## 1 Introduction  
The production of Ordinary Portland Cement (OPC) involves: (i) very high temperatures, usually above 1450 \({}^{\circ}\)C, consequently an enormous energy consumption [1; 2; 3]; (ii) the utilization of large quantities of non-renewable natural raw materials [1; 3], mostly limestone and dolomite (as calcium sources) and marls, clays or shale (as silica and alumina sources) [1]; (iii) generation of particulate material [1; 3], starting in mining process [1]; and (iv) significant CO\({}_{2}\) emissions [1; 2; 3; 4; 5; 6]. Being mostly generated on the calcination (decomposition of limestone) [1; 2; 6] but also from the consumption of electricity (air coolers and ball mills) [1; 2] and fossil fuels (preheater, calicner and kiln) [1; 2; 6]. Worldwide those emissions are around 8 to 10% of the anthropogenic global CO\({}_{2}\) emissions, and it is expected to grow [5]. To limit the rise in global temperatures this century to less than 2 \({}^{\circ}\)C above preindustrial levels the International Energy Agency has issued a technology roadmap for reducing CO\({}_{2}\) emissions in the cement industry through 2050 [7]. The manufacture of OPC is then not considered an environmentally friendly process [1]. Producers are being confronted to reduce their environmental impact, which has led to many studies aimed at reducing the environmental footprint of cement-based materials. The substitution of OPC by supplementary cementitious materials, especially by-products or wastes of distinct industrial processes, in the formulation of cement-based products might be a way to reduce its environmental footprint. Nowadays, one of the main supplementary cementitious materials used is siliceous fly ash (FA) [5; 8], fundamentally because of its pozzolanic reactivity, which is a by-product of coal combustion in electric and thermal-electric power stations for heat and power production [8]. The pozzolanic reactivity is the ability that the material has to react, at ambient temperature, with the clinker hydration by-product Ca(OH)\({}_{2}\) forming compounds with binding potential [9]. This property has been linked to the material's chemical composition, particle size, shape and surface texture, and degree of crystallinity [9]. SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) present in FA can react with Ca(OH)\({}_{2}\) during cement hydration to form hydrated calcium silicate (C-S-H) and hydrated calcium aluminate (C-A-H). Both compounds contribute to strength improvement [10]. Other supplementary cementitious materials can possess hydraulic activity, meaning that they can chemically react with water, set and harden [11]. FA have also been used with success in the development of alkali-activated binders [12; 13; 14; 15] a topic that as gaining increasing interest for the development of more sustainable building materials [13; 14; 15] alternatives to those based on OPC [14; 15]. Due to the implementation of decarbonization policies in the power sector, such as the roadmap for transforming the EU into a competitive low carbon economy by 2050, published by the European Commission [16], availability of FA from coal combustion will predictably decrease in the near future [17; 18]. In pulp and paper production plants enormous quantities of FA are produced from biomass combustion in bubbling fluidized bed boilers, for heat and power production. Worldwide, only for power production, it was estimated that in 2018 were generated 10 million tons of biomass ash [11]. This inorganic solid waste has been looked at as a candidate to substitute coal FA [17; 18], however, most of it is still being disposed in landfills [3; 6; 18; 19]. Nevertheless, this substitution might not be simple since physical characteristics and chemical and mineralogical composition [4] of biomass fly ash (BFA) differs from those of coal FA.