{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,9]],"date-time":"2026-07-09T17:37:24Z","timestamp":1783618644182,"version":"3.55.0"},"reference-count":30,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2025,10,16]],"date-time":"2025-10-16T00:00:00Z","timestamp":1760572800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"West Virginia Department of Transportation, Division of Highways","award":["RP328"],"award-info":[{"award-number":["RP328"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>This study presents an amplitude-based non-destructive testing (NDT) approach for estimating reinforcement bar diameter in reinforced concrete members using ground-penetrating radar (GPR). The novelty of this work lies in the use of normalized amplitude-diameter-depth (NADD) relationships, which link the reflected electromagnetic wave amplitude to both rebar diameter and cover depth through an exponential attenuation model. Normalization was applied to remove the influence of varying signal energy and antenna coupling, thereby allowing consistent comparison of amplitudes across different depths and improving the reliability of amplitude-depth interpretation. The NADD equation was developed from GPR measurements obtained on a reinforced concrete slab containing bars with diameters ranging from 9.5 mm (#3 bar) to 25.4 mm (#8 bar) and then validated using data from three prestressed concrete box beams recovered from a decommissioned bridge managed by the West Virginia Department of Highways. The normalized amplitude prediction error (Ea) was calculated to quantify model performance. The minimum mean error of approximately 4.7% corresponded to the 12.7 mm (#4 bar), which matched the actual reinforcement used in the beams. The results demonstrate that the proposed normalization-based approach effectively captures the amplitude-depth-diameter relationship, offering a quantitative framework for interpreting GPR data and improving the evaluation of reinforcement characteristics in existing concrete structures.<\/jats:p>","DOI":"10.3390\/ma18204748","type":"journal-article","created":{"date-parts":[[2025,10,17]],"date-time":"2025-10-17T07:33:50Z","timestamp":1760686430000},"page":"4748","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Enhancing Structural Integrity Assessment Through Non-Destructive Evaluation"],"prefix":"10.3390","volume":"18","author":[{"given":"Wael","family":"Zatar","sequence":"first","affiliation":[{"name":"Encova Center for Engineering and Safety, Department of Civil Engineering, Marshall University, Huntington, WV 25755, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Felipe","family":"Mota Ruiz","sequence":"additional","affiliation":[{"name":"Department of Civil Engineering, Marshall University, Huntington, WV 25755, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hien","family":"Nghiem","sequence":"additional","affiliation":[{"name":"Encova Center for Engineering and Safety, Department of Civil Engineering, Marshall University, Huntington, WV 25755, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,10,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"168781402091376","DOI":"10.1177\/1687814020913761","article-title":"Non-destructive testing and evaluation of composite materials\/structures: A state-of-the-art review","volume":"12","author":"Wang","year":"2020","journal-title":"Adv. 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