General durability General durability General durability General durability

concrete durability

1. UNIVERSITY INSTITUTE OF ENGINEERING
CIVIL ENGINEERING DEPARTMENT
BE Civil Engineering
FIFTH SEMESTER
Health Monitoring, Repair and Rehabilitation of Structures
(23CET-353)
Dr. Pankaj Kumar (E12065) [email protected]
Assistant Professor
Academic Session 2025-26
ODD Semester Jul-Dec 2025

2. What is durability?
•Durability of hydraulic-cement concrete is defined
as its ability to resist weathering action, chemical
attack, abrasion, or any other process of
deterioration (ACI)
•Durable concrete will retain its original form,
quality, and serviceability when exposed to its
environment

3. Durability of concrete
Concrete is subjected to a host of durability problems,
which typically result in:
- Progressive loss of mass from the surface
- Volume changes, which can be of three types: (1) both
paste and aggregate expand, (2) the paste expands,
while the aggregate is inert, or (3) only the aggregate
expands; also, cracking can be caused due to volume
expansions of the reinforcing steel upon its corrosion

4. Durability of concrete
•Primary issues
- Corrosion of rebars
- Chemical attack
- ASR / DEF
•Multiple transport mechanisms involved
•Typically countered by choice of material and mix
design
•Rarely checked in the specimens / structure

5. Durability and permeability
•Water is common to all the durability problems in
concrete. The presence of water, or its involvement
in the reactions is necessary for the problems to
occur. Thus, the durability of concrete is intrinsically
related to its water-tightness, or permeability.

6. Permeability and porosity
•Permeability of concrete is a function of the
permeability of the cement paste, of the
aggregate, and of the interfacial transition
zone. The permeability of these
components is in turn related to the porosity.
•Porosity and permeability need not be
directly related. The interconnectivity of
pores is generally responsible for a high
permeability.

7. Permeability and Porosity
•Paste capillary porosity is typically 30 – 40%, while normal aggregates have a
porosity of 2 – 3% (and rarely greater than 8 – 10%). The transition zone is
highly porous due to the presence of flaws such as microcracks and bleed-
channels.
•Both porosity and permeability increase with an increase in the water to
cement ratio. Both the threshold diameter and cumulative intruded volume (as
measured by mercury intrusion porosimetry) increase with the w/c. The
permeability also depends on the degree and nature of curing, and the
presence of mineral admixtures, which can act as fillers densifying the
transition zone.

8. Pore structure parameters
•The threshold pore size or breakthrough pore size is the minimum continuous pore size for the
sample obtained from the cumulative volume intrusion curve
•The critical pore size corresponds to the peak in the differential pore volume curve indicating the size
corresponding to the maximum volume intrusion.
Dhandapani and Santhanam
(2017)

9. Effect of water-binder ratio and curing period
Dhandapani and Santhanam (2017)Santhanam et al. (ACF, Thailand, 2017)
Effect of water-binder ratio
Effect of curing period

10. Porosity and Permeability
Permeability and porosity are related by the Kozeny equation:
 
          
K = ε
3
/ (S
2
K
k
), where
 
                      
K = coefficient of permeability,
ε = porosity,
S = volume specific surface area of the particles
(surface area per unit volume), and
K
k
= Kozeny constant.

11. Kozeny constant
The Kozeny constant, K
k
is defined by:
 
          
K
k
= K
t
x K
o
,
where K
t
represents the tortuosity of flow, as shown in the figure, and K
o
is the
shape factor, that represents the shape of the pore. For spherical particles,
assuming circular pores, the Kozeny constant works out to be equal to 5.0.

12. Design for durability

13. Conventional wisdom
•Durability (and other engg. properties) =
f{Compressive Strength}
•If cube strengths are OK, then concrete in the
structure is fine!
•Concrete is very forgiving – will take care of
itself!

14. TYPICAL SECTION THROUGH AN RC MEMBER
Cover-crete
Heart-crete
Progressive hydration
results in decreased
porosity and reduced
interconnection of
pores – ie. reduced
fluid transmissibility
The real picture
Strength
Durability!!
Ballim, 2008

15. The Problem in Reinforced Concrete
Alexander, 2008

16. The Problem (Cont’d)
•Deterioration begins immediately after casting – plastic cracking,
bleeding, segregation and thermal effects.
•Hardened concrete affected by a variety of internal and external
factors which cause damage by physical and/or chemical
mechanisms.
•Deterioration often associated with ingress of aggressive agents, so
that near-surface concrete quality largely controls durability.
•The problem is then the adequacy of protection to steel offered
by the concrete cover layer.

17. DURABILITY
THE CONCRETE
SYSTEM
AGGRESSIVENESS
OF THE
ENVIRONMENT
MATERIALS PROCESS
PHYSICAL CHEMICAL
•Binder type
•Binder content
•Aggregates
•Admixture
•Mix design
•Mixing
•Transporting
•Compaction
•Curing
•Temperature
•Workmanship
•Abrasion
•Erosion
•Cavitation
•Freeze-thaw
•Dissolution
•Leaching
•Expansion
•Alteration
Specification issues!
Ballim, 2008

18. How to specify for durability?
•Placing restrictions on cement content, w/c,
grade of concrete, cover etc. = Prescriptive
specifications
•Judging the compressive strength, shrinkage,
durability properties required in the concrete at
a certain time period = Performance
specfications

19. Thank You
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