Rainwater Reservoirs above Ground Structures for Roof Catchment (GTZ, 1989, 102 p.) 6. The reinforced bricktank 6.1 The technology 6.2 Tendering a reinforced bricktank 6.3 Tables of material and quantities

Rainwater Reservoirs above Ground Structures for Roof Catchment (GTZ, 1989, 102 p.)

6. The reinforced bricktank

6.1 The technology

In most cases, it might be appropriate to engage a contractor to build the reservoir. There are several reasons why this is recommended. A contractor is accustomed to organizing material supplies and the work at the site. He knows his staff, and can arrange for the best artisans for the more complicated work. Usually, a contractor is equipped with the necessary scaffolding and shutter material. The larger the reservoir to be built, the more important these become. On the other hand, the contractor probably has no experience with this type of structure. To cope with the different possibilities, this chapter deals with aspects of the construction work in a similar way as with the ferro-cement tanks. Chapter 6.2 provides Standard Specifications and Bills of Quantities to allow tendering of the proposed reservoir. Chapter 6 should provide the necessary information for supervising the construction work.

It should be stressed that, in all cases where tank structures are made at the site, qualified staff are needed. This means, first of all, experienced plasterers are required for ferro-cement structures, as well as for bricktanks. The bricktank requires bricklayers and plasterers, but as these are more or less the same trade, there are few differences between them. While ferro-cement reinforcement can be done by skilled artisans not necessarily experienced~ in the technique, it becomes more difficult-with bricktanks, as qualified reinforcement work must be executed. In many countries, reinforcement binding is a different trade. In this chapter, however, schedules and drawings have been made in such a way as to simplify reading them.

The relatively heavy reinforced foundation for this type of tank may cause surprise, but one must remember concrete is not ferro-cement, and it differs in its properties. Reinforced concrete and brickwork are not as elastic as ferro-cement, It is important to know there are two different forces which influence the structure; one is the soil settlement, the other temperature expansion. Both forces should be controlled by the reinforcement. Cracks in the foundation must not occur because of slight soil settlement, as cracks lead immediately to leaking. Slight soil movement can occur even after years (e.g. tree roots can create soil movement). Temperature variations can be tremendous. In the sun, a reservoir can develop an outside surface temperature of 90°C or higher, while the water in the tank might be 25°C or less. Temperatures on the outside of the tank may also vary. For example, the side of the tank which is in the shade could reach only 30°C. The case becomes even more complicated depending on the amount of water in the tank. If the tank is filled to one-quarter capacity or less, the outside heat could warm up the entire thickness of the wall of the upper part of the tank. Therefore, as demonstrated, there could be totally different temperatures at different points of a reservoir at the same time, and these temperature tensions must be kept under control by reinforcing the brick wall. Experience has shown that the temperature influence becomes clearly visible if a reinforced brickwork reservoir is plastered outside with cement plaster. After some time, microcracks occur. These cracks are not structurally important, but influence the appearance. For this reason, if possible, brick reservoirs should not be plastered outside with cement mortar. Cement mortar also increases the cost of the project, and in most cases is not used, but is replaced with a white plaster limewash which reflects the sun and partially reduces temperature tensions. Plastering bricktanks is sometimes desirable, however. Such a case might arise if the bricktank was constructed together with a new house. The house should be located in line with catchment needs, and the reservoir, although a large structure, should harmonize with the house when covered with lime plaster with a rough surface. As lime is more elastic than cement, fewer cracks will result and, if the surface is rough, they may never be visible.

Procedures for Construction Work:

- Choose the reservoir size according to the advice given in Chapter 2.4. Remember it is usually cheaper to build one large reservoir than two smaller ones which add up to the same capacity. Figure 6.1 shows a 68-m3 reservoir built at Hill School, Lobatse, Botswana, where rainwater from three roofs is drained into one tank.

- Mark the diameter of the tank foundation on the ground to make sure no passage is blocked by the proposed reservoir. Methods of bridging downpipes are explained in Chapter 7.

