This thesis is a detailed investigation on the suitability of secondary aggregates for use in concrete production. The aggregates under investigation, originated from construction and demolition sites of the Greater London area and were mainly from reinforced concrete structures dating back to the 60's-70's. The study investigated three sources of recycled concrete aggregate (RCA I, RCA II and RCA III). The first step in the investigation involved the characterisation of the aggregates through an extensive testing regime including physical, mechanical and chemical-mineralogical assessments. Aggregates where then classified based on the requirements of BS 8500 and BSEN 12620 which provide the main guidance for aggregates for concrete. All sources conformed to the relevant standard requirements and RCA I was selected for the next step of this investigation. Following the establishment of conformity of these aggregates for concrete production a further in depth investigation involved the production of designated concrete mixes conforming to BS 8500 and BSEN 206 using coarse RCA I at various proportions up to 100%, totally replacing coarse natural aggregate. The investigation included assessment of equivalent strength concrete in the fresh (workability, stability, air entrainement etc.) and hardened states (engineering properties and durability performance). Concrete performed satisfactorily in most of its performance aspects. In order to demonstrate the performance of RCA concrete and compare with conventional concrete containing natural aggregates, a full scale demonstration programme was devised. It involved the construction of industrial pavements in real construction sites, using conventional concrete and concrete containing up to 100% coarse RCA. Site visits and site inspections at 3 and 6 months into service revealed concrete performing satisfactorily regardless of the RCA content. These findings were in line with those of the scientific investigation carried out in the laboratory.

The Near Surface Mounted (NSM) strengthening is an emerging retrofitting technique, which involves bonding Fibre Reinforced Polymer (FRP) reinforcement into grooves cut along the surface of a concrete member to be strengthened. This technique offers many advantages over external bonding of FRP reinforcement, for example, an increased bond capacity, protection from external damage and the possibility of anchoring into adjacent concrete members. To date, significant research has been conducted into the NSM FRP strengthening technique. However, there are still some areas which need further research in order to fully characterise bond and anchorage of NSM FRP bars. Lack of experimental data, design tools and analytical models addressing these areas create obstacles for the efficient use of these advanced polymer materials. The particular objectives of the research are; to investigate bond behaviour between NSM FRP bars and concrete, to understand the critical failure modes involved and their mechanics, and to develop a rational analytical model to predict bond strength and anchorage length requirements for NSM FRP bars. Several significant variables affecting bond, such as bond length, size, shape and type of bar, resin type, groove dimensions and concrete strength, have been considered. In particular, attention has been focussed on the effect of bar shape on bond behaviour. A comprehensive set of laboratory testing and their results, including the effect of the investigated parameters are presented. Various modes of anchorage failure of NSM FRP bars are identified and the underlying mechanics are investigated. Analytical models are developed to predict bond capacity and anchorage length requirements of NSM FRP bars, and are verified with experimental results.

Summary Background: Previous studies report that women are failing to make informed choices with regard to antenatal screening, due to significant deficits in knowledge. However, current definitions dictate that informed choice occurs not merely as a result of sufficient knowledge, but by acting in line with one’s attitudes despite perceived social pressure (Dormandy et al., 2002). Objective: To investigate whether women are making informed choices with regard to Combined Ultrasound & Biochemical (CUB) screening, using more substantial criteria. Design: Prospective non-experimental. Setting: The Queen Mother’s Maternity Hospital in Glasgow. Sample: 63 women due attend their first antenatal appointment. Outcome measures: responses to a questionnaire constructed for the purposes of the study. Methods: A multidimensional questionnaire measure encompassing demographic factors, areas of knowledge recommended by The Royal College of Obstetricians and Gynaecologists (RCOG, 1993) and all aspects of the Theory of Planned Behaviour (TPB; Ajzen, 1985). Results: Women appeared to be well informed, though there were some worrying misconceptions. Women appeared to intend to act in line with their attitudes, although small numbers of women planning to refuse screening limited findings. Attitude was the strongest predictor of behavioural intention. Conclusions: There appears to be moderate support for the hypothesis that women would make ‘informed choices’, though this is limited by a number of factors which require further investigation.

