Concrete Crack Detection and Monitoring Using a Capacitive Dense Sensor Array

Cracks in concrete structures can be indicators of important damage and may significantly affect durability. Their timely identification can be used to ensure structural safety and guide on-time maintenance operations. Structural health monitoring solutions, such as strain gauges and fiber optics systems, have been proposed for the automatic monitoring of such cracks. However, these solutions become economically difficult to deploy when the surface under investigation is very large. This paper proposes to leverage a novel sensing skin for monitoring cracks in concrete structures. This sensing skin is constituted of a flexible electronic termed soft elastomeric capacitor, which detects a change in strain through changes in measured capacitance. The SEC is a low-cost, durable, and robust sensing technology that has previously been studied for the monitoring of fatigue cracks in steel components. In this study, the sensing skin is introduced and preliminary validation results on a small-scale reinforced concrete beam are presented. The technology is verified on a full-scale post-tensioned concrete beam. Results show that the sensing skin is capable of detecting, localizing, and quantifying cracks that formed in both the reinforced and post-tensioned concrete specimens

3D printed cement-based repairs and strain sensors

This paper presents 3D printed strain sensors based on alkali activated cement repairs, demonstrating a fixed-cost method for remotely deploying a combined monitoring and maintenance technology for construction. Experimental protocols to quantitatively assess the compatibility of cements and 3D printing processes are defined and investigated in this paper. The strain sensing response of printed self-sensing cements is then investigated under compression and tension by monitoring changes in material electrical impedance. Gauge factors for self-sensing repairs printed onto concrete substrates were 8.6 ± 1.6 under compression, with an average adhesion strength of 0.6 MPa between printed repair and concrete substrate. Gauge factors for repairs printed onto glass fibre reinforced polymers were 38.4 ± 21.6 under tension: more variable than for concrete substrates due to incompatibilities between the repair and the polymer substrate. This proof-of-concept is a step towards monitoring and maintenance methods that are more compatible with the time and cost drivers of modern construction

Durability and weatherability of a styrene-ethylene-butylene-styrene (SEBS) block copolymer-based sensing skin for civil infrastructure applications

Structural health monitoring of civil infrastructure requires low-cost, scalable, long-term, and robust sensing technologies due to the size and complexity of the geometries under consideration. This paper investigates the durability and weatherability of a large area sensing skin engineered for civil infrastructure applications. This sensing skin is based on a soft elastomeric capacitor made of three thin layers based on an SEBS block co-polymer matrix. The inner layer is filled with titania and acts as the dielectric, while the external layers are doped with carbon black and work as the conductive plates. In this work, a variety of specimens, including the dielectric layer without the conductive plates, were fabricated and tested within an accelerated weathering chamber by simulating thermal, humidity, and UV radiation cycles. Beyond the accelerated weathering tests, a sensor deployed on a bridge in Iowa for six and a half years was removed from the field and analyzed in the laboratory. A variety of other tests were performed in order to characterize the specimens’ mechanical, thermal, optical, and electrical performance. Additionally, strain sensitivity analyses were performed on specimens of interest. Results showed that titania inclusions improved the sensor dielectric\u27s durability against weathering, while the carbon black doped conductive layers provided the skin sensor with a high level of durability and weatherability protection. The results in this work contribute to a better understanding of the degradation of SEBS-based matrices as well as the behavior of these skin sensors when deployed for the monitoring of civil infrastructure

