International Concrete Abstracts Portal

Environmental factors are major considerations of health monitoring of structures. A new system has been developed for measuring the internal relative humidity and temperature in concrete laboratory specimens and field structures. Internal relative humidity measurements in concrete are useful for evaluating shrinkage stress development and assessing structural susceptibility to durability problems. This paper describes the system, presents the essential elements of analysis that relates RH to internal stress in porous materials, and presents field applications that shows how environment data can facilitate analysis of stress and deformation of pavement. The new system has been used in laboratory and field experiments. Advantages of the new system are summarized. Some problems encountered in measuring relative humidity, especially in the field, are discussed.

Traditional methods of condition assessment frequently rely on manual inspections of a structure to locate signs of aging and deterioration. In comparison, the sensor-based health monitoring shows several advantages including increased accuracy and frequency of the measurements, possibility of remote sensing, and ability to determine the rate of damage and remaining life of a structure. Although the embedded electrical sensors provide valuable measurements enabling prediction of concrete durability, proper calibration of the measurements is essential. As an example, the electrical conductivity measurements of concrete are shown to be simultaneously influenced by four parameters: (a) concrete microstructure, (b) pore fluid composition, (c) moisture content, and (d) temperature. Experimental evidence is provided suggesting that the sensor measurements must be calibrated to account for these parameters; otherwise, the results can be misleading. A combination of several sensors can provide the information needed for proper calibration of the measurements. Several sensors have been developed to monitor the durability of concrete. Among these, a series of electrical/electro-chemical sensors have been recently introduced that enable measuring the transport properties of concrete as well as monitoring the corrosion process of the reinforcing steel. In his paper, several types of such electrical sensors are introduced and the theoretical background behind each measurement is discussed. For example, it is shown that measurement of the electrical conductivity of concrete can be used to estimate the permeability, ion diffusivity, or moisture content of concrete.

Routine management and maintenance of civil infrastructure is undertaken based on structural health indicators from qualitative information gathered during inspections. The need to measure and collect data reflective of the true state of the infrastructure is crucial for proper management of the system. Presented in this paper are methods for incorporating field measurements for improved condition assessment. A full scale field deployment of a wireless, lowcost and automatic system for structural health management and condition assessment of highway structures is shown to demonstrate the ability of obtaining the necessary behavior characteristics. A short-span integral-abutment bridge was instrumented with a developed wireless sensor system measuring strain, in real time through a single network, monitoring the behavior of the structure under various loading conditions. Measurements validated the performance characteristics of the bridge, including transverse moment distribution, end fixity, and composite action of the girders and bridge deck.

This paper provides an overview of three different instrumentation schemes used to monitor long term performance of FRP repaired piles in tidal waters. These schemes were evaluated in four demonstration projects extending nearly five years. Two of these used linear polarization to estimate the corrosion rate while the third focused on the variation in the corrosion current. Problems associated with selection, installation and monitoring are described and representative results presented from all three systems. The results suggest data from linear polarization is more consistent. Findings indicate FRP wrapping lowers the prevailing corrosion rate.

In this research, a series of innovative optically-based sensors, which were designed, fabricated and characterized were created for potential evaluation for applications in determining moisture ingress in a range of concrete materials subjected to various environmental conditions. The approach taken to the creation of these novel humidity sensors is using long period grating (LPG) technology in an optical fibre. Several sensor configurations are fabricated by coating LPGs and then characterizing and cross-comparing and evaluating the resulting sensor performance. The thin layer of polyvinyl alcohol (PVA), whose refractive index varies as a function of humidity level when coated onto a LPG written into an optical fibre, provides a means to change the optical propagation in the fibre and thus to induce the a wavelength shift in the attenuation bands of its transmission spectrum, which then is calibrated against the measurand, humidity. When compared to the more familiar optical fibre-based humidity sensors, using Fibre Bragg gratings (FBGs), the LPG-based devices show a much higher measurement sensitivity, with more relaxed requirements for coating thickness and uniformity.