Cement is an essential material in today’s society because, as a major constituent of concrete, it forms a fundamental element of any housing or infrastructure development. The chemical process of making cement clinker produces CO2, a major greenhouse gas contributing to climate change. This makes it imperative for us to find ways of using this resource more efficiently. Using waste from other industries, as a raw material is a huge opportunity for the cement industry to reduce its environmental impact. Cement extenders are used as a substitute for some of the Portland cement in concrete. The reasons for the use of extenders, is a growing awareness of the engineering, economical and ecological benefits and the variety of useful enhancements, which they give to the concrete properties. The aim of the research is to determine whether a gasification ash can be used as a cement extender in concrete. In this study the properties of cement and concrete containing gasification ash was compared to the properties of cement and concrete containing fly ash. The physical, chemical and mineralogical composition of a gasification ash sample was investigated, and it was found that gasification ash has an angular shape and a similar chemical composition as fly ash. The chemical requirements of the gasification ash meet the majority of the requirements specified for cement extenders. Where limits are exceeded it is by a very narrow margin. The effect of a gasification ash on the short and long term properties of concrete of both interblending and intergrinding was investigated. The experimental work revealed that gasification ash improves the compressive and tensile strength of concrete in both interblending and intergrinding. Gasification ash does not have a detrimental effect on stiffness of concrete, and did not creep significantly more than concrete containing fly ash. The porosity and permeability does not increase when gasification ash is used as a cement extender. Gasification ash should therefore not decrease the durability of concrete. The use of gasification ash as a cement extender has advantages to both the cement industry and the environment. / Dissertation (MEng(Structural))--University of Pretoria, 2007. / Civil Engineering / unrestricted

This study presents rigid-plastic methods of analysis of shear failure in reinforced concrete (R. C.) wall-beam type structures when subjected to in-plane loading. The upper-bound approach is emphasised. Present shear design practice (e.g. BS8110:1985) relies much upon empirical solutions, but it is inadequately Substantiated by theoretical analyses when compared with design against bending moments. Review of previous work on shear failure in R. C. beams demonstrates the need for a rational analysis approach which broadly represents the important physical characteristics and mechanics of shear failure and which can reliably predict the shear capacity. The rigorous theory of plasticity in shear which was introduced by researchers in Denmark in the early 1970's has proved successful for some limited cases. At failure, a simple kinematic rigid-plastic solution was derived for a stringer model with a straight 'yield line'. Recently, evidence has emerged that the best single yield line between two rigid wall portions may well be curved and not straight. There are different stress states in yield lines and consequently three types of yield line are identified in analysis. These findings enable us to apply for the first time combinations of yield lines to analyse shear failure mechanisms of R. C. wall-beam type structures. The principles of rigid-body plane motion are used to describe the deformations of failure mechanisms. The search for the best mechanism at failure is made automatically by computer. The model predicts reasonably well the strength and mechanism for the test results reported in literature. The model is extended to a wall-beam with openings loaded in plane. Tests were made on shallow beams without shear reinforcement and deep beams with and without web openings to study the accuracy of the fundamental calculations made by the model. The most critical mechanism predicted by the model is reasonably representative of the observed failure mechanism. The strength prediction is in substantial agreement with the experimental tests. The conclusions drawn from the study are: (1) If a correct mechanism is predicted then a rigid-plastic solution is close to the true behaviour otherwise it is an upper bound, and (2) The plastic solution of R. C. is only an approximate solution.

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The effect of a number of variables upon prestress anchorage length was investigated. The end zones of prestressed pretensioned concrete members were simulated by casting against steel bulkheads. 3/8" diameter strands and .276" diameter wires were used. Fifty specimens were tested. The variables investigated were; surface condition of prestressing steel, speed of release of prestress, water/cement ratio of concrete, age of concrete, stress in concrete, and vibration. A relationship between free end pull-in and anchorage length was found and is compared with the results of other investigators. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This thesis is to determine the shear capacity of a reinforced concrete beam column connection at zero moment. The joint under study is formed by casting the beam against a smooth column face with the top and bottom reinforcing bars projecting through the joint and no key or surface roughening provided. The variables considered are the size of reinforcing bars and the distance to the first beam stirrup. The strength of the joint is broken down into components of a) top dowels b) bottom dowels and c) interface bond and friction. The components and the entire joint strength are investigated theoretically and experimentally. Comparisons of both theoretical and experimental results are compared and show that the strength of the joint can be predicted from the sum of the top and bottom dowel strengths. The strength of this beam column connection is shown to provide adequate strength and a method is suggested for calculating the shear capacity of the joint. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The optimum design, with respect to cost, of reinforced concrete structures, satisfying Building Code Requirements (ACI 318-63), is investigated, using Box's Complex Method. Variables considered are: geometry, topology, member sizes and material properties. The optimum design, with respect to volume of single span, pin-connected, plane trusses, is investigated, using Box's Complex Method. Variables considered are: member sizes and nodal co-ordinates. The feasibility of the Complex Method is probed by checking the results, either by conducting exhaustive search or comparing them with solutions obtained with linear programming methods. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate