International Concrete Abstracts Portal

This CD contains 10 papers presented at the ACI Spring Convention, Dallas, TX, March 2012, and sponsored by ACI Committee 222, Corrosion of Metals in Concrete. The papers cover a variety of subject areas, including mechanism of corrosion of reinforcing steel in concrete; identifying, investigating, and quantifying corrosion; corrosion control measures for new and existing structures; and innovative materials and testing techniques. Engineers, scientists, researchers, inspectors, technicians, academics, materials manufacturers, and suppliers will all benefit from this SP. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-291

Electrochemical polarization and Raman spectroscopy were used to investigate the passive film formation of four grades of stainless steels in concrete and synthetic concrete pore solutions. Steels tested were austenitic grades UNS S24100 and UNS S31603, and duplex grades UNS S32101 and UNS S32304. These techniques have identified both similarities and differences in the protective films. The air-formed Cr2O3 film is not stable on any of the steels at potentials more anodic than approximately -100 mV SCE. In its stead, CrO3 and mixed spinels form at more anodic potentials. The manganese-bearing grades (S24100 and S32101) exhibited Raman peaks attributed to manganese-bearing spinels, indicating that these steels form unique passive films. These films show similar stability and breakdown behaviour in chloride-free pore solutions; studies in chloride-bearing solutions are on-going.

The presence of chlorides in cementitious materials results in corrosion of the embedded metallic materials. Early construction practices (pre 1960s) relied on admixed calcium chloride to accelerate the early strength gain of concrete. Until the 1950s, few publications focused on the effects of chlorides in concrete on corrosion and the use of chlorides was well established. However, in the 1960s significant publications reported on the effects of chlorides on the corrosion of prestressed wires and strands – these publications were the result of several failures of prestressed systems. Later, significant research was performed on the corrosion of steels in cementitious materials―a significant portion of this work attributable to the researchers being recognized in this symposium: Brian Hope and Morris Schupack. Their considerable efforts led to new knowledge regarding corrosion durability of reinforced and prestressed systems. Recently, ACI Committees 201 and 222 standardized limits on allowable admixed chlorides in the constituent materials. However, more standardization is needed―ACI Committees 318 and 349 report different admixed chloride limit requirements than Committees 201 and 222. This paper provides an overview of past research, analyzes the effects of chlorides on service life and economy and provides data from a research project. Using this information, the authors propose a standardized limit for chlorides in concrete.

Different anti-icing agents are used in various locations in Ontario to meet the specific climate needs of the area in order to minimize, or help remove, snow and ice build-up. These anti-icing agents are generally applied in liquid form and, due to their low freezing temperatures, are able to stay liquid, thus also allowing them to penetrate concrete structures. It has been shown in previous studies that the cations of some of the solutions can react with the cementitious materials to form precipitates of expansive nature. In this project, concrete exposed to the different solutions has been subjected to freezing and thawing both in laboratory tests and in outdoor exposure and to compression testing. However, the salts prevented freezing at the lowest temperatures tested. Therefore, it has been observed that reactions with the calcium and magnesium chlorides can have a positive effect at early ages but a potentially detrimental effect over the long term. The penetration of salt into the dry concrete was determined to be very fast and resulted in a rapid initial increase in the concrete compressive strength but little subsequent strength gain, whereas the strength of concrete exposed to water continues to increase over a longer period.

The variability and uncertainty associated with chloride thresholds can be partly explained by the surface conditions of carbon steel rebar, in particular, by the presence of crevices on the steel surface. It has been suggested in the literature that pore solution in the crevices on the steel surface may be different from that of the bulk pore solution, and this difference may create the necessary conditions for the breakdown of the passive film. To test this hypothesis, a numerical investigation was carried out using a non-linear transient finite element algorithm, which involved the solution of coupled extended Nernst-Planck and Poisson’s equations in a domain that represented typical surface crevices on carbon steel rebar. The numerical simulations showed that the chemistry of the pore solution, in particular pH and Cl-/OH-, within crevices provided more favourable conditions for depassivation than the bulk concrete pore solution. Local acidification and increase in Cl-/OH- within the crevice were observed in all simulations, albeit to different degrees. Simulations supported the hypothesis that the chemical composition of the pore solution within the crevices differs from that of the bulk solution through a process similar to the suggested mechanism of typical crevice corrosion.