Mechanical performance of embedded polymer optical fibers versus equivalent holes in cementitious mortars

This study investigates the mechanical effects of embedded poly(methyl methacrylate) (PMMA) optical fibers in cementitious composites, separating the contribution of the fiber material from geometric disruption by comparing fibers directly with equivalent-geometry holes. Both were tested in two mortar formulations, a reference mixture (CSA A3000 Class N) and a limestone calcined clay cement (LC³)-inspired eco mixture. In compression, fibers outperformed equivalent holes at selected inclusion counts, including a 5.5 MPa difference at nine inclusions in the reference mixture, indicating that the solid fiber can influence strength beyond geometry. In the eco mixture, nine fibers and nine holes increased strength, whereas one fiber and sixteen inclusions of either type reduced it below the control. In flexure, tested longitudinal configurations increased strength relative to the reference-mixture control by up to 16.5% for nine holes and 15.6% for four fibers, whereas transverse configurations exhibited lower strength at higher inclusion densities. Scanning electron microscopy observations at one year were consistent with a weaker fiber-matrix interface in the eco mixture, yet embedded fibers still provided a significant compressive strength gain of 11.5% over the control at nine inclusions, showing that the reduced-cement matrix remained mechanically compatible with embedded fibers in this configuration. These results indicate that the mechanical responses to fibers and holes depend on inclusion configuration, loading mode, and matrix composition under the investigated conditions. Within this mechanical scope, the findings support further investigation of optical-fiber cementitious composites as multifunctional materials, with dedicated optical and functional testing and fracture-based analyses required before application-level performance can be established.