DETERMINATION OF APPARENT CHLORIDE DIFFUSION COEFFICIENT FOR SELF COMPACTING CONCRETE CONTAINING NANO SILICA UNDER EFFECT OF SULFATE ATTACK

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 1, January 2017, pp , Article ID: IJCIET_08_01_047 Available online at ISSN Print: and ISSN Online: IAEME Publication DETERMINATION OF APPARENT CHLORIDE DIFFUSION COEFFICIENT FOR SELF COMPACTING CONCRETE CONTAINING NANO SILICA UNDER EFFECT OF SULFATE ATTACK Dr. Ghalib Mohsin Habeeb Professor, Civil Engineering Department, College of Engineering, University of Babylon, Iraq Zahraa DhurghamHashim Hadi Civil Engineering Department, College of Engineering, University of Babylon, Iraq ABSTRACT The objective of this work is devoted to determine the apparent chloride diffusion coefficient of self compacting concrete (SCC) with Nano Silica which is subjected to severe saline conditions contain sulfates and chlorides at concentrations similar to those existing in soils and ground water of the middle and southern parts of Iraq. Four basic mixes of SCC were performed with and without addition of Nano Silica, and with two types of cement (ordinary Portland cement and sulfate resistance Portland cement). The workability properties of mixes were evaluated by fresh tests such as slump-flow test, T50cm, L-box and V-funnel tests. The apparent chloride diffusion coefficient was determined at90 and 180 days. Test results exhibited that the presence of Nano Silica in concrete decreases the apparent chloride diffusion coefficient at age of 180 days which was ranged between ( )% measured relative to its reference mixes without Nano silica addition. Also, the results revealed that SRPC specimens have higher chloride content than OPC mixes especially at 90 days. while at 180 days, SRPC specimens have lower chloride content than OPC specimens. Key words: Nano Silica, sulfate attack, chloride diffusion, concrete, self compacting Fick s second law, fresh properties Cite this Article: Dr. Ghalib Mohsin Habeeb and Zahraa Dhurgham Hashim Hadi, Determination of Apparent Chloride Diffusion Coefficient for Self Compacting Concrete Containing Nano Silica under Effect of Sulfate Attack. International Journal of Civil Engineering and Technology, 8(1), 2017, pp INTRODUCTION The Chloride ions are in advertently associated with sulfate in the attack of groundwater on concrete. Chloride reacts with the hydrates of cement and form Freidel s salt (3CaO.Al O.CaCl.10H O)that does not have any harmful effects on concrete, but when chloride content in concrete reaches more than the editor@iaeme.com

2 Determination of Apparent Chloride Diffusion Coefficient for Self Compacting Concrete Containing Nano Silica under Effect of Sulfate Attack threshold value, the protective alkaline layer of steel reinforcement is broken and in the presence of oxygen and humidity, steel reinforcement gets corroded. Presence of chloride in sulfate solution affects the deterioration of concrete under sulfate attack (Prasad et al., 2006). The chloride diffusion test is used to determine the apparent chloride diffusion coefficient of hardened concrete by bulk diffusion. The apparent chloride diffusion coefficient is considered as an indication of the capacity of any type of concrete to resist chloride penetration and also can use to predict the service life of reinforced concrete structures. The resistance to penetration of chloride is affected by many factors such as the environment, finishing, mix composition, workmanship, curing and age. Apparent chloride diffusion coefficient is a chloride transport parameters calculated from acid soluble chloride profile data obtained from saturated specimens exposed to chloride solutions (without correction for chloride binding).diffusion is a process by which ions can pass through a saturated concrete. The driving factor in diffusion is the concentration gradient. The aggressive ions, such as chloride, when they are in contact with the surface of concrete will diffuse through the concrete from regions of a high concentration to a low concentration until a state of equilibrium in ion concentration is achieved. If the concentration of ions at the surface is very high, diffusion may result in corrosion-inducing concentrations at the level of the reinforcement (Moradi, 2014). On the other hand, the concrete structures subjected to sulfate attack which is likely to suffer from two types of deterioration; loss of strength of the matrix resulting from degradation of calcium silicate hydrate (C-S-H), and volumetric change leading to expansion due to the formation of gypsum or ettringite that leads to the cracking(al-rawi, 1985).The protection against sulfate attack and chloride diffusion requires to reduce the permeability of concrete and improve the microstructure of concrete. So, the addition of Nano Silica to concrete can consume calcium hydroxide crystals, reduce the size of the crystals at the interface zone and transmute the calcium hydroxide feeble crystals to C-S-H crystals and improve the interface zone and cement paste structures (Khanzadi et al., 2010) and (Saloma, 2015). This research focuses on the effect of Nano Silicaon the apparent chloride diffusion coefficient for SCC exposed to sulfate solutions. 2. EXPERIMENTAL PROGRAM 2.1. Materials and SCC Mix Design In this research, two types of Portland cement were used: Ordinary Portland Cement (OPC) (ASTM type I) and Sulfate Resistance Portland Cement (SRPC) (ASTM type V) manufactured by united cement company, commercially known (TASLUJA-BAZIAN). These types complied with the Iraqi specification (IQS No.5, 1984). The sand used from Al-Ekadir region in Iraq with a fineness modulus (2.51). Rounded gravel of 14 mm maximum size from Al-Nebai quarry was used as a coarse aggregate in all mixes. Sand and gravels conform to the Iraqi specification (IQS No.45, 1984).Nano Silica used in this work was produced in China by precipitation method in powder form making Nano Silica to have a high degree of purity about 99.96% and diameter for the particles (35nm). Silica fume used as a replacement with (5%) by weight of cement. Super plasticizer was also used, which is known commercially Glenium 54 to achieve high workability needed to produce SCC. Four mixes were investigated, all based on the same control mixture. These mixes were designed according to (European Project Group, 2005) and divided into two series each one with different type of cement (I or V).The main details of SCC mixes used in this study are presented in Table (1) editor@iaeme.com

