Chloride Penetration Profiles and Diffusivity in Concrete under Different Exposure Conditions

Transcription

1 Chalmers Tekniska Hogskola Institutionen for byggnadsmaterial Publikation P-973 Arb nr 546 Chloride Penetration Profiles and Diffusivity in Concrete under Different Exposure Conditions Tang Luping Chalmers University of Technology Department of Building Materials Goteborg, March 1997

2 Key Words: Cement Chlorides Concrete Penetration ISSN X Chalmers University of Technology Department of Building Materials S Goteborg Sweden Telephone: Telefax: Expabrn. chalmers. se Internet: http ://m. bm. chalrners. se

3 Chloride Penetration Profiles and Diffusivity in Concrete under Different Exposure Conditions Tang Luping Department of Building Materials Chalmers University of Technology Abstract A plenty of data of chloride penetration profiles as well as chloride diffusivity, measured from concrete structures under different exposure conditions, are summarised in this report. The measurement techniques involved in the determination of diffusivity and penetration profiles are briefly described. The exposure conditions include the laboratory environment, the Swedish east coast and west coast, and the Danish west coast environments. Keywords: Cement, chlorides, concrete, penetration.

4 Contents Abstract P. Introduction 2. Measurement Techniques 2.1 CTH rapid test for determining chloride 2.2 Sampling for chloride profile measurement 2.3 Chloride content analysis 2.4 Calcium content analysis 23 Estimation of binder content 3 Exposure in the Laboratory 3.1 Concrete specimens 3.2 ~x~osure conditions 3.3 Sampling 3.4 Chloride profiles after one year exposure in the laboratory 4 Exposure at the West Coast of Sweden 4.1 Concrete slabs 4.2 Exposure conditions at Traslovslage 4.3 Sampling 4.4 Chloride profiles after years exposure at Traslovslage 4.5 Chloride diffusivity measured at different ages 5 Exposure at the East Coast of Sweden 5.1 Chloride penetration in the concrete of the new Oland bridge 5.2 Chloride diffusivity in the concrete of the new 0land bridge 5.3 Effect of forrnwork 6 Exposure at the West Coast of Denmark 6.1 Chloride penetration in the concrete of the Esbjerg harbour 6.2 Reference chloride diffusivity 6.3 Chloride diffusivity after exposure Acknowledgements References Appendixes Al. Chloride penetration data after one year exposure in the laboratory. A2. Concrete mixes for the exposure at the Traslovslage field station. A3. Chloride penetration data after years exposure at the Traslovslage field station. A4. Chloride penetration data after 4 years exposure in the east coast of Sweden (Oland bridge). A5. Chloride penetration data after 3 6 years exposure in the west coast of Denmark (Esjberg harbour). A6. Accumulative chloride flow curves from the steady state migration test for the concrete from the Esj berg harbour. A7. Data of chloride diffusivity measured using the CTH rapid method.

5 Introduction Chloride penetration into concrete is a hot topic in regard to the durability of reinforced concrete structures. In the past years, a series of research projects about chloride transport in concrete have been conducted at the Chalmers university of Technology. Through these projects, many chloride penetration profiles as well as chloride diffusivity were measured from concrete structures under different exposure conditions, including the specimens from the laboratory exposure, from the new Oland bridge in the Swedish east coast, from the Trasliivslage field station in the Swedish west coast, and from the Esbjerg harbour in the Danish west coast. These measured data, as the "first hand's" information about chloride transport, are believed valuable for the examination of modelling for chloride penetration. It is worth, therefore, to summarise and publish them for public use.

6 2 Measurement Techniques 2.31 CTH rapid test for determining chloride diffusivity The CTH rapid method 11, 21 involves applying a potential of V across a 50 mm thick specimen for a certain test duration, then splitting the specimen and measuring the penetration depth of chlorides by usimg a colourimetric method. The diffusion coefficient can be obtained by using the following equation: where DGm: R: diffusion coefficient according to the CTH rapid test, m2/s; gas constant, R = J/(K*mol); solution temperature, K; thickness of the specimen, m. absolute value of the ion valence, for chloride ions, z = 1; Faraday constant, F = X l~?j/(~*mol); absolute value of the potential difference, V; penetration depth, m; test duration, S; laboratory constant, 2) RTL a = 2, zfu / r a eri-l(l - where c0 is the chloride concentration in the bulk solution, cd is the chloride concentration at which the colour changes when using a colourimetric method to measure xd, and erf -' is the inverse error function. The experimental arrangement of the CTH rapid method is shown in Fig The detailed test procedure is published elsewhere 11, 21.

7 Potential a b C d e f g h a. Rubber sleeve e. Catholyte b. Anolyte f. Cathode c. Anode g. Plastic support d. Specimen h. Plastic box Fig Experimental arrangement for the CTH rapid method Sampling for chloride profile measurement To determine the chloride penetration profiles, concrete cylinders parallel to the penetration direction were drilled fi-om the exposed structures or specimens. The drilled cylinders were sealed with plastic bags to prevent moisture evaporation and stored in the laboratory before sampling. Pulverised samples were taken fi-om the cylinder by dry-grinding on a lathe with a diamond tool, successively from the exposed surface to a certain depth. The depth of each sample was measured from the lathe with an accuracy of 0.5 mm. After the grinding, the pulverised samples were immediately dried at 105 'C and stored in a desiccator to avoid excessive carbonation Chloride content analysis The total chloride content in each sample was determined principally in accordance with AASHTO T , except that a sample size of about 1 gram was used so as to make it easier to analyse the calcium content later. The apparatus Metrohm 702 SET T Titrino and a chloride selective electrode were used for potentiometric titration with a silver nitrate solution of 0.01 N. The chloride content in a sample was calculated by the following equation: where VA~NO~ : Volume of the silver nitrate solution consumed at the endpoint, ml; NAg~03: Actual normality of the silver nitrate solution;

8 V, : Volume of the silver nitrate solution consumed in blank running, T/, = ml in this study; W : Weight of the sample, g. 2.4 Calcium content analysis In most cases the calcium content in a sample was determined in order to estimate the binder content. ARer titration of chloride ions, 5 ml of I : I diluted triethanolamine was added to the sample solution and the ph-value of the solution was adjusted to >l2 using NaOH. The calcium content was determined by using the same apparatus as mentioned above, but with a calcium ion selective electrode and an EDTA solution of 0.1 N. The calcium content in a sample was calculated by the following equation: where: V ~A: Volume of the EDTA solution consumed at endpoint, ml; Nm~: Actual normality of the EDTA solution; f. Titration factor calibrated by using a hydrochloric acid as the extraction solution, f = in this study. 2.5 Estimation of binder content In many countries the criterion of chloride content in concrete is based on the weight of binder. It is important, therefore, to know the binder content in concrete, which varies in general from sample to sample due to the heterogeneity of concrete and the limited sample size. If the aggregates contain little acid soluble calcium, it is possible to estimate binder content in the pulverised sample from the CaO content which is relatively stable and constitutes largest percentage in normal cementitious binder.

9 3 Exposure in the Laboratory 3,1. Concrete specimens Three types of binders were used in the study of the laboratory exposure. The aggregates were 0-8 mm natural sand and 8-16 mm granite gravel, which contain negligible amount of acid soluble CaO so that the binder content in concrete samples could be determined by calcium analysis. The mixture proportions of concrete and the chloride diffusion coefficients measured using the CTH rapid test (see 2.1 and 4.5) are listed in Table 3.1. The concrete slabs of 1000x700x 100 mm were cast at the Swedish National Testing and Research Institute (SP). After about one week moisture curing, the prisms of size 500x 100x 100 mm were cut from the central portion -of the slabs, as shown in Fig The prisms were then transported to the laboratory at CTH where they were stored under the wet burlap. At the age about three months some of the prisms were exposed to the air to surface dry and then all the surfaces, except one cut surface of area 500x100 mm, were coated with epoxy. These epoxy coated prisms were later used for the unidirectional chloride penetration. ARer the hardening of epoxy, the prisms were again stored under the wet burlap for another half of month and then exposed to the chloride environment. Table 3 B. Mixture proportions of concrete for the laboratory expos I I I Binder Aggregate Water Mix No. Binder type I kg/m3 1 kg/m3 Binder Air content DCTH * 100% Degerhamn SRPC 100% Slite OPC 95% Degerhamn SRPC + 5% Silica fume (SF) * Measured at the age about 6 months. Fig. 3.1 Prisms cut from a concrete slab.

