عنوان مقاله [English]
The development of self compacting concrete, SCC, is a relatively new type of concrete made with conventional concrete materials and, in some cases, with a viscosity-modifying admixture (VMA). It fills all sections of formwork, encapsulates the reinforcement without any mechanical compaction (vibration) and has reasonable flow-ability, homogeneity, resistance against segregation and mechanical strength. The key point in achieving the self compacting property is providing high flow-ability and deformability, while maintaining a resistance to segregation and sedimentation. This can be achieved by proper balance between constituent materials. Okamura and Ozawa proposed the limiting of the volume of coarse aggregates, along with the use of high amounts of powder, controlling the water-powder ratio by volume and the use of proper super-plasticizers. The lower time and cost of construction, the lower sound pollution and the high homogeneous concrete are some advantages of SCC. In recent years, there have been a number of significant developments in the SCC precast industry. However, very limited reports are available on prestressed SCC elements and, therefore, more research is urgently needed in order to understand the use of SCC in precast prestressed lightweight slabs (hollow core slabs) to formulate design rules. The deficiencies of industrial precast prestressed constructional members, such as the lack or unbounding of concrete cover on prestressing strands, weakness in holding the prestressed jacking forces in precast prestressed end supports in industry, the loss of high amounts of prestressed jacking forces of strands before transferring the forces into the members and etc, are some cases which can cause irreparable damage. It is, therefore, for better investigation of such cases that three precast prestressed hollow core SCC slabs with dimensions of 2m length, 1.2m width and 0.2m height were industrially cast and then experimentally load tested up to failure. Their ultimate state and experimental deflection and curvature ductility are measured and the results are compared theoretically. The results show that production of such industrial products is unsafe and uneconomic.