2. Head line News dated 21.09.2020
2
A building, situated at Patel compound of Narpoli near Dhamankar
Naka, Bhiwandi in Thane collapsed at around 3.40 am on 21.09.20,
while the residents were asleep. About 39 people lost their life. The 36-
year-old building had 48 flats in total out of which 24 collapsed.
The owner of the building has been booked for culpable homicide and
negligence causing hurt.
Such headlines are not uncommon
India is a Country Familiar With Building Collapses
As per NCRB a total of 13,473 cases of structural collapse were
reported across India between 2010 and 2014. in these, 1,614
people were crushed under commercial buildings, while 4,914 died
when residential buildings collapsed.
Shockingly, man-made disasters put together have caused more
deaths in the country than natural disasters did, which killed nearly
2,500 people between 2010 and 2014.
4. Deterioration of concrete structures
4
freshly laid concrete, New structure
Deteriorated concrete
Deterioration at early ages…
Frequent repairs, ….demolition.. reconstruction
5. (Gehlen et al., 2010; Germany)
General
5
Deterioration of RC structures
(Cont’d.)
6. DURABILITY OF CONCRETE
• Definition-
A durable concrete is one that performs satisfactorily in the
working environment during its anticipated exposure conditions
during service life.
• Definition as per ACI-
Durability of concrete is determined by its ability to resist
weathering action, chemical attack, abrasion, or any other
process of deterioration, and will retain its original form,
quality, and serviceability when exposed to its environment.
6
7. DURABILITY OF CONCRETE
Concrete structure should continue to perform
its intended functions i.e.
- Maintain its required strength and serviceability, during
the specified or traditionally expected service life.
- Concrete must be able to withstand the processes of
deterioration to which it is expected to be exposed.
• The materials and mix proportions specified and used
should be such as to maintain its integrity and, if
applicable, to protect embedded metal from corrosion.
- Durability does not mean an indefinite life.
7
8. DURABILITY & CUBE STRENGTH
• The cube strength only indicates the strength of
the structure at the time of construction.
• Whereas Durability is the long term guarantee
of the same strength and serviceability of the
structure.
• Concrete may have strength initially but may
not be durable.
8
9. DURABILITY OF CONCRETE
The main characteristics influencing the DURABILITY of
concrete is its PERMEABILITY to the ingress of water,
oxygen, carbon dioxide, chloride, sulphate and other
potentially deleterious substances.
Voids increase the permeability of concrete.
Permeability causes rusting of steel and spalling
(disintegration) of concrete.
Impermeability is governed by the constituents and
workmanship used in making the concrete
9
10. DURABILITY OF CONCRETE
Factors influencing durability are
• The environment/exposure conditions
• Cover to embedded steel
• The type and quality of constituent materials
• The cement content and W/C ratio
• Workmanship to obtain full compaction & efficient
curing
• Shape & size of the member
10
11. DURABILITY OF CONCRETE
• Voids reduce the strength of concrete. With every
one percent entrapped air, the strength is
reduced by about 5% to 6%.
• Five percent entrapped air mean 30% loss of
strength.
• Compacting also helps eliminate stone pockets
and thereby eliminate all types of voids that may
possibly be left in the concrete, which causes
reduction in strength as well as durability.
11
12. PERMEABILITY OF CONCRETE
• Concrete is a composite material comprising of Cement, Sand
& coarse aggregate. Every material has pores, which contains
voids in it.
• Aggregates have a more substantial void ranging from 1 mm
to 10 mm which are filled by cement paste. Even cement has
voids ranging from 1 micron to 10 micron.
• Due to this interconnected and continuous link to fill one void
by other material concrete is prone to permeate fluid or gases
into it.
• In simple words, presence of voids in concrete makes
permeable which in turn allows water or gas to flow into it.
• The impermeability of concrete is the ability of concrete to
resist the water flow or any other substance into it when the
external force is applied. 12
13. Why the Permeability of Concrete
is Important?
• Durability of concrete is most important and complex
property of concrete.
• If concrete is permeable, deleterious materials like water,
CO2, SO2 & Cl which permeates through the pores of the
concrete and reacts with the reinforcement forms rust which
increases the volume of the reinforcement and damages the
structure. Prior understanding of the extent and rate of
permeation helps to design structure better.
13
14. Factors affecting Permeability
1. Water-Cement ratio:
Excessive water is added to the concrete mix to increase
the workability of concrete. This additional mixing of water,
more than required increases the porosity in concrete and
degrades the durability of concrete. To resist the entry of
water into the concrete 0.4 water-cement ratio is adopted.
Experiments proved that taking a water-cement ratio of 0.4
makes concrete impermeable.
2. Improper compaction of concrete:
Improper compaction in concrete is the major problem for
porosity in concrete. Concrete should be adequately
compacted using hand compaction method or machine
compaction methods. Poorly compacted concrete leads to
the formation of honeycomb which ultimately makes steel to
corrode and forms surface cracks.
14
15. Factors affecting Permeability
3. Improper Curing:
Concrete should be adequately cured by considering the
atmospheric weather. Improper curing in concrete leads to
the formation of cracks and in turn, it increases the
permeability of concrete.
15
16. Permeability test as per CBC
As per CBC cs no.1,
(i) Permeability test has been made mandatory for
- all major bridges in all exposure conditions
- all RCC/PSC bridges when exposure condition is
severe/very severe or extreme.
(ii) Under mild and moderate environment, permeability
test shall be mandatory for
- all major bridges and
- for other bridges permeability test is desirable to the
extent possible.
16
19. PROCEDURE FOR MEASURING PERMEABILITY OF
CONCRETE APPENDIX – G (Clause 5.4.2.1) CBC
Test Specimen
• Test specimen of 200 mm dia and 120 mm thick shall be used.
After 24 hours of casting of specimen, central circular area of
100mm diameter shall be roughened with a wire brush on the
side on which the water pressure is to be applied. The
unroughened part of the side of the test specimen which is
subjected to water pressure is to be sealed with two coats of
cement water paste (W/C = 0.4).
Procedure:
a) After 28 days curing, test specimen is fitted in to a test
apparatus where water pressure acts on the required face and
remaining faces can be observed
19
20. PROCEDURE FOR MEASURING PERMEABILITY OF
CONCRETE
b) At first, a pressure of 1 bar (1kg/cm2) is applied for 48 hours,
then 3 bar for 24 hours and 7 bar for 24 hours.
c) After the test, the specimen is split in the middle by
compression applied on two round steel bars lying on opposite
sides, above and below. The side after test specimen exposed to
the water pressure should face downwards.
• The greatest water penetration depth, is taken as the average
value of the greatest penetration depths on three test specimen.
• The depth of penetration of water should not be more than
25mm other wise it is considered to be failed in permeability
test. 20
23. Transport Mechanisms in Concrete
Transport properties of cementitious materials are a key
factor , since deterioration mechanisms such as corrosion,
leaching or carbonation, etc., are related to the ease with
which the fluid or ion can move through the concrete
The mechanisms/process involved in fluid and ion
movement include-
Distinct mechanisms Material property
Capillary action, sorptivity,
Fluid flow under pressure, permeability,
Flow under a concentration gradient diffusivity
Movement due to an applied electric field conduction/
migration
23
24. Sorption refers to uptake of liquids into a solid by capillary
suction. It is measured using parameters such as bulk absorption,
or sorptivity
Permeability of concrete is defined as the capacity of concrete to
transfer fluids through its pore structure under an externally
applied pressure while the pores are saturated with that fluid.
This is predominantly influenced by the permeability of cement
paste, especially at the interface with aggregate particles
Diffusion is the movement of gases, ions and/or molecules under
a concentration gradient, from an area of high concentration to
one with a low concentration
Migration (also referred to as accelerated diffusion, electro-
diffusion, or conduction) is the movement of ions in a solution
under an electrical field. It is the transport mechanism most often
used in laboratory accelerated chloride tests
24
25. Corrosion of steel in reinforced concrete
Sulphate and other chemical attack of concrete
Alkali-aggregate reaction
Freezing and thawing damage
Common Durability Problems in Concrete
25
30. Provision in IS: 456-2000 on
Durability of concrete structures
30
31. TYPES OF CEMENTS IN Clause 5.1 OF IS:456-2000
The cement used shall be any of the following and
The type selected should be appropriate for the intended use
a) 33 Grade ordinary Portland cement conforming to IS 269
b) 43 Grade ordinary Portland cement conforming to IS 8112
c) 53 Grade ordinary Portland cement conforming to IS 12269
d) Rapid hardening Portland cement conforming to IS 8041
f) Portland slag cement conforming to IS 455
g) Portland pozzolana cement (fly ash based conforming to IS 1489 (Part1)
h) Portland pozzolana cement (calcined clay based) conforming to IS 1489
(Part 2)
i) Hydrophobic cement conforming to IS 8043
j) Low heat Portland cement conforming to IS 12600
k) Sulphate resisting Portland cement conforming to IS 12330
31
32. TYPES OF MINERAL ADMIXTURES IN IS456-2000
MineralAdmixtures
Pozzolanas
Fly ash (Pulverised fuel ash)
Silica fume
Rice husk ash
Metakaoline
Ground Granulated Blast France Slag
32
33. Code prescribes :
minimum cement content,
maximum free water-cement ratio,
and minimum grade of concrete for different exposure conditions
•Table of Code considers MAs such as FA, GGBS, etc. (listed in Clause
5.2) as part of cement content (though maximum amount that can be
taken into account is as per limit given in BIS codes for blended cements
(IS:1489 part I for FA and IS:455 for GGBS)
•Actual OPC content of concrete for durability considerations is less in
present revised Code (IS:456-2000) comparative to pre-revised Code
(IS:456-1978).Thus, contribution of MAs to durability of concretes. is
recognised.