10 3.2 Exposure conditions In this study, two main factors were considered, A) chemical composition of "sea water7' and B) variations in climate. The exposure programs are listed in Table 3.2. For each exposure program, two parallel prisms from each concrete mixture were placed into the chloride solution according to Fig. 3.2 for a period of one year. In the program Al, the fi-esh sea water was continuously pumped into the containers placed in a simple building at Fiskeback, and the water temperature was monitored. In the other programs, the chloride solutions were monthly refreshed. In the program A2, nitrate acid was used to adjust the ph-value of the solution. In the program B1.4, a speed controllable pump was used to achieve the continuous change of the solution level. In the program B4, a fan was used for each container to accelerate the dry process, and a floating lid was added to the surface of solution to protect the solution from excessive evaporation. Table 3.2. Exposure programs. a1 A2 A3 A4 A5 B 1.1 B 1.2 B 1.3 B 1.4 B4 In sea water at the Fiskeback field station, chloride content = gcv1, High-Low level weekly change, Water temperature? 'C. In artificial sea water*, with ph-regulation (ph=7-8), High-Low level weekly change. cial sea water, without ph-lregdation, High-Low level weekly change. In NaCl solution* *, without ph-regulation, High-Low level weekly change. In NaCl solution with a concentration of 10 times as much as in A4, without ph-regulation, High-Low level weekly change. In artificial sea water, without ph-regulation, High-Low level weekly change. In artificial sea water, without ph-regulation, 1 week High level and 3 weeks Low level. In artificial sea water, without ph-regulation, 1 week High level and 5 weeks Low level. In artificial sea water, without ph-regulation, High-Low level continuous change,2 cycleslday. In artificial sea water, without ph-regulation, Constant high level, accelerated drying "fater temperature for the programs other than A1 were estimated about "C (normal laboratory temperature). * According to ASTM D , diluted to a salinity (Conductivity = 25 kps) similar to the sea water at Fiskeback. Measured chloride content: 10.3 g CM. ** 2% NaCl solution, conductivity w 25 kps, chloride content = 12.1 g CVI.

11 Specimen m m solution - Fig Placement of the specimens in the container. 3.3 Sampling Mer one year exposure, the cores were taken from the specimen at the positions as shown in Fig Pulverised samples for chloride analysis were then taken from the core by drygrinding as described in 2.2. Owing to the limited time and labour, only limited cores, mostly of Mix I, were sampled. E: Tidal 1 80 mm Atmospherical zone zone Submerged zone Fig Positions for taking cores from the prisms exposed for one year. 3.4 Chloride profiles after one year exposure in the laboratory The measured chloride profiles after one year exposure in the laboratory are presented in Figs. 3.4 to 3.21 and the original data are listed in Appendix Al. Some of the results were previously published in 181, that also includes a discussion.

12 Depth, mm Fig Chloride profiles after one year exposure at the Fiskeback field station. Degerhamn SRPC, waterhinder = L, AI Fiskeback Depth, mm Fig Chloride profiles after one year exposure at the Fiskeback field station. Degerhamn SRPC, waterlbinder = 0.40.

13 Depth, mm Fig Chloride profiles after one year exposure at the Fiskeback field station. Degerhamn SRPC, waterhinder = L, A1 Fiskeback Depth, mm L Fig Chloride profiles after one year exposure at the Fiskeback field station. Degerhamn SRPC with 5% silica Eurne, waterhinder =

14 Q Depth, mm Fig Chloride profiles after one year exposure at the Fiskeback field station. Degerharnn SRPC with 5% silica fume, waterhinder = L, A2-A5 Low-High level weekly changed L Q) =a.e 2 a W Ō l Q +.r 0 c. u A 2, Tl --o--a3, Tl X A4 Tl 0.---AS, TI A2 S --W--A3, S ----CB--- A4, S A A5 S 0 0 I Depth, mm Fig Chloride profiles after one year exposure at the laboratory ~ tdaerent h chloride sources. Degerhamn SRPC, waterhinder = 0.35.

15 "1-46) A39A4 Low-High level weekly changed Depth, mm Fig Chloride profiles after one year exposure at the laboratory with different chloride sources. Degerhamn SRPC, waterbinder = L, A3-A4 Low-High level weekly changed --O--A3, Tl --U---A3, S Depth, mm Fig Chloride profiles after one year exposure at the laboratory with Merent chloride sources. Slite OPC, waterbinder = 0.75.

16 1-75L, A2-A4 Low-High level weekly changed Depth, mm Fig Chloride profiles after one year exposure at the laboratory with clifferent chloride sources (except for A5). Degerhamn SRPC, waterhinder = L, A5 Low-High level weekly changed 5 li, Q) U.E 4 Q ' S l. +li 0 I- l I' Depth, mm Fig Chloride profiles after one year exposure at the laboratory with concentrated chloride solution (A5). Degerhamn SRPC, waterhinder = 0.75.

17 1-35L, B11 Low-High level weekly changed Depth, mm Fig Chloride profiles at different height after one year exposure at the laboratory. Degerhamn SRPC, waterhinder = Depth, mm Fig Chloride profiles at different height after one year exposure at the laboratory. Degerhamn SRPC, waterhinder = 0.40.

18 1-75L, B11 Low-High level weekly changed I I Depth, mm Fig Chloride profiles at different height after one year exposure at the laboratory. Degerhamn SRPC, waterhinder = l -35L, 81.2: L3w-Hlw change B1.3: LSw-Hlw change Depth, mm Fig Chloride profiles after one year exposure at the laboratory with different dry SWC, waterhinder = 0.35.

