The Effect of Glass Fiber-Reinforced Mortars on Physical and Mechanical Performance: An Examination of Length and Ratios

This study systematically investigates the combined effects of three different glass fiber lengths (3, 6, and 12 mm) and three different fiber ratios (1%, 2%, and 3%) on the physical, mechanical, and microstructural properties of cement mortars. Glass fibers are known to enhance mortar performance, yet the simultaneous influence of fiber length and proportion on fresh, hardened, durability, and microstructural characteristics has not been comprehensively addressed in a single experimental framework. The parameters investigated include flow diameter, dry unit weight, water absorption, flexural and compressive strength (at 7 and 28 days), ultrasonic pulse velocity, water sorptivity, as well as SEM/EDS and XRD analyses. Results demonstrated that increasing fiber length and content decreased flow diameter and increased porosity within the mortar compositions. At a 3% fiber inclusion, dry unit weight values decreased, with the lowest value (below 2100 kg/m3) observed for the 12 mm-3% mixture. Flexural strength results highlighted the critical role of the curing process on fiber-matrix interface development. At 7 days, only 1% fiber content improved flexural strength, while higher contents reduced it. At 28 days, however, increasing fiber content generally enhanced flexural strength, particularly for 6 mm fibers, albeit at the expense of compressive strength. The capillarity test revealed that the optimal fiber proportion was 1%, with mixtures achieving compressive strengths exceeding 50 MPa and capillarity coefficients below 0.10 mm/min0.5, while higher fiber contents led to elevated capillarity coefficients. The study concluded that, under the specific conditions tested, the most suitable fiber length is 6 mm, with a recommended fiber content of 1–2%. The 6 mm-1% combination delivered the best overall performance, achieving 60.18 MPa compressive strength, a capillarity coefficient below 0.10 mm/min0.5, and enhanced flexural strength. While increasing fiber content improved flexural strength, it reduced compressive strength and increased the capillarity coefficient. These findings underscore the importance of using appropriate fiber proportions to optimize mortar performance and provide practical guidance for designing fiber-reinforced mortars in structural and construction applications.