International Concrete Abstracts Portal

SP-163 This specialized publication offers 24 papers presented at the Third CANMET/ACI International Conference held on August 4 -9, 1996 in New Brunswick, Canada on the subject of Performance of Concrete in Marine Environments.

For an undersea tunnel project, laboratory and field tests were carried out to study the influence of permanent submersion in re-circulating seawater on the corrosion of steel in reinforced concrete. For each concrete mixture, cube specimens of plain concrete and beams of reinforced concrete were made. Sound as well as precracked beams with a crack width of about 0.03, 0.3, and 1.0 mm were produced. The following parameters were measured as a function of time by visual and microscopic examinations: chloride penetration and electrical resistivity in plain concrete specimens, as well as the corrosion rate of steel in reinforced concrete beams. Results show that chloride diffusion rate in concrete was reduced by decreasing the water-cement ratio (w/c) and by using fly ash or silica fume. In polymer impregnated concrete (PIC) specimens, chloride penetration was negligible until about three months of permanent submersion in seawater; after this period, the penetration rate surprisingly increased according to a capillary suction mechanism. The electrical resistivity results were in agreement with those on chloride diffusion. The corrosion rate, in terms of corroded surface area and pit depth, was not detectable on sound uncracked beams within a two year period of permanent submersion in seawater, regardless of the w/c (0.65 to 0.35). It is expected that, even at longer ages, the corrosion rate will be negligible due to lack of oxygen which is needed for the corrosion process. In precracked concrete beams with crack widths greater than 0.2 mm, a pitting corrosion process was observed on the steel reinforcement close to the crack tip. No technical advantage in reducing the corrosion of steel was recorded when PIC, instead of regular concrete, was used.

Concrete has been used for ship construction for over 100 years; many of these ships are in locations where they can be readily examined. The condition of some of these ships is discussed in this paper and the results of tests on the ships reported. Instances of improper design, detailing, and construction have been identified. Most of the ships inspected were built under wartime conditions, with limited time for design and construction. Nevertheless, they performed well and, although many are now used for purposes which the designers had not anticipated, they continue to serve a useful purpose. The results of inspection and testing of various ships are given, including compressive strength, depth of carbonation, and chloride content. Recommendations are made for improvements in design, detailing, and construction that, combined with enhanced concrete material properties, should assure that concrete ships built in the future will perform even better than those in the past.

The deterioration of concrete structures for breakwaters in cold marine environment, situated in the northernmost part of Japan, was examined by means of physical inspections as well as chemical analysis. A total of 76 points from 16 breakwaters were selected for measuring deterioration. The 16 breakwaters consisted of 10 fishing ports: four of them are situated in the north islands; two are situated along the Sea of Japan; and four are along the Sea of Okhotsk. At the time of examination, the ages of concrete ranged from six to 35 years. Physical inspection entailed measuring the vertical profile using a special frame. In addition, nondestructive tests were conducted to estimate the compressive strength of the concrete. Cylindrical cores (diameter 150 mm) were drilled from each breakwater for measuring the compressive strength, chloride contents, and degree of carbonation. Chloride contents were measured at several depths, from the submerged surface to 80 cm inside of concrete. X-ray diffraction analysis, as well as atomic absorption spectrometry, were conducted for microscopic analysis. In some instances, more than 1.0 m depth of wear was found at the tidal zone between high and low tide level. The shapes of wear showed the typical hourglass shape. A high value of correlation coefficient was found between the wear depth and in situ compressive strength estimated by a nondestructive test method. No significant correlation was found between the wear depth and the age of construction. It was found that the maximum chloride content was not always at the skin of concrete breakwaters, but was frequently deep inside of the structures. From the test results of the X-ray diffractometry and the atomic absorption spectrometry, aragonite, gypsum, ettringite, and calcite were observed. This indicates the possibility of decomposing action of seawater on the constituents of hydrated portland cements. Finally, reliability analysis was used to predict the remaining service time based on the field data collected. Three factors were selected by the statistical significance, these are the strength of concrete from nondestructive test results, the chloride penetration content, and the depth between high and low tide levels.

Research on high-performance concrete structures in the field have revealed large variations in chloride penetration into the concrete and in corrosion rates of the reinforcement. High-performance concrete is considered to be highly resistant to the initiation of reinforcement corrosion. The rate of chloride transport decreases with time to extremely low values (10 -13/10 - 14 m 2/sec). However, since concrete often is cracked, the occurrence and effect of cracks are also important factors for corrosion initiation in chloride environment. The effect of cracks on the corrosion rate of steel in high-performance concrete is under study in a Swedish research program. Reinforced concrete slabs with cracks of different widths are placed on floating platforms in the sea; the lower part of each slab is submerged, while the upper part is exposed in the splash zone. Corrosion rates, half-cell potentials (CSE), and concrete resistivities are measured regularly. Parallel specimens are similarly exposed in saline solution in the laboratory. This paper presents interim results of this project. The results so far show little effect of crack width and concrete cover thickness. Addition of microsilica (silica fume) is positive, by increasing the concrete resistivity and, thus, reducing the rate of corrosion; the corrosion behavior of such concretes is close to passive, even with cracks.