MINIMUM CEMENT CONTENT
33
34. 8.2.2.1 General Environment
The general environment to which the concrete will be exposed during its
working life is classified into 5 levels of severity
Table 3 Environmental Exposure Conditions (Clauses 8.2.2.1 and 3 5.3.2)
Sl. No Environment Exposure Conditions
i Mild Concrete surface protected against weather or aggressive conditions,
except those situated in coastal area.
ii Moderate Concrete surfaces sheltered from severe rain or freezing whilst wet;
Concrete exposed to condensation and rain; Concrete continuously under
water; Concrete in contact or buried under non-aggressive soil/ground
water; Concrete surfaces sheltered from saturated salt air in coastal area
iii Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or
occasional freezing whilst wet or severe condensation; Concrete
completely immersed in sea water; Concrete exposed to coastal
environment
iv Very severe Concrete surfaces exposed to sea water spray, corrosive fumes or severe
freezing conditions whilst wet; Concrete in contact with or buried under
aggressive sub-solid/ground water
v Extreme Surface of members in tidal zone; Members in direct contact with
liquid/solid aggressive chemicals
34
35. Exposure Nominal concrete
Cover in mm not
Less than
Cover as per
CBC
slab
Cover as per
CBC
beam
Cover as per CBC
Column /Well/ pile/ footing
cl. 15.9.2.1
Mild 20
Moderate 30 25 35 50
Severe 45 35 50 75
Very severe 50
Extreme 75 50 60 75
Table 16 Nominal Cover to Meet Durability requirements
(Clause 26.4.2)
35
NOTES: For main reinforcement up to 12 mm diameter bar for mild
exposure the nominal cover may be reduced by 5 mm, Unless specified
otherwise, actual concrete cover should not deviate from the required
nominal cover by +10/-0 mm, For exposure condition `severe' and
`very severe' reduction of 5 mm may be made, where concrete grade is
M35 and above
36. Table 7 Limits of Chloride Content of Concrete (Clause 8.2 5.2)
Sl.
No.
Type or Use of Concrete Maximum Total Acid
Soluble Chloride Content
Expressed as kg/m3 of
Concrete
(1) (2) (3)
i Concrete containing metal and steam
cured at elevated temperature and
pre-stressed concrete
0.4
ii Reinforced concrete or plain
concrete containing embedded metal 0.6
iii Concrete not containing embedded
metal or any material requiring
protection from chloride
3.0
36
37. Table 5 Minimum Cement Content, Maximum W/C Ratio and Minimum Grade of
Concrete for Different Exposures with Normal Weight aggregates of 20 mm Nominal
Max. Size (Clauses 6.1.2, 8.2.4.1 and 9.1.2)
Sl.
N
o
Exposure Plain Concrete Reinforced Concrete
Min.
Cement
Content
kg/m3
Max.
Free
W/C
Ratio
Min.
Grade of
Concrete
Min.
Cement
Content
kg/m3
Max.
Free
W/C
Ratio
Min.
Grade of
Concrete
(1) (2) (3) (4) (5) (6) (7) (8)
i Mild 200 0.60 - 300 0.55 M 20
ii Moderate 240 0.60 M 15 300 0.50 M 25
iii Severe 250 0.50 M 20 320 0.45 M 30
iv Very
severe
260 0.45 M 20 340 0.45 M 35
v Extreme 280 0.40 M 25 360 0.40 M 40
37
38. Water content
Depends on workability and type, shape and grading of aggregate
Slump Water(kg/m3
) for Maximum size of aggregate
9.5mm 12.5mm 19.0mm 25mm
Crushed aggregate
25-50mm 207 196 190 179
75-100mm 228 216 205 193
150-175mm 243 228 216 202
Rounded aggregate
25-50mm 185 175 165 155
75-100mm 200 195 185 175
150-175mm 220 210 200 195
Lyse’s rule – constant water content gives constant concrete
consistency irrespective of w/c ratio
38
39. Variation of slump with SP dosage for concrete mixture having different
water content
100
50
0
150
200
0 0.5 2 2.5
1 1.5
SP dosage (% of binder)
Slump,
mm
196
190
180
170
160
Water Content
kg/m3
39
40. Carbonation of concrete
• The term “Carbonation” of concrete means the chemical reaction between
carbon dioxide in the air and hydration products of the cement. The process
includes:
1. Diffusion of CO2 in the gaseous phase into the concrete pores,
2. Its dissolution in the aqueous film of these pores,
3. The dissolution of solid Ca(OH)2in the water of the pores,
4. The diffusion of dissolved Ca(OH)2in pore water and its reaction with
the dissolved CO2,
• Calcium carbonate is formed by the following reaction which is assumed to
be irreversible.
• Ca2+(aq) + 2(OH¯)(aq) + CO2(aq) CaCO3(s) + H2O
• When Ca(OH)2 is removed from the paste, hydrated CSH, C3S and
C2S will also carbonate.
3CaO·SiO2·3H2O+3CO2 3CaCO3+2SiO2+3H2O 40
41. Factors affecting Concrete Carbonation
• The rate of carbonation depends on porosity (for CO2to Diffuse) &
moisture content of the concrete (for dissolution of solid
Ca(OH)2).
• The diffusivity of CO2 depends upon the pore system of hardened
concrete and the exposure condition.
• The pore system of concrete depends upon the type and the
content of binder, water/binder ratio, and the degree of
hydration.
Thus, the main factors affecting concrete carbonation are:
• Pore system of Hardened Concrete which in turn depends upon
w/c ratio, type of binder, and degree of hydration,
• Relative humidity (for dissolution of Ca(OH)2),
• The concentration of CO2.
Optimal conditions for carbonation occur at a RH of 50% (range 40–
90%).
41
42. Carbonation and Concrete Durability
Carbonation results in a decrease of the porosity making the
carbonated paste stronger. Carbonation is therefore an advantage
in non-reinforced concrete.
