SEM analysis of rebar corrosion in mortars containing calcareous filler

O.R. BATIC; J.D. SOTA; J.L. FERNÁNDEZ; B. DEL AMO; R. ROMAGNOLI

Quito

Congreso; VII Congreso Latinoamericano de Corrosión. LATINCORR 2010; 2010

OCP Ecuador S.A. NACE Internacional Sección Ecuador

Rebars corrosion is of great concern because it is probably the most widespread cause of reinforced concrete degradation. Rebars corrosion depends on several factors such as: composition, type and surface configuration of rebars, the type of cement, the dose of concrete, the permeability of concrete, etc. Mineral admixtures can replace a definite percentage of cement without impairing the properties of concrete and; sometimes, this replacement may be beneficial for concrete. The most common mineral admixtures are: puzzolans, granulated blast furnace slag, calcareous filler, flying ash with high or low lime content, condensed silica fumes and rice hush ash [1, 2]. The incorporation of mineral admixtures does modify the properties of concrete and influences rebar corrosion [1-8].             More recently, calcareous filler was employed massively as a mineral admixture for portland cement with contents ranging from 5-35% [9-11]. There are strong arguments about the addition of limestone which lie on both sides of the question [11-24]. Although many investigations have been carried out on the effect of limestone on the hydration of portland cement, little information is available about the influence of calcareous filler on rebar corrosion. Tsivilis et al reported that the highest the amount of calcareous filler added to the mortar, the more positive the corrosion potential resulted [19].  The objective of this research was to study rebar corrosion in mortars elaborated with portland cement added with calcareous filler and two different water/cement (w/c) ratios (0.50 and 0.65, respectively). The study was conducted in parallel with mortars without the admixture. The behaviour of rebars was evaluated, at the end of the test period, by electrochemical techniques: the measurement of corrosion potential and linear polarization tests, in tap water and 3% sodium chloride. The nature of the protective layer formed on rebars was observed by scanning electron microscopy (SEM) and its composition obtained by X-rays energy dispersive analysis (EDX). It was found that the presence of carbonate addition did modify the structure of the passive layer.