PSI - Issue 64

Antonella D’Alessandro et al. / Procedia Structural Integrity 64 (2024) 1160–1167 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction In recent years, significant advancements in concrete material have emerged, driven by progress in chemistry, materials science, and technology (Zamora-Castro et al. 2021). The need for innovation in cementitious materials stays in the need of higher durability and safety of structures and their users, especially for concrete ones which are prone to cracks due to the low tensile strength of the material. Moreover, concrete is the most widespread one in constructions for its versatility and easiness of use, condition that further demonstrates the high impact of its enhancement (Setareh and Darvas 2017). In particular, the availability of novel high-performance fillers allows the development of modified cement-based composites with improved or novel capabilities (Han et al. 2016, Hao et al. 2023). As a matter of fact, the integration of innovative fillers, macro-, micro- or nano-sized ones, into cement mixes has notably improved the strength and durability of such materials ( Makul 2020, D’Alessandro et al. 2024 ). Laboratory experiments demonstrated that including carbon fibers in the mix enhances the tensile strength and fracture resistance of mortars, while fiber reinforcements increase the energy absorption capacity before material failure. Specifically, carbon nanofibers (CNFs) and microfibers (CMFs) can improve the cracking resistance of cement-based materials by effectively bridging cracks (Azhari and Banthia 2012, Galao et al. 2017). Experimental studies on carbon-doped cementitious mortars show significant improvements in flexural strength, toughness, and electrical conductivity compared to standard cementitious specimens (Donnini et al. 2018, Sony et al. 2019). Indeed, carbon-based inclusions, comprising carbon nano- and micro-fibers, carbon nanotubes, graphene, carbon black, and graphite, hold promise for various engineering applications (Li et al. 2004, Coppola et al. 2011, Lee et al. 2017 Frąc and Pichór 2020). These materials exhibit excellent mechanical and electrical properties, with potential applications in enhancing thermal and electrical conductivity and enabling self-sensing for structural health monitoring (Chung 2020, Han et al. 2014). Smart cementitious materials with carbon inclusions have the potential to monitor strain and stress, allowing for the assessment of building performance and integrity. However, research has primarily focused on small-scale samples, and further investigations for scaling this technology are highly needed before reaching the market (Banthia et al. 1992, Castañeda-Saldarriaga et al. 2021). In particular, the challenges for the enhancement of the application of this new material are still open, such as ensuring filler dispersion for uniformity, addressing the impact of coarse aggregates on strain sensitivity, optimizing electrode placement in larger structures and processing electrical materials outputs to achieve an effective structural condition assessment in a changing environment (Han et al. 2007, Meoni et al. 2021, Thomoglou et al. 2022). In recent years, the authors have developed the technology of intelligent construction materials capable of monitoring deformation and tension states, considering changes in electrical resistance (Birgin et al. 2021, D’Alessandro et al. 2022a,b), variations in capacitance measured from voltammetry methods (Triana Camacho et al. 2023a), and software development to process those electromechanical properties, such as strain, stress and electrical ones (Triana-Camacho et al. 2023b). However, the characteristics evaluated so far need to be expanded to consider configurations and composites specifically developed to assess the damage detection and propagation of cracks at full-scale (Nalon et al. 2024). Following this purpose, the present work aims to evaluate suitable characteristics for producing a cement-based mortar providing key information for damage detection within masonry elements and structures for real-world applications. Unlike materials commonly studied in the literature, smart mortar for masonry, especially in restoration projects, needs to be specifically developed. This development should facilitate the scaling of technology and the optimal setup for damage detection in non-homogeneous construction materials like masonry. Specific focus of the study is the feasibility of producing carbon microfiber-doped cementitious mortar for new structures or local repairs of existing ones. The paper discusses material properties, preparation procedures, and characterization tests, including both electrical and sensing tests. The results are presented and discussed, followed by conclusions, evidence, and future directions. 2. Aim of the research Monitoring constructions, particularly ancient buildings and those with significant cultural value, is crucial for preserving these structures and preventing potential structural collapses or damage. Masonry, in particular, is highly susceptible to sudden damage due to its fragile nature. This work explores the possibility of achieving continuous and widespread monitoring of masonry elements using smart mortars capable of revealing dangerous behavioral changes, such as early stage cracks able to change its electrical properties. For a real use in full-scale structures, the tailoring of