Hydraulic ram pumps and Sling Pumps

D WATER RESOURCES AND USE: SHIRIMA22nd WEDC Conference New Delhi, India, 1996REACHING THE UNREACHED: CHALLENGES FOR THE 21ST CENTURYReinforced blockwork water storage tanksLaurent M. Shirima, TanzaniaONE OF THE most important needs of any communitydevelopment is a safe and adequate supply of potablewater. Unfortunately, there is still a shortage of cleanwater supply in rural regions of many developing countrieslike, for example, in Tanzania. A large proportion ofthe rural population in such countries rely on the availabilityof man-made wells, natural springs and rivers,and recently on limited piped water supply schemes. Themajority of such sources are not at economical distancesfrom the dwellings.The effectiveness of piped water supply depends on theavailability of water storage tanks. Reinforced blockworktanks are used as water distribution and storage facilitiesin some rural areas in Tanzania. They consist of reinforcedconcrete roof and floor slabs while the walls aremade of reinforced blockwork. The blockwork is made ofconcrete blocks that contain grooves into which reinforcingbars are laid and embedded in cement mortar.This paper will discuss matters related to design andconstruction of such tanks. Since severe cracking andleakage were observed physically to be the major problems,the authors intend to present, in view of researchresults, ways by which the tanks can be designed tominimise crack widths and water losses through them.Economic importance of storage tanksPiped water supply schemes are costly but necessaryinfrastructural requirement for the development of anycommunity. A survey which was conducted in Tanzania(Senyange, 1985) indicated that water storage tanks constituteabout 30 per cent of the total cost of water schemes.The majority of large tanks are made of reinforced concretewhile smaller ones (< 150m³) are made of reinforcedblockwork walls and are mainly located in rural areas.Suitability of blockwork for tank wallsRural areas of developing countries are characterized bylow technology in terms of skilled manpower, equipmentand transportation means. Construction of reinforcedconcrete walls for water retaining structures requires:• adequate compaction of concrete by using surfacevibrators;• low water-cement ratio by using admixtures for enhancingflowability;• sufficient curing under tropical temperatures, whichcan hardly be fulfilled in rural areas of developingcountries.Blockwork construction is one of the appropriate technologiesin such a situation because it requires simpleskills and tools, it is labour intensive, may create jobs andis cheaper. Basic materials for the wall construction areconcrete blocks with grooves, cement mortar and reinforcingbars, all of which are locally available.Problems for designersThe major problem with the existing tanks is cracking andleakage that is accompanied with heavy water losses. Inorder to reduce the heavy losses it is recommended todesign future tanks by taking account of crack widthlimitations. The designers of existing tanks lacked adequateknowledge about the behaviour of reinforcedblockwork in tension, crack formation, and the control ofshrinkage and load induced crack widths. The majority oftanks were designed for ultimate limit state to bear thetensile ring forces caused by water pressure .Research on reinforced blockworkIt is well known from reinforced concrete structures thatthe reinforcement ratio required for controlling crackwidths to specified sizes is significantly higher than thatrequired purely for the stability of the structure. This wasthe reason for conducting a research to investigate:• tensile strength of blockwork;• crack formation, initial and final crack patterns;• tension stiffening after cracking has taken place;• crack widths in relation to steel stresses;• water flow through separation cracks in blockwork;• bond characteristics of reinforcing bars in mortar.The investigations involved testing of 18 reinforcedblockwork wall panels in axial tension for which axialdeformation, crack widths and spacing, as well as reinforcingsteel stresses were measured. Bond stresses ofplain and deformed bars in mortar were investigated on45 specimens by pull-out tests and 21 beam splice testmethods. A total of 18 axial tensile tests on mortar andsmall aggregate concrete were carried out as well toinvestigate crack widths, crack spacing and their relationto bond stresses.In addition water permeability of cracked blockworkwas performed by which the amount of water flowingthrough a crack of particular width and length was measured.In such tests water pressure was varied and D’Arcysformula for lamina flow through parallel walls was appliedfor the determination of flow coefficients.205