In vitro and in situ tests to evaluate the bacterial colonization of cementitious materials in the marine environment

Abstract

Civil engineers have a responsibility to take measures to protect marine biodiversity by selecting more bioreceptive construction materials in the design of marine infrastructure, for better biodiversity conservation. In this study, it was shown that pre-carbonation of cementitious materials accelerates their bacterial colorization by lowering the pH of their surface. It has been shown both in the laboratory and in-situ tests that the bacterial colonization of cementitious materials is influenced by the pH and the type of cement. By comparing the bacterial colonization of Portland cement mortars, CEM I, and slag cement, CEM III, mortars, it was found that the CEM III mortars are more bioreceptive than the CEM I mortars. This study presented and verified a novel experimental laboratory approach which can be used to evaluate the bacterial colonization (bioreceptivity) of cementitious materials in marine environment. The approach could be taken up in future recommendations to enable engineers to eco-design more eco-friendly marine infrastructure and develop green-engineering projects.

Influence of the Intrinsic Characteristics of Cementitious Materials on Biofouling in the Marine Environment

“…Moreover, the seawater pH remained constant at an average of 8.16 throughout the experiment (Figure 9). This value was consistent with the literature; the pH of seawater varied between 7.5 and 9.0, with an average of around 8.2 [69,94,95]. Seawater alkalinity was hence unaffected by the immersion of cementitious material specimens (the release of Ca(OH) 2 and KOH resulting from the leaching reaction) and remained optimal for the growth of marine bacteria [96][97][98].…”

“…However, these factors are less well known in the marine environment [9,67,68]. We showed in a previous study that the bacterial colonization of cementitious materials in seawater is influenced by the pH and the type of cement [69,70]. In this present paper, the effect of several parameters in the two main stages (microfouling and macrofouling) of cementitious material biocolonization in the marine environment is tested.…”

“…The alkalinity of the medium and the surface of a submerged cementitious material can affect biocolonization [70,84,85]. Therefore, the pH of the seawater and the surface of the mortar specimens were measured in triplicate throughout the immersion period using a pH electrode (Hanna instrument, HI1230, accuracy 0.1 pH unit) and pH indicator paper (Whatman, 0.0 to 14.0, accuracy 1 pH unit), respectively, according to the protocol described by Hayek et al [69]. The pH of the mortar specimens was verified using phenolphthalein indicators (which go from colorless to pink at pH ≥9).…”

“…Due to this very basic pH, their constituent materials have been cited as inhibitors of the recruitment of marine biota [36]. In addition, a decrease in pH from 13 to around 9 has been reported as necessary for bacterial colonization of cementitious materials submerged in seawater [69,103]. Therefore, the pH of the mortar surfaces was evaluated throughout the experiment in order to discern whether the pH was indeed responsible for inhibiting bacterial colonization when obtained.…”

“…Moreover, when CEM I was replaced by CEM III, the pH of the CEM III mortar specimens (OM3 and BM3) at T0 was around 10 (due to the carbonation reaction). This difference in pH between the CEM I and CEM III specimens was probably one reason why the cementitious materials prepared with CEM III were more bioreceptive than those formulated using CEM I, according to [69,70,106].…”