# Feasibility of Non-Remanufactured Waste Bottle Glass as Supplementary Cementitious Material
## 1 Introduction  
Concrete, a mix of cement, aggregate and water, is essential to the basic needs of 21 st-century society, such as housing, shelter, workplace, and transport infrastructure. Concrete is, in fact, the most consumed human-made material. This is because of the abundant raw constituent materials worldwide, the ability to set in various environments, and long-lasting durability and versatility [1]. The global demands for cement and concrete have been growing, mainly in emerging regions, motivated by rapid population growth and economic development [2]. Portland cement (PC) clinker is the most widely used binder for concrete production. The last forecast of the International Energy Agency Cement Roadmap estimates that cement demand may grow up to 23% by 2050 [3], and the Organisation for Economic Co-operation and Development admits that its demand might double by 2060 [4]. Unfortunately, the use of PC has a high environmental cost due to being responsible for the use of 7 billion tons/year of non-renewable natural materials and 2% and 5% of global primary and industrial energy consumption, respectively, resulting in 842 kg of CO\({}_{2}\) emissions, on average, per ton of Portland cement produced [5]. Worldwide, efforts have been made to reduce the environmental footprint of PC. The United Nations Environment Program Sustainable Building and Climate Initiative admits that the use of low-CO\({}_{2}\) supplements (supplementary cementitious materials--SCMs) as partial PC replacements and the optimisation of PC dosage in mortars and concrete products are the main pillars (considering a product-based approach) to substantially reduce cement and concrete global carbonic emissions over the next 30 years [5]. The partial replacement of Portland cement clinker with other materials, known as SCMs, has been under scrutiny [5; 6; 7; 8; 9]. SCMs include fly ash, clays, ground granular blastfurnace slag, limestone filler, silica fume, and metakaolin [9; 10]. Besides ecological and economic benefits, partial cement replacement by SCMs also offers engineering advantages, such as improving workability and segregation risk and reducing shrinkage and cracking risk. It may provide better mechanical strength and durability [9; 11]. Limestone filler (LF), fly ash (FA), and granulated blast furnace slag (GBFS) presently constitute the overwhelming majority of SCMs, but the ready availability differs by country/region. Other SCMs, such as silica fume or metakaolin, are also used in cement/concrete but may not be readily available and are more expensive. For instance, in Portugal, LF is the available SCM on the market. Thus, new sources of SCMs are sought for further CO\({}_{2}\) reduction for clinker Portland substitutes [5]. In particular, it is essential to study waste or by-product materials that can partially replace clinker Portland (low-embodied CO\({}_{2}\) materials) [5; 6; 7], similar to what has been done in the past with other standardised SCMs [1]. An amorphous material constituted by silica, alumina, and/or lime can potentially become an SCM. So, beyond LF, GBFS, and FA, other materials, including industrial or agricultural wastes, can partially replace PC. Furthermore, using waste materials as SCMs diverts waste from landfills and gives rise to a value-added product, which offers additional economic and ecological benefits [5; 12; 13]. The main barriers are the lower reactivity of these alternative materials compared with cement [14] and the need for additional chemical/physical treatments to increase their reactivity [15]. Moreover, waste materials or by-products may present contaminants or elevated alkali levels, which may provide deleterious reactions when incorporated into cement-based materials, which limits the actual use of such materials [15].