However, main consequence of carbonation is the drop in the pH
of the pore solution in the concrete from the standard values
between 12.5 and 13.5, to a value below 9 in the fully carbonated
zones, so that the passive layer that usually covers and protects
the reinforcing steel from corrosion becomes unstable.
Once this layer is destroyed rusting of iron bars and subsequent
expansion of the concrete takes place and durability of concrete
decreases. Hence Carbonation is harmful for reinforced concrete.
42
43. Methods to Measure Carbonation
Measure the concentration of CO2 absorbed by the concrete
specimen by IR Spectrum analysis .
• Measure extent of Carbonation of specimen by spray a pH
indicator mainly Standard solution of 1% phenolphthalein in 70%
ethyl alcohol
• In the noncarbonated region with pH values above 9.2, the
phenolphthalein indicator turns purple-red; and in the carbonated
portion with pH less than 9.2, the solution remained colorless.
43
44. Carbonation depth V/S Compressive strength
The plot shows that concretes with mixed pozollonic
materials (till 30%) are more reliable w.r.t. carbonation
depth as compared to normal concrete or concretes
with only one pozollonic material.
44
45. Carbonation depth for different type of mixes
45
Samples made
with different
mineral
admixures viz
Fly ash and
silica fumes .
Carbonation
test with
conditions of
70% CO2 and
50% RH at 20-
220 C in
carbonation
chamber.
Sample broken
and depth of
carbonation
measured .
46. Conclusions
• As strength increases the carbonation depth values are
decreasing.
• Higher the carbonation depth, lower will be durability.
• 6% replacement by Silica Fume showed significant decrease in
Carbonation Depth, hence is more durable.
• 15% Flyash and 6% silica Fume replacement shows further fall in
carbonation depth values, hence it is even more durable.
• Concrete made by double replacement of cement generally shows
better durability property as compared to single replacement or
no replacement.
46
47. Rebar embedded in fresh concrete is passivated by the high alkaline
environment (pH is in between 12 – 13)
This passivation may be disrupted and initiate corrosion by
(i) the presence of sufficient amount of chloride ions or
(ii) a reduction in alkalinity due to carbonation
Corrosion is an electrochemical process in which both chemical
reactions and flow of electrons/ions are involved
There is a need to understand the mechanism of corrosion process in
RC towards enhancement of the service life
Corrosion of Rebars in Concrete
47
48. Fe Fe2
2e
2
H O 2e
2(OH)
2
1
O2 2
Two separate, however coupled, chemical reactions take place
simultaneously on rebar/steel surface
Anodic reaction
Cathodic reaction
The actual loss of metal in the corrosion processes takes place
near the anodic sites
Fe2+
2
-
Concrete
cover
-Electrons
2
H O
(OH)
O
Porous
concrete
Electrical
current
products
Corrosion
Rebar
Anode Cathode
4Fe(OH)2 O2 2H2O 4Fe(OH)3
2Fe(OH)3 Fe2O3 .H2O 2H2O
Corrosion of Rebars in Concrete
48
Corrosion products
Fe2
2(OH)
Fe(OH)
(Cont’d.)
49. Requirements of a Corrosion Cell
49
Anode Cathode
• Four requirements
Ionic path
Electron path
Elimination of any of the four requirements for the corrosion cell
stops the corrosion reaction
51. Mechanism of Chloride Induced Corrosion
51
Breakdown of
passivity layer
Fe2
2Cl
FeCl2 (soluble in pore solution)
Corrosion of steel
Fe Fe2
2e
(oxidation)
1/2 O2 H2 O 2 e
2(OH)
(reduction)
Formation of rust
Fe2
2(OH)
Fe(OH)2
The actual mechanism of corrosion initiation by chloride ions is not yet
completely known (ACI 222R)
Chlorides react with ferrous oxide (passive layer), and forms a soluble
complex that dissolves in the surrounding solution and does not provide
any protection (Bentur et al., 1998, and Callister 2000)
4Fe(OH)2 O2 2H2O 4Fe(OH)3
2Fe(OH)3 Fe2O3 .H2O 2H2O
52. The parameters that influence the corrosion process are
(i) cover thickness,
(ii) quality of concrete in cover region, and
(iii) surrounding environment
Corrosion in RC – Influencing Parameters
52
Durability of Cover Concrete
53. Importance of Cover Concrete (Covercrete)
53
Cover concrete
(Covercrete)
Core concrete
(Corecrete)
Durability of structural members mainly depends on the
penetration resistance of cover concrete (covercrete)
Covercrete acts as barrier against the ingress of
aggressive substances like chloride ions, carbon dioxide, etc.
Entry of deteriorating agents
2
(moisture, CO , Cl-
, etc.)
54. Diffusion
of oxygen
Concrete
Cover
Anode
Rebar
Resistance
Cathode
O2
CONCRETE
Delaying of Corrosion Process
54
Increased cover thickness
Impermeability (the structure of the concrete is so dense that the
pores are not very well interconnected, the flow of ions and diffusion of
O2 through the pores becomes difficult)
Electrical resistivity (the electrical resistance of concrete is high,
the rate of flow of ions will be low)
55. Common Corrosion Control Measures
55
Corrosion control measures
Good quality concrete with low water-to-cement-ratio and use
of superplasticizers
Provision of adequate cover thickness
Use of epoxy coated and galvanized steel
Concrete coatings
Use of pozzolanas (fly ash, silica fume, rice husk, etc.)
