about #+ to #' percent less weight for

the same volume, for example &+ kg of lime instead of '+ kg of cement. 9imeconcrete is not as strong as cement concrete:

• &ast$r which is used for making smooth wall surfaces. 2moother thancement mortar, it is made with a range of mixes from 1717' to 17$71# byvolume of cement7lime7sand:


58/81

• soi c$#$nts and concr$t$ in which cement sometimes lime! is mixedwith local soil. Ideally the soil should be reasonably well graded see Table for suitable soil types! and free from vegetation or organic matter. 5atios ofcement7soil are typically 17$ to 173. The ;uality of soil cement variesconsiderably7 it is not normally recommended for structural use, but may be

used for reinforcing channels, tops of dikes or pathways.

3.@ 2abions

$ntroduction

1. % gabion is a 1ir$ #$s/ ca+$ or bas*$t '$d 1it/ ston$s. abions areuseful in construction works, for example to protect earth embankments, to linechannels, to manage or divert river or stream Mow and to protect river banks orcoastlines.

#. Cou can buy wire mesh baskets and make your own gabions. The standard gabion

basket consists of a single piece of wire mesh that can be assembled to form arectangular box with a lid.

Ston$5'$d +abion 2a"ani=$d 1ir$ #$s/r$ad! to b$ ass$#b$d

ir$ #$s/ bas*$tass$#b$d

$. *ire mesh baskets for gabions can usually be found in two standard si"es. Theyare for7

• fullheight standard! onemetre gabions:

• halfheight halfmetre gabions.

&. The width of a standard basket is usually 1 m, and the length varies from # to 'm or more.

Standard +abion 7a(5/$i+/t +abion



59/81

'. alvani"ed steel wire is used formaking baskets for gabions. The wire isusually $ mm in diameter and is twistedto form a mesh opening from 1++ to 1#+mm wide. )oth single and double twist

mesh are available, although doubletwist is better.

%dvantages of gabions

3. abions have a number of important advantages in construction7

• /o#o+$n$it! and stabiit!, holding together and maintaining strongresistance to water current. %lthough containing small units rocks, stones!,

each basket acts like a single large unit:• &iabiit!, adapting their shape easily to the ground contours even as these

change gradually:

• &$r#$abiit!, allowing water to run through and act as lters for ner soilparticles, thus giving protection to less stable materials:

• si#&icit! of design and easy, rapid construction:

• $cono#!, using locally available stones that cost nothing.

S/a&$ $asi! ada&t$d A t/r$$5+abion barra+$


60/81

Designing gabion structures

4. abion structures normally consist of two parts7

• t/$ (oundation, which mustprotect the structure againstundermining. It is usually madeof halfheight baskets andshould extend well beyond the

main structure body:

• t/$ bod!, which should resistthe forces present. It is made ofstandard baskets of varioussi"es that are piled up in one ormore rows according to the totalheight re;uired.


61/81

. Dalfheight gabions may also beplaced on sloping river or stream

banks or terraces. The gabions mustbe well supported at their base.

/. @or most sh farm uses, structuresare not more than two or threegabions in height. %long stream banksor channels, a single gabion width isusually ade;uate. 2tructures two orthree gabions or more in width may beneeded for stream diversions inrapidly Mowing water. Hormally, the

slope of gabion structures is from &'Sto near vertical.

Ri"$r or str$a# ban*s

Ri"$r or str$a# di"$rsion


62/81

Ri"$r4 str$a# orc/ann$ ban*s%K ban*

30K ban* N$ar! "$rtica ban*

&uilding a gabion structure

1+. *ire mesh baskets are built one at a time, put in place according to the designof the structure and then lled with stones. The following steps will tell you what todo.

a! )egin the rst basket byunfolding a section of wire meshand stretching it out Mat on the

ground.

b! @old the front, back and sides to form a boxwith the lid open.

c! 2ecurely wire the four cornersof the mesh box together asshown. This should be done verycarefully using galvani"ed steelwire of the same ;uality anddiameter as the mesh wire. =o notpull the wire with pliers, becauseyou may tear and weaken the box.


