Mechanical Fracture Parameters of Cement Based Mortars with Waste Glass Powder

Glass is an amorphous solid substance with pozzolanic properties that can be used as a partial substitute for ordinary Portland cement (OPC) in cement based composites. In the research conducted for this paper, the PC was partially replaced by fine-ground waste laboratory borosilicate glass (in mixtures where 5, 10, 15 and 20% by mass was substituted). Beam specimens with the dimensions 40 × 40 × 160 mm were prepared from each mixture. After demoulding, the specimens were kept under standard laboratory conditions. Basic tests were conducted at the age of 7, 28, 56, and 90 days: the compressive (fc) and flexural (ff) strengths were determined according to the ČSN EN 1015-11 standard. Specimens were also subjected to fracture testing at the age of 28 days. The beam specimens with an initial central edge notch were tested in three-point bending. Load vs. displacement diagrams were recorded and modulus of elasticity (E), fracture toughness (KIce) and fracture energy (GF*) were determined. It was found, that strength increased with specimen age: at the age 28 days this increase was 12-33% in case of fc, and 6-15% as regards ff. The values obtained for almost all the parameters decreased with the increasing dosage of glass as a replacement for cement: compared to a reference composite this decrease was 22-40% in the case of fc, 24-28% for ff, 3-5% for E, 9-29% for KIce, and 30-50% for GF*; exceptions were recorded for glass replacement doses of 5 and 10%, where increases of 2-6% for fc and 8-10% for E were obtained.