The main aim of the presented work is the development of a reliable and coherent solution approach to investigate thermo-hygro-mechanical behaviour of concrete, especially under severe heating conditions. The work focuses on the development and extension of an existing analytical, numerical and constitutive model developed at the University of Glasgow. This is then used as a predictive modelling tool to investigate the response of concrete structures subject to combined thermo-mechanical loads. The thesis focuses initially on the coupled heat and mass transport model. A novel alternative formulation for sorption isotherms, that is applicable to both normal and high strength concrete, is developed. Furthermore, the effect of the slip flow effect is included and several state equations, including relative permeability and saturation vapour pressure, are adopted. Additionally, the effect of polypropylene fibres as a spalling prevention technique is modelled via a modification of the intrinsic permeability formulation. The transport model is further coupled with a damage-based mechanical model for concrete. The fully coupled thermo-hygro-mechanical model is presented through validation and verification problems and case studies. The model is implemented in a finite element formulation and behaves in a robust manner. The predictions of moisture state for the benchmark problems of drying and heating compare well with experimental results. Classical behaviour associated with heated concrete, such as moisture clog, gas pressure build-up, etc. are all captured by the presented model. The thesis concludes by considering the analysis of prestressed concrete pressure vessel.

The dumping cost of wasted concrete including the rejected units in precast concrete plants is expected to keep rising as the production increases. The waste material from precast concrete hollow core floors (hcu) is high grade and uncontaminated material. This research work was carried out to investigate mainly the strength and other engineering properties of high strength concrete made with recycled concrete aggregate derived from rejected hcu. Three major categories (based on a questionnaire) were investigated: (i) Type of crushers and the crushing method, (ii) The properties of RCA output from these crushers, (iii) The performance of fresh and hardened concrete, including prestressed concrete, with these RCA. The input material for the crushers was from the same origin of disposed hcu's. The waste concrete was crushed to -14 mm using three different types of crushers - the cone, impact and jaw crushers. The recycled material was separated into fractions of 14 mm, 10 mm and - 5 mm, and tested for physical and mechanical properties relevant to use in concrete. Concrete was then made using zero (control mix), 20% and 50% replacement of recycled coarse (RCCA), recycled fine (RCFA) and mixed (RCCA+RCFA) aggregates. All three crushers produced acceptable shape and strength of RCCA. Some properties are competitive to that of natural limestone aggregate. RCFA was much coarser than river gravel and just complied with the British Standard coarse grading limits. The impact crusher performed best with regard to most aggregate properties, e. g. flakiness, strength and water absorption, but has a disadvantage in producing a large amount of fine-to-coarse RCA. Concerning shape and strength, RCA showed similar properties, and in some cases better, than the conventional limestone aggregate. The water absorption for RCA is 3 to 4 times greater than the natural aggregates. For that reason an extra amount of water (called free water) will be added to the mix to compensate the water absorptions for aggregates. Some proportions of this extra added water may not be absorbed by the aggregates and will float to interrupt the design W/C ratio and caused it to increase. The slump value of fresh concrete made with RCA varied widely depending on the percentage and type of replacement, and the type of crusher. The compaction factor of fresh concrete made with RCA was more consistent and logical. Compressive strength of concrete made with RCA were generally within ±5 N/mm2 of the control. For tensile strength, RCA showed similar performance to that of natural limestone. The SS density of concrete with RCA is lower than that of the control concrete and is lower if the replacement percentages increase. Using RCFA causes higher bleeding rate and considerably reduces density and strength, and the severity increases as the replacements of RCFA increases. Using natural limestone aggregates with RCFA will minimize this poor behaviour and maintain the strength to certain extent. However joining RCCA with RCFA will not limit the poor behaviour and is not recommended. For bonding reinforcing bars most methods indicated that high replacement (100%) of CA cause some reduction in bond strength. In pretensioning wires the RCA concrete had a better performance in bond but some reduction was still reported. Prestressed X-shape beams were used to assess the effects of using of RCA on the performance of hollow core slabs. For 20% RCCA replacements, the prestressing loss, deflection and X-beam flexure crack failure were similar to the standard X-beam, at least and within the design limit. However at higher replacements (50%) some deterioration starts to reveal and the effects are even greater when using a combination of RCCA and RCFA.

