@article{rashetnia_ghasemzadeh_hallaji_pour-ghaz_2018, title={Quantifying prestressing force loss due to corrosion from dynamic structural response}, volume={433}, ISSN={["1095-8568"]}, DOI={10.1016/j.jsv.2018.07.012}, abstractNote={In prestressed concrete structures, corrosion of prestressing strands is a major durability concern. In advanced stages, corrosion may result in the rupture of strands. At early stages, corrosion of strands results in microcracking, deterioration of bond between strands and concrete, and therefore, in the loss of prestressing force. These effects, in turn, result in the change of dynamic response of prestressed elements. In this paper, we investigate whether the prestressing force of prestressed beams can be estimated indirectly using dynamic vibration test. For this purpose, six prestressed concrete beams were manufactured. Two beams were kept as control, two beams were corroded along the entire length of the strand, and two beams were corroded along one-third of the strand length. The induced accelerated corrosion was monitored by corrosion current measurements and passive acoustic emission. Two system identification approaches were developed where both utilize the free vibration response of an Euler-Bernoulli beam to estimate prestressing force of strands. Due to the ill-possedness of the identification problems and the presence of random and systematic errors in the experiment, Tikhonov regularization method was used. Finally, results were compared with analytical solution of vibration of a simply supported beam with external compressive force. It was concluded that using dynamic vibration of prestressed concrete beams and using indirect estimation approaches, it is possible to quantify the loss of prestressing force due to corrosion.}, journal={JOURNAL OF SOUND AND VIBRATION}, author={Rashetnia, Reza and Ghasemzadeh, Farnam and Hallaji, Milad and Pour-Ghaz, Mohammad}, year={2018}, month={Oct}, pages={129–137} }
 @article{seppanen_hallaji_pour-ghaz_2017, title={A functionally layered sensing skin for the detection of corrosive elements and cracking}, volume={16}, ISSN={["1741-3168"]}, DOI={10.1177/1475921716670574}, abstractNote={In this paper, we propose an electrical impedance tomography (EIT)-based multifunctional surface sensing system, or sensing skin, for structural health monitoring. More specifically, the EIT-based sensing skin is developed for detecting and localizing the ingress of chlorides and cracking: two phenomena which are of concern in many structures, including reinforced concrete structures. The multifunctional sensing skin is made of two layers: one layer is sensitive to both chlorides and cracking, and the other layer is sensitive to cracking only. In the experiments, the sensing skin is tested on a polymeric and concrete substrate. The results demonstrate the feasibility of using the multifunctional multi-layer sensing skin for detecting and localizing corrosive elements and cracking, and for distinguishing between them.}, number={2}, journal={STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL}, author={Seppanen, Aku and Hallaji, Milad and Pour-Ghaz, Mohammad}, year={2017}, month={Mar}, pages={215–224} }
 @article{rashetnia_hallaji_smyl_seppanen_pour-ghaz_2017, title={Detection and localization of changes in two-dimensional temperature distributions by electrical resistance tomography}, volume={26}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665x/aa8f75}, abstractNote={This paper studies the feasibility of applying electrical resistance tomography (ERT) to detect changes in two-dimensional (2D) temperature distributions with potential applications in sensor development. The proposed sensor consists of a thin layer of porous metal film manufactured by spraying colloidal copper paint to a solid surface. A change of the temperature distribution on the surface changes the 2D distributed electrical conductivity of the metal film. The change of the electrical conductivity is localized and quantified with ERT, and further, to convert the estimated conductivity change of the sensor to temperature change, an experimentally developed model is used. The proposed temperature sensor is evaluated experimentally by applying it to a polymeric substrate, and exposing it to known temperature changes using heat sources of different shapes. The results demonstrate that the proposed sensor is capable of detecting and localizing temperature changes, and provides at least qualitative information on the magnitude of the temperature change.}, number={11}, journal={SMART MATERIALS AND STRUCTURES}, author={Rashetnia, Reza and Hallaji, Milad and Smyl, Danny and Seppanen, Aku and Pour-Ghaz, Mohammad}, year={2017}, month={Nov} }
