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The purpose of this research was to determine the accuracy of two test methods used in measuring the water to cement ratio (w/c) of fresh and hardened concrete. The microwave oven test based on a current ASTM Draft was used in determining the w/c of fresh concrete while the modified Norwegian PF-method was used to determine the w/c of hardened concrete. The microwave oven evaporates the water of a 1500 gram sample of fresh concrete to determine a w/c and can accurately measure the w/c within 0.05 of the true value. The modified PF-method uses an absorption method similar to ASTM C97 and Powers’ hydrations models to determine the w/c of hardened concrete. 100mm diameter concrete cores were prepared from slabs and 50mm thick concrete cylinders were tested. The results from this hardened concrete test had a large degree of variability; however, it was a useful indicator of concrete segregation.

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The possibility of using demolished concrete waste as aggregate in fresh concrete in the production of prestressed concrete beams is checked in this research. As opposed to the use for road foundations or as fill-in material the use of the Recycled Aggregate (RA) for concrete structures requires more tests and processing of results. In fact to be able to use a material for construction it is essential to assess more than just its compressive strength. After the physical and chemical characteristics of the RA and the properties of both the wet and hardened Recycled Aggregate Concrete (RAC) have been determined, it is important to check if the mathematical models and numerical correlation normally used for design of ordinary concrete (such as mix-design procedure, design codes, non-linear analysis) are suitable for RAC. For this reason the main task of this investigations has been to ensure that RAC has satisfactory mechanical performance for structural use and later to guarantee a consistency of the results using methods checked for RAC. A mix-design procedure suitable for RAC to attain the desired workability and the target strength was the first step. Tests on durability of RA and RAC have been performed and the results reported. Finally three 15.0 metres span prestressd beams cast with different percentages of RA (one with 100% of RA, one with 100% of Natural Aggregate NA, and one with 50% of RA and 50% of NA) have been tested. The results show that it is practicable to make prestressed concrete elements using concrete made with Recycled Aggregate and that these elements can have satisfactory and predictable mechanical performance.

Nonlinear response of a structure to progressive loading may originate from two different sources viz, geometric nonlinearity and material nonlinear behaviour. For a rationally proportioned concrete structure, the material nonlinear responses are believed to contribute the major part of its total nonlinear behaviour. Geometric nonlinearities, become significant only when the structure is relatively slender. It is the material nonlinearities of reinforced concrete structures that are of interest in this investigation. Two plate bending finite elements have been generalised to include coupling of inplane actions with the bending effects. This was achieved through layering concept. One of these elements had been employed by some previous researchers. But the present formulation is different from theirs in that a numerical integration scheme is introduced to evaluate the stiffnesses and internal equivalent forces. A number of schemes for solving the nonlinear equations have been included in the present formulation. Suitability and effectiveness of these schemes in tracing the material nonlinear responses of concrete slabs have been examined. The numerical material model behaviour is based on the experimental observation reported by various authors. Readily available material characteristic properties are used in the description of the model. The overall response of reinforced concrete slabs is found to be significantly influenced by the cracking and post cracking treatment of concrete. Some form of tension stiffening scheme seems necessary to represent the structural response realistically. A number of conventional tension stiffening schemes have been incorporated, including a simple alternative formulation. The effect of different tension stiffening schemes and some other numerical parameters on the numerical solution of concrete structures have been investigated. Laboratory tests were carried out on a number of square and rectangular model slabs. The supporting arrangement and the applied loading systems were the main variables. These experimental records were later compared with the numerical predictions. Some other test results from literature have been included also.