19 140L, B1.4 Two-cycleslday Low-High level continuously change I Depth, mm Fig. 3.18, Chloride profiles after one year exposure at the laboratory with different dry periods. Degerhamn SRPC, waterhinder = L, 51.2: L3w-Hlw change 51.3: L5w-Hlw change 0 I Depth, mm Fig Chloride profiles after one year exposure at the laboratory with different dry SWC, waterhinder = 0.75.

20 1-35L, B4 Accelerated Drying Depth, mm Fig Chloride profiles after one year exposure at the laboratory with accelerated drying. Degerhamn SRPC, waterlbinder = L, B4 Accelerated Drying t;; 3.- -a E.Q ul i 2 0 Q * z Depth, mm Fig Chloride profiles after one year exposure at the laboratory with accelerated drying. Degerhamn SRPC, waterhinder = 0.75.

21 4 Exposure in the West Coast of Sweden 4. P Concrete slabs Totally 39 mixes of concrete with different binders, water-binder ratios and air contents were used in the study of the exposure at Traslovslage in the west coast of Sweden. The mixture proportions of concrete are summarised in Table 4.1 on the next page and other information about mix design is attached in Appendix A2. The concrete slabs of 1000x700x100 mm were cast in the steel mould at SP. After about two weeks moisture curing, the slabs were transported to the Traslovslage field station and mounted on the sides of the pontoons for exposure, as shown in Fig If not otherwise stated, the concrete bottom surface was always facing the sea water. / Stainless steel counter electrode / Ref. electrode = internal Mn02 or external AgCl Fig A concrete slab mounted on the side of a pontoon at Traslovslage 141.

22 18 Table 4.1. Mixture proportions of concrete for the exposure at Traslovslage. 1) Swedish Degerhamn SRPC 2) Swedish Slite OPC 3) Silica fume 4) Danish Cement 5) Fly ash

23 4.2 Exposure conditions at TrislSvslgge At the Traslovslage field station, the chloride concentration in sea water is about g C1 per litre 141, and the typical water temperature is illustrated in Fig Annual Temperature, "C - - Measured Mean S i n e curve In the sine function: T,, = 20 "C, Tmin = 2 "C, to =1 19 days is taken as the original point Fig Annual temperature in sea water at the Traslovslage field station Sampling At the specified exposure duration, the concrete slabs were taken back to the laboratory. For each slab, a slice of mm thick was cut away to avoid the influence of two-dimensional penetration, and a prism of size l OOOx 100x 100 mm was then successively cut as the sample specimen for different penetration zones, as shown in Fig After cutting the specimens, the slabs were sent back to the field station to continue the exposure. The cores were drilled in the exposure direction from different zones of each prism and the pulverised samples at different depth from the bottom surface of the slab were then taken from each core by dry-grinding as described in 2.2. The chloride content in each pulverised sample was determined by potentiometric titration as described in 2.3.

24 Atmospheric zone Submerged zone 10 cm for specimens " 33-5 cm cut away Fig Sampling illustration of a concrete slab after exposure. 4.4 Chloride profiles after years exposure at Traslovslage The measured chloride profiles after years exposure at the Traslovslage field station are presented in Figs. 4.4 to 4.41 and the original data are listed in Appendix A Traslovslage ;L. Q) W.E 2 --&--#QV Depth, mm Fig Chloride profiles after 286 days exposure at the Traslovslage field station. Degerhm SRPC, waterhinder = 0.35.

25 10 20 Depth, mm Fig Chloride profiles after 286 days exposure at the Traslovslage field station. Degerhamn SRPC, waterhinder = Traslovslage. p-., I I I 'a \ \ Depth, mm Fig Chloride profiles after 286 days exposure at the Traslovslage field station. Degerham SRPC, waterlbinder = 0.50.

26 Fig Chloride profiles after 286 days exposure at the Traslovslage field station. Degerham SRPC, waterhinder = Traslovslage --*--M v - - -, ?" -. 0 X X Depth, mm Fig Chloride profiles after 482 days exposure at the Traslovslage field station. Slite OPC, waterhinder =

27 Depth, mm 20 Fig Chloride profiles after 483 days exposure at the Traslovslage field station. Slite OPC, waterhinder = Traslovslage L Q) -a.s 2 Q W- O k # -? UV ' 5 -/ --+--a v S d X #-2 (jv 0 X Depth, mm \ Fig Chloride profiles after 334 days exposure at the Traslovslage field station. Slite OPC, waterhinder = 0.50.

28 10 20 Depth, mm Fig Chloride profiles after 487 days exposure at the Traslovslage field station. Slite OPC, waterhinder = Traslovslage L 4 a, E E 2 0 m Depth, mm Fig Chloride profiles after 488 days exposure at the Traslovslage field station. Slite OPC, waterhinder = 0.75.

29 Depth, mm Fig Chloride profiles after 281 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = Traslovslage L Q) W E CB +=J g Depth, mm Fig Chloride profiles after 285 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = 0.40.

