Insitu electrical sensing and material health monitoring in concrete structures
Abstract
While several structural health monitoring methods are available for assessing the applied loads, displacements, stresses, and strains in a concrete structure, very few techniques are available to enable condition assessment from a material durability viewpoint. Material health monitoring provides a valuable tool in assessing the current durability condition of a concrete structure (i.e., diagnosis), determining if and what preventative measures need to be taken to reduce future maintenance (i.e., prescription), and evaluating the remaining life and the future performance of the material (i.e., prognosis). The objective of this research is development of a new material sensing system that is designed to measure several properties and state parameters of concrete necessary for evaluation of the material's performance. This sensing system is composed of three electrical conductivity-based sensors and a temperature sensor. The electrical sensors include a concrete conductivity (σ t) sensor (that monitors setting and hardening and measures microstructural and transport properties of concrete), a pore solution conductivity (σ o) sensor (that monitors changes in the internal chemistry of the system due to ion penetration or carbonation), and a conductivity-based relative humidity (RH) sensor (to monitor moisture transport and shrinkage of the material). The temperature (T) sensor enables determination of the rate of hydration and strength development of concrete while it provides information needed for temperature calibration of the electrical sensors. It is shown that the combined measurements of the three electrical sensors and the temperature sensor provide sufficient calibration information that enables determination of the desired material properties and state parameters of concrete. This document provides a comprehensive description of several phases of the process used for development of the three conductivity-based sensors. To develop the prototype of these sensors, the mechanism of electrical conduction inside concrete and similar porous materials must be well understood. Several composite conductivity models are studied in this research to describe changes in the electrical conductivity of hydrating cement systems and specimens exposed to drying. It is concluded that the electrical conductivity of concrete is a function of the composition (i.e., ion concentrations), volume fraction, and connectivity of the material's liquid phase (i.e., liquid filled pores).
Degree
Ph.D.
Advisors
Weiss, Purdue University.
Subject Area
Civil engineering|Materials science
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