- In Tables 8-14 the amount of material required is specified, including a calculation for wastage. Sand for mortar and the number of bricks required are based on a brick size of 110 mm × 230 mm × 70 mm in Southern Africa. If your brick size differs considerably, you must recalculate the number of bricks and the amount of sand and cement required for bricklaying. Slight differences should be ignored. In Botswana, cement bricks have been used, but burned clay bricks can be used if available according to standard. As tests for quality need to be made in a laboratory, finding out about the quality of a brick on the work site is very difficult. If the supplier cannot submit a certificate, and there are doubts about the quality of the bricks, they should be sent for testing before they are used. For example, if a back is not as hard as it should be for brickwork, you can rub dust off it with your hand. Bricks should be hard-burned and blue in colouring, rather than red in colouring. Burned bricks often differ in size. This makes working with them more difficult and requires skilled bricklayers. If bricks differ in length, build up the wall from the inside to achieve a smooth surface, as this is the side where the waterproof plastering must be done.

- When the material is on site, and arrangements have been made for securing storage space, mark the external diameter of the foundation on the ground. Different techniques for unstable ground are discussed in Chapter 5.2. In principle, these techniques are the same as those required for the reinforced bricktank. The foundation trench can be dug only after the topsoil inside the circle has been removed. All measurements given in the technical drawings assume the ground is stable. In cases where topsoil is not of equal depth, it must be removed to the greatest depth required to hit stable ground at all points (e.g. if the topsoil is about 300 mm in depth, it must be dug out entirely, as the foundation can only start at that depth). When all topsoil has been removed to stable ground, levelling can begin. If there is no topsoil, a foundation should be dug to 100 mm before the trench is dug. This is usually necessary to avoid soil erosion. If there are pockets of topsoil after a layer of 100 mm has been removed, they must be filled with lean concrete. When all topsoil has been removed and the stable ground has been levelled, the ring foundation should be dug as shown in Figure 5.3.1. Measurements for the size of the ring foundation and the thickness of the slab are the same for all tank sizes. All tanks with an internal diameter of 5.5 m or more require a centre pier to support the roof slab (for foundation see technical drawing).

Reinforcement work must be done on site, but a metal workshop should probably bend the stirrups, as they must be of equal size and shape. Dimensions given for the rods are the minimum. It is always possible to increase the dimensions if the scheduled size is not available. For the wall reinforcement, this is crucial. Vertical rods in the wall and ring reinforcement, which can be done with 6-mm rods, should not exceed 10 mm in diameter. This is necessary, as rods cannot disturb the brick bond or the joints which are equal in size. As Figure 6.4 shows, the reinforcement must be placed in the centre of the wall. It is therefore imperative to fix the vertical rods precisely onto the foundation reinforcement and to make sure they are not dislocated during the process of concreting the foundation and ground slab. The horizontal ring reinforcement must be tied to the vertical bars from inside, using binding wire and pliers as shown in Figure 6.2. As the joints can be only 10 mm thick, and the reinforcement steel must be covered entirely by cement mortar, any dimension exceeding the one indicated will cause problems. Reinforcement not covered with cement mortar will rust. Therefore, flush-jointed bricklaying is necessary. To maintain the required height and assure an equal and. solidly filled brick wall, all courses should be indicated on a timber board which should be used as a control mechanism. As shown in Figure 6.5, keeping all vertical bars in position while bricklaying is usually difficult if the height of the tank exceeds 2.00 m. For taller structures, rods can be cut into two pieces, extending the one fixed into the foundation in such a way that it overlaps the other rod by at least 100 mm. The rods should be tied tightly together, above the 1.50-m mark.

