*2.1. Materials*

Reactive Magnesia (r-MgO), with the commercial name "Calcined Magnesite 92/200", was supplied by Richard Baker Harrison Ltd., Liverpool, England. Its reactivity was recorded as 48 s [11], thus classifying it as medium-reactive magnesia [12]. Biomass fly ash (BFA) was used as it was received and consisted of residual energy production material from a burning forestry source, which was supplied by Central de Biomassa do Fundão, Unipessoal LDA, Fundão, Portugal. The fine aggregate used was river sand (RS), supplied by Tabal-Sepor Areias e Argamassas LDA, Salvaterra de Magos, Portugal, which presented a medium particle diameter (D50) of 1.08 mm and a coefficient of uniformity of 3.02. It is important to note that RS was employed in the devised materials to represent their true condition aside from facilitating the CO2 diffusion into the specimens' core although the use of fine aggregates is known to cause quartz contamination that, in turn, may lead to awkwardness in phase identification.

The raw materials' oxide composition is displayed in Table 1, which was estimated through Energy-dispersive X-ray spectroscopy (EDX) analysis (S-3400N Spectrometer, Hitachi, Tokyo, Japan). The raw materials' physical properties, namely true density, Blaine fineness, and Loss on Ignition (LOI), are shown in Table 2. The true density was determined through a helium gas displacement pycnometer equipment (AccuPyc 1330, Micromeritics, Norcross, GA, USA). The Blaine fineness of the powders (r-MgO and BFA) was determined using a Blaine air permeability apparatus (BSA1, Acmel Labo, Champlan, France). The LOI was obtained through TG-DTG analysis (SDT Q-50, TA Instruments, New Castle, DE, USA).




