Brief explanation of distress in concrete structures...

2. Introduction:
 All concrete structure in service will be subject to chemical and
physical changes. A durable concrete is one which does not
detrimentally affect its performance within its life period
 As per case studies shows that many reinforced structures get
deterioration with in a life period of 15years or so , suffered
from of durability distress
 Although it is difficult to generalise the causes of deterioration
due to so many factors and the types factors are

3. Types of deterioration in concrete structures
 Distress in concrete
 Permeability of concrete
 Aggressive deterioration agents

4. Types of deterioration in concrete structures
 Distress in concrete
1. Physical
2. Chemical
3. mechanical
4. Design deficiency
5. Environmental effects
 Permeability of concrete
1. Capillary porosity
2. Air voids
3. Micro cracks
4. Macro cracks
5. Dampness
6. seepage
 Aggressive deterioration agents
1. Chloride
2. Sulphate
3. Alkali silica reaction

5. Distress in concrete
Physical:
1)High w/c ratio
2)Inadequate curing
3)Poorly graded aggregates
4)In adequate compaction
5)Cover thickness being
lesser
6)wrong placement of
reinforcement
Poorly graded aggregates

6.  Chemical-
1)chloride :these may be present in the fresh mix or may penetrate from
external source in to the hardened concrete . during the use of structures,
chloride may penetrate in to the concrete from various sources . the most
important of these are sea water . the chloride in water is contact with
reinforced steel and destroy the thin film on the steel
2) sulphate: In this the reaction between the physical and chemical
interactions between the minerals in hardened Portland cement paste and
sulphate ions from the environment . the sulphate attack on concrete
manifests in the form of expansion , cracking , loss of mass and
disintegration
3) alkali silica reaction : when the aggregates in
cement concrete contain reactive forms of silica ,
the phenomenon of chemical reaction is referred
to as ASR .Expansion and cracking , leading to
loss of strength

7.  Mechanical:
1) Impact load: Impact is a high force or shock applied over a short time
period when two or more bodies collide. Such a force or acceleration
usually has a greater effect than a lower force applied over a proportionally
longer period.
2) Over loading : Due to excessive load the structure may collapse
3) Un even movement caused by settlement: Depends on ground water and
soil conditions
4)Vibration: while vibrating the propagation of waves leads to form the crack
on the structure
5)Blasting: This is one of the main factor because while doing blasting the
energy can push the structure and leads to form cracks on near structures

8.  Impact load: over loading
 Un even movement
caused by settlement Vibration

9.  Design deficiency- 1)wrong assessment of design loads
2)thermal movement, shrinkage, structural
behaviour
 Environmental – 1)Heating/Cooling
2)wetting/drying
3)Abrasion

10. Permeability of concrete
Capillary porosity: the extra volume of water entrapped in the
cement paste after completion of hydration leaves
interconnected pores called capillaries in hardened concrete ,
which becomes passage for external chemicals this porosity is
termed as capillary porosity
Causes due to:
1)High w/c ratio
2)In adequate curing

11. • Air voids: These voids are much larger than capillary pores,
due to inadequate compaction in the form of discrete air
bubbles
• Causes:
Improper compaction

12. Micro cracks: The crack which is less than 0.1mm considered
as micro cracks
Causes: loading effects, weathering,
Initial care and After care

13.  Macro cracks: the crack is between 0.1 to 0.3mm
 Causes: improper placement of concrete

14.  Dampness : Dampness is the presence of unwanted moisture in
the structure of a residential or commercial building
 Causes : Use of poor quality bricks which ultimately absorb a lot
of water.
 Moisture entrapped during construction

15. • Seepage : The slow escape of a liquid or gas through porous
material or small holes
• Causes: leakages in drainage pipes
less maintenance of water proof course

16.  Aggressive deterioration agents
I) corrosion of reinforced bar due to
1)carbonation of concrete
2)due to ingress of chloride
Ii)sulphate
Iii)alkali silica reaction (ASR)

17.  carbonation of concrete: The alkalinity in concrete is
provided by hydroxides of calcium, sodium and potassium
present in the hardened cement gel , permeation of carbon
dioxide in to concrete through interconnected pores and its
reaction with these hydroxides causes chemical reaction

18.  Sulphate: In this soil contains sulphates of calcium , sodium,
potassium and magnesium are the primary source of sulphate ions in
ground water. The sulphate attack on concrete causes cracks and
disintegration

19.  alkali silica reaction (ASR)

20. Thank You!