Effects of aggregate addition on alkali-activated binders and mortars based on rock sawing sludges

In the context of reducing the consumption of geo-resources and promoting circular use of industrial wastes, recent studies have focused on rock-sawing sludges as precursors for alkali-activated materials. This study focuses on the effects induced by adding different aggregates to three alkaline-activated binders to create mortars. Binders are sustainable products synthesised using rock-sawing sludge as waste precursors. Two types of aggregates, Mt. Etna crushed volcanic rocks (azolo), and quartz-sand, were added to basaltic-sawing, granitic-sawing, and mixed-sawing sludges. Synthesised materials were analysed through X-ray diffractometry, scanning electron microscopy, uniaxial compressive strength, ultrasound pulse velocity and dynamic vapour sorption to compare their behaviour. Results showed that aggregates reduce by 23-40% salt content and by 14-50% the amorphous phase. Azolo's glassy/microcrystalline structure promotes stronger bonding with the binder matrix than quartz-sand, enhancing basaltic mortars' uniaxial compressive strength by 34-54%. Quartz-sand remained almost completely unreacted, decreasing or not affecting strength. Mortars showed higher ultrasound pulse velocity than binders (3350 vs 3260 m/s on average), with improved homogeneity in azolo-bearing materials. Dynamic vapour sorption indicated lower hygroscopicity in mortars, though a retention of similar to\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document}0.5-1.0 wt% residual moisture was registered for both binders and mortars, suggesting small irreversible structural changes during absorption-desorption. These findings are important to establish the compositional, microstructural, and mechanical characteristics of alkaline-activated binders, and clarify how the aggregates influence mortars' properties. The study casts new light on the potential application of sustainable alkaline-activated materials realised using wastes as precursors for their synthesis.