{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,31]],"date-time":"2026-03-31T17:01:26Z","timestamp":1774976486990,"version":"3.50.1"},"reference-count":23,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2016,12,7]],"date-time":"2016-12-07T00:00:00Z","timestamp":1481068800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/s16122083","type":"journal-article","created":{"date-parts":[[2016,12,8]],"date-time":"2016-12-08T10:39:01Z","timestamp":1481193541000},"page":"2083","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":85,"title":["Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method"],"prefix":"10.3390","volume":"16","author":[{"given":"Mingzhang","family":"Luo","sequence":"first","affiliation":[{"name":"Electronics and Information School, Yangtze University, Jingzhou 434023, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weijie","family":"Li","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA"},{"name":"School of Civil Engineering, Dalian University of Technology, Dalian 116023, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chuang","family":"Hei","sequence":"additional","affiliation":[{"name":"Electronics and Information School, Yangtze University, Jingzhou 434023, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5135-5555","authenticated-orcid":false,"given":"Gangbing","family":"Song","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, University of Houston, Houston, TX 77004, USA"},{"name":"School of Civil Engineering, Dalian University of Technology, Dalian 116023, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2016,12,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"583","DOI":"10.1061\/(ASCE)0733-9445(1997)123:5(583)","article-title":"Behavior of concrete columns confined by fiber composites","volume":"123","author":"Mirmiran","year":"1997","journal-title":"J. Struct. Eng."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"04014060","DOI":"10.1061\/(ASCE)CC.1943-5614.0000523","article-title":"Behavior of concrete-filled frp tubes under cyclic axial compression","volume":"19","author":"Zhang","year":"2014","journal-title":"J. Compos. Constr."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"962","DOI":"10.1016\/j.ultras.2012.12.012","article-title":"Compressive strength evaluation of structural lightweight concrete by non-destructive ultrasonic pulse velocity method","volume":"53","author":"Bogas","year":"2013","journal-title":"Ultrasonics"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"113001","DOI":"10.1088\/0964-1726\/24\/11\/113001","article-title":"Monitoring of concrete structures using the ultrasonic pulse velocity method","volume":"24","author":"Karaiskos","year":"2015","journal-title":"Smart Mater. Struct."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"04013010","DOI":"10.1061\/(ASCE)ST.1943-541X.0000781","article-title":"Monitoring crack propagation in reinforced concrete shear walls by acoustic emission","volume":"139","author":"Farhidzadeh","year":"2012","journal-title":"J. Struct. Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"075034","DOI":"10.1088\/0964-1726\/25\/7\/075034","article-title":"Detection of bond failure in the anchorage zone of reinforced concrete beams via acoustic emission monitoring","volume":"25","author":"Abouhussien","year":"2016","journal-title":"Smart Mater. Struct."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"19069","DOI":"10.3390\/s150819069","article-title":"Non-destructive evaluation for corrosion monitoring in concrete: A review and capability of acoustic emission technique","volume":"15","author":"Zaki","year":"2015","journal-title":"Sensors"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"3901","DOI":"10.3390\/s120403901","article-title":"Monitoring and failure analysis of corroded bridge cables under fatigue loading using acoustic emission sensors","volume":"12","author":"Li","year":"2012","journal-title":"Sensors"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"350","DOI":"10.1016\/j.compositesb.2014.10.002","article-title":"Evaluation of gluing of cfrp onto concrete structures by infrared thermography coupled with thermal impedance","volume":"69","author":"Alexis","year":"2015","journal-title":"Compos. Part B Eng."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.ndteint.2015.05.003","article-title":"Determination of the applicability and limits of void and delamination detection in concrete structures using infrared thermography","volume":"74","author":"Bosiljkov","year":"2015","journal-title":"NDT E Int."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1016\/S0266-3538(99)00094-9","article-title":"Non-destructive detection of fatigue damage in thick composites by pulse-echo ultrasonics","volume":"60","author":"Mouritz","year":"2000","journal-title":"Compos. Sci. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Yin, H., Wang, T., Yang, D., Liu, S., Shao, J., and Li, Y. (2016). A smart washer for bolt looseness monitoring based on piezoelectric active sensing method. Appl. Sci., 6.","DOI":"10.3390\/app6110320"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Shao, J., Wang, T., Yin, H., Yang, D., and Li, Y. (2016). Bolt looseness detection based on piezoelectric impedance frequency shift. Appl. Sci., 6.","DOI":"10.3390\/app6100298"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Jiang, T., Kong, Q., Wang, W., Huo, L., and Song, G. (2016). Monitoring of grouting compactness in a post-tensioning tendon duct using piezoceramic transducers. Sensors, 16.","DOI":"10.3390\/s16081343"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"5","DOI":"10.1177\/1475921706057978","article-title":"Debond detection using embedded piezoelectric elements in reinforced concrete structures-part I: Experiment","volume":"5","author":"Wu","year":"2006","journal-title":"Struct. Health Monit."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1435","DOI":"10.1061\/(ASCE)ST.1943-541X.0000632","article-title":"Active debonding detection for large rectangular cfsts based on wavelet packet energy spectrum with piezoceramics","volume":"139","author":"Xu","year":"2012","journal-title":"J. Struct. Eng."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"125026","DOI":"10.1088\/0964-1726\/24\/12\/125026","article-title":"Bond slip detection of concrete-encased composite structure using shear wave based active sensing approach","volume":"24","author":"Zeng","year":"2015","journal-title":"Smart Mater. Struct."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"095003","DOI":"10.1088\/0964-1726\/25\/9\/095003","article-title":"Bond-slip detection of concrete-encased composite structure using electro-mechanical impedance technique","volume":"25","author":"Liang","year":"2016","journal-title":"Smart Mater. Struct."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"154","DOI":"10.1016\/j.conbuildmat.2016.10.061","article-title":"Experimental studies on void detection in concrete-filled steel tubes using ultrasound","volume":"128","author":"Dong","year":"2016","journal-title":"Constr. Build. Mater."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"345","DOI":"10.1016\/j.measurement.2016.01.042","article-title":"Damage detection of concrete piles subject to typical damage types based on stress wave measurement using embedded smart aggregates transducers","volume":"88","author":"Feng","year":"2016","journal-title":"Measurement"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"801","DOI":"10.21595\/jve.2016.16631","article-title":"Damage detection of concrete piles subject to typical damages using piezoceramic based passive sensing approach","volume":"18","author":"Feng","year":"2016","journal-title":"J. Vibroeng."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"115020","DOI":"10.1088\/0964-1726\/24\/11\/115020","article-title":"Crack detection and leakage monitoring on reinforced concrete pipe","volume":"24","author":"Feng","year":"2015","journal-title":"Smart Mater. Struct."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1080\/19475411.2015.1089525","article-title":"Water presence detection in a concrete crack using smart aggregates","volume":"6","author":"Kong","year":"2015","journal-title":"Int. J. Smart Nano Mater."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/16\/12\/2083\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T19:28:08Z","timestamp":1760210888000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/16\/12\/2083"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2016,12,7]]},"references-count":23,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2016,12]]}},"alternative-id":["s16122083"],"URL":"https:\/\/doi.org\/10.3390\/s16122083","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2016,12,7]]}}}