30 10 20 Depth, mm Fig Chloride profiles after 285 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = 0.40, water curing Traslovslage b. 0) 5 2 W Ō (FT CI g Depth, mm Fig Chloride profiles after 285 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica hme, waterhinder = 0.50.

31 IQ 20 Depth, mm Fig Chloride profiles after 286 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = Traslovslag e b Q) W.E 2.a rc Q -W 0 E Depth, mm Fig Chloride profiles after 253 days exposure at the Traslijvslage field station. Degerhamn SRPC with 10% silica fume, waterhinder = 0.40.

32 10 20 Depth, mm Fig Chloride profiles after 25 1 days exposure at the Traslovslage field station. Danish OPC with 5% silica fume, waterhinder = Traslovslage Depth, mm Fig Chloride profiles after 245 days exposure at the Traslovslage field station. Danish cement with 17% fly ash and 4.5% silica fume, waterlbinder = 0.40.

33 10 20 Depth, mm Fig Chloride profiles after 245 days exposure at the Traslovslage field station. Danish cement with 10% fly ash and 5% silica fume, waterhinder = Traslovslage L d) =a E: 2 yl 0 S (B 0 l= Depth, mm Fig Chloride profiles after 25 1 days exposure at the Traslovslage field station. Degerhm SRPC with 10% fly ash and 5% silica m e, waterhinder = 0.35.

34 10 20 Depth, mm Fig Chloride profiles after 210 days exposure at the Traslovslage field station... Degerhamn SWC, waterhinder = H 1 Traslovslage L a, W E 2 Q cc 0 3 g v (jv --*--#Q #l Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = 0.30.

35 10 20 Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerharnn SRPC with 10% silica fume, waterhinder = H3 Traslovslage tii W S 2 a W Ō 5 S 0, 1 (V CI g Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC, waterhinder = 0.30.

36 10 20 Depth, mm Fig Chloride profiles after 2 15 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume (slurry), waterhinder = H5 Traslovslage 0 ~epth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = 0.25.

37 10 20 Depth, mm Fig Chloride profiles after 3 68 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% fly ash, waterhinder = H7 Traslovslage Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder =

38 10 20 Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC with 20% fly ash, waterhinder = H9 Traslovslage L a 'D E #4 v W- O * cfl 0 k Depth, mm Fig Chloride profiles after 368 days exposure at the Traslovslage field station. Degerhamn SRPC, waterhinder =

39 Traslovsl3ge waterlbinder Depth, mm Fig Chloride profiles after days exposure at the Traslovslage field station. Degerhamn SRPC with 0% (0) and 5%silica fume (3-402 and H4). Traslovslage waterlbinder Depth, mm Fig Chloride profiles after days exposure at the Traslovslage field station. Degerhamn SRPC with 0% (1-50) and 5%silica fume (3-50), and Slite OPC (2-50).

40 Depth, mm Fig Chloride profiles after 439 days exposure at the Traslovslage field station. Degerhamn SRPC with 0% (1-75) and 5%silica firrne (3-75). 5 Traslovslage Depth, mm Atmospheric --o-- Splash -+ Submerged Fig Chloride profiles after 797 days exposure at the Traslovslage field station. Degerhamn SRPC, waterlbinder = 0.50.

41 Tr3slijvslage b a, 4 99 E:.I a % 2 S Q.W 0 1 l Depth, mm -U--- Atmospheric Splash -Submerged Fig Chloride profiles after 796 days exposure at the Tr'dslovslage field station. Degerhamn SRPC with 5% silica fume, waterhinder = Tr~slovslage L, m- a 3 ( E ' E+ Depth, mm Atmospheric --U-- Splash - Submerged Fig Chloride profiles after 756 days exposure at the Tr'dslovsl~ge field station. Danish cement with 17% fly ash and 4.5% silica fume, waterhinder = 0.40.

42 Depth, mm ---U--- Atmospheric --C-- Splash ---U-- Submerged Fig Chloride profiles after 762 days exposure at the Traslovslage field station. Degerhamn SRPC with 10% fly ash and 5% silica fume, waterhinder = Traslovslage 0 4 L ar.- 3 Q rc S 0 d 1 0 t= Depth, mm Atmospheric o - Splash ----U-- Submerged Fig Chloride profiles after 721 days exposure at the Traslovslage field station. Degerhamn SRPC, waterhinder = 0.40.

