COMPARISON OF RESISTANCE TO CHLORIDE PENETRATION OF CONCRETES AND MORTARS FOR REPAIR

Transcription

1 COMPARISON OF RESISTANCE TO CHLORIDE PENETRATION OF CONCRETES AND MORTARS FOR REPAIR Luca Bertolini, Maddalena Carsana, Matteo Gastaldi Politecnico di Milano Dipartimento di Chimica, Materiali e Ingegneria Chimica G.Natta, Italy Mario Berra Enel-Hydro - Polo Idraulico e Strutturale, Italy Abstract The paper reports the results of accelerated tests aimed at studying the resistance to chloride penetration of cementitious materials used in the conventional repair of reinforced concrete structures damaged by corrosion of embedded steel. Tests were carried out on two repair mortars (a commercial polymer-modified mortar and a mortar with pozzolanic cement and 0.4 water/cement ratio). For comparison, four types of concrete made with different water/cement ratios (0.5 and 0.65) and cement types (portland-limestone and slag cements) were also tested. Specimens were subjected to wetting-drying cycles with a 3.5% NaCl solution and profiles of total chloride content were measured after different times of exposure. Other types of tests aimed at studying the chloride ingress were also carried out and the corrosion behaviour of steel embedded in the tested materials was studied. The results of different tests are discussed in order to investigate on their significance with regard to the actual behaviour of the repair materials in chloride environments. 1. Introduction Reinforced concrete structures exposed to marine environments or subjected to de-icing salt contamination may suffer chloride-induced corrosion [1]. Once chlorides have penetrated the concrete cover and a critical content is reached at the steel surface, pitting corrosion initiates on the steel reinforcement and then propagation of corrosion may damage the structure [2-5]. For new structures, EN 206 standard [6] and Eurocode 2 [7] provide indicative recommendations on the maximum water-to-cement ratio and the minimum cover thickness, aimed at assuring a service life of the order of 50 years, depending on the exposure class. Nevertheless, the design of a structure exposed to chloride environments cannot be simply based on the prescriptions of these values.

2 Under conditions of high aggressiveness (e.g. in critical parts of the structure, such as the splash zone of marine constructions or joints in bridges) or when a longer service life is required, a specific design procedure is required. More restrictive requirements on the water/cement ratio, the cover thickness, the type of cement, or the use of preventative techniques (e.g. stainless steel reinforcement, surface treatments or cathodic prevention) should be defined [5]. Owing to the ageing of reinforced concrete buildings and infrastructures, as well as the low quality of concrete made in the last decades, the rehabilitation of reinforced concrete structures is very frequent. In that case, a thorough analysis of the structure is required to diagnose the cause of deterioration (e.g. carbonation, chlorides, construction defects, etc.), to evaluate the damage of the structure and its future evolution. Eventually, a repair intervention can be designed not only to remedy to the present damage but also to prevent future degradation of the structure (which continues to be subjected to the action of the aggressive environment). Several repair strategies are available for structures subjected to chloride induced corrosion [8]. Among these, the electrochemical methods of cathodic protection or chloride removal are of particular interest since they do not require the removal of the chloride contaminated concrete that is mechanically sound [5]. On the other hand, the conventional repair is often used. In that case, the protection of the reinforcement is achieved by replacement of the chloride-contaminated concrete with a new cementitious and chloride-free material. A suitable repair material should be selected and a proper cover thickness should be designed to guarantee that, after the repair, the chloride penetration from the environment will not damage the structure within the required residual life. Nowadays, the durability design of new structures and the design of conventional repair is rarely based on calculations. This is a consequence of the scarce knowledge of degradation phenomena by civil and building engineers, the unavailability of generally accepted procedures for the design of durability, and the lack of information on the performance of materials. With regards to the last point, simple tests should be found to characterise the resistance to chloride penetration of cementitious materials used for new structures or in the repair of existing ones. Unfortunately, although a large number of methods have been proposed to study the chloride penetration into concrete [2], there is not a generally accepted one. Penetration of chlorides in a real structure is related to the properties of concrete, but also largely depends on the exposure conditions and the mechanisms of transport (e.g. diffusion, suction, or permeation). It is difficult to extrapolate to a time scale typical of the service life of real structures the results of shortterm tests. Furthermore these tests are normally carried out on early-age specimens which may not be representative of the well-cured material. Several field data are now available from real structures made with many types of concrete, subjected to a great variety of exposure conditions to chloride environments for different lengths of times [9-15]. The experience on existing structures can thus provide valuable information data for the design, which can also be used to validate the results of

3 short-term tests. As far as the materials used in the repair works are concerned, however, field data are lacking. Specific mortars are normally used for this purpose, often of unknown proprietary compositions. Their mix may be quite different from that of bulk concrete used for new structures. They may contain different types of pozzolanic additions, have a very low water-to-cement ratio, be modified with polymers, contain expansive agents or fibres, etc. As a consequence, the correlations between the parameters obtained from short-term tests and the actual chloride penetration in real structures may be different from those expected for ordinary concrete. This paper reports the results of a laboratory study on the effects of chloride penetration in specimens that simulated a structure repaired by replacing the chloride-contaminated concrete with repair mortars. Exposure tests were carried out to simulate chloride penetration under wetting/drying cycles with seawater. Chloride penetration was studied in the concrete left in place and in the repair mortars, and effects on the embedded steel were investigated. 2. Experimental procedure Four concretes and two repair mortars were tested. Concretes were made with portlandlimestone cement (CEM II/A-L 42.5R) and blast-furnace cement (CEM III/B 42.5). Two mixes were considered for each type of cement with water-to-cement ratios of 0.5 and The first mix was obtained with 330 kg/m 3 of cement, 160 kg/m 3 of water, 1950 kg/m 3 of crushed limestone aggregate, and a superplasticizer; in the second mix the dosage of cement was reduced to 280 kg/m 3 and the water content was increased to 180 kg/m 3. One of the mortars was made with 700 kg/m 3 of pozzolanic cement (CEM IV/A 32.5R), 1050 kg/m 3 of sand, 280 kg/m 3 of water, and addition of a superplasticizer and an expansive agent. The other one was a commercial polymer-modified repair mortar (Mapegrout BM). 200 mm cubes were cast to study chloride penetration into concretes and mortars (Figure 1a). After 28 days of wet curing, an epoxy mortar was applied on four sides of the cubes, leaving uncovered only two parallel faces. Then the specimens were placed in a chamber that automatically produced cycles of immersion in a 3.5 % NaCl solution (2 days) alternated to drying with air at 40 C (2 days). Chloride analyses were carried out after 15 days, 2, 3, 5 and 11 months of exposure. 50 mm cores were taken from each specimen. Holes were filled with epoxy before further exposure to chloride cycles. Cores were split in two halves; one half was cut in 10 mm thick slices which were grounded. A sample of about 3 g of dry powder was digested in hot nitric acid. The chloride content was analysed with an automatic titrator (based on potentiometric titration with silver nitrate). The chloride content is expressed as percentage of the cement, by considering the dosage of cement in each material (for the commercial mortar a dosage of 700 kg/m 3 was assumed). In the second half of the cores a colourimetric analysis was carried out: an aqueous solution with 70% of alcohol and 1 g/l of fluoresceine and then a 0.01M AgNO 3 solution were sprayed on the dry fracture surface [16-17].

4 Figure 1 Schematic illustration of the specimens to study: a) chloride penetration, b) corrosion of steel, c) electrical resistivity. The colour of the surface was observed along the time; when a stable colour was reached (usually after several days of exposure to natural light) the depth of the front where the colour had changed was measured. Stationary diffusion tests were also carried out on discs of diameter 100 mm and 10 mm thick that were cored from some cubes. Tests were carried out in diffusion cells [18] that were initially filled with 3.5% NaCl in one side and distilled water in the other side. The chloride concentration in the diluted chamber was regularly measured for 2.5 months. Figure 1b shows mm 3 specimens that simulated a repaired area; half of the specimen was made with one of the concretes and the other half with one of the repair mortars. Reinforcing bars (φ = 10 mm) were embedded in the concrete and in the mortar. An activated titanium electrode was fixed near each bar and a stainless steel wire was also embedded in concrete (used as counter-electrode for polarisation resistance measurements). The specimens were exposed to the chloride cycles described above; corrosion potential and corrosion rate of steel (polarisation resistance method) were monitored; the two bars in each specimen were also externally connected for 1 minute and the galvanic current was measured. After 5 and 11 months, these specimens were removed from the chloride chamber and were exposed for one month to 25 C and 90% R.H. to achieve stable corrosion conditions on the embedded steel. Then the two bars were electrically connected for one month to measure long-term galvanic effects. The electrical resistivity of concretes and mortars was studied with specimens of Figure 1c that have dimensions of mm 3 and contain four parallel wires of stainless steel. Electrical conductance was measured with a conductivitymeter between wires 1-4 and 2-3. Resistivity of concrete was then calculated using cell constants that were determined with solutions of know resistivity. 3. Results and discussion 3.1 Characterisation of materials Table 1 shows the mechanical properties of the tested materials; each material has been identified with a capital letter. 28-day compressive strength of concrete made with portland-limestone cement increased from 36 MPa with w/c = 0.65 (A) to 49 MPa with w/c = 0.5 (B). Higher strengths of 44 and 56 MPa were obtained in concretes made with

5 blast-furnace cement (GGBS concretes named C and D). The two mortars (X and Y) had strengths of 45 and 40 MPa. The elastic moduli of the repair mortars were about half of those of the concretes. 3.2 Chloride profiles Figure 2 shows the results of the chloride analyses carried out on the cores extracted from the cubes. Total chloride contents measured at various depths are plotted as a function of time. Results obtained on the two exposed sides of each core are shown with the same symbol (black and white); they are in good agreement, showing that chloride penetration was similar in both sides. In general the chloride content at a certain depth tends to increase with a roughly square root of time trend. In the more external layer (0-10 mm) the chloride penetration was nearly the same after 15 days and two months; only afterwards a progressive increase of chloride content was observed in time. The rapid initial ingress of chlorides in the surface layer could be attributed to the capillary suction that occurs when the specimens are wetted after drying. In the more porous concrete B this effect was observed even at deeper depths (Figure 2b). In the concrete made with portland-limestone cement (Figures 2a and 2b), the chloride content reached significant amounts even at depths higher than 30 mm. The higher resistance to chloride penetration of GGBS concrete led to a significant penetration of chloride only at depths up to mm, even in the concrete made with the high w/c ratio of 0.65 (Figure 2d). (It should however be observed that a constant content of about % by mass of cement was measured since the first measurement throughout the thickness of the specimens. Obviously this chloride content is not due to the penetration of the NaCl solution but to the presence of chlorides in the blast-furnace cement). It should be pointed out that the GGBS contains some initial amount of chlorides (probably due to the use of seawater for the granulation of the slag). This was confirmed by chemical analyses of the cement. Even though European standard EN admits the possibility of exceeding the limit of 0.1% of chloride by mass for blast-furnace cements, the high chloride content in the cement leads to a significant reduction in the amount of chloride that can penetrate from the environment. Due to this, the GGBS concrete samples contain about % chlorides. Table 1 Properties of tested materials after 28 days of curing (average of 4 specimens). Concretes Repair mortars Cement CEM II/A-L CEM III/B 42.5 CEM Commercial 42.5R IV/A water/cement Denomination A B C D X Y Density (kg/m 3 ) Compressive strength (MPa) Static elastic modulus (GPa)

6 Figure 2 Chloride content measured in time at different depths in the tested materials.

7 Consequently, the well-known beneficial effects of blast-furnace cement in increasing the resistance to chloride penetration of concrete may be reduced. In fact, only a small amount of penetrated chlorides is sufficient to reach the chloride threshold for pitting corrosion initiation, that may be of the order of 0.4% by cement mass for aerated structures [1-4]. Chloride penetration in the two repair mortars was observed only in the external samples taken in the first 10 mm. Only at 11 months, some chlorides were detected at mm. Figure 3 shows, as an example, the chloride profiles measured after 11 months of tests. A horizontal line shows the chloride content of 0.4% by mass of cement. Chloride profiles are interpolated with the erf function [19], modified in order to take into consideration the initial chloride content (C i ) in the GGBS concrete [2]: x C x = Ci + ( Cs Ci ) 1 erf (1) 2 D t app where: C x = chloride content (% by mass of cement) at time t (s) and depth x (m); D app = apparent diffusion coefficient (m 2 /s); C s = surface content (%). All the points obtained on both sides of the cores, included the superficial ones, where considered in the interpolation. All the experimental profiles were accurately fitted and thus the penetration profiles can be described by means of values of D app and C s of the fitting curve (plus C i for GGBS concretes). Similarly to results normally obtained on real structures, however, values of D app and C s changed in time. The surface content increased during the first three months and then it reached a value around 4% by mass of cement, showing only small differences between the tested materials (Figure 4). The apparent diffusion coefficient decreased in time in all the materials (Figure 5). It reached constant values after 5 months in the concretes made of portland-limestone concrete. Conversely, it further decreased in the GGBS concretes and especially in the repair mortars. Figure 5 shows that the values of D app, that were calculated from the chloride profiles determined from specimens subjected to the chloride cycles, could clearly discriminate the higher resistance to chloride penetration of the repair mortars compared to the concrete samples. Therefore, even though these values cannot be used as absolute values in the design of repair works, they may provide useful information on a comparative basis with traditional concretes. 3.3 Colourimetric method The colourimetric method based on the spray of fluoresceine and silver nitrate solutions on the fracture surface of cores was always able to distinguish the external part of the cores, with a higher chloride content, from the inner part. For instance, the vertical lines in Figure 3 show the depths detected in the different materials after 11 months of testing. The depths found in the repair mortars were similar to those found in the GGBS concrete and slightly lower than those found on the concretes made with limestone-portland cement. This technique was therefore not able to detect the improved resistance to chloride penetration of the repair mortars.

8 Figure 3 Chloride profiles of different materials after 11 months of exposure cycles. The vertical lines show the depths detected with the colourimetric method.

9 Figure 4 Surface chloride contents calculated from chloride profiles measured on the tested materials after different times of exposure to chloride cycles. Figure 5 Apparent diffusion coefficient (D app ) calculated from chloride profiles measured on the tested materials after different times of exposure to chloride cycles. Furthermore, it was not possible to attribute a meaning to the measured depths, since the chloride content at such depths was rather variable. Figure 6 plots the total chloride content (calculated from the fitting profiles) at the depth shown by the colourimetric tests, as a function of the material and the time of exposure. Figure 6 Chloride content estimated at the depths detected by the colourimetric method after different times of exposure to chloride cycles. Figure 7 Change of chloride concentration in time in the diluted chamber of the diffusion cell during of stationary diffusion tests (concentrated chamber: 0.5M NaCl; thickness of specimen = 10 mm).

10 The penetration front detected by this method, corresponds to chloride contents variable from less than 0.1% to more than 1%. Even if a single material is considered, the variability with time is very high. This variability cannot be explained even if it is assumed that the colourimetric method only detects free chlorides [17]; in fact, such remarkable variations with time or between different materials cannot be justified by changes in the binding capacity. Conflicting results on the use of colourimetric methods on different types of cementitious materials were also reported by other Authors [20]. 3.4 Stationary diffusion Test with diffusion cells were also carried out on the concretes and mortars (after curing); Figure 7 shows an example of the results. The stationary chloride diffusion coefficient of about m 2 /s was found for the two concretes with w/c 0.65, while it was around m 2 /s and m 2 /s for concretes with w/c 0.5 made of limestoneportland cement and blast-furnace cement respectively. No flux of chlorides could be detected in the repair mortars even after more than two months of testing. Therefore, although these tests showed the higher resistance to chloride penetration for the repair mortars, no quantitative data could be obtained for a comparison with concretes. 3.5 Corrosion tests To study the effects of chloride penetration into the concretes and the repair mortars, corrosion tests were carried out on specimens of Figure 1b subjected to the chloride cycles. Figure 8 shows the corrosion potential and the corrosion rate of steel measured on steel embedded in the different materials at the end of curing (i.e. before exposure to chloride cycles) and after 5 or 11 months, when the specimens were exposed to 20 C and 90% R.H. Corrosion initiation was detected on steel embedded in the concrete made with limestone-portland cement with w/c of 0.65 (concrete B); after 11 months a corrosion rate of about 10 ma/m 2 was measured (Figure 8b) and the corrosion potential was lower than -500 mv vs Ag/AgCl (Figure 8a). Reinforcing steels were placed at depths of mm where, according to the chloride profiles measured on cubes (Figure 2b), the chloride content reached values higher than 1% by mass of cement after three months of testing. The steel bars embedded in the concrete A showed a decrease in potential over time, but the corrosion rate did not increase significantly. The bars embedded in the other materials confirmed the negligible chloride penetration at the depth of the reinforcement, showing no significant changes in the corrosion rate throughout the exposure period. The bars in the repair mortars had corrosion potentials around -100 mv vs Ag/AgCl and showed the lowest corrosion rates. Visual observation of the bars at the end of the tests showed corrosion attacks on 40-50% of the surface of bars in concrete B. Small crevice attacks were also observed in correspondence of a plastic strip used to fix the activated titanium electrode on the surface of bars embedded in other materials. This could explain slightly higher values of corrosion rate that were measured after exposure to the chloride cycles. The crevice attack was more evident on the bars embedded in the GGBS concretes (C and D). This is

11 probably a consequence of the significant chloride content that was initially present, due to chloride contamination of the blast-furnace cement. Tests were also carried out to study the effects of the macrocell that may form between bars in the repaired area and those in the surrounding concrete [8, 21]. The two bars of specimens of Figure 1b (one embedded in a concrete and the other one embedded in a repair mortar) were electrically connected. Figure 9 shows tests carried out after 5 months of chloride cycles; the macrocell current density was measured for one month. The macrocell current density was significant (>1-2 ma/m 2 ) in the coupling with bars embedded in concrete B, where corrosion rate was initiated (Figure 8b). No significant differences where observed when the cathodic bar was embedded in mortar X (coupling B-X) or in mortar Y (coupling B-Y). The macrocell current density was appreciable in all the other couplings only in the measurements taken 1 minute after the connection (Figure 9). Figure 10 shows the average value of the electrical resistivity of the tested materials measured at 28 days (in wet conditions at the end of curing). Resistivity of GGBS concretes ( Ω m) was 5-10 times higher than resistivity of concrete made of limestone portland cement ( Ω m). Resistivity of the two repair mortars had intermediate values ( Ω m). Therefore, the electrical resistivity measured at the end of curing was not representative of their improved resistance to chloride penetration in comparison with the concretes. This could be a consequence of the slower hydration of pozzolanic additions in the cement of mortar X and of pozzolanic materials presumably added to mortar Y, even in comparison to blast-furnace slag [22]. Figure 10 also shows the resistivity measured after 5 months of chloride cycles on the specimens conditioned at 20 C and 90% R.H. Figure 8 Corrosion potential (a) and corrosion rate (b) measured on bars embedded in the tested materials at the end of curing and after different times of exposure to chloride cycles (average values of different specimens).

12 Figure 9 Macrocell current density measured between bars in different couplings during tests carried out after 5 months of chloride cycles (specimens conditioned at 20 C and 90%R.H.). Figure 10 Resistivity of the tested materials measured at 20 C at the end of curing and after 5 months of chloride cycles (specimens conditioned at 90%R.H.). Even though the humidity content in this environment was lower than that of specimens at the end of curing, a decrease in the electrical resistivity was observed, due to chloride penetration. This was remarkable in concretes A and B due to chloride penetration, while only a slight decrease was observed in concretes C and D and in mortar X. Conversely, resistivity of mortar Y continued to increase in time and reached values higher than 1000 Ω m after five months. 4. Conclusions Resistance to chloride penetration was studied in two repair mortars and four ordinary concretes. Chloride profiles measured on specimens exposed to cycles that simulated wetting with seawater alternated to partial drying were used to compare the behaviour of the materials under exposure to marine environments. These profiles confirmed the improved resistance to chloride penetration of materials with additions of pozzolans or blast-furnace slag. A significant amount of chloride was however initially present in GGBS concrete due to chloride contamination of the blast-furnace cement used in this work, which may diminish the advantage of this type of addition in relation to the protection of embedded steel. The apparent diffusion coefficient, calculated from the experimental profiles by applying the widely used erf-function, could be used to compare the behaviour of different materials. The absolute value of this parameter, however, changed depending on the duration of the test and stable values were not reached on the repair mortars even after eleven months of testing.

13 Parameters obtained from other types of tests could not provide useful information for the repair mortars, even for a simple comparison with the concretes. The chloride penetration in the simulated marine environment could not be correlated to the 28-day compressive strength, or the electrical resistivity, or the results of chloride analyses with a colourimetric method. No stationary diffusion coefficient could be obtained for the repair mortars during tests with diffusion cells. In the absence of direct experience, it may be difficult to estimate the actual resistance to chloride penetration of a repair material. In fact, some of the short-term tests that are normally used to evaluate the resistance to chloride penetration of concrete may not be reliable when applied to repair mortars. 5. References 1. C.L.Page, Corrosion and its Control in Reinforced Concrete, The sixth Sir F. Lea Memorial Lecture, 26 th Annual Convention of the Institute of Concrete Technology, Bosworth (UK), 6-8 April J.M.Frederiksen (Ed.), HETEK - Chloride Penetration into Concrete. State of the Art. Transport Processes, Corrosion Initiation, Test Methods and Prediction Models, The Road Directorate, Report No. 53, Copenhagen, G.K.Glass, N.R.Buenfeld, Chloride Threshold Level for Corrosion of Steel in Concrete, Corrosion Science, 39, pp , C.Alonso, M.Castellote, C.Andrade, Dependence of Chloride Threshold with the Electrical Potential of Reinforcements, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept COST 521, Corrosion of Steel in Reinforced Concrete Structures: Prevention - Monitoring - Maintenance, Final Report, Ed. R. Weydert, IST, Luxembourg, February EN 206, Concrete Part 1. Specification, Performance, Production and Conformity (2001). 7. pr-en1992:1 (Eurocode 2), Design of Concrete Structures: Part I: General Rules and Rules for Buildings, Draft standard (2001). 8. RILEM Technical Committee 124-SRC, Draft Recommendation for Repair Strategies for Concrete Structures Damaged by Reinforcement Corrosion, Materials and Structures, 27, (1994) P.B.Bamforth, J.Chapman-Andrews, Long Term Performance of RC Elements under UK Coastal Exposure Condition, Proc. of Int. Conf. Corrosion and Corrosion Protection of Steel in concrete, Sheffield, July R.B.Polder, J.A.Larbi, Investigation of Concrete Exposed to North Sea Water Submersion for 16 Years, Heron (Delft), 40 (1), (1995) L.O.Nilsson, A.Andersen, T.Luping, P.Utgenannt, Chloride Ingress Data from Field Exposure in a Swedish Environment, Proc. 2nd International RILEM Workshop

14 Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept A.Lindvall, A.Andersen, L.O.Nillson, Chloride Ingress Data from Danish and Swedish Road Bridges Exposed to Splash from De-icing Salt, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept T.Luping, A.Andersen, Chloride Ingress Data from Five Years Field Exposure in a Swedish Marine Environment, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept C.Andrade, J.L.Sagrera, M.A.Sanjuán, Several Years Study on Chloride Ion Penetration into Concrete Exposed to Atlantic Ocean Water, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept D.Izquierdo, C.Andrade, O.de Rincon, Statistical Analysis of the Diffusion Coefficients Measured in the Piles of Maracaibo s Bridge, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept UNI 7928, Determination of Penetrability of Chloride Ions (in Italian), Italian standard (1978), retired in M.Collepardi, Quick Method to Determine Free and Bound Chlorides in Concrete, Proc. Int. RILEM Workshop Chloride Penetration into Concrete, Saint Rémy lès Chevreuse, Oct C.L.Page, N.R.Short, A.El Tarras, Diffusion of Chloride Ions in Hardened Cement Pastes, Cement and Concrete Research, 11 (3), (1981) M.Collepardi, A.Marcialis, R.Turriziani, Penetration of Chloride Ions into Cement Pastes and Concretes, Journal of American Ceramic Society, 55 (10), (1972) D.Henry, V.Baroughel-Bouny, T.Chaussadent, Evaluation of Chloride Penetration into Concrete by Various Methods, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept G.Sergi, C.L.Page, Sacrificial Anodes for Cathodic Prevention of Reinforcing Steel Around Patch Repairs Applied to Chloride-Contaminated Concrete, Int. Conf. Eurocorr/99, European Federation of Corrosion, Aachen, 30 August-2 September 1999, R.B.Polder, Simulated De-icing Salt Exposure of Blended Cement Concrete - Chloride Penetration, Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, Eds. C.Andrade, J.Kropp, Paris, Sept