| In this research, two types of concrete whose performance relies on their fresh-state abilities will be discussed. The first is self-consolidating concrete, which possesses high flowability without aggregate segregation. Quality control of flowability is typically predicted by the final diameter ( Df) of the slump-flow test, which in turn, has been related to yield stress of the fresh concrete. Currently, there are no reliable measures of viscosity from a field-friendly test such as the slump-flow test. It will be demonstrated that the viscosity can be related to the time to final diameter (Tf) from the minislump-flow tests for cement pastes. This relationship is extended to concrete systems where T f of the slump-flow test is correlated to dynamic segregation. For the concrete system, Tf was increased systematically using a viscosity modifying agent, while the Df was kept constant by adjusting the superplasticizer content. Segregation is determined by measuring the radial aggregate distribution from the slump-flow test. The results demonstrate that increasing the Tf improves dynamic segregation resistance. Furthermore, Tf was more indicative of viscosity than the time to reach a diameter of 50 cm (T50), which is currently used in the field as a measure of viscosity. Computational models are implemented to investigate these relationships for both cement and concrete systems.;The second type of concrete is an improved slipform concrete with the ability to consolidate under minimal external energy yet maintain shape stability after being slipformed. This balance between flowability and shape stability is achieved through combination of fly ash and small dosages of micro and nano clays. A microstructural investigation of the effect of clays on the fresh state is carried out to relate macro behaviors with changes in the paste microstructure. Shear and compressive rheology techniques are used to measure how the solids volume fraction of the suspensions with different admixtures evolve with stress. Based on these relationships, the influence of clays on the balance between flowability and shape stability are measured. Results are consistent with green strength and minipaver tests performed on concrete mixes derived from these cement paste mixes. |
