Cementitious Matrix is Used to Bond High-Strength Polymeric Mesh to Concrete and Masonry, Fallis
Fiber-reinforced polymer (FRP) systems are now widely used for retrofit and repair of concrete and masonry. The development of these systems has allowed repair and strengthening projects to be performed that, in the past, would not have been possible. Their benefits are well known and include a high ratio of strength to added weight, high durability, and ease and flexibility of installation.
FRP systems, however, are not without their drawbacks. Recently, Ruredil introduced a new fiber-reinforcement system that maintains the benefits of traditional FRP systems while overcoming some of their drawbacks. This product consists of a polyparaphenylene benzobisoxazole (PBO) mesh (Ruredil X Mesh Gold) and a stabilized, inorganic, cementitious mortar matrix (Ruredil X Mesh M750) designed to connect the mesh to concrete and masonry substrates. The unique structure of the PBO fiber allows it to bond directly to the mortar matrix, eliminating the need for an epoxy resin to bond the fiber to the concrete or masonry substrate. (read more)
Long-term Performance and Versatility of Zinc Sacrificial Anodes for Control of Reinforcement Corrosion, Sergi, Simpson & Potter
Since its development in the mid-nineties, numerous installations of the Fosroc zinc sacrificial anode have been carried out in repairs to steel reinforced concrete structural elements suffering from corrosion. From these, more than a dozen sites have been thoroughly monitored in the UK and worldwide. Results so far have been very encouraging with current densities ranging between 0.8 mA/m2 and 10 mA/m2 of steel surface depending on the type of application which includes cathodic prevention, corrosion control and cathodic protection. These levels of currents were shown to be sufficient to overcome any further visible corrosion of the steel reinforcement extending the service life of the repairs significantly. Some of the early trials have been monitored for nearly ten years now. This presents an opportunity for the results to be analysed and the performance of the sacrificial anodes to be critically assessed medium to long term. This paper reviews the performance of the anodes in terms of current output and steel polarisation levels over the years. The prospects of a further recently developed improved sacrificial anode system achieving substantially improved performance are reviewed and discussed. (read more)
Corrosion of Steel in Concrete & Assessment Techniques, Sergi
Concrete is a porous material whose pores contain an electrolyte made up primarily of sodium and potassium hydroxides. Steel reinforcement is normally protected in such an electrolyte owing to the formation of a dense and uniform passive oxide film. Carbonation of the concrete (neutralisation of the alkali constituents by CO2 gas from the atmosphere), or infestation of the concrete with salt from seawater or from deicing agents leads to the breakdown of the protective oxide film and to corrosion of the steel. Corrosion of steel in concrete is an electrochemical process whereby anodic and cathodic reactions occur simultaneously on the surface of the steel resulting in the dissolution of the metal at the anodic sites. (read more)
Corrosion Investigation & Testing of Post-Tensioned Cables, Fallis & Arnesen
The Post-Tech Corrosion Evaluation (CE) System provides a method for evaluating the potential for corrosion activity in un-bonded post-tension cables that if left untreated can be the cause of structural concerns with the un-bonded post-tensioned structures. This system has been successfully performed on several hundred structures in the past 15-years. It provides a method to restore the wet post-tension cables back to the environment for which they were originally designed. Un-bonded post-tensioned cables can not only be evaluated for their potential for corrosion, but also for identifying possible locations for un-bonded post-tension strand failure and the possible related structural deficiency.
The Post-Tech Cable Break (CB) system relies on the remanent magnetism method (RM-Method) to identify damaged or unsafe high strength individual or bundled pre-stress strands. This is a non-destructive test for evaluating the magnetic field or flux of externally magnetized tendons. Characteristic fracture readings of the magnetic leakage field are used to evaluate the extent of damage or amount of steel cross-section loss of the cables, which could include single or multiple wires in the strands. Wire or even strand fractures can happen abruptly and there are often no external visible signs of this type damage. (read more)
Embedded Galvanic Anodes for Targeted Protection in Reinforced Concrete Structures, Ball & Whitmore
Corrosion of reinforcing steel in concrete is a major cause of structure maintenance and repair. Oxidation at the anodic sites on the steel reinforcement causes expansive forces that leads to visible concrete distress such as rust stains, cracks, spalling, or delaminations. Corrosion can also cause delaminations in the concrete cover (which may not be visually apparent), potentially with large sections of concrete dislodging from the structure. Additionally, loss of section due to reinforcement corrosion can cause structural issues. Advancements in concrete repair methods and corrosion mitigation systems have given structural engineers many options to repair and extend the service life of actively corroding structures. Today, most structures suffering from corrosion can benefit from some level of electrochemical corrosion protection.
In some cases, a global protection strategy using electrochemical chloride extraction, impressed current cathodic protection, or galvanic protection is a preferred solution. Global protection should be considered if: 1) a long service life is desired; 2) corrosion activity is widespread; 3) the structure is considered to be critical in nature; 4) access is difficult and/or cost of future repairs are high; or 5) a high level of protection is required over large areas. n other cases, corrosion is not widespread or budget limitations prevent a more comprehensive approach from being implemented. In these cases, implementing a targeted corrosion mitigation approach is generally preferred rather than not providing any protection whatsoever. Targeted corrosion protection can be economically implemented to provide an extension of service life at a moderate incremental cost and reduce the risk of serious corrosion damage.
For almost a decade, embedded galvanic anodes in a discrete or “point” form have been used to provide localized corrosion prevention around concrete repairs. Embedded discrete anodes are installed around the perimeter of the concrete repair as close as practical to the patch edge. The anode units are prewet and tied directly to the reinforcing steel. The anode spacing is dependent on the amount of steel protected, but is generally in the range of 12 to 24 in. (305 to 610 mm).
For over 5 years, galvanic anodes in a ribbon or strip form have been used to provide protection in reinforced concrete. As opposed to discrete or point anodes, these anodes are referred to as distributed anodes and are provided in various shapes and lengths up to 7.5 ft (2.3 m). Distributed anodes are placed across the surface of the concrete to be protected then embedded in a reinforced concrete jacket or overlay. The distributed anode systems are used to provide galvanic protection over a larger area but can be easily used to protect small structural elements such as a single pile, column, or wall. This type of system can also be referred to as a galvanic encasement. (read more)