this is about durability of concrete

1. Durability of concrete
Made by – Satya mishra. MIT 11-A-03 –G-CIVIL -7339

2. a) Durability –introduction of
the durability concept.
b) The factors affecting
durability of concrete
c) Different attacks on concrete
affecting durability .
i) sulfate attack.
ii) origin of problems.
d) Loss of strength and mass
e)ACI building code 318
i) negligible attack
ii)moderate attack
iii)severe attack
iv)very severe attack
f) History of concept
g)Examples of major damaged
monuments.
h) Prevention for factors
affecting durability.
i) bibliography/references.
contents

3. Durability concept
->Definition-Durability of concrete :ability to
resist weathering action ,chemical attack ,
abration or any process of deterioration.
-> A durable concrete will retain its original
form quantity and serviceabilty when
exposed to its environment .
Water causes –
a)Chemical processes of
degradation .
b)Physical processes of
degradation.

4. Factors affecting durability of concrete
Physical causes concrete deterioration
deterioration by surface wear
a) Abration :dry attribution (wear on pavements and
industrial floors by traffic.
b)Erosion :wear produced by abration action of fluids
containing solid particles in suspension.(canal lining
,spillways and pipes.)
c) cavitation: loss of mass by formation of vapor
bubbles and their subsequent collapes.

5. Abration; erosion
•The deterioration starts at the surfaces there fore special attentions should be
given to quantity of concrete surface.
•Avoid laitance (layers of lines of cements and aggregate)
Deterioration by frost action
When water freezes ,there is an exopansion of 9% however, some
of the water may migrates through the boundary ,decresing the
hydraullic pressure.
•Hydraullic pressure depends on
•Rate at which ice is formed
•Permeabilty of the material
•Distance to an “escape boundary”.
•Problem: the transformation of ice from liquid water generates a
volumetric dilation of 9% .if the transformation occurs in small
capillary pores ,the ice crystal can damage the cement pastes by
pushing the capillary walls and by generating hydraullic pressure

6. Solution to the problem-
Air voids can provide an effective escape boundary to reduce this pressure.
Picture showing the effect caused by frost action

7. Frost action by aggregate
Factors controlling
frost
resistance of concrete.

8. Deterioration by fire
Consequences:-
Fire in chunnal->

9. Effect of temperature
Corrosion Reinforce concrete

10. Electrochemical process of steel corrosion in concrete
Volumetric changes
Carbonate of concrete->

11. Alkali –silica reaction
ASR chemistry

12. Repairing ASR Damage to a concrete Dam ASR damage examples

13. Sulfate attack
*sulfate attack on concrete has been reported from many other parts of the world .
•As early as 1936 the concrete construction in annual published by US bureau
of reclamtion warned that concentrations of sulfate greater tha 0.1% in siol may have
a deleterious effect on concrete ,and more tha 0.5 % soluble sulfate in soil may have a
serious effect.
Origin of the problem
•most soil contains some sulfate in form of gypsum (typically 0.01% to 0.05%
expressed as So4 ); this amount is harmless to concrete .
• higher the concentrations of sulfate in ground water are generally due to presence
of magnesium and alkali sulfates.
•Ammonium sulfate is frequently present in agriculture soil and water effluents
from furnances that use high sulfur fuels and from chemical industries may contain
sulfuric acid.

14. Expansion of concrete
•When concrete crack ,its permeability increases and aggressive water penetrates
More easily into the interior thus accelerating the process of deterioration .
•Sometimes the expansion of concrete causes serious structural problem.
Loss in strength and mass
* sulfate attack can also take the form of progressive loss of strength and loss of mass due
to loss of cohesiveness in the cement hydration product.
Expansion reaction sulfate attack
•gypsum formation leads to
reduction of stiffness and strength
•,then by expansion and cracking.
•Sodium sulfate attack

15. Sodium sulfate attack
•The formation of sodium hydroxide as a by product of the reaction ensures the
•continuation of high alkalinity in the system which is esential for the stability
•of cemetitious material C-S-H.
Magnesium sulfate attack

16. Factors influencing sulfate attack
•Amount and nature of the sulfate present
•Level of the water table and its seasonal variations.
•Flow of ground water and soil porosity.
•Form of construction,
•Quantity of concrete.
ACI building code 318
•Negligible attack : when the sulfate content is under 0.1% in soil ,under 150 ppm
(mg/liters) in water ,there shall be no restriction on the cement type and
water /cement ratio.
*moderate attack: when the sulfate content is 0.1 to 0.2% in soil ,or 150% to 1500 ppm
In water ,ASTM type 11 portland cement or portland pozzolan or portland cement shall
Be used ,with less than on 0.5 water /cement ratio for normal –weight concrete.
•Severe attack: when the sulfate content is 0.2 to 2% in soil ,or 1500 to 10,000 ppm
•in water ,ASTM type V portland cement ratio ,shall be used 0.45 water /cement ratio,
Shall be used.
•Very severe attack: when the sulfate content is over 2% in soil ,or over 10,000 ppm in
water, ASTM type V cement plus a pozzolanic admixture shall be used ,with
less than an 0.45 water /cement ratio.

17. freeze thaw
•expansion and cracking occurs when water in
paste
Freezes .
Volume expansion
Hydraullic pressure.
Ice lens

19. Reactive aggregates
*Amorphous silica (glass
,opal).
Unstable crystalline
polymorphs of
silica.(tridymite,cristobalite
, strained quartz).

21. PREVENTIONS
* Recognize and avoid susceptible aggregates .
*use low alkali cement.
•Use supplement cementing material.
Making durable concrete
•Make good –quality concrete low w/c .
•Test materials.
•Use air entrainment if concrete will be frozen.
•Recognize and avoid material known to cause deterioration (D-
cracking ASR)