GOOD TIPS TO KEEP IN MIND

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1 Page 1 of 13 GOOD TIPS TO KEEP IN MIND ABOUT BRICKMAKING WHAT ARE RAW MATERIALS? This refers to cement, aggregate, water GOOD TIPS TO KEEP IN MIND ABOUT CEMENT 1. Always use a reputable cement e.g. Blue Circle, OPC, PCI 2. Cement doesn t like getting wet before it is used. 3. After one has made the blocks, bricks with the cement, then remember that they have to be watered

2 Page 2 of 13 in order to cure them. 4. In a block yard, the best way to store cement is in a silo, but unless you run a fair sized operation, you cannot afford such a site for your cement. 5. When you get your cement in pockets, you should make a plan to store them in a shelter e.g. a shed. Remember to put the first row of cement pockets on some wooden planks or something similar to keep it off the floor as it tends to be damp there. 6. Also remember to use your cement on the basis of first in first out 7. It is important not to use old cement maximum period of tolerance is 3 months. 8. If you cannot afford a shed then it is important to store your pockets in stacks raised above the ground and keep them completely covered in tarpaulins 9. Never use old cement GOOD TIPS TO KEEP IN MIND ABOUT AGGREGATES 1. Aggregates must be kept clean. 2. If possible store aggregate on a solid floor, e.g. a concrete floor. 3. Be careful not to mix looses ground in with aggregate when you dig into it. 4. Keep your aggregates in piles of the same sort. 5. Don t mix aggregates in the stockpiles only mix them when you put them into the mixing process. 6. Never use only very fine sand 7. Never use sand with clay content 8. Never use ordinary soil. GOOD TIPS TO KEEP IN MIND ABOUT WATER 1. Any drinking water is deemed suitable to be used in the brick making process. 2. Unsuitable drinking water may contain chemicals or impurities that will affect the strength of your product. 3. A laboratory test will be able to tell you if your water contains harmful chemicals. 4. Never use brak water HOW ARE THE RAW MATERIALS MIXED TOGETHER? The above tips pertain to the storing of aggregates that you will be using in your block yard. However the way in which they are mixed together is extremely important. 1. A good mix should compact well in order to make a dense block normally the denser the block, the higher the strength 2. A good mix should extrude well from the mould and have enough internal cohesion not to crumble during and after the extrusion. The mix proportions. The factors that will decide this are: The grading (particle distribution) of the aggregates. The amount of water added to the mix. WHAT ARE THE MIX PROPORTIONS? 1. Start out with the stipulated proportions that are given to you- leave the experimenting until you have sorted out general problems that tend to occur in your start up phase. 2. The mix ration of 8:1 is the recommended proportion for making bricks and blocks. Please understand that this refers to equal parts for both the cement and the aggregate, i.e. 8 wheelbarrows of aggregate mixed with 1 wheelbarrow of cement. Often a common mistake is mixing 8 wheelbarrows of aggregate with 1 pocket of cement. Obviously this is not going to work. 3. If you are going to measure the cement with a tin for example be very sure as to how many tins fill

3 Page 3 of 13 up a wheelbarrow! 4. Be sure that workers understand how to mix properly keep instructions on aggregate: cement ratios very simple. 5. Mix thoroughly making sure there are no dry sections in your mix. 6. Add water slowly into the dry mix if you are mixing by hand. 7. If mixing with a pan mixer, first add the dry ingredients before adding the water. 8. Oxide is added before the water is added. WHAT IS THE GRADING (PARTICLE DISTRIBUTION) OF THE AGGREGATES? Sand and stone are fragments of rock and differ only in size. Sand particles will pass through a sieve with 4.75mm square openings. Stone particles will not. Sand and stone vary greatly in grading, shape and texture and together with the variations in the performance of cement, can influence the strength of your final product. Sometimes it is necessary to mix bad sand with another aggregate in order to equalize the proportion of particles, in other words al particles end up being more or less the same size. If your sand is not of a good quality, try adding a small amount of builders lime to your mixture to improve the quality HOW TO IDENTIFY THE VARIOUS TYPES OF AGGREGATES? Here are some photos illustrating the various kinds of sand and stone sizes that you will come across: 1: 9 MM STONE This stone cannot be used on its own for blockmaking. This is a stone that mixes well will all other sands, however too much of it and you will create a problem so experiment with it. 2: 6.7 MM STONE

