School of Civil and Environmental Engineering
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Item Generalized storage-yield-reliability relationships for analysing shopping centre rainwater harvesting systems.(MDPI, 2017-10-10) Ndiritu, John; Moodley, Yashiren; Guliwe, MondliThe objective of this study was to develop guidelines for analysing rainwater harvesting (RWH) systems of shopping centres in South Africa. A model consisting of three dimensionless relationships relating rainwater supply and demand to storage capacity, yield and reliability was formulated. Data from daily simulation of potential RWHsystems of 19 shopping were used to obtain the relationships. The simulations revealed within-year storage behaviour with considerable variation of annual yield. By applying the Weibull plotting position formula, yield-reliability relationships were derived. The aim to maximize yield and reliability whilst minimizing storage identified Pareto-optimal combinations of the three variables and these combinations were used to develop two dimensionless relationships. An additional relationship based on the dependence of the slope of the yield-reliability plots on yield was formulated to enable analysis of hydrologically non-optimal systems. Verification tests using four RWH systems obtained results that matched those from simulation and the model could therefore be applied for RWH feasibility analysis and preliminary design. This study highlights the need to incorporate inter-annual variability in RWH analysis and shows how reliability can be used to quantify this. This study further demonstrates how reliability can be fully integrated into regression relationships for generalized RWH analysis.Item Treated wastewater reuse in South Africa: Overview, potential and challenges.(Elsevier, 2010) Adewumi, J.R.; Ilemobade, A.A.; Van Zyl, J.E.Many communities in South Africa struggle to access reliable and adequate quantities of potable water for diverse water requirements. This is against the backdrop of decreasing freshwater availability and increasing water demands. Currently, interest in the reuse of wastewater for non-drinking water requirements is increasing. This paper therefore provides an overview of the South African water resources situation and wastewater 1 generation in order to put the need for wastewater reuse into perspective. Potential for broader implementation and parameters influencing wastewater reuse based on local attitudes and experience were discussed with recommendations to facilitate broader implementation of wastewater reuse. This paper concludes that significant potential exists for implementing wastewater reuse for large non-drinking applications (e.g. landscape irrigation and industrial processes) in arid areas of South Africa especially Western Cape Province. Parameters highlighted from local attitudes and experience to influence broader implementation in addition to aridity include distance from source, retrofitting versus new installations, quantity of reuse, tariffs, source quality, public health, willingness, public trust and knowledge, and regulations and guidelines for reuse. Prior to implementation, it is recommended that these parameters be addressed.Item Effectiveness of the fineness of two South African Portland cements for controlling early-age temperature development in concrete.(The South African Institution Of Civil Engineering., 2011) Graham, P.C.; Ballim, Y.; Kazirukanyo, J.B.Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension, coarse-ground cements show lower levels of temperature reduction but also lower thermal gradients.Item Assessment of two cone penetration test based methods for evaluating the liquefaction potential of tailings dams.(2013-06-12) Torres Cruz, Luis AlbertoThe stability of tailings dams is of great importance to the mining industry. It is well known that soil liquefaction is one of the mechanisms that can compromise the stability of such structures. Given the difficulty of extracting undisturbed samples of any cohesionless material, the use of in situ tests to assess liquefaction potential has been intensely researched. The purpose of this work was to assess the applicability to tailings dams of two CPT-based liquefaction assessment methodologies, namely, the Robertsonbased and the Olson and Stark methodologies. Ten case histories were evaluated. When considering triggering of liquefaction, the Robertson-based and Olson and Stark methodologies correctly predicted the behaviour of four out of five and seven out of ten case histories, respectively. When considering the onset of flow failure, the Olson and Stark methodology correctly predicted the behaviour in four of seven case histories for which a post-triggering analysis was made. The results are useful in understanding the shortcomings of implementing these methodologies on TSFs and the limits of their predictive power.Item Reflections on future needs in concrete durability research and development(2012-02-03) Ballim, Y.; Alexander, M.G.; Beushausen, H.D; Moyo, P.There is no doubt that, over the past two decades, we have made enormous advances in the understanding and practice of concrete durability. Spurred by the often experienced early deterioration of reinforced concrete structures, with high capital investment for repair and rehabilitation, conceptions of design for durability have gained an increasingly higher level of importance in recent years.Item Effectiveness of the fi neness of two South African Portland cements for controllingearly-age temperaturedevelopment in concrete(2011-04-01) Graham, P.C.; Ballim, Y.; Kazirukanyo, J.In developing an assessment of the quantum and rate of heat evolution from hydrating cement, an important controllable variable is the fineness of grinding of the cement. This paper presents the results of a project in which two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were subjected to testing in an adiabatic calorimeter to determine the heat evolution characteristics. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the potential benefits of a so-called low heat cement can be lost if the cement is too finely ground. Based on simulations of temperature development using the different cement types tested, the results indicate that the fineness of grinding of cement is a more important parameter in the case of concrete elements with high cement contents but of moderate dimensions. In sections of larger dimension, coarse ground cements show lower levels of temperature development with lower thermal gradients.Item Deterioration Presentation(2012-01-30) Ballim, Y