Revised Model of Chloride Diffusion in Concrete Bridge by Considering Complex Action of Load and Chloride Binding Capacity

Transcription

1 4 th International Conference on the Durability of Concrete Structures 4 6 July 14 Purdue University, West Lafayette, IN, USA Abstract Revised Model of Chloride Diffusion in Concrete Bridge by Considering Coplex Action of Load and Chloride Binding Capacity Yiqiang Xiang and Dongei Guo Departent of Civil Engineering, Zhejiang University Dongei Guo Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University Coastal concrete bridges will suffer fro deterioration of Rtructural porance and resistance attenuation because of the chloride penetration and other environent factors. This article discusses current different chloride diffusion odels and puts forward the revised odel of chloride diffusion in concrete bridge by considering the coplex action of load influence and chloride-binding capacity. Coparison of nuerical predicted values and relative experiental tests show the presented chloride diffusion odel to be ore accurate. It provides a theoretical basis for the porance assessent and accurate prediction of the reaining life of highway concrete bridges. Keywords: analysis, chloride diffusion, coplex action, concrete bridge, revised odel. 1. INTRODUCTION Chloride ion is the ain factor affecting the durability of in-service concrete bridge, which leads to rebar corrosion. Rebar corrosion and load variation shorten the reaining useful life of bridges. Konin, Francois, and Arliguie (1998) showed that load level has a significant ipact on the penetration of chloride ion. Yoon and Wang () deonstrated that the loading ethod and load level have an iportant ipact on the corrosion of rebar. Shui (5) explored the load action that affects the echanics of chloride diffusion. Currently, the study on chloride ion diffusion is based on Fick s second diffusion law and considers the different factors.. THE REVISED CHLORIDE DIFFUSION MODEL.1 The existing chloride diffusion odel When all or part of voids of concrete structures are full of water, chloride ions enter into the concrete. Chloride ion penetration occurs by eans of the suction of the capillary pore or crack penetration diffusion (Kropp & Hilsdorf, 1995). Buenfeld, Glass, Hassanein, and Zhang (1998) assued that chloride diffusion is a physics process, and the diffusion characteristic of aterials does not change with tie, and the concentration of diffusion, chloride diffusion equation is: C t C = D x (1) where C is chloride concentration, x is diffusion depth, t is diffusion tie, and D is diffusion coefficient. Costa and Appleton (1999a) assued that chloride diffusion of solution is a sei-finite and unidirectional process, and that the process corresponds to Fick s second diffusion law: x C x, s 1 Dt ( () where x, t, D are the sae as in Equation (1), is chloride concentration of concrete surface, ( x) = x t e dt is error function. Based on Fick s second diffusion law, Yu, Sun, and Yan, () deduced the new chloride diffusion equation considering the chloride cobining capacity of concrete, tie-dependent chloride diffusion coefficient and defects of concrete structure: C f x + ( C s C ) (3) KDt t (1 + R)(1 ) where C f is free chloride concentration, C is initial chloride concentration of concrete, t is base tie, D is diffusion coefficient corresponding to base tie t, K is deterioration coefficient of chloride diffusion porance for concrete, R is the cobining capacity 176

2 Revised Model of Chloride Diffusion in Concrete Bridge by Considering Coplex Action 177 of chloride (noral concrete, 4), and is the tiedependent coefficient of chloride diffusion. Based on Fick s second diffusion law, Hao (4) developed the new chloride diffusion equation considering the stable and unstable environent. Chloride diffusion equation of stable environent: x C( x, + ( Cs C) 1 (4) kcdt t Chloride diffusion equation of unstable environent: C( x, = k x t exp 4Dt x π x 1 Dt Dt where k is a epirical constant of chloride concentration for the concrete surface, and k c is a aintenance coefficient. Considering load factor, Wang (1) researched the chloride diffusion odel in a different environent: (5) x C( x, + ( Cs C) (6) α f ( δ ) Dt α t α p where f (d ) is load factor; d is stress level factor; =, P is tensile stress of load; p u is ultiate flexural strength; a is related to water-ceent ratio, adixture varieties, quantity, and environent. Wang, Zhu, and Li (4) developed the transport odel of chloride diffusion theory considering coprehensive influence echanis, deterined the relation of teperature, tie and deterioration action, and chloride diffusion coefficient: x ρf ( xt, ) = ρ + ( ρs ρ)1 * D. t p u (7) λ. D * ref t ref U 1 1 D =.. exp. 1 ρ b 1 t R Tref T (8) +. ω ρ e f where t ref is initial aintenance age of concrete, T ref is initial teperature of concrete, D ref is a referenced diffusion coefficient, r b is the cobining chloride concentration of concrete aterials, r f is free chloride concentration of concrete surface in x, w e is volue ratio of water content, U is activation energy of diffusion process, R is olar gas constant, and D* is diffusion coefficient of teperature-tie dependent, chloride cobining, and deterioration action. Considering chloride cobining capacity and flaw factor, Xue and Xiang (1) put forward to chloride diffusion odel: x C( x, + ( Cs C) (9) KRDt t where the eaning of sybols in Equation (9) is the sae as front equations.. Chloride diffusion odel of load factor and chloride cobining capacity coplex Buenfeld et al. (1998) proposed chloride diffusion coefficient is constant, but Mangat and Molloy (1994) only considered chloride diffusion coefficient is variation with tie. Here, load factor f (d ) is introduced into the chloride diffusion coefficient. Hence, the expression is written: t D( = f ( δ ) D (1) t In ters of Yu and Xue work, further considering chloride cobining capacity R, this article revised odel of chloride diffusion, as follows: C( x, + ( C s C) x f ( δ ) RDt t (11) where the eaning of c, c s, (x), R are the sae as in Equation (9); the eaning of f(d ) is the sae as in Equation (6)..3 The paraeters of the revised odel (1) Load factor f (d ) To deterine the value of load factor under different environents and stress states, He (4) and Zhang (1) siulated the experiental results of tidal cycle, sub-water area, and offshore atospheric zone using quadratic polynoial to obtain the load factors. The relative expressions are shown in Table 1; the sensitive analysis of load factor is shown in Figure 1. Table 1. Values of load factor. Environent type Stress state f (c) Tidal cycle tension f (d ) = d d press f (d ) = d d Subwater zone tension f (d ) = d +.9 d Offshore atospheric zone tension f (d ) = d d

