IN THIS PRESENTATION, DURABILITY OF CONCRETE UNDER VARIOUS ATTACKS AND ITS BEHAVIOR AND MANY MORE ARE KNOWN

1. ADVANCED CONCRETE
TECHNOLOGY
DURABILITY OF
CONCRETE
BY
T.DURGA RAGHAVI
ANDHRA UNIVERSITY

2. TOPICS TO BE DISCUSSED:
• Carbonation
• Chloride attack
• Corrosion of steel
• Corrosion control
• Effects of some materials on durability
• Surface treatments of concrete
• Short term and long term tests on durability of concrete
• Concluding remarks on durability

3. CARBONATION:
• Carbonation of concrete is a process by which carbondioxide from air penetrates into concrete and reacts with calcium
hydroxide to form calcium carbonates.
• CO2 by itself is not reactive. In the presence of moisture, CO2 changes into dilute carbonic acid which attacks the
reinforcement and reduces alkalinity of concrete.
• Rate of Carbonation:
The rate of Carbonation depends on :
• The level of pore water ( relative humidity)
• Grade of concrete
• Permeability of concrete
• Whether the concrete is protected or not
• Depth of cover
• Time

5. DEPTH OF CARBONATION W.R.T STRENGTH OF CONCRETE:

6. DEPTH OF CARBONATION FOR PROTECTED AND UNPROTECTED CONCRETE:

7. AGE-YEARS DEPTH OF CARBONATION( mm)
M20 M40
2 5.0 0.5
5 8.0 1.0
10 12.0 2.0
50 25.0 4.0
DEPTH OF CARBONATION WITH AGE AND GRADE OF CONCRETE:

8. APPROXIMATE RELATIONS BETWEEN W/C, DEPTH OF COVER AND TIME IN
YEARS FOR CARBONATION DEPTH TO REACH THE REINFORCEMENT:
W/ C DEPTH OF COVER(mm)
RATIO 15 20 25 30
0.45 100+ 100+ 100+ 100+
0.50 56 99 100+ 100+
0.55 27 49 76 100
0.60 16 29 45 65
0.65 13 23 36 52
0.70 11 19 30 43
TIME IN YEARS FOR CARBONATION

9. • The highest rate of Carbonation occurs at a relative humidity of between 50 and 70%.
• The rate of Carbonation depth will be slower in case of stronger concrete( lower w/c ratio
and low permeability).
MEASUREMENT OF DEPTH OF CARBONATION:
A common and simple method for establishing the extent of Carbonation is to treat the
freshly broken surface of concrete with a solution of phenolphthalein in diluted alcohol. If
Ca(OH)2 is unaffected by CO2 the colour turns out pink. If the concrete is carbonated it will
remain uncoloured.

11. CHLORIDE ATTACK:
• Chloride attack mainly causes corrosion of reinforcement.
• Protective oxide layer which is formed due to high Alkalinity of concrete is lost due
to presence of chloride in presence of water and oxygen.
• Chloride enters the concrete from cement, water, aggregate and sometimes from
admixtures and also by diffusion from environment.
• According to Bureau of Indian Standard, the maximum allowable chloride content
in cement as 0.4%.

12. The following are the threshold values of chloride ion have been established for
intitation of reinforcement corrosion in uncarbonated concrete:
• upto 0.2% by weight of cement. = No risk of corrosion
• 0.2% to 0.4% by weight of cement. = Low risk of corrosion
• 0.4% to 1.0% by weight of cement. = Moderate risk of corrosion
• more than 1.0% by weight of cement= High risk of corrosion

13. LIMITS OF CHLORIDE CONTENT OF CONCRETE(IS 456 OF
2000):
SL. NO
TYPES OR USE OF
CONCRETE
MAXIMUM TOTAL ACID
SOLUBLE CHLORIDE CONTENT
EXPRESSED AS kg/m3 OF
CONCRETE
1
Concrete containing metal and
steam cured at elevated
temperature and prestressed
concrete
0.4
2
Reinforced concrete or plain
concrete containing embedded
metal 0.6
3
Concrete not containing embedded
metal or any material requiring
protection from chloride
3.0

14. AMERICAN CONCRETE INSTITUTE(ACI) LIMITS FOR CHLORIDE
CONTENT:
TYPE OF STRUCTURE CHLORIDE CONTENT% BY
WEIGHT OF CEMENT
Prestressed concrete 0.06
Conventionally reinforced
concrete in a moist environment
and exposed to external sources
of chloride
0.10
Conventionally reinforced
concrete in a moist environment
but not exposed to external
sources of chloride
0.15
Above ground building
construction where the
construction will stay dry
No limit