4 Page 4 of 13 This stone is another that cannot be used on its own for blockmaking. This is a stone that mixes well will all other sands, however too much of it and you will create a problem so experiment with it. 3: CRUSHER SAND This type of sand, as the name implies, is produced in a crushing plant. It is a good sand for blockmaking as it blends both with coarse as well as fine particles to give good finishes and cohesiveness. It can be used as follows: On its own Blended with medium natural sand. Blended with a medium natural sand & stone Blended with a small proportion of stone All sand particles will pass through a sieve with 4,75 mm square openings 4: COARSE NATURAL SAND

5 Page 5 of 13 This sand is drawn from river beds or pits. It is very good sand for block making. Some types of river sand do not have enough fine particles in them. If you find that this sand produces a mix that lacks cohesiveness blocks which crumble when demoulding you will need to introduce some fine particles. This sand can be used as follows: Used on its own Blended with a crusher sand Blended with fine pit or plaster sand In the case of economy, it may be necessary to introduce a small amount of stone, however if the main sand is very coarse, the stone is better left out. All sand particles will pass through a sieve with 4,75 mm square openings 5: MEDIUM NATURAL SAND This sand is also found in river beds or pits. It tends to be somewhat difficult to use in mixes, as it is lacking in coarse and fine particles. This kind of sand can be used as follows: Blended with crusher sand Blended with stone If used with crusher sand, it is possible to add a small amount of stone. All sand particles will pass through a sieve with 4,75 mm square openings 6: FINE PIT OR PLASTER SAND

6 Page 6 of 13 This sand is normally found in pits It is made up of primarily very small, fine particles. This kind of sand can be used as follows: Blended with coarse natural sand Blended with a medium natural sand Blended with small stone If blended with a sand mixture, it is possible to introduce a small amount of stone- especially if blended with the medium natural sand Crusher sand does not normally go very well with this sand All sand particles will pass through a sieve with 4,75 mm square openings 7: BEACH, DUNE OR SEA SAND This sand is normally found on beaches or in the coastal regions. By using this sand only, it will result in a mix that does not want to compact properly in the mould. It is difficult to extract and shows poor strength. It is very difficult, dead sand. This kind of sand can be used as follows: Blended with a crusher sand Blended with coarse natural sand and pit/plaster sand. Blended with pit/plaster and stone A small amount of stone can also be blended in with the first two alternatives if this practical. This sand should be kept well away from medium natural sand All sand particles will pass through a sieve with 4,75 mm square openings

7 Page 7 of 13 THE AMOUNT OF WATER ADDED TO THE MIX WATER CEMENT RATIO It has been established that, other things being equal, the strength of concrete depends on the relevant proportion of water and cement. The higher the proportion of water, the weaker the concrete. The quantity of water per 50kg of cement pocket of cement should be 0.40 x 50 kg or 20 litres. The mixes used in blockmaking are semi dry. The water acts as a lubricant permitting greater compaction of the concrete under pressure and vibration. The best way to judge whether enough water has been added to the mix is by doing the following simple test: 1. Make a ball of concrete in your hand 2. If the mix is too dry, a ball cannot be formed because the mix is too crumbly 3. If it is too wet, the ball loses its shape and considerable moisture sticks to the hands 4. If the moisture content is about right, the ball can be formed and a slight water sheen can be noted on the surface of the concrete. 5. If your mix sticks to the floor- it is too wet. Another quick check is to take a handful of the mix and rub it against a steel bar and observe the glisten and compaction of the rubbed surface. Try and measure how much water is added to the mixture, so that you can establish the correct amount of water needed in the mixture. This can still vary however depending on the amount of the moisture content in the aggregates which also varies from time to time. STRENGTH AND QUALITY The South African Bureau of Standards requires nominal strengths of 7 MPa for solid bricks and 3.5 MPa for hollow blocks. Every city should have a lab facility for testing blocks. Ask at your local cement distributor. The lab in P.E. is LABCO (Tel; ) Ideally, blocks should be laboratory tested for strength. However this is not always possible especially in rural areas. The block density is a good indicator of strength. By weighing the block, you will be able to ascertain its density and strength. The heaviest block will be the densest and strongest. The next step in assessing the strength of your block is to look out for breakages to corners and edges of cured blocks- if the block breaks when handled, they are clearly too weak. Strength can also be assessed by knocking two blocks together after curing and drying out. A ringing sound indicates good strength while a hollow thud probably means that the blocks are too weak. Also, look at the surface of the blocks. If the texture is too smooth, reduce the amount of fine material in the mix, if it is too coarse- increase the amount of fine material. SETTING UP THE BRICKYARD 1. FEASIBILITY STUDY It is essential to do a feasibility study before you set up a block yard Determine what the demand for blocks is in the area and also find out what competition there is in the area It is important to draw up a simple business plan to establish basic costs Factors which influence unit costs include the following: Purchase price or rental Cost of any site improvements- fencing, paved areas for production and stockpiles, pathways, roadways Cost of Equipment, concrete mixer, blockmaking machine, miscellaneous equipment, e.g. wheelbarrows and trolleys and tools. Cost of services: water and electricity

