Yunus Ballim

Reinforcement corrosion and the deflection of RC beams––an experimental critique of current test methods

Abstract This paper presents an experimental critique of the current test methods used to assess the effects of reinforcement corrosion on the serviceability deflections of reinforced concrete beams. Importantly, the work reported here highlights the weakness of tests aimed at assessing the deflection behaviour of beams in which the corrosion of the steel and the application of the service loads are undertaken as two separate and sequential processes. In the present series of tests, the central deflections of beams subjected to 23% and 34% of the design ultimate load, under 4-point loading subjected to simultaneous accelerated corrosion, were monitored over a period of approximately 30 days. Uncorroded beams were used as control samples and tested in parallel with the corroded samples. The results show the importance of assessing the structural effects of reinforcement corrosion under simultaneous load and corrosion conditions, as would occur in situ. In this situation, when 6% of the mass of steel is corroded, beam deflections are increased by 40–70% relative to the deflection of the control samples.

A numerical model and associated calorimeter for predicting temperature profiles in mass concrete

Abstract This paper describes the development and operation of a finite difference heat model for predicting the time-based temperature profiles in mass concrete elements. The model represents a two-dimensional solution to the Fourier heat flow equation and runs on a commercially available spreadsheet package. An important problem facing heat modelling of concrete is that the rate of heat evolution at any point in the concrete element depends on concrete mixture parameters, time and position within the element. The present model resolves much of this complexity by using, as input, the results of a heat rate determination using a low-cost adiabatic calorimeter together with the Arrhenius maturity function to indicate the rate and extent of hydration at any time and position within the structure, based on the time–temperature history at that point. The paper presents a discussion of the structure of the finite difference model and its application to spreadsheet architecture. A brief description of the calorimeter is also presented together with the results of a verification exercise that was carried out to assess the accuracy of the model using a block of concrete instrumented with thermal probes. The results show that the model is able to predict the temperature at any point in the concrete block to within 2 °C of the measured values.

Early-age heat evolution of clinker cements in relation to microstructure and composition: implications for temperature development in large concrete elements

Abstract This paper presents an assessment of the range and extent of variation of heat evolution of nominally similar cement clinkers from a range of cement production facilities in South Africa. Clinker samples were collected at nine cement plants and cements were prepared by grinding each clinker with a uniform quality of gypsum. X-ray fluorescence and optical microscope techniques were then used to characterise each clinker and cement in terms of chemical composition and cement compound morphology. Concretes were then prepared with the laboratory-manufactured cements and these were tested in an adiabatic calorimeter in order to determine the rate of heat evolution from each of the clinker samples. The results of these tests were related to the chemical and morphological characteristics of the corresponding cement clinkers. The results indicate a clear differentiation of clinker cements into low, medium and high heat cements. The relationships between this classification of the heat performance of the cements and the chemistry and morphology of the clinker is not clear at this stage. However, using a finite difference heat model, the paper presents an indication of the implications of the measured heat characteristics of the cement for early-age temperature distributions in large concrete elements.

The effect of shale in quartzite aggregate on the creep and shrinkage of concrete—A comparison with RILEM model B3

This paper presents the results of an investigation into the effects of increasing shale content in nominally “quartzite” aggregates on the creep and shrinkage behaviour of concretes made with such aggregate. The investigation was prompted by concern because of the increasing presence of the weaker and poorly shaped shale particles appearing in the quartzite aggregates being used in the Gauteng region of South Africa. In this investigation, two strength grades of concrete were prepared using varying proportions of shale in the stone and sand fractions of the quartzite aggregates. A secondary outcome of this investigation was the opportunity to assess the effect of aggregate type on the prediction of concrete creep and shrinkage using Model B3.The results indicate that increasing shale content in concrete has a significant effect in increasing both creep and shrinkage strains. Shrinkage increases almost linearly with increasing shale content of the total aggregate. On the other hand, shale in the sand fraction appears to have a larger effect in increasing creep than shale in the stone fraction. An assessment of the need for an aggregate-based adjustment to Model B3 is also presented.RésuméCet article présente les résultats d’une recherche relative aux effects que peut avoir l’augmentation de la teneur en schiste dans des granulats nominalement “quartzites” sur le comportement des bétons faits avec de tels granulats. La présente recherche est née du souci de comprendre la teneur croissante des particules de schiste plus faibles et mal formées apparaissant dans les granulats quartzites utilisés dans la région de Gauteng en Afrique du sud. Au cours de cette recherche, deux gammes de résistance de béton ont été préparées en utilisant des proportions variables de schiste dans les fractions de pierre et de sable des granulats quartzites. La recherche a aussi été l’occasion d’évaluer les effets du type granulat sur la prévision du fluage et du retrait du béton en utilisant le modèle B3. Les résultats indiquent qu’une augmentation de la teneur de schiste dans du béton a un effet significatif sur l’augmentation des contraintes du fluage et du retrait. Le retrait augmente presque linéairement avec l’augmentation de la teneur en schiste du granulat total. D’autre part, le schiste dans la fraction de sable semble avoir un plus grand effet sur l’augmentation du fluage que le schiste dans la fraction en pierre. Une évaluation du besoin d’un réglage basé sur le granulat par rapport au modèle B3 est également présentée.

Professional bodies and quality assurance of higher education programmes in South Africa : towards an appropriate framework

Collaboration between universities and professional bodies is neither new nor unique to South Africa. It occurs in many higher education systems and revolves around the role that professional bodies play in the quality assurance and accreditation of the relevant higher education programmes. In South Africa, this relationship has become increasingly problematic over the recent past due to a number of factors. This article begins by exploring those factors before highlighting the legal framework governing the role of professional bodies in University programmes. A critique of the said role is then undertaken against the backdrop of views and opinions from academics involved in professional programmes in some South African universities, including the thorny issue of who should meet the costs of accreditation. The article concludes with suggestions on the principles that should underpin a revised framework, under the custodianship of the Council on Higher Education, to govern the relationship between universities and professional bodies.