Synopsis This paper examines the relationship between mix proportions, electrical properties of the constituents of concrete and the over-all electrical resistivity for concrete. The mechanisms for the conduction of electricity through the heterogeneous medium of concrete are discussed and an electrical model is proposed. Analysis from a purely theoretical standpoint is also described and the values of electrical resistivity obtained experimentally are shown to compare favourably with the theoretical model.

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A method for estimating the composition and size of metal particles is described. An inductive coil sensor is used which, on the introduction of a metal particle, changes impedance. The nature of the impedance change, for a given coil, depends on the composition and size of the particle which can be detected by incorporating the coil into a marginal oscillator circuit and effecting amplitude and frequency demodulation. Experimental results are given for various materials and an application of the method to lubricant wear-debris condition monitoring is described.

Gaseous emissions from fossil-fuelled electricity generation are major contributors to climate change. Limiting the extent of such change will depend, among other things, on the continuing and increased use of renewable sources including hydropower. Paradoxically, climate change itself may alter the availability of this natural resource, adversely affecting the financial viability of both existing and potential schemes. Here, a model is described to assess the relationship between changes in climate and the viability, technical and financial, of hydro development. A case study is presented both to validate the model and to predict the impact of climate change on a large potential scheme in Africa.

The continuing and increased use of renewable energy sources, including hydropower, is a key strategy to limit the extent of future climate change. Paradoxically, climate change itself may alter the availability of this natural resource, adversely affecting the financial viability of both existing and potential schemes. Here, a model is described that enables the assessment of the relationship between changes in climate and the viability, technical and financial, of hydro development. The planned Batoka Gorge scheme on the Zambezi River is used as a case study to validate the model and to predict the impact of climate change on river flows, electricity production and scheme financial performance. The model was found to perform well, given the inherent difficulties in the task, although there is concern regarding the ability of the hydrological model to reproduce the historic flow conditions of the upper Zambezi Basin. Simulations with climate change scenarios illustrate the sensitivity of the Batoka Gorge scheme to changes in climate. They suggest significant reductions in river flows, declining power production, reductions in electricity sales revenue and consequently an adverse impact on a range of investment measures.