International Concrete Abstracts Portal

In the late 1990’s stainless steel has gained increased acceptance as an economically viable material for concrete reinforcement in bridge decks. Its ease of fabrication and outstanding resistance to corrosion caused by chlorides and other corrosive effluents have allowed it to be used in new bridge construction as well as rehabilitation projects. Corrosion studies have indicated that the material may have easily a life cycle of between 50 and 100 years even with heavily salted highways. Additions of nitrogen and special processing have also allowed the project designers to save weight and reduce the use of special membrane layers and other concrete additives to the bridge design. This therefore in part defrays the higher initial cost of using stainless steel reinforcement as compared to either epoxy coated or plain black steel. Before 1995, several projects in the USA, the UK and in Europe had employed 304 grade stainless as reinforcement. In North America in the last several years, higher-grade alloys of stainless such as 3 16LN and Duplex 2205 have been used more prevalently. This paper will examine the benefits of the use of these alloys. We will address why they have become increasingly accepted as well as the reasons for their selection in specific bridge projects in North America. We will also examine the specific role of moly and nitrogen as alloying elements in stainless steel rebar. A general review of corrosion mechanisms, potential problems and the physical and mechanical properties of these alloys as compared to other potential alloy selections will also be presented.

Experimental results of the bond behavior of 10, 13, 19, and 25-mm diameter bars corroded to various levels are presented. A total of forty specimens were tested to obtain the bond - slip behavior. The corrosion level ranged from 0 to 4.79 percent diameter loss. Externally applied current was used to induce controlled amount of corrosion. The results were analyzed to study the influence of bar diameter and corrosion level on bond strength, slip at peak load, and overall bond - slip behavior. The results indicate that exponential reduction in bond strength occurs once the diameter loss exceeds a fraction of a millimeter. At a diameter loss of O.l-mm, the strength reductions are substantial. The reduction in slip at maximum load is even more significant with corrosion. The actual magnitude of corrosion can be predicted using the applied current input with reasonable accuracy.

Fiber reinforced polymer composite (FRPC) wraps are increasingly being used for rehabilitation and strengthening of concrete structures This paper presents the results of an experimental study on the tensile performance of cement-based specimens wrapped with FRPC sheets subjected to wet-dry and freeze-thaw cycles. The tensile strength values were evaluated using the ASCERA hydraulic tensile tester. This simple testing technique provides a uniform stress distribution throughout the specimen, thus minimizing eccentricity and gripping effects, which can be of a significant source of error. Cement-based specimens were wrapped with three different types of FRP tow sheets: two carbon and one glass. Test variables included the type of fiber (Cl, C5, and GE) and the environmental exposure conditions. The specimens were conditioned in three different environments, as follows: a) room temperature (23C), b) 300 wet-dry cycles using salt water and c) 300 freeze/thaw cycles. At the end of each exposure, ultimate strength and load-extension behavior were obtained and then compared to the performance of unconditioned samples. Results show that specimens wrapped with carbon fiber reinforced polymer (CFRP) experienced no reduction in strength due to exposure, whereas specimens with glass fiber reinforced polymer (GFRP) experienced a significant reduction in strength. Fractography was used to identify the failure initiating flaw and failure mode for the fractured tensile specimens.

Three repair mortars were compared in terms of chloride attack preventive capability to propose an appropriate repair method applicable to the damaged concrete structure by chloride-induced corrosion. The repair methods were the cover replacement method and the surface coating method. The ability of these two methods to prevent corrosion were compared in terms of corrosion area and mass loss after 10 years’ outdoor exposure. It was proven that the cover replacement method extending over the backside of reinforcing steel using SBR polymer cement mortar with a corrosion inhibitor was effective while the surface coating method was applicable when the amount of chloride in concrete structures was excessive.

The effects of slag content and polymer-binder ratio on the properties of autoclaved and combined wet/dry-cured polymer-modified mortars using ground granulated blast-furnace slag (slag) and polymer dispersions such as a styrene-butadiene rubber (SBR) latex, and poly (ethylene-vinyl acetate) (EVA) and polyacrylic ester (PAE) emulsions are examined. As a result, the strength of the autoclaved polymer-modified mortars reaches a maximum at a slag content of 30% except for the autoclaved EVA- and PAE-modified mortars, and tends to increase or decrease with increasing polymer-binder ratio. The strength of the combined wet/dry-cured polymer-modified mortars reaches a maximum at a slag content of 40%, and is inclined to increase with increasing polymer-binder ratio. Irrespective of the curing conditions, their water absorption and chloride ion penetration depth tend to decrease with increasing slag content and polymer-binder ratio except for the autoclaved PAE-modified mortars. Their carbonation depth increases or decreases with increasing polymer-binder ratio.