Brahim Touil

Dr Pr F Ghomari

A Bezzar

Dr Pr A Khelidj

Stephanie Bonnet

EFFECT OF TEMPERATURE ON CHLORIDE DIFFUSION IN SATURATED CONCRETE

Keywords: Concrete, Pozzolan, Coefficient of migration of chlorides, Temperature, Activation energy

sustainability and diffusion test chloride ions

INTRODUCTION

The corrosion of steel reinforcements is a major cause of the degradation of reinforced concrete (RC) structures exposed to sea water. It is due to the ingress of chloride ions into concrete. Indeed, chlorides can penetrate through the porous media of concrete to reach embedded steel, which leads to depassivation and corrosion initiation. Corrosion of steel can start when a sufficient amount (i.e., the threshold) of chloride ions accumulates at the steel surface and breaks down the passive layer of iron oxide that developed due to the high alkalinity of the concrete medium [START_REF] Verbeck | Mechanisms of corrosion in concrete[END_REF][START_REF] Hassain | Chloride threshold for corrosion of reinforcement in concrete[END_REF] . This phenomenon depends on the speed of chloride penetration into concrete. This is conditioned by several factors such as the water/binder ratio (w/b), the age of concrete [START_REF] Kondraivendhan | Effect of age and water-cement ratio on size and dispersion of pores in ordinary portland cement paste[END_REF] , the type of binder [START_REF] Ellis | Comparative results of utilization of fly ash, silica fume and GGBFS in reducing the chloride permeability of concrete[END_REF][START_REF] Mehta | Role of pozzolanic and cementitious material in sustainable development of concrete industry[END_REF][START_REF] Collepardi | Durability of high-performance concretes with pozzolanic and composite cements[END_REF] , the porosity [START_REF] Das | Implication of pore size distribution parameters on compressive strength, permeability and hydraulic diffusivity of concrete[END_REF][START_REF] Hu | Effect of Pore Structure on the Chloride Permeability of Concrete with Mineral Admixture[END_REF] and the environmental conditions 9-10 (temperature, humidity, etc…). The temperature variations have a significant effect on the properties of transfer, particularly on the kinetics of chloride diffusion [START_REF] Dhir | PFA concrete: exposure temperature effects on chloride diffusion[END_REF] . Hence, it is judicious to study the impact of the temperature variations on the process of chloride diffusion in concrete.

During the last decades, several researchers have studied the chlorides diffusion coefficient using different test methods [START_REF] Alexander | Performance of cement-Based materials in aggressive aqueous environments[END_REF][START_REF] Alfarabi | Determination of the Effective Chloride Diffusion Coefficient in Concrete via a Gas Diffusion Technique[END_REF][START_REF] Castellote | Measurement of the steady and nonsteady state chloride diffusion coefficients in a migration test by means of monitoring the conductivity in the anolyte chamber -Comparison with natural diffusion tests[END_REF][START_REF] Stephen | Testing Transport Properties of Concrete[END_REF] , standards [START_REF] Astm C | Standard Test Method for Electrical Indication of Chloride's Ability to Resist Chloride[END_REF][START_REF] Astm C | Determining the apparent Chloride Diffusion Coefficient of Cementitious Mixtures by Bulk Diffusion[END_REF] and numerical prediction models [START_REF] Maage | Service life prediction of existing concrete structures exposed to marine environment[END_REF][START_REF] Luciano | Predicting chloride diffusion coefficients from concrete mixture proportions[END_REF][START_REF] Thomas | Life 365: computer program for predicting the service life and life-cycle costs of reinforced concrete exposed to chlorides[END_REF] . It should be noted here that the most of the studies focus on the chloride diffusion into cementitious materials either on effective or apparent diffusion coefficient, at constant temperature [START_REF] Andrade | Calculation of chloride diffusion coefficient in concrete from ionique diffusion measurements[END_REF][START_REF] Truc | A new way for determining the chloride diffusion coefficient in concrete from steady state diffusion test[END_REF][START_REF] Luping | A rapid determination of chloride diffusivity in concrete by applying an electrical field[END_REF][START_REF] Tong | Chloride diffusivity based on migration testing[END_REF] .

However, the temperature is a catalyst which acts on the kinetics of diffusion. The increase of the temperature accelerates the chloride diffusion because molecular speed increases with increasing temperature. In fact, high temperature may both decrease physical binding of chlorides because of higher thermal vibration and increase the content of chemically bound chloride ions, because of the increase in the speed of reactions [START_REF] Dhir | PFA concrete: exposure temperature effects on chloride diffusion[END_REF][START_REF] Detwiler | Resistance to Chloride Intrusion of Concrete Cured at Different Temperatures[END_REF][START_REF] Al-Khaja | Influence of temperature, cement type and level of concrete consolidation on chloride ingress in conventional and high-strength concretes[END_REF][START_REF] Yuan | Effect of temperature on transport of chloride ions in concrete[END_REF][START_REF] Panesar | Effect of cold temperature on the chloride-binding capacity of cement[END_REF] .

There are few studies concerning the apparent diffusion coefficient which took into account the temperature effect [START_REF] Dhir | PFA concrete: exposure temperature effects on chloride diffusion[END_REF][START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Detwiler | Resistance to Chloride Intrusion of Concrete Cured at Different Temperatures[END_REF][START_REF] Al-Khaja | Influence of temperature, cement type and level of concrete consolidation on chloride ingress in conventional and high-strength concretes[END_REF][START_REF] Yuan | Effect of temperature on transport of chloride ions in concrete[END_REF][START_REF] Panesar | Effect of cold temperature on the chloride-binding capacity of cement[END_REF] . This effect was evaluated on samples subjected to heat treatment before chloride diffusion test or by using a test bench conditioned at desired temperature for immersion or transient diffusion/migration tests. Some experimental results obtained in previous studies were explained by the theoretical equation based on the Arrhenius law using the concept of activation energy as shown in Eq.

(1) [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Yuan | Effect of temperature on transport of chloride ions in concrete[END_REF] .

))

1 1 ( exp( ) ( ) ( 0 0 T T R E T D T D a   (1)
Where D(T) (m 2 /s) (ft 2 /s) and D(T 0 ) (m 2 /s) (ft 2 /s) are the diffusion coefficients at T (K) (F) and T 0 (K) (F) respectively, E a (kJ/mol) is the activation energy of diffusing of chloride transport in concrete, R (kJ/(mol.K)) (kJ/(mol.F)) is the ideal gas constant. [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF] have shown significant differences in diffusion coefficients between ordinary concrete and concrete mixtures from which the activation energies values were 31.9 kJ/mol and less than 30.9 kJ/mol respectively.

Concerning modelling of chlorides penetration into concrete, there are many approaches in literature. However, when the temperature effect is considered, there are few models such as FIB model code [START_REF] Fib | Model code for service life design[END_REF] and Life-365 model [START_REF] Thomas | Life 365: computer program for predicting the service life and life-cycle costs of reinforced concrete exposed to chlorides[END_REF] . These models considered that the effect of temperature on chloride diffusion coefficient is in agreement with the Arrhenius law. The activation energy values proposed by such models are 40 kJ/mol and 35 kJ/mol, regardless of concrete mixture type.

However, no report was found on studying the influence of coupling directly temperature with the coefficient of migration under an electric field in steady state in saturated concrete.

This work aims to characterize and analyze the effect of temperature upon the chloride diffusion under electric field of an ordinary and pozzolanic concrete, in saturated conditions;

which leads to the objectives and research methodology adopted in this work.

In this study the temperatures selected were 5, 20, 30, 40 and 50°C (41, 68, 86, 104 and 122°F), wich reflects the ranged typical ambient temperatures of the Mediterranean Sea.

RESEARCH SIGNIFICANCE

The durability is increasingly decisive for the design of reinforced concrete structures in a saline environment. In such ambiance conditions, the temperature process is known to cause faster penetration of chloride, and it's relevant for the service life design and reassessment of reinforced concrete structures. The originality of the present work lies in the new test experimental setup developed in order to apply a controlled range of temperature at same time as the chloride migration occurs into saturated concrete conditions. The results presented in this paper are part of a comprehensive study of ordinary concrete and pozzolanic concrete to evaluate the porosity, and relationship between the coefficient diffusion subjected to the variation of temperature. Such information can aid in designing and selecting mixtures concrete throughout the sea environment by taking into account the fluctuation of the temperature.

EXPERIMENTAL STUDY

Materials

The binder used is a Portland cement composite CEM II/A 42.5 from the factory of Beni Saf, located in north-west Algeria, as specified in Standard NA 442 [START_REF]Cement: Composition, specifications and conformity criteria for common cements[END_REF] . It consists of 85% clinker, and 12% natural pozzolan and 3% gypsum. Its density is 3070 kg/m 3 (191.65 lb/ft 3 ) and Blaine specific surface area is 2705 cm 2 /g (1320.67 ft 2 /lb). Its chemical composition is given in Table 1 and its mineralogical compositions is presented in Table 2.

The natural pozzolan used is extracted from the Bouhmidi deposit of pyroclastic rocky of volcanic origin located in Beni-saf (north-west of Algeria). It is generally accepted that the pozzolan sample is chemically suitable with a total content (SiO 2 + Al 2 O 3 + Fe 2 O 3 ≥ 70%) as mentioned in ACI report 37 , then satisfying the ASTM C 618 [START_REF]Standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete[END_REF] requirements. And can be used to replace up to 40% of ordinary Portland cement in accordance with EN 197-1 and ASTM C

The natural pozzolan was dried at 105°C (221°F) and used as a powder resulting from a grinding and clipping sieve of 80 μm (0.00314 in). Its density is 2500 kg/m 3 (156.06 lb/ft 3 )

and Blaine specific surface area is 3360 cm 2 /g (1640.46 ft 2 /lb), The chemical analysis of the resulting powder crushed at 80μm is reported in Table 1 [START_REF] Kaid | Durability of concrete containing a natural pozzolan as defined by a performance-based approach[END_REF] .