63/81

d! %fter you have wired the fourcorners together, carry the basketto where you will use it.

e! *hen a basket is in position, make surethat it is straight and s;uare. To do this,stretch the front, back and side, driving a 1.'m iron bar into each corner as shown. %s eachcorner becomes straight and s;uare, drive thebar into the ground to hold it in place.

11. 0ach mesh basket must also

have $>tra 1ir$ bracin+ to helpsupport the weight of the stoneswhen the basket is lled. %sbraces, you can use the same wireyou used to secure the fourcorners of the box.

1#. The vertical braces areattached as soon as the basket isin place. The hori"ontal and anglebraces are added as the baskets

are lled with stones.

1$. The drawings show you whereto put vertical, hori"ontal andangle braces, both for a fullheightgabion and for a halfheightgabion.

Brac$s (or (u5/$i+/t +abion 5 > > %

# a H an+$ / H /ori=onta " H "$rtica


64/81

Brac$s (or /a(5/$i+/t +abion 5 0.% > > %#

1&. 0ach brace is attached by threadingit through several of the wire meshopenings.

1'. How you are ready to start lling

the basket with stones.

13. % (oundation bas*$t is best lledwith round or rounded stones at leastoneandahalf times as large as theopenings in the wire mesh. %void usingstones larger than this. If the stonesare too large, you cannot easily deformthe basket to t irregular or curvedsites such as stream banks.

Not$7 try to choose stones that tclosely together so that there will be nolarge empty spaces in the basket.


65/81

14. % structur$ bas*$t is also bestlled with stones, at least oneandahalf times as large as the openings inthe wire mesh. Dowever, if you do nothave enough large stones, you can use

smaller stones in the centre of thebasket if they are at least cm indiameter. If you use smaller stones,rst line the bottom and sides withlarge stones, then ll the centre withsmaller stones and nally cover the topwith a layer of large stones.

1. *hen you are lling baskets withstones, #a*$ sur$ t/at t/$ "$rtica1ir$ brac$s sta! "$rtica.

1/. %ttach the /ori=onta

brac$s and an+$ brac$s from time totime as you put in the stones.

Not$7 use hard stones such as granites, ;uart"ites, sandstones, laterite and hardcalcareous stones for lling baskets. =o not use schists, gneiss or serpentine, whichare too friable, may break down in strong water currents and may eventually washout of the baskets causing them to collapse.

#+. *hen the basket is lled with stones, you can remove the iron bars from eachcorner.

#1. -lose the lid of the basket, pull the edges tight and fasten them every #+ cmwith galvani"ed steel wire, using a short piece of iron for a lever as shown.


66/81

##. @inish the basket by attaching thevertical braces to the lid.

#$. %fter the rst basket is in place and lled, add $#&t! bas*$ts one by oneaccording to the design of the gabion structure.

a! *ire the back and sides of each new basket to the lled baskets already inposition.

b! 2tretch the front corners of each empty basket using a 1.'m iron bar until thebasket is straight and s;uare. Then hold it in place by driving the iron bar into theground or into the gabion below.

c! %ttach the braces and ll the basket with stones as before. 5emove the ironbars. @asten the lid and attach the vertical braces.

#&. -ontinue to add more empty baskets until the gabion structure is nished.


67/81

3. at$r &i&$s and t/$ir disc/ar+$ ca&acit!

1.


68/81

should be limited to a maximumof '+ cm. It is best to lay themunder ground, at least '+ cmdeep.

3. R$in(orc$d concr$t$&i&$s are rarely used in shfarming, perhaps only when verylarge diameters are needed.

4. Asb$stos5c$#$nt &i&$s aremade by adding asbestos bresto the concrete to increasestrength. These pipes are morecostly but have the advantage of being lighter, stronger andavailable in longer standardlengths $ to 3 m!. This reducesthe number of ?oints to be sealedwith cement mortar. The inside

diameter usually varies from 1'to $+ cm. The pipes are laiddown in a trench deep enough toprotect them with at least '+ cmof soil. The foundationsupporting them should becarefully built to accommodatethe reinforced collars of thepipes.