The thermodynamic properties of chloride, nitrate and nitrite AFm hydrates have been determined. Investigations of solid solutions and thermodynamic calculations on the influence of these anions on mineralogical changes in cement paste were performed and compared with experiments. To calculate volume changes, densities of principal crystalline phases occurring in cement were critically assessed and tabulated, in some cases with addition of new data. Database was obtained by calculating densities from crystallographic data and unit cell contents. In hydrated cements, anion sites in AFm phase are potentially occupied by OH, SO₄ and CO₃ ions. C1, NO₃ or NO₂ ions readily displace hydroxide, sulfate and carbonate in the AFm structures. Nitrates and nitrites do not have ability to displace chloride from the Friedel’s salt (C1-AFm) though. The binding power of AFm for nitrite/nitrate/chloride was calculated and confirmed experimentally at 25°C. It was observed that presence of chloride, nitrate or nitrite alters the AFm/Aft balance and thereby affect the specific volume of paste solids. It was found that the success of nitrite as a corrosion inhibitor for protection of embedded steel arises from its “smart” behaviour. AFm normally stores and sequesters nitrite. If chloride ingress occurs in service, the AFm undergoes ion exchange, gaining chloride and forming Friedel’s salt, while releasing soluble nitrite ions to the pore fluid. As a result, the aqueous ratio of [NO₂^-]/[C1^-] increases and remains within the passivation range for steel.

The actual shear capacity of existing concrete structures is often unable to meet current standard requirements. This may be attributable to increased load requirements, inadequate shear provisions in the original design or increased demand in shear capacity owing to flexural strengthening. However, available methods of assessment are often conservative, and the actual strength may be sufficient to sustain the specified assessment load. Therefore, it is important that realistic assessment methods are employed. This research comprises an investigation into the shear capacity of prestressed concrete bridges and into the feasibility of a novel strengthening approach, both through comprehensive laboratory experimentation and theoretical analyses. The laboratory testing indicates that the shear capacity of prestressed concrete bridges, post-tensioned transversely to form a deck, can be significantly greater than suggested by the relevant standards. The strengthening method proposed, namely deep embedment of steel or fibre-reinforced polymer (FRP) bars, is found to be feasible and very effective for reinforced concrete (RC) and prestressed concrete (PSC) beams of any size. Analytical models based on the upper-bound theorem of plasticity theory are successfully developed and applied, resulting in much more realistic predictions than those from current standards and codes when assessing shear capacity. For the strengthened beams, in addition to an upper-bound model, a strengthening design method based on a truss analogy is developed, which can be directly implemented into codes of practice. The analytical methods permit the assessment of existing longitudinally and laterally prestressed concrete bridges for shear capacity in a rational manner, and then to determine the capacity of a practical shear strengthening system if the bridge turns out to actually be understrength. Use of the proposed methodology will allow significant savings, as the costs associated with replacing or strengthening the structure can be avoided or minimised, encouraging a sustainable approach.