Use of corrosion inhibitors
Use of electrochemical techniques such as cathodic protection,
chloride extraction
Use of stainless steel (very high Cr) that
produces a stable passivating film
56. • Service life refers to the period of time during which a structure meets or
exceeds the minimum requirements set for it.
• Generally, service life can be defined as the period until repair becomes
necessary
• The requirements limiting the service life can be technical, functional or
economical (Sommerville, 1986; ACI 365.1R, 2017)
Service Life of RC Structures
56
Damage
Level
Initiation Phase Propagation Phase Repair Phase
Overall Service Life
Maximum Allowable
Damage Level
Last Repair
Intermediat
e Repairs
First
Repair
Time
Different stages of deterioration in RC structure (Pillai, 2003)
57. Service Life of RC Structures
57
(Cont’d.)
Hence,
service life (years) 𝑡𝑡𝑜𝑡𝑎𝑙 = 𝑡𝑖 + 𝑡𝑠𝑝
where: t = initiation period
i
tsp = propagationperiod
Time
Initiation Propagation
Corrosion
damage
Acceptabledegree
Servicelife
Diffusio
n of Cl-
• Deterioration stages of RC
structure due to rebar corrosion
can be classified into:
(i) initiation,
(ii) stable propagation and
(iii) unstable propagation
• Durability based service can be
expressed into two stages:
(i) initiation stage and
(ii) propagation stage
58. Corrosion Initiation
58
The initiation period (ti) is the time from the construction to the time of
initiation of corrosion.
In other words, in the case of chloride induced corrosion, ti defines the
time it takes for chlorides to penetrate the concrete cover and
accumulate in sufficient quantity (i.e., threshold/critical chloride content,
Clth) at the depth of the embedded rebar to initiate corrosion
Diffusion is the main transport mechanism of chloride ions
59. Durability based Service Life Estimation
59
Corrosion initiation period (ACI 365.1R, 2017, Life-365, 2014)
C(x,t) = Chloride concentration at depth x (or Clth in this case) after time ti, as a % weight of
concrete
Cs = Surface chloride concentration, % weight of concrete
Dc = Chloride ion diffusion coefficient, mm2/year
erf = Gaussian error function, and
x = Depth of rebar from concrete surface or cover thickness, mm
Once the values of Clth, Cs and Dc are available, the time for C(x,t) at the depth of
the rebar to reach Clth gives ti
Stable propagation period (Rodriguez et al 1996)
𝜃(𝑡) = 𝜃(0) − 𝑝(𝑡)
𝑝(𝑡) = 0.0116 ∝ 𝑖𝑐𝑜𝑟𝑟𝑡𝑠𝑝
p(t)”: penetration of corrosion attack (in mm);
Icorr: average corrosion current density (in μA/cm2); 0.0116 is the factor that converts μA/cm2 to mm/year,
α: factor that accounts for highly localized pitting, associated normally with chloride induced corrosion (α = 5
to 10)
& 𝜽(𝒕): initial and final diameter of the rebar (in mm);
𝜽(𝟎)
60. Cements- OPC and PPC
Mix – w/c - 0.57; 0.47 and 0.37
TMT bar of 12mm dia.
Durability based Service Life Estimation for OPC and PPC concretes
60
Quantities (kg) per cubic metre
Concrete cubes, cylinders and U – shaped RC specimens
Diffusion coefficient, Dc and Corrosion current density, icorr
evaluation
w/c Cement Sand Coarse
Aggregates
0.57 300 870 1056
0.47 362 815 1056
0.37 460 732 1056
61. Diffusion Coefficient Test
61
The chloride diffusivity is a parameter reflecting the resistance of the
concrete to chloride ion penetration
The diffusion test has been carried out as per Nordtest Method (NT
Build 355, 1997)
Display unit
Provision for filling
Wire mesh
Plexy
glass
container
container
Concrete test disk
(100 mm dia. and 50 mm thick)
0.25 N
NaOH
0.25 N
NaCl
Power supply
12 V
Diffusion test set-up
63. Apparent Diffusion Coefficient (Dc)
63
Plot between chloride ion concentration and time
10
9
8
7
6
5
4
3
2
1
0
0 20 40 60
Chloride
concentration,
mmol/cm
3
80 100 120 140
time, hours
dc
dt
𝐷𝑐 = 𝛽°
300𝑘𝑇 𝐿𝑉 𝑑𝑐
𝑧𝑒𝑜𝛻𝜑 𝑐𝑜𝐴𝑜 𝑑𝑡
Concrete Apparent diffusion
coefficient, Dc (m2/sec)
OPC-0.57 7.67×10-13
PPC-0.57 3.92×10-13
OPC-0.47 4.40×10-13
PPC-0.47 1.25×10-13
OPC-0.37 2.40×10-13
PPC-0.37 5.20×10-14
64. Accelerated Corrosion Test
64
3.5% NaCl solution
300
Plastic tub
Horizontal beam
Tie rods
300
150
Power supply
unit
Bottom clear cover 20mm
Electric wire
Electric wire
Vertical stub
Cathode plate
Vertical stub
Rebar 12mm dia.