E>a#&$s o( asb$stos 5 c$#$nt &i&$

Selecting ceramic pipes

. C$ra#ic &i&$s are made ofbaked clays, usually with a hardgla"ed exterior nish, with typicaldiameters of 1+ to #+ cm. Theyare normally in short lengths, '+

Enar+$d $>a#&$ o( c$ra#ic &i&$


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cm to + cm, with a collar ttingat one end, sealed with mortar.-eramic pipes are not strong andare easily broken in handling. %swith plain concrete pipes, they

must be well protected underground.

Selecting galvani'ed pipes and plastic pipes

/. @or smaller water Mows, +a"ani=$d iron &i&$s inside diameter ' or 3 cm!or &astic &i&$s are normally preferred. The standard lengths available are usuallylonger $ to 3 m!, which reduces or may even eliminate the need for ?oints.

1+. @or plastic pipes, &r$ssur$&i&$s are stronger, heavier, and more

expensive than draina+$ &i&$s. Theyare suitable for higher water pressures,for example pumped water supplies,and wall thickness depend on thepressure rating needed. Draina+$&i&$s are lighter, have thinner walls,are cheaper and are suitable for lowpressure, for example pond drains. Theexample below shows a drainage pipewith a Mexible 8o8 ring inset in the collarfor a 8push t ?oint8.

Enar+$d $>a#&$ o( &astic draina+$ &i&$ s/o1in+ d$tai o( coar 1it/?$>ib$ :o: rin+

11. It is best to protect plastic pipes from the sunlight, as they can become brittle ifkept exposed.

Determining the pipe si'es re#uired


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1#. To select the correct si"e of pipes to be used on your sh farm, for example atthe inlet and outlet of sh ponds, you should rst know which water discharge isre;uired in each case. Cou should then determine which si"e of pipe will have thecapacity for such water discharge. @inally, it is best to standardi"e the pipes and toselect only a limited number of dierent si"es.

1$. The 1at$r disc/ar+$ ca&acit! of a pipe increases with the pressure headmeasured in cm! at the entrance of the pipe see 2ection $.4,at$r4!. This is alsoshown in Tab$ 9 for pipes of dierent si"es.

TABLE 9 at$r disc/ar+$ ca&acit! ),s- o( concr$t$ &i&$s und$r "arious &r$ssur$/$ads

Insid$dia#$t$r o( &i&$ )c#-

Pr$ssur$ /$ad )c#-

% 0 % 90 9% 00

900

#+1.4

#3.&

$#.$

$4.$ &1.

#'#/.#

&1.$

'+.'

'.& 3'.#1#+

13+

$+

.

+

'/.

&

4#.

&.+ /&.+

$''4.#

+./

//.1

11&.&

1#4./

1/+

$#+

(stimating pipe capacity

1&. Pery often, the &r$ssur$ /$ad "ari$s, for example on the outlet pipe as thesh pond is being drained. It is best, therefore, to estimate the capacity of the pipesby one of the following simple methods.

a! Asing Table 1$ and raph 1, you can estimate the water discharge capacity ofpond outlet pipes of various diameters.b! Asing Table 1&, you can estimate the pipe si"es re;uired to drain a pond of aparticular si"e in a specied time.c! Cou can use #at/$#atica (or#ua$ to estimate7

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• the water disc/ar+$ ca&acit! in litres per second, l(s! for a given pipewith an insid$ dia#$t$r D in cm!, using the formula7

H 0.0@ D9.

so, for a pipe with D K #+ cm, K +.+4 x #+# K $1.# l(s:• the insid$ dia#$t$r D in cm! of the pipe re;uired for a given water

discharge capacity in l(s!, using the formula7

D H 3.%6

so, for K 13 l(s, you re;uire a pipe with D K $.'3 13 K $.'3 x & K.9 c#: andyou will probably use a 1'cm pipe.

Not$7 all of these methods assume you are using a simple, short pipe with noobstructions to water Mow, such as complicated sluice gate assemblies, screens, dirt

or fouling inside the pipeOs internal edges, or lips or edges at the mouth or ?oints ofthe pipe. %ny of these will reduce the Mow. If you have or expect to have anyobstructions in the pipe, use a larger si"e. If the pipe is made up of several sectionsof dierent diameters, estimate the water Mow on the basis of the smallest diameterpipe you use.

