# CIVE1173 Service Life Modelling

### Card Set Information

 Author: Anonymous ID: 224411 Filename: CIVE1173 Service Life Modelling Updated: 2013-06-19 21:20:35 Tags: Service LifeModelling Folders: Description: Week 7 lecture notes summary. Exam Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user Anonymous on FreezingBlue Flashcards. What would you like to do?

1. Damage Propagation vs Time
2. SLM Limit States/Evidence
• Entrance of aggressive agents/Cores or Drilling
• Initiation of corrosion/LPR or half-cell
• Rust staining/visual
• Cracking/visual
• Spalling/visual
• Structural failure/closure
3. SLM Phases
• Initiation
• Propagation
4. Initiation phase
• Deterministic; measured values, well established models, single output value
• Probabilistic; distribution curves/mean and standard deviation, probability/reliability as output
5. SLM - chloride models
• Data from cores, labs, literature
• NaCl ponding test, seal all faces except top with epoxy, determine chloride profile after 90 days
6. Chloride Initiation Phase - Diffusion model

• Cx,t = chloride depth x, at time t
• Cs = surface chloride
• Dapp = chloride diffusion coefficient apparant
• T = time
• x = cover depth
• erf = error function
• requires concentration of chlorides at bar to initiate corrosion to predict service life.  Chloride % by weight can be expected to decrease exponentially as depth increases
• Reaches max. value
7. Chloride diffusion coefficient, Dapp
• Dtm chloride diffusion coefficient at time tm and n is the material coefficient. e.g. tm at age zero is 1
• n factor; OPC -0.264, PFA -0.699, GGBS -0.621
8. Chloride Diffusion Model; surface chloride Cs
• where Cs < 0.06 (or any other pre-set value)
• alpha is a constant depending upon exposure conditions
• C0 is the initial surface concentration
• t time in years
• e.g. mean values OP cement 0.36%, Blended cements 0.51%
9. Chloride Diffusion Model
Rate of chloride build up at surface in different marine environments
10. Using Chloride Diffusion Model to determine cover required
11. Chloride Propagation Phase - Diffusion model
• Diffusion Model can be used as basis for propagation but considerable uncertainty exists.
• Uncertainty increases as the propagation continues from cracking to spalling to structural failure.
• If using then predict corrosion rate first. Actual measurements or:
• CR = a.ebCxmicron/year
• CR – corrosion rate, a and b are constants and Cx is the chloride content
12. Calculating chloride corrosion rate for propagation phase for uncracked concrete
• CR = 0 (Cx <0.46% by weight of cement)
• CR = 0.55e1.564Cx (0.46%<Cx <3.0% by weight of cement)
• CR = 60 (3.0%<Cx by weight of cement)
13. Chloride corrosion propagation. Crack penetration
• pcr = (83.4 + 7.4c/db - 22.6fct)/1000
• c – cover
• db – bar diameter
• fct – tensile splitting strength of concrete
14. Chloride corrosion propagation. Crack propagation
• wcr = 0.05 + Beta(p(t) - pcr) >0
• Where
• Beta – 12.5 top cast, 10 bottom cast bars
• p(t)– mean corrosion penetration at time t
15. Chloride corrosion propagation. Residual cross section
Ares = pi(db – 2p(t))2/4
16. SLM - carbonation modelling
• Depth of Carbonation =
• Q + k1.k2.k3.k4.k5.C.tx
• Q = Instantaneous Carbonation
• C = Carbonation Coefficient for Concrete (Assumptions for C are made for differing grades of concrete)
• t = time
• k1 = factor - effect of CO2 concentration in the air
• k2 = factor - effect of Exposure
• k3 = factor - effect of orientation (N,S,E,W)
• k4 = factor - effect of Curing
• k5 = factor - effect of supplementary cementitious materials (e.g. - flyash, BFS)
• x = factor- effect of asset type and method of construction
17. SLM - carbonation initiation phase
• xc(t) = Kt0.5
• t – time
• xc(t) – carbonation depth at time t
• K – constant
• K can be determined from site data given carbonation depth at time t.
18. Carbonation initiation impacted by:
The environment. Time of wetness & temperature
19. Carbonation initiation, rates for various concrete strengths
20. SLM Initiation Phase - Probabilistic models
• Distribution function for each variable
• Normal, t, chi squared, Wei-Bull, etc
• Surface chloride, chloride diffusion coefficient, cover depth (age factor, temperature)
• Monte Carlo simulation (or similar) to build up a distribution pattern for results
• Analyse probability that result gives desired service life
21. SLM Initiation Phase - probabilistic models examples
• RMIT research project
• Model uses analogy between heat transfer and diffusion
• Time dependant analysis
• Variation in models
• Model replicates at concrete pile with different rates of chloride build up
• FEA Mesh
• Comparison at point y (mid-point)
• Other models. Questionable accuracy:
• Freeze/Thaw
• Sulphate attack
• ASR

What would you like to do?

Home > Flashcards > Print Preview