3 Dr. Ghalib Mohsin Habeeb and Zahraa Dhurgham Hashim Hadi Table 1 The main details of SCC Mixes used in the present study Mix Notation Cement Silica fume Cementitious Material OPC- 0%NS (OR) OPC- 3%NS (ON3) SRPC- 0%NS (SR) SRPC- 3%NS (SN3) Nano Silica Sand Gravel SP % Water w/b ratio 2.3. Mixing Procedure Mixing process is conducted in pan mixer with a capacity of The 3/4 dosage of super plasticizer was added to mixing water and mixed about 30 second in a small pan mixing separately from other material then the Nano Silica was stirred with this solution and mixed about 3 minutes in order to disperse uniformly and avoid agglomerations of Nano Silica since it has a high surface energy. before 2 minutes from the end of pervious mixing, the cement and silica fume had been added in pan mixer and mixed for 1minute in dry state.the fine aggregate was added to the drying materials and mixed for 1minute.The prepared solution of (superplasticizer, water and NanoSilica) was added and mixed for 3 minute. Thereafter, gravel was added and mixed for 1 minute, Then the remaining dosage 1/4 of super plasticizer is added and mixed for 2 minute. The mixture is then discharged, tested and placed. The total time of mixing process was about 8 minutes. 3. TESTING METHODS 3.1. Fresh Concrete Tests The fresh concrete tests are required to assess filling ability (flow ability), passing ability (passibility) and segregation resistance (stability) of SCC. But, there is no unique test to measure the three properties together. So, different test methods have been developed in attempts to characterize the properties of SCC. In this study three tests were used slump flow test, V-funnel test and L-box test Hardened Concrete Test- Chloride Diffusion Test The average of three specimens for chloride diffusion test were used (concrete cylinders, diameter of 100 mm and height of 100 mm). Diffusion test was determined at the age of 90 and 180 days. This test was performed according to (ASTM C1556, 2003). All sides of the test specimens were coated with epoxy paint with two layers except for the finished surface which left uncovered in order to allow the chloride to penetrate the samples just from one surface. After that, the specimens were placed in tap water for 28 days in a plastic container, then the specimens immersed in the exposure solution (sulfate-chloride solution in this research which consists of pure salts, these salts were 1.5% MgSO.7H O, % Na SO, 0.7% CaCl.2H O and 5% NaCl by weight of cement).after a specified exposure period, thin layers were obtained from the test specimens by grinding the materials in layers parallel to the exposed surface. The produced powder was collected by using rotary impact drill for the determination of the total chloride concentration profile. Figure (1) illustrates the details of grinding process for test specimens. The total initial chloride concentrations are determined at 28 days and total concentrations at different depths after an exposure to chloride solutions were also determined through acid-soluble chloride content that described in (ASTM C 1152/ C 1152M, 2003), Plate (1) represents the powder collection process to editor@iaeme.com

