PSI - Issue 13

Yoshitaka Nara et al. / Procedia Structural Integrity 13 (2018) 222–225 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

223

2

1. Introduction

Silicate rock masses are used for various geomechanical and engineering purposes. Therefore, investigating the fracturing in silicate rock, especially time-dependent fracturing, is crucial to consider the long-term integrity of silicate rock mass surrounding structures. Subcritical crack growth (SCG) is one of the main causes responsible for the time-dependent behaviors in rocks (Atkinson, 1984). SCG was initially attributed to stress corrosion, which is the chemical reaction between siloxane at the crack tip under tension and water (Anderson and Grew, 1977). It is well-known that SCG in silicate rock is influenced by the surrounding environment. Nara et al. (2010, 2011) reported that the crack velocity in igneous rocks and sandstones in air increases as the temperature and/or relative humidity increases. According to Nara et al. (2009), the crack velocity in water was much higher than that in air. Nara et al. (2014) reported that the crack velocity in sandstone in salt water with 1 mol/l electrolyte concentration was the lowest. Considering the construction of structures using a rock mass such as an underground repository of radioactive waste and underground power plant, numerous amounts of cementitious materials will be used. The calcium ion concentration in water in the surrounding rock mass should be high. Therefore, Nara et al. (2018a) studied SCG in granite in water under different calcium ion concentrations. Since the influence of calcium ions on SCG in sedimentary rock has not been studied yet, it is thus important to measure SCG in sedimentary rock and to investigate the influence of calcium ions to ensure the long-term stability of the sedimentary rock mass. In this study, SCG in distilled water and a calcium hydroxide (Ca(OH) 2 ) solution was investigated using Berea sandstone (Nara et al., 2011, 2012, 2014) to clarify the influence of calcium ions on SCG. Especially, the difference of the crack velocity in distilled water and a calcium hydroxide solution was investigated. We used the double-torsion (DT) method to measure the crack velocity and stress intensity factor. Especially, we used the load relaxation (RLX) method (Evans, 1972; Williams and Evans, 1973). The RLX method gives a wide range of data for the relationship between the stress intensity factor and the crack velocity, generally from 10 -2 to 10 -9 m/s in a single experimental run. The loading configuration of DT method is shown in Fig. 1. In this study, we set the width W , the length L , the thickness d , and the reduced thickness d n at 55, 145, 3.5, and 2.5 mm, respectively. The depth of the guide groove was 1 mm. A photo of the experimental apparatus is shown in Fig. 2. This apparatus was set in a room where the temperature and the relative humidity could be controlled and kept constant. Therefore, all measurements in this study have been conducted under a controlled temperature condition. 2. Methodology

Fig.1 Illustration of specimen and loading configuration. 㻌

Fig.2 Photo of experimental apparatus. 㻌