semi destructive tests on concrete _Imran_bk

SEMI DESTRUCTIVE TESTS ON CONCRETE
REHABILITATION AND RETROFITTING OF STRUCTURES (15CV753)
MODULE 2 : DAMAGE ASSESSMENT
Topic : SEMI DESTRUCTIVE TESTS ON CONCRETE
CBCS 2015
PROF. MOHAMMED AYYAD
DEPT. OF CIVIL ENGINEERING
AITM,BHATKAL
STUDENT: IMRAN BK (2AB16CV402)
DEPT. OF CIVIL ENGINEERING
AITM,BHATKAL
Keywords—Damage assessment, semi destructive tests on
concrete, tests on concrete
I. INTRODUCTION
This paper consists of various methods of semi
destructive tests on concrete.
II. METHODS
The different types of semi destructive test are as follow :
1. Core Sampling Test
2. Permeability Test
3. Carbonation Test
4. Resistivity Test
5. Half cell electrical potential method
6. Pull out &Pull off test
7. Abrasion resistance Test
8. Chloride content Test
9. Penetration test
10. Breakoff Test
1. Core sampling Test
concrete cores are used for testing of actual properties of
concrete in existing structures such as strength, permeability,
chemical analysis, carbonation etc. Sampling of concrete
cores and testing its strength is described.
1.1 Core Sampling and Testing of Concrete
Concrete cores are usually cut by means of a rotary
cutting tool with diamond bits. In this manner, a cylindrical
specimen is obtained usually with its ends being uneven,
parallel and square and sometimes with embedded pieces of
reinforcement.
The cores are visually described and photographed,
giving specific attention to compaction, distribution of
aggregates, presence of steel etc.
The core should then be soaked in water, capped with
molten sulphur to make its ends plane, parallel, at right angle
and then tested in compression in a moist condition as per BS
1881: Part 4: 1970 or ASTM C 42-77.
1.2 The core samples can also be used for the following:
o Strength and density determination
o Depth of carbonation of concrete
o Chemical analysis
o Water/gas permeability
o Petrographic analysis
o ASHTO Chloride permeability test
The strength of a concrete core test specimen depends on
its shape, proportions and size. The influence of
height/diameter (H/D) ratio on the recorded strength of
cylinder is an established fact.
Strength of core have to be related to the standard cylinder
strengths, i.e. for H/D ratio of 2. Thus core should be
preferably have this ration near to 2.
For values of H/D less than 1, between 1 and 2, a
correction factor has to be applied. Cores with H/D ratio less
than 1 yield unreliable results and BS 1881: Part-4:1970
prescribes a minimum value as 0.95. The same standard
specifies the use of 150mm or 100mm cores. However, cores
as small as 50mm are also permitted in the standards.
Very small diameter cores exhibit more variability in
results than larger diameter cores, hence their use is
generally not recommended.
The general rule adopted for fixing the core size, besides
the H/D ratio, is the nominal size of stone aggregate and the

dia should be not less than 3 times the maximum size of
stone aggregate. For diameter of core less than 3 times the
size of the stone aggregate, an increased number of cores
have to be tested.
1.3 Factors Affecting Strength of Concrete Cores
Following are the factors which affect the compressive
strength of extracted concrete cores:
1.3.1 Size of stone aggregate
If the ratio of diameter of core to maximum size of stone
aggregate is less than 3, a reduction in strength is reported.
For concrete with 20mm size aggregate, 50mm dia core has
been tested to give 10% lower results than with 10mm dia
cores.
2 Presence of transverse reinforcement steel
It is reported that the presence of transverse steel causes a
5 to 15% reduction in compressive strength of core. The
effect of embedded steel is higher on stronger concrete and
as its location moves away from ends, i.e. towards the
middle. However presence of steel parallel to the axis of the
core is not desirable.
3 H/D ratio
This has been already discussed above. However its
value should be minimum 0.95 and maximum 2. Higher ratio
would cause a reduction in strength
4 Age of concrete
No age allowance is recommended by the Concrete
Society as some evidence is reported to suggest that in-situ
concrete gains little strength after 28 days. Whereas others
suggest that under average conditions, the increase over 28
days‟ strength is 10% after 3 months, 15% after 6 months.
Hence it is not easy to deal the effect of age on core strength.
5 Strength of concrete
The effect in reducing the core strength appears to be
higher in stronger concretes and reduction has been reported
as 15% for 40 MPa concrete. However a reduction of 5 50
7% is considered reasonable.
