PSI - Issue 42

Martina Drdlová et al. / Procedia Structural Integrity 42 (2022) 1391–1397 Drdlova et al/ Structural Integrity Procedia 00 (2022) 000 – 000

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Keywords: RPC; Reactive powder concrete; SHPB; high strain rate;

1. Introduction Reactive powder concrete is specific type of ultra-high performance concrete (UHPC). The term ‘reactive powder’ in general refers to the idea that powder components in the concrete react chemically (Ahmed, et al. 2021). Regarding the parameters, it exhibits high compressive and tensile strength (more than 150 and 20 MPa respectively); Abid et al. (2017) and Ahmad et al. (2015) reported also high fracture energy in range of 12-40 kJ/m 2 , modulus of rupture between 25-150 MPa and great durability. These properties are connected with the absence of coarse aggregates, reduced w/c ratio, fiber inclusion, higher cement content, the presence of ultrafine SiO 2 particles, optimized S/C ratio and particle packing.

Nomenclature RPC

Reactive powder concrete SHPB Split Hopkinson Pressure Bar S SiO2 C CaO UHPC Ultra-high performance concrete f c dyn Dynamic compressive strength DIF Dynamic increasing factor f c ds Quasi-static compressive strength

The properties of RPC can be modified to high extent by the selection of the production technology and the curing regime. The traditional method of curing cement precast elements is thermal and hydrothermal treatment. Hydrothermal treatment allows to start and accelerate the pozzolana reaction of quartz powder included in RPC with subsequent material parameters improvement. Several studies have been performed assessing the influence of curing regimes on the parameters of the RPC, e.g. by Hiremath (2017), Mostofinejad (2016) and Xun (2020), which reported higher effectivity of hot air curing compared to hot water curing in achieving better mechanical resistance. Yazici et al. (2013) investigated the effect of autoclave pressure, temperature and duration time on the mechanical properties of RPC. He reported a 63% increase in the compressive strength when the autoclaving process was applied to specimens containing SF and fibres. The ideal regime to achieve the highest compressive strength has been determined 2 MPa and 10 hours. The previous studies show that the mechanical parameters are highly dependent on the temperature and duration of the curing regime. Although comparing different studies may be difficult due to variations in materials used and curing parameters, it can be generally concluded that autoclaving improves the strength the most, followed by hot water curing, hot air curing, and steam curing (Ahmed, 2021). While treatment methods have received considerable attention in research on the properties of RPCs, the mixing method and production technology have been overlooked so far. Only one study regarding the evaluation of both the mixing technology and curing regimes on the mechanical parameters of RPC has been found – the effect of vacuum mixing and curing conditions on mechanical properties and porosity of RPC was studied by Zdeb (2019). However, this study was focused on materials characteristics obtained under a quasi-static loading regime and did not cover the mechanical properties at high strain rates. The material's response at a high strain rate load can differ compared to quasi-static conditions. Therefore, it is crucial to determine the dynamic behaviour of RPC because of its potential to be applied in protective engineering. Recently, the research on RPC behaviour at high strain rates has been focused on determining the effect of composition, type and amount of reinforcing fibres on the final mechanical properties. In contrast, the influence of production technology and curing regime has not been investigated. The presented research contributes to the findings in the area and enlarges the knowledge necessary for designing protective structures based on RPC composites.