Assoc.Prof.BOONCHAI STITMANNAITHUM. Department of Civil Engineering, Faculty of Engineering Chulalongkorn University, Thailand

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1 Modeling of Chloride Penetration into Concrete Structures under Flexural Cyclic Load and Tidal Environment Assoc.Prof.BOONCHAI STITMANNAITHUM Department of Civil Engineering, Faculty of Engineering Chulalongkorn University, Thailand

absorption Mono layer, anodic and cathodic

2 INTRODUCTION In marine environment, the deterioration of concrete structures is mainly due to chloride induced corrosion. Capillary absorption Diffusion Physical absorption Mono layer, anodic and cathodic reactions Cl - O 2 Cl - Cl - Factors needed for steel corrosion

3 Chloride penetration is due to adsorption Chloride penetration is due to both diffusion and adsorption Chloride penetration is due to diffusion

4 Modeling of chloride penetration with Fick s second law This model considers diffusion alone, constructed on Fick s second law and Crank s solution. C t = D 2 C 2 x a C C x s = 1 erf x 2( D. t) C x : Chloride concentration at depth x at time t C s : Surface chloride concentration. D a : Apparent diffusion coefficient C x = 0 at t = 0 and 0 < x < C x = C s at x = 0 and 0 < t < a 0.5 Kimitaka Uji et al.(1994) proposed: C s = S. t Where S is the surface coefficient and t is the time (s)

5 (Saetta, 1993) Chloride diffusion C t t = div[ D a. ( C t Chloride adsorption C t w )] +. φ t C t : The total chloride concentration w : Relative humidity φ: Chloride binding capacity D a = D i /φ : The apparent diffusion coefficient D i : Intrinsic diffusion coefficient Chloride diffusion coefficient and chloride binding capacity are major parameters covering chloride ingress into concrete structures

6 Chloride content Not take in to account bound chloride Take in to account bound chloride Concrete depth The binding of chloride retards the penetration process which extends the initiation time of corrosion.

increasing the chloride diffusion coefficient.

7 Practically, concrete structures carry loads during service life. Loads that generate either micro cracks or optical cracks result in increasing the chloride diffusion coefficient. Chloride penetration into concrete structures is accelerated with mechanical induced cracks. Cl - Cl - Cl - Cl - Crack

8 In this study, a model to account for the chloride penetration into plain concrete under flexural cyclic load and tidal effect was proposed. Compression Tension

9 FLOW CHART OF RESEARCH STEPS Verification Test of flexural cyclic load Verification Test of optical microscopy Predict crack growth under flexural cyclic load Short term test of chloride diffusion coefficient Long term test of chloride diffusion coefficient Predict chloride diffusion coefficient under flexural cyclic load Convert equation Chloride binding isotherm Test of total chloride content Predict chloride penetration into concrete under flexural cyclic load and tidal effect Verification

10 EXPERIMENTAL PROGRAM Mixture proportions of concretes Series w/c Ordinary Portland Cement (C) Kg Water (W) litre Coarse Aggregate (CA) Kg Sand (S) Kg S/(S+CA) M M M Cement type Chemical composition (%mass) C 3 S C 2 S C 3 A C 4 AF Density (g/cm 3 ) Blaine surface area (cm 2 /g) Ignition loss (%) OPC MC RHC LHC

Flexural cyclic loading Load (kn) 18 16 14 12 10 8 6

4 Deflection (mm) SR= P app P max Load (kn) P app

flexural cyclic loading test will be conducted with

11 Flexural cyclic loading Load (kn) P max Deflection (mm) SR= P app P max Load (kn) P app Time (s) N 1 Load Cracks widen faster Deflection The flexural cyclic loading test will be conducted with different flexural cyclic load levels: SR = 0.5; 0.6; 0.7; 0.8.

12 Long-term chloride diffusion test Establish relation Short-term chloride diffusion test Convert equation 30V Seal on all faces except one 10% NaCl Sodium 75mm 3%NaCl Chloride penetration 0.3N NaOH Brass mesh Concrete sample, 50mm long, 100mm diameter

13 EXPERIMENTAL RESULTS 3.00E E-11 Long term te est, m 2 /s 2.00E E E E E E E E E E E E E E E E-11 Short term test, m 2 /s

14 Effect of flexural cyclic load on chloride diffusion coefficient Relationships of Chloride diffusion coefficient and load levels Normalize ed D Compression zone-m1 Compression zone-m2 Compression zone-m3 Tenssion zone-m1 Tenssion zone-m2 Tenssion zone-m3 Normalize ed D Tension zone Compression zone Load level, SR Load level, SR Tension zone: y=0.0985e x Compression zone: y= x x

15 Chloride binding isotherms of cements Total Cl - (%by mass cement) Hydration degree (%) O PC MC RHC LHC Free Cl - (%by mass cement) W/C OPC MC RHC Bound Cl - (%by mass cement) AFm hydrate(%by mass paste) LHC 0 0 O PC MC RHC LHC Free Cl - (%by mass cement) OPC MC RHC LHC C 3 A(%by mass cement) Chloride binding isotherms of cements can be described by Freundlich isotherm. OPC has the highest chloride binding capacity, whereas, LHC has the lowest one.

