2. Causes of Concrete Deteriorations
Freezing and Thawing
Corrosion
Mechanism
Recommendations
3. Concrete Durability
Definition - its ability to resist weathering
action, chemical attack, w/cm ratio
considerations, mass concrete, abrasion, or
any other process of deterioration.
Session 1 will discuss Freezing-thawing
distress in detail
6. Thawing Distress caused by Scaling Distress
– Hydraulic & Osmotic Pressures
photos courtesy of M. Thomas
7. Frost Damage by to cyclic F-T damage
photos courtesy of M. Thomas
8. Frost Damage by to cyclic F-T damage
photos courtesy of M. Thomas
9. Recommended Air Content
Effective For Durability:
When volume of air in mortar fraction of
concrete is about 9 ± 1% (or about 18% by
paste volume).
Required air increases as coarse aggregate size
is reduced (due to greater paste volume)
Required air increases as exposure conditions
become more severe.
11. Recommended Average Air Content
Percentage for Level of Exposure
Nominal maximum sized of aggregates
Exposure
3/8 in.
(9.5 mm)
1/2 in.
3/4 in.
(12.5 mm) (19 mm)
1 in.
(25 mm)
1 – 1/2 in. 2 in.
(37.5 mm) (50 mm)
Mild
4.5
4.0
3.5
3.0
2.5
2.0
Moderate
6.0
5.5
5.0
4.5
4.5
4.0
Severe
7.5
7.0
6.0
6.0
5.5
5.0
12. Control of Air Content Materials
• Cement content;
Fineness, Alkali
• Aggregates;
Fineness, Shape
• Admixtures
• Pigments
13. Control of Air Content
Mixture Parameters, Etc.
• w/cm
• Slump;
<3-in. (75mm)
>6-in. (150mm)
• Temperature
• Altitude
• Mixing Speed, Time,
Capacity
14. Placement Issues which Affect
Control of Air Content Placement
•
•
•
•
Transportation
Placement; Pumping
Consolidation
Finishing
15. Why do we need Air-Entrainment?
DEFINITION: Air-Entraining Admixtures are primarily used to
stabilize tiny bubbles generated in concrete to protect against
freezing and thawing cycles.
20. Mechanism of
Protection by Air Voids
Air-entrained
32oF
23oF
As the temperature of saturated
concrete(.91.7%) in service is lowered, the
water held in the capillary pores of harden
concrete as paste freezes.
Saturation > 91.7%
21. Mechanism of
Protection by Air Voids
Air-entrained
32oF
23oF
As microscopic air bubbles are filled with
freezing of water causes an increase of
volume by 9%,thus the excess water in the
cavity is expelled by hydraulic pressure.
Saturation > 91.7%
22. Mechanism of
Protection by Air Voids
Air-entrained
32oF
23oF
Diffusion of water leading to a growth of a
relatively small number of bodies of ice.
When salts are used for de-icing, they are
absorbed by the upper part of the
concrete. This produces an osmotic
pressure with a consequence movement of
water towards the coldest zone where
freezing takes place.
Saturation > 91.7%
23. Mechanism of
Protection by Air Voids
Air-entrained
32oF
23oF
Each cycle of freezing and thawing causes
a migration of water to locations where it
can freeze. Subsequent freezing repeats
the development of pressures and
consequences of re-freezing, further
expansion takes which has an cumulative
effect.
Saturation > 91.7%
24. Air Void Spacing & Volume
• Spacing factor ( L ): the
maximum distance of any
point in the cement paste
from the periphery of an air
void.
L
L
• Specific surface: the
surface area of a quantity
of air voids that have a total
volume of 1 in.3 (25 mm3).
25. Characteristics of an Adequate
Air Void System (ASTM C 457)
Test method ASTM C457 recommendations for an
adequate air-void system.
Spacing factor < 0.008 in. (0.203 mm)
Specific surface > 600 in.2/in.3 (24 mm2/mm3)
Voids per linear inch: 1.5 - 2 times the percentage of
air
26. Please return to Blackboard and watch
the following videos:
Video 1: Durability
Video 2: Air Entrainment
