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In environments of high moisture exposure, carbon fibre-reinforced polymer (CFRP) reinforcement is believed to be a good alternative to steel due to its non-corrosive properties. However the CFRP matrix experiences other types of changes, mechanical deterioration and transverse swelling, with exposure to moisture and sustained stresses. Specifically for structural applications, few studies have investigated the effects of moisture and stress-induced matrix-dominated changes to the CFRP-concrete bond when the CFRP rods are cast into concrete as prestressed reinforcement. Experiments were conducted to measure the transverse swelling and moisture uptake rates of stressed and unstressed CFRP rods immersed in water and concrete pore solution (CPS). CFRP rods were also embedded in concrete and immersed in water to observe whether the transverse swelling of the rods would cause the concrete to crack. Pull-out tests were conducted on stressed and unstressed CFRP rods cast in concrete cubes and immersed in water for up to 125 days. Six CFRP prestressed concrete prisms were fabricated, three were immersed in water for over 125 days and three were left in lab conditions before being tested in three-point bending. Moisture-induced transverse swelling did not appear to cause cracking of the concrete covering CFRP rods in water, contrary to the prediction of the thick-walled cylinder model, but possibly caused an increase in the CFRP-concrete radial contact pressure. The imposition of sustained bending stresses on wet CFRP rods was found to cause premature failure, believed to be a result of matrix softening and microcracking. These observations of swelling and matrix degradation were believed to affect the CFRP-concrete bond. The pull-out tests of unstressed CFRP rods indicated an increased likelihood for bond failure in the CFRP matrix with moisture exposure. This resulted in greater variations in the ultimate and residual bond stresses of the wet samples compared to the dry controls. For the prestressed pull-out samples, higher magnitudes of prestressing resulted in lower bond failure loads. Both outcomes are indicative of matrix weakening with moisture and stress exposure. However despite this, the three-point bending tests revealed no significant differences in behaviour between the wet and dry prestressed prisms. Although the wet prisms exhibited slightly greater variation in their post peak load behaviour compared to the dry prisms, in line with the observations from the pull-out tests. The work from this thesis reveals that despite observations of matrix deterioration and transverse swelling in CFRP rods exposed to moisture and stress, the effect of these changes to the overall behaviour of a CFRP prestressed concrete member are minimal. Any long-term effects are unlikely to cause significant changes to the behaviour of the member. However, the CFRP-concrete bond may be more variable in members exposed to moisture, which should be allowed for in the design process. Therefore CFRP is a promising alternative to steel reinforcement in high moisture environments, with good long-term durability.

