Combined protective action of barnacles and biofilm on concrete surface in intertidal areas Tom Chlayon ⇑ , Mitsuyasu Iwanami, Nobuhiro Chijiwa Department of Civil and Environmental Engineering, Tokyo Institute of Technology, 2-12-1-M1-21 Ookayama, Meguro, Tokyo 152-8552, Japan highlights  Barnacles and bacterial film help improving chloride resistance in concrete.  Without bacterial film and barnacles, chloride penetrates faster.  The chloride ion is traced by chloride migration test and EPMA (SEM-WDX).  Weathering damage to plain concrete is marginal during the initial 40-day exposure. article info Article history: Received 27 October 2017 Received in revised form 16 April 2018 Accepted 26 May 2018 Keywords: Biofilm Barnacle Concrete durability SEM Chloride attack Microcrack abstract This study investigated the effect of biofilm and barnacles on the surface of concrete. The specimens were set in an intertidal environment and divided into two study groups: one whose bacterial film was removed, and the other whose bacterial film was left intact. The chloride migration test and EPMA (SEM-WDX) were used as the study methods. The findings suggest that barnacles pose no threat to con- crete. On the contrary, barnacles and biofilm were found to improve concrete durability by attaching to the surface of the concrete and sealing underlying microcracks. Further, chloride diffusion rates were lowered due to crack-closing. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Marine growth is inevitable and needs to be considered in the design and maintenance of offshore platforms and offshore struc- tures. Despite the fouling behavior of marine growth, some researchers have suggested that certain intertidal species such as barnacles and bacterial films extend concrete life [1–5]. Further, low-tidal zones experience significant chloride ingress [6]. Should barnacles and biofilm have a protective effect on the surface of concrete, they could be widely applied because they are abundant in the ocean. To date, the combined bio-protective effect of barna- cles and biofilm remains unclear, and this raises the complexity of determining the factors that contribute to concrete durability. In consideration of the above, this topic merits investigation. This research contributes knowledge mainly regarding the effects of barnacles and bacterial film (Fig. 1) especially during the initial period when the marine growth does not fully occupy the struc- tural surface. The utilization of marine growth as an additional bio-coating could be an alternative solution to destruction of same. This research focuses on the use of natural marine bio-protection on concrete structures by taking advantage of existing local habi- tats. Possible beneficial outcomes include maintenance-cost sav- ings, long-term sustainability, and a more healthy coastal ecology through reduced use of environmentally toxic antifouling materials. Biogenic crusts of barnacles have been found to improve con- crete durability against chloride attack [4,5], while the giant Pacific oyster, Crassostrea Giga, has been shown to have a similar surface- coating effect [7]. Further, such biogenic structures have been observed to stabilize surface temperature and protect substrates https://doi.org/10.1016/j.conbuildmat.2018.05.223 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author: Infrastructure Management Laboratory, Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Room 512 Midorigaoka Bldg. 1, 2-12-1-M1-21 Ookayama, Meguro, Japan. E-mail addresses: chlayon.t.aa@m.titech.ac.jp (T. Chlayon), iwanami@cv.titech. ac.jp (M. Iwanami), chijiwa@cv.titech.ac.jp (N. Chijiwa). Construction and Building Materials 179 (2018) 477–487 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat