# Durability of Mortars with Partial Cement Replacement by Recycled Brick Powder
## 4 Conclusions  
In this study, the durability-related properties of eight different mortars in which Ordinary Portland Cement (OPC) was partially replaced with recycled brick powder (RBP) at substitution levels ranging from 5% to 45% were analysed. The results obtained led to the following conclusions:  
1. RBP was identified as an effective supplementary cementitious material due to its pozzolanic reactivity, which was evaluated by measuring the electrical conductivity and pH of aqueous calcium hydroxide/RBP suspensions. When RBP partially replaces Ordinary Portland Cement (OPC), it reacts with the calcium hydroxide (Ca(OH)\({}_{2}\)) released during cement hydration, leading to the formation of C-S-H gels. This secondary reaction produces additional solid phases that obstruct the capillary pore network, resulting in pore refinement and a more tortuous microstructure.
2. The formation of additional C-S-H gels resulted in an increase in compressive strength when OPC was partially replaced with RBP. In mixtures where the substitution level was 35%, compressive strength increased by more than 50%. However, no significant effect on flexural strength was observed.
3. The partial replacement of OPC with RBP resulted in a reduction in water-accessible porosity, with a decrease of up to 43% observed at a substitution level of 40%.
4. Carbonation resistance remained virtually unaffected by the introduction of RBP at replacement levels of 35% or lower. However, at higher replacement levels, carbonation resistance decreased by 30% to 60%.
5. Chloride diffusion resistance improved with the partial replacement of OPC by RBP. In this case, at a substitution level of 35%, the chloride diffusion values were four times lower than those of the reference specimens.
6. The partial replacement of OPC with RBP also influenced the electrical resistivity of the material, increasing as the substitution level rose. At substitution levels of 40% and 45%, electrical resistivity increased by a factor of eight to nine, while at levels of 30% and 35%, the increase ranged from four to five times compared to the reference mixture (without RBP).  
Based on the results obtained, a substitution level of 35% was identified as the optimum in this study. This substitution level not only resulted in the highest compressive strength but also led to notable improvements in durability-related properties, such as water-accessible porosity, resistance to chloride penetration, and electrical resistivity. Although higher substitution levels may still provide benefits compared to mixtures without any replacement, carbonation resistance can be significantly reduced, potentially affecting the long-term durability of the material.  
Conceptualisation, J.R.L.-F., A.A.-B. and M.V.; methodology, J.R.L.-F., A.A.-B. and M.V.; software, J.R.L.-F.; validation, J.R.L.-F., A.A.-B. and M.V.; formal analysis, J.R.L.-F., A.A.-B., P.M.-B. and M.V.; investigation, J.R.L.-F., A.A.-B., P.M.-B. and M.V.; resources, J.R.L.-F. and M.V.; data curation, J.R.L.-F., A.A.-B. and M.V.; writing--original draft preparation, J.R.L.-F., A.A.-B. and M.V.; writing--review and editing, J.R.L.-F., A.A.-B., P.M.-B. and M.V.; visualisation, J.R.L.-F., A.A.-B. and M.V.; supervision, P.M.-B. and M.V.; project administration, M.V.; funding acquisition, J.R.L.-F. and M.V. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Universitat Politecnica de Valencia, grant number PAID-06-24.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author.  
**Acknowledgments:** The authors would like to thank the Catedra de Cambio Climatico (Universitat Politecnica de Valencia) and the Conselleria de Medio Ambiente, Infraestructuras y Territorio (Generalitat Valenciana) for the internship grant awarded to [PERSON].  
**Conflicts of Interest:** The authors declare no conflicts of interest.