8 Page 8 of 13 Material Costs (Presume that 1 m3 of looses aggregate will yield 0,7 m3 of block volume) Wastage Maintenance costs of site and equipment Output: number of blocks per day Labour costs Cost of finance 2. SELECTING A SITE In selecting a site, consider location, access, ground slope and size. LOCATION This should be considered in relation to: Supply of raw materials Market for blocks Location of the labour force Security of the area Availability of services, i.e. roads, water, sewerage, electricity, etc. ACCESS The site must be accessible to trucks delivering aggregates and cement and collecting finished blocks. GROUND SLOPE Ideally, the site should be level or nearly so. Steep slopes make handling and production difficult. Terracing a steep slope is expensive. 3. ESTABLISHING THE SITE This site should have provision for stockpiling aggregates and storing cement, a production area, a stacking area, staff facilities, an office and access between different areas and facilities: Aggregate Stockpiles Aggregates must be stored in such a way that they do not become contaminated by soil, leaves etc Ideally different aggregates should be separated by partitions and it must be ensured that rainwater is able to drain away by keeping the aggregate stockpiles; this can help to drain the water away. Ideally aggregates should be stockpiled on a concrete slab. If this is not possible, the layer of aggregate in contact with the soil should not be used for production Aggregates should not be stockpiled under trees Partitions should be erected between piles of different types of aggregate. Cement Store The best way to store cement is in a silo. For smaller blockyards, this is too expensive and cement should be stored in the bags in which it is delivered in a weather proof room/area. Bags should be stacked on a plastic tarpaulin or on closely spaced wooden strips so that they do not absorb damp from the floor. There should be space in this area to store about a week s supply of cement. At the very least, cement should be stored in stacks raised above the ground and completely covered with tarpaulins. Production Area The size of this area depends on the method of producing blocks A stationary machine, which uses pallets, needs a relatively small area with space around it for operators. A mobile egg laying machine needs a fairly large slab on which blocks are made Details of laying a production slab; 1 A flat concrete slab, big enough for at least two days production is required 2 As a rough guideline, a slab of 50m2 in area is suitable for a production of bricks or 200 blocks 3 The block production should have a minimum slope of 1 in 100 to ensure proper drainage 4 The minimum thickness of the slab is normally 125mm. In the case of producing with a small had

9 Page 9 of 13 operated machine, a thickness of 100mm could be considered. 5 Large production machines may require a minimum slab of 150 mm 6 If you intend to mix the concrete yourself, the following proportions should be used; Size of Stone- mm Proportions by volume Cement Sand Stone 19,0 or bag 75 L 75 L 13, /3 1 bag 75 L 55 L Size of Stone Quantities per cubic metre of concrete Cement -bags Sand m 3 Stone m 3 19,0 or 26,5 8,7 0,7 0,7 13,2 10 0,8 0,8 TINS TINS TINS Wall Foundations- 20mm stone Ordinary grade concrete for walkway paving, steps, light duty floors, general re-inforced concrete work- 20 mm stone Higher grade concrete for driveways & carports, flagstones & other precast units, important precast concrete work- 20 mm stone Higher grade concrete using 10 mm stone, for thin precast work, slabs & flagstones less than 50 mm thick, garden fence posts The amount of water is not given in the table because it depends on the materials used. Use enough water to make a workable mix that can be properly compacted. 8. When ordering concrete from a ready mix suppliers specify a strength of30 MPa at 28 days and 19 mm stone. Slump should be 75 mm if the concrete is to be hand compacted by mechanical vibration and 125 m for hand compaction 9. To prevent uncontrolled cracking of the slab, it should be divided into panels which should be kept as square or as close to square as possible. 10. It is not necessary to reinforce the panels with steel rods or mesh. Stacking Area An area big enough to stack two weeks production is needed for curing and drying To avoid muddy conditions, a layer of concrete stone, about 100 mm thick should be enough. Staff Facilities These include toilets, ablutions, and perhaps change rooms Minimum requirements of local authorities should be met. Office An office should be provided for all but the smallest of yards

