International Concrete Abstracts Portal

Presents results of a study on the effect of several types of coatings and surface treatmets on the corrosion activity on specimens containing U-shaped epoxy-coated reinforcing bars cast in concrete slabs. These reinforced concrete slabs were subjected to severe exposure conditions and evaluated after four years. To obtain results in a short time period, a high water-cement ratio of 0.6 and concrete cover of only 20 mm were used. Four different types of epoxy coatings were investigated, with some bars being coated before bending and some coated after bending. The reinforcing steel had been surface treated by the supplier in seven different ways before coating, with some of the bars receiving a primer coating before application of the epoxy coating. Also, the surfaces of some bars were contaminated with salt prior to coating. Some reinforcing steel bars were intentionally damaged with the damaged area being seven 6 mm x 6 mm square spots evenly distributed over the surface of each bar. The exposure conditions were a laboratory test chamber simulating a marine environment and a natural marine environment site at Treat Island, Maine. Assessment of corrosion activity was carried out using linear polarization resistance and open circuit potential techniques. A visual survey was done as well. The results indicated that undamaged epoxy-coated reinforcing steel bars performed very well, with no corrosion occurring after four years of severe exposure conditions with low strength concrete (w/c=0.6) and only 20 mm of cover. The test results indicate that, after four years of exposure, most of the various surface treatments or types of coating were equally effective in terms of long-term corrosion protection of the reinforcing steel. However, the exception was a salt contaminated surface, in which a corrosion rate of up to 50 percent of that for uncoated reinforcing steel was observed.

The concrete lining the outfall canal of Munmorah Power Station, built by the Electricity Commission of New South Wales (now operating as Pacific Power) in the mid-1960s, has been subjected to flowing seawater for 30 years. Two types of concrete, a portland cement concrete and a fly ash concrete, were used for the construction of the canal. This presented an ideal opportunity for a comparison to be made of the performance of the two binders in concretes which were subjected to the same aggressive environment. Limited information was available on the concretes from trial mixture records. A recent field investigation revealed similar chloride ingress into the two concretes in the tidal zone. This was so despite the fact that the fly ash concrete had a lower binder content than the portland cement concrete. As such, a lower strength grade and, hence, a fly ash concrete with higher water permeability can perform as well as a portland cement concrete. In the dry area above the high tide mark, the carbonation depth of the fly ash concrete was greater than the portland cement concrete. No corrosion was found in any reinforcing steel, as there was sufficient cover in both concretes to prevent the chloride ions or carbonation front reaching the steel. The effectiveness of a number of investigative techniques was evaluated during the investigation. It was found that the apparent chloride diffusion coefficients, determined from short-term immersion, the water permeability coefficients, and copper to copper sulfate half-cell potential measurements were poor indicators of the real long- term performance.

Electrical potential technique was used as an accelerated testing method to determine the chloride diffusion coefficient of high-performance concrete. An electrical potential difference of 15 volts was applied to a disc-shaped concrete specimen of 50 mm in thickness. This direct current voltage increased the flux of chloride ions migrating through the concrete and permitted the determination of the chloride diffusion coefficient (D CL) within three to four weeks of the testing period. The water-to-cementitious materials ratio (W/C) had a significant effect on D CL, where the relationship between W/C and D CL was expressed as D CL={0.32EXP[5.47(W/C)]} x 10 -8 cm 2/s for normal concrete without any mineral additives. Concretes with five and 10 percent silica fume replacements for ordinary portland cement were also tested and had D CLs equal to 3.14 and 2.99 x 10 -8 cm 2/s, respectively, after a 28- day moist curing period. These D CL values were lower than that of concrete containing only portland cement, being 4.3 x 10 -8 cm 2/s for concrete with the same W/C of 0.45 and a moist curing time of 28 days. Furthermore, super- workable concrete which had a W/C of 0.3 and was moist cured for 28 days had a D CL of 1.97 x 10 -8 cm 2/s.

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.