In situ observation for the influence of hydraulic pressure on internal damage of cement-based materials

Abstract

The influence of hydraulic pressure (max. 20 MPa) on the internal damage of cement-based materials is experimentally studied. In order to observe in situ the internal damage of cement-based materials under hydraulic pressure, a new testing apparatus equipped with an X-ray micro-computed tomography (X-μCT) scanner is developed. The behaviors of water infiltration and strain development are evaluated for mortar specimens with different water-to-cement ratios. Although the internal damage of the mortar specimens under hydraulic pressure was not detected by the X-μCT scanner and fluorescent imaging, the mechanical properties tested after hydraulic pressure loadings were altered, indicative of the occurrence of microcracks (<50 μm) below the resolution of these observation techniques. It is concluded that the internal damage of mortar specimens under hydraulic pressure is strongly influenced by two mechanisms: hydraulic pressure as a mechanism of external confinement and water infiltration as a mechanism of stress relaxation. The volumetric strain development due to hydraulic pressure varies greatly with location, owing to heterogeneous water infiltration in mortar. Therefore, the balance of these two mechanisms must be taken into account to assess the risk of internal damage of cement-based materials under hydraulic pressure.

Keywords

• Cement-based materials
• Hydraulic pressure
• In-situ observation
• X-ray microcomputed tomography
• Image analysis