The size grading curve for the natural pozzolan was determined by laser granulometry. The average of three test shown that the diameter at 90% is 69 μm (27.16 x 10 -4 in), at 50% is 16 μm (6.299 x 10 -4 in) and at 10% is 2 μm (0.787 x 10 -4 in) (see Fig. 1).

The crushed aggregates used are limestone from the career of the National Company of Aggregates (ENG) located in west of Algeria. The maximum size of coarse aggregate is 25 mm (0.984 in) and their specific gravity is 2.58. The maximum size, fineness modulus and specific gravity values of sand are respectively 4 mm (0.157 in), 2.95 % and 2.50.

Mixture proportions

Two concretes designated OC and CPZ10 were used in this study. An ordinary concrete (OC) which many experimental data are available within our team [START_REF] Boukli | Contribution à l'étude de la résistance caractéristique des bétons de la région de Tlemcen[END_REF] , was designed with binder content of 350 kg/m 3 (21.84 lb/ft 3 ) and water-binder ratio of 0.55. Another concrete (CPZ10) containing pozzolanic substitution of 10% of the mass of cement was used to evaluate the effect of pozzolanic admixture on concrete proporties. The details of the concrete mixtures are summarized in Table 3.

Sample Preparation

In this test campaign, specimens were moulded in 11x22 cm (4.33x8.66 in) PVC cylinders.

After casting, they were demoulding after 24 hours and then immersed in water at 20°C (68°F) for 28 days for each concrete in accordance with EN 206-1. At the end of the moist cure, these specimens were cut in order to extract three discs of 5 cm (1.96 in) thick, which are then sealed on their curved surface with epoxy resin to ensure a uniaxial flow inside the discs and rectified to have plane and cleaned surfaces. Then, they were dried at 105°C (221°F) until reaching constant weight [START_REF] Afpc-Afrem | Durabilité des bétons : Méthode recommandée pour la mesure des grandeurs associées à la durabilité[END_REF] ; the middle disc was chosen and saturated [START_REF] Fraj | New approach for coupled chloride/moisture transport in non-saturated concrete with and without slag[END_REF] to evaluate the water porosity and the effective chloride diffusion coefficient.

Chloride diffusion test

The assessment of diffusion coefficient take long time with natural diffusion test (minimum 9 month), Migration test were developed to accelerate the transport of chlorides [START_REF] Andrade | Calculation of chloride diffusion coefficient in concrete from ionique diffusion measurements[END_REF][START_REF] Truc | A new way for determining the chloride diffusion coefficient in concrete from steady state diffusion test[END_REF][START_REF] Djerbi | Influence of traversing crack on chloride diffusion into concrete[END_REF] and recently standardized as NF XP P18-461 [START_REF] Nf Xp P | Essai sur béton durci : Essai accéléré des ions chlorure en régime stationnaire, détermination du coefficient de diffusion effectif des ions chlorure[END_REF]

J zFEC RTL Dmig         0 (2)
Where C 0 (mol/m 3 ) (mol/ft 3 ) is the chloride concentration of the upstream compartment (0,513),J (mol/(m 2 s)) (mol/ft 2 s) is the flux of chloride ions, z (z=1) is the chloride ion valency, F is the Faraday constant (F=96480 J/(V mol)), E (V) is the actual potential drop between the surfaces of specimen, R is the gas constant (R=8.3144 J/(mol K)) (J/mol F), T (K) (F) is the absolute temperature, L (m) (ft) is the sample thickness.

Evaluation of diffusivity coupling with temperature

To undertake a study that takes into account the diffusion coupling with temperature, an experimental device has been realized in EOLE laboratory (University of Tlemcen, Algeria). This experimental apparatus is composed of a caulked water tank of capacity 15 liters (3.96 gal). A heater is disposed on the left side to generate heat and on the right side, a coil for the circulation of the refrigerant gas which is connected to the compressor and to the evaporator to generate cold. Both components are flooded in a liquid water mixed with rapeseed oil and are connected directly to the control panel by two thermostats respectively controlling the high and low temperatures. The apparatus is also equipped with a variable temperature that controlled hot and cold temperature (see Fig. 2).

A circular coil connected to the tank is installed around the disc of concrete for conditioning specimen at temperature fixed in advance; all pipes are protected by a caulking to prevent loss of temperature. The circulation of the coolant liquid is provided by a closed circuit provided with a peristaltic pump. The controlled temperature is maintained constant for at least four hours, so as to enable the latter to reach the heart of concrete disc. Finally, the migration under electric field is generated, once the temperature is uniform throughout all the sample of concrete.

One migration test was performed for each temperatures: 5, 20, 30, 40 and 50°C (41, 68, 86, 104 and 122°F). And for each temperature, a diffusion coefficient is obtained. The effect of temperature on the chloride diffusivity was taken into account, which was often expressed theoretically by Arrhenius law (Eq. 1). Hence, the relation of the chloride diffusion coefficients Ln(D(T)) versus the inverse of the absolute temperature (1/T) is depicted. These data can be fitted by linear regression analysis to an unique straight line using the Arrhenius law . Then, the activation energy Ea is equal to the slope of the straight line [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Goto | Diffusion of ions through hardened cement pastes[END_REF][START_REF] Page | Diffusion of chloride ions in hardened cement pastes[END_REF][START_REF] Nguyen | Effect of the environment temperature on the chloride diffusion through CEM-I and CEM-V mortars: an experimental study[END_REF] .

