L.X. Xiong
Keywords: Concrete; erosive solution; creep property; compressive strength
Abstract:
Creep test on concrete under simultaneous long-term compressive stress and sea water corrosion was carried out, and the effects of stress level, the type and the concentration of erosive solution on the creep property of concrete were studied. The research results show that the expansive strain of specimen immersed in sodium sulfate solution is largest and immersed in sodium chloride solution is smallest under the same small stress level. The expansive strain of specimen under compressive stress is smaller than that under no stress immersed in the same erosive solution at the same erosive time. The compressive strength of specimen is largest after immersed in sodium sulfate solution and is smallest after immersed in sodium chloride solution at the same erosive time.
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ISSN 1466-8858 Volume 16, Preprint 40 submitted 13 June 2013 Experimental study on creep property of concrete corroded by sea water Liangxiao Xiong* Faculty of Architectural, Civil Engineering and Environment, Ningbo University, Ningbo, Fenghua Road 818, PR China *Corresponding author. Tel.: +86 574 87600316; Fax: +86 574 87600514. E-mail address: xiongliangxiao@163.com (L. X. Xiong). Abstract:Creep test on concrete under simultaneous long-term compressive stress and sea water corrosion was carried out, and the effects of stress level, the type and the concentration of erosive solution on the creep property of concrete were studied. The research results show that the expansive strain of specimen immersed in sodium sulfate solution is largest and immersed in sodium chloride solution is smallest under the same small stress level. The expansive strain of specimen under compressive stress is smaller than that under no stress immersed in the same erosive solution at the same erosive time. The compressive strength of specimen is largest after immersed in sodium sulfate solution and is smallest after immersed in sodium chloride solution at the same erosive time. Key words: Concrete; erosive solution; creep property; compressive strength 1. Introduction The mechanical property of concrete under corrosion of sea water is an important factor for evaluating the durability of concrete structure in the marine environment, and the erosion of sea water on concrete is mainly caused by the chloride ion and the sulfate ion. Therefore, lots of researchers investigated the mechanical property of concrete under corrosion of sea water through compressive strength test. For instance, Kumar et al. (1995) presented the results of an experimental study on the deterioration in the strength of concrete when subjected to sulfate attack. [1]. Park et al. (1999) investigated the damage of chemical attack by magnesium sulfate and sodium sulfate on normal and high strength concretes [2]. Bakharev et al. (2002) performed the compressive strength test and the XRD test to investigate the durability of alkali-activated slag concrete in sulfate environment [3]. Lee et al. (2005) conducted detailed experimental study on the sulfate attack of Portland cement mortars and the effectiveness of silica fume in controlling the damage arising from such attack [4]. Sotiriadis et al. (2012) investigated the sulfate resistance of limestone cement concrete exposed to combined chloride and sulfate environment at low temperature [5]. Liu et al. (2012) carried out axial compressive strength tests for concrete columns with different strain rates to investigate the effects of sulfate attack on the dynamic strength and deformation characteristics of concrete [6]. Ramadhansyah et al. (2012) performed compressive strength test to evaluate the effect of RHA replacement of cement on the resistance of concrete to chloride attack with drying-wetting cycles [7]. In addition, few researchers © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 40 submitted 13 June 2013 investigated the variations of the tensile strength and the flexural strength of concrete attacked by sulfate ions. Boyd et al. (2004) used tensile strength test to investigate the effect of W/C ratio and the cement type on the resistance of concrete to sulfate attack [8]. Zhang et al. (2008) investigated the variation of the flexural strength of cement mortar under sulfate erosion [9]. The researchers mentioned above generally placed the concrete specimens into erosive solution for long time immersion, and the specimens were not sustained to any external force in the process of immersion, and then take the corroded specimens out for conducting compressive stength test or tensile strength test to study the evolution of compressive strength of concrete with erosing time. In fact, the experimental procedure does not consist with the actual situation. Many marine structures are often corroded by sea water under stress condition, and this phenomenon is called as stress corrosion. So far, some scholars had carried out reseaches on the mechanical property of concrete corroded by sea water under stress condition. Piasta et al. (1989) studied the durability of concretes with limestone and granite aggregate under simultaneous long-term compressive stress and sulfate attack [10]. Schneider and Piasta (1991, 1992) presented the study on the behavior of concrete