 @inproceedings{hallaji_seppaznen_pour-ghaz_2015, title={Electrical impedance tomography-based sensing skin for structural health monitoring}, DOI={10.12783/shm2015/381}, abstractNote={In this paper, we develop a multi-layer multi-functional electrical impedance tomography-based sensing skin. This sensing skin is made of two layers. The electrical conductivity of one layer changes due to cracking and the presence of chloride ions, while the electrical conductivity of the other layer changes only due to cracking. We monitor the local change in conductivity of each layer with Electrical Impedance Tomography (EIT). This sensing skin enables detection and differentiation of both cracking and the presence of chloride ions. We apply this sensing skin to concrete substrate. The results indicate that the developed technology can be potentially used for health monitoring of critical infrastructure systems where cracking and leakage of certain ions might be of concern. doi: 10.12783/SHM2015/381}, booktitle={Structural health monitoring 2015: system reliability for verification and implementation, vols. 1 and 2}, author={Hallaji, M. and Seppaznen, A. and Pour-Ghaz, M.}, year={2015}, pages={3081–3088} }
 @article{hallaji_seppanen_pour-ghaz_2015, title={Electrical resistance tomography to monitor unsaturated moisture flow in cementitious materials}, volume={69}, ISSN={["1873-3948"]}, DOI={10.1016/j.cemconres.2014.11.007}, abstractNote={Traditionally the electrically-based assessment of the moisture flow in cement-based materials relies on two- or four-point measurements. In this paper, imaging of moisture distribution with electrical resistance tomography (ERT) is considered. Especially, the aim is to study whether ERT could give information on unsaturated moisture flows in cases where the flow is non-uniform. In the experiment, the specimens are monitored with ERT during the water ingress. The ERT reconstructions are compared with neutron radiographs, which provide high resolution information on the 2D distribution of the moisture. The results indicate that ERT is able to detect the moisture movement and to show approximately the shape and position of the water front even if the flow is nonuniform.}, journal={CEMENT AND CONCRETE RESEARCH}, author={Hallaji, Milad and Seppanen, Aku and Pour-Ghaz, Mohammad}, year={2015}, month={Mar}, pages={10–18} }
 @article{hallaji_pour-ghaz_2014, title={A new sensing skin for qualitative damage detection in concrete elements: Rapid difference imaging with electrical resistance tomography}, volume={68}, ISSN={["1879-1174"]}, DOI={10.1016/j.ndteint.2014.07.006}, abstractNote={In this paper we investigate whether a thin layer of electrically conductive materials that is painted to the surface of concrete elements can be used as sensing skin to detect and locate cracking and damage in the concrete substrate. Cracking of the concrete results in the rupture of the sensing skin, thus locally increasing its electrical resistivity. We monitor the local change in the electrical resistivity of the sensing skin using electrical resistance tomography. In this work, we utilize difference imaging scheme. Experiments on polymeric substrates as well as on concrete substrates are performed. The results indicate that the developed sensing skin can be successfully used to detect and locate cracking and damage on concrete and potentially other nonconductive substrates.}, journal={NDT & E INTERNATIONAL}, author={Hallaji, Milad and Pour-Ghaz, Mohammad}, year={2014}, month={Dec}, pages={13–21} }
 @article{hallaji_seppanen_pour-ghaz_2014, title={Electrical impedance tomography-based sensing skin for quantitative imaging of damage in concrete}, volume={23}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/23/8/085001}, abstractNote={This paper outlines the development of a large-area sensing skin for damage detection in concrete structures. The developed sensing skin consists of a thin layer of electrically conductive copper paint that is applied to the surface of the concrete. Cracking of the concrete substrate results in the rupture of the sensing skin, decreasing its electrical conductivity locally. The decrease in conductivity is detected with electrical impedance tomography (EIT) imaging. In previous works, electrically based sensing skins have provided only qualitative information on the damage on the substrate surface. In this paper, we study whether quantitative imaging of the damage is possible. We utilize application-specific models and computational methods in the image reconstruction, including a total variation (TV) prior model for the damage and an approximate correction of the modeling errors caused by the inhomogeneity of the painted sensing skin. The developed damage detection method is tested experimentally by applying the sensing skin to polymeric substrates and a reinforced concrete beam under four-point bending. In all test cases, the EIT-based sensing skin provides quantitative information on cracks and/or other damages on the substrate surface: featuring a very low conductivity in the damage locations, and a reliable indication of the lengths and shapes of the cracks. The results strongly support the applicability of the painted EIT-based sensing skin for damage detection in reinforced concrete elements and other substrates.}, number={8}, journal={SMART MATERIALS AND STRUCTURES}, author={Hallaji, Milad and Seppanen, Aku and Pour-Ghaz, Mohammad}, year={2014}, month={Aug} }
 @article{ghasemzadeh_sajedi_shekarchi_layssi_hallaji_2014, title={Performance evaluation of different repair concretes proposed for an existing deteriorated jetty structure}, volume={28}, number={4}, journal={Journal of Performance of Constructed Facilities}, author={Ghasemzadeh, F. and Sajedi, S. and Shekarchi, M. and Layssi, H. and Hallaji, M.}, year={2014} }