Figure 6 - uploaded by Marcus Perry
Content may be subject to copyright.
PCB of final ConcrEITS circuit with addressing wires. A UART to USB or UART to BLE module is used for data transmission.
Source publication
Concrete infrastructure requires continuous monitoring to ensure any new damage or
repair failures are detected promptly. A cost-effective combination of monitoring and maintenance would be highly beneficial in the rehabilitation of existing infrastructure. Alkali-activated materials have been used as concrete repairs and as sensing elements for te...
Context in source publication
Citations
... Among the alternative methods mentioned, coatings are rather versatile as they can be used to monitor both existing and new structures. In addition, they possess flexibility in terms of a) their geometry as they could be tailored to meet the dimensional requirements of each substrate, and b) their attachment method e.g. they could adhere to the substrate through both mechanical and chemical means (Vlachakis et al., 2023a;Gomaa et al., 2020;McAlorum et al., 2021). While limited compared to bulk applications, both geopolymers and OPC binders have been used in sensing coating applications. ...
... As such this makes these materials more suitable for monitoring compared to traditional ordinary Portland cement (OPC) binders. Consequently this has allowed geopolymers to be used in numerous filler-free applications measuring strain [7], damage [18], temperature [19], moisture [20], sodium chloride [21] and acids [22]. Despite their promising nature in self-sensing and monitoring applications, geopolymers are relatively under-researched when compared to OPC self-sensing binders. ...
... Low-cost electronic devices compatible with field conditions and wireless data transmission methods for real-time data processing and monitoring would also be required for such applications. While significant progress in this area has been made [18,70], further work is required to develop a more robust and holistic system to implement this sensing technology into the field. ...
Self-sensing cementitious materials are an effective method of monitoring existing infrastructure due to their high durability and high sensing performance. Geopolymers are ideal candidates for such applications due to their enhanced ionic mobility, high mechanical properties and compatibility with ordinary Portland cement structures. In this paper, self-sensing filler-free metakaolin geopolymer binders and coatings are explored under repeated compression. Polypropylene fibers were added to the mix design to tackle shrinkage issues making these materials more suitable for site and field applications. The sensing performance of metakaolin geopolymers is examined under various loading patterns and their strain sensing performance is characterized. The geopolymer sensors displayed high repeatability and stability under different loading regimes over multiple cycles. The gauge factor for non-fiber and fiber geopolymer binders ranged from 18.3 to 38.3. Similarly, the gauge factor for geopolymer coatings ranged from 20.7 to 43.2. Based on the findings of this study, these materials have displayed the potential as a viable means of monitoring civil infrastructure under repeated compression.
... Another approach for characterizing the electrical properties of the rubber compounds would be by assessing the electrical impedance, which can be achieved by applying an alternating current (ac) potential and then measuring the phase and amplitude ac voltage response current, which carries more information on the system. In particular, the impedance is a combination of the resistance and of the reactance, which measures the opposition of the system to changes in electric current [32]. ...
Elastomeric bearings are widely used in bridges to support the superstructure, to transfer loads to substructures, and to accommodate movements induced by, for example, temperature changes. Bearing mechanical properties affect the bridge’s performance and its response to permanent and variable loadings (e.g., traffic). This paper describes the research carried out at Strathclyde towards the development of smart elastomeric bearings that can be used as a low−cost sensing technology for bridge and/or weigh−in−motion monitoring. An experimental campaign was performed, under laboratory conditions, on various natural rubber (NR) specimens enhanced with different conductive fillers. Each specimen was characterized under loading conditions that replicated in−situ bearings to determine their mechanical and piezoresistive properties. Relatively simple models can be used to describe the relationship between rubber bearing resistivity and deformation changes. Gauge factors (GFs) in the range between 2 and 11 are obtained, depending on the compound and the applied loading. Experiments were also carried out to show that the developed model can be used to predict the state of deformation of the bearings under random loadings of different amplitudes that are characteristic of the passage of traffic over a bridge.
... Currently, several methods have been employed to measure the electrical resistivity of cement-based materials, which include the Wenner method [28][29], two-probe method [16,23], embedded four-probe method [10,14], impedance spectroscopy [22,30], and ASTM C1760-12 method [16]. Recently, more advanced techniques including electrochemical impedance spectroscopy (EIS) [31][32], electrical impedance tomography (EIT) [33][34], and electrical resistance tomography (ERT) [35][36] have also been employed to investigate the electrical properties of cementitious materials. EIS is a powerful technique to characterize the electrochemical property of cementitious materials by using alternate currents [31], however, it fails to assess the spatial variations of electrical resistivity within the specimen. ...