4 Determination of Apparent Chloride Diffusion Coefficient for Self Compacting Concrete Containing Nano Silica under Effect of Sulfate Attack determine the chloride on content. The obtained chloride concentration profiles were fit to the solution of Fick s second law by means of a non-linear regression analysis using least squares of error, in order to determine the apparent chloride diffusion coefficient and the chloride concentration in the surface layer of concrete. Figure 1 Sketch of Grinding Process for Test Specimens Plate 1 Powder Collection Process and Determination the Acid-Soluble Chloride Content 4. RESULTS AND DISCUSSIONS 4.1. Fresh Concrete Fresh concrete tests were carried out to ensure that the mixes satisfy the requirements of SCC. Table (2) illustrates the results of the fresh properties for each mix. These results explain that the SCC used is conformed to the requirements of (European Project Group, 2005) (i.e. has a good consistency and workability at fresh state) editor@iaeme.com

5 Dr. Ghalib Mohsin Habeeb and Zahraa Dhurgham Hashim Hadi Table 2 Results of Fresh Properties of SCC Mixes 4.2. Hardened Concrete Test- Chloride Diffusion Test In Figures (2) and (3) the obtained apparent chloride diffusion coefficients (Da) for SCC mixes exposed to chloride solution (sulfate-chloride e solution in this work), at 90 and 180 days respectively are illustrated. It can be observed at 90 days of exposure that ON3 specimens exhibited a lower chloride concentration profile than SN3, also OR specimens have also lower chloride content than SR specimens. In other words, SRPC specimens have lower resistance to chloride than OPC specimens. This is due to low C 3 A content in SRPC specimens compared with OPC specimens, hence the high C 3 A contentt binds with high amount of chloride ions to form further amount of stable chloro complexes which called Freidel s salt ( 3CaO.Al 2 O 3. CaCl 2.10H 2 O) that cannot penetrate the concrete, so the total chloride content is reduced, therefore, SRPC specimens have higher total chloride contents which can diffuse to the steel rapidly and exacerbate the corrosion problem, that is relative to OPC specimens. When the higher chloride content reaches more than threshold value, the protective alkaline layer of steel reinforcement is broken and in the presence of oxygen and humidity, steel reinforcement gets corroded. The same conclusion is obtained by (Hussein, 2003) and (Rodriguez et al., 2013). Whereas, it is clear at 180 days that SRPC specimens showed a lower chloride concentration profiles as compared with OPC specimens. This may be related to the formation of expansive salts result from sulfate attack in OPC specimens such as gypsum and ettringite in a high amount when compared with SRPC specimens, these compounds result in expansion, cracking and deterioration of concrete; so, the cracking permits to penetrate more amount of chloride ions to the concrete (Breke et al., 1990) and (Wang and Ueda, 2011). Also, from the results, it has been shown that the presence of Nano Silica in concrete mitigates the total chloride content especially at deeper depths relative to corresponding reference mixes regardless of the type of cement. So, Tables (3) and (4) explain this reduction in the chloride content of SCC mixes containing Nano Silica for both 90 and 180 days of exposure ages relative to corresponding reference mixes (without Nano Silica). The reduction is due to physical effect of fine Nano particles, which were responsible for formation of less porous, denser microstructure and a discontinuous pore system. Additionally, the Nano particles acted as filler to enhance the density of concrete, which reduced the porosity of concrete. Also, the addition of Nano Silica created a finer particle size distribution. The finer particle size distribution of Nano Silica enhanced the pore structure of concrete and filled the voids at various size levels. As well as Nano Silica particles were able to enhance the concrete pastes chemically by their rapid reaction with free calcium hydroxide, which seemed to be able to create a discontinuous pore system more readily by consuming free calcium hydroxide. Nano particles acted also as nucleus in cement paste to make calcium hydroxide crystals smaller and accelerated the cement hydration due to their high activity editor@iaeme.com

6 Determination of Apparent Chloride Diffusion Coefficient for Self Compacting Concrete Containing Nano Silica under Effect of Sulfate Attack Figure 2 Chloride diffusion profiles Figure 3 Chloride diffusion profiles of SCC mixes at 90 days of exposure of SCC mixes at 180 days of exposure Table 3 Percent of Decrease in Chloride Content at 90 Days of Exposure at Selected Depths of SCC Mixes Mid-layer Depth (mm) Reduction in Chloride Content (%) from Reference Concrete at 90 Days of Exposure OR ON3 SR SN Table 4 Percent of Decrease in Chloride Content at 180 Days of Exposure at Selected Depths of SCC Mixes Mid-layer Depth (mm) Reduction in Chloride Content (%) from Reference Concrete at 180 Days of Exposure OR ON3 SR SN editor@iaeme.com

