metals Article Austenitic Stainless-Steel Reinforcement for Seawater Sea Sand Concrete: Investigation of Stress Corrosion Cracking Xiang Yu 1 , Saad Al-Saadi 2 , Isha Kohli 2 , Xiao-Ling Zhao 3 and R. K. Singh Raman 1,2, *   Citation: Yu, X.; Al-Saadi, S.; Kohli, I.; Zhao, X.-L.; Singh Raman, R.K. Austenitic Stainless-Steel Reinforcement for Seawater Sea Sand Concrete: Investigation of Stress Corrosion Cracking. Metals 2021, 11, 500. https://doi.org/10.3390/ met11030500 Academic Editor: Anna Hojná Received: 20 February 2021 Accepted: 13 March 2021 Published: 17 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia; xiang.yu@monash.edu 2 Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia; saad.al-saadi@monash.edu (S.A.-S.); Isha.Kohli1@monash.edu (I.K.) 3 School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia; xiaolin.zhao@unsw.edu.au * Correspondence: raman.singh@monash.edu Abstract: Seawater and sea sand concrete (SWSSC) is a highly attractive alternative to normal concrete (NC) that requires huge amounts of fresh water and river sand. However, reinforcements of stainless steel (instead of mild steel that is used in NC) may be required for SWSSC. This article reports investigation of stress corrosion cracking (SCC) of AISI 316 stainless steel (SS) in simulated SWSSC and NC environments, with and without addition of silica to SWSSC and NC, employing slow strain rate testing (SSRT) at 25 and 60 ◦ C. For the purpose of comparison, SCC of SS was also investigated in simulated seawater (SW) solution. SS showed no SCC at 25 ◦ C in any of the test solutions. Indications of SCC were seen in SW at 60 ◦ C, but no features of SCC in SWSSC and NC at 60 ◦ C, as suggested by scanning electron microscopy (SEM) fractographs. While the absence of SCC in SWSSC and NC is attributed to the highly passivating alkaline condition, its absence in SWSSC also indicates the role of alkalinity to predominate the deleterious role of chloride content of SWSSC. However, the addition of silicate to SWSSC or NC triggers transgranular SCC to SS at 60 ◦ C, as evidenced by the fractography. Keywords: seawater sea sand concrete; normal concrete; stress corrosion cracking; AISI 316 stainless steel; slow strain rate testing (SSRT) 1. Introduction Increasing population and industrial development cause a rapid increase in the de- mand of concrete. Concrete production requires massive amounts of fresh water that contributes significantly to water scarcity [1–3]. Concretes also use huge amounts of river sand that negatively impacts the river ecosystem, navigation and flood control [4]. In order to circumvent these problems, the use of seawater and sea sand concrete (SWSSC) is an attractive alternative. SWSSC is a recent type of concrete that can be improved further by use of alkali-activated slag as binding material. The mechanical properties of SWSSC are reported to be similar to those of the conventional Portland cement concrete [5–7]. The Japan Concrete Institute reported that the strength of the slag-containing concrete produced with seawater tends be higher as compared to the concrete produced using tap water [8]. Furthermore, the alkali-silica reaction has a detrimental effect on integrity of ordinary Portland cement concrete [9,10], whereas the geo-polymer concrete or the high-performance concrete that utilizes industrial waste materials such as fly ash or slag, instead of cement, is designed to reduce effect of the alkali-silica reaction. Generally, mild steel rebars are employed as reinforcements to the concrete for high tensile strength and ductility; however, austenitic stainless steels have also been used because of their greater corrosion resistance. Steel bars develop a protective passive layer in the highly alkaline environment of concrete (pH > 10) [11]. However, this layer can be Metals 2021, 11, 500. https://doi.org/10.3390/met11030500 https://www.mdpi.com/journal/metals