Deterioration Models and Service Life Planning (Part 1)

Rak-43.3301 Repair Methods of Structures I (4 cr)

Esko Sistonen

MICRO-LEVEL DURABILITY AND LOADING FACTORS

• pore size distribution of the cement paste in sandwich-element concrete facade

• total air content and protective pore ratio in cement paste• water-cement ratio• tensile strength of cementpaste, especially in tranzition layer

near aggregate stones• micro-cracking of concrete due to chemical reactions and

crystallizations of materials• carbonation rate of different concrete mixtures • corrosion rate of reinforcement in carbonated and cracked

concrete• critical moisture content of concrete for reinforcement

corrosion

MICRO-LEVEL DAMAGE MECHANISMS

• correlation between air pore amount, moisture content and freeze-thaw cycle resistance of concrete

• salt crystallization and its effect on concrete damages• chemical reactions in concrete under Finnish climate• stresses and cracks due to temperature changes and

gradients in conrete• changes of pore structure of concrete• mathematical evaluation methods of the durability of

concrete under Finnish climate

MACRO-LEVEL DURABILITY AND LOADING FACTORS

• moisture distribution of impregnated or coated sandwich-element concrete facade compared with plain concrete facades (due to rain water or heat and moisture transfer)

• temperature distribution in outer panel of sandwich-facades during the year

• carbonation rates of impregnated or coated concrete facade

• chloride content in concrete facades

MACRO LEVEL DAMAGE MECHANISMS• frost damage mechanisms of concrete in sandwich-

facades• corrosion mechanisms of reinforcement in sandwich-

facades• cracking of concrete and stresses between inner and outer

panel due to temperature variation and shrinkage• strains in facade elements due to temperature gradients• chemical and salt problems in Finnish concrete facades• effect of different impregnations and coatings to moisture

content, carbonation and damages in sandwich-facades • service life calculation methods and formulas for

sandwich-facades

Agents aggressive to inorganic materials

Nature Origin Physical agents - thermal - moisture - radiation - electrochemical

-heat, frost, thermal changes and gradients, thermal shock - shrinkage, wetting, rain - solar radiation, ultraviolet radiation - corrosion of reinforcement

Chemical agents - water - air humidity, condensation, precipitation, rain - air - carbonation, oxygenation - solvents - dissolution of cement or calcium hydroxide Mechanical agents - deformations - gravitation - vibrations

- shrinkage, thermal changes - weight of element itself - wind, explosions, shocks

Biological agents - vegetable and microbial - bacteria, moulds

Common defects in facades due to the different causes

Causes Deterioration causes Defect Physical - freezing and thawing - cracking - moisture changes - shrinkage cracking, delamination - temperature changes and gradients - cracking - curving of elements and plates - detaching of outer panels Chemical - carbonation - reinforcement corrosion

(and spalling of concrete) - alkali-aggregate reaction - cracking

- delamination - salt crystallization - cracking

- spalling - ettringate reaction - cracking

- decrease of frost resistance -spalling

- dissolving - decrease of frost resistance Mechanical - deformations - cracking - cracking of joints - curving -penetration of water to insulation layer Biological - biological growth - mould problems - dirt

MICRO-LEVEL REPAIR METHODS

• methods to decrease moisture content and carbonation in concrete (effect on decrease in frost damages and reinforcement corrosion)

• impregnation of concrete• coatings for concrete surface• cathodic protection of reinforcements• realkalisation of concrete• critical chloride content

Random-Variable Degradation Model in case of a single inspection.

J.M. van Noortwijk, M.D. Pandey, A stochastic deterioration process for time-dependent reliability analysis

Service life of concrete structures – a two-phase modeling deterioration

FIB (CEB-FIP), Bulletin 3 – Structural Concrete – Textbook on behaviour, Design and Performance (Updated knowledge of the CEB/FIP Model Code 1990), Vol. 3, December 1999.

Relationship between durability and performance

CEB-FIP: Durable of Concrete Structures, Design Guide, T. Thelford, London, 1992.

Transport mechanisms for aggressive substances influence on concrete and reinforcement, and importance of the protective concrete layer – to protect the structure against deterioration

FIB (CEB-FIP), Bulletin 3 – Structural Concrete – Textbook on behaviour, Design and Performance (Updated knowledge of the CEB/FIP Model Code 1990), Vol. 3, December 1999.

td= γt tg

td = the design service life,

γt = the lifetime safety factor, and

td = the target service life.

Service life predicted with only mean values and mean values and scatters of the parameters

in the prediction models. R(t) and S(t) are expressed with both mean values and scatters. DuraCrete (1999)

Increase of failure probabilitythe resistance R of a structure, and of the load effect S

FAILURE = R < S; the probability of failure defined as: Pf (t) = P{R(t) < S(t)}

The meaning of lifetime safety factor in a performance problem

Durability Design of Concrete Structures- RILEM Report 14:(Ed. A. Sarja and E. Vesikari), Spon, London, 1996. p.155.

The meaning of lifetime safety factor in degradation problem

Durability Design of Concrete Structures- RILEM Report 14:(Ed. A. Sarja and E. Vesikari), Spon, London, 1996. p.155.

Probability density function for strength (fR) and action - load (fS) and failure probability (shaded area)

Calculation of failure probability (Thoft-Christensen &Baker 1982).

Full-probabilistic performance concept.

Ferreira, R.M. (2004), PROBABILITY-BASED DURABILITY ANALYSIS OF CONCRETE STRUCTURES IN MARINE ENVIRONMENTS

Reliability index b

Relationship of failure probability pf and reliability index β fora normal distributed reliability function.

Ferreira, R.M. (2004), PROBABILITY-BASED DURABILITY ANALYSIS OF CONCRETE STRUCTURES IN MARINE ENVIRONMENTS

Exposure Classes for concrete structures according to EN 206-1:2000

Exposure Classes for concrete structures according to EN 206-1:2000

Classification of concrete facade structure into carbonation and frost exposure classes.