# Durability of Mortars with Partial Cement Replacement by Recycled Brick Powder
## 1 Introduction
However, their effect on mechanical properties remains relatively limited [34, 35, 36, 37]. Within this subgroup of SCMs derived from agricultural wastes, wood waste ash and biomass fly ash can also be considered. These by-products, owing to their high pozzolanic content, can improve mechanical properties such as compressive and flexural strength when used as a partial replacement for OPC. However, their replacement levels are generally very low, typically not exceeding 5% [38]. Some researchers suggest that the replacement level can be increased to as much as 20% without significantly affecting the mechanical properties. However, the durability of the material may be compromised due to increased porosity or reduced resistance to chloride diffusion [38,39]. The primary drawback of this subgroup of SCMs is their limited availability, as they are confined to regions where these residues are generated, such as natural environments typically located far from industrial and urban centres. This geographical limitation poses challenges and hinders their widespread implementation. However, among the materials generated in large cities, as well as in urban and industrial centres, construction and demolition waste (CDW) stands out as a potential SCM. According to various authors, CDW accounts for more than 30% of the total solid waste produced globally, a proportion that is expected to increase in the coming years [40]. In countries such as The Netherlands or Spain, bricks constitute more than 50% of CDW, offering significant potential for recycling and reuse in concrete production [41]. Their most widespread application is as a partial replacement for fine and coarse aggregates [42, 43, 44, 45, 46]. However, this approach does not contribute to reducing cement consumption. An alter native that can effectively lower cement consumption is the use of finely ground recycled brick powder (RBP) as an SCM [47]. Although this topic holds significant social and scientific interest, it has received limited attention in the literature to date. However, a few studies have begun to examine this scenario. Existing works have primarily focused on the mechanical properties of the material, yet their results reveal notable discrepancies. Most researchers report an improvement in mechanical properties when incorporating RBP as an SCM. For instance, [PERSON] et al. observed that at a 10% replacement level, both compressive and flexural strength exhibited a slight increase (\(\approx\)10%) [48]. [PERSON] and [PERSON] obtained similar results but observed that when the replacement percentage increased to 20%, both compressive and flexural strength experienced a decrease, which could reach up to 50% [49], similar data to those obtained by [PERSON] et al. [50] and [PERSON] et al. [51]. In contrast, [PERSON] et al. and [PERSON], with OPC replacements of up to 30% and 35% using RBP, respectively, observed negligible variations in these properties, including in the modulus of elasticity, with result variability remaining below 5% [52; 53]. On the other hand, [PERSON] et al. explored replacement levels of up to 40% and identified 20% as the threshold for enhancing the material's properties [54]. However, the same authors highlight that increasing the replacement percentage beyond 40% is counterproductive, as it results in a decline in the material's compressive strength (from 54 MPa to 38 MPa) [54]. This trend was also observed by [PERSON] et al. and [PERSON] et al., who successfully replaced OPC with RBP at levels of up to 50% [55; 56]. Conversely, other researchers, including [PERSON] et al. [57] and [PERSON] et al. [20], reported a strength loss ranging from 20% to 30% at a 30% replacement level, similar to the data obtained by [PERSON] et al. [58], while [PERSON] et al. documented a strength reduction exceeding 50% at a 40% replacement level. In contrast, [PERSON] et al. indicated a compressive and flexural strength reduction lower than 30% at a 50% replacement level [59].