Blended Portland cement with high limestone loads modified with a waste glass based sodium silicate of different ratios SiO2/Na2O

Abstract

This paper presents the results of one-part alternative low CO2 cements made of 60%limestone-30% portland cement ((LS-PC)m) and modified with 10% of a waste glass-based sodium silicate (SWG) synthesized by thermochemically processing blends of waste glass-NaOH of 3 different SiO2/Na2O ratios. The added alkali (from NaOH) contents in the (LS-PC)m was kept low, leading to under 2% Na2Oeq. The reaction products were characterized in pastes and the strength development in mortars. The addition of SWG and its SiO2/Na2O ratio had significative effects in the setting time, heat released, flowability, early and late mechanical strength, as well as in the reaction products formed. Lower alkali contents in the SWG did not drastically affect the flowability and setting time, also, the early strength was enhanced without impairing the late strength; in contrast, the opposite occurred for SWG with high alkali contents. The mortars reached acceptable 28-day strengths and similar 180-day strength as a reference Portland cement mortar. The results suggest that the SWG promoted the early formation of carboaluminates and C-S-H of different compositions, evidenced by the signals of six-fold coordinated Al and Q1, Q2(1Al) and Q2 sites, respectively, in the 27Al and 29Si RMN spectra. The studied binders could be a promising alternative, along with other low carbon binders, to contribute to reduce CO2 emissions.