Abstract
Alkali activated materials as possible sustainable alternative to cementitious binders showed competitive performances in terms of mechanical and durability properties and high temperature stability. For this reason, light weight fly-ash based mortars have already been optimized as passive fire protective coating for steel structures. However, a lack of information about the durability of these innovative systems in terms of steel corrosion resistance is still present. Thus, this study aims at investigating the durability of steel coated with a 20-mm thick light weight mortar layer in a neutral environment (tap water) and in presence of chloride-containing solution (0.2 M NaCl). In addition, the influence of pore solution chemistry and pH was discussed through electrochemical testing in leachate pore solution and NaOH aqueous solutions at different concentrations. It was found that almost complete protection ability of light weight mortar was obtained when coated steel is exposed to neutral solution for 60 days, while in presence of chlorides, steel is more susceptible to corrosion already after 40 days of exposure. In addition, the developed open porosity of the light weight mortars, it was found that pH and the chemistry of the pore solution in contact with steel strongly influenced the steel corrosion resistance.
Highlights
IntroductionCompared to ordinary Portland Cement (OPC)-based materials, parameters, such as precursor and activator chemistry and concentration, rather than pore distribution, microstructure and composition of the pore solution, can strongly influence the steel corrosion behavior [18]
The present study aims at the assessment of the chloride-induced steel corrosion when light weight alkali activated mortars (LWM) were applied
MIP results reported in Figure 3 showed a strong difference in pore size distribution and total open porosity between M and LWM: while M sample exhibited a total cumulative intruded Hg volume of 52 mm3 /g and a total open porosity of 11%, LWM sample showed values of 367 mm3 /g and 48%, respectively
Summary
Compared to OPC-based materials, parameters, such as precursor and activator chemistry and concentration, rather than pore distribution, microstructure and composition of the pore solution, can strongly influence the steel corrosion behavior [18]. Scattered results have been obtained among different studies that introduced chlorides in the material during mixing or through exposure to chloride-containing solutions [15,16,21,22,23] This confirms that factors related to the binder microstructure and to the precursor chemistry, regulate the corrosion behavior. To better investigate these behaviors, electrochemical corrosion tests performed in simulated pore solutions highlighted that the alkalinity strongly influences the chloride-induced corrosion of the embedded steel [17].
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