Properties of eco-friendly cement mortar designed with grounded lead glass used as supplementary cementitious material

Abstract

The purpose of this research is to highlight the effect of adding Leaded Glass Powder (LGP) to cement matrices. To achieve this, glass from Cathode-Ray Tube (CRT) with reactive elements (SiO2 + Al2O3 + Fe2O3) of 26.66% (determined by XRF) is collected and grounded to a particle size of 75 μm, before adding to a CPJ CEM II/A-P 42.5 cement, from 5% to 35% with a step of 5%, to make the pastes and mortars that are subsequently studied during 300 curing days. The analysis results show that the initial setting time increases linearly from 180 min (OPC) to 245 min (35 wt%) and the final setting time from 405 min (OPC) to 550 min (35 wt%). Moreover, LGP additions of 5 wt%, 10 wt%, and 15 wt% show better compressive strengths than OPC after 56 curing days, with 29 MPa, 30 MPa, and 30.9 MPa versus 26.9 MPa for OPC. The corresponding growth rates are 7.8%, 11.52%, and 14.87% respectively. Better compressive strengths are also obtained between 90 and 150 days by adding up to 20 wt% of LGP. At 300 days, only the 10 wt% and 15 wt% substitutions exhibit superior characteristics to OPC (32.1 MPa), with 33 MPa and 34.4 MPa, respectively, which translates to growth rates of 2.8% and 8.41%. The optimal substitution percentage was 15 wt% over the entire cure time investigated. The variations in porosity and water absorption of mortar specimens with the addition of glass show convex trends, indicating good correlations confirmed by the Pearson correlation test results (0.99). Furthermore, these parameters have strong correlations with the curing time (−0.65 and −0.63, respectively) and the compressive strengths (−0.84 and −0.82). The apparent density of the specimens does not describe a uniform variation, as evidenced by the low correlation coefficient with curing time (−0.49), whereas the correlations with porosity (0.76), water absorption (0.76), and compressive strength (−0.6) are strong. According to the hydrate analysis, the Alkali-Silica Reaction (ASR) is marginal in the matrix studied, and the pozzolanic reaction of the second generation involving the free lime of the cement intervenes faster than the pozzolanic reaction of the first generation, which produces the portlandite. The polynomial regression models of compressive and flexural strengths developed have correlation coefficients R2 = 0.94 and R2 = 0.91, respectively. Based on these findings, the substitution rate of cement by CRT glass recommended is 15 wt%.