Durability of concrete structures in Bangladesh against some environmental related deterioration

2. Durability of concrete structures in Bangladesh
against some environmental related deterioration .
Presented by :
Engr. Md. Arafat Hasan
A PRESENTATION
ON
Structural Engineer at Parent Construction & Consultancy Ltd.

3. Introduction:
 Basic definition of durability: “Durability is the ability of a
Material or Structure to withstand its design service
conditions for its design life without significant
deterioration.”
 According to ACI 201.2R-08 “Durability of hydraulic-cement
concrete is determined by its ability to resist weathering action,
chemical attack, abrasion, or any other process of deterioration.”

4. Objectives :
Main objectives of our study are:
 (1) to identify some common causes of deterioration of
concrete structure in Bangladesh;
 (2) to find out the possible solution to make concrete more
durable to resist these common deterioration problems.

5. Durability problems of concrete
structures in case of Bangladesh
Reinforced concrete structures have the potential to be very durable
and capable of withstanding a variety of adverse environmental
conditions. However, failures in the structures do still occur as a result
of premature reinforcement corrosion which are Durability problems related
to environmental causes deterioration. Some common causes of deterioration
of concrete structures in Bangladesh are (A) Carbonation induced corrosion of
steel bar, (B) Chloride induced corrosion, (C) Sulphate attack.

6. A. Carbonation induced corrosion of
steel bar
It is a process by which CO2 from the air penetrates into
concrete and reacts with calcium hydroxide to form calcium
carbonates in presence of water [2]. Thus reduce pH value,
finally breaking the passivation film of concrete which leads to
corrosion of steel.

7. Chemical Reactions
 The first reaction is in the pores where carbon dioxide (CO2) and water (H2O)
react to form carbonic acid (H2CO3):
CO2 + H2O H2CO3
 carbonic acid then reacts with the calcium phases:
H2CO3 + Ca (OH)2 CaCO3 + 2•H2O
Once the Ca(OH)2 has converted and is missing from the cement paste, hydrated CSH
(Calcium Silicate Hydrate - CaO•SiO2•H2O) will liberate CaO which will then also produce
carbonate:
H2CO3 + CaO CaCO3 + H2O

8. Why it occurs
 If clear cover depth is not sufficient carbonation induced
corrosion will occur shortly after construction.
Lack of Cover

9. Formation of a thin passive film at a high pH protects from corrosion.
The passive oxide film can be broken with the
reduction of pH.
Steel bar in concrete.
Steel
Bar
Why steel bars in Concrete are not Corroded?
Steel bar in atmosphere
No protection from corrosion
Concrete

10. Carbonation-induced Corrosion
OHCaCOCOOHCa H
23
0
22
2
)( 
CO2
pH in Concrete drops significantly. The passive film
is lost. Corrosion continues depending on the
moisture condition, oxygen permeability through the
cover concrete, etc.
Moist Concrete
Carbonation Depth

11. Corrosion cells formation:
Rust has a lower density than steel. Hence, as corrosion takes place, the volume
increases and since the expansion is restrained by the surrounding concrete, bursting
stresses are induced, resulting in cracking, spalling or delamination of the concrete
cover.
Figure : Corrosion Cells formation After Carbonation Figure: Volumetric Expansion due to the Oxidation
of Fe

12. EFFECT OF CARBONATION
 It can cause soft surface, dusting and color change
 It reduces quality concrete
 It reduces the concrete ability to protect reinforcement from
corrosion (in an exposed environment).
 It will result in additional shrinkage in carbonated region.

13. DETECTING CARBONATION
 Depth of carbonation can be detected using an indicator.
 A chemical such as Phenolphthalein sprayed on to freshly broken
concrete.
 Areas remaining alkaline will turn in a bright purply-pink color.
 Carbonated areas of concrete will remain unchanged in color.

14. CARBONATION TEST
Test Cylinder After Phenolphthalein Indicator Applied.
PREPARATION OF TEST SURFACE:
 By breaking a piece of concrete from the main area and spraying the
underlying surface immediately
METHODOLOGY OF CARBONATION TEST (Phenolphthalein Test)
100ml of 1% Phenolthalein solution
Generally Phenolphthalein indicator is used which indicate the carbonated
concrete. The uncolored layer is considered to be carbonated.

15. Field Investigation Method of Measuring Carbonation Depth :
 By drilling a hole into the concrete either at a given depth or in small
increments at a constant speed throughout the operation. The first
powder coming out is collected at the bottom of the picker and the
last at its top
PHASES OF THE INVESTIGATION :
 PHASE 1 – CHOOSING A TEST POINT
 PHASE 2 – COLLECTING THE SAMPLE :
 PHASE 3 – MEASURING HOLE AND SAMPLE :
Using the ruler with the graded scale, one
establishes the exact length of the collected
powder sample, and this is compared with
the measurement of the actual depth of the
hole in the item.

