International Concrete Abstracts Portal

This paper describes the results of a ten-year marine exposure test of reinforced concrete. Sixteen pre-cracked test specimens were examined. The target crack width was 0.2mm. The dimensions of the specimens were 15x15x100cm. Ordinary deformed bars and epoxy-coated deformed bars, as well as normal portland cement and portland blast-furnace slag cement were used. The water-cement ratio in the mixture proportions ranged from 0.320I to 0.483%. The effect of nitrite-based corrosion inhibitor was also examined. From the exposure test results, the following conclusions were drawn: When the water-cement ratio was low, the penetration of chloride ions into the concrete was low; the chloride-ion content on the surface of blast-furnace slag cement concrete was greater than on the surface of concrete made with ordinary cement, but was smaller inside; there was a tendency for the chloride-ion content around the reinforcing bars in concrete portions with small cracks to be greater than in portions with large cracks; ten years of exposure caused an increase in crack width due to the corrosion of the reinforcing bars; although the effectiveness of epoxy-coated reinforcing bars in preventing corrosion was obvious, severe corrosion was found in one coated bar. The epoxy-coated bars used were produced for the first time in Japan, and test results indicate that there were problems with the early production technology; there was no beneficial effect from corrosion inhibitor after ten years.

For cathodic protection of reinforcing steel in concrete, a layer of zinc sprayed on the concrete surface can be used. This study presented the following concerns: the definition of concrete surface properties for adequate adhesion; the definition of the adequate spraying procedure, depending on the type of metal--pure zinc or zinc-aluminum alloy; the performance of cathodic protection systems in reinforced concrete slabs, under aging cycles. These slabs were stored outdoors. The aging cycles of the concrete slabs included: freezing during about 2 hr, by pouring liquid nitrogen on the surface of the slabs, so that a temperature gradient appeared in concrete; and thawing by natural heating, then by pouring water saturated with sodium chloride. This solution was then left flowing on the slab surface. The performance of the cathodic protection systems was checked by the usual procedures such as measuring the reinforcing steel potential and by checking the condition of the anode. It has been shown that cathodic protection can be fully achieved with zinc-spraying the concrete surface and application of impressed current. The experimentation on protection with sacrificial anode has given promising results. It also appeared that even when thin cracks are formed on the concrete surface, zinc spray coatings are still bonded, and the cathodic protection performances are changed only if cracks are wide enough to allow the salt solution to reach the embedded reinforcing steel.

In France, water towers, reservoirs, tanks, and basins constitute extensive facilities requiring inspection and maintenance. The survey recently conducted on the performance and durability of waterproofing in these structures is of considerable importance at the present time, with the publication of the new French professional recommendations, the revision of Section 74 of the CCTG (general technical specifications governing public contracts entered into in the name of the state), and the negotiation of future European Community regulations. This survey enables us to better understand existing facilities and to obtain precise information on such structures, with details on capacities, heads, and commissioning dates, but also on the selection of the initial waterproofing used, which may be a sealed structure itself or a support for waterproofing.

An overview of the scientific and technical literature published on the subject is presented. The first part of this report is devoted to the fundamentals of frost action in concrete. The mechanisms of freezing and hypotheses explaining the detrimental effects of deicing salts are discussed. Special attention is paid to the influence of the concrete curing temperature and moisture history on its frost durability. A critical appraisal of three different test procedures designed to assess the deicer salt scaling resistance of concrete is given in the second section. Each test method is evaluated on the basis of reproducibility, variability of test results, operating cost, and relationship to field exposure conditions. Finally, the influence of various parameters on the deicer salt scaling resistance of concrete is discussed. Topics such as mix composition, air entrainment, casting operations, curing, and use of concrete sealers are reviewed.

This laboratory and field investigation studied the deicer scaling resistance of ground granulated blast furnace (GGBF) slag concretes. The laboratory part of the investigation used the ASTM C 672 test with up to four different curing routines: air, curing compound, the standard procedure, and intermittent wet cure. The field part evaluated three curing routines: air, curing compound, and intermittent wet cure. It also evaluated two different finishing tools, and the effect of a linseed oil-kerosene sealer applied at 90 days. Overall, regarding the effect of GGBF slag dose on scaling resistance, and relative to portland cement content: 25 percent improved resistance, 35 percent was better in the laboratory and similar in the field, 50 percent was variably better or the same or worse, and 65 percent scaled more in the laboratory and less in the field.