under Na2SO4 solution and sustained compressive or bending stress[11, 12]. Zivica et al. (1994) studied the effect of applied compressive stress on the sulfate corrosion rate of cement composites [13]. Werner et al. (2000) studied the stress corrosion of plain cement paste specimens under three different solution and sustained bending stress [14]. Jin et al. (2008), Bassuoni et al. (2009), Gao et al. (2012) and Yang et al. (2012) studied the damage of concrete under flexural stress and sulfate solution [15, 16, 17, 18]. Most of these researchers studied the stress corrosion of concrete under bending stress or flexural stress. Thus only the change law of flexural strength was usually attained. The compressive strength of concrete is far higher than its tensile strength, and the main function of concrete in the engineering structure is to sustain compressive stress. In addition, sodium sulfate solution was mostly used in these studies. In fact, the mechanical property of concrete will also vary under the erosion of chlorine ion. Therefore, lots of influencing factors on stress corrosion of concrete need further investigation. In this study, the author developed testing apparatus through which the concrete specimen can be subjected to long-term compressive stress, placed the concrete specimens into sodium sulfate solution and sodium chloride solution separately, and read the deformations of specimens every five to seven days. Finally, the effects of the stress level, the type of erosive solution and the mass fraction of erosive solution on the creep property of concrete were analyzed. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 2. Experimental program Volume 16, Preprint 40 submitted 13 June 2013 2.1. Specimen preparation The experiment used C30 grade concrete. The dimensions of the specimens were 150 mm×150 mm×300 mm. Type 32.5 Portland cement, gravel with particle size ranging from 5 to 30 mm, standard river sand and tap water were used for making the concrete specimens. The details of the concrete mixture proportions used are given in Table 1. 2.2. Testing apparatus The author developed testing apparatus through which the concrete specimen can be subjected to long-term compressive stress. The testing apparatus is shown in Fig. 1. One test apparatus consists of three steel plates (2 cm thickness), four high-strength rebars (30 mm diameter) and eight high-strength bolts. Gasket is placed between the bolt and the plate. A pressure sensor is placed between the first plate and the second plate, and the pressure sensor is connected to a data recorder during the time of creep test. Three specimens were conducted for uniaxial compression tests and the pressure sensor was calibrated before creep test. Two strain gages (10 cm length) were bonded to a group of parallelly vertical planes of one specimen, and the strain gages were coated with epoxy resin and connected to the another data recorder. The compressive stress was applied on the specimen by tightening the bolts. The deformation of the pressure sensor was read from the data recorder during the process of tightening. The testing apparatus together with the specimen were placed into the erosive solution after the compressive stress reaching the predetermined value. The deformations of specimens were recorded every five to seven days. The bottom of the testing apparatus could not be fixed. So, the compressive stress applied on the specimen through this apparatus is relatively small, and the maximum value of stress / strength ratio is 0.1. The deformation of pressure sensor were also recorded every five to seven days. The stress level will be stabilized by tightening the bolts when the deformation reduce. The creep tests were condcuted in the curing rome in which the temperature remained at 20°. The ersoive solutions were prepared each month. Therefore, the concentration of solution could be ensured to change unsignificantly during the testing time. 2.3. Testing procedure (1) The uniaxial compression test before creep test Put specimens in standard curing room for 28 days, and then take three specimens for uniaxial compression tests with strain rate of 10-5S-1. The compressive strengths of specimens before corrosion were attained. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 (2) Creep test Volume 16, Preprint 40 submitted 13 June 2013 The rest specimens were applied long-term compressive stress by using the test apparatus shown in Fig. 1, and then these specimens were placed into five kinds of solutions for erosion. They were tap water, sodium chloride solution with concentration of 3%, sodium chloride solution with concentration of 8%, sodium sulfate solution with concentration of 3%, and sodium sulfate solution with concentration of 8%. There were two specimens in each kind of solution, i.e., one specimen was under long-term compressive stress and one specimen was not. Therefore, the effects of the stress level, the type of solution and the concentration of solution on the creep property of concrete specimen could be studied through test. The erosive solution will gradually seep into the specimen and the strain gauges will gradually be ineffective with increasing erosion time. Therefore, the time for creep test lasted only about 120 days which is not long. (3) The uniaxial compression test after creep test After the above creep tests, the corroded specimens were conducted for uniaxial compression test again. 