INVESTIGATION OF CONCRETE JETTIES AT CFB 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, , 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 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. 50-75 0.018 75-97 <0.007 10A 0-25 0.167 -drilled beside crack near 25-50 <0.007 sample 10. 50-75 0.014 75-100 <0.007 100-125 <0.007 11 0-25 0.451 -drilled on crack 25-50 0.350 -refusal (steel?) at 60 mm 50-60 0.526 11A 0-25 0.543 -drilled beside crack 25-50 0.095 -refusal (steel?) at 112 mm. 50-75 0.014 75-100 <0.007 100-112 <0.007 (1) Chloride Content is expressed as water soluble % by mass of cement for an estimated concrete density of 2350 kg/m3 and cement content of 350 kg/m3. 4 Predicting the future service life

As discussed above, the C-Jetty is showing no signs of distress due to corrosion of the reinforcement at the present time. However our opinion is, that the service life of the deck may be compromised by the extensive cracking which has developed in the topping concrete, and subsequent chloride contamination at crack locations. This increases the possibility of chloride induced corrosion occurring and shortening the service life of the structure. Various means of remediation were reviewed including the possibility of chloride removal either by flushing the cracks with clean water or by electrochemical means. Neither was determined to be feasible. The flushing did not change the chloride concentrations significantly and electrochemical removal of the chlorides is not considered appropriate because the reinforcement is epoxy coated, and the developments of an electropotential driving force for chloride removal would be weak. Consequently, it was elected to attempt to apply a low viscosity sealer capable of penetrating the cracks. It was hoped that the sealer would reduce the permeability of the surface and provide some water repellancy in the cracks, thereby reducing the quantity of moisture and salts reaching the reinforcement. To assist in the process of deciding whether or not to apply a sealer we have used the analytical model developed by Yokozeki et al. (1997). Several models including those developed by Weyers et al. (1994) and Maage et al. (1997) have been reviewed. The model by Yokozeki et al. (1997) appears to best fit the example of the C-Jetty. Many of the Service life models are based on the progress of chloride-induced corrosion and deterioration. This is illustrated in Figure 3. The model is separated into two parts.

Fig. 3: Graph illustrating corrosion damage vs time

T0 = the time for onset of chloride induced corrosion; and T1 = the time for corrosion and crack development. The time for the onset of chloride induced corrosion is based on Ficks Law of diffusion and is given by:

L 2 To = 1 [ ] –1 Dcl 2 erf { 1 - Ccr – CI } Cod - Ci

Dcl = Diffusion coefficient of chloride in concrete. (mm/year) Ccr = The limit amount of chloride ions against corrosion Ci = Initial chloride ion content in concrete Cocl = Chloride ion content in concrete surface L = Concrete cover thickness (mm)

For the C-Jetty, we have estimated the diffusion coefficient, Dcl from Maage et al. (1997) to be 30 mm/year

Ccr = 0.15 % by mass of cement Ci = 0 Cocl = 0.4 % by mass of cement L = 50 mm

With this data the predicted time to the onset of corrosion is 42 years. However, if we assume that the cover has been significantly reduced as a result of the cracking the time T0 is reduced as follows.

Cover L (mm) 0 10 20 30 40 50

T0 (years) 0 1.7 6.8 15.3 27.2 42

Secondly, the time for initiation of crack development is determined from the following equation

2) T1 = Critical Corrosion Amount (mg/cm Wcr Rate of Corrosion (mg/cm2/year), W where W=742/L (from Table 1 of Yokozeki et al. (1997))

-1.194 -0.8361 and Wcr = 1.841f (f -8.661)+145.1a +3809D +10.60x1,-72.30 where f = creep coefficient = 0.4 a = vol. expansion ratio for corrosion products = 3.2 D = 360o X1= L/d (in this case) As for T0, we have computed T1 at various concrete cover thickness.

