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INVESTIGATION OF CONCRETE JETTIES AT CFB ESQUIMALT AND PREDICTION OF FUTURE SERVICE LIFE Investigation of concrete jetties G. OVSTAAS Principle, G. Ovstaas & Associates D.R. MORGAN Chief Materials Engineer, AGRA Earth & Environmental Durability of Building Materials and Components 8. (1999) Edited by M.A. Lacasse and D.J. Vanier. Institute for Research in Construction, Ottawa ON, K1A 0R6, Canada, pp. 46-55. Ó National Research Council Canada 1999 Abstract The concrete jetties at the Canadian Forces facilities at Esquimalt and Nanoose Bay are of similar design and age. They consist of a 300 mm reinforced concrete topping which acts compositely with square box girder beams which span between pile bents. The concrete topping at both jetties has undergone severe cracking, which has been attributed to drying and autogenous shrinkage aggravated by the use of epoxy coated reinforcement. Many of the cracks are aligned with the reinforcement and have created reservoirs for chloride ions concentrated very near the reinforcement. Condition surveys indicate that while the chloride ion concentrations adjacent to the reinforcement are high, no corrosion damage has occurred to date. Various analytical models have been investigated to estimate the future service life of the structures and the potential effectiveness of the remedial work such as the application of surface sealants. Keywords: Epoxy coated reinforcement, cracking, predicted service life, sealants. 1 Introduction C-Jetty, which is located at CFB Esquimalt and Ranch Point Jetty at Nanoose Bay in British Columbia were investigated to evaluate the condition of the concrete and the state of the reinforcement in the reinforced concrete decks (Ovstaas 1994). These investigations were completed in 1996 at C-Jetty and in 1993 at Ranch Point Jetty. They were performed in part to obtain baseline information on the Jetty conditions and also to evaluate the nature and severity of cracking which had been observed in the concrete deck surface, with a view to the design of appropriate remedial procedures. 2 Structure Both Ranch Point and C-Jetty were designed in a similar manner. The jetties consist of rectangular box girders supported on pile bents at 19 m centres, overlain by a 200 to 250 mm thick reinforced concrete topping. Both jetties were constructed in approximately 1989-1990. Some known differences in the jetties are that epoxy coated reinforcement was used in both the top and bottom mats in the topping concrete at Ranch Point Jetty, while at C-Jetty the top mat was epoxy coated and the bottom mat was plain reinforcing steel. Secondly, the Ranch Point Jetty deck is on cathodically protected steel piles while the C-Jetty deck is on concrete piles. These two details have had considerable effect on the copper-copper sulphate half cell data measured on each deck. 3 Observations Both jetties were observed to be in a very similar condition. In general, there was little evidence of deterioration of either the concrete, or the reinforcing steel in the decks. However, the topping concrete on each deck contained severe shrinkage cracking. Typical examples of the cracking are illustrated in Figures 1 and 2. Fig. 1: Portion of C-Jetty showing cracking 3.1 Deck cracking The deck cracking in C-Jetty was mapped for most of the jetty surface and the floor of the Ship Repair Unit (SRU) Building. The cracking is extensive over the deck surface and in many areas was found to be aligned along the axes of the deck; i.e., the cracks are predominantly longitudinal and transverse to the length of the fingers. This is illustrated in the photograph shown in Figure 1 which were taken at approximately 8.00 am as the morning dew dried from the deck surface. The cracks were accentuated by the presence of moisture. Fig. 2: Cracking on West finger of C-Jetty The cracking in C-Jetty and the SRU building is very similar to the cracking observed at the Ranch Point Jetty at Nanoose. For both structures, it appears that the cracking is primarily the drying shrinkage and the plastic shrinkage induced, aggravated by the use of epoxy coated reinforcing steel. Previous work by Litvan (1989) has indicated that there is reduced bond of concrete to epoxy coated bars and that this may contribute significantly to the extent and width of cracking. This is reinforced by the cores undertaken which revealed that many cracks appear to originate at the location of the epoxy coated reinforcing steel. 3.2 Concrete cores Concrete cores were extracted from eight locations on C-Jetty. At least three cores were extracted at each location. These cores were used for a variety of laboratory tests including compressive strength, depth of carbonation, chloride ion profile and density. 