Abstract

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.

Highlights

  • The purpose of this study was to design an efficient sensor to measure the concrete interstitial pore pressure at high confining pressure

  • The pore pressure was calculated by using Equation (4c), where the total deformation of the sensor et was measured by means of the gauge, the applied confinement p was provided from the Giga press confining cell pressure sensor and Kd and K p were identified from the calibration tests

  • The concrete pore pressure measured by the Hydrostatic Sensor (HS) and Membrane Sensor (MS) sensors remained at a quasi-null value until 40 MPa of confinement pressure

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Summary

Introduction

The purpose of this study was to design an efficient sensor to measure the concrete interstitial pore pressure at high confining pressure. A research program was launched in 2004 aiming at characterizing concrete triaxial behavior under high confinement pressure in quasi-static conditions with the Giga press (Section 2.1). Sci. 2019, 9, 2610 concrete increases linearly with the confining pressure, while the shear strength of saturated concrete exhibits a plateau These studies have shown that the presence of free water inside concrete pores has a preponderant role on its behavior under high confinement. A fluid pump equipped with valves and pressure transducer was used by the authors of [19,20], who estimated the permeability and the Biot’s coefficients for tight and Bakken rocks Such systems concern moderate stress levels and cannot be adapted to the Giga press since it would require considerable modifications. The sensors validation (Section 6) demonstrates the capability of this novel technique to measure the interstitial pore pressure into concrete under high level of confinement pressure

Giga Press Overview
Drainage System
Pressure Sensor Concept and Design
Geometry and Design
Loading and Boundary Conditions
Effect of Interstitial Pore Pressure
Effect of the Confining Pressure on the Sensor
Sensors Calibration Tests
HS Calibration
MS Calibration
HS and MS Signals Comparison
Validation of Sensors for the Measurement of Concrete Pore Pressure
Conclusions and Outlooks
Methods
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