What can I do with a bag of cement (Start simple and upgrade for toilets and wells)

Transcription

1 What can I do with a bag of cement (Start simple and upgrade for toilets and wells) Peter Morgan 2016

2 Introduction Start simple and upgrade over time sounds to me like a good idea. It s a method which has been used in Africa for generations especially when it comes to building houses. Start with the foundation, then one room, then two, then three and more as more finances become available. The same logical method can also apply in the water supply and sanitation section of development. It can be applied to both the construction of family toilets and family wells for those who are poor and unable to afford the complete process at one time. Portland cement is a remarkable medium. When mixed with sand and allowed to cure is can become very strong indeed. Well that s well known look at all the high rise buildings. But it can also apply to the simplest of structures. Let s stick to Portland cement not masonry cement. In our work on designing low cost BVIP toilets we found that Portland cement, when mixed with 20 times the volume of pit sand could make an excellent mortar for bonding the bricks together. Years of testing have shown us clearly that this can work, especially underground where the curing time can be longer in cooler conditions. And we have constantly found that concrete slabs can be made with a mixture of clean river sand and Portland cement mixed 5 parts sand to one part cement. Using these simple guidelines and following them closely, it is possible to make a 1.2m diameter concrete slab for a toilet and fit it on the rim of a brick lined pit (corbelled in this case) using about 500 fired bricks bonded with a mortar using one part Portland cement and 20 parts pit sand. It works! Most builders frown on the idea at first, until they have tried it. Sub-structures built like this have been in use in Zimbabwe for at least 10 years and are quite fine if the bricks are well fired. Once the toilet slab has been placed on top of the lined pit, the toilet house can take many forms from simple grass structures to a fully functional brick build Blair VIP. They can all be built over and around the same substructure and concrete slab. Remember - we are not building skyscrapers but simple units for the homestead and the strict rules required for large construction enterprises do not apply. The same logic is true for building simple upgraded family wells. This can also use a 1.2m diameter slab, built to the same diameter as the toilet slab, but with one central hole in the middle, and not two for the squat hole and vent pipe is the case for the toilet slab. It is best to line the well with bricks if the soil is less stable, but many wells, built in firmer soils, need not be fully lined to be functional. So in many cases, the simple family well may not require a full brick lining at first, but can be dug down inside a sturdy radially placed ring beam of bricks formed partly below ground level and raised above ground. A concrete well cover slab is placed on top of the ring beam of bricks formed above ground level. Then the headworks is completed with a rim of bricks around the slab, a raised concrete collar and a water run-off and seepage area. This simple start, using just one bag of Portland cement and about 120 fired bricks, can improve the safety of the well and the quality of the water raised and also looks smart. With an extra bag or bags of cement the well can be partly or fully lined with bricks, depending on its depth, which makes it more stable and the extracted water is clearer. But huge numbers of wells have operated for years without a full well lining. It very much depends on the nature of the soil. An upgrade can involve fitting a windlass system on top with windlass supports secured in a concrete anchor which is cemented on top of the well slab. Lining the well, adding a windlass system and even making the apron wider can be seen as upgrades. It s all rather simple and low cost but it can work. At least it is a start. And once a start is made, then improvements over time are possible and can be made. More detailed descriptions of the techniques shown here can be found on the Aquamor website, Peter Morgan Harare April

3 The technique for upgradeable toilets Well it s been written before. You start by digging a hole, making a concrete slab and then lining the hole with bricks. It the slab on top of the lines pit. What you build on top is up to you. The target to aim for is the Blair VIP. It uses a vent pipe to control flies and reduce odours. But simpler structures can be built first and then upgraded. Stage 1. Dig the pit STAGES OF CONSTRUCTION The pit is dug 1.7m wide and 2m deep. Walls are straight and bottom flat Stage 2. Make the concrete slab The concrete slab is 1.2m in diameter and made within shuttering of brick or steel. It is best laid over plastic sheet. The 3mm 4mm reinforcing wire (or barbed wire) is cut and laid beforehand to ensure correct size. This should take about 14m of wire. The vent pipe and squat-hole moulds are placed within the shuttering at the appropriate places see diagrams. A short length of 140mm PVC pipe can be used for the vent hole, but a one litre paint tin (diameter 130mm) can also be used. A mix of 12litres of cement (one slightly heaped 10litre plastic bucket) and 60 litres of clean river sand (five slightly heaped 10 litre plastic buckets) are thoroughly mixed and water added to make a slurry-like concrete. The sand should be clean, sharp river sand and the cement fresh PC15 (Portland). This concrete mix is added into the shuttering around the vent and squat hole moulds first, which are held in position whilst the concrete is added. Half the concrete mix is added first and levelled off. Then the lengths of 3-4mm reinforcing wire or barbed wire are added in a grid formation about 15cm apart. Extra wires are added between the vent hole and the slab rim. The remainder of the concrete mix is added and smoothed down. After about 2 hours the squat-hole and vent-hole moulds are removed. The slab is covered with plastic sheet and left overnight to harden. The following morning it is carefully watered and covered again. The shuttering can then be removed. The slab should be kept wet and covered for at least 7 days. It can then be lifted carefully and place on the upper course of the pit lining brickwork in a bed of weak cement mortar. It must be level. 3

4 Dimensions of the concrete slab Half the concrete mix is added first. Then the wire reinforcing is added (about 14m of 3mm or barbed wire cut and laid in a grid formation (see photo). Then the remainder of the concrete is added and smoothed down flat. The curing of the slab is important. After construction it should be covered with a plastic sheet and left to harden overnight. Then it should be watered daily for at least 7 days to develop strength before lifting. The longer it is left to cure in the wet state the stronger it will be. The slab should be close to 50mm thick. 4

