PSI - Issue 78

Israel Sousa et al. / Procedia Structural Integrity 78 (2026) 1815–1822

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fundamental material in conservation efforts due to their compatibility with historic substrates and traditional construction techniques. It is well established in the literature that the integration of conductive fillers into the cementitious matrix can provide piezoresistive properties, enabling the material to respond to strain (Laflamme et al. (2023)). These fillers can include a wide range of materials, such as carbon nanotubes (D’Alessandro et al. (2016); Wang & Pang (2020); Cerro Prada et al. (2021)), carbon fibers (Chung (1994); Hao et al. (2023)), graphene (Lim & Lee (2022); Sevim et al. (2022)), among others. The integration of such piezoresistive behavior into lime-based mortars, however, remains relatively unexplored in the literature (Drougkas et al. (2023)). This approach enhances structural performance while enabling real-time monitoring capability, which can be especially useful during seismic events. This study investigates the effect of different conductive fillers on the damage-sensing capabilities of lime-based mortar (LBM) beams doped with carbon fibers and carbon nanotubes. The experimental program includes the analysis of beams with 1% carbon nanotubes (CNT), 0.5% chopped carbon microfibers (CCMF), and a reference mix, incorporating strain measurements obtained through a digital image correlation (DIC) system. The study aims to evaluate the influence of each filler on sensing performance and identify which composition is more suitable under the proposed conditions. 2. Background 2.1. Samples production Three different lime-based mortar formulations were prepared: one incorporating 0.5 wt.% of CCMF, SIGRAFIL® C M150-4.0/240-UN, another with 1.0 wt.% of CNT, and a reference mix. The percentages were selected with the intent to produce overpercolated composites, and are based on previous results obtained by the authors on cementitious doped materials (D’Alessandro et al. (2016); D’Alessandro and Ubertini (2024)) All mixes were based on natural hydraulic lime (NHL 3.5) as the binder, combined with fine siliceous river sand (0 – 3 mm) at a 1:3 lime-to-sand ratio by volume. A fixed water-to-lime ratio of 1.54 was used for all mixtures. For the mortar containing CCMF, lime, sand, and fibers were first dry-mixed manually until a homogeneous distribution was achieved. Water was then added in two steps, first 80% of the total volume, followed by the remaining 20%, under continuous manual mixing to ensure uniform consistency and to minimize CCMF agglomeration. The reference mix followed the same procedure, excluding the fiber component; this procedure is summarized in Fig. 1.

Fig. 1. Preparation procedure for lime-based mortar samples CCMF and REF mix.

For the CNT-based lime mortar, lime and sand were initially dry-mixed until homogenized. In parallel, 1.0 wt.% of CNT was dispersed in 80% of the total mixing water and subjected to sonication for 30 minutes. The resulting CNT suspension was then added to the dry mix, followed by the remaining water, with continuous manual mixing to ensure complete homogenization (Fig. 2).