figure 6.4

figure 6.5

Seating roof slabs is a crucial detail. As previously explained, temperature variations can be tremendous, and these create movement in the slab which is difficult to control. Therefore, provision must be made for this movement so that it does not create structural damage. A sliding joint is the best way to control this movement. Technical drawing No. 3 illustrates two different types of sliding joints. The first method is as follows: the top of the tank wall must be plastered with a smooth surface, and finished with a steel trowel. This plaster should be applied after the second coat of plaster has been applied to the inside of the tank, and then must be separated from the wall plaster by cutting through the fresh plaster in the form of a V-joint. In this method, shuttering the slab height should be done with hardboard strips nailed to the outside of the wall, exceeding the plaster slab seating by 60 mm or 80 mm, depending on the dimension of the slab. Two layers of thick plastic foil or bituminous roof felt must then be laid on the plastered seating. This will allow expansion of the slab without creating cracks in the wall. The second method can be used if hardboard for shuttering is not available, but requires strips of softboard or a material with similar properties. The shutter for the slab height is one course of half-stone, as shown in technical drawing No. 3. The remaining half-width of the wall is sufficient as slab seating. Again, the seating must be plastered and two layers of plastic foil must be put under the slab. There must be 15 mm of softboard stripping between the wall and the fresh concrete to prevent the expanding slab from pushing the half-stone wall which acts as a permanent shutter. This material should be removed a few hours after finishing the concreting and the open space should be cleared. Although this method is not as good as the first method described, it will serve the purpose if it is properly implemented. If the slab still pushes the half-stone course, it is easy to remove the entire course and, by doing this, the problem of visibility of movement is eliminated It must be stressed that the seating for the slab on half the wall is sufficient, but the lintel must be seated on the whole width of the wall.

Waterproof plaster should be handled with special care according to standards described in Chapter 3. Waterproof plaster consists of three coats, each applied to the previous coat while still fresh. Keeping the plaster fresh is often a major problem in hot, arid climates, but this can be done by covering the fresh plaster and by splashing it with water before applying the next coat. Plastic sheets make the best covers.

First Coat:

Before plastering, make sure the wall is moist. Make sure there are as many labourers on site as required for the job, and organize the work in such a way that the mixing, delivery and application of the plaster can be accomplished in a continuous fashion. Remember even a large tank must be completely coated in one operation. This is best done by having two teams of plasterers working at the same time, but starting opposite each other, -working anti-clockwise towards the other team's starting point. Figure 6.6 shows two plasterers working in the same direction: one on the floor and the other on a scaffold. The plasterer on the floor starts plastering an area larger than the area covered by the scaffold. The scaffold is then moved to the wall and the second plasterer starts plastering the upper wall, while the first plasterer continues on the lower part of the wall. There should be no joint between the two working areas or at the meeting point. This might require extra curing of the meeting point until the coat of plaster is closed.

figure 6.6

The first coat of mortar should be composed of three parts river sand and one part cement, as described in Chapter 3. The river sand must be passed through a screen sieve not exceeding 3 mm. If a 3-mm sieve is not available, the sand used in the first coat can consist of the same core size as used in the second coat. The first coat should be a minimum of 10 mm thick and wooden-floatfinished. Before the second coat is prepared, the wall must be covered from the inside with plastic sheeting to prevent it from drying out.

Second Coat:

The second coat differs from the first, as the sand must be passed through a screen sieve of 1.5 mm, as required for ferro-cement. This process is described in Chapter 3. This coat should be a minimum of 5 mm thick, and wooden-float-finished. The working procedure is the same as that of the first coat. Before starting the second coat, the first coat must be wet, and the starting point should be changed so the meeting points of the first and second coats do not coincide.

Third Coat:

If the second coat can be applied in less than a day' the third coat can be applied when the second coat has been finished. The third coat is the 'nil coat' composition, as described in Chapter 3. As the third coat is applied with a steel trowel, and is no thicker than 2 mm, it can be applied quite quickly. Remember the nil coat should be applied in one continuous process, and make sure enough cement is prepared before starting. as the nil coat consumes about one 50 kg bag of cement per five square metres. The nil coat should not cover the lower 100 mm of the wall, as the corner must be executed as shown in Figure 5.23.