100
Specimens were put in
3.5% NaCl solution
A 10V potential is applied
Exposed for the specified
Durations
𝑖𝑐𝑜𝑟𝑟 =
icorr values are estimated based
on the weight loss
measurements
𝑊𝑖𝐹
𝜋𝑑𝑙𝑊𝑡𝑖
𝑐
W = equivalent weight of steel, ratio of atomic weight of
iron to the valency of iron (27.925 g)
Wl = weight loss in the rebar after 22 days (g)
F = Faraday’s constant (96487 Amp-sec)
l = length of rebar considered (25 cm)
d = diameter of the rebar (1.2 cm)
tic
) = duration of induced corrosion (22 days = 1900800 sec)
65. Concrete icorr
(µA/cm2)
Concrete icorr
(µA/cm2)
OPC-0.57 768 PPC-0.57 289
OPC-0.47 581 PPC-0.47 212
OPC-0.37 500 PPC-0.37 191
Corrosion current density, icorr
65
It was observed that the icorr-values obtained under accelerated conditions
are much higher than those occurring in the field (Andrade et al. (1990) and
González et al. (1995)).
The reported field icorr-values range for OPC concrete: 1 to 3 μA/cm2 in the
case of active corrosion.
The corresponding field icorr-values for concretes with fly ash have been
assumed to vary proportionally to the icorr-values obtained in the accelerated
corrosion tests
𝑐𝑜𝑟𝑟, 𝑋𝐶 𝐹𝑖𝑒𝑙
𝑑
𝑖 =
𝑖𝑐𝑜𝑟𝑟, 𝑋𝐶
𝑖𝑐𝑜𝑟𝑟, 𝑂𝑃𝐶−0.57 𝐿𝑎
𝑏
× 𝑖 𝑐𝑜𝑟𝑟,𝑂𝑃𝐶−0.57 𝐹𝑖𝑒𝑙𝑑
66. Durability based Service Life Estimation
66
Corrosion initiation period:
Concrete Apparent
diffusion
coefficient, Dc
(m2/sec)
ti, in years
x = 20 mm x = 30 mm x = 40 mm x = 60 mm
OPC-0.57 7.67×10-13 2.1 4.8 8.6 19.4
PPC-0.57 3.92×10-13 4.2 9.5 16.8 37.9
OPC-0.47 4.40×10-13 3.8 8.4 15.0 33.8
PPC-0.47 1.25×10-13 13.2 29.7 52.8 118.9
OPC-0.37 2.40×10-13 6.9 15.5 27.5 61.9
PPC-0.37 5.20×10-14 31.7 71.4 127.0 285.7
Apparent diffusion coefficient and estimated corrosion initiation
periods (ti, in years) for different cover thicknesses (x)
67. Durability based Service Life Estimation (Cont’d.)
67
Type of concrete Stable propagation
period (tsp), years
OPC-0.57 8.6
PPC-0.57 23.3
OPC-0.47 12.3
PPC-0.47 28.7
OPC-0.37 14.4
PPC-0.37 43.1
Stable propagation period:
𝑡𝑠𝑝 = 𝑝(𝑡)/0.0116 ∝ 𝑖𝑐𝑜𝑟𝑟
End of the stable propagation period (tsp) is taken to be reached when the
cross-sectional area of the steel rebar has decreased by 10%, in
accordance with CEB (1983) and Andrade et al. (1990).
The pitting factor α has been taken as 6 for both OPC and PPC concretes.
icorr-value of OPC-0.57 concrete = 1 μA/cm2
68. Durability based Service Life Estimation
(Cont’d.)
68
Type of concrete Corrosion initiation
period (ti), years
Stable propagation
period (tsp), years
Service life (ttotal), years
icorr-value of OPC-0.57 concrete = 1 μA/cm2
OPC-0.57 2.1 8.6 10.7
PPC-0.57 4.2 23.3 27.5
OPC-0.47 3.8 12.3 16.1
PPC-0.47 13.2 28.7 41.9
OPC-0.37 6.9 14.4 21.3
PPC-0.37 31.7 43.1 74.8
icorr-value of OPC-0.57 concrete = 5μA/cm2
OPC-0.57 2.1 1.7 3.8
PPC-0.57 4.2 4.6 8.8
OPC-0.47 3.8 2.4 6.2
PPC-0.47 13.2 5.8 19.0
OPC-0.37 6.9 2.8 9.7
PPC-0.37 31.7 8.6 40.3
icorr-value of OPC-0.57 concrete = 10 μA/cm2
OPC-0.57 2.1 0.9 3.0
PPC-0.57 4.2 2.3 6.5
OPC-0.47 3.8 1.2 5.0
PPC-0.47 13.2 2.9 16.1
OPC-0.37 6.9 1.4 8.3
PPC-0.37 31.7 4.3 36.0
Total service live estimates for concretes with different field icorr-values
69. Loss in Rebar Cross Section with Time for
Different Icorr Values
69
(Bhaskar et al., 2015; Jl. of Mat. Civ. Eng.,ASCE)
70. Summary
70
In the above study, durability based service life estimation of RC
structural elements in chloride environment is discussed.
The total service life has been taken as the sum of corrosion
initiation period (ti) and stable propagation period (tsp).
ti and tsp has been estimated based on experimentally obtained
values for diffusion coefficient (Dc) and the estimated field values
of corrosion current density (icorr).
when the icorr-values are low, both ti and tsp contribute significantly
to the total service life. At higher icorr, only ti is significant as tsp
becomes very short.