TABLE 3 A&&ro>i#at$ 1at$r disc/ar+$ca&acit! o( out$t &i&$s

Insid$dia#$t$r o( &i&$)c#-

at$r ca&acit!

),s-

),#in-

)#3,/-

)#3,9 /-

' 1. 1+ 3.' 1''

1+ &+ #/ 3/1

1' 1 1++ 3' 1'''

#+ $1 13+ 11# #34

$+ 4+ ++ #'# 3+&

&+ 1#3 4'3+ &'& 1+3

TABLE Ti#$ ta*$n to drain &onds )in/ours-1it/ di$r$nt drain &i&$ si=$s

Insid$dia#$t$r o(&i&$)c#-

Pond ar$a )/a-

0.

0.9

0.%

9 %

1+ /31/#

&+

#+ 1' $+ 4'

1'

+

$+

+

'+1.'

$.'

13 $# +

1++ # $. 4 14.


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'+ 1/31143+

4+3 13/$&

x 3+x $.3x 3.&x

L )ased on a pressure head of about 1'cm

' '

Not$8 these gures assume an initialinternal water depth of 1 m, with pipevelocity limited to 1 m(s: for two pipes,

etc., time is divided by #

2RAP7 A&&ro>i#at$ 1at$r disc/ar+$ ca&aciti$s o( out$t &i&$s )&r$ssur$ /$adabout % c#-

Designing longer pipelines

1'. To design a &i&$in$, you have to use a dierent method to determine its waterdischarge capacity, taking into account its $n+t/ and the /$ad oss from start toend. In addition, you should check that the water velocity in the pipeline will notexceed a critical value.


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a! 2elect a pipeline inside diameter and calculate its 1at$r disc/ar+$ca&acit! in l(s! as7

H ;)7 L-

where ; is the conveyance factor in l(s!, see Table 1': 7 is the head loss in m! over the pipeline length:L is the total length in m! of the pipeline.

E>a#&$

% concrete pipeline has an inside diameter of #+ cm. It is 1++ m long 9!, and itstotal head loss D! is # m. Its water discharge capacity is7 NK $//.4 l(s # R 1++!K $//.4 +.+# K '3.'$ l(s

A 005# concr$t$ &i&$in$ 1it/ a strai+/t run

b! -alculate the 1at$r "$ocit! a#&$

Asing the same example, the calculated water velocity


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TABLE % Basic con"$!anc$ (actors (or t/$ d$si+n o( &i&$in$s

Pi&$

insid$dia#$t$r)c#-

Pastic andn$1 cast iron

&i&$s

Concr$t$ andod cast iron

&i&$s

S$1a+$&i&$s

Ma>i#u

#1at$r"$ocit!)#,s-M

)#,s-; ),s-

M)#,s-

; ),s-

M)#,s-

; ),s-

'.+ 3.&+' 1#.''& '.14& 1+.1 &.+'3 4./'+ +.3+

4.' .# $3.&4 3.44/ #/.$ '.&+4 #$.4/ +.4+

1+.+ /.$ 44.' .1& 3$./3 3.'3 '1.'3 +.4'

1#.' 11.&1$ 1$/.#& /.&3# 11'.&& 4.3 /$.4/ +.4'

1'.+ 1#.3& ##&.'1 1+.'3# 13./' .3$#1'#.4

+.+

14.' 1$.//3 $$'./ 11.3/3 #+.4 /.3+& #$+.' +.'

#+.+ 1'.1 &43./ 1#.4#/ $//.41+.&/&

$#/.' +./+

##.' 13.$## 3&.+ 1$.41' '&&.'11.$&'

&'+.& +./'

#'.+ 14.$31 '#.& 1&.31/ 414.1#.1#3

'/'.& 1.++

$+.+ 1/.&$# 1$4$./ 13. 1131.&1$.3/+

/34./ 1.1+

Not$8 G and B are constants

"he e)ects of pipe *ttings

13. The formulae you have ?ust used are suitable for straight pipes, but the Mow ofwater is reduced by bends on the pipe or any ttings. The simplest way to allow for


75/81

these is to think of each bend or tting as being e;uivalent to an extra length ofpipe of an $Gui"a$nt $n+t/. Table 13 shows $Gui"a$nt $n+t/s for typicalttings.

