# Preliminary Study of New Sustainable, Alkali-Activated
## 1 Introduction
The CSP residue contains approximately 80 wt % of glass, around 4 wt % of ceramic, and 4 wt % of porcelain; the remaining components are small pieces of metals, polymers, papers, and organic materials. According to the Catalan recycling glass companies, around 4-5 wt % of the recycled glass is CSP, which is more than 30,000 t of CSP per year in Catalonia. Currently, as this residue cannot be valorized, the main destination of CSP in Spain is landfill, where accessibility in the EU is increasingly restricted [16] due to the environmental problems [17; 18; 19; 20] generated by the waste deposits. In recent years, to increase sustainable and environmental criteria, the authors seek possible potential uses of this particular residue [21]. Regarding the elemental composition of CSP, it is rich in silicon, alkali metals, and to a lesser extent aluminosilicate (e.g., mullite), making it a suitable raw material to obtain alkali-activated cements (AAC) [22; 23]. Obtaining AAC consists of the reaction of an aluminosilicate powder precursor with a highly alkaline activator solution to form sodium aluminosilicate hydrate (NASH; when CaO amount on precursor \(<\)10%) or calcium aluminosilicate hydrate (CASH; when CaO amount on precursor \(>\) 10%) gels [23]. Also, it is possible to obtain CSH (calcium silicate hydrate) gel depending on the amount of the precursors [24]. The result of these reactions, after a proper curing time and temperature, is a compact solid with good mechanical properties. AAC are considered as a sustainable alternative to OPC, due to low carbon emissions during their manufacture, as well as their appropriate mechanical properties, chemical stability, acid resistance, and fire resistance [19], among others. There are several publications about the compressive strength of AAC developed by using glass wastes as precursors, such as that by [PERSON] et al., where 70 MPa were reported when the specimens were cured at 75 \({}^{\circ}\)C and 98% relative humidity for 3 days [25]. [PERSON] et al. obtained compressive strength values around 49 Mpa after combining glass wastes with fly ash (FA); the samples were cured at 60 \({}^{\circ}\)C in an oven for 48 h, and consequently cured at 23-25 \({}^{\circ}\)C and 50% relative humidity to be tested at 7 days [26]. [PERSON] et al. obtained around 30 MPa at 28 days when FA and glass waste were combined in a 1:3 weight ratio with 5 M NaOH solution and cured at room temperature [27]. A large variety of industrial waste and by-products can be used as precursors, with the purpose of developing new sustainable binders or AAC [28; 29]. All these alkali-activated waste solid precursors are rich in silica and alumina, with the highest possible amorphization degree. Hence, there are several publications, including urban and industrial waste glass, which is specifically glass as a precursor in alkaline activation [30; 31; 32]. However, unlike what happens with this kind of waste glass, CSP is a residue that is discarded in the glass cullet recycling industry, and for this reason, it is currently disposed of in landfills because of its 20 g of ceramic or porcelain per ton of glass content. In this regard, the use of CSP as a raw material in the AAC formulations must allow valorizing this rejected fraction generated during the glass recycling process. Aiming to contribute to the development of new sustainable materials, the present work was focused on studying CSP for its valorization and using it in high-benefit applications that definitively close the cycle of glass recycling. In this way, the main objective of the present study was to evaluate the potential of CSP for its use as a precursor in the synthesis of AAC (as sustainable cement), with NaOH as an activator. Consequently, different formulations from CSP generated in a glass treatment plant to develop sustainable binders were studied to reduce the material disposed of in landfills (with important environmental and economic advantages), and to obtain more ecological and respectful cements with the environment.