Floor screed mixture should be of the same composition as the first coat of plaster. After the screed is mixed, apply it to the corner with a glass bottle, as described in Chapter 5.1 and Figure 5.23. The nil coat should be applied to the floor the following day, and two-three hours after finishing the nil coat application, the floor should be covered with water for at least three days.

When handling the formwork for the roof slab, make sure the floor is not damaged.

6.2 Tendering a reinforced bricktank

How to use the information in this section

If a reinforced bricktank is to be tendered, the dimensions and amount of material required for building it can be selected from Tables 8-14. This information can then be written in the relevant space on the Bill of Quantities.

This is not the place to explain the entire tendering process, but this brief information will assist you in reaching an agreement with a contractor. Tender documents should be given to at least three contractors, in order to receive competitive prices. There are three different tendering documents: Conditions of Contract, Standard Specifications and Bill of Quantities After the documents have been completed by the contractors, they should be compared to ascertain the differences in prices. The cheapest contractor is not always the best, however, and workmanship demonstrated on previous projects should be taken into consideration.

Examples of the above-listed tendering documents follow.

Contract Conditions

After the tender has been accepted, an agreement shall be made and entered into by and between
(Name of Client)_____hereinafter called 'Employer' on the one part, and
(Name and address of contractor) _____hereinafter called 'Contractor' on the other part.

Whereas the Employer is desirous of the erection and completion of a rainwater reservoir as a reinforced brickwork structure, and has caused drawings of the work to be prepared, and whereas said drawing Nos.____ have been signed by or on behalf of the Employer and the Contractor, the following is hereby agreed:

1. For consideration hereinafter mentioned, the Contractor will upon and subject to the conditions annexed hereto as Standard Specifications execute and complete the works shown and described upon the said drawings, and as quoted for in the Bill of Quantities.

2. The Employer will pay the Contractor the sum of____ (hereinafter referred to as the Contract Sum) for the erection of the reinforced brickwork.

3. Date of Completion

Possession of the site shall be given to the Contractor on or before (Day, Month, Year)
____who shall thereupon and forthwith begin the works, and regularly
proceed with and complete the same on or before (Day, Month, Year) ____

4. Damage and Non-Completion

If the Contractor fails to complete the works by (Day, Month, Year)____
or within any extended time given by the Employer in writing, the Contractor shall pay or allow to the Employer as liquidated and ascertained damages the sum of_____ for every day of non-completion. The Employer may deduct such damages from any
money due to the Contractor.

5. Certificates of Payments

The Contractor shall be entitled to a Certificate of Payment on the day of commencing the construction work, not exceeding 33% of the Contract Sum. Final payment shall be due the day of completion providing proof the mentioned structure is waterproof.

Signed and deted by the Contractor_____________________________________

1. As Witness (Date______________________ Signature ___________________)
2. As Witness (Date______________________ Signature ___________________)

Signed and deted by the Employer_______________________________________

1. As Witness (Date______________________ Signature ___________________)
2. As Witness (Date______________________ Signature ___________________)

Standard Specifications for Reinforced Bricktanks

Material and Workmanship

The whole of the works shall be carried out and completed in the best and most workmanlike manner, and with the best materials of the kind respectively specified. No second-hand materials shall be used.

Protection

The Contractor shall protect all materials and work from damage during the progress of the works, until completion and handover.

Excavation

Nature of Soil

The Contractor shall base his contract sum on excavations in 'pickable' materiel. Should soft or hard rock be encountered, the contract sum shall be adjusted in accordance with the schedule of rates and measurements taken on site.

Hard Rock

When used, the term 'hard rock' means granite, quartzite or other rock of similar hardness which, in the opinion of the Clerk of Works (Site Supervisor), can only be removed by wedging, drill splitting or blasting.

Soft Rock

The term 'soft rock' is understood to mean all hard ground such as ouklip, shale, decomposed rock and small loose boulders or large stones.

