Effect of fiberglass waste and fly ash addition on the mechanical performance of Portland cement paste

Ordinary Portland cement (OPC) mortar and concrete products are designed to withstand compressive loads. However, these products show low deformation before fracture because they are fragile materials, also showing low tensile strength in comparison to compressive strength. These limitations can be minimized by adding fibers, as reinforcement, to the cement matrix. Therefore, in this work the mechanical behavior of cement pastes reinforced with fiberglass waste and fly ash was studied. A 2 k factorial design was used and the experimental factors were the fiberglass waste content (0.2-0.8 mass %), fiberglass length (0.3-1 cm) and fly ash content (0-10 mass %). Fly ash was added to reduce the alkalinity of the cement paste and, therefore, to avoid the chemical attack on the glass fibers. Nine compositions were made, and their compressive strength, tensile strength, apparent density, and microstructure were determined. Type III Portland cement, class F fly ash, and type E fiberglass were used and characterized by XRF. The composites were characterized by XRD and optical microscopy. The ANOVA for compressive strength at 30 days shows that the combined effect of fiber addition and fiber length increased the strength of the samples by 27 % (30.3 MPa). At 60 days the fly ash raised the compressive strength by 32 % (37.4 MPa) regarding the reference sample, probably because the filling effect. The tensile strength at 60 days was influenced by the fiber length, with an increase of 71 % (6.31 MPa). The apparent density was reduced 19 % (1.50 g/cm3) with addition of fly ash and fibers. The fibers can reduce the crack propagation in the matrix, in a typical bridging effect. The cement hydration was not affected by the addition of fiberglass waste.