3D printed alkali-activated sensors for civil infrastructure

Multifunctional cement-based materials have seen increasing interest in structural health monitoring due to their high sensing performance. While these materials typically involve the fabrication of large construction elements, smaller sensing patches can be deployed onto existing surfaces as an alternative means of monitoring. This thesis presents the development of 3D printed self-sensing alkali-activated material patches for monitoring the strain and temperature of concrete substrates. Changes in the inherent ionic conductivity of metakaolin-based alkali-activated material patches are used to demonstrate sensing and monitoring of infrastructure without the need to use electrically conductive fillers. The additive manufacturing, meanwhile, presents a convenient method of improving the repeatability and economic viability of deploying self-sensing materials in construction contexts. The work in this thesis includes first time demonstration of 3D printed alkali-activated sensors for temperature and strain monitoring and outlines the current state of the art on self-sensing alkali activated materials. The fabrication, development, automated deployment, and sensing performance in strain and temperature of these novel materials are investigated throughout this thesis and the final printing design requirements are compared to applications that use additive manufacturing to produce construction elements. By combining a monitoring and maintenance technology with an automated approach to deployment, the work carried out as part of this thesis addresses important barriers to the implementation of civil structural health monitoring & maintenance technologies. It is the author’s hope that the work outlined here eventually leads to an enhanced uptake of structural health monitoring by the construction sector. This will allow for prioritised maintenance of the ageing and degrading civil assets that currently underpin infrastructures across Europe and the US.Multifunctional cement-based materials have seen increasing interest in structural health monitoring due to their high sensing performance. While these materials typically involve the fabrication of large construction elements, smaller sensing patches can be deployed onto existing surfaces as an alternative means of monitoring. This thesis presents the development of 3D printed self-sensing alkali-activated material patches for monitoring the strain and temperature of concrete substrates. Changes in the inherent ionic conductivity of metakaolin-based alkali-activated material patches are used to demonstrate sensing and monitoring of infrastructure without the need to use electrically conductive fillers. The additive manufacturing, meanwhile, presents a convenient method of improving the repeatability and economic viability of deploying self-sensing materials in construction contexts. The work in this thesis includes first time demonstration of 3D printed alkali-activated sensors for temperature and strain monitoring and outlines the current state of the art on self-sensing alkali activated materials. The fabrication, development, automated deployment, and sensing performance in strain and temperature of these novel materials are investigated throughout this thesis and the final printing design requirements are compared to applications that use additive manufacturing to produce construction elements. By combining a monitoring and maintenance technology with an automated approach to deployment, the work carried out as part of this thesis addresses important barriers to the implementation of civil structural health monitoring & maintenance technologies. It is the author’s hope that the work outlined here eventually leads to an enhanced uptake of structural health monitoring by the construction sector. This will allow for prioritised maintenance of the ageing and degrading civil assets that currently underpin infrastructures across Europe and the US

Strain Transfer for Optimal Performance of Sensing Sheet

Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sensors designed to enable reliable early-stage detection of local unusual structural behaviors. Such a device consists of a dense array of strain sensors, patterned onto a flexible polyimide substrate along with associated electronics. Previous tests performed on steel specimens equipped with sensing sheet prototypes and subjected to fatigue cracking pointed to a potential issue: individual sensors that were on or near a crack would immediately be damaged by the crack, thereby rendering them useless in assessing the size of the crack opening or to monitor future crack growth. In these tests, a stiff adhesive was used to bond the sensing sheet prototype to the steel specimen. Such an adhesive provided excellent strain transfer, but it also caused premature failure of individual sensors within the sheet. Therefore, the aim of this paper is to identify an alternative adhesive that survives minor damage, yet provides strain transfer that is sufficient for reliable early-stage crack detection. A sensor sheet prototype is then calibrated for use with the selected adhesive

Strain Transfer for Optimal Performance of Sensing Sheet.

Sensing sheets based on Large Area Electronics (LAE) and Integrated Circuits (ICs) are novel sensors designed to enable reliable early-stage detection of local unusual structural behaviors. Such a device consists of a dense array of strain sensors, patterned onto a flexible polyimide substrate along with associated electronics. Previous tests performed on steel specimens equipped with sensing sheet prototypes and subjected to fatigue cracking pointed to a potential issue: individual sensors that were on or near a crack would immediately be damaged by the crack, thereby rendering them useless in assessing the size of the crack opening or to monitor future crack growth. In these tests, a stiff adhesive was used to bond the sensing sheet prototype to the steel specimen. Such an adhesive provided excellent strain transfer, but it also caused premature failure of individual sensors within the sheet. Therefore, the aim of this paper is to identify an alternative adhesive that survives minor damage, yet provides strain transfer that is sufficient for reliable early-stage crack detection. A sensor sheet prototype is then calibrated for use with the selected adhesive