E>a#&$

If the pipe used previously #+cm diameter and 1++ m long! has four /+S bends,two check valves fully open! and a reducer outlet, its discharge capacity is still7 H 3.@ 7 L

L is now the total e;uivalent length TEL! or the length of the pipe plus thee;uivalent lengths of the ttings.

Thus TEL K 1++ m Q e;uivalent lengths in m! of four /+S bends Q # check valvesQ reducer outletK 1++ m Q &+.&D! Q #+.4'D! Q +.+ D!.

@or the pipe diameter D K #+ cm,TEL K 1++ m Q &+.& x #+! m Q #+.4' x #+! m Q

+.+ x #+! m K63.6 #.

Then K $//.4 # R 13$.3 K &&.1/ l(s, which is less than + percent of the Mow ofthe straight pipe, as calculated in the previous example.

TABLE 6 EGui"a$nt $n+t/ o( &i&$ b$nds and 'ttin+s

R$(.no.

Pi&$ b$nd,'ttin+EGui"a$nt$n+t/ )#-

1 lobe valve, open #.' =L

# ate valve, open +.+' =

$ -heck valve, open +.4' =

& &'S bend +.1' =

' /+S bend or T +.#+.& =

3 2;uare elbow +.4 =

45educer outlet three;uarters of originaldiameter!

+.+ =



76/81

Not$8 these are typical values and may vary according to design andmanufactureL = K pipe inside diameter cm!

A 005# concr$t$ &i&$in$ 1it/ (our 0K b$nds

3. S$$ctin+ a 1at$r &u#&

1. If you intend to use a pump, you will need to know the right si"e or power P ink*! of the pump for the ?ob. Cou need to consider the head 7in m!, the waterMow in m$(s! and the e>ciency Ein percent! of the pump. Cou can use a simplee;uation such as7

P )*- H ). > >7- E

where the pumping head 7 m! is calculated as the sum of the suction head hs!,delivery head hd! and pipe loss head /&!.

a! @or the commonly used eld pumps, the suction /$ad /s! should be kept assmall as possible. Gost suction heads will not draw up more than $ to ' m in elduse.b! The d$i"$r! /$ad /d! is generally in the range of # to 1+ m.c! The &i&$ oss /$ad /&! can be calculated from the formula used in 2ection$., K ;/& L, and therefore7

/& K L

9

;

9

where is the known water discharge in l(s!:L or TEL! is the total length or total e;uivalent length! of the pipeline in

m!:; is the conveyance factor in l(s!, see Table 1':/& is the pipe loss head in m!.

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T/$ d$'nition o( suction /$ad )/s-and d$i"$r! /$ad )/d-

Not$7 hsKdistance from lower water levelto pump centre line

hdKdistance from pump centre lineto upper water level

#. *ith simple, short lengths of pipe of at least the same si"e as the pump inletsand outlets, the pipe loss head can be ignored.

E>a#&$

Asing a pump of 3+ percent e>ciency in the middle of the pipe system describedearlier, where TEL K 13$.3 m, the Mow rate K + l(s, the suction head /s! K 1 mand the delivery head /d! K # m, the power re;uired is7 Pk*! K /.1 x x 7!R E.-alculated total head 7 is 1 m Q # m Q pipe head loss /&!, where hp K L9 R ; 9 K

U13$.3 m x + l(s!#

V R $//.4 l(s!9

K 3.'' m. Thus total head 7 K 1 m Q # m Q 3.'' m K .%% #.

$. Table 14 shows the power in k*! re;uired for various rates of Mow m$(s! andtotal heads m!, assuming a typical pump e>ciency of 3+ percent the usual rangeis &+ to 4' percent!. To convert these to horsepower 7P!, divide the k* value by+.4'.



