This thesis presents experimental and numerical results on the application of Fracture Mechanics to concrete materials. In the experimental work, a study of the general properties of plain and fibre-reinforced concrete has been carried out with particular emphasis on Mode II as wellas Model failure. A numerical study of the test specimens used in the experimental work has been carried cut using constant strain triangular elements. Three new fracture toughness tests are proposed. Two of these tests are based on the traditional standard concrete quality control specimens. The tests are relatively easy to apply requiring a minimum of specimen preparation. The fracture toughness values have been determined from the finite element results. Stress intensity factor is readily determined from a knowledge of the load at failure and the configuration of the test specimen. The effect of the test specimen geometry has been investigated. The results indicate that the fracture toughness value was independent of the proposed specimen geometry. A good correlation of results was obtained in the split cube specimens with the coefficient of variation generally within ten percent. The effect of varying the modulus of elasticity in concrete was also investigated. The results show that Kic is dependent on the modulus of elasticity value for the Finite Element Analysis used in this work. The tests developed in this study have been applied to polypropylene fibre reinforced concrete and glass fibre reinforced cement composites. The effects of varying quantities of fibre on the stress intensity factor have been investigated. Conclusions from this project and possible future work are summarised in the last chapter.

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A detailed review of moisture sorption kinetics and equilibria within polymers and fibre reinforced composites (FRC) provides an indication of the mechanisms which may affect moisture transport in FRCs. Three reviewed models are investigated for their applicability to the sorption behaviour of a FRC. The first considers only classical Fickian diffusive transport, while the other two include additional parameters to account for dual sorption phenomena or matrix relaxation respectively. An edge diffusion correction technique is developed to correct experimental 3D sorption data to equivalent 1D data for ease of modelling. The sorption data used to assess the suitability of the models is used also to examine the effects of lay-up, environmental conditions, multiple sorption cycling and long term exposure on the sorption behaviour of the a FRC. Each model is numerically assessed for its ability to represent the experimental sorption data. The more complex models provide good representation of the slightly anomalous FRC absorption data while the Fickian model is acceptable for desorption. The effect of absorbed moisture on the mechanical performance of the FRC is assessed and found to be especially detrimental to the matrix dominated properties. The glass transition temperature of the FRC is also found to be reduced by absorbed moisture. The effects of post-join (atmospheric) and pre-join (substrate) moisture on the durability and strength of bonded joints with FRC substrates are assessed using a scarf joint. One months exposure to high environmental humidites after bonding is found to reduce the strength of the joints significantly. A similar loss in performance is also observed if the FRC has a high substrate pre-join moisture content. Pre-drying of moist substrates is found to be beneficial in regaining the performance of the joint. Joint strength is found to be directly related to the quantity of moisture desorbed from the substrates during joint/adhesive cure. A model for the drying process is subsequently developed and found capable of estimating the ideal drying conditions for a given substrate moisture content.

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There is great scope for problems and deficiencies in the workmanship of concreting operations namely. batching. mixing. transporting. placing. compacting. finishing and curing. These problems will adversely affect the quality of the finished concrete. Improving the knowledge and experience of the supervisory staff and workmen on construction sites is essential if these defiCiencies are to be minimized. It has been observed that specifications for concreting activities contain insufficient information regarding workmanship. This causes difficulties in controlling the concreting operations. This thesis addresses the problems associated with the transfer of knowledge from acknowledged experts in concreting operations to site practitioners. It is proposed that an appropriate tool for this information transfer is the use of computer based expert systems. Therefore, an expert system. called ESCON. has been developed to advise on concreting activities. The knowledge of this system was acquired from technical literature, site visits, self experience, and by interviewing experts in the domain. ESCON is capable of: 1) defining and diagnosing concreting problems; 2) giving expert recommendations for the solution of these problems. including the reasons behind the solution; 3) educating inexperienced staff by improving their appreciation of the domain; 4) preparing comprehensive specifications including information on the. workmanship requirements of concreting procedures; 5) calculating the expected loss in the strength of concrete when recommendations are ignored. Experimental work was undertaken at CRIB (Construction Industry Training Board), Bircham Newton, Norfolk, to assist in the verification of the model. The model was tested by undertaking five evaluation methods, including comparison of the result with an objective standard, sensitivity analysis, expert's experience, novice users, and a real life case study.

Relevant literature on plain and hybrid unidirectional fibrous composites is critically reviewed and the difficulty of assessing previous work due to insufficient data is emphasized. A systematically varied series of hybrid composites based on vinyl ester resin and unidirectional carbon and E-glass fibre reinforcements is studied and the constituent materials characterized. Particular attention is given to the effect of total and relative fibre volume fractions, geometrical arrangements and fibre surface treatments on the tensile characteristics and interlaminar shear strength of the composites. Certain hybrid tensile specimens exhibited what is termed a 'hybrid effect', their first failure strain being greater than the expected failure strain of the parent carbon composites. This is discussed in terms of the data and information obtained from the tensile and interlaminar shear strength tests and from a study of the tensile fracture surfaces. Theoretical models for the tensile failure of hybrid composites are critically examined. The tensile fracture mode and the importance of the statistical nature of fibre tensile strength are discussed. Modifications are made to existing statistical failure theory which result in two equations for the ratio of the lower bound on hybrid composite first tensile failure strain to that on the tensile failure strain of the lower elongation fibre parent composite. Comparison between the two equations enables the prediction of the composite failure mode. Where appropriate the theories are applied to the experimental results. Factors controlling the initial failure strain are shown to be the relative volume fractions and statistical characteristics of the two fibre types, the fibre ineffective length and the stress concentrations acting on fibres adjacent to a failed fibre.

This research has tackled the major problem in the field of sprayed fibre reinforced concrete composites, the lack of detailed design information. An extensive series of sprayed fibre concrete field trials and laboratory testing of hardened specimens was complemented by an investigation of flexural testing of cast specimens. Post-cracking toughness and ductility were examined in accordance with the current ASTM (1989a) proposals for toughness index determination. Some of the requirements of ASTM standard C1018 were shown to be impractical.

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