Although self-compacting concrete (SCC) has matured beyond laboratory studies and has now become an industrial product, its characteristics behaviour and performance, in the fresh and hardened states alike, still need to be thoroughly comprehended. This thesis presents the results of a study on behaviour of SCC in the fresh and hardened states. The work was divided into three main parts of research. In the first part, the focus was to develop a simple and rational method for designing SCC mixes based on the desired target plastic viscosity and compressive strength of the mix. The expression for the plastic viscosity of an SCC mix developed using the so-called micromechanical principles has been exploited to develop this rational method. The simplicity and usefulness of this method was enhanced by the provision of design charts for choosing the mix proportions that achieve the mix target plastic viscosity and compressive strength. Experimental work was performed attesting the validity of this mix design procedure via a series of SCC mixes in both the fresh and hardened states. The test mixes were found to meet the necessary self-compacting and the compressive strength criteria, thus fully validating the proposed mix proportioning method. Therefore, this method reduces considerably the extent of laboratory work, the testing time and the materials used. The second part addressed the other important properties of hardened SCC: specific fracture energy ( ), direct tensile strength ( ), critical crack opening ( ), characteristic length ( ), which are no less important than the compressive strength. Combined work with two other PhD candidates (in Cardiff University) has been carried out in order to get a much clearer picture by investigating in detail the role of several parameters - coarse aggregate volume, paste volume and strength grade - of SCC mixes in their , , and . Also addressed in this part is the corresponding bilinear approximation of the tension softening diagram using a procedure based on the non-linear hinge model. It is found that all the mentioned properties are dominated by the coarse aggregate volume (or, conversely the paste volume) in the mix and the mix grade. The third part of this thesis is dedicated to simulating the flow of SCC through gaps in reinforcing bars using the J-ring test. This has been performed by implementing an incompressible mesh-less smooth particle hydrodynamics (SPH) methodology. A suitable Bingham-type constitutive model has been coupled with the Lagrangian momentum and continuity equations to simulate the flow. The capabilities of SPH methodology were validated by comparing the experimental and simulation results of different SCC mixes. The comparison showed that the simulations were in very good agreement with experimental results for all the test mixes. The free surface profiles around the J-ring bars, the spread at 500 mm diameter and the final flow pattern are all captured accurately by SPH. In term of segregation assessment, it is revealed that SPH allows the distribution of large aggregates in the mixes to be examined in order to ensure that they have not segregated from the mortar. The SPH simulation methodology can therefore replace the time-consuming laboratory J-ring test, thereby saving time, effort and materials.