Pickable Material

The term 'pickable material' is understood to mean all earth, clay, gravel, soft shale, made-up ground, etc., which can be removed by means of a pick and shovel.

Trenches/Excavations

The foundation shall not be concreted until the Clerk of Works has signified his opinion in writing that proper bottom has been obtained' and reinforcement shall not be placed until all necessary variations have been measured.

Any excavated matter taken out below the level shown as required to obtain a solid bottom shall be filled up by the Contractor with lean concrete. Measurements of the amount of lean concrete required shall be taken before backfilling begins.

Backfilling

Return and fill around foundations with selected clean, hard, dry earth from the excavation. Backfill should be watered and rammed.

Filling under the Floor Slab

Fill in under solid floor slabs with selected clean, hard, dry earth from the excavation. Water the fill and ram it in layers not exceeding a thickness of 250 mm. The fill should be consolidated and levelled as required.

Should the earth from the excavation be unsuitable or insufficient for this purpose, the Contractor is to supply the required material. No pot clay should be used for filling.

Concrete Work

Concrete work shall consist of providing, placing, curing, etc., the concrete specified in terms of 28-day strength, inclusive of all formwork.

Material Storage

All material shall be as described hereunder. Cement shall be stored in a cool, dry place and used in the order of delivery to the site. Cement which has become damp or has deteriorated in any way shall be removed from the site immediately.

Sand and stones shall be stored in separate bays and heaps, and shall not be placed with earth, grass or other impurities.

Cement

Only Portland cement of an approved brand shall be used, and shall conform to latest British standard specifications in force at the time the tender is submitted.

Stones

Stones for concrete shall be clean, hard, durable particles without soft weathering properties, and shall vary in size from a minimum which fails to pass through a mesh sieve screen of 5 mm to the maximum of 20 mm.

Sand (Concrete)

Sand for concrete shall be clean, sharp, or other approved sand. It shall be graded free from soft particles, clay, organic matter or other impurities, and washed if so directed by the Clerk of Works. Crusher sand shall not be used.

Water

Clean, fresh water from an approved source shall be used throughout. The water shall be free of vegetable or organic matter, earth, clay, acid or alkaline substances, either in suspension or in solution.

Mixing, Transport and Placing Concrete

1:2:1 = one part cement, two parts 20-mm aggregate, one part river sand shall be mixed in an appropriate concrete mixer at a time specified by the Clerk of Works, and shall not exceed the amount required for immediate use.

Concrete shall be transported by suitable means without causing any segregation or loss of ingredients, and shall be placed within 10 minutes of leaving the mixer. The mixture shall be plastic in consistency, and under no circumstances be of a consistency which can be poured (chuted concrete). The Contractor shall be directed when and where to use mechanical vibrators. Tamping rods or other suitable means of compacting the concrete may be adopted.

Curing

The concrete shall be covered with a layer of sacking, canvas hessian or similar absorbent material, and shall be kept wet constantly for seven days. Alternatively, when thoroughly wet, the concrete may be covered by a layer of approved waterproof material, which shall be in contact with the concrete for seven days.

Reinforcement

Unless otherwise described, mild steel rod or bar reinforcement which complies with British standards shall be used, and shall be supplied truly straight. Fabric (mesh) reinforcement shall also comply with British standards, and all fabric reinforcement shall be held in place securely by welding. Fabric reinforcement shall be supplied in flat sheets, unless approved otherwise. If fabric reinforcement is supplied in rolls' it shall be cut to the required size immediately, placed on flat ground and straightened for several days, by pressing it with a heavy weight.

Reinforcement shall be bent to the required detail, and cold-formed by approved means. Reinforcement shall be free from loose mill scale, rust, oil, grease or other harmful matter.

Unless otherwise directed, reinforcement shall be covered with the following: slab -15 mm, beam -25 mm, foundation -50 mm. Concrete covering for reinforcement shall be maintained as shown on detailed drawings, using all necessary spacers and other temporary supports as required.