The service life of PPC based concrete is nearly twice that of the
service life of corresponding OPC based concretes.
71. Laboratory studies
• Laboratory study on different concrete mixtures towards durability
performance in chloride induced environment
• Concretes with OPC and PPC (fly ash based) cements with three
water to cement ratios
71
72. W/b = 0.50 A AF15 AF25 AS15 AS30 AS50
Cement (kg/m3) 340 289 255 289 238 170
Fly ash (kg/m3) -- 51 85 -- -- --
Slag (kg/m3) -- -- -- 51 102 170
Fine aggregate (kg/m3) 819 800 787 819 819 819
Wet density (kg/m3) 2340 2338 2342 1338 2330 2333
Compressive strength
at 7 days 29.29 26.34 24.71 30.05 27.41 23.30
28 days 40.93 35.28 33.53 35.61 38.28 40.03
56 days 44.84 43.52 44.18 44.35 46.17 46.44
90 days 43.52 45.97 45.46 46.09 47.57 48.85
Water absorption (%) 4.91 4.70 4.60 4.65 4.52 4.39
Sorptivity, x 10-5 (m/√s) 1.14 1.47 1.38 1.04 1.09 0.99
Water content 170 lit/m3 and CA 1054 kg/m3
72
73. w/b = 0.42 B BF15 BF25 BS15 BS30 BS50
Cement (kg/m3) 405 345 304 345 283 203
Fly ash (kg/m3) -- 80 101 -- -- --
Slag (kg/m3) -- -- -- 60 122 202
Fine aggregate (kg/m3) 765 742 726 765 765 765
Wet density (kg/m3) 2365 2371 2376 2369 2360 2360
Compressive strength
at 7 days 46.00 43.67 38.77 45.14 43.32 33.23
28 days 53.47 54.80 53.39 54.10 52.84 52.62
56 days 60.33 61.15 61.42 62.95 63.37 64.97
90 days 64.17 66.90 65.87 65.90 68.82 68.89
Water absorption (%) 3.64 3.57 3.49 3.51 3.62 2.90
Sorptivity, x 10-5 (m/√s) 1.00 0.76 0.71 1.01 0.99 0.71
Water content 170 lit/m3 and CA 1054 kg/m3
73
74. w/b= 0.35 C CF15 CF25 CS15 CS30 CS50
Cement (kg/m3) 486 413 365 413 340 243
Fly ash (kg/m3) -- 73 121 -- -- --
Slag (kg/m3) -- -- -- 73 146 243
Fine aggregate (kg/m3) 684 652 631 684 684 684
Wet density (kg/m3) 2417 2393 2397 2411 2402 2415
Compressive strength
at 7 days 63.67 59.95 51.56 60.54 59.60 53.95
28 days 75.07 72.06 65.58 70.08 72.93 75.46
56 days 79.31 76.96 73.00 74.78 77.72 79.36
90 days 79.64 79.01 76.57 80.71 79.91 81.28
Water absorption (%) 3.64 3.55 3.51 3.68 3.49 3.49
Sorptivity, x 10-5 (m/√s) 0.95 0.85 0.81 0.85 0.71 0.62
Water content 170 lit/m3 and CA 1054 kg/m3
74
76. RESULTS OF THE MIXES
Series Cement GGBS Compressive
strength
(MPa)
Flexural
strength
(MPa)
Water
Absorption
(%)
Chloride
permeability
(Coulombs)
OPC Based
AO (40MPa)
BO (60MPa)
CO (70MPa)
300
375
450
--
--
--
41
62
71
4.8
5.3
6.9
3.95
2.83
2.5
2710
2374
2335
GGBS based
(40% CRM)
AS
BS
CS
198
247
310
132
166
206
43
62
69
4.53
5.59
6.20
2.75
2.66
1.79
1610
1291
1202
GGBS based
(70% CRM)
AS
BS
CS
103
131
161
241
300
375
40
59
67
4.40
5.20
6.30
- 2.35
-
- 907
-
76
77. Investigations
• Laboratory study on different concrete mixtures towards durability
performance in chloride induced environment
• Concretes with OPC and PPC (fly ash based) cements with three
water to cement ratios (w/c = 0.55, 0.45 and 0.35)
77
78. Sample/Specimen Test
150×150×150mm Compressive strength test
150×150×150mm German water permeability test
150×150×150mm Din water penetration test
100×50mm Rapid chloride penetration test
100×50mm Rapid chloride migration test
100×50mm Water sorptivity test
Sample details
78
79. 100 mm
50 mm
Wire mesh
4±1mm Water level above the
bottom surface of the specimen
Water
Supports
PVC Container
Specimens
Sorptivity Test
In unsaturated concrete, the rate of ingress of water or
other liquids is largely controlled by absorption due to
capillary rise.
