Effect of polymer modified cementitious coatings on chloride‐induced corrosion of steel in concrete

Abstract

The paper deals with the study of the effect of polymer modified cementitious mortars on chloride-induced corrosion of steel reinforcement in concrete. Nowadays, many results obtained by standard and short-term tests are available in the literature. The paper reports more than 15 years exposure testing on two commercial coatings, with different polymer/cement ratio. The effect of coatings on corrosion initiation and propagation has been studied by the monitoring of corrosion potential and corrosion rate of rebars in concrete subjected to chloride ponding; chloride profiles, coating adhesion, water content, and corrosion morphology have been also analyzed. It was demonstrated that polymer modified cementitious mortars can delay corrosion initiation caused by chloride penetration into concrete. Owing to high resistivity of coated concrete, corrosion rate is reduced. The protective effect is more pronounced as the polymer content increases from 0.35 to 0.55. The results have been elaborated to estimate the possible increase of service life gained with this additional protection method, compared with other solutions. K E Y W O R D S chlorides diffusion, concrete coatings, corrosion of reinforcements 1 | INTRODUCTION Rebar corrosion is one of the most important cause of premature failure of reinforced concrete structures. Steel reinforcements in concrete are in passive conditions, protected by a thin oxide layer, promoted by the concrete alkalinity. 1,2 Depassivation may occur because of concrete carbonation, due to the reaction of atmospheric carbon dioxide with cement paste that lowers pH and causes general corrosion, and by the presence of chlorides in concentration higher than a critical level, that is generally considered in the range of 0.4-1% by cement weight for concrete structures exposed to atmosphere. 1 Chlorides can be added erroneously into concrete through mixing water or aggregates or they can penetrate from external sources, by diffusion or capillary suction, for example, in highway viaducts where de-icing salts are used, or in marine structures. 1 The prevention of reinforcement corrosion is primarily achieved in the design phase by using high quality concrete, adequate concrete cover, and suitable casting and curing procedures. 3,4 Additional prevention methods are adopted when severe environmental conditions occur

The Improvement of Durability of Reinforced Concretes for Sustainable Structures: A Review on Different Approaches

“…Hydrophobic treatment and polymer modified mortars showed the best efficiency on corrosion prevention. A long-term chloride corrosion test, lasting 17 years, showed that polymer modified coatings both delay the initiation of chloride corrosion, thanks to a strong decrease in the chloride penetration, and reduce corrosion rate [38,39]. The higher the polymer/cement ratio, the higher the coating effectiveness.…”

Big milestones in the study of steel corrosion in concrete

“…117 Polymer-modified cementitious mortars have been studied in the same university 113 and at Politecnico di Milano, where the effect of different composition (polymer/cement ratio) on short-term properties (water and water vapor permeability, stationary chloride diffusion) and long-term performances have been addressed. 118,119…”

“…Water repellent‐type coatings have been studied at Università Politecnica delle Marche, where the effect of silane treatments, water‐to‐cement ratio, and concrete cracking on corrosion behavior was reported 117 . Polymer‐modified cementitious mortars have been studied in the same university 113 and at Politecnico di Milano, where the effect of different composition (polymer/cement ratio) on short‐term properties (water and water vapor permeability, stationary chloride diffusion) and long‐term performances have been addressed 118,119 …”

Chloride Diffusion in Concrete Protected with a Silane-Based Corrosion Inhibitor

“…In agreement with the diagram of Tuuti [9], one of the main goals consists in slowing down the chloride diffusion inside the matrix in order to delay the onset of the corrosion process. Several alternative strategies have been proposed for increasing the durability of reinforced concrete structures exposed to chloride-rich environments such as coatings [10,11], cathodic protection [12,13], chloride extraction [14], and use of corrosion inhibitors [15][16][17][18][19]. Among these, the use of corrosion inhibitors (CI) is one of the most effective and cheaper ways to prevent the chloride-induced corrosion of reinforced concrete structures.…”