{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,27]],"date-time":"2026-10-27T17:42:46Z","timestamp":1793122966808,"version":"4.5.0"},"reference-count":36,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T00:00:00Z","timestamp":1785715200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Shandong Natural Science Foundation Youth Program","award":["ZR2023QE015"],"award-info":[{"award-number":["ZR2023QE015"]}]},{"name":"National Natural Science Foundation of China and China Railway","award":["U2368209"],"award-info":[{"award-number":["U2368209"]}]},{"award":["U2368209"],"award-info":[{"award-number":["U2368209"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]},{"name":"CAS Pioneer Hundred Talents Program"},{"name":"Taishan Scholars Program"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Cover cracking induced by steel corrosion is a critical issue governing the durability degradation of reinforced concrete structures in marine environments. The crack initiation and propagation processes dominated by non-uniform rust expansion stress fields urgently require high-resolution continuous monitoring techniques. In this study, based on the principle of Rayleigh backscattering, distributed optical fibers were embedded along the upper surface of specimens to conduct in situ monitoring of surface strain in concrete. The effects of specimen length, biochar content, cover thickness, and rebar diameter were systematically investigated. The results indicate that the surface strain evolution follows a two-stage pattern\u2014a slow growth stage followed by a rapid rise stage\u2014corresponding respectively to the early-stage filling of interfacial pores and stress accumulation, and the later-stage propagation of macroscopic cracks. Increasing specimen length significantly amplifies the spatiotemporal non-uniformity of strain, characterized by \u201clocally high peak strains but low overall mean values,\u201d with the onset time of strain surges differing by more than 50 h across different cross-sections. The incorporation of 0.5% biochar reduces the average strain by approximately 17% and delays crack initiation to 260 h. Increasing cover thickness from 25 mm to 40 mm exhibits the most pronounced inhibitory effect, achieving a 39% reduction in strain and delaying crack initiation to 320 h, primarily attributed to the extended chloride transport path and enhanced hoop confinement stiffness. Reducing rebar diameter from 20 mm to 12 mm decreases the peak strain to 79% of that of the standard specimen, owing to reduced rust product volume and increased relative cover thickness. The macro-cell effect driven by chloride concentration gradient transition zones is identified as a key factor governing crack initiation locations. Theoretical crack widths derived from strain integration of optical fiber data are slightly lower than measured values, yet the overall trends remain consistent. This study provides a quantitative basis for continuous monitoring and durability assessment of corrosion-induced cracking in marine environments.<\/jats:p>","DOI":"10.3390\/s26154889","type":"journal-article","created":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T11:50:21Z","timestamp":1785757821000},"page":"4889","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Surface Strain Evolution and Cracking Behavior of Concrete Under Non-Uniform Corrosion-Induced Expansion Monitored by Distributed Fiber Optics"],"prefix":"10.3390","volume":"26","author":[{"given":"Qiangqiang","family":"Ma","sequence":"first","affiliation":[{"name":"School of Civil Engineering, Qingdao University of Technology, Qingdao 266520, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5287-5608","authenticated-orcid":false,"given":"Liang","family":"Fan","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Advanced Marine Materials, Shandong Key Laboratory of Marine Environmental Corrosion and Bio-Fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7182-263X","authenticated-orcid":false,"given":"Yongjun","family":"Zhang","sequence":"additional","affiliation":[{"name":"School of Civil Engineering, Qingdao University of Technology, Qingdao 266520, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Baorong","family":"Hou","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Advanced Marine Materials, Shandong Key Laboratory of Marine Environmental Corrosion and Bio-Fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.corcom.2026.02.002","article-title":"What is the future of modern corrosion electrochemistry?","volume":"22","author":"Cao","year":"2026","journal-title":"Corros. Commun."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"02013","DOI":"10.1051\/matecconf\/201713802013","article-title":"Investigation of non-uniform rust distribution and its effects on corrosion-induced cracking in reinforced concrete","volume":"138","author":"Sutrisno","year":"2017","journal-title":"MATEC Web Conf."