The objective of this study is to measure the interstitial pore pressure into saturated concrete under hundreds of megapascals of confinement. This study is carried out within a more general context aiming to understand the behavior of concrete structures under impact. It is well known that the water saturation in massive concrete structures evolves from quasi-dry state at the surface to reach a quasi-saturated state at the core. Since the response of these structures under impact is highly linked to the state of saturation into the material, it is suspected that the pore pressure plays a major effect. This paper presents a new testing technique developed to measure the concrete pore pressure at high confining pressure. This latter is generated by means of a high capacity GIGA press. The new concept consists in implementing a pressure sensor into a water collecting cap. This cap is designed specially to collect water from concrete subjected to mechanical confinement pressure. Experimental results show that concrete pore pressure can reach values of the order of the confining pressure.
Previous studies have shown the strong influence of free water saturation ratio on the triaxial behavior of concrete at high confinement. This influence of the free water is usually attributed to a pore pressure effect. This article presents an experimental method aiming at measuring the pore pressure of free water into concrete samples under very high mean stress. Two types of deformable pressure sensors were designed and tested. The first one works in hydrostatic compression while the second one acts as a flexible membrane. The two sensors give comparable results and show that pore pressure may reach several hundred MPa in saturated concrete sample under a maximum 400 MPa hydrostatic compression. Such levels of pressure may explain the loss of shear strength and increase in volumetric stiffness observed on the macroscopic behavior of concrete due to the presence of free water.
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