43 -- Atmospheric Depth, mm Splash - Submerged Fig Chloride profiles after 726 days exposure at the Traslovslage field station. Degerhamn SRPC with 5% silica fime (slurry), water/binder = Chloride diffusivity measured at different ages The CTH rapid test was employed to determine the chloride diffusion coefficients of concrete at different ages. For the unexposed concrete, two specimens were cut from each concrete slab as shown in Fig In the test, the skin side of the specimen was exposed to the chloride solution. For the exposed concrete, the inner portion of the cylinder used for measuring chloride profile *as used for the diffusivity test. The average values of the test results are listed in Table 4.2 and the original data are attached in Appendix 7. Some relationships between diffusion coefficient and water-binder ratio, binder type and concrete age are shown in Figs and Specimen 1 \ Specimen 2

44 Fig Schematic of sampling from unexposed concrete slabs for the CTJ3 rapid test. Fig Chloride diffusion coefficient from unexposed concrete slabs measured at an age of 0.5 years.

45 Table 4.2. Chloride diffusion coefficients of concrete for the exposure at the Traslovslage filed station. Mix No. Water Binder Exposed Age 2~ H %~nl I 1) Swedish Degerhamn SRPC 2) Swedish Slite OPC 3) Silica fume 4) Danish Cement 5) Fly ash

46 Fig Chloride di.ffusion coefficient measured at different ages.

47 Exposure in the East Coast of Sweden 5.1 Chloride penetration in the concrete of the new 0land bridge About 4 years after reparation, some of the repaired piers of the Oland bridge in Kalmarsund, south of the Baltic sea, were investigated for chloride penetration. The chloride concentration in the east coast of Sweden is about g C1 per litre, lower than in the west coast of Sweden. The concrete for the pier repair is similar to that with Mix No. "0 in Table 4.1. The sampling positions and the measured chloride profiles are shown in Fig. 5.1, and the original data are listed in Appendix A4. The New ~landsbro, Sweden 0.5 m m m * m ~ 0.6 m High T LOW water I 0.5 m #23 several crack systems Atmospheric zone Splash zone Submerged zone Depth. mm Fig Chloride profiles from the new Oland bridge after 4 years exposure 161. Chloride diffusivity in the concrete of the new eland bridge The central portion of the drilled cylinders were used for determining chloride diffusion coefficients. The measured results are summarised in Table 5.1.

48 Table 5.1. Chloride sivity in the concrete drilled from the new Olmd bridge after 4 years exposure. nexposed, wooden formwork During the rehabilitation, two types of formwork: wooden and textile, were used for concreting. In order to investigate the effect of formwork, some specimens taken hom the unexposed concrete beam were subjected to an electrical field parallel to the original surface, as shown in Fig After testing, the chloride penetration depths were measured at different distances from the original surface and the diffusion coefficients at different distances were calculated. The results are listed in Table 5.2 and the relative diffusivity calculated from the mean values two specimen is illustrated in Fig Fig Illustration of chloride penetration parallel to the original surface of concrete.

49 45 Table 5.2. Chloride difksivity at different distances from the original surface. Fig Relative dfisivity of two types of formwork.

50 Exposure in the West Coast of Denmark 6.1 Chloride penetration in the concrete of the Esbjerg harbour After about 36 years exposure, the concrete sheet pilings at the Esbjerg harbour in the west coast of Denmark were investigated for chloride penetration. The sheet pilings were built in According to the documents, the concrete mix is: cement content 3 10 kg/m3, fine aggregate 8 10 kg/m3 and coarse aggregate kg/m3, with a water-cement ratio The concrete cores with the diameter about 100 mm were taken from the different exposure zones and then sent to the laboratory for determining chloride profiles according to the methods described in sections The measured chloride profiles are shown in Figs. 6.1 to 6.4, and the original-data are listed in Appendix A Depth, mm X Atmospheric --o-- Tidal ---U-- Submerged Fig Chloride penetration profiles in Piling 2 of the Esbjerg harbour after 36 years exposure.

51 Piling 8 5 Depth, mm X Atmospheric - o -- Tidal U Submerged Fig Chloride penetration profiles in Piling 8 of the Esbjerg harbour after 3 6 years exposure. 5 L CZI E El 'E a II W d 1 f 0 Piling Depth, mm X Atmospheric --o- - Tidal -+I-- Submerged Fig Chloride penetration profiles in Piling 22 of the Esbjerg harbour after 36 years exposure.

52 Piling 31 L ).a 'i a.i d Depth, mm m.-s--. Atmospheric Tidal Submerged Fig Chloride penetration profiles in Piling 3 1 of the Esbjerg harbour after 36 years exposure. 6.2 Reference chloride diffusivity One concrete core marked with "LERA" was taken from the unexposed part of the pilings which were inserted in clay. Its central portion was used for determining the reference chloride diffusion coefficient according to the CTH rapid test (non-steady state procedure). In order to evaluate the effect of concrete surface on diffusivity, a cubic specimenwas cut from the cylinder in the way as shown in Fig The electrical field was applied parallel to the original surface as shown in Fig The test results are shown in Fig Original Surface /--- Fig Concrete cubic specimen for evaluating the effect of concrete swface on diffusivity.

