Crushing Performance and Crack Development in Polymer-Fiber-Reinforced Precast Concrete Manhole Rings

Abstract

Precast concrete manhole rings are exposed to localized tensile stresses and cracking during handling, transport, installation, and service. This study evaluates the effect of macro-synthetic polymer fibers on the crushing behavior, crack development, and failure mechanism of precast rings. Three reference rings and three polymer-fiber-reinforced rings made of C45/55 concrete were tested horizontally under monotonic displacement-controlled loading in accordance with EN 1917. Deformations and cracking were monitored using LVDTs, strain gauges, and digital image correlation. Both series satisfied the serviceability crack-width requirement and the minimum crushing-load criterion while showing comparable initial stiffness. The mean ultimate crushing load increased from 30.70 kN for the reference rings to 41.03 kN for the rings reinforced with MP40 macro-synthetic polymer fibers, corresponding to a 33.6% increase. At comparable advanced post-cracking deformation, the fiber-reinforced rings carried 73.6% more load. Polymer fibers promoted distributed cracking, reduced damage localization, and enabled stable load transfer after matrix cracking, whereas the reference rings developed a dominant crack and showed rapid post-peak strength reduction. The deformation criteria adopted from the fib Model Code 2010 were also satisfied. For the tested MP40 macro-synthetic fibers at a dosage of 4.0 kg/m3, the results demonstrate improved post-cracking resistance and ductility, supporting further assessment of reduced conventional steel reinforcement in precast manhole rings.