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Developing ductile and durable cement-based materials that incorporate fibers has been a subject of extensive investigation to improve the performance of new and existing concrete infrastructure, especially with the advent of novel materials. In this study, properties of a novel type of cementitious composite consisting of nanosilica and a high volume of slag or fly ash were investigated. These composites were reinforced with innovative basalt fiber pellets (BFPs), which consist of basalt fiber strands encapsulated by a polymeric resin, with a specially designed grooved texture. Six mortar mixtures were designed based on cement with high-volume (50 %) slag or fly ash and 6 % nanosilica. The mixtures incorporated different dosages of BFPs (2.5, 4.5, and 6.9 % by volume). Fresh mechanical and durability tests were conducted to evaluate the behavior of the composites. In addition, thermal and microscopy studies were performed to examine the microstructural evolution of the mixtures. The results showed that the slag-based composites exhibited improved performance, especially at early ages, with a compressive strength of 57–78 MPa and toughness of 30–44 J at 28 d. Comparatively, the fly ash–based mixtures had a compressive strength and toughness of 46–53 MPa and 27–39 J, respectively at 28 d. As the dosage of pellets increased, the compressive strength was reduced, whereas the flexural behavior was significantly enhanced in terms of strain-hardening, toughness, and postcracking control. In addition, all mixtures had reduced penetrability with total passing charges less than 700 C and acceptable resistance to salt-frost scaling. Hence, all the developed composites herein had balanced plastic, mechanical, and durability performance, which makes them a viable option for a suite of infrastructural applications.

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