3 178 Transport Properties () suarized the chloride concentration on the surface of concrete in the sea salt fog area, as listed in Table 5. Concrete standard of civil engineering of Japan (The Chinese Acadey of Engineering and Architecture Departent in Water Resources, 4) suggested the chloride concentration on concrete surface in offshore atospheric zone, as listed in Table 6. Table 3. Chloride concentration on the surface of concrete eber. Figure 1. Sensitive analysis of load factor for chloride diffusion odel. Figure 1 gives the relationship of the distance fro concrete surface versus chloride diffusion in different load factors. When f (d ) > 1, the rate of chloride diffusion is fast, but when f (d ) < 1, the rate of chloride diffusion is slow. () Coefficient Costa & Appleton, 1999b, and BE suggested the values for the coefficient, as listed in Table. Table. Suggested values of. Marine environent Ordinary portland ceent Ceent type Flyash Slag Silica power Subwater zone Splash zone Offshore atospheric zone (3) Chloride cobining capacity of concrete R Experient and field test results (Mohaed & Haada, 3; Zhao, 4;) showed that R = for ordinary porance concrete or high porance concrete; when lacking the relative data, we can select R =.85. (4) Chloride concentration of concrete surface Sub-water zone, tidal zone, splash zone, and offshore atospheric zone have chloride source. Chlorides of sub-water zone in coastal area coe fro the salt in seawater; chlorides of tidal zone and splash zone coe fro dry and wet cycles of wave or spray water. Moreover, chlorides of offshore atospheric zone coe fro the arine environent. Wang (1) obtained the expression of chloride concentration of concrete surface and tie for splash zone, tidal zone, sub-water zone, and offshore atospheric zone by eans of the nuber of experiental data and least square ethod, as listed in Table 3. Table 4 shows the values of chloride concentration for concrete surface of different environents developed by Vu and Stewart (). These values are taken to be log norally distributed. Thoas and Bentz Environent Expression (%) R Splash zone ( = ln(.96 Tidal zone ( = ln(.93 Coastal atospheric zone ( = ln(.89 Underwater area ( = Table 4. Chloride concentration on the surface of concrete eber based on Stewart s study. Environent Mean (kg/ 3 ) CV Splash zone Offshore atospheric environent.1 k.95.7 Distance fro coast 1 k General atospheric environent.3.5 Table 5. Chloride concentration on the surface of concrete (life-365). Environent Cuulative rate (%) Value Tidal zone/splash zone The instantaneous constant value.8 Sea salt fog area.1 1. Distance fro coast Distance fro coast 1.5 k..6 Table 6. Chloride concentration on the surface of concrete (Japan). Splash zone Near the coast Distance fro coast (k) %.45%.5%.15%.1%.75% Note: Chloride concentration of Tables 5 and 6 is percentage of concrete weight (3 kg)..4 Case analysis (1) Case 1 In offshore area, a siply-supported bridge Qinggang Bridge, with spans of and width of 6, was constructed in The bridge was tested with five saples of chloride ions content. This article analyzed a saple of the outside of the lateral bea and deck water penetration. The paraeters of the revised odel are listed in Table 7.

