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The Arthur Laing Bridge was constructed in 1975. At a relatively early age of about 6 years it began to suffer damage due to corrosion of the deck reinforcement. A major rehabilitation and resurfacing program was implemented in 1987, which included the installation of a cathodic protection system on about 45 percent of the 21,200 mý deck. This is one of the largest installations of cathodic protection on a reinforced concrete bridge deck. The original deck was milled to a depth of 15 to 25 mm to remove chloride-contaminated concrete. A catalyzed titanium wire mesh anode system was installed on the milled surface after delaminations had been patched. Finally a 50 mm thick low-slump dense concrete overlay was placed. This paper describes the design and construction of the cathodic protection system. Technical details of the cathodic protection and overlay system and construction costs are also presented.

The impressed current-type of cathodic protection was evaluated for controlling of marine concrete structures as follows: To establish criteria of cathodic protection on marine concrete structures, to develop a system that can distribute current uniformly to all reinforcement, and to investigate the over-protection problem that effects the bonding of reinforcement and durability of anode material. The application of the cathodic protection system for the rehabilitation of a harbor concrete structure in Japan was also examined.

Seventeen concrete mixtures were prepared to evaluate the deicer salt scaling resistance of some high-strength concretes with a 28-day strength in the 60 to 90 MPa range. A 0.30 water/(cement + silica fume) ratio was used for most of the mixtures and 3 additional mixtures were prepared with a 0.26 water/(cement + silica fume) ratio. In the 0.30 mixtures, two types of cements and a silica fume were used (Type III, Type III + percent silica fume, Type 1 + 6 percent fume), and in the 0.26 mixes, only Type 1 + 6 percent silica fume. Most of the concrete specimens were prepared with different air contents to produce a relatively low spacing factor and a high spacing factor. A very dense dolomitic limestone and a granitic gravel were used as a coarse aggregates. The curing period varied between 1 and 28 days. All the specimen were submitted to 150 daily cycles freezing and thawing in accordance with ASTM C 672, using sodium chloride as a deicer. Weight loss was measured to evaluate the deterioration of the concrete surfaces. The scaling resistance of the specimens made with a Type III cement (with the limestone aggregate or the granitic aggregate) was found to be very good in all cases, irrespective of the length of curing, the silica fume content or the spacing factor values. The non-air-entrained concretes made with a Type I portland cement also had a good scaling resistance after 24 hr of curing but, in this case, a better durability was obtained by using a longer curing period (7 to 28 days). For all concretes, the weight loss after 50 cycles was lower than 0.75 kg/mý and under 2 kg/mý after 150 cycles, and no clear relationship was found between the scaling resistance and the spacing factor. However, there are indications that when a high strength concrete can perform very well in a scaling test without air entrainment, the use of a relatively high air content can somewhat reduce its scaling resistance. Based on these results and others from recent publications, it seems that the use of a water/(cement + silica fume) ratio of 0.30, a good quality coarse aggregate and a portland cement with silica fume generally allows the production of non-air-entrained concretes with a good deicer salt-scaling resistance, even after only 24 hr of curing. It is also possible, with certain Type III cements, to produce deicer salt scaling resistant non-air-entrained concretes without using silica fume.

This paper gives the results of an investigation undertaken to determine the scaling resistance of concrete incorporating fly ash, and discusses factors affecting that resistance. A total of 21 air-entrained concrete mixtures were made. Water/(cement + fly ash) ratios of 0.35, 0.45, and 0.55 were used, and reference concrete (without fly ash) and concrete incorporating 20 and 30 percent fly ash as replacement by mass for cement were made. Two aggregate types were used in the investigation. The test results show that concrete incorporating up to 30 percent fly ash performed satisfactorily under the scaling test with minor exceptions. Extended moist-curing or drying periods did not affect significantly the performance of the reference and fly ash concretes in the scaling test, at least within the periods investigated. Membrane curing appears to improve somewhat the durability of concrete under the combined action freezing and thawing and deicing salts; this is especially true for fly ash concrete.

The use of high-strength concrete with compressive strengths between 60 and 100 MPa has been studied in Finland since the early 1980s. This study stated that the frost resistance and salt-frost resistance of non-air-entrained, high-strength concrete is generally high. The best results were achieved with rapid hardening portland cement with or without silica fume. Blended slag cement and slow-hardening portland cement did not show as good resistance, and especially after ageing their resistance was decreased. The microstructure of high-strength concrete is dense. According to the porosity and optical studies, the frost damage causes first the increase of size of pores with initial diameter more than 50 to 100 nm and secondly increase in size of pores with initial diameter more than 50 to 100 nm, and secondly an increase of pore volume but not average size in capillary range.