PSI - Issue 64

Wenkui Dong et al. / Procedia Structural Integrity 64 (2024) 1152–1159 Wenkui Dong and Marco Liebscher et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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reinforcement in concrete and fulfill the functional application of concrete in various infrastructures. In this scenario, mineral-impregnated carbon fiber (MCF) yarns manufactured by cement slurry or geopolymer slurry have been boldly proposed as a viable substitute for steel reinforcement in concrete with notable benefits in enhanced corrosion resistance, temperature resistance, lightweight, better bonding to the concrete substrate as well as technological and structural flexibility, etc. (Mechtcherine et al., 2020). The production of MCF by utilizing microsized, cement-based suspensions for impregnating carbon fiber yarns is initially conducted by Schneider et al. (2019), to replace the conventional polymeric-matrix composites. They observed that the maximum particle size of the suspension plays a crucial role in obtaining a uniform and homogenous impregnation quality and herewith optimum mechanical performance of MCF. In addition to providing raw materials with different proportions to enhance the performance of the impregnation suspension, special surficial modification of MCF structure also contributes to improving its mechanical properties, e.g., spiral profiling to the surface of MCF (Zhao et al., 2023a). It not only improves the shape stability and the fiber packing density of MCF but also enhances the bonding properties between the MCF and the surrounding concrete matrix. Due to the excellent electrical conductivity of carbon fibre yarns, the MCF also shows satisfactory conductivity, thereby possessing multifunctional capacities such as electrothermal heaters or thermoelectric generators. Studies have proposed the MCF-based multifunctional reinforcing grid-building material as a thermoelectric generator. The MCF-based grid exhibited a voltage output of 1.8 mV and a generated power of 22.3 nW upon exposure to the temperature difference of 50 K (Zhao et al., 2023b). Furthermore, the MCF-based grids embedded into concrete/geopolymer plate can be exploited as Joule heating devices for self-deicing applications in an efficient and low-power-consuming way. A former study revealed that the grid-reinforced concrete exhibited de- icing effectiveness at an applied DC voltage of 2.2 V, equivalent to a surface temperature of 45 °C with a notably low required heating power of 95.6 W/m 2 (Karalis et al., 2024). Electrically conductive cementitious composite materials have a strong potential to monitor external stress and deformation through piezoresistive or piezoelectric capacities (Dong et al., 2019a). Especially cementitious composites filled with discrete carbon fibres have been demonstrated its improved electrical conductivity and traffic monitoring capacities (Dong et al., 2022b). However, the feasibility of continuously reinforced carbon fibre yarns- cementitious composite for stress/strain sensing has never been reported, despite its technological and economic advantages compared to dispersed composite systems. In this study, MCF with excellent electrical conductivity are investigated with regard its potential for stress/strain sensing applications. The experiments for assessing the stress sensing capacity were tested by two different electrode configurations. The results will promote the on-site field applications of MCF, not only as effective structural reinforcements but also in the field of multifunctional concrete pavements or elements, to achieve smart concrete infrastructures. This study employed the commercially accessible Mikrodur R-X® and Mikrodur P-U® (Dyckerhoff®, Wiesbaden, Germany) micro-cement as the hydrating binder in the cement-based suspension, to impregnate the carbon yarns effectively. To attain a particle-size distribution within the desired fine size range, an EMSAC 500E micro-silica suspension (MBCC Group, Mannheim, Germany) was introduced. This suspension contains a solid content of around 50%. The incorporation of the naphthalene-sulfonate-based superplasticizer, Master Rheobuild 30 (BASF, Germany), at a dosage of 2% by mass of the suspension successfully achieved the desired viscosity essential for the impregnation process. The carbon fiber selected for this study was SIGRAFIL® C T50 – 4.4/255-E100, sourced from the SGL Group in Germany. This carbon fiber is composed of 50,000 individual filaments, each having a diameter of approximately 7 μm. The specific physical and electrical properties can be found in Table 1. To produce the MCF, the compositions of impregnation suspension are shown in Table 2. 2. Materials and preparations 2.1. Raw materials and mixture

Table 1. Basic properties of used carbon yarn (Schneider et al., 2019). Properties SIGRAFIL® C T50 – 4.4/255-E100