Impact of saturating fluids on mode-I fracture toughness of a porous siliceous sandstone and a granitic rock

Fluids affect the mechanical behavior of geomaterials and a number of experimental evidences are available to describe their impact over relevant properties such us unconfined compression strength, brittleness, etc. However, the impact of saturating fluids (either reactive or not) over fracture toughness has not received much attention so far. In this contribution we have performed a series of mode-I fracture toughness tests employing the pseudo-compact tension test (pCT) approach and two types of rock: a porous siliceous sandstone (Corvio) and a high-strength, low porosity granite (Blanco Mera). The pCT test configuration is advantageous to this respect because it allows the insertion of the sample into a fluid bath that keeps the sample saturated all along the experiment. Taking as reference the results obtained in dry tests, specimens of the two selected lithologies were tested under identical experimental conditions (diameter, thickness, depth of notch, room temperature, loading rate, etc.). We have used different saturating fluids to explore their impact over fracture toughness: 1) deionized water; 2) seawater; 3) NaCl-saturated water; 4) mineral oil; 5) diesel fuel; 6) an acidic HCl solution; and 7) a caustic NaOH solution. Acoustic emissions were also monitored during the execution of the test. In the presentation we will illustrate the results obtained and discuss the associated implications.