53 Fig Relative diffbsivity of concrete from the Esbjerg harbour. 6.3 Chloride diffusivity after exposure Since in most cases chlorides had penetrated through the concrete cylinders, the non-steady state procedure does not work in this case, the steady-state procedure, therefore, must be considered in order to determine the chloride diffusivity. A 30 mm thick disc was cut from the outside end of the cylinder and the curved surface of disc was coated with epoxy. For the cylinders from the tidal zone, about 10 mm eroded surface layer was cut away before cutting a 30 mm thick disc. As comparison, a disc was cut from the central portion of the cylinder. In order to shorten the time needed to reach a steady state flow, some of the discs were vacuum saturated with 3% NaCl solution. The same test set-up as in the CTH non-steady-state procedure was employed, except that the platinum electrode was used as anode to avoid the corrosion. A solution of 3% NaCl in saturated lime water was used as the bulk chloride solution, and a 0.3 M WNa(0H) combined solution was used as the chloride-free solution. An electrical filed of 800 V/m was applied across the disc. Periodically, the 500 m1 of solution in chloride-free side was replaced with fresh solution and the chloride content in the replaced solution was analysed. The relationship between accumulative chloride flow, Q, and testing duration, t, was plotted. The test finished when the relationship became obviously linear.

54 The chloride diffusivity was calculated using the follo g equation 11,2/: where D=: diffusion coefficient from the steady state migration test, m2/s; -" : slope of Q-t plot in the linear portion, kds. At Other symbols as defined in equations (1) and (2). It should be noticed that D, is different from Dcnr and cannot be compared directly with each other. A concept of "intrinsic diffusion coeficient" Do could be introduced to compare D, with D- Ill: where E: fraction of pore solution in concrete, or water accessible porosity; Kb: binding constant involved in the non-steady state migration test, -3 3 Kb=0.59~10 m solution/kggel; a Vgel: hydrate gel content in concrete, kggel/~'conaete. For specimens A3 and K3, &er the normal test, the experiment was continued by changing the bulk chloride solution to a concentration of 40 and 78 g C1 per litre, respectively. For specimen A21 and T21, &er the normal test, the experiment was continued by changing the electrical field to 400 Vlm. The calculated results are summarised in Table 6.1 and the accumulative chloride flow curves are attached in Appendix A6. It can be seen that the chloride diffusivity decreases as the chloride concentration increases or as the external potential decreases. Notice that it is the same specimens which were in succession subjected to the concentration increase and the potential decrease. Do these phenomena show a concentration or an electrical, field dependency of diffusivity, or due to the blocking effect of pores? Further study is needed to '' find out the reasons. The intrinsic diffusivity seems correspond well from two different migration procedures.

55 Table 6.1. Summary of the Wsivity calculated from the steady state migration test. Density of Chloride electrical field concentration E, Vlm c, moll1 Diffusivity ~ s s m XI 0-' m2/s Exposure conditions Atmospheric zone lbm Tidal zone zone Unexposed * assuming a porosity of according to ly, ax0.25 and a gel content of 329 hglm3 according to W,,, = 1.25aC, with a = ** disc specimen successively cut after T23-l

56 Acknowledgements The data presented in this report are results of satisfactory co-operation between Chalmers University of Technology and other institutions including Lund Institute of Technology, Swedish National Testing and Research Institute, and AEC Consulting Engineers AIS, Swedish Cement and Concrete Research Institute. Special thanks are extended to Paul Sandberg at Lund Institute of Technology, who was the co-ordinator of the research project "Durability of Marine Concrete Structures7'. Financial support from the Swedish Council for Building Research through a frame project and Cementa Ltd. through the project "Durability of Marine Concrete Structures7' are greatly appreciated. -

