Carbon dioxide (CO$_2$) emissions represent a major environmental challenge, with the cement industry contributing around 8% of total global emissions. The necessity to reduce the carbon footprint makes the search for alternatives that can partially or fully replace the use of cement of paramount importance. One perspective solution is alkali activated materials (AAMs), which represent a potentially more environmentally acceptable substitute for Portland cement. To prepare them, you need an alkali activator and mineral waste (precursor). Currently, sodium or potassium silicate and hydroxides are the most used commercial activators. Again, the production of these activators generates substantial CO$_2$ emissions. Alternative alkaline activators (AAA) can be used instead. These are made with waste which contains a high proportion of silica (Si). We prepared AAA from waste glass (WG), glass wool (GW), stone wool (SW), glass wool without binder (GWc), stone wool without binder (SWc) and microsilica (MS). Different solutions of sodium (NaOH) and potassium (KOH) hydroxide were used as the alkaline medium. Two different methods were used for their preparation, hydrothermal method and microwave digestion-extraction. This was followed by the determination of Si and Al concentrations by inductively coupled plasma optical emission spectroscopy (ICP-OES) and determination of functional groups present in the samples by Fourier transform infrared spectroscopy (FTIR). Mixtures were then prepared from the AAAs containing the highest Si concentrations to produce AAM. Metakaoline (MK) and metallurgical slag (BFS) were used as precursors, which were followed by compressive and flexural strength measurements. The selected AAMs were also looked at with a scanning electron microscope (SEM) and their microstructure was compared with the mechanical properties and Si concentrations of the AAAs used.
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