Self-compacting concrete: mix proportioning, properties and its flow simulation in the V-funnel

Self-compacting concrete (SCC) is a type of concrete, which flows under the sole influence of gravity up to leveling, air out and consolidates itself without any external compaction energy. It was a response to the lack of qualified skilled workers at the construction sites and a solution for the accomplishment of durable concrete structures. Self-compactability of a concrete mix is widely affected by the characteristics of ingredients and their proportions. Thus, it becomes necessary to develop a successful procedure for mix proportioning of SCC. The heuristic nature of the early mix proportioning methods motivated researchers to carry out extensive research on the rheological properties of SCC that has significantly improved the proportioning of SCC mixes. A rigorous proportioning method for SCC based on sound physical principles was proposed. However, such a method produces a bewildering array of mixes that reach the target plastic viscosity but does not give any practical guidelines on how to choose the most appropriate mix and does not explicitly impose compressive strength as a design criterion. These shortcomings were overcome in this work by developing a new mix proportioning method. Indeed, practical guidelines in the form of design charts were provided for choosing the mix proportions that achieve a target plastic viscosity in the range 3 to 15Pa s (the lower limit varies with target cube compressive strength) and a target cube compressive strength in the range 30 to 80MPa. To verify the proposed mix design method, an experimental validation was performed on a series of SCC mixes in both the fresh and hardened states. Three sets of SCC mixes were prepared jointly with other two PhD students (Abo Dhaheer, 2016; Al-Rubaye, 2016). These mixes are designated A, B, and C for the low, medium and high paste to solids ratios, respectively. (Note that mixes designated A and C were contributed by the other two named PhD students). Tests on these mixes conclusively proved the validity of the mix design approach in the sense that all the mixes met the self-compactability criteria and achieved the desired target plastic viscosity and cube compressive strength. vii Although SCC has passed from the research phase into the real application, the differences in its composition (i.e. higher paste volume and lower coarse aggregate volume) from normal vibrated concrete (NVC) raise concerns among researchers about its fracture behaviour. Thus, an experimental study has been carried out to investigate in detail the role of several composition parameters of SCC mixes on their fracture behaviour differing by the coarse aggregate volume, paste to solids ratio (p/s) and water to cementitious material (w/cm) ratio. The specific fracture energy and the tension-softening diagram of a concrete mix are the most critical parameters that describe its fracture behaviour as they form a basis for the evaluation of the load carrying capacity of cracked concrete. First, the size-dependent fracture energy (Gf) has been determined using the RILEM work-of-fracture test on three point bend specimens of a single size, half of which contained a shallow starter notch (notch to depth ratio=0.1), while the other half contained a deep notch (notch to depth ratio=0.6). Then the specific size-independent fracture energy (GF) was calculated using the simplified boundary effect formalism in which a bilinear diagram approximates the variation in the fracture energy along the unbroken specimen ligament. Finally, the bilinear approximation of the tension softening diagram corresponding to GF has been obtained using the non-linear hinge model. Predicting the flow behaviour in the formwork and linking the required rheological parameters to flow tests conducted on the site will help to optimise the casting process. A Lagrangian particle-based method, the smooth particle hydrodynamics (SPH) is used to model the flow of SCC mixes in the V-funnel. An incompressible SPH method was employed to simulate the flow of such a non-Newtonian fluid whose behaviour is best described by a Bingham-type model, in which the kink in the shear stress versus shear strain rate diagram is first appropriately smoothed out. The basic equations solved in the SPH are the incompressible mass conservation and momentum equations. The simulation of the SCC mixes emphasised the distribution of larger aggregates particles of different sizes throughout the flow in the 3-dimensional V-funnel configuration. The capabilities of this methodology were validated by comparing the simulation results with the V-funnel tests carried out in the laboratory