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"110039","DOI":"10.1016\/j.engstruct.2019.110039","article-title":"Monitoring corrosion of steel bars in reinforced concrete based on helix strains measured from a distributed fiber optic sensor","volume":"204","author":"Fan","year":"2020","journal-title":"Eng. Struct."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Fan, L., Bao, Y., and Chen, G. (2018). Feasibility of distributed fiber optic sensor for corrosion monitoring of steel bars in reinforced concrete. Sensors, 18.","DOI":"10.3390\/s18113722"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1879","DOI":"10.1177\/14759217211030911","article-title":"Techniques of corrosion monitoring of steel rebar in reinforced concrete structures: A review","volume":"21","author":"Fan","year":"2022","journal-title":"Struct. Health Monit."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"685054","DOI":"10.1155\/2012\/685054","article-title":"Distributed strain sensor networks for in-construction monitoring and safety evaluation of a high-rise building","volume":"2012","author":"Ye","year":"2012","journal-title":"Int. J. Distrib. Sens. Netw."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"142197","DOI":"10.1016\/j.conbuildmat.2025.142197","article-title":"Investigation of the impact of protective layer thickness and chloride ion penetration direction on macro-cell corrosion of reinforcement in mortar columns under marine environment","volume":"489","author":"Fan","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"121240","DOI":"10.1016\/j.conbuildmat.2020.121240","article-title":"Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring","volume":"269","author":"Rodrigues","year":"2021","journal-title":"Constr. Build. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"104314","DOI":"10.1016\/j.cemconcomp.2021.104314","article-title":"Real-time strain monitoring of reinforced concrete under the attacks of sulphate and chloride ions based on XCT and DIC methods","volume":"125","author":"Wang","year":"2022","journal-title":"Cem. Concr. Compos."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Omoniyi, T.M., Abel, B., Omoebamije, O., Onimisi, Z.M., Matos, J.C., Tinoco, J., and Minh, T.Q. (2025). The Effect of Data Augmentation on Performance of Custom and Pre-Trained CNN Models for Crack Detection. Appl. Sci., 15.","DOI":"10.3390\/app152212321"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"119383","DOI":"10.1016\/j.conbuildmat.2020.119383","article-title":"Automated Crack Detection and Measurement Based on Digital Image Correlation","volume":"256","author":"Gehri","year":"2020","journal-title":"Constr. Build. Mater."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Komi, D., Yoshida, D., and Kameyama, T. (2025). Development of an Automated Crack Detection System for Port Quay Walls Using a Small General-Purpose Drone and Orthophotos. Sensors, 25.","DOI":"10.20944\/preprints202505.1112.v1"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Ribeiro, D., Rakoczy, A.M., Cabral, R., Hoskere, V., Narazaki, Y., Santos, R., Tondo, G., Gonzalez, L., Matos, J.C., and Massao Futai, M. (2025). Methodologies for Remote Bridge Inspection\u2014Review. Sensors, 25.","DOI":"10.3390\/s25185708"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"81","DOI":"10.1007\/s44290-024-00089-5","article-title":"Condition Assessment of Concrete Structures Using Automated Crack Detection Method for Different Concrete Surface Types Based on Image Processing","volume":"1","author":"Shalaby","year":"2024","journal-title":"Discov. Civ. Eng."},{"key":"ref_15","unstructured":"(2023). Standardization Administration of the People\u2019s Republic of China. Common Portland Cement (Standard No. GB 175-2023)."},{"key":"ref_16","unstructured":"(2021). Standardization Administration of the People\u2019s Republic of China. Test Method of Cement Mortar Strength (ISO Method) (Standard No. GB\/T 17671-2021)."},{"key":"ref_17","unstructured":"(1978). Specification for Artificial Sea Water for Laboratory Use (Standard No. IS 8770:1978)."},{"key":"ref_18","unstructured":"(2020). Standard Test Method for Water-Soluble Chloride in Mortar and Concrete (Standard No. ASTM C1218\/C1218M-20)."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"679","DOI":"10.1016\/j.compositesb.2019.02.051","article-title":"In-situ monitoring of corrosion-induced expansion and mass loss of steel bar in steel fiber reinforced concrete using a distributed fiber optic sensor","volume":"165","author":"Fan","year":"2019","journal-title":"Compos. Part B Eng."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"102354","DOI":"10.1016\/j.yofte.2020.102354","article-title":"Quantitative strain measurement and crack opening estimate in concrete structures based on OFDR technology","volume":"60","author":"Wu","year":"2020","journal-title":"Opt. Fiber Technol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"103583","DOI":"10.1016\/j.cemconcomp.2020.103583","article-title":"Characterization of the corrosion profiles of reinforcement with different impressed current densities by X-ray micro-computed tomography","volume":"109","author":"Hong","year":"2020","journal-title":"Cem. Concr. Compos."