Performance of glass fiber reinforced cementitious boards: evaluation of luminous transmittance and flexural strength

Abstract

This study investigated the performance of cementitious boards incorporating glass fibers, with emphasis on light transmittance and flexural tensile strength. Three types of boards were produced: a reference mix without fibers (TR), a mix with glass fibers dispersed within the matrix (T1), and a mix with fibers vertically arranged in the mold (T2). The fibers employed exhibited a flexural strength of 193 MPa and an elastic modulus of 8,900 MPa. The tests were conducted in accordance with NBR 15498:2021, using specimens specifically prepared for each assessment. Flexural tensile strength was determined from six samples of each mix, while light transmittance was evaluated on boards exposed to solar radiation, employing a sealed MDF box and a luxmeter. The results indicated that only the boards with vertically arranged fibers allowed the passage of natural light, registering 2.4 lux, whereas the others exhibited null transmittance. However, this configuration resulted in the lowest mechanical strength (0.33 MPa), followed by the boards with dispersed fibers (0.77 MPa), both lower than the reference mix (1.44 MPa). The reduction in strength was attributed to poor matrix–fiber adhesion and the formation of voids, particularly at the points of vertical fiber concentration. It is concluded that, although vertical fiber orientation enhances light transmission capacity, it significantly compromises mechanical properties. The study highlights the potential of glass fibers for the development of translucent cementitious materials, with possible applications in sustainable buildings prioritizing natural lighting, but underscores the need to optimize fiber volume fraction and arrangement to balance structural and functional performance.