5 Stage 3. Line with pit with bricks A technique known as corbelling is used where the upper courses of brickwork are stepped in, so the diameter of the pit is reduced nearer the top of the pit. This allows a large diameter pit to be used together with a smaller concrete slab which fits over the pit. The pit is shallower (2m) and wider (1.4m internal) compared to earlier Blair VIP pits (3m X 1.1m) which makes it easier and faster to build, whilst keeping the same pit volume. Corbelled pits have been made by the boy pupils of the school, but in this exercise we decided to ask an artisan to dig the pit and line it with bricks first. Cross section of lined pit Cement mortar mix for bonding brickwork 20 parts of pit sand (100 litres) and 1 part Portland cement (5 litres) are thoroughly mixed first and then water added to make the mortar mix. About 5 mixes (25 litres) are required to mortar all the bricks. The mortar is laid thin between bricks. Building up the brickwork The inside diameter of the first 1.4 m of brickwork must be 1.4m diameter (about 19 bricks per course). Retain this internal diameter (1.4m) diameter for 1.4m above the pit bottom and then start to step in the brickwork. Each additional course above 1.4m should be stepped in by about 20mm above the lower course. The brickwork should be built up above ground level by about 2 3 courses so the full pit depth is about 2.2m. This will take about 24 courses of bricks depending on brick size. The outside diameter of the uppermost course should be 1.2m. The total number of bricks is about

6 Photos of lining pit structure Lay the bricks against the edge of the pit wall. The mortar is quite weak but sufficient to bond the bricks together. It cures into a hard and durable bonding material. The internal diameter is 1.4m. Continue with this diameter for 1.4m from the bottom. After 1.4m from the bottom each brick course is stepped in (corbelled) by about 20mm per course. This corbelling continues till the brickwork is about 2 to 3 courses above ground level, with a final external diameter of just over 1.2m The space between pit wall and brickwork is filled in with soil and rammed hard and a layer of cement mortar laid over the uppermost bricks. Then the cured slab can be laid on top of the ring of bricks, made level and then plastered I place. This is the starting point for further construction and up to this point has used one bag of Portland cement. There are many types of structures that can be built on top. 6

7 Types of structure that can be built on top of the toilet slab A simple grass structure can be built to start mainly for privacy. It first no vent pipe is fitted, but to reduce flies and odours a plate can be fitted over the squat hole and vent hole. If a roof and pipe are fitted, the toilets starts to operate like a BVIP The simple spiral brick structure is low cost and easy to build. On the right this structure has been built by school girls. A PVC pipe (110mm diameter) fitted with aluminium fly screen has been fitted to both these toilets. The standard Blair VIPs can also be built over the same slab and substructure. 7

8 The technique for upgradeable family wells A single bag of Portland cement can be used to build a good headworks for an upgradeable Upgraded family well. The main purpose of the head works is to improve the hygiene of the well head and make a water run-off channel so that waste water can flow away from the well head. The headworks can be fitted around the top of an existing well or at the top of a well which is to be dug. Ideally the well chamber should be lined with fired bricks from the start, but many wells have survived for years without a full well lining. Whether the well requires a full brick lining or not depends on the nature of the soil. This must be judged on site by an artisan. Whether the well chamber is lined or not a strong ring beam of bricks laid down at the head of the well will greatly improve the stability of the head works. Once the ring beam and headworks have been built, the well can, in suitable situations, be lined later and a windlass system can be fitted. The initial headworks including the ring beam, cover slab, raised collar, apron rim and water run-off channel can be built with a single bag of Portland cement, pit and river sand. Stages of construction Stage 1. Make the concrete well slab In this case the 1.2m concrete slab is made with 10 litres Portland cement and 50 litres of sharp river sand. It is reinforced with 3mm wire or barbed wire. The shuttering can be made of steel as seen above or in bricks. The inner hole is 40cm wide and requires a mould. Stage 2a. Make the raised collar as part of the slab The raised collar which is an important part of the design can be caste together with the slab as shown with special shuttering. The tin lid will fit over this raised collar 8

9 Stage 2b. Make the raised collar separate to the slab In this option the concrete raised collar is made in high strength concrete separate from the slab, so it can be added to the simple structure built without a windlass or can be added to an upgraded structure with a windlass. In the case shown here the collar is caste within the future steel lid of the well with the 40cm mould laid centrally. The collar is high strength (3parts river sand and 1 part Portland cement) with wire reinforcing. Stage 2 Make the ring beam Making the concrete collar separately In this case (which is a demonstration) the ring beam of radially laid bricks has been built just below ground level rising to one course above ground level. A new well could be dug within the ring beam. Or the ring beam could be built above an existing well. Stage 3 fit the slab and build the slab rim to make the apron The slab is laid centrally over the raised ring beam and a circle of bricks mortared around the slab to make a rim. The rim extends to the water run-off channel. 9

10 Stage 4. Complete the head works and water run-off The water run-off is built with bricks and mortar and should be at least 2-3m long. A seepage area is located at the end. A step can be made next to the rimmed slab which also acts as an apron. The headworks is fully plastered. Stage 5. Add the concrete collar around the well access hole. Once the concrete access hole has been fitted with the raised collar, which is mortared in place, the unit must be left to cure. Then a tin lid and suitable buckets can be used to raise water from the well. This is the basic unit. The seepage area is planted with shrubs or a fruit tree. UPGRADING In suitably firm soils, the well may work in this simple form for years. If the soil is less stable the well must be lined with fired bricks. Upgrading to fit a windlass system is possible on the existing unit. Upgraded family wells fitted with a windlass system are a valuable family asset. 10