6 Drilling operations
The strength of cores is generally less than that of
standard cylinders, partly as a consequence of disturbance
due to vibrations during drilling operations. Whatever best
precautions are taken during drilling, there is always a risk of
slight damage.
7 Site conditions vis-a-vis standard specimens
Because site curing is invariably inferior to curing
prescribed for standard specimens, the in-situ core strength is
invariably lower than the standard specimens taken and
tested during concreting operations.
2. Permeability test
2.1 FUNDAMENTAL PRINCIPLE
Permeability of concrete is important when dealing
with durability of concrete particularly in concrete
used for water retaining structures or watertight
sub-structures.
Structures exposed to harsh environmental
conditions also require low porosity as well as
permeability. Such adverse elements can result in
degradation of reinforced concrete, for example,
corrosion of steel leading to an increase in the
volume of the steel, cracking and eventual spalling
of the concrete. Permeability tests measure the ease
with which liquids, ions and gases can penetrate
into the concrete. In situ tests are available for
assessing the ease with which water, gas and
deleterious matter such as chloride ions can
penetrate into the concrete.
2.2.TYPE OF PERMEABILITY TEST
2.3.1. Initial surface absorption test
Details of the ISAT is given in BS 1881:Part 5
which measures the surface water absorption. In
this method, a cup with a minimum surface area of
5000 mm2 is sealed to the concrete surface and
filled with water. The rate at which water is
absorbed into the concrete under a pressure head of
200 mm is measured by movement along a
capillary tube attached to the cup. When water
comes into contact with dry concrete it is absorbed
by capillary action initially at a high rate but at a
decreasing rate as the water filled length of the
capillary increases. This is the basis of initial
surface absorption, which is defined as the rate of
water flow into concrete per unit area at a stated
interval from the start of test at a constant applied
head at room temperature.
2.3.2. Modified Figg permeability test
The modified Figg permeability test can be used to
determine the air or water permeability of the
surface layer of the concrete. In both the air and
water permeability test a hole of 10 mm diameter is
drilled 40 mm deep normal to the concrete surface.
A plug is inserted into this hole to form an airtight
cavity in the concrete. In the air permeability test,
the pressure in the cavity is reduced to –55 kPa
using a hand operated vacuum pump and the pump
is isolated. The time for the air to permeate through
the concrete to increase the cavity pressure to –50
kPa is noted and taken as the measure of the air
permeability of the concrete.
Water permeability is measured at a head of 100
mm with a very fine canula passing through a
hypodermic needle to touch the base of the cavity.
A two-way connector is used to connect this to a
syringe and to a horizontal capillary tube set 100
mm above the base of the cavity.
Water is injected through the syringe to replace all
the air and after one minute the syringe is isolated
with a water meniscus in a suitable position. The
time for the meniscus to move 50 mm is taken as a
measure of the water permeability of the concrete.

2.3.3. In situ rapid chloride ion permeability test
This method was originally designed for laboratory
application but has been modified for in situ use. The
procedure for the laboratory test is given in AASHTO T277
and ASTM
C1202. The technique is based on the principle that charged
ions, such as chloride (Cl- ), will accelerate in an electric
field towards the pole of opposite charge. The ions will
reach terminal velocity when the frictional resistance of the
surrounding media reaches equilibrium with the accelerating
force. This is the basis of “electrophoresis”, which is
utilized in many chemical and biological studies.
A DC power supply is used to apply a constant voltage
between the copper screen and the steel reinforcement. The
total current flowing between the mesh and the reinforcing
bar over a period of six hours is then measured. The total
electric charge (in coulombs) is computed and can be related
to the chloride ion permeability of the concrete.
2.3. APPLICATIONS OF PERMEABILITY TEST
The methods described do not measure permeability directly
but produce a „permeability index‟, which is related closely
to the method of measurement. In general, the test method
used should be selected as appropriate for the permeation
mechanism relevant to the performance requirements of the
concrete being studied. Various permeation mechanisms
exist depending on the permeation medium, which include
absorption and capillary effects, pressure differential
permeability and ionic and gas diffusion.
Most of these methods measure the permeability or porosity
of the surface layer of concrete and not the intrinsic
permeability of the core of the concrete. The covercrete has
been known to significantly affect the concrete durability
since deterioration such as carbonation and leaching starts
from the concrete surface. This layer thus provides the first
defense against any degradation.
