Definition and types of cause of Deterioration of Concrete

1. THE DETERIORATION OF CONCRETE
HARIKRISHNA M.S

2. Introduction
• The pH of concrete is very high (about 13
initially), providing a non-corrosive, durable
alkaline environment to the reinforcement.
• But many a times, due to various factors, the
pH value of concrete reduces, inducing
corrosion in the reinforcement.

3. Cause of Deterioration are

4. 1. Chemical
• Aggression by carbon dioxide
• Aggression by sulphates
• Aggression by chlorides
• Alkali-aggregates reaction

5. Aggression by carbon dioxide
• In constructions exposed to the atmosphere, Carbonatation of concrete takes place,while in
hydraulic constructions, there is an occurance known as leaching which acts upon the
cementitious paste.
• Carbonation is due to the penetration of CO2 into the concrete
• phenomenon consists in the transformation of the lime, which then generates hydration of
the cement into calcium carbonate
• Due to
• the presence of carbon dioxide, the level of which
• depends on the environment in which the construction is located
• the occurance of Carbonatation is only damaging for reinforced structures

6. Aggression by sulphates
•the sulphates come from the ground or from the water in contact with the structure,
the sulphate ions carried inside the cementitious matrix by water (fundamental for
transportation) reacts with the calcium hydroxide to form gypsum.
•reacts with the hydrated calcium aluminates (C-A-H) to form secondary
ettringite,which increases in volume and causes delamination, swelling, cracking and
detachment

7. Aggression by chlorides
•contact with environments with a high chloride
content, such as seawater or de-icing salts, or if it is
prepared using contaminated raw materials
•chloride penetrates into the concrete and reaches
the reinforcement rods, it eliminates the passivating
ferrous oxide film on the rods so that they are
exposed to the corrosion process

8. Alkali-aggregates reaction
• cause considerable expansion and serious deterioration of concrete structures
• aggregate which contain reactive silicon, react with two alkalis contained in the cement,
potassium and sodium
• reaction forms a gel which is highly expansive if exposed to humidity, and the gel creates
forces which break the concrete around the aggregates.

9. 2. Aggression by physical elements
1. Freezing and thawing
2. High temperatures
3. Shrinkage and cracking

10. Freezing and thawing
• Occurs when the concrete is critically saturated, which is when
approximately 91% of its pores are filled with water
• When water freezes to ice it occupies 9% more volume than that of water.
• If there is no space for this volume expansion in a porous, water containing
material like concrete, freezing may cause distress in the concrete.

11. High temperatures
• During a fire, the temperature may reach up to 1100◦C in
buildings and even up to 1350◦C in tunnels, leading to severe
damage in a concrete structure

12. Shrinkage and cracking
• Newly-placed concrete develops tensile stresses as differences in
temperature and moisture content develop in the drying concrete and
shrinkage occurs in it
• These stresses are relieved by cracking

13. 3. Aggression by mechanical elements
1. Abrasion
2. Impact
3. Erosion
4. Cavitation

14. Abrasion
• Abrasion is the process of scuffing, scratching, wearing down, marring, or
rubbing away.
• It can be intentionally imposed in a controlled process using an abrasive

15. Impact
• concrete is a fragile material which, if subject to impacts of a certain intensity,
deteriorates and its strength will is reduced
• Caused by various agents like vehicles, machines, earthquake etc.

16. Erosion & Cavitation
• Erosion is a particular form of wear due to wind,
water or ice which provokes the removal of
material from the surface. It depends on the
speed, the content of hard dust particles and the
quality of the concrete
• Cavitation is a problem where flowing water (> 12
m/s) is present. The high speed of the water,
together with an irregular surface where the
water flows, provoke turbulence and areas of low
pressure, and vortexes will form which erode the
substrate.

17. 4. Deterioration due to Defects
• Defects due to poor/incorrect deign of the
mix;
• Defects due to the wrong composition;
• Defects due to incorrect/poor quality
installation

18. Exposed reinforcement
rods in concrete
Segregation of the
aggregates in concrete

19. Thank u