78/81

&. In some cases, pumps are dened by the dia#$t$r o( t/$ir out$t &i&$s,usually expressed in inches. Then you can tell whether a certain pump is su>cientfor your needs, by estimating its horsepower as

7P H 3. D9 90

where D is the inside diameter of the outlet pipes in inches.Not$7 one inch is e;ual to #.'& cm.

'. If the pump is to be run for long periods of time, you should increase the powerby at least $+ percent, as most pumps should not be run fully loaded for too long.

The power of the motor should be at least 1+ percent more than the pump power.

E>a#&$


79/81

TABLE @ Pu#& &o1$r (or di$r$nt ?o1 and /$ad r$Guir$#$nts)in *4 assu#in+ a &u#& $ci$nc! o( 60 &$rc$nt-

Tota/$ad)#-

Fo1 rat$ r$Guir$d

,#in8

0 90 %0 00 900 %00000

9000

%000

#3,s8

0.000@

0.00033

0.0003

0.006@

0.00333

0.0033

0.066@

0.03333

0.0333

#3,/8

0.60 .90 3 6 9 30 60 90 300

1 +.++$ +.++' +.+1& +.+#4 +.+'' +.1$3 +.#4$ +.'&' 1.$3$

#+.++'

+.+11

+.+#4

+.+''

+.1+/

+.#4$

+.'&'

1.+/+

#.4#'

'+.+1&

+.+#4

+.+3

+.1$3

+.#4$

+.31

1.$3$

#.4#'

3.1$

1++.+#

4

+.+'

'

+.1$

3

+.#4

$

+.'&

'

1.$3

$

#.4#

'

'.&'

+

1$.3

#'

#++.+''

+.1+/

+.#4$

+.'&'

1.+/+

#.4#'

'.&'+

1+./++

#4.#'+

'++.1$3

+.#4$

+.31

1.$3$

#.4#'

3.1$

1$.3#'

#4.#'+

3.1#'

1++

+.#4$

+.'&'

1.$3$

#.4#'

'.&'+

1$.3#'

#4.#'+

'&.'++

1$3.#'+

#++

+.'&'

1.+/+

#.4#'

'.&'+

1+./++

#4.#'+

'&.'++

1+/.+++

#4#.'++

L To convert these k* values to horsepower, divide them by +.4'


80/81

4. If you have a choice, try to use the pump which is t/$ #ost $ci$nt (or t/$1or* , as this reduces running costs. 0>ciency is often shown on the same headoutput curve or can be estimated. The pump usually works most e>ciently ataround 3+ to 4+ percent of its maximum head or output.

. Gost generalpurpose eld water pumps are suitable for sh farms, although ifthe water is brackish or carries a lot of mud, you should check that the pump issuitable. Cou should t a screen at the pump intake. @or centrifugal pumps the mostcommon type!, a foot valve is useful for keeping water in the pipe when the pump isstopped. The pipe is lled with water primed! before starting, as the pump cannotsuck the water into the pipe by itself.

S$"$ra 1a!s to startc$ntri(u+a &u#&s

/. If a pump is already available, and you do not know its dist as follows.

a! 0stimate its horsepower 7P from the outlet pipe inside diameter D in inches!,as 7P K $.1& D9 R #+.b! Gultiply 7P by +.4' to obtain the pump power P in kilowatts.c! -heck its maximum head 7 in m! by running the pump and lifting the outletpipe until the Mow stops. The pump can usually operate in the range of $+ to 4+percent of this maximum head.d! 0stimate the discharge capacity in m$(s! from values of power P! and head7!, as

H )PE- ).7-

where E is the pump e>ciency in percent.

E>a#&$

If a pump has an outlet pipe diameter of $ inches 4.' cm!7


81/81

7P is approximately K $.1& = # R #+ K . 7P.ciency, is K a#&$

If a pump lls a '+litre barrel in 1+ seconds, with an estimated total head of 1+ m,e>ciency is estimated at $+ percent as the pump is near its maximum head found

to be 1# m!. N m$

(s! K volume(time +.+' m$

R 1+ s K 0.00% #3

,s.

Basic Constructin

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