Properties of Concrete Durability Factors affecting durability Permeability

1. 2.2 CONCRETE PROPERTIES
Concrete Properties are mainly influenced by many factors such as
mix proportioning in different ratios. Mainly the properties of
concrete are classified into the following types :
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Concrete Properties
Fresh
Workability Bleeding Segregation
Hardened
Strength Permeability
Thermal
Properties
Cracking

2. 2.2 CONCRETE PROPERTIES
STRENGTH
The Hardened Properties of Concrete is classified into
• Strength
• Permeability
• Durability
• Shrinkage, Creep & Cracks
• Stress-Strain variation
• Temperature variation
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Hardened Properties of Concrete
https://www.youtube.com/watch?v=PpUnxU57vAM

3. 2.2 CONCRETE PROPERTIES
• Strength of the concrete is commonly considered as the most
valuable property, although in many practical cases and other
characteristics, such as durability and permeability may infact is
important.
• Strength usually gives an overall picture of the quality of concrete
because strength is directly related to the structure of the
hydrated cement paste.
• Strength of concrete could be defined as the ultimate load that
causes failure (or is its resistance to rupture) and its units are
force units divided by area .
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Strength Properties
https://www.youtube.com/watch?v=DGhQYSlzTUw

4. 2.2 CONCRETE PROPERTIES
Strength of the concrete mainly depends on
Water/cement ratio and degree of compaction
Ratio of cement to aggregate
Grading, surface texture, shape, aggregate particles
Maximum size of aggregate.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

5. 2.2 CONCRETE PROPERTIES
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Factors affecting the strength of the concrete
Based on Testing methods
• Size of specimen
• Size of specimen to maximum size of aggregate used
• Moisture condition of specimen
• Rate of loading
• Type of testing machine
Those independent of testing methods
• W/C ratio
• Gel/space ratio
• Type & age of cement used
• Type & Max. size of aggregate
• Aggregate – cement ratio
• Curing method
• Degree of compaction
Factors affecting the strength of the concrete
https://www.youtube.com/watch?v=bMKFi1nhZIA

6. 2.2 CONCRETE PROPERTIES
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

7. 2.2 CONCRETE PROPERTIES
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
WATER CEMENT RATIO(W/C Ratio)
Strength of the concrete
https://www.youtube.com/watch?v=sQtOP7iN1Hw

8. 2.2 CONCRETE PROPERTIES
Gel Space Ratio
• Defined as the ratio of the volume of the hydrated cement paste to
the sum of volumes of the hydrated cement and of the capillary
pores.
• Relationship between the strength and water/cement ratio will hold
good primarily for 28 days strength for fully compacted concrete.
• Relationship between the strength and gel/space ratio is
independent of age.
• Gel/space ratio can be calculated at any age and for any fraction of
hydration of cement
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Gel Space Ratio – on Strength
https://www.youtube.com/watch?v=Td_0VJPlhdA&pbjreload=101

9. 2.2 CONCRETE PROPERTIES
GAIN OF STRENGTH WITH AGE
• The rate of gain of strength is faster to start with and the rate gets
reduced with age.
• It is customary to assume the 28 days strength as the full strength of
concrete.
• Actually concrete develops strength beyond 28 days also.
• Earlier codes have not been permitting to consider this increase of
strength beyond 28 days for design purposes.
• The increase in strength beyond 28 days used to get immersed with
the factor of safety.
• In this direction, the increase in strength beyond 28 days is taken
into consideration in design of structures.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Strength with Age
https://www.youtube.com/watch?v=Yw7WCsbb2iE

10. 2.2 CONCRETE PROPERTIES
Max. Size of Aggregate
• The larger maximum size aggregate gives lower surface area for
developments of gel bonds which is responsible for the lower
strength of the concrete.
• Bigger aggregate size causes a more heterogeneity in the concrete
which will prevent the uniform distribution of load when stressed.
• When large size aggregate is used, due to internal bleeding, the
transition zone will become much weaker due to the development of
micro cracks which result in lower compressive strength.
• Generally, high strength concrete or rich concrete is adversely
affected by the use of large size aggregate.
• It is interesting to note that in lean mixes larger aggregate gives
highest strength while in rich mixes it is the smaller aggregate which
yields higher strength.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Aggregate – on Strength
https://www.youtube.com/watch?v=IXYDrV-K2Bw

11. 2.2 CONCRETE PROPERTIES
Durability of Concrete
• Durability is the ability to last a long time without significant
deterioration.
• A durable materials helps the environment by conserving the
resources by reducing wastes and environmental impacts of repair
and rehabilitation.
• A durable concrete is one which performs satisfactorily under
anticipated exposure conditions during its service of life span.
• Volume change is the main cause for durability problems.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

12. 2.2 CONCRETE PROPERTIES
Durability of Concrete
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Durability of Concrete
https://www.youtube.com/watch?v=2Q7-o0HZTOE

13. 2.2 CONCRETE PROPERTIES
Durability of Concrete
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Durability of Concrete
https://www.youtube.com/watch?v=2Q7-o0HZTOE

