Experimental and numerical study of time-dependent behaviour of reinforced self-compacting concrete slabs

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Developments in concrete technology provide engineers, designers, suppliers and contractors with new methods of approaching engineering problems. Many of these developments are engineered solutions to technical and commercial problems, by either improving the current practices or overcoming limitations in the existing technology. One of the developments is Self-Compacting Concrete (SCC). SCC refers to a ‘highly flowable, non-segregating concrete that can be spread into place, fill the formwork, and encapsulate the reinforcement without the aid of any mechanical consolidation’ as defined by the American Concrete Institute (ACI). SCC is regarded as one of the most promising developments in concrete technology due to significant advantages over Conventional Concrete (CC). Many different factors can influence a decision to adopt SCC over CC ranging from structural performance to associated costs. These decisions should be well informed and based on a sound understanding of such factors. In addition, Fibre Reinforced Self-Compacting Concrete (FRSCC) is a relatively new composite material which congregates the benefits of the SCC technology with the profits derived from the fibre addition to a brittle cementitious matrix. Fibres improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. For a structure (made by CC, SCC and FRSCC) to remain serviceable, crack widths must be small enough to be acceptable from an aesthetic point of view, to avoid waterproofing and deterioration problems by preventing the ingress of water and harmful substances. Crack control is therefore an important aspect of the design of reinforced concrete structures at the serviceability limit state. Limited researches have been undertaken to understand cracking and crack control of SCC and FRSCC members. Since, the time-dependent mechanisms of SCC and FRSCC are still not completely understood; a reliable and universally accepted design procedure for cracking and crack control SCC and FRSCC members has not been developed yet. There exists a need for both theoretical and experimental research to study the critical factors which affect the time-dependant crack of SCC and FRSCC members. In this study cracking caused by external loads in reinforced SCC and FRSCC slabs is examined experimentally and analytically. The mechanisms associated with the flexural cracking due to the combined effects of constant sustained service loads and shrinkage are observed. One of the primary objectives of this study is to develop analytical models that accurately predict the hardened mechanical properties of SCC and FRSCC. Subsequently, these models have been successfully applied to simulate time-dependent cracking of SCC and FRSCC one-way slabs. Series of tests on eight prismatic, singly reinforced concrete one-way slabs subjected to monotonically increasing loads or to constant sustained service loads for up to 240 days, were conducted. An analytical model is presented to simulate instantaneous and time-dependant flexural cracking of SCC and FRSCC members. It should be emphasized that any analytical model developed for calculation of crack width and crack spacing of reinforced SCC and FRSCC slabs must be calibrated by experimental data and verified by utilizing Finite Element Method (FEM). The analytical predictions of crack width and crack spacing for the SCC and FRSCC one way slabs are in reasonably good agreement with the experimental observations.
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