4 Revised Model of Chloride Diffusion in Concrete Bridge by Considering Coplex Action 179 Table 7. Paraeters in the chloride diffusion odel of Qinggang Bridge. Paraeters Value Paraeters Value.65 D /s R.85 t 8 d (.6% f (δ).947 Figure. Coparison of testing values and predicted values on chloride content in concrete. Figure shows coparison of predicted values and testing values. The penetration of deck water leads to a large difference when cover depth is >15. () Case Zhang and Wei (1999) chose the batch of ordinary Portland concrete saples exposed to engineering aterials test station of seaport for south China, inspected the saples of continuous 3, 5, and 1 years, and obtained the series of data of relative chloride concentration. The saples were divided into plain concrete and reinforced concrete, which were ade in accordance with Specification (JTJ8-87). Test ethod of chloride content is based on Ref. JTJ5-87. Environent is divided into tidal zone, sub-water zone, and splash zone. The paraeters of revised odel for tidal zone and splash zone are listed in Table 8. The predicted values are copared with results gained by Wang (1), and the coparison curves are shown in Figure 3(a) (d). It is found fro Figure 3 that the prediction values of revised odel were close to test values exposed to Figure 3. Coparison of testing values and values predicted by the different odels in different cases.

5 18 Transport Properties splash zone, while the prediction values were different fro the test values exposed to tidal zone. Therefore, it is liited only considering chloride cobining capacity. Table 8. Paraeters in revised odel. Paraeters Splash zone Tidal zone R (.36,.51.56,.75 D /s /s t 1a 1a f (δ) Conclusions This article discusses current different chloride diffusion odels, and puts forward the revised odel of chloride diffusion by considering the coplex action of load influence and chloride binding capacity. The proposed odel is verified by the relative testing data. Copared with the traditional single factor odel, the revised odel of concrete chloride diffusion is ore reasonable and accurate. It ay be used to predict the reaining useful life of concrete bridges. ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No and No ) and Cyrus Tang Foundation-Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University. REFERENCES BE (1995). General guidelines for durability design and redesign Brussels, Belgiu: European Union. Buenfeld, N. R., Glass, G. K., Hassanein, A. M., & Zhang, J. (1998). Chloride transport in concrete subjected to electric field. Materials in Civil Engineering, 1(4), 8. Costa, A., & Appleton, J. (1999a). Chloride penetration into concrete in arine environentpart II: Prediction of long ter chloride penetration. Materials and Structures, 3(6), Costa, A., & Appleton, J. (1999b). Chloride penetration into concrete in arine environent-part I: Main paraeters affecting chloride penetration. Materials and Structures, 3(4), Hao, X. L. (4). Durability and service life prediction of reinforced concrete structure exposed to chloride environents (Master Dissertation). Xi an University of Architecture and Technology. He, S. Q. (4). Experiental studies on durability of reinforced concrete ebers in chloride environent. (Master dissertation). Dalian University of Technology. JTJ5-87. (1987). Test ethod for concrete of harbor engineering. Industry standard of the People s Republic of China. JTJ8-87. (1987). Corrosion prevention specification for reinforced concrete structures of harbor. Industry standard of the People s Republic of China. Konin, A., Francois, R., & Arliguie, G. (1998). Penetration of chlorides in relation to the icrocracking state into reinforced ordinary and high strength concrete. Materials and Structures, 31, Kropp, J., & Hilsdorf, H. K. (1995). Porance criteria for concrete durability. London, England: E&FN Spon. Mangat, P. S., & Molloy, B. T. (1994). Prediction of long ter chloride concentration in concrete. Materials and Structures, 7(7), Mohaed, T. U., & Haada, H. (3). Relationship between free chloride and total chloride contents in concrete. Ceent and Concrete Research, 33(3), Shui, J. F. (5). Durability study for reinforced concrete bridges exposed in arine environent (The Master Dissertation). Dalian University of Technology, Dalian. The Chinese Acadey of Engineering and Architecture Departent in Water Resources. (4). The durability of concrete structure design and construction guide. Beijing, China: China Architecture & Building Press. Thoas, M. D. A., & Bentz, E. C. (). Life-365 coputer progra for predicting the service life and life-cycle costs of reinforced concrete exposed to chlorides. October. Vu, K. A. T., & Stewart, M. G. (). Structural reliability of concrete bridges including iproved chloride-induced corrosion odels. Structural Safety,, Wang, R. C., Zhu, L., & Li, Z. F. (4). A study on ulti-nisic chloride diffusion and transport odel and sensitivity. Journal of Harbin Institute of Technology, 36(6), Wang, Y. Z. (1). Chloride diffusion odel of RC eber in various arine environents considering loading effect. Waterway and Harbor, 31(), Xue, P. F., & Xiang, Y. Q. (1). Corrected diffusion odel of chloride in concrete and its engineering

6 Revised Model of Chloride Diffusion in Concrete Bridge by Considering Coplex Action 181 application. Zhejiang University (Engineering Science), 44(4), Yoon, S., & Wang, K. (). Interaction between loading, corrosion and serviceability of reinforced concrete. ACI Materials Journal, 97(6), Yu, H., Sun, W., Yan, L., & Ma, H. (). Study on prediction of concrete service life I theoretical odel. The Chinese Ceraic Society, 3(6), Zhang, B. L., & Wei, S. S. (1999). Test of reinforced concrete structure at sea port of south China exposure ten years. Port and Waterway Engineering, (3), Zhang, D. F. (1). Durability study of odern PC structure. Nanjing, China: Southeast University. Zhao, Y. (4). Service life design of reinforced concrete structures exposed to chlorine environent. Concrete, 6(1), 3 1.