7 Dr. Ghalib Mohsin Habeeb and Zahraa Dhurgham Hashim Hadi It is also clear from these results that lowest chloride diffusion was computed for ON3 (D a = 3.50 *10-12 m 2 /s) at 90 days, while (D a = 2.66 *10-12 m 2 /s) at 180 days for SN3. So, this refers to the influence of Nano Silica in reducing the diffusion coefficients for SCC mixes because the Nano particles increase the density of concrete. The percentage of decrease of chloride diffusion coefficient after 180 days found for SN3 specimens was (50.83%), while for ON3 specimens was (54.40%). This is in agreement with (Quercia et al., 2012). 5. CONCLUSIONS The presence of Nano Silica in concrete mitigates the total chloride content especially at deeper depths relative to corresponding reference mixes regardless of the type of cement. The chloride diffusion coefficient for SCC with Nano Silica was lower than that without Nano Silica. The percentage of decrease in chloride diffusion coefficient after 180 days was found for SN3 specimens was (50.83%) while for ON3 specimens was (54.40%). Generally, the results reveal that SRPC specimens have higher chloride content than OPC mixes especially at 90 days. while at 180 days, SRPC specimens havelower chloride content than OPC specimens. REFERENCES [1] Al-Rawi R.S., ( 1985), Internal sulfate attack in concrete related to gypsum content of cement with pozzolan addition, ACI-RILEM, Joint Symposium, Monterey, Mexico, pp [2] ASTM C1152 /C 1152M, 2003), " Standard test method for Acid-Soluble chloride in mortar and concrete" ASTM international west Conshohocken, PA, [3] ASTM C1556, (2003), " Standard test method for determing the apparent chloride diffusion coefficient of cementitious mixtures by bulk diffusion", ASTM international west Conshohocken, PA, [4] Berke, N.S., Chaker, V., and Whiting, D., (1990)," Corrosion rates of steel in concrete", No. 1065, ASTM International. [5] European Project Group, (2005), ''The European Guidelines for Self-Compacting Concrete: Specification, Production and Use'', may, 2005, PP.63. [6] Hussein, M.T., (2003), " The effect of cement Type on the potential and corrosion behavior of steel Reinforcement ", Ph.D. thesis, University of surrey. [7] Iraqi Organization of Standards, (IQS), No.45/1984, for Aggregate. [8] Iraqi Organization of Standards, (IQS), No.5/1984, for Portland Cement. [9] Khanzadi, M., Tadayon, M., Sepehri, H., and Sepehri, M.,(2010), " Influence of Nano-Silica Particles on Mechanical Properties and Permeability of Concrete", HBRC Journal, vol.20, No. 20, April 2010, p.p. (1-13). [10] Thallapaka Vishnu Vardhan Rseddy, K. Rajasekhar and Seelanani Janardhana. Study and Performance of High Strength Concrete Using with Nano Silica and Silica Fume. International Journal of Civil Engineering and Technology (IJCIET), 6(11), 2015, pp [11] Moradi, B., (2014),"Transport Properties of Nano-Silica Contained Self-Consolidating Concrete", M.Sc. Thesis, University of Nevada, Las Vegas. [12] Prasad, J., Jain, D.K., and Ahuja, A.K., (2006)," Factors Influencing the Sulfate Resistance of Cement Concrete and Mortar", Asian Journal of Civil Engineering, Vol. 7, No. 3 (2006), pp. ( ). [13] Quercia, G., Spiesz, P., Husken, G., & Brouwers, J. (2012), "Effects of amorphous nano-silica additions on mechanical and durability performance of SCC mixtures", In Proceedings of the International Congress on Durability of Concrete (ICDC 2012), (pp ) editor@iaeme.com

8 Determination of Apparent Chloride Diffusion Coefficient for Self Compacting Concrete Containing Nano Silica under Effect of Sulfate Attack [14] Rodriguez, G.R., Aperador, W., Delgado, A., (2013), " Calculation of concrete structures ", International Journal electrochemical science, No. 8, pp. ( ). [15] Saloma, Nasution, A., Imran, I., and Abdullah, M., (2015)," Improvement of concrete durability by nanomaterials" Procedia Engineering, Vol.125,( 2015), pp. ( ). [16] Arun Nishchal Guleria and Sandeep Salhotra, Effects of Silica Fume (Micro Silica or Nano Silica) On Mechanical Properties of Concrete: A Review. International Journal of Civil Engineering and Technology (IJCIET), 7(4), 2016, pp [17] Wang, L., and Ueda, T., (2011), "Mesoscale modeling of the chloride diffusion in cracks and cracked concrete", Journal of advanced concrete technology, Vol. 9, No. 3, pp.( ), October 2011, copyright 2011 Japan concrete institute editor@iaeme.com