10 Page 10 of 13 On site Access Pathways and roadways between the different parts of the yard should be wide enough for barrows, trolleys or trucks and this area may have to be paved or covered with aggregate to make them usable in wet weather. Paving would in any case be necessary where trolleys are to be used to move blocks. 4. EQUIPMENT Block yard equipment consists essentially of: a means of moulding blocks, a concrete mixer and various general purpose tools and equipment. BLOCKMAKING EQUIPMENT 1. There are two basic types; stationary machines that mould blocks, one or more at a time, on pallets or egg laying machines that mould blocks on a concrete slab. 2. Both types come in differing sizes from small hand operated devices, which have limited output, and a range of electrically powered machines of high output. 3. Doubell Machines are available from the small QAA range, through the very popular JJMK2 AND JJMK3 ranges to the very successful Hyperstat range. 4. Machinery can either be manually operated or electrically operated, depending on the needs of the customer. 5. Please check the brochure of the Doubell machinery which gives an idea of expected daily production as well as costing on the production ADVANTAGES OF STATIONARY MACHINES- A relatively small space is needed for production DISADVANTAGES OF STATIONARY MACHINE- This machine needs pallets upon which to make the bricks/blocks/pavers. Pallets are expensive initially to purchase and can increase the set up cost. Pallets also need to be replaced as they can become damaged or stolen ADVANTAGES OF EGG LAYING MACHINE MACHINES- Pallets are not necessary DISADVANTAGES OF EGG LAYING MACHINE MACHINES- A fairly large slab is needed for production of blocks. The slab is expensive to lay and increases the size of the site necessary for a blockyard. PAN MIXERS Although it is possible to make blocks on a small scale without a concrete mixer, output is limited and the mixing may not always be thorough. Hand mixing should be done with shovels on a concrete slab or flat steel sheet. Never mix by hand directly on the ground as this can cause contamination of the mix. Panmixers, with their forced mixing action can cope with the semi dry mixes used for making blocks. Drum mixes do not work because they require a wetter mix. The output of the mixer should match that of the blockmaking machine. The Doubell range of Panmixers can compliment any brickyard, by speeding up the mixing process. The mixers are durable and reasonably priced. OTHER EQUIPMENT This includes wheelbarrows, batching containers, trolleys (for moving blocks), shovels, hosepipes and plastic sheeting. 5. MATERIALS FOR BLOCKMAKING Materials for blockmaking have been discussed previously under the headings; Cement Aggregate Water 6. MIXES *The aim should be to find a mix that will produce blocks that have an acceptable texture and be strong enough, but as cheap as possible. Because cement is more expensive than aggregates, the lower the

11 Page 11 of 13 cement content the cheaper the block. The strength of well cured blocks depends on; Aggregate: cement ratio Degree of compaction The degree of compaction depends on: Overall grading of the aggregates Aggregate: cement ratio Water content Compactive effort The strength depends on a number of interrelated factors The ideal mix which suits a particular blockyard has to be found out through trial and error using the equipment in the blockyard. Starting Points; 1. General Information; 1 Pocket cement = 50 Kg 1 wheelbarrow holds +/- 100 Kg sand/grit 1 m3 sand weighs +/ Kg = =/- 16 wheelbarrows 1 wheelbarrow of cement = =/- 2 pockets cement Therefore 5 wheelbarrows of sand to 1 pocket cement is a 10:1 mix And 4 wheelbarrows of sand to 1 pocket of cement is a 8:1 mix 2. Recommended Ratios: Start with an 8: 1 mix. This is 2 pockets of cement to 8 wheelbarrows of aggregate After 7 days, test for soundness- this is done by knocking two blocks together. If they make a ringing sound it shows good strength. If they make a dull thus, it shows poor strength. If a greater strength is required, use a stronger mix, i.e. 1: 6 mix. Which is 2 pockets of cement mixed with 6 wheelbarrows of aggregate If a lower strength is needed, use a 10: 1 mix. This is 2 pockets of cement mixed with 10 wheelbarrows of aggregate If a large number of bricks are cracked in each day s production, this is a good indication of a poor mix. Too little cement or poor compaction 3. Examples of Recommended Proportions A. Reservoirs, tanks, dams and other waterproof structures 1 part cement to 4.5 parts sand 1 part cement to 3 parts sand and 2 parts stone 1 part cement to 5 parts grit B. External Walls to houses, factories etc. including face bricks or paving stone 1 part cement to 7 parts sand 1 part cement to 6 parts sand and 2 parts stone 1 part cement to 8 parts grit 1 part cement to 2 parts stone and 7 parts grit C. General purpose interior walls, stables and sheds etc 1 part cement to 10 parts sand 1 part cement to 7 parts sand and 4 parts stone 1 part cement to 8 parts grit and 2 parts stone 1 part cement to 4 parts ash and 7 parts sand/grit Colouring of units Oxide is used to colour your mix. It is available for sale in bags from various distributors, e.g. Bayferrox or Protea chemicals. The Bayferrox toll free number is About 1 Kg of oxide is added per wheelbarrow of dry mix- again this is a trial and error exercise depending on the colour that you want to obtain. Adjust the oxide to suit your desired colour The oxide is added to the dry mix and mixed thoroughly before adding the water (also note that a little more water is necessary when using oxide) Stacking and Curing

12 Page 12 of 13 After +/- 3 Hours the bricks/blocks must be sprayed lightly with water so as to keep them damp until stacking, which is done after 24 Hours. For the next few days the stock pile must be kept wet and if possible covered with old sacks, grass or anything that would prevent them from drying out in the initial stages. Bricks/ blocks should not be used for a minimum of 10 days preferable 20 days for the best results. Other information on brickmaking is available from Portland Cement Institute. 7. PRODUCTION Aggregates and cement should be ordered in good time. Stocks should be sufficient to prevent stoppages due to lack of material. As a rough guide using an aggregate: cement ratio of 8:1 by loose volumes, three and a half bags of cement and a cubic metre of aggregate will be enough to make about 400 bricks. The number of blocks produces from the same quantity of material will depend on block size and whether they are solid or hollow. Mixing Hand mixing should be done with shovels on a level concrete slab or steel plate. First spread the aggregate out to 50 to 100 mm thick. Then distribute the cement, and stone if any, evenly over the surface and mix. Continue with this process until the right amount of water has been mixed in. For machine mixing, first mix aggregate and cement then add water gradually while mixing until water content is correct. Stacking and Curing After +/- 3 Hours the bricks/blocks must be sprayed lightly with water so as to keep them damp until stacking, which is done after 24 Hours. For the next few days the stock pile must be kept wet and if possible covered with old sacks, grass or anything that would prevent them from drying out in the initial stages. Bricks/ blocks should not be used for a minimum of 10 days preferable 20 days for the best results. Other information on brickmaking is available from Portland Cement Institute. 8. QUALITY CONTROL Quality of bricks should be controlled so that strengths are adequate to avoid breakages or rejects. Mixes should be as economical as possible. Ideally, blocks should be regularly tested for strength and mixes and production modified as necessary. Strength can be assessed by knocking 2 blocks together and listening for the ringing sound which shows a good strength block. A dull thud probably means that they are too weak. Shrinkage- Concrete masonry units shrink slightly after manufacture. In order to avoid this happening in the wall, blocks should be allowed to dry out for at least seven days before being used for construction. As a brief guide to your costing, the following information is also given: SIZE POCKET OF CEMENT NUMBER OF BLOCKS 190 x 190 x / x 190 x / x 190 x /- 42 Stock Bricks 73 x 105 x /- 200 Paving Bricks 100 x 200 x /- 300

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