16 NUMERICAL ANALYSIS Prediction of deformations of concrete beams under flexural cyclic load Series Input Parameters of numerical analysis of fatigue deformations w i, mm (SR) P app, max, kn (SR) (0.5) (0.6) (0.7) (0.8) (0.5) (0.6) (0.7) (0.8) P ult, kn σ c, MPa σ t, MPa M M M E, GPa Applied load, kn P app, max P app, min Time

17 Crack width, mm 0.12 M1-SR 0.5 M1-SR M1-SR 0.7 M1-SR No ormalized crack length M1-SR 0.5 M1-SR 0.6 M1-SR 0.7 M1-SR Number of cycles Number of cycles The fictitious crack width and crack length increased with increasing either the number of cycles, N, or the load level, SR. The numerical simulation clearly showed that fictitious crack growth, in terms of crack width and crack length, can be divided into three stages; a decelerated stage; a steady stage; an accelerated stage towards fracture. These results are consistent with other reports and with experimental data.

18 width, mm Crack Crack width before considering microcracks Measured crack widths Crack width after considering microcracks Number of cycles Relationships of crack width and number of cycles, model prediction and experimental results Crack density parameter 1 2 µ = Log( N) SR

19 Model prediction data clearly proposes that the chloride diffusion in the tension zone increases with increasing either the number of cycles or the load level. Overall, flexural cyclic load makes the chloride diffusion coefficient, which is estimated in the tension zone of concrete beam, increase and be divided into two stages as the monotonously increasing and accelerated stage. Normalized D 3.5 M1-SR M1-SR 0.6 M1-SR 0.7 M1-SR 0.8 Normalized D M2-SR 0.5 M2-SR 0.6 M2-SR 0.7 M2-SR Number of cycles Number of cycles Model prediction for the influence of cyclic load on the chloride diffusion coefficient in tension zone of plain concrete beam

20 When tortuosity parameter, τ, with τ=1.65, is introduced to account for the intrinsic tortuosity of the crack, good agreement between model predictions and measured results, simulated crack width after considering the crack density divided byτ, can be found. Normalized D Model results not considering tortuosity parameter Measured results Model results considering tortuosity parameter Normalized D M1-measured M2-measured M3-measured M1-modeled M2-modeled M3-modeled Load level, SR Number of cycles Relationships of flexural load and normalized D, model prediction and experimental results,

21 Prediction of chloride penetration under fatigue and tidal environment Cl - cont tent (wt% of cement) w/c=0.4 SR=0 SR=0.5 SR=0.6 SR=0.7 SR= Concrete depth, mm Cl - cont tent (wt% of cement) w/c=0.5 w/c=0.5 Concrete depth, mm SR=0 SR=0.5 SR=0.6 SR=0.7 SR=0.8 Prediction of chloride profiles of concretes subjected to coupling cyclic loads and 10 year exposure to tidal environments Modeling results indicated that the cyclic flexural load accelerated the chloride penetration into concrete. At higher cyclic flexural load levels, the chloride penetration was faster, and the acceleration rates of the chloride penetration into concretes became more distinct with cyclic flexural load levels, SR, of 0.6, 0.7, and, especially, 0.8.

22 Cl - content (kg/m 3 ) Concrete depth (mm) Comparison between results of numerical solution and measured results of concrete exposed to tidal environment in 7.6 years The numerical analysis fits quite well with that measured by Uji et al, Hence, the numerical analysis mentioned above is reliable and capable of applying to predict chloride penetration into plain concrete subjected to both flexural cyclic loads and tidal environments.

23 Cl - content (wt% of cement) Model result Experimental result Cyclic flexural load level, SR=0.5 Exposed time: 10 days Exposed condition: Drying-Wetting (NaCl 10%) Cl - content (wt% of cement) Model result Experimental result Cyclic flexural load level, SR=0.6 Exposed time: 10 days Exposed condition: Drying-Wetting (NaCl 10%) Concrete depth (mm) Concrete depth (mm) Cl - content (wt% of cement) Model result Experimental result Cyclic flexural load level, SR=0.7 Exposed time: 10 days Exposed condition: Drying-Wetting (NaCl 10%) Concrete depth (mm) Cl - content (wt% of cement) Model result Experimental result Cyclic flexural load level, SR=0.8 Exposed time; 10 days Exposed condition: Drying-Wetting (NaCl 10%) Concrete depth (mm)

24 CONCLUSIONS A model of the influence of flexural cyclic load on the chloride diffusion coefficient in the tension zone of plain concrete using the stress degradation law and the steady-stead transport of chloride ions as the fundamental assumptions was presented. When the crack density parameter, µ, and the tortuosity parameter, τ, were introduced, the model predictions fit well with experimental results. Under flexural cyclic load, model predictions show an increasing tendency of the chloride diffusion coefficient in tension zone with increasing number of cycles and load level, SR, especially at SR=0.7 and 0.8. Values of the chloride diffusion coefficients got from short-term test (D) are always higher those got from long-term test (D a ). There is the linear relation between results of short-term and long-term test. We can apply this linear equation to determine more precisely the chloride diffusion coefficient of concrete as converting values of short term test to those of long term test.

25 Of the four cement types, OPC has the highest capacity to bind chloride ions, whereas LHC has the lowest chloride ion binding capacity. The chloride binding capacities of MC and RHC are very similar. The chloride binding isotherms of the four cement types can be fitted to Freundlich isotherms. The AFm is responsible for binding chemically bound chloride by the formation of Friedel s salt. The C-S-H binds the physically bound chloride. The proposed model showed that the flexural cyclic load accelerated chloride penetration into concrete. This means the decrease in the durability of concrete structures under service loads and aggressive environments.

26 Thank you for your attention

EXPERIMENTAL STUDY ON CHLORIDE PENETRATION DEPTH IN CRACKED REINFORCED CONCRETE

Int. J. Struct. & Civil Engg. Res. 2013 Hoang Quoc Vu et al., 2013 Research Paper ISSN 2319 6009 www.ijscer.com Vol. 2, No. 2, May 2013 2013 IJSCER. All Rights Reserved EXPERIMENTAL STUDY ON CHLORIDE PENETRATION