Formwork

Formwork shall be approved and shall conform to the shape, lines, levels and dimensions of the concrete, as shown in the drawings, and shall be true, rigid, properly braced and sufficiently strong enough to prevent bulging or distortion. All joints shall be sufficiently tight to prevent loss of liquid from the concrete. Immediately before concreting, the area of timber in contact with the concrete shall be thoroughly wet or, preferably, treated with shutter oil. When shutter oil is used, none of it shall come into contact with the reinforcement. The Contractor shall be responsible for any damage to work and any consequent damage caused by negligent handling of formwork. Formwork for roof slab shall not be removed before permission to do so has been given by the Clerk of Works. The minimum period required before removal is 14 days, during which the slab shall be kept wet at all times, or covered with an approved waterproof material which shall be in contact with the concrete for the entire period.

Brickwork
Cement
See Concrete Work above.

Sand

Pit sand free of clay and vegetable matter shall be mixed with fine river sand to produce a workable and strong mortar. Sand for mortar shall be fine-grained and, if required, shall be screened through a 3-mm sieve screen.

Cement Mortar

Cement mortar shall be made of three parts sand to one part cement by volume. Cement mortar shall be mixed in small quantities and shall be used within 30 minutes of mixing.

Bricks

The dimensions, crushing strength and absorption of clay bricks or cement bricks shall comply with standard specifications. Before use, all bricks shall be saturated with water.

Brickwork

Brickwork shall be well bedded and flushed up solid in mortar throughout the whole wall. No one portion of the wall shall be raised more than one metre above the remaining wall. Mortar joints shall be 10 mm thick. All wall reinforcement shall be covered entirely with cement mortar joints.

Brickwork shall be built in cross bond; no false headers shall be used. Horizontal reinforcement shall be tied with binding wire on vertical rods from the inside.

Cement Screed

Cement screed shall comprise one part cement to three parts sand and shall be floated to a true plane surface with a wooden float. Sand used for screed shall be screened through a 3-mm mesh screen to expel all vegetable matter, pebbles, etc. Sand used shall be pure river sand with less than 6% clay, silt, etc. Before commencing work, the quality of the sand shall be proven by test, and submitted to the Clerk of Works. After the float-frushed screed has been watered for 24 hours, the nil coat shall be applied, using a steel trowel.

Waterproof Plaster
Three-Coat Plaster
First Coat: 10 -15 mm cement plaster of one part cement and three parts river sand screened through a 3-mm sieve screen shall be wooden-float-finished.

Second Coat: 5-8 mm cement plaster mixture, as described in First Coat above, shall be screened through a 1.5-mm sieve screen.

Third Coat: This shall be a nil coat composed of pure cement with a consistency of water, and shall be steel-trowel-finished. The plaster shall be cured after each coat has been applied, and when the third (nil) coat has been applied, it shall be covered with waterproof material or soaked thoroughly for seven days.

