# Durability of Mortars with Partial Cement Replacement by Recycled Brick Powder
## 1 Introduction  
Globally, concrete is the most widely used construction material [1, 2]. Its widespread use is attributed to several advantages, including its favourable mechanical properties, adequate durability, abundant availability, low-cost raw materials, and versatility in design [3]. However, one of its primary drawbacks is the significant environmental impact associated with its production [4]. Recent studies indicate that the production of 1 m\({}^{3}\) of concrete generates approximately 1 tonne of carbon dioxide (CO\({}_{2}\)), which is released into the atmosphere [5]. It is further estimated that the concrete industry is responsible for 8% of global CO\({}_{2}\) emissions [6]. Of this amount, nearly 90% is generated during the cement manufacturing process [7, 8, 9]. This is primarily due to the chemical reactions that take place in the initial stages of production, particularly during the preheating phase (550 \({}^{\circ}\)C to 960 \({}^{\circ}\)C) of the powdered raw materials, when limestone (CaCO\({}_{3}\)) and magnesium carbonate (MgCO\({}_{3}\)) begin to decompose into calcium oxide (CaO), magnesium oxide (MgO), and carbon dioxide (CO\({}_{2}\)) [10]. In addition, the energy demands associated with the entire cement production process must be considered, as calcination requires temperatures exceeding 1200 \({}^{\circ}\)C [11]. Furthermore, the latest data indicate that the cement sub-sector accounts for approximately 12-15% of total industrial energy consumption [10]. Moreover, it is essential to consider the annual volume of cement produced and its projected consumption in the coming years. According to the European Cement Association (CEMBUREAU), global cement production in 1900 was merely 10 million tonnes. However, over the course of a century, this figure increased a hundredfold, surpassing 1.6 billion tonnes by 1998 [12]. Since then, production has continued to rise, reaching 4.1 billion tonnes in 2013--a level that has remained relatively stable up to 2023, according to CEMBUREAU [13,14]. Over the next 30 years, annual cement production is expected to reach 5 billion tonnes [15]. These figures underscore the crucial role of the cement industry in global development, as it is fundamental to the construction of key infrastructure and the advancement of nations [16]. However, despite both the recorded and projected growth in the coming years, the Cement Sustainability Initiative, in collaboration with the International Energy Agency, has set a target to reduce CO2 emissions from Portland cement production by 45% by 2050. This objective has driven, among other initiatives, a search for materials capable of partially replacing Ordinary Portland Cement (OPC) in concrete production--commonly referred to as supplementary cementitious materials (SCMs). Among the most well-known SCMs are those derived as by-products of industrial processes. These materials have been extensively studied since the late 1990s, and include fly ash (FA), granulated blast furnace slag (GBFS), and silica fume (SF). When used in varying proportions, the partial replacement of OPC with these materials can enhance not only the mechanical properties of concrete but also its durability by improving characteristics such as porosity, permeability, and chloride diffusion resistance [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]. However, one of the main drawbacks of these SCMs is their limited availability, as well as their high economic cost compared to cement. While FA and GBFS are only slightly more expensive than OPC, the cost of SF can be between two and five times higher than that of OPC [32,33]. These limitations have driven researchers worldwide to investigate alternative SCMs, including agricultural wastes such as rice husk ash (RHA) and sugarcane bagasse ash (SBA). These by-products are distinguished by their high silica content, and when used as a partial replacement for OPC at levels ranging from approximately 20% to 30%, they can significantly improve concrete durability.