16.  PHASE 4 – ANALYSIS WITH
PHENOLPHTHALEIN :
 PHASE 5 – MEASURING CARBONATION :
the graded scale ruler allows to measure to the
millimeter the length of the carbonatated part,
distinguishing it from the non degraded part.
Comparing the measurement with the scale ratio
established during Phase 3, one can calculate the
actual value of the depth of the carbonation
front at the point of the item being analyzed.
 PHASE 6 – CLOSING THE HOLE :
 At the end of the test, the hole made to carry out the
collection is closed. Using the quick drying cement plaster.

17. Where it occurs
Carbonation mainly occurs preferentially on prism faces of calcium hydroxide crystals [3].
 Also other hydration phases with greater surface
areas, such as calcium silicate hydrates, have
carbonated

18. How to prevent corrosion due to Carbonation
 Use good quality concrete air-entrained with a w/c of 0.40 or less.
 Use a minimum concrete cover of 1.5 inches .
Increase the minimum cover to 2 inches for deicing salt exposure and
to 2.5 inches for marine exposure.

19. Chloride enters the concrete from cement,water,aggregets and sometimes
from admixtures. Chloride attacks the reinforcement rather than Concrete.
Nothing happens to concrete in the beginning except the reduction in ph.
Chloride induced corrosion:
Chloride helps to destroy the passivation (protection) film over the steel bar that
prevent it from corrosion.If chloride level over the steel bar reach the threshold level
(0.4 % of cement or 1.2 kg/m3) the protection film will be broken.After broken down the
passivation film, corrosion over steel bar will start → Rust Formation (6 ~ 7 times
volume increase) → cracking → Spalling of concrete.

21. Progress of Corrosion
Passive Steel
Break Down of the
Passive Film and
Initiation of
Corrosion
Cracking Spalling
Cl-, CO2,..

22. Control of chloride attack :
1.Extra concrete cover.
2.Well curing .
3.Impermebilty .

23. Sulfate attack is a chemical breakdown mechanism where sulfate ions attack
components of the cement paste. The compounds responsible for sulfate attack are water-soluble
sulfate-containing salts, such as alkali-earth (calcium, magnesium) and alkali (sodium, potassium)
sulfates that are capable of chemically reacting with components of concrete.
Delayed Ettringite Formation:
Deleterious formation of ettringite.Late formation causes expansion distress.
Expansion causes cracking –premature deterioration
3CaO.Al2O3.CaSO4.18H2O + Sulfate → 3CaO. Al2O3. 3CaSO4.32H2O
(monosulfate) (Ettringite)
o If concentration of sulfate is high, the sulfate will consume CSH of concrete and will
reduce the strength of concrete significantly.
(i) MgSO4 + Ca(OH)2 + 3CaO.Al2O3.CaSO4. 18 H2O → 3CaO.Al2O3. 3CaSO4.32H2O + Mg(OH)2
(Ettringite) (Brucite)
↓
volume expansion and hence crack and strength reduction

26. Main factors affecting sulphate attack:
1.Cement type and content:
The most important mineralogical phases of cement that affect the intensity of
sulphate attack are: C3A, C3S/C2S ratio and C4AF.
2.Effect of w/c ratio :

27. Control of sulfate attack:
 The quality of concrete, specifically a low permeability, is the best
protection against sulfate attack.
 Adequate concrete thickness
 High cement content
 Low w/c ratio
 Proper compaction and curing

28. Conclusions: So in sum up we found there are two fundamental ways to make concrete
durable by addressing the properties of the concrete like proper mix design with low w/c ratio, etc.
Second by providing protective systems external to the concrete surface and by providing enough
cover of concrete on reinforcement.
References:
[1]. ACI 201.2R-08, Guide to Durable Concrete.
[2]. Notes on concrete durability by DR. M NAGESH. Professor and Head Civil Engg. Dept. Government
Engineering College.
[3]. Journal on Carbonation as an Indicator of Crack Age by ACI member Dipayan Jana and Bernard.
4. Carbonation of concrete by DR. AYUB ELAHI professor of UNIVERSITY OF Engineering and
Technology Taxila.
5. Durability of Reinforced Concrete Structures, Theory vs Practice by Albert K.H. Kwan and Henry H.C.
Wong Department of Civil Engineering, The University of Hong Kong, Hong Kong.
6. PPT on Concrete Durability Design by Donald Meinheit, WJE (retired) on Minnesota Concrete Council .