14. 2.2 CONCRETE PROPERTIES
Permeability of Concrete
• Permeability is defined as the property that governs the rate of flow
of a fluid into a porous solid.
• For completing hydration of cement about 38 % of water by weight
of cement is required to fill the gel pores.
• If more than 38 % of water is used, than excess water will cause
undesirable capillary cavities and the concrete becomes porous.
Porous concrete has a higher permeability.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Permeability of Concrete
https://www.youtube.com/watch?v=TJhElJEDt3s

15. 2.2 CONCRETE PROPERTIES
Pores in cement Paste
A. Gel pores
B. Capillary pores
Gel pores : It is so small that hardly any water can pass through under
normal condition.
Its permeability is 7 × 10-16 m/s which is about 1/100 of that paste
hence it do not contribute to permeability
Capillary pores : It consist about 0 to 40 % of the paste volume.
They are much larger than gel porous
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

16. 2.2 CONCRETE PROPERTIES
Importance of Permeability
• In reinforced concrete, ingress of water and air will result in
corrosion of steel leading to expansion, cracking, and disruption of
concrete.
• The penetration of deleterious material in solution may adversely
affect the durability of concrete. Ca(OH)₂ leaches out and
aggressive liquids attack the concrete.
• If concrete becomes saturated with water due to permeability, it is
more vulnerable to frost action.
• The permeability is very important in case of liquid retaining
structures like water tanks and dams where water-tightness is
necessary.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Concrete Pores
https://www.youtube.com/watch?v=nxSZvC4dBPE

17. 2.2 CONCRETE PROPERTIES
Importance of Permeability
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

18. 2.2 CONCRETE PROPERTIES
Factors affecting Permeability
Absorption and
homogeneity
of concrete
W/C Ratio
Curing Use of Admixtures
& Age
Aggregate
Cement Properties
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

19. 2.2 CONCRETE PROPERTIES
Factors Affecting Permeability
Water Cement Ratio:
• The permeability is lower with lower water/ cement ratio & with
higher cement content permeability becomes less.
Properties of Cement:
• For the same water/ cement ratio, coarse cement tends to
produce a paste with higher porosity of cement than a finer
cement.
• In general, higher the strength of cement paste, the lower will be
the permeability
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
Permeability of Concrete
https://www.youtube.com/watch?v=FrMg_3xWxh0

20. 2.2 CONCRETE PROPERTIES
Factors Affecting Permeability
Aggregate:
Larger the sizes of aggregates higher is the voids so permeability will
be higher.
Absorption and homogeneity of concrete
• The volume of pore space in concrete is measured by absorption
of water in concrete.
• The absorption depends upon the structure of the concrete.
• Non homogeneity affects the permeability.
• If the concrete is homogeneous then the water absorption is less
& Permeability decreases
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

21. 2.2 CONCRETE PROPERTIES
Factors Affecting Permeability
Curing:
• Continued hydration of the cement paste results in the reduction in
the size of the voids which decreases the permeability.
• Proper curing of concrete decreases the permeability of concrete.
• Permeability of steam cured concrete is generally higher than that
of wet-cured concrete.
Use of Admixtures
• Use of water proofing admixtures reduces permeability .
• In general, the use of extra cement will be more effective in
reducing the permeability.
• In case of porous concrete surface treatment decreases
permeability.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

22. 2.2 CONCRETE PROPERTIES
Effect of air entrainment
• An air entrainment up to 6% can make the concrete more
impervious.
• Steam curing of concrete using pozzolana decreases permeability
due to formation of courser C-S-H gel, low drying shrinkage &
accelerate conversion of Calcium hydroxide into cementitious
product.
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES

23. Thermal properties of concrete
• Thermal conductivity
– measures the ability of material to conduct heat.
– measured in joules per second per square metre of area of body
when the temperature difference is 1°C per metre thickness of
the body.
– depends on type of aggregate, moisture content, density, and
temperature of concrete
– When the concrete is saturated, the conductivity ranges
generally between about 1.4 and 3.4 j/s/m2
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
2.2 CONCRETE PROPERTIES
Thermal Properties of Concrete
https://www.youtube.com/watch?v=IG22Ojx3p9Q

24. • Thermal diffusivity
– Represents the rate at which temperature changes within the
concrete mass.
Diffusivity = Conductivity / Cρ
– The range of diffusivity of concrete is between 0.002 to 0.006
m2/h
• Specific heat
– defined as the quantity of heat required to raise the temperature
of a unit mass of a material by one degree centigrade.
– The common range of values for concrete is between 840 and
1170 j/kg per °C
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
2.2 CONCRETE PROPERTIES
Concrete Temperature
https://www.youtube.com/watch?v=dNadlBF8rzU

25. Coefficient of thermal expansion
– Defined as the change in unit length per degree change of
temperature.
– In concrete it depends upon the mix proportions.
– The coefficient of thermal expansion of hydrated cement paste
varies between 11 x 10–6 and 20 x 10–6 per °C.
– Coefficient of thermal expansion of aggregates vary between 5 x
10–6 and 12 x 10–6 per °C.
– Limestone and Gabbros – Low
– Gravel and Quartzite - High
17CE401- MAINTENANCE AND REHABILITATION OF STRUCTURES
2.2 CONCRETE PROPERTIES
Thermal Cracking
https://www.youtube.com/watch?v=LGImMUs7AS0