Papers by Author: Deon Kruger

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Authors: Jannes Bester, Deon Kruger
Abstract: Concrete repair with polymer modified materials has become an integral part of the civil construction industry. Often, under-performance or even failure of such repairs can be attributed to the incorrect selection, preparation, application or care of the repair process. The root cause of this is basically the lack of adequate knowledge and understanding of the repair material and the repair process by the applicator, the supplier, the consultant and the client. Unfortunately, it seems that there is very little done in terms of the training of these four stakeholders. Decisions regarding repair materials and processes are often based on personal preferences, an elementary cost analysis and convincing sales pitches by some snake-oil salesmen.By using questionnaires designed specifically for each of the four different sectors of the concrete repair industry, a survey was done with regards to the state of training in South Africa in this specialized field. The results indicate that, although there is agreement that polymer-modified concrete patch repair is a highly specialized field; there is an unacceptably low level of training in each of these sectors with regards to the correct selection, application and care of such repair materials. Incorrect specification, inappropriate material selection, misunderstanding of the material properties and inadequate quality control are outcomes of this lack of knowledge and understanding which subsequently may lead to premature failures and/or under-performance of the repair. In addition, the survey results also indicate that the workforce performing the physical repair work, is mainly unskilled and some serious intervention is required to correct this situation.
Authors: Jannes Bester, Deon Kruger
Abstract: In recent years, concrete repair has become an integral part of the construction industry. With the vast quantity of concrete used in the South African construction industry over the past 100 years, one can expect an increase in repair and rehabilitation requirements during the extended lifecycle of exposed concrete structures. Crack repair, re-profiling of spalled areas and surface sealing with polymer related materials forms the bulk of such repair and rehabilitation operations. Due to the complexity of these projects and the variety of professionals and other stakeholders involved from the diagnostics to the implementation phase (specialists consultants, contractors, suppliers and owners of the structures), considerable problems seem to have surfaced to ensure cost-effective but sustainable and durable outcomes. It has been found that in many concrete repair projects, the responsibility for the repair work, adequate quality control and the assessment of successful patch repairs are not fully embraced by the various stakeholders.This concern has led to the research as reported in this paper. The research entailed a series of questionnaires drawn up specifically for the four different stakeholder sectors of the concrete repair industry. The results indicate that, although there is agreement that concrete repair is a highly specialized field, there is not enough training in the correct use of the repair materials, nor enough knowledge regarding the diagnostics or material specification and selection processes. Knowledge on polymer modified mortar are also minimal. These problems are compounded by inadequate quality control and lack of ongoing monitoring of patch repair failure. The paper concludes with suggestions on the way forward.
Authors: Deon Kruger, Michael van der Westhuizen
Abstract: Certain construction situations call for the use of ultra-lightweight concrete materials. The properties of such materials allow for the utilisation of concrete in weight critical applications, for example precast elements, roofing panels, flooring and cladding of structures. The weight saving benefits of lightweight concrete are evident, yet a trade-off in the strength and durability characteristics of the concrete are made. This paper sets out to develop an ultra-lightweight thin filmed polymer modified concrete material for such applications. This material may incorporate specialised aggregates and admixtures to meet performance requirements but the effects of these on the performance of the lightweight concrete are to be carefully evaluated. This paper presents some of the results obtained by means of laboratory testing as well in-situ testing. As part of the in-situ testing, the paper also reports on the practical evaluation of the ultra-lightweight material characteristics performed through the construction of a light weight concrete racing canoe. This allowed for the evaluation of the material performance characteristics and the establishment of acceptable work and application methods when constructing with this material.
Authors: Refilwe Lediga, Deon Kruger
Abstract: This paper presents an overview of an investigation into the application of additive manufacturing commonly known as 3D printing specifically within the construction industry. 3D concrete printing is a new and innovative way of construction and can be used for the manufacturing of micro to macro high precision construction components. If correctly designed and used, this method has various advantages over traditional construction methods as it creates opportunities to reduce time and cost. A crucial component for success is an optimized concrete or mortar mix to ensure proper feed, placement and hardening during the 3D printing process. A 3D concrete printer uses a chemically altered concrete or mortar mix, which is pumped through a concrete extruder/nozzle that is carefully controlled in three dimensions. This extruder is controlled by a computerised gantry system, and prints components and structures layer by layer. The key components in such a system are therefore a concrete pump, an extruder, an optimized printable concrete mix and a computerised gantry system. The paper will present an investigation into the criteria for an optimum concrete mix design to be used in a 3D concrete printing machine.
Authors: Deon Kruger, Neil Herbst, Jannes Bester
Abstract: With millions of square meters of ageing exposed concrete surfaces throughout the world, concrete patch repair is becoming a major component of the civil construction industry. To ensure effective and efficient repairs and rehabilitation of deteriorating concrete surfaces, patch materials with excellent workability during the repair phase and durability during its design life cycle are required. The addition of polymer emulsions to cementitious repair mortars increase the setting time, crack resistance while negatively affects the strength properties of the mortar. Polymer emulsions include natural rubber, polyacrylonitrile and polivinylacetate, to name just a few [1]. This paper focus on the effect of adding different polymer emulsions at varying dosages to cementitious repair mortars to obtain a better understanding of the influences on setting times, crack formation properties and curing regime requirements for optimal strength development. Ambient temperature and relative humidity were kept constant during the testing cycles. The results obtained indicated that the introduction of a polymer emulsion tend to reduce both the initial and final setting times of the repair mortars but that is extends the duration between initial and final set when compared to unmodified repair mortars. Compressive strength reductions were observed when adding polymer emulsions to the repair mortar but it was clear that crack formation was eliminated with the addition of the emulsions
Authors: Jannes Bester, Deon Kruger
Abstract: Concrete patch repair is becoming an important facet of the civil construction industry when considering the large quantity of exposed concrete surfaces requiring maintenance and rehabilitation during its design life cycle. Patch repairs are more often than not done with a specialized polymer-modified mortar which requires adequate quality control and quality assurance during application and curing to ensure long-term success. Unfortunately, there have been many patch repair projects where there has been poor performance of the patch repairs resulting in debonding, cracking and discolouration. In this paper, poor or inadequate quality control during the patch repair process is investigated as one of the possible reasons for poor performance and premature failure . It is postulated that because of the lack of adequate knowledge and understanding of the repair material and the repair process by the various stakeholders (applicator, supplier, consultant and client), deficiencies in the quality control and quality assurance before, during and after the repair project often exists. In many patch repair projects, the responsibility for the successful completion of the patch repair work and the assessment of long term performance of patch repairs is not fully embraced by all of the parties involved.This postulation has led to the research, by using questionnaires designed specifically for the four different stakeholder categories of the concrete repair industry. The results indicate that there is very little discussion amongst the stakeholders regarding quality control and acceptance criteria when performing concrete patch repairs, neither for the identification of patch repair failure directly after the completion of the patch repair, nor for long term performance of the patch repairs.
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