2. Important points and item in the casting process:

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1 Project: Ferro Cement Pits for Toilet. 1. Project Objective: Main object of the project is to provide healthy safe septic tank at affordable price for ordinary people. (To reduce the cost of the pit.) To reduce the weight of the pit. (Easy to handle) 2. Important points and item in the casting process: 2.1 Tank geometry: In this case, dimension of the available concrete cylindrical tanks is used. It is checked with the requirement in the code of practice. (SLS 745: Part I: 2004) ie, Length between 2 to 4 times the width Minimum surface area (m 2 ) = Working capacity of tank (m 3 )/3 2.2 Access openings: Two access openings were provided for desludging and inspection and no changes done in size. 2.3 Freeboard: According to the code of practice for the design and construction of septic tanks (ie, SLS 745: Part I: 2004) minimum of 200 mm free board shall be provided between the liquid level and the highest point on the ceiling of the tank and it is also provided. So the air space thus provided shall have a volume equivalent to at least 10 per cent of the total tank volume. This requirement also provided. A1/ (A1 + A2) =0.29 > 10% A1 =7.33 ft 3 A 2 =17.78 ft 3 Free air space Sludge 3.0 Material and construction: Septic tanks can be constructed in-situ or pre-cast. It should be water tight, structurally sound and resistance to the corrosive nature of a septic anaerobic environment.

2 3.1 Mould 1 For the casting work, steel shutters are recommended. Necessary bracing have to be fix to get the rigidity. Spaces between the steel plate joints of the shutter should be filled with permanent filling materials (Cataloy paste) to avoid the cement-grout leakage. This filling should be done having a curved surface to make it easy when removing of shutter. 3.2 Materials: Steel (Reinforcement) G-18, 1 x 1, G.I. welded mesh is used as reinforcement and 5 mm diameter mild steel used to get the required shape for the reinforcement cage and it gives additional strength for the tank Sand Particle size 3mm size is recommended and it should be free from impurities Cement Normal Portland cement is recommended Water Potable water is good for Ferro cement and it is very important to maintain water to cement ratio. Strength and surface finish of the product depends on this factor. Water to cement ratio of is recommended for this casting work. 3.3 Methodology: In this project, It is used two methods to cast the pits that is using a shutter and without using a shutter. The following are the major steps in making of the Ferro cement septic tank First method: With out using a shutter Preparation of reinforcement cage according to the required dimension.(fig-1) Plastering using cement sand mortar from inside of the reinforcement cage and simultaneously cut off the excess mortar part at outside surface. Plastering at out side surface Casting of circular ferrocement plates for two ends and partition.(fig-2) Assembling of components. Advantages of this method: No shutter cost Size can be change at manufacturing stage.

3 Disadvantages: More labour compare to the second method. (It is required 6 labour days for casting of a 2-0 x 8-0 size tank) It is very difficult to maintain the shape. (Thickness and the circularity) So high material cost compare to the second method, It is required more time. Tend to buckle while casting Second method: Using a shutter Advantages of this method: Preparation of reinforcement cage according to the required dimension. Placing of the reinforcement cage on the lover part of the shutter. Fixing of the upper part of the shutter.(see fig 3) Plastering from inner side of the lower and outer side of the upper shutter. (See fig 4--6) Casting of circular Ferro cement plates for two ends and partition Removing of cylindrical part of the tank from shutter in the following day. Assembling of components and finishing. Disadvantages: Labour cost is less -It is required only 4 labour days. It is very easy to maintain the shape and thickness. Cylindrical portion can be cast within 2 hours. Size cannot be change and it is depend on the size of shutter Steel shutter cost is very high. 4.0 Inspection and testing: After the casting of the septic tank inspect for the structural defects and defects in construction. (Rectified the defects such as small cavities in the cylindrical surface of the tank) 4.1 Load test: Load test is done to check the structurally soundness. (See Fig-7, 19 x 35.0 kg =665.0 kg load applied at the centre of the tank with out any crack) 4.2 Water tightness: After the construction and installation completed, empty the tank and clean the internal surface and kept for 24 hours. No signs of water leakage in. Then filled the tank with water and kept for 24 hours.

4 There was a drop in water level, then top up to the liquid level and re-checked after 24 hours. No drop in water level. So tank is complying with the water tightness test Partition test: Filled one side of the tank with water up to the lowest opening in the partition wall, kept other side empty. Let it remain 24 hours and checked the partition wall for crack. No crack or leakage of water. Then repeat the test for other side. So tank is complying with the partition test. 5. Comparison between concrete tank and ferro cement tank. 5.1 Cost: Concrete tank: Volume of the required concrete quantity= πh(r 1 2 -r 2 2 )+3π r 2 2 t Where r 1 -External diameter of the tank r 2 -Internal diameter of the tank t- Wall/partition thickness =π.8( ) + 3π = ft 3 Ferro cement tank: Volume of the required mortar quantity= π.8( ) + 3π = 3.83 ft 3 Saving in cost = Cost for concrete tank-cost for ferro cement tank x 100 Cost for concrete tank =18.75% 5.2 Weight: = x Density of the concrete and ferro cement is almost equal Concrete tank Ferrocement tank Qty Density kg Qty Density kg Weight of concrete / cement motar Weight of mild steel Weight of welded mesh Total weight Reduction in weight %

5 4 APPENDIX A Fig-1, Reinforcement cage for the cylindrical Ferro cement septic tank Fig -2, Reinforcement Cage and Mould Fig-3, Finishing work of the Plastering Fig-4, Ferro-Cement Septic Tank