3.2.1 Compressive strength and density The average strength for each location is listed in Table 1. It is understood that the specified compressive strength was 35 MPa at 28 days. As shown in Table 1, the cores from all areas tested (except at location 7) meet this criteria. At location 7 the compressive strength is very close to the specified 35 MPa value. Table 1: Compressive strength and density Compressive Location Density (kg/m3 ) Strength(MPa) 1 2367 47.2 2 2332 46.3 3 2408 62.0 4 2400 57.9 5 2322 35.7 6 2401 48.3 7 2340 34.6 8 2397 35.7 AVG=46.0 3.2.2 Depth of carbonation Treating the core samples with phenolphthalein indicator solution showed that no measurable carbonation has taken place to date. It is, however, recommended that the depth of carbonation be determined at regular intervals, particularly at locations where cracks intercept the reinforcing steel. If the concrete around the reinforcing steel becomes carbonated, then the concrete’s ability to inhibit corrosion may become compromised. 3.2.3 Chloride ion content The samples for chloride ion determination were obtained by dry drilling the cores at the desired depths perpendicular to the core axis. Typically samples were obtained at depths of 25 mm, 50 mm, 75 mm and 150 mm. The procedure used for determination of the chloride ion content was the “water soluble chloride ion concentrations have been calculated for a concrete with an average density of 2350 kg/m3 and cement content of 350 kg/m3. The results are presented in Table 2. Additional samples were also obtained by dry drilling to specified depths into the in-place topping concrete. Companion samples were obtained in this manner both at the location of the cracks and immediately beside cracks (Samples 9 to 11). According to the American Concrete Institute, ACI 318-95, recommended limit for water-soluble chloride ion content in conventionally reinforced concrete in a moist environment and exposed to chlorides is 0.15 % by mass of cement. At levels higher than 0.15 % there is a significant increase in the potential for chloride induced corrosion of the reinforcing steel. As shown in Table 2., there are many areas where the chloride contents are below the detection limit of 0.007 %. However, near the surface of the concrete and in the cracks, the levels can be much higher than the ACI 318-95 recommended limit. 1. In the sound, uncracked concrete the chloride concentrations were measured to vary from 0 to 0.215 % at a depth of 25 mm. At depths of 50, 75 and 150 mm the chloride levels were in many cases either undetectable or relatively low. 2. At the cracks in the concrete topping, however, the higher chloride levels can occur at the base of the crack as shown for Samples 9 and 11. Because many of the cracks have originated at the reinforcing steel, elevated chloride levels have been found at the steel. As shown in Samples 9 and 11, these levels are 3 to 5 times the limit for controlling corrosion recommended in ACI 318. 3.3 Half cell potential measurements Copper - Copper sulphate half cell measurements were obtained for the four areas shown in the C-Jetty plan. The half cell data is typically in a range which is less than -350 mV. The exceptions are the area East of the SRU Building and along the rail on the two fingers. The elevated potentials along the rails can most likely be explained by the corrosion occurring at the rails and base plates within the rail trench and the considerable surface area of steel available for corrosion sites. The rail trench is filled with hot mix asphalt concrete and therefore does not benefit from the usual corrosion inhibiting qualities of alkaline concrete. In addition, the trench can act as a collector for the surface runoff and chlorides from both salt spray and deicing salts. Test results for the area to the east of the SRU Building which also exhibited high half-cell potential readings (ie; -600 to -800 mV) are not as easy to explain. They do not, however, appear to be the result of corrosion of the reinforcing steel. Because of the consistency of the signal, it appears that a stray current within the reinforcement has been detected. Inspection of the area below the slab revealed that a ground wire is attached to many of the piles and this may be contributing to a portion of the measured signal. This area will be investigated further since (as discussed by Clifton (1991)) stray currents, may accelerate the corrosion process. Table 2: Water soluble chloride ion content Sample Depth (mm) Chloride Ion Content (1) Comments (% by mass of cement) 1B 25 0.215 -samples from core 50 0.034 75 <0.007 150 0.045 7A 25 0.164 -samples from core 50 <0.007 75 <0.007 150 <0.007 9 0-25 0.404 -drilled samples on crack 25-50 0.444 -refusal (steel?) at 53 mm 50-53 0.710 -outside SRU door 9A 0-25 0.125 -drilled beside crack and 25-50 0.013 sample 9 50-75 <0.007 75-125 <0.007 9B 45-53 0.252 -drilled beside crack -refusal (steel?) at 53 mm 10 0-25 0.356 -drilled on crack 25-50 0.172 -refusal (steel?) at 97 mm.

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