Doctor of Philosophy
Civil and Environmental Engineering
Prof. Moncef Nehdi
Reinforced concrete (RC) pipes are widely used as open channels (non-pressurized pipes) for sewage and storm water conveyance. RC pipes have generally achieved a reliable long-term performance. Depending on multiple parameters (e.g. pipe diameter, pipe wall thickness, required strength, etc.) the pipe may have up to three welded reinforcement cages in order to resist anticipated loads. Each cage is an assembled unit of steel reinforcement consisting of circumferential and longitudinal bars or wires. The fabrication process of a steel cage reinforcement is time and labour consuming. Thus, eliminating the steel cage reinforcement will yield an overall reduction in the production cost of precast concrete pipes. Dispersed steel fibres can be an effective alternative for the reinforcement of concrete pipes.
The aim of this study is to explore using steel fibres as reinforcement in dry-cast concrete pipes. Mechanical properties of dry-cast steel-fibre reinforced concrete (DCSFRC) fabricated using multiple steel fibre types at various dosages were characterized. Consequently, precast pipes reinforced with Dramix RC-65/35-CN and Dramix RC-80/60-CN fibres at various dosages were fabricated. An extensive experimental program was carried out in order to evaluate the structural performance of the full-scale steel fibre-reinforced concrete (SFRC) pipes that were produced in comparison to plain concrete (PC) and RC pipes. Precast pipes had internal diameters of 300, 450, and 600 mm as well as a Type C wall thickness. The structural performance of pipes was characterized using both the continuous and cyclic three-edge-bearing tests (TEBT). Furthermore, the soil-pipe interaction of buried full-scale SFRC pipes was investigated. Finally, a three dimensional non-linear finite element model of the TEBT of SFRC pipes was developed. Subsequently, a parametric study covering multiple pipe configuration and reinforcement parameters was conducted.
Results showed that hooked-end fibres with the largest fibre aspect ratio (Dramix RC-80/60-CN) induced the best flexural performance of DCSFRC specimens while crimped fibres (Novocon XR) were the least effective in enhancing the flexural strength and post-peak behaviour of DCSFRC. The load carrying capacity of SFRC pipes increased with increased fibre dosage. Results of the TEBT for 300 mm diameter pipes showed that the reinforcement specified for Class V pipes in ASTM C76 “Standard Specification For Reinforced Concrete Culvert, Storm Drain, And Sewer Pipe” could be achieved using a steel fibre dosage of 20 kg/m³, while a fibre dosage of 30 kg/m³ was sufficient for 450 and 600 mm diameter pipes to satisfy the same strength class (Class V). Furthermore, provided using a sufficient fibre dosage, SFRC pipes exhibited higher residual strengths and less deformations than that of RC pipes when subjected to small to moderate loading levels. In addition, results showed that using a hybrid system of short (Dramix RC-65/35-CN) and long (Dramix RC-80/60-CN) fibres did not result in synergetic effects.
Full-scale testing results of buried SFRC pipes indicated that the pipes could sustain live loads consisting of a fully loaded 625CL Standard Ontario Truck without exhibiting any cracks or significant deformations, even when the pipe was installed in the least quality installation type (Type IV). This indicated that the current design recommendations for the pipe wall thickness in ASTM C76 (Type C wall) are overly conservative. Furthermore, it was found that the post-cracking behaviour of buried SFRC pipes was more sensitive to the installation type than to the type of steel fibre reinforcement. Finally, the findings of the parametric study were presented in a tabular form that can be used as a design aid supplementary to the newly released ASTM C1765 “Standard Specification for Steel Fiber Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe”.
The experimental findings of this study should assist the precast concrete industry in producing more economical SFRC pipe without the need for costly and time consuming welded steel cage reinforcement. The numerical and analytical study findings provided a simple and rational tool for the design of such SFRC pipes.
Mohamed, Nedal, "Experimental and Numerical Study on Full-Scale Precast Steel Fibre-Reinforced Concrete Pipes" (2015). Electronic Thesis and Dissertation Repository. 2795.