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- Volume 49, Issue 4, 2007
Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese - Volume 49, Issue 4, 2007
Volumes & issues
Volume 49, Issue 4, 2007
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 2 –9 (2007)More Less
There are over 500 000 km of unsealed roads in South Africa. Unacceptable levels of dust, poor riding quality and impassability in wet weather are experienced on much of this road network. A potential solution to this ever-increasing problem is the use of soil stabilisers (additives), yet the level of research done on these additives consists mostly of small ad hoc studies.
The aim of this paper is to report on the performance of selected soil stabilisers used on South African unpaved roads with respect to their effect on material strength. The behaviour of the soil stabilisers were tested by determining the effectiveness of the stabilisers in improving the strength of unpaved roads as a function of gravel with different properties for a range of soil stabilisers under wet and dry conditions. The effectiveness was tested over a period of nine months. Four different stabilisers were used on four different wearing-course materials.
The conclusion reached was that there are certain stabilisers that do improve the strength behaviour of pavement material under certain conditions. It was found that the enzyme and sulphonated oil-treated materials had an increase in strength over the test period, and it was concluded that these stabilisers need a curing time of a few dry months to reach their maximum strength. The materials treated with the two polymers gained their maximum strength within two months after construction. It was found that the enzyme-treated material showed an increase in strength when applied to a sandy material with a low PI and the sulphonated oil-treated material performed well when applied to a clayey material containing a reactive clay mineral. The polymers showed no material-specific properties.
Most of the stabilised panels showed an increase in dry strength eight months after construction and this was attributed to the fact that the panels had enough time to dry out and reach their maximum strength over the dry winter months.
The final conclusion was that there are some soil stabilisers available that do improve the strength behaviour of pavement materials. It is, however, important to choose the correct stabiliser for the intended purpose.
Source: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 10 –18 (2007)More Less
This paper describes two-dimensional mathematical modelling of reservoir hydrodynamics and cohesive sediment transport processes, using advection-dispersion theory. Creating such a numerical model involves setting up a suitable curvilinear grid and requires data of the bathymetry, recorded inflows and water levels. It also requires sediment characteristics and transport parameters. These parameters have to be specified by the user based on previous experience and field measurement data.
The Mike21C software from DHI Water and Environment, modified for reservoir sedimentation processes, is used to model the transport of fine cohesive sediment for Welbedacht Reservoir. The reservoir has a relatively narrow basin that constantly experiences extremely large sediment load inputs from the Caledon River. The parameters of flow, sediment characteristics and sediment transport are investigated, calibrated and validated for the Welbedacht Reservoir case study. The calibrated model is then further applied to determine the long-term future equilibrium sedimentation levels as well as future flood levels.
Benchmarking water use and infrastructure based on water services development plans for nine municipalities in the Western CapeAuthor J.A. Du PlessisSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 19 –27 (2007)More Less
With municipalities constantly under pressure due to staff shortages, the need for benchmarks to assist them with the planning process of their water infrastructure becomes an important tool to ensure effective water management. The lack of available and trustworthy data plays an important role. The use of the data provided in the Water Service Development Plan (WSDP), as required by legislation, provides municipalities with a starting point that can be used to measure their performance against other municipalities in similar positions, or against which they can measure their progress towards set goals.
An analysis of the data provided in the WSDPs of nine municipalities, representing 56 communities in the Western Cape, provides the basis for the setting of benchmarks in consumption, non-revenue water, storage capacity, treatment capacity and the re-use of treated effluent.
Effect of grinding time on the particle size distribution of gasification ash and Portland cement clinkerSource: Journal of the South African Institution of Civil Engineering = Joernaal van die Suid-Afrikaanse Instituut van Siviele Ingenieurswese 49, pp 28 –34 (2007)More Less
In recent years the cement and concrete industry has reduced its environmental impact by increasing the use of waste materials as both cement extenders and fillers in concrete. Fly ash has been widely used as a cement extender in concrete for many years but the use of ash from other industries has been limited. In this study the use of ground coarse gasification ash as cement extender is investigated. The effect of grinding time on the particle size distribution (PSD) of gasification ash (GA) and Portland cement (PC) clinker was investigated. The PSD was determined for both blended GA and PC clinker that were first ground separately and interground GA and PC clinker. There appeared to be an optimum grinding time for the GA and interground of GA and PC clinker beyond which the fineness did not increase significantly. The particle size range was narrow after two hours' grinding and any increase in grinding time made it wider for GA and the blended cement. The fineness and Blaine specific surface area of GA and PC clinker increased with an increase in grinding time. However, this increase was less significant beyond two hours. The fineness had an effect on the rate o strength development of the blended cement. The compressive strength, particle size and Rosin-Rammler distribution parameters clearly indicated that grinding time should not be shorter than two hours for interblending and intergrinding of GA and PC clinker