... EIS is a powerful technique to characterize the electrochemical property of cementitious materials by using alternate currents [31], however, it fails to assess the spatial variations of electrical resistivity within the specimen. Both EIT and ERT are soft-field imaging techniques using a set of boundary electrical measurements to estimate the distribution of electrical conductivity of the tested objects [34]. The main difference between EIT and ERT lies in that the capacitive nature of the tested material is considered in EIS [33]. ...
The electrical resistivity of cement-based materials is an important index that can be used for designing durable, multifunctional, and smart concrete structures. However, the measurement and prediction of electrical resistivity are far from being well addressed for cement-based materials. In this study, a modified four-probe test using embedded fine copper rods as electrodes was developed to measure the electrical resistivity of cement-based materials. A coupled thermal-electrical analysis was conducted to verify the feasibility of the modified four-probe method. The simulated results show that a linear relation between the electrical resistivity and the apparent electrical resistance. The contact resistance of the interface between the specimen and the electrodes has little effect on the electrical resistivity. The applied voltage ranging from 4 V to 28 V has a minor influence on the measured electrical resistivity. The electrical resistivity of the specimens cured under standard condition is greater than that under sealed condition. The electrical resistivity of cement-based materials cured under both sealed and standard conditions increases with increasing curing age. A higher volume fraction of sand contributes significantly to a higher electrical resistivity of cement-based materials. Moreover, the homogenization results indicate that the differential scheme predictions coincide quite well with the measured electrical resistivity of cement-based materials with a wide range of sand volume fractions (0%∼60%). The Voigt scheme, the self-consistent scheme, and the Mori-Tanaka scheme can predict well the electrical resistivity of cement-based materials with a low volume fraction of sand (<20%), but fail to give a good prediction at a higher sand content.
... Civil asset managers have a clear need for tools that reduce the costs and risks of concrete monitoring and maintenance, so that they can ensure the continued resilience of ageing critical infrastructure. Selfsensing cements may provide one pathway to improving efficiency, as they act as traditional concrete binders and repairs [1,2] while also encoding local changes in strain [3], damage [4], temperature [5] and moisture [6] as measurable shifts in their electrical impedance. Alkali activated materials (AAM) are a low-carbon alternative to ordinary Portland cements (OPC) that are particularly well-suited to self-sensing, as their inherently high electrical conductivity (~10 − 6 S/cm), negates the need to use electrically conductive additives [7][8][9]. ...
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.
... The performance of AACs is strongly influenced by different factors, such as the aluminosilicate source (precursor), alkaline source concentration (activator), and curing temperature. In previous literature, the production of AACs with self-sensing properties has been generally applied to the best-known conditions, with metakaolin [91][92][93][94], FA [95,96], and GGBFS [97] as the main precursors. There is great research potential to be explored in this area, since the migration of free alkaline ions resulting from the geopolymerization process is able to improve the conductivity of these composites [98], so that their application for production of SSCs is naturally advantageous. ...
The construction industry is currently facing the great challenge of applying sustainable materials with suitable mechanical properties and durability performance. Among the different strategies used to meet technical and sustainable criteria, two interesting approaches can be highlighted: the reuse of materials to produce sustainable construction materials and the development of smart concretes for Structural Health Monitoring. The first strategy consists of using recycled materials, co-products, and by-products of industrial processes to replace primary raw materials used to produce blocks, ceramics, mortars, and concrete. The second strategy is associated with the development of multifunctional cementitious and alkali-activated concretes with strain and damage self-sensing properties in response to the growing concerns related to the increase in the durability of civil structures. This paper presents a critical review of previous studies that combine both strategies, i.e., research works investigating smart construction materials that incorporate recycled and waste materials and exhibit self-sensing properties. Sustainable self-sensing composites (SSCs) incorporating different types of recycled and waste materials were presented. These sustainable admixtures provided different benefits to self-sensing composites, such as improvements in the conductive path within the matrices and improvements in the dispersion of other conductive fillers. The effects of silica fume, fly ash, steel slag, red mud, and other recycled materials on the electrical resistivity, strain-sensing properties, and damage-detection properties of SSCs were discussed. Promising SSCs were identified based on comparisons between gauge factor, stress sensibility, linearity, strain amplitude, and stress amplitude of SSCs produced with one single type of waste or combination of various types of wastes. In this sense, SSCs were found to be a viable alternative for modernization and greater sustainability of the construction industry.