Bill of Quantities

		Quantity Unit Rate Amount
Earth: Excavate oversite average 100 mm deep to remove vegetable soil, remove, and deposit according to Employer's advice, not exceeding 50 m		m²
Earth: Excavate foundation trench to 'Barth' not exceeding 0.50 m deep and remove, part-return, fill in and ram around foundation		m³
Earth: Additional excavations for trenches to reach stable ground		m³
Earth: Additional excavation for inner circle to reach stable ground		m³
Earth: Backfilling and ramming of hardcore approved material in layers not exceeding 200 mm		m³
Earth: Lean concrete for backfilling: 1 part cement: 2 parts river sand: 4 parts gravel		m³
Reinforcement: Supply and place reinforcement cage for ring foundation and welded reinforcement mesh for bottom slab consisting of
	Mild steel rods Ø 20	m²
	Mild steel rods Ø8	m
	Welded reinforcement mesh	m
Concrete: 1 :2 :1 -20-mm aggregate as specified in ring foundation and slab compacting by mechanical vibrator		m³
Reinforced Brickwork: 240-mm brick wall in cross bond reinforced vertically by 10-mm mild steel rods and horizontally by 6-mm mild steel rods
	Brick wall	m²
	Mild steel rods Ø10	m
	Mild steel rods Ø6	m
Waterproof cement plaster consisting of 3 coats as specified, inclusive curing		m²
Concrete Slab Seating: Plaster of the wall top steel-trowel-finished and placing of 2 layers plastic sheeting to provide for sliding joint under roof slab
Reinforcement of Roof Slab: Supply and place mild steel reinforcement cage for roof lintel and welded reinforcement mesh for roof slab consisting of
	Mild steel rods Ø6	m
	Mild steel rods Ø20	m
	Welded mesh	m²
Formwork and Concreting Roof Slab: Concrete 1: 2: 1 as specified compacting by mechanical vibrator		m²
Supply and place water tap unit according to drawing		1	Nº
Supply and place overflow 150 mm Øasbestos pipe of 800 mm length provided with galvanized gauze wire cover		1	Nº
Supply and place manhole cover 600/450 mm cast iron painted 3 times with bitumen-protected nontoxic paint		1	Nº
Cement floor screed 1 = 3 inclusive concave moulding of corner		m²
Lime whitewash of 1 part lime and 1 part river sand for outside elevation		m²
	Carried to Summary

6.3 Tables of material and quantities

Example 1

A reservoir of 76.0 m³ storage capacity is to be built. According to Table 5 this can have an inner diameter of 5.30 m and a filling height of 3.45 m. The construction work is to be performed by employed craftsmen of repute and labour provided through self-help. Supervision and technical advice are to be provided by a building technician who has fully understood the information given in this booklet. Material must be ordered on time and stored according to advice given in Chapter 3.

Portland cement:

Cement consumption is given in Table 8. The first column indicates the internal diameter. The construction height of the reservoir with filing height 3.45 m is 3.60 m. This is shown in the last column. According to this table the total cement consumption for a reservoir of the given size will be 113 bags of 50 kg each. This is the amount needed for the reinforced concrete, the mortar for bricklaying and the plaster, including a certain amount of waste. If the concrete and mortar are mixed following the advice, the amount of cement will be sufficient for the entire reservoir. The amount should be entered in a "Schedule of material for price comparison".

: figure

Fine aggregate (river sand)

Quality according to Chapter 3. Table 10 provides the amount of sand needed for concrete, the mortar for bricklaying and the plaster. The 12.50 m³ include a certain amount of waste.

Coarse aggregate 20 mm Ø

For foundation, floor slab and roof slab. The last column of Table 13 shows the amount needed: 5.50 m³

Cement bricks

Burned clay bricks also possible if according to standard specification. Table 9 shows the number of bricks for wall height 3.52 m. This is equivalent to construction height of 3.60 m which includes the height of the roof slab. The wall of 3.52 m must be made of 44 courses, based on a brick size of 70 mm and 10-mm joint. This shows the number of bricks needed is 5960, that will be 6000 bricks.

BRC welded mesh

The quality definition 6" × 6" mesh No. 65 or 66 in rolls or sheets. Table 11 last column under internal diameter 5.30 m shows 74 m² for ground and roof slab reinforcement.

Reinforcement rods 20 mm Ø

This is the major reinforcement of the ring foundation. The amount needed is shown in Table 12, being 134 metre run. The next column indicates the distribution which is shown in drawing No. 1 for this diameter, the number being seven.

In addition 20-mm rods are used for the lintel reinforcement. Table 13 provides the information in column six = 25.00 m which has to be added to the 134.0 m and entered in the schedule.

Reinforcement rods 10 mm Ø

It is assumed that rods of 8 mm Øare available and therefore 10-mm rods are only to be used where this diameter is needed. Table 11 indicates the amount for the vertical wall reinforcement, distribution shown in drawing No 2. The Table shows under construction height 3.60 m and internal diameter 5.30 m an amount of 66.0 m.