Sorptivity is the measure of the rate of absorption of
water by capillary suction/rise
79
80. Germann Water Permeability Test
Germann Water Permeability Test (GWPT) is used for testing the concrete
permeability on-site or in laboratory
-A sealed pressure chamber is attached to the concrete surface
-Specified water pressure is established by turning an adjustable screw
-Pressure is kept constant using the micro meter gauge screw
Coefficient of water permeability,
m2/sec
Quality
< 10-12 and above Good
10-12 and 10-10 Normal
> 10-10 Poor
Ref.: RILEM TC 230-PSC
80
81. The test specimen is wet cured for 28 days
After 28 days of curing, test specimen is fitted into the machine frame
Apply bar pressure (0.5 MPa or 5 bar) for required time duration (3
days)
After the test duration, split the specimen into two halves
Measure the penetration depth of water
The maximum value of water penetration is the permeability of
concrete
DIN Water Permeability Test
The test is used to determine the penetration
depth of pressurized water into a concrete
sample
81
82. Rapid Chloride Permeability Test (RCPT)
3%
NaCl
0.3N
NaOH
Concrete test disk
Plexiglass
container
(100 mm dia.x50 mm thick)
Wire mesh
Provision for filling
container
Power supply
60V
Display unit
Charge Passed
(coulombs)
Chloride Permeability
> 4,000 High
2,000 – 4,000 Moderate
1,000 – 2,000 Low
100 – 1,000 Very Low
< 100 Negligible
RCPT as per ASTM C 1202
Total amount of charge passed is used to
predict chloride ion permeability or quality
Measurement of electrical conductivity
Charge passed is related to all ions in
pore solution
High voltage may lead to increase in
temp.
Addition of admixtures may alter pore
solution characteristics
Diffusivity of concrete - No
82
83. 90-day Salt ponding test (SPT)
3% NaCl ; 15mm
depth
Diffusion is the dominant mechanism
Specimen coats on sides only
90-day testing, longer time
High performance /low w/c take still longer duration
Powder samples at various depth intervals
14 days moist curing and
28 days drying
Transport mechanisms such as sorption and wicking action may also be present
83
84. Bulk diffusion test
Diffusion is the dominant mechanism
35 day testing, may go for longer durations
Specimen coated all three sides
Powder samples at various depth intervals
Error function solution of Fick’s second law is used to find the diffusion
and surface chloride concentration
84
85. 0.3N NaOH
10% NaCl
Applied voltage
and duration varies
Accelerated test; dominant mechanism is chloride migration
Accounts concrete resistance; applied voltage and test duration varies
accordingly
Test results are less affected by the presence of admixtures
Chloride penetration depth – migration coefficient using Fick’s II law
(needs chloride concentration at c/c boundary)
Rapid Migration Test or Accelerated Chloride Migration Test
(NT BUILD 492)
85
86. Chloride Penetration Depth and Migration Coefficient
PSC
PPC
OPC
The chloride ion penetration depths are 40mm, 28mm and 17mm,
respectively for OPC, PPC and PSC concretes
The non-steady-state migration coefficients are found to be 30.1×10-12
m2/sec, 11.3×10-12 m2/sec and 6.1×10-12 m2/sec,
PSC concrete is more durable in terms of resistance to chloride ion
penetration
86
88. Test results - Durability parameters (Cont’d.)
Moderate
Low
Very Low
Chloride ion permeability as per RCPT (ASTM C 1202)
High
Poor
Normal
Good
Very good
Concrete quality as per
RCMT (Bjegovic et al. (2015))
88
89. Performance specification –RCMT & RCPT
Age at testing: 28 & 56 days
Quality limits based on RCPT and RCMT – Transport mechanism: Migration
E-Excellent V-Very good G-Good P-Poor
RCPT (Coulombs) 100-1000 1000-2000 2000-4000 >4000
RCMT (×10-12 m2/s) 2-8 2-8 8-16 >16
89
90. Excellent Very good Good Poor
PPC 0.35-56d PPC 0.35-28d OPC 0.35-28d OPC 0.55-28d
PPC 0.45-56d PPC 0.45-28d OPC 0.45-28d
PPC 0.55-56d OPC 0.35-56d OPC 0.45-56d
OPC 0.55-56d
PPC 0.55-28d
Performance specification –Different Mixes
Age at testing: 28 & 56 days
For chloride induced environment
-based on performance specification of RCPT and RCMT parameters Transport
mechanism: Migration
90
91. Performance specification –RCMT & GWPT
Age at testing: 28 & 56 days
E- Excellent V- Very good G - Good P - Poor
RCMT (×10-12 m2/s) 2-8 2 - 8 8-16 >16
GWPT (×10-4 mm/s)
<0.5 0.5 - 1 1 - 2 >2
Proposed quality limits based on RCMT & GWPT
– Transport mechanism: Migration & permeation
91
92. Excellent Very good Good Poor
PPC 0.35-56d PPC 0.35-28d OPC 0.35-28d OPC 0.55-28d
PPC 0.45-56d OPC 0.35-56d OPC 0.45-56d
PPC 0.55-56d OPC 0.45-28d
PPC 0.45-28d
PPC 0.55-28d
OPC 0.55-56d
For chloride induced environment
- based on performance specification of RCPT and
GWPT parameters Transport mechanism: Migration & permeation
Performance specification –Different Mixes Age at
testing: 28 & 56 days
92
95. Interpenetrating polymer network (IPN) is a novel type of
polymer hybrids, which possess physicochemical properties
suitable for high per- formance coatings. Heat-resistant IPN have
been prepared from immiscible resins, epoxy and silicones using a
cross-linking agent and a catalyst
95
