Alkali activation of waste materials: sustainability and innovation in processing traditional ceramics

Abstract

Environmental issues linked both to OPC production and waste management brought researchers to find new solutionsfor the production of more eco-efficient binders. In this frame, alkali-activated materials are receiving increasing attention. They are obtained by reaction of an alkali metal source, generally sodium or potassium, with amorphous calcium-aluminosilicate precursors. More recently, also the reuse of mining wastes was investigated due to the impressive production of sludges and muds which do not have practical applications and shall be landfilled. The aim of our researches was to investigate the use of semi-crystalline/high-crystalline by-products in the production of alkali-activated materials. Thus, two different powders were used: an alumino silicate mud, composed by quartz, feldspars, biotite and dolomite; and a carbonatic one, composed of calcite and small amounts of dolomite. Both powders were alkali-activated using a solution of NaOH and Na2SiO3. Pastes were produced mixing the activating solution and the powder in different liquid/solid ratiosandinvestigatingthe use of waste glass powder as further source of amorphous silica. Samples were oven-cured for 24h at 60-80 °C and then cured in different environments (dry, humid and immersed in water) for other 27 days before testing physical and mechanical properties. Very promising results were obtained in terms of compressive strength (about 30 MPa for the aluminosilicate sludge and up to 45 MPa for the carbonatic one), showing their potential as innovative building products

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