Crack prediction in reinforced block work storage tanks.

Community development depends, among other things, on the adequacy of safe and clean water supply. With increasing population and bad environmental policies which have led to rapid growth of drought and drying of sources of water there exists a need therefore to have good water storage facilities for reliable water supply. These storage facilities must reflect the real socioeconomic situation in the country especially that of a typical rural society, i.e. they must be economic and requiring simple technology, cheap and locally available materials and should not demand highly skilled workmanship in erection, maintenance and operation. This type of storage facility is identified to be the reinforced blockwork storage tank. Reinforced blockwork is composed of reinforcing bars, mortar and blocks. The reinforcing bars are embedded in mortar. Joints composed of mortar only are more prone to cracking, which suggests more study on the behaviour of reinforced mortar. It is the aim of this study therefore to look into the behaviour of reinforced mortar, to compare it with that of reinforced concrete to which it is much analogous, and to understand how they relate. The concrete used is of grade 20 and mortar of ratio 1:3 cement:sand. These are the type of mixes widely used in the majority of construction sites in Tanzania. Mortar and concrete have almost equal compressive strengths, which differ by 0.8 %. Tensile strengths of the two materials on the other hand differ significantly. The variation is of the order of 193 %. Both compressive and tensile strengths of mortar have been confirmed by this study to be greater than those of concrete. Performance of high yield bars is generally better than that of mild steel bars in both matrices. Concrete has much shorter crack spacings than mortar for both types of steel bars, likewise high yield bars produce much shorter crack spacings as compared to mild steel bars. Formation of cracks takes place sequentially with an increase in load and the stable state of no more formation of cracks is reached by mild steel bars much earlier than by high yield bars. Generally, performance of ribbed bars in crack control is observed to be better than that of plain bars due to the superior bond quality of ribbed bars.