Electric arc furnace dust (EAFD) is a by-product of the electric steelmaking industry produced in large quantities around the world. In Saudi Arabia, a form of EAFD known as Bag House Dust (BHD) is being used in small amounts as concrete additive, because higher levels of addition caused excessive retardation of setting and hardening. The use of this material is recent, therefore little is known about its effects on durability. This research aims to examine effects of BHD additions on certain properties of cement pastes, mortars and concretes, particularly those believed to affect the susceptibility of embedded steel reinforcement to chloride-induced corrosion as this is a major cause of degradation of reinforced concrete structures in the Arabian Gulf region. Studies of the effects of 2 % BHD addition on pore solution chemistry of hydrated-cement pastes with various levels of internal chloride contamination indicated that both free chloride concentration and hydroxyl ion concentration increased. Electrochemical monitoring of the corrosion behaviour of embedded steel in chloride-contaminated mortars showed that the rates of corrosion were reduced slightly in the presence of BHD. Measurements of the coarse capillary porosities of hydrated-cement pastes revealed significantly lower results in 2-3 % BHD-specimens compared to plain cement pastes. Attempts to measure the consequent changes in apparent diffusion coefficients of chloride in related concrete specimens showed that the BHD additions caused no adverse effects on chloride penetration rates. Electrochemical monitoring of the corrosion behaviour of steel bars embedded in mortars exposed to chloride ingress at 20 °C and 40 °C demonstrated that the threshold chloride level for the initiation of crevice corrosion was significantly increased by the presence of BHD. This was thought to be partly influenced by BHD in reducing bleeding which affects the integrity of the layer of hydration products formed around the steel surface. Having found that 2-3.5 % BHD additions had no detrimental effects on the properties studied, the possibility of using chloride-free accelerators to increase levels of BHD addition without causing excessive retardation of cement hydration was investigated. Calcium nitrite and calcium formate were both found to be reasonably effective in increasing the rates of hardening of specimens with 8 % addition of BHD.

Owing to developments in materials and in structural analysis, the control of deflection under service loads has recently began to play a large part in the design of reinforced-concrete structures. Creep and shrinkage of plain concrete has been the subject of a considerable amount of research during the last fifty years and there have been several studiers of the behaviour of statically-determinate beams under sustained load. However, most reinforced concrete structures are statically indeterminate and the behaviour of this type of structure under sustained load has received very little attention. It is important to establish the main differences in time dependent behaviour of statically determinate and indeterminate structure under sustained load so that the validity of extending existing methods of calculation of long term deflection (developed with limited success for determinate structures) to indeterminate structures may be assessed. This investigation is an experimental and theoretical study of the behaviour of statically-indeterminate structures under sustained service loads. All the experimental work was performed in a laboratory where the temperature and humidity were maintained constant. Concrete of the same mix proportions and strength was used throughout the programme and control shrinkage and creep tests were performed on the plain concrete. A theoretical study of the behaviour of plain concrete was made and compared with the experimental results. The sustained moment-curvature relationships of two reinforced concrete cross sections was investigated experimentally over eighteen months. The investigation was limited to the service moment range. A typical beam cross section, which was 200 x 380 mm and reinforced with approximately 1.5% of tensile steel, was studies using seven specimens and each subjected to a different value of sustained pure moment. The curvature of each specimen was measured at intervals over eighteen months so that sustained moment curvature diagrams could be plotted. A typical column cross section, which was 200 mm square and reinforced with approximately 1% of steel symmetrically distributed was studies under combined sustained axial load and moment. Each specimen was subjected to the same value of axial load but a different value of sustained moment. The curvature and axial strain of each specimen was measured at intervals over eighteen months and sustained moment curvature diagrams plotted. Computer programs were developed for the analysis of continuous beams and two storey single bay reinforced concrete portal frames under sustained service loads. The programs are based on the finite difference treatment of the basic equations of bending and include the effects of cracking in flexure and redistribution of moments under sustained load. The behaviour of the individual cross sections of the frame is defined by moment-curvature data input to the computer which calculates the force and deformation fields at various time and loading. Three full structures were tested under sustained service loads so that the results of the computer analysis could be compared with experimental results. Each member of each frame had one of the two cross sections tested under sustained load.

This thesis presents a rational and unified approach for determining the strength of reinforced and prestressed concrete rectangular beams subjected to combined bending, torsion and shear. In this study failures have been classified into three broad categories: 1) yield modes (3 cases) 2) partial yield modes (6 cases) 3) over-reinforced modes (3 cases). The effect of dowel action, aggregate interlock, uncracked concrete and spacing of stirrups on the resistance of applied torque have been examined. The predictions of the proposed theories have been compared with more than a thousand test results available in literature. In general the agreement is good. A method for predicting cracking strength for reinforced and prestressed concrete beams subjected to bending, torsion and shear is given. The results of tests on 25 thin-walled prestressed concrete box-beams subjected to torsion, bending and shear are presented. Experimental and theoretical investigations on the behaviour and strength of dowels in concrete are given.