Mercury intrusion porosimetry test (MIP)

The mass transport in cement-based materials is largely controlled by the porosity, also considered as a first durability index. Thus the porosity of cement-based materials and it's microstructure are the main factors that affect the penetration of chlorides [START_REF] Mehta | Concrete: Microstructure, Properties and Materials[END_REF][START_REF] Thomas | Supplementary cementing materials[END_REF] .

For the characterization of porosity and pore size distribution of the studied materials, an investigation by mercury intrusion porosimetry (MIP) measurements was conventionally performed for its convenience and reliable results for all size of pores especially capillary pores [START_REF] Kumar | Study on some factors affecting the results in the use of MIP method in concrete research[END_REF] . Moreover, the MIP provides information on the threshold pore size which is considered relevant for the assessment of the resistance to transport of substance in the material [START_REF] Li | A pore size distribution-based chloride transport model in concrete[END_REF] .

For this test campaign, two cubic samples of each mixtures having dimensions of 1.5x1.5x2 cm 3 (0.59x0.59x0.78 in 3 ) cut from cylindrical disc ø110×50 mm (ø 4.33 x1.96 in) specimens were prepared and dried by putting them in an oven at T = 40°C (104°F) until reached a constant weight and stored in sealed containers for the MIP test. The MIP test was carried out on a Micromeritics AutoPore-9500 mercury intrusion porosimeter capable of generating pressure in the range of subambient to 414 MPa 50 (60000 psia).

RESULTS AND DISCUSSION

The accumulation of chloride ions in the downstream compartment is shown as a function of time for OC and CPZ10 in Figure 3 for different exposure temperatures.

From the results obtained in this study, summarized in Fig. 3 andTable 4, the results emphasize the effect of the type of concrete on diffusion coefficients. The chloride migration coefficients calculated at the temperature level for the mixture concrete containing pozzolan is lower than the migration coefficient of chloride through the ordinary concrete. Intuitively, a lower effective chloride diffusion coefficient value is expected to increase the time to corrosion initiation, consequently service life of the structure. For all temperature range 5 to 50°C (41 to 122°F), the use of 10% pozzolan reduce the CPZ10 migration coefficient by about 32% compared with OC migration coefficient. This result is in agreement with other researchers who have studied concrete with pozzolanic additions 10,28, . Moreover, the water porosity of OC concrete is higher than the porosity of CPZ10 concrete (15.08% vs. 13.79%), as presented in Table 3. As shown by Fig. 4, the pore structure of the two kinds of specimen's concrete is characterized by MIP and presents the pore size distribution at the age of 90 days. The discussed results below are the average of two tests per sample concrete. It can be noticed that the cumulative volume of pores for OC (0.0493 ml/g) (0.75615 fl.oz/lb) showed high values than CPZ10 (0.0393 ml/g) (0.60277 fl.oz/lb), thus the volume of pores is reduced by about 20%; and the critical pore diameter which corresponds to the maximum of porosity given by the pore size distribution of CPZ10 report a distinctly different pore size diameter relative to OC (0.0935 vs. 0.0481 µm) (0.03681x10-4 vs. 0.01893x10-4 in) but still remaining in the range of meso-pores. The reason for these differences in the main peak and the cumulative pore volume of concrete CPZ10 compared to OC is related to two effects, first the total volume of capillary is reduced, and second there is a shift of the curve to the left characterizing the reduction of capillary-sized pores which is explained by the refinement of the porosity due to lower amounts of pore inter-gel particles and macro-pores due to the substitution in mass content in cement by pozzolanic addition [START_REF] Thomas | Supplementary cementing materials[END_REF] . Indeed, the substitution of 10% mass content in cement by pozzolan reacts with portlandite outcome from cement hydration and form additional calcium silicate hydrates which are filling the voids and thus reduce the interlayer interconnectivity of the pores [START_REF] Khan | Properties of natural pozzolan and its potential utilization in environmental friendly concrete[END_REF] . Therefore, the results show that mercury porosity of CPZ10 (9.85%) is less than OC porosiy (11.39%) (see Table3): the decrease of porosity is in accordance with the reduction of water porosity. The pozzolanic substitution induces a more compact microstructure and a lower pore connectivity.

The concrete sustainability performance is improved by substituted Portland cement by pozzolanic admixture. Indeed, the lowest porous concretes (with pozzolan) are less sensitive to environmental conditions and the mass transport is slower in these concretes [START_REF] Kaid | Durability of concrete containing a natural pozzolan as defined by a performance-based approach[END_REF][START_REF] Touil | Les bétons aux pouzzolanes en façade maritime[END_REF] . As results, the size of paths of chloride penetration is modified and the transport mode occurring causes a decrease in coefficient of migration of CPZ10 than OC. This is in accordance with many researchers which have proposed various relationships between diffusion chlorides and the microstructure of cement based materials such as its evolution of pore structure [START_REF] Fraj | New approach for coupled chloride/moisture transport in non-saturated concrete with and without slag[END_REF][START_REF] Yang | On the relationship between pore structure and chloride diffusivity from accelerated chloride migration test in cement-based materials[END_REF][START_REF] Sun | Relationship between chloride diffusivity and pore structure of hardened cement paste[END_REF] .

