Recycling of concrete, ceramic, and masonry waste via alkaline activation: Obtaining and characterization of hybrid cements

This research aims to obtain and characterize alkali-activated hybrid cements based on concrete (Co), ceramic (Ce), and/or masonry (M) waste powders from crushed construction and demolition waste (CDW). Hydrated lime (Ca(OH)2) and ordinary Portland cement (OPC) were evaluated as sources of calcium. As an alkaline activator (AA), mixtures of sodium hydroxide and sodium silicate (NaOH + Na2SiO3) were used. The effects of the OPC (0–20%) and AA (0.1–0.4) contents were evaluated. The possibility of combining the Co, Ce, and/or M waste powders (mixed waste) was also studied for a wide range of proportions. The characterization of the hybrid cements included compressive strength determinations at 1, 7, 14, 28, 60, and 90 days of curing (25 °C and 60 °C−24 h), reaction kinetics (setting time) evaluations, and microstructural analysis by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS). Hybrid cements (10% OPC) based on 90% Co, 90% Ce, and 90% M reached maximum compressive strength values (90 days at 25 °C) of up to 16.9, 36.5, and 25.2 MPa, respectively. The hybrid cement (10% OPC) based on the 30%Co–30%Ce−30%M mixed waste reached a strength of 32.2 MPa at 90 days (25 °C). The results obtained validate the potential of Co, Ce, and M waste powders to be used as geopolymeric precursors, even in scenarios where their separation is not possible (mixed wastes).