Weijie Li

Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method

Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs.

Corrosion detection of steel reinforced concrete using combined carbon fiber and fiber Bragg grating active thermal probe

Steel reinforcement corrosion is one of the dominant causes for structural deterioration for reinforced concrete structures. This paper presents a novel corrosion detection technique using an active thermal probe. The technique takes advantage of the fact that corrosion products have poor thermal conductivity, which will impede heat propagation generated from the active thermal probe. At the same time, the active thermal probe records the temperature response. The presence of corrosion products can thus be detected by analyzing the temperature response after the injection of heat at the reinforcement-concrete interface. The feasibility of the proposed technique was firstly analyzed through analytical modeling and finite element simulation. The active thermal probe consisted of carbon fiber strands to generate heat and a fiber optic Bragg grating (FBG) temperature sensor. Carbon fiber strands are used due to their corrosion resistance. Wet-dry cycle accelerated corrosion experiments were performed to study the effect of corrosion products on the temperature response of the reinforced concrete sample. Results suggest a high correlation between corrosion severity and magnitude of the temperature response. The technique has the merits of high accuracy, high efficiency in measurement and excellent embeddability.

Feasibility study of using smart aggregates as embedded acoustic emission sensors for health monitoring of concrete structures

Acoustic emission (AE) is a nondestructive evaluation technique that is capable of monitoring the damage evolution of concrete structures in real time. Conventionally, AE sensors are surface mounted on the host structures, however, the AE signals attenuate quickly due to the high attenuation properties of concrete structures. This study conducts a feasibility study of using smart aggregates (SAs), which are a type of embedded piezoceramic transducers, as embedded AE sensors for the health monitoring of concrete structures. A plain concrete beam with two surface mounted AE sensors and two embedded SAs was fabricated in laboratory and loaded under a designed three-point-bending test. The performance of embedded SAs were compared with the traditional surface mounted AE sensors in their ability to detect and evaluate the damage to the concrete structure. The results verified the feasibility of using smart aggregates as embedded AE sensors for monitoring structural damage in concrete. Potentially, the low cost smart aggregates could function as embedded AE sensors, providing great sensitivity and high reliability in applications for the structural health monitoring of concrete structures.

Acoustic emission monitoring and finite element analysis of debonding in fiber-reinforced polymer rebar reinforced concrete:

The acoustic emission technique is widely used for mechanical diagnostics and damage characterization in reinforced concrete structures. This article experimentally investigated the feasibility of debonding characterization in fiber-reinforced polymer rebar reinforced concrete using acoustic emission technique. To this end, carbon-fiber-reinforced polymer rebar reinforced concrete specimens were prepared and they were subjected to pullout tests to study the interfacial debonding between concrete and reinforcement. Test results showed that the debonding failure between concrete and reinforcement was characterized by the total peeling off of the helical wrapping layer of the carbon-fiber-reinforced polymer reinforcement. The response of acoustic emission activity was analyzed by descriptive parameters, such as cumulative acoustic emission hits, amplitude, and peak frequency. The evolution of debonding failure is thus characterized by these acoustic emission parameters. The results demonstrated a clear correlation between the damage evolution of carbon-fiber-reinforced polymer rebar pullout and the acoustic emission parameters. In addition, finite element analysis was adopted to study the stress field during the pullout of the reinforcement. The simulation results agreed well with the experimental investigations.

Interfacial debonding detection in fiber-reinforced polymer rebar–reinforced concrete using electro-mechanical impedance technique

For reinforced concrete structures, the use of fiber-reinforced polymer rebars to replace the steel reinforcement is a topic that is receiving increasing attention, especially where corrosion is a serious issue. However, fiber-reinforced polymer rebar–reinforced concrete always carries the risk of structural failure initiated from the debonding damage that might occur at the reinforcement–concrete interface. This study employed an electro-mechanical impedance–based structural health monitoring technique by applying lead–zirconate–titanate ceramic patches to detect the debonding damage of a carbon fiber–reinforced polymer rebar reinforced concrete. In the experimental study, a carbon fiber–reinforced polymer rebar reinforced concrete specimen was fabricated and it was subjected to a pullout test to initiate the debonding damage at the reinforcement–concrete interface. The impedance and admittance signatures were measured from an impedance analyzer according to the different debonding conditions between the reinforcement and the concrete. Statistical damage metrics, root-mean-square deviation and mean absolute percentage deviation, were used to quantify the changes in impedance signatures measured at the lead–zirconate–titanate patches due to debonding conditions. The results illustrated the capability of the electro-mechanical impedance–based structural health monitoring technique for detecting the debonding damage of fiber-reinforced polymer rebar–reinforced concrete structures.

Interlayer Slide Detection Using Piezoceramic Smart Aggregates Based on Active Sensing Approach

Interlayer slide is a common type of damages in geological and civil engineering. Interlayer slide damage is an internal cause of landslide and collapse, which may further result in catastrophic losses. It is desirable to develop a real-time monitoring system that is able to detect this kind of damage. In this paper, an experimental feasibility study on interlayer slide detection using piezoceramic smart aggregates based on the active sensing approach was performed. A mortar specimen, sandwiched with a weak interlayer, was fabricated before conducting the loading test. Two pairs of smart aggregates were installed at specific positions inside of the formwork before pouring the mortar. With the embedded piezoceramic patch transducers, the smart aggregates possess both the actuation and sensing functions. Two smart aggregates were employed as actuators, which generated the stress wave to propagate through the weak interlayer. The other two smart aggregates were used as sensors to receive the wave responses. In addition, a wavelet packet analysis was applied to develop a damage index to assess the initiation and development of the interlayer slide. Experimental results show that the proposed method was able to detect the interlayer slide damage.

Electro-Mechanical Impedance (EMI) Based Interlayer Slide Detection Using Piezoceramic Smart Aggregates—A Feasibility Study

Interlayer slide damage is one of the main causes of landslide hazard, inflicting huge economic losses and casualties. It is urgent to accurately detect the initiation and development of the interlayer slide damage in real time. In this paper, a study on the feasibility of using the electro-mechanical impedance (EMI) technique to detect the interlayer slide damage was presented. The main purpose of this paper is to investigate the application of the EMI technique for interlayer slide detection using piezoceramic smart aggregates (SAs). In the experimental study, three small landslide specimens with a weak interlayer in the middle were fabricated. For each specimen, three piezoceramic SAs were post-embedded at specific positions, which were located above the weak interlayer inside the structure. The specimens were subjected to a compressive test to initiate an interlayer slide along the weak layer. The whole loading process was monitored with a precision impedance analyzer by measuring the admittance (reciprocal of impedance) of the SAs over time. The statistic metrics, including root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD), were introduced to quantify the variations in admittance signatures due to interlayer slide damage. It was found that the admittance signatures and statistic metrics were sensitive to the interlayer slide damage. The experimental results verify the feasibility and practicality of using EMI technique to detect the interlayer slide.