Influence of alkali, silicate, and sulfate content of carbonated concrete pore solution on mild steel corrosion behavior

Abstract

The increase in the rebar corrosion rate due to the concrete carbonation is the major cause of reinforced concrete degradation. The aim of this study was to investigate the corrosion behavior of mild steel rebars in simulated carbonated concrete solution. For this purpose, thermodynamic calculations, electrochemical techniques, gravimetric measurements, and surface analyses were used. Thermodynamic investigations of the nature of the interstitial solution provides an estimation of the influence of sulfate (SO 2À 4 ) and alkali (Na þ , K þ ) content on carbonate alkalinity of the CO 2 /H 2 O open system (pCO 2 ¼ 0.3 mbar). In this system, calcium-silicate hydrates (C-S-H) remain thermodynamically unstable and amorphous silica controls silicate aqueous content at 100 ppm. Electrochemical results highlight a decrease in the corrosion rate with increasing carbonate alkalinity and the introduction of silicate. The introduction of sulfate at fixed carbonate alkalinity shows a dual effect: at high carbonate alkalinity, the corrosion rate is increased whereas at low carbonate alkalinity, corrosion rate is decreased.Those results are supported by surface analysis. Authors conclude that silicate and sulfate release from cement hydrates and fixation of alkali on carbonated hydrates are key parameters to estimate mild steel corrosion in carbonated concrete.

Corrosion of steel in carbonated concrete: mechanisms, practical experience, and research priorities – a critical review by RILEM TC 281-CCC

“…1 order of magnitude. In addition to an increase in Clconcentrations, elevated sulphate and bicarbonate concentrations in the pore solution of carbonated concrete may play a role in the destabilization of the passive layer [34,35]. , measured with combined pH and chloride sensors embedded in a Portland cement based mortar exposed to carbonation under laboratory conditions (adopted from [33]).…”

“…Finally, the corrosion rate may be influenced by the chemical composition of the electrolyte. A number of species are known to affect the corrosion kinetics, including carbonate, bicarbonate, nitrate, nitrite, sulfate, and sulfide ions [35,42,51,52]. Studies quantifying the effect of the electrolyte chemistry on the corrosion rate are, however, limited.…”

Long‐term corrosion of rebars submitted to concrete carbonation

“…Active corrosion patterns are studied first for steel samples immersed in different aqueous solutions, by simulating different states of concrete carbonation. [ 6 ] As the chemistry of interstitial solutions of carbonated concrete is not well known in the literature, several scenarios are devised. Hence, the alkaline, silicate and sulphate contents are varied in a calcite‐based solution to assess whether those species (or related variables) have a direct or indirect impact on corrosion mechanisms (Table 2).…”

Pore Solution Chemistry of Calcium Sulfoaluminate Cement and Its Effects on Steel Passivation

“…The protection provided by Al(OH) 4 − is attributed to its ability to release hydroxyl. In the corrosion process, localized acidification occurs in the active point because of the hydrolysis of metal ion [38][39][40], as explained by Equation (6). If there is no immediate additional supplement of OH − from the adjoining solution, this active point will not be repaired (repassivation) and corrosion occurs.…”