NON-DESTRUCTIVE TESTING OF ACCELERATED CORROSION OF REINFORCED MORTAR POZZOLANIC

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1 11-13 June 214, Zagreb, Croatia NON-DESTRUCTIVE TESTING OF ACCELERATED CORROSION OF REINFORCED MORTAR POZZOLANIC M. Hamadache (1), M. Mouli (1), N. Bouhamou (2), F. Dif (1) and S. Benosman (3) (1) Materials Laboratory, Department of Civil Engineering, National Polytechnic School Oran, Algeria. (2) Department of Civil Engineering, University Abdel Hamid Ibn Badis of Mostaganem, Algeria. (3) Faculty of Science, Laboratory of Polymer Chemistry, University of Oran, Es-senia Algeria. Abstract The objective of this work is the study of the valorization of an addition mortar which is extracted from a natural pozzolan deposit in Bouhamidi located in the region of Beni Safi.We chose to study this natural addition because of its low cost and its pozzolanic reactivity. Thus, we performed several experiments focusing on the influence of the addition amount, as well as the fineness on the corrosion of reinforcement in mortars. We have measured the corrosion potential and the mass variation of different mortars based on pozzolan content (1%, 2% and 3%). The results indicated that is it possible to highlight the beneficial effect of this addition. The analysis of achievements shows that the addition of the pozzolan in optimal quantities has the following advantages: - Protection of reinforcement against corrosion - Increase of the resistance against sulfate attack - Gain in mass of pozzolan mortars in the sulphatic environment. Keywords: pozzolan activity, mortar, corrosion, mass variation 1. INTRODUCTION The use of mineral additives as cement replacement, as well as on site in concrete or mortar ready for use, is a practice unknown to the builders of our country. Therefore, we felt it important to study and evaluate the influence of these additions, substitutions such as cement, on the properties of hardened mortar. A natural pozzolan is used which is available considerable quantities in Western Algeria (Beni-Saf) and must necessarily add value. For this we crafted three types of mortar containing pozzolana (1%, 2% and 3%), on which we measured corrosion (potential) [1], [2] and a control mortar without pozzolan used as a reference. 133

2 11-13 June 214, Zagreb, Croatia 2. MATERIALS USED 2.1. Cement The cement used in all tests is a CPA-CEM I 42.5 N cement from the Zahana, It comes in a 5 kg bag with a sheet No. FR-26LAB Version 2 according the Algerian Standard NA442. The guaranteed minimum compressive strengths at 2 days and 28 days are 8MPa and 4. MPa respectively. The Blaine specific surface area of the cement is S SB = 338 cm²/g and the absolute density of the cement is = 3.16 g/cm 3. The chemical compositions of cement and clinker mineralogical data are shown in Tables 1 and 2. Table 1: The chemical composition of cement CPA-CEM I 42.5 N Constituent CaO SiO 2 Al 2 O 3 Fe 2 O 3 SO 3 K 2 O Na 2 O MgO CaO free % Table 2: Mineralogical composition of clinker Constituent C 3 S C 2 S C 3 A C 4 AF % Natural pozzolan The natural pozzolan used is extracted from a volcanic deposit Bouhamidi south of Beni Saf. The deposit is represented by a conical mountain called El-Kalcoul at a height of 236 m. This pozzolan consists essentially of scoria and pumice well stratified, varying in color from red to black [3]. Natural pozzolans used in all tests is in the form of a powder, crushed slag resulting in pozzolanic, steamed for 24 hours at a temperature of 5 C to eliminate their humidity, and then ground until the resulting powder can pass through a sieve of 8 microns mesh [4]. The chemical composition of natural pozzolan after grinding is shown in Table 3. Table 3: The chemical composition of natural pozzolan Beni-Saf Constituent CaO SiO 2 Al 2 O 3 Fe 2 O 3 SO 3 K 2 O Na 2 O MgO Cl - CaCO 3 % The Blaine specific surface area and the specific density of the natural pozzolan are: S SB = 433 cm²/g and = 2.45 g/cm 3, respectively The sand This is sand sea Terga fixed with 4% Sand Sea, 6% Sand Quarry. The sand is initially prepared to be classified according to French standards NF P 15-43, its particle size distribution curve satisfies the reference spindle indicated in Figure 1. This sand is a granular structure that has the greatest impact on the qualities of concrete and mortar [5]. It plays a vital role in reducing the volume variations, the heat released and the cost of concrete. It must be clean and must contain no harmful elements. The physical characteristics of this sand are given in Table