57 References /l/ Tang, L. (1996),"Chloride Transport in Concrete - Measurement and prediction9', Doctoral thesis, Chalmers University of Technology, Publication P-96:6, Gothenburg Sweden. 121 Tang, L. (1996), "Electrically accelerated methods for determining chloride diffusivity in concrete", Magazine of Concrete Research, Vol. 48, No. 176, pp AASHTO (1984), "Standard Method of Sampling and Testing for Total Chloride Ion in Concrete and Concrete Raw Materials", American Association of State Highway and Transportation Officials, Designation: T Sandberg, P. (1996), "Systematic collection of field data for service life prediction of concrete structures", in Durability of Concrete in Saline Environment, Cementa AB, Tang, L. and Nilsson, L-0. (1996), "Service life prediction for concrete structures under seawater by numerical approach", Proceedings of the 7th International Conference on the Durability of Building Materials and Components, May 19-23, 1996, Stockholm, E & F N Spon, pp Sandberg, P. (1995), "Critical evaluation of factors affecting chloride initiated reinforcement corrosion in concrete", Licentiate Thesis, Lund Institute of Technology, Report TVBM-7088, Lund, Sweden. I71 Ewertson, C. (1999, "Climate data from the field station at Traslovslage harbour". Internal report, Swedish National Testing and Research Institute, Borb. I81 Tang, L. and Sandberg, P. (1996), "Chloride penetration into concretes exposed under different conditions", Proceedings of the 7th International Conference on the Durability of Building Materials and Components, May 19-23, 1996, Stockholm. Appendixes Al. Chloride penetration data after one year exposure in the laboratory. A2. Concrete mixes for the exposure at the Traslovslage field station. A3. Chloride penetration data after years exposure at the Traslovslage field station. A4. Chloride penetration data after 4 years exposure in the east coast of Sweden (0land bridge). A5. Chloride penetration data after 36 years exposure in the west coast of Denmark (Esjberg harbour). A6. Accumulative chloride flow curves from the steady state migration test for the concrete from the Esjberg harbour. A7. Data of chloride diffusivity measured using the CTH rapid method.

58

59 Al-l Appendix Al. Chloride penetration data after one year exposure in the laboratory %C

60

61 l

62 l

63 l3 l l.oi

64 l6 l

65

66 l

67 l

68 l.89 mm OO l.l l l

69 mm Average Average 20.2

70 l l l

71 l Average l

72 mm l I l

73 l Average mm l.l

74 Average

75 l Average l.l

76 mm I

77 l.61 I.93 l.88 l l l

78 mm l l

79 l I Average l.g

80 Average

81 I l mm l

82 mm l

83 l8 l.07 1.oo

84 l.20 l l.l '

85 l mm l I

86 mm I

87 l.l mm l I

88 l

89 mm l.l l l

90 l l

91 l l.l l8 1.l

92 l mm l l l l l

93 Mix No. w/c day in concr. l X mm IZ n I-r n n 77

94 I -3a~ 134, a I lr~ir~iersea YOL~U m~~naer Mix No. wlc day in concr l

95 l

96 l

97

98 l

99 Appendix A2. Data quoted from Sandberg, P. (1 996, see Ref. 4). Appendix Data for concrete exposed at the Tr%lovslage Marine Field Station W(C+SF+O.3FA) Mix design SRPC kg/m3 1 air % 420 / 6.2% 370 / 6.4% 240 / 6.1% cast. date cast cast cast cast slump/remould 10cml1 Orev 12crn/9 rev 10cdlOrev 11 cm/8 rev f'c28dcube/slab 70162MPa 58150MPa 41131MPa 21/16 MPa OPC kglm3 l air % % % 310 / 6.3 % 250 / 5.8 % cast.date cast cast cast cast cast slumplremould. 13cml14rev 12cmllOrev 9cm / 9 rev locm/l lrev 10cm / 8rev f'c 28d cubelslab MPa 54/49 MPa 42/36 MPa 35/29 MPa 26/23 MPa SRPC kg/m3 / air / 5.8% 399 / 6.1 % % % 5% SF cast. date cast cast cast cast i slumplremould 6cm / 18rev 8 cmll4rev 8 cdl lrev 14 cm/8 rev f'c 28d cube/slab 72/62 MPa 61/52 MPa 45/37 MPa 21/19 MPa SRPC kglm3 1 air % 10% SF cast. date cast slump/remould 6 cm/16 rev f'c 28d cubelslab 65/49 MPa SRPC kglm3 / air 399 / 2.9% 5% SF cast. date cast slum plremould 9 cm/ 14 rev f'c 28d cubelslab 81/64 MPa SRPC kgim3lair 427.5/2.1% % 5% SF cast. date cast cast slump/remould 4cml27rev 7cmll8rev f'c 28d cubelslab 93/72 MPa 87/69 MPa SRPC kgim3 l air 450 / 2.4% 420 / 2.1% % cast. date cast cast cast slumplremould 6 cm / 17 rev 5 cm / 23 rev 5 cm116 rev f'c 28d cubelslab 91/81 MPa 79/68 MPa 32/24 MPa OPG kglm3 / air % % 410 / 1.4% 330 / 1.6% 330 / 1.6% cast. date cast cast cast cast cast slumplremould 8cml16rev 8cml15rev 9cmllOrev 7cm113rev 7cml12rev f'c 28d cubelslab 73/71 MPa 67/56 MPa 56/47 MPa 45/39 MPa 37/30 MPa SRPC kg/m3 / air 345 =l% 4.5%SF cast. date cast %FA slumplrem l Ocm / 13rev f'c 28d cubelslab 69/58 MPa WC kg/m3 / air / 5.7% 5% SF cast. date cast lo%fa slump/rem 18cm 1 l lrev f'c 28d cubelslab 84/68 MPa