Reinforcement rods 8 mm Ø

To be used as horizontal wall reinforcement shown in drawing No. 4. Table 12 shows the amount of steel in columns two, three and four. The construction height of 3.60 m has to be provided with 14 ring reinforcements. For this 256 m are needed.

In addition the stirrups for the ring foundation are of the same diameter and have to be added. In Table 12 the last two columns show the amount = 85.0 m and the number of stirrups = 56. The 85.0 m have to be added to the 256 m and to be indicated in the schedule of material.

Reinforcement rods 6 mm Ø

This is needed for stirrups of the lintel reinforcement cage only. If this dimension is not available, 8-mm rods can also be used. In this case the amount has to be added to the previous figures. Table 13 in column seven indicates the amount of 32.0 m and in column eight the number of stirrups to be bent.

After the amount of major building material has been indicated in the schedule, it is recommended that the different prices be investigated. The more suppliers asked to give their rates, the better. It can be experienced that prices differ from item to item, and it might therefore be appropriate to order from different suppliers.

Example 2

A large reservoir of 152 m³ capacity is to be tendered. According to Table 5 this reservoir a construction height of 3.45 m. For the process of tendering all information is provided in Chapter 6.2. To make use of the Bill of Quantities, it is necessary to find the quantities in the different tables and fill them in on the form.

a) Excavation of ground slab 100 mm

Table 13 column two: 5.46 m³

b) Excavation of foundation trench

Table 13 column three: 3.73 m³

c) Reinforcement for foundation and ground slab

Mild steel rods 20 mm Ø , Table 12 column five: 214.0 m run

Mild steel rods 8 mm Ø , Table 12 column seven: 120.0 m run

Welded mesh No. 65 or 66. Table 11 last column gives the amount for ground and roof slab. For the purpose of this tender it is sufficient to divide this amount 2 = 68.5 m²

d) Concrete as specified for foundation and ground slab. Table 13 columns two and three give the exact amount of excavation which is the same as for concrete: 5.46 m³ + 3.73 m³ =9.19 m³

e) Brick wall in square metres

Table 14 shows the square metres of water- proof plaster for the different sizes of reservoirs. This is the same as the square metres of brick wall. The filling height of 3.45 m is equivalent to the height of the brick wall of 3.52 m. The table shows 82.9 m²

Reinforcement for brick wall 10 mmØ

This is the vertical reinforcement shown in drawing No. 2. Table 11 construction height 3.60 m, amount needed 89.0 m run.

Reinforcement for brick wall 8 mm Ø

This is the horizontal reinforcement, distribution shown in drawing No. 4. Table 12 shows the amount needed as 363.0 m run.

f) Waterproof cement plaster

Shown in Table 14: 82.9 m²

g) Reinforcement for roof slab and lintel

Mild steel rods 6 mm Ø for stirrups of the lintel cage

Table 13 column seven: 43.0 m run.

Mild steel rods 20 mm Ø main bars of lintel Table 13 column six: 42.50 m run.

h) Formwork and concreting roof slab in m² Height of the slab 80 mm

Table 13 column five: 49.80 m²

i) Cement floor screed

Table 14 last column: 44.20 m²

1. Lime whitewash outside elevation

Table 14 shows the square metre inside plaster for the proposed 7.50 m diameter and wall height 3.52 m. The table shows 82.90 m² For the external elevation 5.5 m² have to be added (valid for all sizes): 88.40 m²

Table 8 : Consumption of Portland cement for different sizes of reservoirs in number of 50-kg bags

Table 9 : Number of bricks for different sizes of reservoirs including 10% waste

Table 10 : Consumption of sand for different sizes of reservoirs in m3 comprises sand for concrete bricklaying and plastering

Table 11 : Vertical reinforcement of brickwall mild steel 10-m rods ( m run ) for different sizes of reservoirs

Table 12

Table 13

Table 14 : Waterproof cement plaster for different sizes of reservoirs (m2)