3 11-13 June 214, Zagreb, Croatia Table 4: Physical properties of sand used Absolute Gravity (g/cm 3 ) 2.64 Apparent Density (g/cm 3 ) 1.44 Equivalent sand (%) 98.4 Fineness modulus 1.8 Coefficient of curvature 1.2 Coefficient of uniformity 2.4 Nature of the sand Quartz Figure 1: Granular sands curve corrected 2.4. The mixing water The mixing water used for preparation of mortars is potable tap water, its chemical composition is shown [6] in Table 5. Table 5: Chemical analysis of the mixing water Compound Symbol Content (mg / l) chlorides Cl 127 Sulfates SO Magnesium Mg 54 Calcium Ca 86 Carbon dioxide CO Bicarbonates CO 3 H 138 organic matter.12 ph= PREPARATION OF MORTAR AND TEST METHODS Preparation of mortars The preparation of the mortar was carried out according the following steps ASTM C [7]; The sand and cement to be tested are mixed with water in the proportions: 45 ± 2g of cement, 135 ± 5 g of sand and a percentage of water. The W / C ratio of such mortar is between.5. Mortar mixtures have been made from Portland cement CEM I 42.5 N and three combinations of binders obtained following the partial replacement by weight of cement by different levels of natural pozzolan (1%, 2% and 3%). For each binder, were carried out in accordance with the mortar mixtures ASTM C112 [8]. Mortars are used for making test specimens with dimensions of 5x5x5 mm 3 and cylindrical specimens of dimensions 5mm diameter, 1 mm long. Underflow(%) spindle Sieve [mm] sand corrected 135

4 RILEM International workshop on performance-based specificationn and controll of concretee durability June 214, Zagreb, Croatiaa Hardened steel bars (High Adhesion) ) were used with a diameter of 1mm and 1mm long, each bar was divided into two parts; one part protected with w an epoxy resin to a length of 6mmm and the other part exposed to the corrosion. Bars are integrated, Figure 2. Figure 2: Steel bar used in the mortar 3.2. Test methods To evaluate the corrosion properties of mortars and highlight thee influencee of the substitution of cement by natural pozzolan of Beni Saf; the measurement of corrosion potential or electrode potential is the most widely usedd techniquee in the field of nondestructive testing in civil engineering. This method is used to determine the statee of corrosion of steel in i the mortar. Recommendations have been published by ASTM (C876-9) [1] and RILEM TC154-EMC [2]. 4. RESULTSS AND DISCUSSION The objective of the various tests conducted for this study is to determine an accelerated corrosion test that is close to the t natural corrosion " The potential" of the program is to t detect activity in the mortar due to corrosion. The cylindrical mortar specimens, 5mm diameter and 1mm lengthh were immersed in fresh water and a solution of 5% Na 2 SO 4 + 5% MgSO 4. The test was conducted according to ASTM Test of corrosion by apparatus corrosimeter Immersion in the fresh water Figure 3 showss the potential of mortar specimens made pozzolanic versus time of immersion in fresh water. up of different levels based 136

5 RILEM International workshop on performance-based specificationn and controll of concretee durability June 214, Zagreb, Croatiaa M M1 M2 M3-5 potential (mv vs Cu-CuSO 4 ) Low L corrosion Corrosion C uncertain High corrosionn No. of cycles Figure 3: Potential variation as a function of the number of cycles of mortar containing natural pozzolans immersed in fresh water w Initially the specimens are immersed and subjected to a wetting drying cycle. The measurement is carried out forr each 2 day cycle with a device called corrosimeter, Figure 4. The easiest way to assess the degree of corrosion of steel is to measure m the corrosion potential. This technique is well known and is the subject of a process in the American National Standards under the reference ANSI / ASTM C876. Figure 4: The corrosimeter Measuring the potential difference between an ordinary portable half-cell normally consists of a reference electrode placed on the surface of the mortar onn the area exposed to corrosion and the steel reinforcement; Table 6 below, compares the results with reference corrosion potentials according to ASTM C Table 6: Probability of corrosion Potential of corrosion mv vs ECS > to < Potential of corrosion mv vs Cu-CuSO 4 > to -35 < -35- Probability of corrosion Low (<1%) Uncertain (5%)) High (9%) 137

6 11-13 June 214, Zagreb, Croatia Comparing with the values in Table 6, corrosion is high for M2 and M3 after 7 cycles, whereas corrosion is high for M and M1 after 1 cycles Immersion in the mixture solution (5% Na 2 SO 4 +5%MgSO 4 ) Figure 5 shows the variation of potential as a function of number of cycles containing natural pozzolan mortar immersed in the mixture solution (5% Na 2 SO 4 + 5%MgSO 4 ). Potential (mv vs Cu-CuSO 4 ) M M1 M2 M Low corrosion Corrosion uncertain High corrosion N. of cycles Figure 5: Potential variation as a function number of cycles of mortar containing natural pozzolans immersed in the solution of 5% Na 2 SO 4 + 5% MgSO 4. Comparing with the values in Table 6, we see that from the third cycle corrosion is high for both pozzolanic mortar and the control mortar. We note that in Figure 5 that the corrosion in this medium is higher relative to the medium before fresh water for all mortars. 4.2 Test of corrosion by apparatus Potentiostat For the same reasons as for the measurement of potential while impressed current requires an auxiliary electrode. We then measured i directly on the external circuit connecting the two electrodes RILEM TC-154-EMC [2]. It is necessary to understand the evolution of corrosion, so its kinetics to know the evolution of the electrode potential as a function of corrosion current in Figure 6. Thus draw the polarization curves. A speed of thickness loss 1μm/year is a corrosion current of.1 μa/cm 2. The quantitative forecasts require the calculation of an effective corrosion speed of and level of risk of corrosion (Table 7). [2] 138

7 RILEM International workshop on performance-based specificationn and controll of concretee durability June 214, Zagreb, Croatiaa Table 7: Levels of corrosion depending on corrosion rate Corrosion speed Level of corrosion (μm/ year) Below 1 Negligible Between 1 and 5 Low Greater than 1 High Figure 6: The apparatus potentiostat Free sh water 5 % Na 2 SO 4 + 5% MgSO O Higg h corrosion 9 Corrosion speed Moderate corrosioo n Low corrosion 2 1 M% M1% M2% M3 % Pozz zolan conte nts (%) Figure 7: Corrosion speed of the samples of mortar at 2 days. We find in Figure 7 that: In fresh water, all mortars exhibit low corrosion, except the 3% pozzolan which exhibits moderate corrosion. In the sulphatic solutions, all mortars exhibit moderate corrosion, except the 3% pozzolan which exhibits high corrosion. There is a proportional increasee for mortars at different concentrations of pozzolan. 139

8 11-13 June 214, Zagreb, Croatia 5. CONCLUSION The main interest of this study is the possibility of partially substituting an industrial material, cement, with a natural material that is pozzolan of Beni Saf. The costs of the two materials differ. Pozzolan is a natural product and requires no industrial process involving a high energy cost. It is therefore much cheaper than cement, which is produced through a very expensive process. However, the mortars obtained by substituting cement pozzolan with this material can only be selected if their performance is adequate. The main conclusion we reached is that substituting 1% of Portland cement with 1% of the Beni-Saf pozzolana gives a mortar with long term durability (corrosion) characteristics identical to that of the control mortar. ACKNOWLEDGEMENTS Extend my Many thanks to all the existing reference in this article helped me a lot to accomplish all also a writer and assistant and the workshop to organized by RILEM TC 23- PSC and Thanks REFERENCES [1] ASTM C Standard Test Method for Half-Cell Potentials of Uncoated Reinforcing Steel in Concrete. American Society for Testing and Materials, (29) [2] RILEM TC 154-EMC 25 Electrochemical Techniques for Measuring Metallic Corrosion «Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method»; Recommendations; Andrade et Alonso; 3 may 25. [3] Mouli M. 26, Ph.D. Thesis in civil engineering USTO "Study of physical and mechanical properties of the pozzolan to manufacture lightweight concretes and high performance concrete." [4] Ali Aichouba A. 25, Natural pozzolans effect on the properties of cement based on calcium, Magister Thesis, USTMB d Oran, Algeria. [5] Baroghel-Bouny V. 1994, Characterization of cement pastes and concretes, methods, analyzes, interpretations, Central Laboratory for Roads and Bridges, pp.468, 1994 [6] Ghrici M. 26, Study of Mechanical and physical properties and durability of cement-based natural pozzolan, Ph.D. Thesis in civil engineering, USTMB d Oran, Algeria [7] ASTM C 35-99, Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency, [8] ASTM C112-24, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution,