Maley R.,Corrosion Probe Inc
Journal of Protective Coatings and Linings | Year: 2014
The article examines many of the common errors that often occur when concrete substrates are rehabilitated and offers practical solutions for prevention of said errors. The practice of lining concrete substrates has increased exponentially over the last 30 years. Environmental regulations, coupled with changes to treatment processes, have resulted in far more severe environments in which concrete can and will corrode. A lack of understanding and experience extends beyond the contacting level. Many engineers, consultant, and inspectors do not fully comprehend the idiosyncrasies of lining concrete. When all the aforementioned parties converge upon a complex lining project, the potential for a perfect storm exists. The majority of lining failures, regardless of substrate, are often attributed to inadequate surface preparation.
Nixon R.A.,Corrosion Probe Inc
Journal of Protective Coatings and Linings | Year: 2012
A special report on the basics of maintaining and protecting concrete with high performance coatings is discussed. First of all, the engineer should be certain there is a clear understanding of the damage mechanisms that caused the concrete to deteriorate. Testing must be performed to determine the concentration of those ions and how deeply they have penetrated. As with protective coatings adhesion, adequate concrete surface profile, degree of cleanliness, and removal of contaminants are critical to optimizing the adhesion of concrete repair materials to existing concrete substrates. It is essential that substrate contaminants like chlorides and sulfates are removed to acceptable levels to prevent further rebar corrosion or expansive sulfate reactions. If there is a through-crack in the substrate that could manifest structural movement in the future, it must be treated like a moving joint. When making concrete repairs with a radius at inside or outside corners in structures, repairs should be made with a radius that avoids 90 degree transitions.
Nixon R.,Corrosion Probe Inc
Journal of Protective Coatings and Linings | Year: 2013
The basic make up of concrete, characteristics of uncoated concrete that make it susceptible to attack in industrial structures, and main mechanism of concrete deterioration is discussed. There are different types of concrete but all are made from the same types of ingredients. Concrete deterioration can be divided into three types, chemical, physical and thermal. Chemical mechanisms of concrete deterioration begins with a chemical reaction. A chemical substance in the environment comes in contact with a concrete structure, and a reaction occurs between the chemical and the paste. The reaction weakens, dissolves, or otherwise changes the paste, so that the paste can no longer hold the concrete together. Microorganisms such as bacteria and tiny marine organisms called mollusks, can cause concrete to deteriorate. Physical mechanisms start with a physical attack from external objects or equipment. Concrete expands and contracts as temperature rise and fall, causing deterioration.
Nixon R.A.,Corrosion Probe Inc
Journal of New England Water Environment Association | Year: 2010
This two-part article is based on lessons learned concerning biogenic sulfide corrosion of concrete from inspecting combined sewer overflow (CSO) and conveyance tunnels over several years in large wastewater collection systems. In Part 1, design basics for reducing drop shaft turbulence are presented, and corrosion patterns associated with tunnel turbulent zones and air flow conditions are discussed. Part 1 also examines the major design considerations affecting tunnel lining material selection. Part 2 describes the pros and cons of the major types of tunnel lining technologies and provides recommendations for future corrosion prevention in CSO and conveyance tunnels.
Nixon R.,Corrosion Probe Inc
Journal of Protective Coatings and Linings | Year: 2010
Odor control systems do not magically make H 2S gas disappear from the headspaces of wastewater tanks and structures. Rather, odor control ventilation systems pull foul air over headspace surfaces, which are wet and inhabited by sulfur oxidizing bacteria. Additionally, fresh air supply to these headspaces brings an ample supply of oxygen to the aerobic bacteria, ensuring their health and the proliferation of corrosion. Dead spaces in the airflow patterns have been shown to create zones of higher corrosion in headspaces with operating odor control systems, as well. The ductwork and the other air handling and treatment equipment used for odor control systems suffer from biogenic sulfide corrosion when not constructed from corrosion resistant materials. The headspaces of the covered tanks and other wastewater treatment structures are an extension of the odor control air collection system. Hence, concrete and many metal surfaces in these headspaces must also be protected from corrosion Because the sulfide species are in chemical equilibrium in wastewater environments, the free H2S gas removed by ventilation will invariably be replaced by more dissolved H 2S. The dissolved H 2S gas will, in turn, be replaced by the conversion of bisulfide (HS-) to aqueous H 2S. This means that, despite ventilation, H 2S gas will continue to be released into the headspace atmospheres and pulled across the surfaces upon which it will condense and/or be absorbed and be transformed by the ever-present sulfur-oxidizing bacteria to sulfuric acid. Two conditions would mitigate biogenic sulfide corrosion. The H 2S gas concentrations would have to be below 2 ppmv, and the surfaces over which the headspace air was pulled would have to be dry. Neither condition typically occurs in the subject headspaces. If these two conditions exist, they would be extremely short-lived. Creating these conditions through more air changes or better air sweeping is not pragmatic or economical. The end result, thus, is consistent with what we see in real-world field applications. Ventilation associated with odor control cannot mitigate corrosion related to biogenic sulfide production of sulfuric acid. Rather, it simply reduces the severity of sulfide corrosion to our infrastructure. Corrosion protection is therefore required for headspace substrates despite the presence of odor control air treatment systems. In short, corrosion and odor are related issues in wastewater applications and require separate control measures.