Cover L (mm) 10 20 30 40 50

T1 (years) .09 0.4 1.0 2.0 3.1

Thus if we assume that concrete cover is 50 mm then the predicted service life will be;

T = T0 + T1 = 42+3.1 = 45.1 years However, if as we suspect the concrete cover has been reduced because of the extensive cracking in the surface then the service life is substantially reduced. For example if we say that the actual cover is more typically 20 mm, then; T= 6.8 +0.4 = 7.2 years It is difficult to accurately define the reduction in effective concrete cover produced by cracking. However, the calculations of predicted service life show that even a small reduction in cover thickness results in a significant reduction in the service life prediction. It is likely that damage, when it occurs, will start at the larger cracks which permit greater access of chlorides moisture and oxygen to the reinforcing steel. Thus corrosion will likely occur initially at a few localized areas. At these locations, the greatest resistance to corrosion-induced damage is likely the epoxy coating. Thus the epoxy coating life expectancy could be substituted for T0 in the preceding calculation. In studies by others (memo 1992; Hearn 1992; Weyers 1997) it has been indicated that typical epoxy coating life expectancy is in the range of 5-15 years, five years in warm salt water environments and 15 years in colder environments. Victoria has a relatively temperate climate but the Jetty receives substantial applications of deicing salt during the winter. Therefore, an epoxy coating life expectancy of the order of 8 -10 years is anticipated in this environment. According to the study by Weyers et al. (1997), coating debondment occurs mainly as a result of attack by the moisture available in the concrete. Therefore, the two activities of chloride diffusion and coating debondment likely run concurrently. Weyers also showed that 20 years following the successful sealing of several bridge decks, the chloride contents were reduced to approximately 50 % of the original concentration. This reinforces the recommendation to seal the C-Jetty.

5 Conclusions

1. The deck concrete at the C Jetty has been severely affected by shrinkage cracking. The cracking appears to have been increased by the use of epoxy coated reinforcement. 2. The cracks are heavily contaminated with chlorides and act as conduits to the reinforcement. 3. It is postulated that the cracking has reduced the effective concrete cover on the deck. 4. The analytical model developed by Yokozeki et al. (1997) indicates that there may be a significant reduction in the service life; i.e., a reduction in the time to corrosion caused cracking, and the need for repairs. 5. It is recommended that the deck be treated with a sealer capable of penetrating the cracks. It is expected that this will seal the cracks and help to restore the effectiveness of the concrete cover.

6 References

Clifton, J.R. (1991) Predicting the Remaining Service Life of Concrete National Institute of Standards & Technology, Gaithesavy, MD. NISTIR 4712. Hearn N. (1992) Structure Durability Studies - Epoxy Coated Reinforcement, Ontario Ministry of Transportation R+D Project 22132. Litvan, G.G. (1989) Investigation of the Performance of Parking Garage Decks Constructed with Epoxy Coated Reinforcing Steel. Prepared for the Canadian Institute of Public Real Estate Companies, CMHC, NRC, Ontario Ministry of Housing and Public Works Canada, Ottawa, Ontario. Maage M, Helland S. and Cartsen J.E. (1997) Service Life Prediction of Marine Structures ACI SP170, International CANMET/ACI Conference. Memo/Report from Kenneth C. Clear Inc. January 10, 1992. Ovstaas, G. (1994) Report to DND on the condition of Ranch Point Jetty and the cause of the cracking. Weyers R.E., Fitch M.G., Larsin E.P. and Al-Qadi I.L. (1994) Concrete Bridge Protection and Rehabilitation: Chemical and Physical Techniques, Service Life Estimates. Virginia Polytechnic Institute and State University, SHRP-5-668. Weyers R.E., Pye W., Zemajtis J., Liu Y., Mokaeum E. and Sprinkel M.M. (1997) Field Investigation of Corrosion - Protection Performance with Epoxy - Coated Reinforcing Steel in Virginia. Transportation Research Record. Yokozedi K., Motohashi K., Okada K. and Tsutsumi T. (1997) A Rational Model to Predict the Service Life of RC Structures in Marine Environment” ACI SP170, International CANMET/ACI Conference