... Recently, there is a great interest on the applications of FRP profiles to produce hybrid structural systems. FRP-concrete structures improve the benefits of materials by combining FRP, which is highly tensile resistant and lightweight with low-cost compressive-resistant concrete [6]. ...
Recent developments indicate that the application of pultruded FRP profiles has been continuously growing in the construction industry. Generating more complex structures composed of pultruded FRP profiles requires joining them. In particular, I-shape glass fiber pultruded profiles are commonly used and the possible joints to connect them should be specifically studied. The mechanical behavior of adhesively and bolted joints for pultruded Glass FRP (GFRP) profiles has been experimentally addressed and numerically modeled. A total of nine specimens with different configurations (bolted joints, adhesive joints, web joints, web and flange joints, and two different angles between profiles) were fabricated and tested, extending the available published information. The novelty of the research is in the direct comparison of joint technologies (bolted vs. adhesive), joint configuration (web vs. flange + web) and angles between profiles in a comprehensive way. Plates for flange joints were fabricated with carbon fiber FRP. Experimental results indicate that adding the bolted flange connection allowed for a slight increase of the load bearing capacity (up to 15%) but a significant increase in the stiffness (between 2 and 7 times). Hence, it is concluded that using carbon FRP bolted flange connection should be considered when increasing the joint stiffness is sought. Adhesively connections only reached 25% of the expected shear strength according to the adhesive producer if comparing the numerically calculated shear strength at the failure time with the shear strength capacity of the adhesive. Apart from assessing adhesive connections, the implemented 3D numerical model was aimed at providing a simplified effective tool to effectively design bolted joints. Although the accurate fitting between experimental and numerical results of the mechanical response, especially the stiffness of the joint, the local failure experimentally observed was not automatically represented by the model, because of the simplified definition of the materials oriented to make the model available for a wide range of practitioners.
Given the challenges we face of an ageing infrastructure and insufficient maintenance, there is a critical shift towards preventive and predictive maintenance in construction. Self-sensing cement-based materials have drawn interest in this sector due to their high monitoring performance and durability compared to electronic sensors. While bulk applications have been well-discussed within this field, several challenges exist in their implementation for practical applications, such as poor workability and high manufacturing costs at larger volumes. This paper discusses the development of smart carbon-based cementitious coatings for strain monitoring of concrete substrates under flexural loading. This work presents a physical, electrical, and electromechanical investigation of sensing coatings with varying carbon black (CB) concentrations along with the geometric optimisation of the sensor design. The optimal strain-sensing performance, 55.5 ± 2.7, was obtained for coatings with 2 wt% of conductive filler, 3 mm thickness, and a gauge length of 60 mm. The results demonstrate the potential of applying smart coatings with carbon black addition for concrete strain monitoring.
Achieving continuous in-situ monitoring of repaired concrete structures has always been a great challenge. Ultra-high performance fibre-reinforced concrete (UHPFRC), featuring superior mechanical capacity, excellent erosion resistance, and long-life cycle, is expected to realize durable, cost-effective, and aesthetically pleasing repairs and possesses tremendous potential for intrinsic self-sensing. This paper presents the multifunctionality of UHPFRC with integrated self-sensing and repair capabilities using multi-walled carbon nanotube (MWCNT). An experimental evaluation on the bond performance and self-sensing properties, including the bond strength and failure patterns by the three-point bending, splitting tensile, and slant shear tests, electrical properties via alternating current impedance spectroscopy test, and electromechanical properties under three-point bending, was conducted through the designed composite layer between concrete substrate and UHPFRC. The microstructure of the interfacial zone was analysed to reveal the bonding mechanism. Results indicate that the addition of MWCNT improved the bond strength between concrete substrate and UHPFRC as MWCNT can enhance the adhesion and cohesion of the interfacial zone through inactive filling effect, as well as the frictional and mechanical interlocks through increased mechanical properties of repair UHPFRC. Moreover, the repair UHPFRC showed remarkable sensing capabilities for the initial cracking, deflection hardening or softening, and fibre pull-out and debonding processes of the composite layers. The optimal content of steel fibre and MWCNT in multifunctional UHPFRC should be 2 vol.% and 0.2 wt.%, respectively, considering the synergistic damage sensing and bonding properties.
