M.Ing. / It is generally accepted that successful concrete repair is dependent on seven steps. All seven steps of the concrete repair process were investigated in depth. From the seven steps, three of the steps (removal, application and curing) were selected for experimental investigation. Firstly, the removal of damaged concrete was simulated under laboratory conditions. Concrete blocks were prepared through different removal techniques. Repair material was placed on the blocks, and the adhesion between the concrete repair material and the concrete substrate was determined. Secondly, different repair mortar application methods were used, and the effect of application methods on adhesion strengths was determined. Thirdly, the effect of curing on adhesion was determined by curing samples under different conditions. Some in situ test repairs were done at RAU to get an indication of the appropriate repair systems to be used on the RAU buildings. A questionnaire was given out to the industry and analyzed to get an indication of the common practice used for concrete repair in South Africa.

Structural concrete can be treated using a variety of special methods to produce aesthetically pleasing effects. This type of concrete is called architectural concrete. It is possible to produce structures with colourful, smooth or textured surface finishes that will satisfy any of the demands of modern architecture. It is clear that matching the colour and texture of repair work in architectural concrete is problematic. Concrete surfaces with different types of finishes require different rehabilitation processes, just as different ages of concrete require different repair methods. The concrete life cycle is set up for aesthetic repair in this research. Before a repair project is undertaken it is important to ascertain the type of failure. The causes of the failure should be identified and removed if possible. The factors influencing the appearance of the concrete surface should be discussed, in order that the right skills and technical methods are employed during the rehabilitation process. The repair method should be divided into two categories, one is for the young concrete, and another is for the old concrete. A good starting point for the patching mortar of both young and old architectural concrete are suggested as a result of the experiments. Two new factors have been established as a result of this research, namely the colour coefficient and the colour influence coefficient, both of which will be beneficial to future research projects. KEYWORDS: architectural concrete, colourimetric method, discolouration, young and old concrete, colour coefficient, colour influence coefficient. / Mr. Deon Kruger

M.Ing. / Maintaining and repairing building stock, repair and replacement of the infrastructure, has been a facet of the European building industry for more than 50 years. Deterioration of structures to a level that renders them unusable is a more recent occurrence in South Africa. World-wide changes in the proportion of construction expenditure on new construction and repair and refurbishing of existing structures has occurred only the last two decades. Today, nearly 50 % of such expenditure is on repair and renovation in comparison to proportions of 30 % of previous years. Projections indicate that this trend will continue at least to the next coming century. 1171 Such a substantial proportion of construction expenditure must be expected to influence the market for repair materials, specialized techniques and services. Therefore, a good understanding of the all range of modern concrete repair materials, associated techniques and services as well as latest developments in concrete rehabilitation technology is a prerequisite for designers and users of concrete structures. The following pages attempt to present the basic background of modern concrete repair approaches with regard to the intended use of building structures. They will also deal with the management of a repair project with realkalisation as a remediation strategy. The present condition of the Rand Afrikaans University main campus buildings will serve as a case study model.

Concrete possesses inherently durable characteristics due to having chemical and dimensional stability in most environments. This leads to the perception that reinforced concrete structures are expected to be relatively maintenance free. Unfortunately this is not the case as recent years have shown increased emphasis on the repair and refurbishment of all types of concrete structures, in preference to demolition and rebuilding. New concrete repair methods and repair materials have been developed in order to keep up with the growing demand of the concrete repair industry. Diagnostic techniques are constantly upgraded in the hope of quantifying the extent and nature of the repair work to be undertaken. However, contract documents for concrete rehabilitation contracts are currently drawn up with a flexible approach, which is in favour of the contractor and not the client, as the volume and cost of the contract could escalate to unacceptable levels. This dissertation investigates the development of a new technique to accurately predict concrete repair volumes. Artificial neural networks, digital image processing and software creation is combined to achieve what can be seen as the first step towards a quicker and more accurate concrete repair volume estimation. Once implemented, this could result in a revolution of current quantity surveying techniques used for the estimation of quantities in concrete repair projects. / Prof. P.C. Pretorius

M. Phil. / Concrete is worldwide the most commonly used construction material and, although concrete is durable when exposed to aggressive conditions, it requires some maintenance. If this maintenance is neglected for a prolonged period of time, intrinsic and extrinsic factors will cause the concrete to degrade necessitating repair and rehabilitation. The correct diagnosis of the root cause of degradation, proper specification of repair materials and quality execution of the concrete repairs all contribute to the reliability of the repairs. The correct management of the repair process is necessary to ensure reliability in order for the structure to be returned to an acceptable state.

A Damage Assessment Model, Construction Process Model and Parametric Quantity Model were developed with the purpose of capturing the engineering knowledge involved in the estimating process of bridge repair construction projects. The Damage Assessment Model was used to create a sample database in which detailed inspection data was stored in a format compatible with the existing Pontis?tabase. Detailed inspection data, which provided quantitative values for the different damage types observed in bridges, could be retrieved from the sample database so that data could be used as either input parameters in the knowledge rules that triggered the selection of construction tasks in the Construction Process Model, or data could be used as variables in the equations used to estimate quantities in the Parametric Quantity Model. The Construction Process Model was used to incorporate the logic behind the construction process for different repair methods. The Construction Process Model was composed of seven repair matrices that defined specific repair methods for each Pontis?idge element. Construction tasks were grouped in construction modules that were modeled as flowcharts. Each construction module flowchart was composed of construction tasks arranged in sequential order and decision points that triggered the selection of construction tasks based on input parameters and knowledge rules. Input parameters were provided by the user, retrieved from the model or pre-defined in the model by expert knowledge. The construction modules developed involved construction tasks related to the repair of concrete bridge piles that were damaged due to reinforcement corrosion and related concrete deterioration. Data describing the construction tasks that were considered in the construction module flowcharts were modeled using the entity-relationship model and were stored in the sample database described previously. The Parametric Quantity Model combined data generated by the Damage Assessment Model and the Construction Process Model with additional expert knowledge and parameters into equations that were used to estimate quantities. The author investigated the use of neural networks as a tool to predict actual damage in bridge piles, conducted a preliminary survey to define labor productivity factors and collected data to define the duration of construction activities related to bridge repair.

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M. Tech. Civil Engineering.. / Investigates the feasibility of recycling construction waste for re-use as raw material in rehabilitation of roads in Bethal (Govan Mbeki Municipality). Specific Objectives: (a) To identify the causes of roads failure within the study area.(b) To assess feasibility of reuse of construction waste and propose method of road rehabilitation.(c) To recycle unsuitable material through characterisation of the construction waste. (d) To compare the cost implications when recycled construction waste is used with that of normal roads' rehabilitation.