Otherwise, by examining the results of migration test for all temperature, it is clear that the Cl - diffusivity of both concretes increased with the temperature rising.

Additionally, the time lag T lag varies with the diffusion coefficient. It was shown that for T lag of CPZ10 is higher than for OC for the same temperature as shown in Table 4. Firstly, a higher T lag may result from a lower porosity, this is an effect of the material composition that T lag depends on the porosity of concrete as cited in some research [START_REF] Coussy | Non-linear binding and the diffusion-migration test[END_REF][START_REF] Touil | Effect of natural pozzolan on concrete's durability[END_REF][START_REF] Djerbi | Effect of uniaxial compressive loading on gas permeability and chloride diffusion coefficient of concrete and their relationship[END_REF][START_REF] Touil | Etude des performances de durabilité des bétons locaux[END_REF] . Secondly, if we focus on variation of temperature for the two concretes taken separately, increasing of temperature of 5 to 50°C (41 to 122°F), has two effect: one, to release of ions binding and to increase the concentration of free chlorides in the pores and second, catalytic effect of temperature on diffusion speed, then allows to chlorides to accelerate and reach the downstream part of the material more rapidly as confirmed by researchers [START_REF] Nguyen | Effect of the environment temperature on the chloride diffusion through CEM-I and CEM-V mortars: an experimental study[END_REF][START_REF] Jensen | Influence of cement constitution and temperature on chloride binding in cement paste[END_REF] . This phenomenon is more marked for OC than the CPZ10 because the increase of porosity and amount of binding chlorides is lower which results a great chloride diffusion coefficient evidenced by the significant decrease in delay time T lag registered. Furthermore, as shown the experimental results in Fig. 5. It can be concluded that there is a regression relation between the diffusion coefficient and the delay time as mentioned by Djerbi et al. [START_REF] Djerbi | Influence of traversing crack on chloride diffusion into concrete[END_REF] . This variation is depending on the temperature and it is specific for each type of concrete. From these results, a major conclusion leads us to think that the important time lag recorded for low temperature 5 °C (41°F) for both concrete CPZ10 (124 h) and OC (92 h) are due to slowly kinetics chlorides penetration, characterized by small diffusion coefficients.

On the other hand, at temperatures above than 30°C (86°F) the free ions in solution pores become increasingly more constant amount and are conditioning by the porosity of the material, then the diffusion is less dependent on chlorides interactions but rather, it is activated in fact in terms of the speed diffusion by increasing the temperature, it is very clear that delay times are close, and varying respectively around 12% for CPZ and 21% for OC passing from 30 to 50°C (86 to 122°F ), with the increase of the diffusion coefficient.

Probably delay time can still evolve, that if the microstructure is modified by a higher temperature (to beyond 80°C (176°F)) [START_REF] Caré | Effect of temperature on porosity and on chloride diffusion in cement pastes[END_REF] or a mechanical damage [START_REF] Fraj | New approach for coupled chloride/moisture transport in non-saturated concrete with and without slag[END_REF][START_REF] Djerbi | Influence of traversing crack on chloride diffusion into concrete[END_REF][START_REF] Djerbi | Effect of uniaxial compressive loading on gas permeability and chloride diffusion coefficient of concrete and their relationship[END_REF] , resulting in greater porosity making penetration most important. it must be examined whether will there be shifts on time delay for the high temperatures.

Fig. 6, presents the evolution of migration coefficient as a function of temperature. The results show that the relationship diffusion -temperature increases regularly. Indeed, we mentioned that the coefficient of migration increases with increasing temperature from 5 to 50°C (41 to 122°F). This is because the cumulative concentration of chlorides characterized with a diffusion coefficient respectively for CPZ10 and OC, in one hand, decreases by 58 and 60% with lowering the temperature from 20 to 5°C (68 to 41°F), in other hand, an increase of 64 and 66% of diffusion coefficient with increasing temperature from 20 to 50°C (68 to 122°F).

in other words, we can see that a penetration kinetics of chlorides is lower at low temperatures (5°C) (41°F) resulted with an effective diffusion coefficient (D mig ) of more than about two times lower in an ambient temperature of 20°C (68°F), and a penetration rate of chlorides with higher temperature (50°C) (122°F), has led to about three times diffusion coefficient in relation to a temperature of 20°C (68°F). It is worth to mention that the increase of diffusion coefficient with the temperature level for each concrete investigated is consistent with some works without taking reference to the methods used by these authors [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Al-Khaja | Influence of temperature, cement type and level of concrete consolidation on chloride ingress in conventional and high-strength concretes[END_REF][START_REF] Yuan | Effect of temperature on transport of chloride ions in concrete[END_REF][START_REF] Samson | Modeling the effect of temperature on ionic transport in cementitious materials[END_REF][START_REF] Yang | Effect of 95°C temperature on the chloride-migration of concrete using electrical field[END_REF][START_REF] Otsuki | Temperature dependency of chloride induced corrosion in concrete[END_REF] .

In fact, at the temperature of 5°C (41°F), the coefficient of diffusion is lower for both concrete, because ionic diffusion and chemical reaction are showed down; this finding is in accordance with some works [START_REF] Samson | Modeling the effect of temperature on ionic transport in cementitious materials[END_REF]61 .

In the case of temperature 20 and 30°C (68 and 86°F) experimentally, the both concrete diffusion behaved slightly evolution in terms of chloride diffusivity registered; that display limited to a relative variation of 23%.

However, we can also observe that the effect of the increase in temperature causes a large coefficient in the temperature range from 30 to 50°C (86 to 122°F) then the average variation is about 33% for a gap of 10°C (50°F). As a consequence, the effect of the speed level of chloride penetration is due to the impact of the temperature level on the diffusion coefficient in the temperature range above 30°C (86°F). This was evidenced by a bi-linear trend (see Fig. 6), which is more representative of the evolution of diffusion temperature.

In fact, the diffusion coefficient values tend to increase with temperature; that means the temperature modify significantly the diffusion coefficient. Such evolution can be expected to have a substantial impact on the service life of reinforced concrete in chloride environments.

Therefore, structures exposed to hot climates will potentially deteriorate more rapidly due to increased transport and chemical reaction rates. This observation is in accordance with other work on slightly different materials [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Samson | Modeling the effect of temperature on ionic transport in cementitious materials[END_REF]61 .

Of this, it's more important to take role of temperature on ionic transport in cementitious materials, in order not to underestimate the life of structures. 7). The correlation coefficients for the lines obtained for OC and CPZ10 were calculated to be 0.98. Therefore, it can be concluded that the diffusion of Cl -in concrete follows the Arrhenius theory and it can be noted that logarithms of the diffusivity of chloride in concrete, were linearly proportional to the reciprocal of absolute temperature.

The result of activation energy obtained is close to those obtained by some authors [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF][START_REF] Yuan | Effect of temperature on transport of chloride ions in concrete[END_REF][START_REF] Collepardi | Penetration of chloride ions into cement pastes and concretes[END_REF][START_REF] Page | Diffusion of chloride ions in hardened cement pastes[END_REF] cited, a value that fluctuates between 17.9 and 40 kJ/mol for cement, mortar and concrete materials.

We mention that the activation energies obtained from cement paste might be different from those obtained from concrete. Thus, we will compare our activation energies values with those obtained by Dousti et al. [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF] , including control concrete (Ea = 29.40 kJ/mol) and concrete mixture incorporating 10% of the natural zeolite (Ea = 28.88 kJ/mol), which seems close natural pozzolan used in this study [START_REF] Touil | Effect of natural pozzolan on concrete's durability[END_REF] . Then, it seems that the values obtained for the two kinds of concretes are relatively close. This fact indicates that the kinetics chloride diffisuvity in concrete apparently agrees with the Arrhenius theory. At the end, from experimental results, the activation energy calculated can be used into Eq. (1) to estimate diffusion coefficients at different temperatures. Fig. 8 shows the comparison between the experimentally data obtained and the calculated values. Then, we conclude that exists a good agreement as confirmed by Dousti et al. [START_REF] Dousti | Influence of exposure temperature on chloride diffusion in concretes incorporating silica fume or natural zeolite[END_REF] .

CONCLUSIONS

The objective of this study was to evaluate the influence of pozzolanic substitution and the effect of temperature on the effective diffusion coefficient of chloride in the concretes. The main conclusions of the present study are:

1. The characterization by MIP measurements of concrete for substitution of part of the cement mass proportion (10%) of the pozzolan showed a significant reduction in the porosity of the CPZ10 concrete than OC concrete. This was explained by the reduction of the pores volume and the critical diameter, which leads a microstructure more compact; whole largely conditioning the transport mechanisms in the concrete. In terms of sustainability, it is systematically confirmed by recording a reduction of diffusion coefficients.

2. The presence of pozzolan in the cement used as mass substitution (10%) can significantly reduce porosity and effective diffusion coefficient of concrete studied for all temperatures range.

3. The temperature level has an impact on the kinetics of penetration of chlorides. Then, it always recording an increase of the effective diffusion coefficient of both concrete OC and CPZ10 studied when the temperature rising. There is a decreasing regression between coefficient diffusion and time lag. Thus, the time lag (T lag ) was almost decreasing and the influence of temperature is well related to the weakness of binding chloride which becomes minimal above 30°C (86°F) as confirmed by an increase of diffusion coefficient du the speed diffusion and close time lag. 4. The activation energy calculated from the Arrhenius equation remains close to that presented in the literature.

5. Finally, it can be seen that the relationship between the logarithms of diffusion coefficient and reciprocal of absolute temperature are linearly distributed. Therefore, it can be concluded that the behaviour of diffusion Cl-in concrete follows the Arrhenius theory. Also, a good agreement was found between the experimental data and the Arrhenius theory. 61. Lin, S.H., "Chloride diffusion in porous concrete under conditions of variable temperature," Wärme -und Stoffübertragung, Springer Link, V. 28, No. 7, 1993, pp. 411-415.

TABLES AND FIGURES

List of Tables:

Table 1 -Chemical compositions of cement and pozzolan (%).

List of Figures:

Fig.

  according to the following principle : The disc of concrete was placed between the two compartments of a cell migration. A basic solution containing NaOH (0.025 M) and KOH (0.083 M) in the downstream compartment; the same solution laden with NaCl (0.513 M) in the upstream compartment. A 12 V potential difference was applied between the sides of the concrete sample. The downstream solution was sampled, and samples were titrated with silver nitrate (0.05 M). As the flux became constant, the simplified Nernst-Planck relation 20 allowed us to determine the value of the effective coefficient D mig (m 2 /s) (ft 2 /s), as in Eq. (2):

Furthermore 7 .

 7 , the D mig of concrete can be estimate based on the energy calculated by the Arrhenius equation at different temperatures. The relationship of the logarithm Ln (D mig ) as a function of the reciprocal of the absolute temperature is shown in Fig. From these Figure, the adjustment of the curve made by linear regression analysis of the Arrhenius equation, leads us to estimate by means of the slope of this line the value of the activation energy which is respectively about 32.45 kJ/mol for OC and 30.02 kJ/mol for CPZ10 (see Fig.

1 -

 1 Fig. 1 -Laser granulometry of Cement and Natural pozzolan.

Fig. 2 -

 2 Fig. 2 -Migration cell with hot and cold device.

Fig. 3 -

 3 Fig. 3 -Evolution cumulative increase of chloride concentration in downstream cell of OC

Fig. 4 -

 4 Fig. 4 -Measured porosity in OC and CPZ10 specimens using MIP test.

Fig. 5 -

 5 Fig. 5 -Relationship between the time lag and the diffusion coefficient of function of the

Fig. 6 -

 6 Fig. 6 -Chloride diffusion coefficient as a function of temperature.

Fig. 7 -

 7 Fig. 7 -Arrhenius plots of the diffusivity in concrete mixtures.

Fig. 8 -

 8 Fig. 8 -Comparison between the experimentally obtained and calculated diffusion

Fig. 1 -Fig. 2 -

 12 Fig. 1-Laser granulometry of Cement and Natural pozzolan (Note : 1 μm = 3.937 10 -5

Fig. 3 -Fig. 4 -Fig. 5 -

 345 Fig. 3-Evolution cumulative increase of chloride concentration in downstream cell

Fig. 6 -Fig. 7 -Fig. 8 -

 678 Fig. 6-Chloride diffusion coefficient as a function of temperature.

  Khaja[START_REF] Al-Khaja | Influence of temperature, cement type and level of concrete consolidation on chloride ingress in conventional and high-strength concretes[END_REF] studied experimentally the durability performance of high-strength concrete mixes and conventional concrete, exposed to chloride environments (5% NaCl) at temperatures of 20 and 45°C (68 and 113°F). The results noticed that a significant increase in the chloride ingress into concrete was observed when the exposure temperature was increased from 20 to 45°C (68 to 113°F) in both conventional and high-strength concretes. Furthermore, the effect of temperature on chloride ingress is more influential in the conventional concrete than in the high-strength concrete. The activation energy was not determined in this study. Samson and Marchand[START_REF] Samson | Modeling the effect of temperature on ionic transport in cementitious materials[END_REF] proposed a semi empirical function, to estimate variations in diffusion coefficient of concrete when the temperature of the material fluctuates with the values of 4, 23 and 40°C

	(100x200 mm) (3.93x7.87 in), the curing and the test diffusion was conducted under three
	levels of temperature (20, 30 and 40°C) (68, 86 and 104°F). The diffusion coefficient was
	calculated using Fick's first law of diffusion. The activation energies obtained were from 70.4
	to 134.9 kJ/mol.
	Recently Doutsi and al. 10 focused his work on the influence of exposure temperature ranging
	Collepardi et al. 28	studied the chloride diffusion into cement pastes containing natural
	from 22, 35 to 50°C (71.6, 95 to 122°F) on chloride diffusion according to Fick's second law
	pozzolan with water-cement ratio of 0.4: the samples were put in contact with CaCl	2 solution
	in control concrete and six different concrete mixtures containing various amounts of silica
	and kept at 10, 25, 40°C (50, 77, 104°F). The results shows that the pozzolanic cement paste
	fume or natural zeolite. The results obtained by Dousti et al.
	investigated the effect of temperature on chloride diffusion into mortars with Yuan et al. 26 also studied the temperature effect on the transport of chloride ions in concrete with different water-cement ratio and type of cement. The investigation was carried in non-steady state condition for both tests, migration and diffusion coefficient, which were measured at 5, 20 and 40°C (41, 68 and 104°F). They reported that activation energy of concrete measured from non-steady-state diffusion tests ranges from 17.9 to 39.9 kJ/mol, while the activation energy obtained from non-steady-state migration coefficient is around 20 kJ/mol and independent of water to cement ratio. Yang and Wang 33 addressed that the use of accelerated chloride migration test (ACMT) of unheated (20°C) (68°F) and heated concrete (95°C) (203°F) showed a significant increase of the chloride migration coefficients when offer a higher resistance to the Cl Nguyen et al. 31 concrete specimens are exposed from 20 to 95°C (68 to 203°F) temperature. The
	breakthrough time had reduced at room temperature (20°C) (68°F) to a limited range at 95°C
	cement type I and V using an accelerated test method. They found that chloride diffusion
	(203°F).
	Otsuki et al. 34 studied the influence of temperature on the mortar matrix paste specimens
	(5x5x4 mm) (0.19x0.19x0.15 in) from the central part of the cylindrical specimen of concrete

penetration than the portland cement paste and the activation energy determined was 35.56 kJ/mol for the cement paste and 4.12 kJ/mol for the pozzolanic cement paste. Goto et al. 29 has determined a diffusion rates of chlorides ions as a function of several factors in hardened cement paste such as water-cement ratio, curing age, curing temperature and diffusion temperature (27, 35, 45 and 60°C) (80, 95, 113 and 140°F) using a diffusion cell. It is reported there was a significant temperature dependence of apparent diffusion coefficient and they obtained the activation energy of 50.2 kJ/mol with a water-to-cement ratio of 0.4. Page et al. 30 investigated the cement paste and were using the cells diffusion placed in a water bath, with five values of temperature in the range 7 to 47°C (44.6 to 116.6°F); the effective diffusion coefficient measured is affected by the level of temperature and they found that the activation energy was dependent on water-to-cement ratio (w/c), 41.8 kJ/mol for paste with w/c = 0.4, 44.6 kJ/mol for paste with w/c= 0.5, and 32.2 kJ/mol for paste with w/c= 0.6. coefficient and penetration depth increase with temperature level. The activation energy are in the range of literature values 30 : the values are 35.7 kJ/mol and 32.3 kJ/mol for the mortars incorporating cement type I and V, respectively. Al-(39.2, 73.4 and 104°F). The activation energy obtained from migration test is ranging from 17.9 to 21.2 kJ/mol.

Table 2 -

 2 Mineralogical (Bogue) compositions of cement.

Table 3 -

 3 Mixture proportions and physical properties.

Table 4 -

 4 Coefficients of diffusion at different temperatures.

Table 1 -Chemical compositions of cement and pozzolan (%)

 1

		CEM II/A 42.5	Pozzolan
	SiO 2	27.95	46.8

Table 2 -Mineralogical (Bogue) compositions of cement

 2

		Bogue composition (%)
	C 3 S	55.65
	C 2 S	20.18
	C 3 A	9.77
	C 4 AF	9.5
	Gypsum	3

Table 3 -Mixture proportions and physical properties

 3

	Mix ingredients	OC	CPZ10
	Coarse aggregate, (kg/m 3 ) (lb/ft 3 )	1109 (69.23)	1109 (69.23)
	Sand, (kg/m 3 ) (lb/ft 3 )	660 (41.20)	660 (41.20)
	Cement CPA-CEM II/A 42.5 (kg/m 3 ) (lb/ft 3 )	350 (21.84)	315 (21.84)
	Pozzolan (kg/m 3 ) (lb/ft 3 )	-	35 (2.18)
	w/b (%)	0.55	0.55
	Slump (cm) (in)	8 (3.14)	7 (2.75)
	Compressive strength at 28 days (MPa) (psi)	34.10 (4945.78) 32.50 (4713.72)
	Compressive strength at 90 days (MPa) (psi)	37.80 (5482.42) 40.20 (5830.51)
	Water porosity (%)	15.08	9.85
	Mercury porosity (%)	11.39	11.39

Table 4 -Coefficients of diffusion at different temperatures.

 4

	Temp.	Coefficients of diffusion	Lag time (Hours)	Activation Energy
	°C (°F)	D mig m 2 /s. E -12 (ft 2 /s)		T lag	Ea (kJ/mol)
		OC	CPZ10	OC	CPZ10	OC	CPZ10
	5 (41)	2.03 (21.85)	1.49 (16.03)	92.51	124.04
	20 (68)	5.13 (55.21)	3.56 (38.31)	54.84	57.51
	30 (86)	6.71 (72.22)	4.52 (48.65)	47.04	56.73	32.45	30.02
	40 (104)	10.10 (108.71)	6.34 (68.24)	44.18	51.61
	50 (122)	15.32 (164.90)	9.91 (106.67)	41.33	44.34

ACKNOWLEDGEMENTS

The authors would like to acknowledge the financial support of TASSILI project (10MDU811) on durability and aging of concrete materials, maintenance and reliability of structures on the coast, whose funding allowed for this work. Our thanks go also to GeM Laboratory (France) and EOLE Laboratory (Algeria) for their support.