1 DURABILITY OF CONCRETE

PROFESSOR DR MOHAMMAD BIN ISMAIL

ENVIRONMENTAL AGGRESSIVITY AND CLASSIFICATION OF ENVIRONMENTAL EXPOSURE

ASSIGNMENT Go and visit engineering office of property

owner (JKR, Bandaraya, Municipal council, Kementerian pelajaran, Kementerian Pertahanan, ….).

Discuss with the engineer regarding any durability related problem faced by their building, structures, etc. Get information (data, foto,..).

Write brief report

Class Presentation.

Learning outcome

At the end of the course students should be able to: • understand different environmental condition • How these problem related to strength and durability of concrete

Department of Structures and Materials, Faculty of Civil Engineering UTM

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References

1. Advanced Concrete Technology, concrete properties, J. Newman and B.S.Choo, Elsevier, 2003

2. Fundamentals of Durable Reinforced Concrete, M.G. Richardson, Spon Press, 2002

3. Corrosion of Steel in Concrete, L.Bertholini, B.Elsener, P.Pedeferri and R.Polder, Wiley-VCH, 2004

4. Durable Concrete Structures, CEB Design Guide, Thomas Telford, 1992.

INTRODUCTION

• For deleterious processes to develop

– Interaction between materials/structures with environment depend on

• Type

• Intensity and timing of material properties

• Selected structural form

• Position of reinforcement

• Type of aggressiveness of the environment

• Atmospheric Climate

– Macroclimate

– Microclimate (mm or cm away); relevant towards durability

– Condition around buried (foundation or piles) or submerged parts

• CEB-FIP model code:

– MILD

• Interior of buildings

• RH > 60% for less than 3m/year

– MODERATE

• Interior with high RH; presence of corrosive vapour

• Running water

• Inclement weather

• Ordinary soils

• CEB-FIP model code:

– SEVERE

• Liquids containing slight amounts of acids, saline or strongly oxygenated waters

• Corrosive gases or corrosive soils

• Corrosive industrial or maritime atmospheric conditions

AVAILABILITY OF MOISTURE

– All deterioration processes require water

• Moisture in concrete is more important than surrounding

• Internal average humidity tends to be higher than the average ambient humidity; also true for wetting and drying

Table: Influence of moisture state on durability processes

Figure : Influence of moisture on corrosion risk relative to cover

PRESENCE OF AGGRESSIVE SUBSTANCE IN MOISTURE

• Common aggressive substance in moisture

a. Carbon dioxide – for carbonation

b. Oxygen – corrosion

c. Chlorides – promote corrosion

d. Acids – dissolve cement

e. Sulphates – give expansive reaction with cement

f. Alkalis – expansive reaction with aggregate

TEMPERATURE LEVEL

• Influence of temperature sometimes ignored in definition of aggressivity

• Reaction accelerated by increases in temperature

– Increase of 10oC double the rate of reaction

– Tropical environments more aggressive than northen european climates

Influence of temperature on environmental aggressivity relative to cover

• Availability of

– Moisture

– Aggressive substance in moisture

– Temperature; main considerations in characterizing a particular environment

• Carbonation is most rapid when RH 50-60%; at 95% RH corrosion completely inhibited

• Corrosion rate however very low when RH 50-60% and highest when RH 90-95%

• Corrosion due to chloride is different from due to carbonation

• Effect of humidity is irrelevant

• Risk of corrosion damage expected directly related to humidity same as corrosion rate.

CONCRETE COVER

• Corrosion of reinforcement related to:

– Thickness of concrete cover

– Quality (permeability and alkalinity)

Minimum concrete cover in mm for reinforcement of low susceptibility to corrosion

Influence of W/C ratio on permeability relative to the efficiency of cover in protecting reinforcement

CLASSIFICATION OF ENVIRONMENTAL EXPOSURE

DEFINITION OF EXPOSURE

CLASSES

ASSESSMENT OF CHEMICAL ATTACK ON

CONCRETE

Exposure classes for concrete related to

environmental conditions

Exposure classes for reinforcement related to environmental conditions

Assessment of the degree of chemical attack of concrete by waters and soils containing aggressive

agents

KOBE airport

Say: “ If the ocean were ink (wherewith to write out) the word of my lord, sooner would the ocean be exhausted than would the word of my lord, even if we added another ocean like it, for its aid” Say : “I am but a man like yourselves, (but) the inspiration has come to me that your God is one God: whoever expects to meet his lord, let him work righteousness, and, in the worship of his lord, admit no one as partner.” Al-kahfi: 109-110

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