15. CORROSION OF STEEL(CHLORIDE INDUCED):
Corrosion is defined as the “ destruction or deterioration of materials in environments
to which they are exposed”.
• Corrosion of steel in concrete is an electrochemical process.
• When there is a difference in an electrical potential along the steel reinforcement in
concrete, an electrochemical cell is set up.
• Anodic reactions:
. Fe-> Fe++. + 2e-
Fe++ + 2(OH)- -> Fe(OH)2. ( Ferrous Hydroxide)
4Fe(OH)2 + 2 H2O + O2 -> 4Fe(OH)3 ( Ferric oxide)

16. SIMPLIFIED MODEL REPRESENTING CORROSION
MECHANISM

17. • Cathodic reaction:
. 4e- + O2+ H2O -> 4(OH)-
• Corrosion doesn’t takes place if concrete is dry or below relative humidity of 60%
because enough water is not there to promote corrosion. And also if concrete is
fully immersed in water because diffusion of oxygen does not takes place into the
concrete.
• The optimum relative humidity for corrosion is 70-80%.

18. CHEMICAL REACTIONS IN CORROSION OF STEEL:

23. CORROSION CONTROL:
CONTROL MEASURES FOR CORROSION:
• Proper mix design
• Use of right quality and quantity of cement for different exposure conditions.
• Low w/c ratio
• Low permeability
• Use of supplementary cementitious materials such as flyash, ground granulated blast furnace slag, silica fume etc
• Improved microstructure
• Metallurgical methods
• Corrosion inhibitors
• Coatings to reinforcements
• Cathodic protection
• Coatings to concrete

24. METALLURGICAL METHODS:
• Rapid quenching of hot bars by series of water jets
• By keeping the hot steel bars for a short time in a water bath.
CORROSION INHIBITORS:
• By corrosion inhibiting chemicals such as nitrites, phosphates, benzonates etc.
• The typical dosage is of order of 10-30 litres per m3 of concrete depending on
chloride levels in concrete.

25. CORROSION INHIBITING EFFECTS OF CALCIUM NITRITE

26. ELECTRO MICROGRAPH SHOWING CORROSION IN:
POOR CONCRETE GOOD CONCRETE

27. COATINGS TO THE REINFORCEMENTS:
The object of coating to steel bar is to provide a durable barrier to aggressive materials, such as
chlorides.
• Coatings should be rebust to withstand fabrication of reinforcement cage, and pouring of concrete and
compaction by vibrating needle.
• Method for prevention of corrosion In steel:
Derusting
Phosphating
Cement coating
Sealing
Fusion bonded epoxy coating
Galvanised reinforcement
Cathodic protection

30. EFFECTS OF SOME MATERIALS ON
DURABILITY:
The various effects on durability are caused by:
• Action of mineral oils
• Action of organic acids
• Vegetables and animal oils and fats
• Action of sugar on concrete
• Action of sewage

32. SURFACE TREATMENTS OF CONCRETE:
Some of the materials used for surface treatments are listed below:
• Aqueous solution of sodium silicate
• Magnesium or zinc silicone fluoride
• Drying oils such as linseed or Tung oil
• Chlorinated rubber paints
• Neoprene paints
• Epoxy paints or coal tar epoxy paints
• Silicon fluoride(SiF4) treatment

33. Epoxy coating on good will bridge in
australia

36. SHORT TERM AND LONG TERM TESTS ON
DURABILITY OF CONCRETE:

38. WATER PENETRATION TEST:
Water penetration depth can be used for finding the coefficient of permeability (K in m/sec).
K = e2v / 2ht
Where e = depth of penetration of water in concrete in meters
h = hydraulic head in meters( 0.1-0.7 Mpa)
t = time under pressure in seconds, and
V= the fraction of volume of concrete occupied by pores ( 0.02-0.06)
• The depth of penetration less than 50mm can be classified as impermeable and a depth
less than 30 mm can be classified as the concrete impermeable under aggressive
conditions

40. CONCLUDING REMARKS ON DURABILITY:

41. REFERENCES:
• Concrete technology Theory and Practice by M.S.Shetty.
• www.theconstructor.org
• National Council for Cement & Building materials- www.ncbindia.com
• Indian Concrete Institute( ICI).
• NPTEL Videos.
International and Indian Journals:
• Case study of damaged reinforced concrete bridge In Portugal by Alrindo Gonclaves.
• Concrete Floor Hardeners by CBRI, Roorkee.
• Chloride attack on reinforced concrete by Adam Neville.
• Water penetration test on concrete block masonry – 15th International Brick and Block
Masonry Conference

42. Thank you..