Sustainable cementitious materials: exploring alkali-activated binders

Abstract

The potential use of natural pozzolan (NP) from Algeria for the production of a new alkali-activated binder (AAB) was investigated. CEM II 42.5 cement was added to the NP as a calcium resource. The mixtures were then activated by sodium hydroxide, sodium sulfate and sodium silicate at concentrations of 3, 7 and 11%, respectively. The chemical activators were added in liquid or solid forms to develop a one-part alkali-activated material. X-ray diffraction, thermogravimetric analysis/differential thermal analysis and scanning electron microscopy/energy dispersive spectroscopy were used to assess the microstructure and elemental composition of the hydration products. Properties such as the consistency and setting times of various mixtures and compressive strengths of AAB specimens cured for 7, 28, 90 and 420 days were determined. The ratio of cement carbon dioxide footprint to strength ratio is suggested as an indicator to highlight the environmental contributions of the AABs. The AABs showed different strength levels depending on the activator type and its concentration. A maximum 28-day compressive strength of 25.2 MPa was achieved with 7% sodium silicate. High early strength development was also noted; more than 50% of the strength could be achieved within 7 days. Finally, an environmental advantage was noted, as the Global Warming Potential of the AABs could be 70% lower than that of ordinary Portland cement.