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.

Concretes containing either latex, Class F fly ash, ground granulated blast-furnace slag, silica fume, or, in some cases, combinations of these ingredients generally are found to have lower permeabilities than concretes containing only portland cement as the cementitious material. Concretes with low permeability provide high resistance to penetration by chlorides or other aggressive ions, which is essential for insuring their long-lasting performance when exposed to aggressive chemical attack while in service. The tests conducted show that either the rapid chloride- permeability test (AASHTO T 277 or ASTM C 1202) or the ponding test (AASHTO T 259) (used for periods longer than the standard 90 days) can be used to differentiate the permeability of different concretes. General agreement in the findings of the two tests with respect to chloride permeability is expected, provided that the concretes compared have been exposed to similar conditions and periods of exposure, and that possible interferences with the results of the rapid test have been eliminated.

Reduction in the useful service life of bridge decks in the USA and Europe and reinforced concrete structures in tropical countries due to reinforcement corrosion has been of major concern to the engineering community throughout the world. In both situations, the presence of chloride ions in sufficient quantities is the primary cause of the initiation of reinforcement corrosion. Chlorides are contributed by deicer salts in the bridge structures, while soils and groundwater charged with high concentrations of salts in tropical countries contribute significant quantities of chloride ions. In the latter regions, the low precipitation and high evaporation rates result in high salinities in the soil and groundwater. In this investigation, cement paste, mortar, and reinforced concrete specimens made with two plain cements and three blended cements were placed in a 15.7 CL - (26 percent NaCl) solution. The performance of the plain and blended cements in resisting reinforcement corrosion was evaluated by monitoring the corrosion activity at regular intervals. The effect of high concentrations of chloride salts on the physical properties was monitored by measuring compressive strength reduction. Results indicate retrogression of strength in blended cement mortar specimens placed in the chloride solutions compared to those cured in potable water. This behavior was more pronounced in the silica fume cement. However, the resistance to reinforcement corrosion of the blended cements, particularly silica fume cement, was better than the plain cements.

Since 1990, five new methods for testing the potential alkali-reactivity of aggregates have been standardized by AFNOR, the French Bureau of Standards. These methods were all developed out of existing methods such as ASTM C 227 or C 289, CSA A 23.2 14 A, or those proposed by Tamura, Nishibayashi, or Tang Ming Shu. Furthermore, the cement industry has developed a method for testing the stability of a concrete mixture, afterward designated as "concrete test method." All six methods were included in the Recommendations of the French Ministry of Equipment, issued in January 1991, as means for the prevention of damage by alkali-aggregate reaction. The AFREM Working Group on Alkali-Aggregate Reaction started a round robin test on these methods, using the three French reference aggregates. This paper reports the results of this round robin test program, giving comparative data on both the reliability and reproducibility of the five aggregate standard test methods, and showing the good reproducibility of the concrete test method.

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.