3. Test results and analysis 3.1. Results of uniaxial compression tests before corrosion The stress-strain curves of three specimens before erosion are shown in Fig.2. The uniaixal compressive strengths of the three specimens were 28.84MPa, 31.21MPa and 32.87MPa, respectively. The average compressive strength is 30.97MPa. 3.2. Results of creep tests The strain-time curves of specimens of creep tests are shown in Fig.3. The stress that is applied on the concrete specimen through the apparatus could not be high, thus, the maximum vaule of stress / strength ratio is 0.1. The strains of all the specimens under this stress level were expansive when immeresed in these five kinds of solutions. The creep test time for specimen immersed in sodium chloride solution with concentration of 8% under stress lasted 22 days. Therefore, the expansive strains of all the specimens when the erosion time is 22 days are compared in the following discussion. When the erosion time is 22 days, the expansive strains of specimens immersed in sodium sulfate solutions with concentrations of 3% and 8% under no stress are 888.5×10-6 and 888.5×10-6, the expansive strains of specimens immersed in sodium chloride solutions with concentrations of 3% and 8% under no stress are 403.5× 10-6 and 334×10-6, and the expansive strain of specimen under no stress immersed in tap water is 466×10-6. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 40 submitted 13 June 2013 When the erosion time is 22 days, the expansive strains of specimens immersed in sodium sulfate solutions with concentrations of 3% and 8% under stress are 505.5×10-6 and 506.5×10-6, the expansive strains of specimens immersed in sodium chloride solutions with concentrations of 3% and 8% under stress are 341.5×10-6 and 330×10-6 and the expansive strain of specimen under stress immersed in tap water is 394.5×10-6. Therefore, the expansive strain of specimen immersed in sodium sulfate solution is largest and the expansive strain of specimen immersed in sodium chloride solution is smallest at the same stress level and erosion time. The delayed ettringite and gypsum are formed in the specimens during the corrosion of sulfate ions and fill in the initial porosity of the specimen. Thus the strain of specimen is expansive. The hydration products will also slowly fill in the initial porosity of the specimen when immersed in tap water, and the strain of specimen is also expansive. The solubility of calcium hydroxide in concrete will be enhanced by the infiltration of chlorine ion, and this will lead to the damage of concrete. The hydration products will also appear in the specimen when immersed in the sodium chloride solution, thus, the strain of specimen is still expansive. The expansive strain of specimen under stress is smaller than that of specimen under no stress immersed in the same kind of solution at the same erosion time. 3.3. Results of uniaxial compression tests after corrosion The stress-strain curves of specimens after erosion are shown in Fig.4, and the values of compressive strengths are presented in Table 2. The compressive strength of specimen after immersed in sodium sulfate solution is largest and the compressive strength of specimen after immersed in sodium chloride solution is smallest with the same stress level and erosion time. In addition, the compressive strengths of specimens after erosion are higher than those of specimens before erosion. The strength of specimen will increase when immersed in tap water during the process of hydration products filling the initial porosity. The delayed ettringite and gypsum formed in the specimen will also lead to the increase of strength of specimen when immersed in sodium sulfate solution. Though the strength of specimen will decrease due to the enhacement of the solubility of calcium hydroxide in concrete by the infiltration of chlorine ion, the strength of specimen will also colud be increased due to the appearance of hydration products. Therefore, the strength of specimen after immersed in sodium chloride solution is higher than that with no erosion, and is smaller than that immersed in tap water. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 4. Conclusions Volume 16, Preprint 40 submitted 13 June 2013 The compressive stress applied on the specimen could not be higher under the limition of this apparatus. Therefore, the following conclusion of this study is under the condition that the compressive stress is smaller. (1) The expansive strain of specimen immersed in sodium sulfate solution is largest and the expansive strain of specimen immersed in sodium chloride solution is smallest with the same stress level and erosion time. (2) The expansive strain of specimen under stress is smaller than that of specimen under no stress immersed in the same kind of solution at the same erosion time. (3) The compressive strength of specimen after immersed in sodium sulfate solution is largest and the compressive strength of specimen after immersed in sodium chloride solution is smallest with the same stress level and erosion time. 5．Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 41002108), the the Natural Science Foundation of Zhejiang Province (Y13E080109), the Natural Science Foundation of Ningbo City (Grant No.2011A610072), and a COE Program of Zhejiang Provincial Government at Ningbo University (Grant No. zj1008). References 1. Kumar S, Kameswara Rao C V S. (1995). Strength loss in concrete due to varying sulfate exposures. Cement and Concrete Research, 25(1): 57-62. 2. Park Y S, Suh J K, Lee J H, Shin Y S. (1999). Strength deterioration of high strength concrete in sulfate environment. Cement and Concrete Research, 29(9): 1397-1402. 3. Bakharev T, Sanjayan J G, Cheng Y B. (2002). Sulfate attack on alkali-activated slag concrete. Cement and Concrete Research, 32(2): 211-216. 4. Lee S T, Moon H Y, Swamy R N. (2005). Sulfate attack and role of silica fume in resisting strength loss. Cement and Concrete Composites, 27(1): 65-76. 5. Sotiriadis K, Nikolopoulou E, Tsivilis S. (2012). Sulfate resistance of limestone cement concrete exposed to combined chloride and sulfate environment at low temperature. Cement and Concrete Composites, 34(8): 903-910. 6. Liu T J, Zou D J, Teng J, Yan G L. (2012). The influence of sulfate attack on the dynamic properties of concrete column. Construction and Building Materials, 28(1): 201-207. 7. Ramadhansyah PJ, Salwa MZM, Mahyun AW, Abu Bakar BH, Megat Johari MA, Che Norazman CW. (2012). Properties of Concrete Containing Rice Husk Ash Under Sodium Chloride Subjected to Wetting and Drying. Procedia Engineering, 50: 305-13. 8. Boyd A J, Mindess S. (2004). The use of tension testing to investigate the effect of W/C ratio and cement type on the resistance of concrete to sulfate attack. Cement and Concrete Research, 34(3): 373-377. 9. Zhang M H, Jiang M Q, Chen J K. (2008). Variation of flexural strength of cement mortar attacked by sulfate ions[J]. Engineering Fracture Mechanics, 75(17): 4948-57. 10. Piasta W G, Sawicz Z, Piasta J. (1989). Sulfate durability of concretes under constant sustained load. Cement and Concrete Research, 19(2): 216-227. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 16, Preprint 40 solution and sustained compression submitted 13 2013 11. Schneider U, Piasta W G. (1991). The behaviorVolume of concrete under Na2SO or June bending. 4 Magazine of Concrete Research, 43(157): 281-289. 12. Piasta W G, Schneider U. Deformations and elastic modulus of concrete under sustained compression and sulphate attack. Cement and Concrete Research, 1992, 22(1): 149-158. 13. Zivica V, Szabo V. (1994). Behavior of cement composite under compression load at sulfate attack. Cement and Concrete Research, 24(8): 1475-1484. 14. Werner K C, Chen Y X, Odler I. (2000). Investigations on stress corrosion of hardened cement pastes. Cement and Concrete Research, 30(9): 1443-1451. 15. Jin Z Q, Sun W, Jiang J Y, et al. (2008). Damage of concrete attacked by sulfate and sustained loading. University(English Edition), Journal of Southeast 24(1): 69-73. 16. Bassuoni M T, Nehdi M L. (2009). Durability of self-consolidating concrete to sulfate attack under combined cyclic environments and flexural loading. Cement and Concrete Research, 39(3): 206-226. 17. Gao K M, Yu Z X, Song L G, Wang T X, Sun W. (2013). Durability of concrete exposed to sulfate attack under flexural loading and drying-wetting cycles. Construction and Building Materials, 39: 33-38. 18. Yang D Y, Luo J J. (2012). The damage of concrete under flexural loading and salt solution. Construction and Building Materials, 36: 129-134. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Figures Volume 16, Preprint 40 submitted 13 June 2013 Fig.1. The creep test apparatus 40 σ / MPa 30 20 No.1 specimen No.2 specimen No.3 specimen 10 0 0.0000 0.0005 0.0010 ε 0.0015 0.0020 Fig.2. Stress-strain curves of specimens before immersed in solution © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 16, Preprint 40 submitted 13 June 2013 Expansion strain / 10 -6 1500 in water in 3% Na2SO4 1200 in 8% Na2SO4 900 in 3% NaCl in 8% NaCl 600 300 0 0 10 20 30 40 50 60 50 60 t/d (a) Stress / Strength ratio =0.0 900 in water in 3% Na2SO4 Expansion strain / 10 -6 in 8% Na2SO4 in 3% NaCl in 8% NaCl 600 300 0 0 10 20 30 40 t/d (b) Stress / Strength ratio =0.1 Fig.3. Expansive strains of specimens © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 50 σ / MPa 40 Volume 16, Preprint 40 in water in 3% Na2SO4 submitted 13 June 2013 in 8% Na2SO4 in 3% NaCl in 8% NaCl 30 20 10 0 0.0000 0.0002 0.0004 ε 0.0006 0.0008 0.0010 (a) Stress / Strength ratio =0.0 50 σ / MPa 40 30 in water in 3% Na2SO4 in 8% Na2SO4 in 3% NaCl in 8% NaCl 20 10 0 0.0000 0.0002 0.0004 ε 0.0006 0.0008 (b) Stress / Strength ratio =0.1 Fig.4. Stress-strain curves of specimens after immersed in chemical solutions © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. η1b ISSN 1466-8858 Volume 16, Preprint 40 submitted 13 June 2013 Tables Table 1. Mixture design of concrete specimens w/c Ratio Water (kg/m3) Cement (kg/m3) Sand (kg/m3) Gravel (kg/m3) 0.45 195 433 585 1187 Table 2. Compressive strengths and peak strains of specimens after erosion Stress / Strength Ratio 0.0 0.1 Compressive strength Peak Strain (MPa) (10-3) Tap water 41.54 0.593 3% NaCl 37.47 0.689 8% NaCl 34.26 0.583 3% Na2SO4 41.59 0.581 8% Na2SO4 43.21 0.543 Tap water 40.40 0.666 3% NaCl 40.43 0.629 8% NaCl 39.89 0.626 3% Na2SO4 41.90 0.641 8% Na2SO4 41.37 0.568 The type of solution © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.