Mechanical Fracture Parameters of Cement Based Mortars with Waste Glass Powder

Abstract

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 × 160mm 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.