Concrete is a highly non-homogeneous composite with large heterogeneities of quasi-brittle character. Failure of concrete structures is usually accompanied by cracking of concrete, which is strongly affected by the mesoscale structure and the behaviour of the interface between the aggregates and the mortar matrix, especially under complex stress conditions. Analysis of the failure mechanisms of concrete at the mesoscale is therefore crucial for a better understanding of the macroscopic behaviour of the material, which can in turn contribute to improved design of concrete structures and finding new ways to enhance the material properties. This research aims to investigate the intrinsic failure mechanisms of concrete-like materials from a mesoscale point of view. To do this, continued developments from existing work on mesoscale modelling are carried out to cater the needs of realistically simulating the damage process in concrete under complex loading conditions. The new developments focus on two key aspects. Firstly, techniques to realistically simulate the fracture process of concrete are developed and these involve the incorporation of a combined cohesive and contact mechanisms for the interface between aggregates and mortar matrix. Such interface modelling allows the crack initiation and propagation at the mesoscale to be explicitly represented. Secondly, a full 3D mesoscale finite element model for concrete-like materials with random aggregates and the possibility of high packing density is developed. Use is then made of these enhanced mesoscale models to explore the intrinsic mechanism governing the fundamental behaviour of concrete such as fracture propagation in tension and compression, the well-known size effect and the dynamic strain rate effect. The research investigation begins with an analysis of the size effect in plain concrete beams under three-point bending using a generic 2D mesoscale model. The analysis aims to provide preliminary insight into the use of a mesoscopic computational tool for examining the concrete damage mechanisms with the well-known size effect phenomenon as a benchmark scenario. The shapes and the sizes of the fracture process zone (FPZ) during the whole fracture process are captured. The role of detailed FPZ features is discussed accordingly. On the other hand, the results also point out the deficiencies of the continuum-based mesoscale framework at capturing the evolution of the local fracture process, and to resolve this problem requires explicit simulation of the initiation and propagation of the micro-cracks and thus a realistic reproduction of the fracture process zone, and this becomes the subject of research in much of the later chapters of the thesis. To cater to the needs of better representing the fracture process in concrete, a coupled cohesive-contact interface approach is proposed to model the crack initiation, crack propagation and the friction mechanism within the transition zone between the coarse aggregates and the mortar matrix. The cohesive-contact combined model is verified to perform well under simple as well as complex loading conditions. The interface approach in a mesoscale model framework provides a new platform for investigating the failure mechanisms in terms of the cohesive fracture process and the contact friction process. A more comprehensive and robust mesoscale interface modelling approach, in which the cohesive plus contact interface is inserted along all mesh grids, is developed to study the complex dynamic behaviour of concrete with the consideration that fractures can spread in a fine distributed manner within larger damage areas including the strong aggregate, particularly under high loading rate. By allowing local fractures to develop explicitly, the issues with fracture damage description with a continuum material model can be largely resolved. The effectiveness of such an approach is demonstrated and employed in an investigation into the intrinsic mechanisms governing the sensitivity of the dynamic tension resistance with the loading rate. Subsequently, a re-visit of the size effect in terms of the evolution of the fracture process zones using the mesoscale model with cohesive plus contact interface model is conducted and the results are presented. The preliminary observations from using the continuum-based mesoscale model are examined and verified. Additional insight into the fracture processes in the concrete beams with various sizes is obtained and the intrinsic mechanisms of the size effect are further discussed. On the real 3D mesoscale modelling methodology, the new development focuses on achieving a realistic representation of the actual shapes and sizes of aggregate particles and at the same time allowing for high volumetric ratios of aggregates (packing density) to be attained. In addition to specific techniques to enhance the conventional take-and-place procedure, an algorithm to generate supplementary aggregates to allow increased packing density is proposed and implemented. Example 3D mesoscale specimens so created are then verified against standard experimental tests such as uniaxial compression, uniaxial tension and compression with lateral confinements, and applied to examine the dynamic behaviour of concrete under high strain rate compression.

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This dissertation focuses on two different though interconnected uses of the word concrete, both of which were central to a largely overlooked chapter of American history—the American colonization of the Philippines (1898-1945). Originally a logician’s term meaning “actual and solid,” the word concrete only came to refer to the building material in the mid-nineteenth century, a popular usage emerging co-incident with the industrial production of Portland cement—a material that American producers and promoters argued would enable the construction of an era of durable American greatness. The dawn of an American “concrete age”—an era otherwise referred to as the Progressive Era was also a time that saw the emergence of a language of “concrete” values; of actual, specific and measurable results. This period in history saw the apparent focus of American governance shift from the abstract and foundational principles of liberty towards more tangible values of investments and returns, i.e. on ‘development.’  This dissertation examines Daniel Burnham’s City Beautiful plan for Manila in addition to the construction of the colonial institutional and infrastructural projects (government buildings, ports, forts, bridges, roads, housing and prisons) through the analysis of five of concrete’s (and sometimes Portland cement’s) qualities; portability, stability, salubrity, strength, and plasticity. Through these examples I aim to demonstrate that concrete was not only a material used widely across America’s new possession in the Far East, but was also played a role in shaping new forms of global governance.

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