PROBABILISTIC MODELLING OF CONCRETE STRUCTURES DEGRADATION B. Teplý, P. Rovnaníková, P. Rovnaník, D. Vořechovská Brno University of Technology, Czech Republic REC 2012, Brno

Outline Degradation of RC structures …Time aspect …Codes and regulations …Durability limit states Software tool Evaluation of some degradation models …Carbonation m. vs. in situ measurement on cooling tower …Chloride ingress m. vs. in situ measurement on bridge in Italy …Corrosion m. vs. numerical m. Conclusions

Degradation mechanisms vs. time

carbonation and/or chloride ingress

Degradation mechanisms vs. time carbonation and/or chloride ingress steel depassivation

Degradation mechanisms vs. time carbonation and/or chloride ingress steel corrosion steel depassivation

Codes and regulations ISO (2008) General principles on Design of Structures for Durability fib Model Code (2010) Bulletins 55, 56 (First complete draft) Bulletin 34 Model Code for Service Life Design (2006) EN (2000) Concrete – Part 1: Specification, performance, production and Conformity

Durability limit states 1. Service life format 1a. Simplified/initiation LS 2. Limit state format ULS SLS

Durability limit states Steel depasivation (t ini ): Steel corrosion (t prop ):

Software tool FReET-D probabilistic modeling of degradation processes in time (Teplý, Vořechovská, Chromá, Rovnaník – Brno University of Technology) Utilizes probabilistic platform of FReET (Vořechovský, Rusina, Novák – Brno University of Technology) Features: random input variables, MC, LHS, FORM, statistical parameters of result, sensitivity analysis, estimation of probability P f and reliability index , automatic parametric studies, Bayess updating, number of degradation models

FReET-D: implemented models No. of models Outputs Carbonation13 carbonation depth, time to depassivation (concretes with Portland and blended cements) Chloride ingress 1depth of chlorination, time to depassivation 2concentration of chlorides Frost attack3 actual degree of saturation, relative dynamic modulus of elasticity, loosening of concrete at surface Sulphate attack1rate of concrete corrosion Acid attack1depth of concrete corrosion Reinforcement corrosion 1net rebar diameter (uniform cor.) 1pit depth (pitting cor.) 1net cross sectional area (pitting cor.) 2time to cracking (uniform cor.) 1crack width (uniform cor.) 1 stress intensity factor (prestressed reinforcement, pitting corrosion, fracture mechanics approach) 1strength and ductility of corroded steel

Evaluation of carbonation models Cooling tower (Keršner et al. 1996) height of 206 m in-site investigation at the age of 19.1 years the depth of carbonation measured at 75 locations (on both the internal and external surfaces)

Analytical models a)fib Model Code (Bulletin No. 34) b)Papadakis et al. (1992), based on mass conservation c)Papadakis et al. (1992), R.H. function updated d)Morinaga (1992), R.H. function updated Evaluation of carbonation models (Teplý et al. 2010)

Evaluation of carbonation models Carbonation depth (19.1 years) External surface (RH = 70%) Internal surface (RH = 93%) Mean [mm]COV [%]Mean [mm]COV [%] fib Model Code Papadakis et al. (1992) Papadakis et al. (1992) R.H. function updated Morinaga (1992), R.H. function updated In situ measurements (Keršner et al. 1996) (Vořechovská et al. 2010)

Evaluation of carbonation models Carbonation depth (19.1 years) External surface (RH = 70%) Internal surface (RH = 93%) Mean [mm]COV [%]Mean [mm]COV [%] fib Model Code Papadakis et al. (1992) Papadakis et al. (1992) R.H. function updated Morinaga (1992), R.H. function updated In situ measurements (Keršner et al. 1996) (Vořechovská et al. 2010)

Evaluation of chloride ingress models Bridge in Italy Wendner, R., Strauss, A., Guggenberger, T., Bergmeister, K. and Teplý, B., 'Ansatz zur Beurteilung von chloridebelasteten Stahlbetonbauwerken mit Bewertung der Restlebensdauer', Beton- und Stahlbetonbau 12/2010 Chloride concentration measured in the different distances from the nearest surface (from 10 to 50 mm)

Evaluation of chloride ingress models a)fib Model Code (Bulletin No. 34) b)fib Model Code; substituted surface concentration c)Crank´s solution of Fick´s 2nd law d)Thomas and Baumfort (1999) e)Nilsson and Carcasses (2004) and Tang and Gulikers (2007)

Evaluation of corrosion model Analytical model (Li et al. 2006) vs. Numerical computation based on nonlinear FE (Vořechovská and Vořechovský 2010)

Evaluation of corrosion model Analytical model (Li et al. 2006) no corrosion filling of porous zone crack initiation crack on concrete surface, spalling concrete rust crack Constant geometry: thick-wall cylinder (Bažant 1979, Pantazopoulou and Papoulia 2001, Tepfers 1979) steel porous zone

Evaluation of corrosion model Numerical model ►ATENA program (Červenka Consulting) ► constitutive model based on smeared crack approach ► used fracture plastic model NLCEM ► expansion of corrosion products: (negative) shrinkage of reinforcement

Evaluation of corrosion model Comparison of models Identical parameters: geometry, E, f t Extras for numerical model: G F, f c,…

Conclusions Durability design of RC structures is now actual in engineering practice Durability/performance based approach to the specification of concrete durability may be based on predictive (proven!) models utilization FReET-D is a software tool for fully probabilistic performance based design; the other proves of the degradation models are needed FReET-D can be effectively utilized in combination with FReET and ATENA software