International Concrete Abstracts Portal

The objective of this paper is to present a new class of corrosion inhibitors. These organic and mixed (organic/inorganic) inhibitors are used as concrete admixtures or in repair products to delay the onset of corrosion or to reduce the rate of corrosion of steel in concrete structures. The inhibiting properties are documented in solution and in concrete. The interaction mechanism of the inhibitors with a steel surface has been studied using sophisticated surface analytical methods. The transport properties of these inhibitors are shown in mortar and concrete blocks. The inhibitors delay the onset of corrosion and reduce the rate of corrosion. They can be used as a concrete admixture, surface applied on existing structures, in repair mortars, or in grouts for rock bolts and anchors.

High-performance concrete slabs have been field exposed at the Traslovslage marine field station at the Swedish west coast since April 1992 as a part of the Cementa/Euroc sponsored project, "Durability of Marine Concrete Structures." The concrete slabs mounted on a floating pontoon are exposed in three exposure zones: submerged, splash, and upper splash zones. The results after two years of exposure confirmed the expected inverse relationship between chloride ingress and water-to-binder ratio. The use of five to 10 percent silica fume in the binder had a very positive effect on reducing the chloride ingress, but no benefit at all was found for concrete with fly ash in the binder as compared to the use of five percent silica fume. Generally, the results indicated that high-performance concrete may be regarded as extremely resistant to degradation by reinforcement corrosion, as long as effects of cracks are not considered. The extremely low levels of chloride ingress in the high-performance concrete indicated that the service life in practice will be decided by the properties of defects in the concrete microstructure. As a consequence, it was recommended that durability research on high-performance concrete should address the effects of cracks, of voids at the steel surface, and of other defects in the microstructure on the long-term performance. Such studies are currently being undertaken in Sweden, Norway, and Denmark.

Presents the results of a study on hydrogen embrittlement of prestressed concrete (PC) tendons. The purpose of this research work was to make clear the influence of cathodic protection used in PC members. The tests consisted of three series. Series A was carried out to evaluate the relationship between the polarization potential and the period of current supply. In Series B, a countermeasure to mitigate hydrogen embrittlement was investigated. PC members in Series C were cathodically protected and exposed to a sea environment for five years. Cathodic polarization was applied to the wire specimens of Series A under tension stress. After polarization, the wires were soaked in a saturated solution of Ca(OH) 2; slow strain ratio test (SSRT) was carried out. In Series B, polarization was applied to wires under tension stress and were then kept under no current supply for 15 hr to five days. Finally, mechanical properties were evaluated. After exposure of five years to a sea environment, PC tendons were taken out of the Series C concrete specimens; SSRT and tests of hydrogen occlusion were carried out. This test program showed that the harmful effects of hydrogen embrittlement may be mitigated by switching off of the cathodic protection at regular periods.

Concrete structures exposed to a salt-laden environment often suffer from both carbonation and chloride contamination. This paper presents test data on the ability of a highly elastic acrylic rubber coating to resist the penetration of both chloride ions and carbon dioxide. In addition, the bond strength of the coating to the concrete substrate when subjected to repeated cyclic wetting by chloride solution and drying is also reported. The chloride ion penetration resistance of the coating and its bond strength to concrete were studied by exposing reinforced concrete slabs, some fully coated and others half-coated, made with three water-cement ratios, to cycles of wetting with four percent sodium chloride solution and drying. The tests were carried out for 50 cycles extending over a period of over 500 days. The carbonation resistance of the coating was established through tests on cores taken from four structures exposed to aggressive marine conditions and subsequently repaired with the acrylic rubber coating. The results show that this acrylic rubber coating has excellent resistance to both chloride ion penetration and carbonation. No chloride ions were found in slabs fully protected with the acrylic coating. The migration of chlorides from the uncoated into the coated parts was confined to the immediate boundary between the two and was small and slow. Chloride penetration occurred by a time-dependent diffusion process, but largely in the direction of gravity. In a carbonating environment, coated concrete showed significant reduction in carbonation depth; there was evidence of realkalization of the carbonated concrete.

Describes the results of marine durability studies carried out on concretes containing high-alumina cement (HAC) and ground granulated blast furnace slag (GGBFS) blended cements. Concrete cubes of 100 mm were initially cured for 28 days at 5, 20, and 38 C in water and in air at 20 C prior to their storage in the different marine environments. The specimens were exposed for up to four years in spray, tidal, and full- immersion zones at the Building Research Establishment's marine exposure site on the Thames estuary at Shoeburyness. Chloride penetration data down to depths of 36 mm were determined and evidence of frost damage sought in these non air-entrained concretes after four years of marine exposure. All HAC/GGBFS concretes performed well in terms of their low chloride ingress and excellent frost resistance, irrespective of early curing temperature or marine exposure zone. Most of the plain HAC concrete performed equally well, with the exception of the converted specimens, pre-cured at 38 C prior to storage in seawater. These concretes were frost resistant, but showed some signs of chemical attack and had high levels of chloride at 36 mm depths. The practical significance of these data is discussed.