Development of Cementless Concrete Pipes Incorporating Bundled Fibers: An Alternate to Cement Concrete Pipes

The use of cementless concrete (geopolymer concrete (GPC)) incorporating fly ash and bundled steel fibers to produce full-scale precast concrete pipes is an economical, viable and sustainable solution for sewer infrastructure for decreasing the overall carbon impacts. This research explores the mechanical behavior of precast full-scale pipes (450 mm inner diameter) incorporating cementless concrete and bundled steel fibers. The GPC mixture was produced by completely substituting cement with fly ash generated by the local coal power plant. The bundled steel fibers were locally manufactured from long wires. The proportions investigated of the bundled steel fibers in the GPC pipes were 20 and 40 kg/m3. A total of six full-scale GPC pipes and two conventional cement concrete pipes were cast in a commercial precast pipe unit. The crushing strength under external load was evaluated using the three-edge bearing test (TEBT) on the pipes without fibers, showing comparable cracking and ultimate loads of GPC pipes and conventional cement concrete pipes. Both types of pipes satisfied the strength requirement of ASTM C76 class III. The use of bundled steel fibers in GPC pipes improved the cracking and ultimate loads by 18% and 22%, respectively, when 40 kg/m3 of bundled steel fibers were added. This upgraded the ASTM C76 strength class from class III to IV due to the improved crack resistance and ultimate load. Conventional cement concrete pipes and GPC pipes exhibited similar cracks at the critical regions (springlines, invert and crown). However, GPC pipes with bundled steel fibers showed a well distributed pattern of multiple secondary cracks along the longitudinal axis of the pipes. The final failure was governed by the flexure action and radial tension in the tested pipes. The economic analysis of cement concrete and GPC pipes showed comparable costs. However, the incorporation of fibers increased the cost of GPC pipes due to the limited local availability of proprietary fibers. This study highlights a new horizon of GPC for the manufacturing of sustainable and economical precast pipes as an environmentally friendly substitute to conventional cement concrete pipes for sustainable sewer infrastructure and adds novelty to the current state-of-the-art knowledge.