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"288","DOI":"10.1617\/s11527-025-02808-5","article-title":"Corrosion-induced cracking in reinforced concrete: The role of concrete cover thickness","volume":"58","year":"2025","journal-title":"Mater. Struct."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1854","DOI":"10.1016\/j.conbuildmat.2010.11.074","article-title":"Prediction of corrosion-induced cover cracking in reinforced concrete structures","volume":"25","author":"Chernin","year":"2011","journal-title":"Constr. Build. Mater."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"3388","DOI":"10.1016\/j.corsci.2011.06.018","article-title":"Damage analysis and cracking model of reinforced concrete structures with rebar corrosion","volume":"53","author":"Zhao","year":"2011","journal-title":"Corros. Sci."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"75","DOI":"10.1016\/j.conbuildmat.2013.10.042","article-title":"Non-uniform rust expansion for chloride-induced pitting corrosion in RC structures","volume":"51","author":"Cao","year":"2014","journal-title":"Constr. Build. Mater."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"115171","DOI":"10.1016\/j.jobe.2025.115171","article-title":"Enhancing corrosion resistance of reinforcing steel in seawater-mixed mortar using biochar","volume":"119","author":"Ma","year":"2026","journal-title":"J. Build. Eng."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"121142","DOI":"10.1016\/j.conbuildmat.2020.121142","article-title":"Comparing influence of inert biochar and silica rich biochar on cement mortar\u2014Hydration kinetics and durability under chloride and sulfate environment","volume":"268","author":"Gupta","year":"2021","journal-title":"Constr. Build. Mater."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"142386","DOI":"10.1016\/j.conbuildmat.2025.142386","article-title":"Impact of stray current-induced steel fiber corrosion on the durability of ultra-high-performance concrete","volume":"489","author":"Chen","year":"2025","journal-title":"Constr. Build. Mater."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"273","DOI":"10.1016\/j.conbuildmat.2016.04.097","article-title":"Corrosion-induced concrete cracking model considering corrosion product-filled paste at the concrete\/steel interface","volume":"116","author":"Zhao","year":"2016","journal-title":"Constr. Build. Mater."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"121053","DOI":"10.1016\/j.conbuildmat.2020.121053","article-title":"Prediction of corrosion-induced concrete cracking under external loading and stirrup constraint","volume":"266","author":"Zhao","year":"2021","journal-title":"Constr. Build. Mater."},{"key":"ref_31","doi-asserted-by":"crossref","unstructured":"Li, W., Wu, M., Shi, T., Yang, P., Pan, Z., Liu, W., Liu, J., and Yang, X. (2022). Experimental investigation of the relationship between surface crack of concrete cover and corrosion degree of steel bar using fractal theory. Fractal Fract., 6.","DOI":"10.3390\/fractalfract6060325"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"103517","DOI":"10.1016\/j.tafmec.2022.103517","article-title":"Phase field modeling of concrete cracking for non-uniform corrosion of rebar","volume":"121","author":"Fang","year":"2022","journal-title":"Theor. Appl. Fract. Mech."},{"key":"ref_33","first-page":"201900008","article-title":"Distributed fibre optic sensing for crack detection in concrete structures","volume":"1","author":"Fischer","year":"2019","journal-title":"Civ. Eng. Des."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"108945","DOI":"10.1016\/j.measurement.2020.108945","article-title":"Measuring crack width using a distributed fiber optic sensor based on optical frequency domain reflectometry","volume":"172","author":"Xiao","year":"2021","journal-title":"Measurement"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Shao, W., He, X., Shi, D., and Zhu, W. (2023). Prediction of crack width in RC piles exposed to local corrosion in chloride environment. Materials, 16.","DOI":"10.20944\/preprints202308.0862.v1"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"197","DOI":"10.1631\/jzus.A1300280","article-title":"Calculation of corrosion rate for reinforced concrete beams based on corrosive crack width","volume":"15","author":"Wu","year":"2014","journal-title":"J. Zhejiang Univ. Sci. A"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/15\/4889\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T11:55:26Z","timestamp":1785758126000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/15\/4889"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,3]]},"references-count":36,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2026,8]]}},"alternative-id":["s26154889"],"URL":"https:\/\/doi.org\/10.3390\/s26154889","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,3]]}}}