Chloride-Induced Corrosion of Steel in Alkali-Activated Mortars Based on Different Precursors

Abstract

The low environmental impact and high long-term performance of products are becoming imperative for the sustainable development of the construction industry. Alkali-activated materials (AAMs) are one of the available low-embodied-carbon alternatives to Portland cement (OPC). For their application in the marine environment or where de-icing salts are used, it is of utmost importance to demonstrate their equal or better performance compared to OPC. The aim of this study was to compare the corrosion behaviour of the steel in AAMs based on different regionally available by-products with the behaviour of the steel in OPC. The by-products used were fly ash, slag, silica fume, and iron-silica fines. The corrosion process of each system was monitored by the corrosion potential and polarisation resistance during exposure to tap water and chloride solution over a period of almost one year. Certain AAMs showed a higher resistance to chloride penetration compared to OPC, which was attributed to the smaller number of capillary pores and higher gel phase precipitation. The same corrosion resistance compared to OPC was achieved with alkali-activated fly ash and alkali-activated slag mortars. The stability of the systems in tap water and chloride solution was confirmed by the visual assessment of the steel surface at the end of the test period.

Revealing corrosion parameters of steel in alkali-activated materials

“…A lack of O 2 can be caused by sulfide oxidation, which affects the redox potential [16], and the fine porosity and complex pore interconnection can cause low gas diffusion in AAMs, resulting in oxygen deficiency [24,25]. This parameter is strongly influenced by the precursors and the type and amount of activators used [26,27].…”

Characterizing Steel Corrosion in Different Alkali-Activated Mortars

“…One of the main remaining issues regarding the use of AAMs in reinforced structures is the understanding of steel corrosion, which is the main cause of structural failure. The primary causes of steel corrosion in OPC concrete are a loss in alkalinity and the ingress of chloride ions [ 2 ], which are also considered corrosion initiators in AAMs [ 12 , 13 , 14 , 15 ]. The main difference between the corrosion processes in solid porous materials (such as concrete) compared to solutions is the fact that the anodic and cathodic sites are spatially separated, forming a macro cell [ 16 , 17 ], while the distribution of anodic and cathodic sites on a micro scale could also be very important [ 18 , 19 , 20 ].…”

“…Different electrochemical monitoring techniques are commonly used to study corrosion in concrete environments. One such technique used to characterize and quantify the processes of passivation and depassivation in steel used to reinforce concrete is electrochemical impedance spectroscopy (EIS) [ 22 ], which is also used to study the corrosion of steel in AAMs [ 14 , 23 , 24 ]. This non-destructive technique is useful for studying the electrochemical processes of inhomogeneous or multiphase materials.…”

Influence of red mud addition in alkali-activated mortars on corrosion resistance of steel

“…Mix labelled FA 1 was based on fly ash as precursor, while mix labelled FARM 1 was based on the combination of fly ash and red mud. Monitoring of steel corrosion in mortars was performed applying unconventional three-electrode cell suggested by Šoić et al [7] and previously used by Runci et al [8] with a PAR VMP2 potentiostat/galvanostat (Biologic, Seyssinet-Pariset, France). The scheme of the cell set-up is shown in In addition to corrosion parameters, the particle size distribution (PSD) of the red mud, fly ash and cement sample was determined using Mastersizer 2000 instrument with a wet laser diffraction method by dispersing the particles in different solvents.…”