PSI - Issue 64

Amrita Milling et al. / Procedia Structural Integrity 64 (2024) 1009–1016 Milling/ Structural Integrity Procedia 00 (2024) 000 – 000

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1. Introduction Textile-reinforced mortar (TRM) composites are well recognised for their pseudo-ductile behaviour, high tensile strength and energy absorption capacity (de Andrade Silva et al. 2011; Peled et al. 2017). These favourable characteristics render them suitable for retrofitting and reinforcing structures, particularly when subjected to dynamic loading. A comprehensive series of experiments has been carried out to study the tensile properties of TRM composites. RILEM Technical Committee 250-CSM conducted a round-robin test to advance the knowledge of TRM tensile behaviour and develop methodologies for direct tensile testing (Brameshuber et al. 2016). Furthermore, several test standards/guidelines have been developed to characterise the tensile behaviour of these composites (ACI Committee 434 2011; Ascione et al. 2018; Brameshuber et al. 2016). Despite these notable efforts, the tensile behaviour of TRMs at medium to high strain rates is ambiguous since most contributions in the field were performed under quasi-static loadings. The tensile mechanical behaviours of TRMS at quasi-static conditions were found to be markedly different from those observed under medium to high strain rates. At quasi-static and intermediate strain rates, TRMs typically display bi-linear or tri-linear stress-strain relationships (Truong et al. 2022). However, linear elastic behaviours up to the peak stress have been reported for strain rates above 9/s. Zhu et al. (2011) found that polyethylene (PE) and alkali-resistant (AR) glass TRMs tested at 9-28/s displayed linear elastic behaviours up to the peak stress; then, they failed brittle as their strengths were immediately reduced. Gong et al. (2019) found that carbon TRM tested in the 150-160/s range displayed linear elastic behaviour up to the first crack, followed by strain softening. Linear elastic behaviour followed by strain softening and multiple cracking were reported for carbon (Zhu et al. 2011) and glass (Truong et al. 2022) TRM in the 9-11/s and 31-51/s ranges, respectively. In general, the composites tested at a dynamic rate, except Zhu et al. (2011) carbon composite, had a higher tensile capacity but reduced maximum strain compared to those under quasi static loading. Of the few studies conducted, it is evident that the TRM dynamic tensile behaviour is greatly influenced by the type and properties of the fibre reinforcement (textile and short fibres) (Truong et al. 2022; Zhu et al. 2011), the nature of the mortar (Gong et al. 2019) and the interfacial characteristics of fibre reinforcement with the surrounding matrix. However, a wide gap exists in understanding the compounded effect of strain rate with these parameters on the tensile characteristics, primarily due to difficulties in obtaining reliable data using dynamic testing approaches. Hydraulic machines and Split Hopkinson bar equipment (SHTB) are commonly used to perform TRM direct tensile dynamic tests. Both pieces of equipment present challenges such as establishing stress equilibrium, synchronisation and data acquisition issues, and load cell ringing (Gong et al. 2019; Heravi et al. 2019; Zhu et al. 2011). Nevertheless, Zhu et al. (2011) reported a reasonably uniform tensile behaviour for all composites tested with an MTS servohydraulic machine, demonstrating the reliability of the high-speed test method. In addition, Heravi et al. (2019) and Gong et al. (2019) overcame the challenge of obtaining stress equilibrium and measuring the correct stress and strain in the samples by using aluminium adapters to connect the samples to the tension bars. Additionally, the use of high-speed apparatus raises the concern of specimen suitability. The recommended specimen sizes for quasi-static tests are typically too large, making it challenging to obtain dynamic equilibrium, particularly when employing split Hopkinson bar equipment (Heravi et al. 2019). As a result, TRM dynamic specimens that allowed for achieving dynamic equilibrium have not exceeded 150mm in length. Although smaller specimens demonstrated satisfactory performance in dynamic testing, comparative analyses uncovered undesirable failure mechanisms and atypical stress-strain behaviour when subjected to quasi-static loading (Gong et al. 2019; Heravi et al. 2019). The results reported in the paper are part of a more extensive study in which the dynamic mechanical characteristics of basalt TRM, its constituents, and reinforced structures are explored. Only the tensile characteristics of basalt textile reinforced mortar (BTRM) at dynamic loading rates of 0.5 to 10/s are presented in this paper. Even though basalt has been trending as the preferred reinforcement type, the dynamic tensile behaviour of BTRM composites has not yet been investigated. Moreover, the behaviour of TRMs in the low-intermediate strain rate range is unexplored. The BTRM composite consisted of a bi-directional basalt fibre textile and a commercially available mortar strengthened with short glass fibres. Coupon specimens with aluminium tabs were tested with high-speed servohydraulic equipment. Strain and failure propagation were captured with a high-speed camera and analysed by the digital image correlation