Thesis (Ph.D.) - University of St Andrews, April 2009.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Rational decisions about cost-effective maintenance and structural repair are hampered by the absence of comprehensive data on structural performance of generic repair materials acting compositely with deteriorated concrete elements. In the present climate of durability problems in concrete construction such information is of critical importance. In order to assess long-term structural performance of repaired elements, basic short and long-term properties of generic repair materials are required under various exposure conditions. The principle requirements to ensure satisfactory long-term performance of the repair have always been high dimensional stability and relatively high early bond strength of the repair material with the substrate concrete. As part of a "Brite Euram" project, sponsored by E.E.C., the author has obtained considerable experimental data on properties of three commercially available generic repair materials, which are significant to the subsequent structural behaviour of repaired concrete members. A comparison is also made between the performance of these repair materials with a plain concrete mix of similar strength and stiffness. The following generic repair materials were used: a high performance non-shrinkable concrete, a mineral based cementitious material with no additives and no coarse aggregate size particles, and a cementitious mortar which contains styrene acrylic copolymer with fibre additives. The repair materials are supplied as single component systems by their manufacturers, ready for on-site mixing and use, and require only the addition of clean water. Data on strength, stiffness, post peak-load ductility under compression, swelling, shrinkage and creep deformations under various curing conditions are presented in this thesis. In addition water permeability coefficients and chloride penetration profiles of the materials at various ages of exposure have been determined. A comprehensive compilation of chloride diffusion data is made and an empirical expression is derived for the prediction of long-term chloride penetration profiles based on data obtained at relatively early ages. Application of this prediction model to the field data of some Arabian Gulf structures is made. The influence of repair materials on the performance of reinforced concrete compression members has been studied. A theoretical model is also derived to predict the long-term structural interaction between a repair patch and substrate concrete in short compression members of reinforced concrete. The model is based on the basic properties of materials, such as creep deformation, drying shrinkage and modulus of elasticity. The validity of the model is established on the basis of the experimental data obtained in this study. At the end of the thesis, conclusions and recommendations for future research are made.

Unrepaired, or misrepaired, DNA damage can be carcinogenic or mutagenic; thus functional DNA damage repair pathways are essential for the safeguarding of the genome. SNM1B is a 5' to 3' exonuclease implicated in the repair of damaged DNA, particularly the repair of interstrand crosslinks. Genetic studies have identified SNPs in the SNM1B gene as related to cancer risk. One of these (rs11552449) encodes a single amino acid change, H61Y. This study shows that WT and H61Y SNM1B have comparable in vitro biochemical and biophysical characteristics. The structures of both WT and H61Y C-terminally truncated SNM1B (Δ-SNM1B) were solved to 2.8 and 3.1 Å, respectively, and reveal similar structural properties. The structure of WT Δ-SNM1B was also reported (to 1.8 Å) with two 2'-deoxy-5'- adenosine monophosphate molecules in the active site. The structure of SNM1B shows an accessible extended active site, which may facilitate the binding of a variety of non-canonical DNA substrates. Accordingly, in vitro, WT and H61Y SNM1B are able to exonucleolytically process a wide range of structurally diverse DNA substrates. By utilising SNM1B depleted cell lines, this study also shows that SNM1B is required for DNA repair in response to treatment with DNA-crosslinking genotoxic agents (including cisplatin and SJG-136). This study also identifies the novel double strand break repair factor, EXD2, as having intrinsic 3' to 5' exonuclease activity. EXD2 was shown to have enzymatic activity on a variety of substrates in vitro, including replication fork intermediates, 'nicked' or 'gapped' DNA duplexes, and RNA based substrates. Together with the cellular data this suggests a role for EXD2 in nucleolytically processing RNA or DNA-based intermediates in damage repair pathways.

Oestrogen is believed to be a potent antioxidant, with potential membrane stabilising and gene regulatory effects. Oestrogen has been shown to be an effective cardioprotectant, with for example a lower incidence of atherosclerosis in pre menopausal females compared to age-matched males and in post menopausal females on hormone replacement therapy compared to age-matched males. What has yet to be determined is the extent to which oestrogen can protect skeletal muscle. It has been shown that certain markers of exercise-induced muscle damage (EIMD) are lower in females in both animal and human studies, but as yet no conclusive evidence from human studies has shown that oestrogen provides a protective mechanism against ERvID or whether susceptibility to EIKID varies across the normal menstrual cycle, where oestrogen fluctuations are high. Furthermore, if oestrogen provides a protective mechanism against EIlVID, it is unknown at which phase during the muscle damage and repair cycle this occurs. It is also debatable if the potential inhibitory effects that oestrogen has on the inflammatory response, with regard to repair and regeneration of the skeletal muscle are positive or negative. The thesis is comprised of a critical review of the nature of EIMD and the potential effects that oestrogen has on the muscle damage and repair cycle. This is followed by three empirical studies which were designed to explore this question. These are outlined below: Study 1 Study one was in two parts. The first part of this study aimed at determining if the phase of the menstrual cycle, could in anyway affect eumennorheic (normally 2 menstruating) females in their susceptibility to exercise-induced muscle damage. An eccentric exercise procedure (elbow flexor muscle group) was performed on a randomly assigned arm during either the menses or ovulatory phase of the menstrual cycle. The contra-lateral limb underwent the same procedure during the alternate phase (random assignment determined in which phase the participant was first damaged). Simple markers of EDM were assessed at baseline and every 24 h up to three days post exercise, during both phases. No significant differences were seen in any markers of BIMD across phases of the menstrual cycle. The second part of this study investigated whether prolonged ingestion of exogenous oestrogen, in the form of the combined oral contraceptive pill attenuated any of the symptoms associated with EIMD. The only symptom to show a significant interaction between groups was perceived soreness, with the pill users reporting significantly (P<0.01) less soreness than the eumennorheic females in the days following the exercise protocol. This suggested that oestrogen may modulate the pain associated with EIMD. Study 2 The second study focussed on gender differences in exercise-induced muscle damage, with particular focus on the secondary symptoms and events which occur following ERVID. Male and female participants performed a bout of eccentrically biased exercise. Markers of both EIMD and inflammation were taken prior to the eccentric exercise and across a 7-day follow up period. Gender differences in the response to EIMD were seen in creatine kinase activity and mid-thigh circumference, with males showing a larger response on both variables. In addition to this, males reported significantly less soreness than females following the exercise protocol. 3 Interestingly, with the exception of neutrophil elastase release, there were no differences in other markers of inflammation between men and women. Total elastase concentration, a marker of neutrophil activation, did not differ between genders. However, elastase release per neutrophil was significantly lower in females, which may be indicative of gender differences in the inflammatory response associated with EDvID. Study 3 With the recognition that oestrogen could potentially reduce or inhibit the inflammatory response the third and final study investigated whether female skeletal muscle was more susceptible to exercise-induced muscle damage after a second bout of eccentric exercise, due to poor regeneration and repair following the initial bout. Males and females performed a bout of eccentrically biased exercise. Markers of EEVM included creatine kinase, soreness, isometric strength and isokinetic strength assessment. The procedure was then repeated two weeks later to determine if gender differences existed in terms of the repeated bout effect associated with EIlvID. Only one variable showed a gender x time x bout interaction (P<0.05), that was the fatigue index. It was shown that following the initial bout of damage, males and females responded very differently, with female muscle being less fatiguable in the 48 h following damage compared to the males, but with both groups responding very similarly in the repeated bout. This may be due to differences in gender and their response to EIlVID, or due to differences in fibre type between genders.

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

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