Guidelines on the different categories of permeability are
given in Table.
2.4. RANGE AND LIMITATIONS OF
PERMEABILITY TEST
For the ISAT, tests on oven dried specimens give reasonably
consistent results but in other cases results are less reliable.
This may prove to be a problem with in situ concrete.
Particular difficulties have also been encountered with in
situ use in achieving a watertight fixing. The test has been
found to be very sensitive to changes in quality and to
correlate with observed weathering behaviour. The main
application is as a quality control test for precast units but
application to durability assessment of in situ concrete is
growing.
The main difficulty in the modified permeability test is to
achieve an air or watertight plug.
The electrical properties of concrete and the presence of
stray electric fields affect the rapid chloride permeability
test results. Some concrete mixes that contain conductive
materials, e.g. some blended cements, in particular, slag
cement, may produce high chloride ion permeability though
such concrete is known to be very impermeable and dense.
The test is also affected by increases in temperature during
measurements. However, reasonably good correlation has
been obtained between this technique and the traditional 90
day ponding test (AASHTO T259) in the laboratory.
3. Carbonation Test
3.1. FUNDAMENTAL PRINCIPLE
Carbonation of concrete occurs when the carbon dioxide, in
the atmosphere in the presence of moisture, reacts with
hydrated cement minerals to produce carbonates, e.g.
calcium carbonate. The carbonation process is also called
depassivation. Carbonation penetrates below the exposed
surface of concrete extremely slowly. The time required for
carbonation can be estimated knowing the concrete grade
and using the following equation:
where
t is the time for carbonation,
d is the concrete cover,
k is the permeability.
Typical permeability values are shown in Table
The significance of carbonation is that the usual protection
of the reinforcing steel generally present in concrete due to
the alkaline conditions caused by hydrated cement paste is
neutralized by carbonation. Thus, if the entire concrete
cover over the reinforcing steel is carbonated, corrosion of
the steel would occur if moisture and oxygen could reach
the steel.
3.2. EQUIPMENT FOR CARBONATION DEPTH
MEASUREMENT TEST
If there is a need to physically measure the extent of
carbonation it can be determined easily by spraying a
freshly exposed surface of the concrete with a 1%
phenolphthalein solution. The calcium hydroxide is
coloured pink while the carbonated portion is uncoloured.
3.3. GENERAL PROCEDURE FOR CARBONATION
DEPTH MEASUREMENT TEST
The 1% phenolthalein solution is made by dissolving 1gm
of phenolthalein in 90 cc of ethanol. The solution is then

made up to 100 cc by adding distilled water. On freshly
extracted cores the core is sprayed with phenolphthalein
solution, the depth of the uncoloured layer (the carbonated
layer) from the external surface is measured to the nearest
mm at 4 or 8 positions, and the average taken. If the test is
to be done in a drilled hole, the dust is first removed from
the hole using an air brush and again the depth of the
uncoloured layer measured at 4 or 8 positions and the
average taken. If the concrete still retains its alkaline
characteristic the colour of the concrete will change to
purple. If carbonation has taken place the pH will have
changed to 7 (i.e. neutral condition) and there will be no
colour change.
Another formula, which can be used to estimate the depth of
carbonation, utilizes the age of the building, the water-to-
cement ratio and a constant, which varies depending on the
surface coating on the concrete.
3.4. RANGE AND LIMITATIONS OF CARBONATION
DEPTH MEASUREMENT TEST
The phenolphthalein test is a simple and cheap method of
determining the depth of carbonation in concrete and
provides information on the risk of reinforcement corrosion
taking place. The only limitation is the minor amount of
damage done to the concrete surface
by drilling or coring.
4. Resistivity measurement Test
4.1. FUNDAMENTAL PRINCIPLES
There are many techniques used to assess the corrosion risk
or activity of steel in concrete. The most commonly used is
the half cell potential measurement that determines the risk
of corrosion activity. Whilst the half cell potential
measurement is effective in locating regions of corrosion
activity, it provides no indication of the rate of corrosion.
However, a low resistance path between anodic and
cathodic sites would normally be associated with a high
rate of corrosion than a high resistance path. Such resistivity
measurements determine the current levels flowing between
anodic and cathodic portions, or the concrete conductivity
over the test area, and are usually used in conjunction with
the half-cell potential technique. This is an electrolytic
process as a consequence of ionic movement in the aqueous
pore solution of the concrete matrix. An alternative
technique to estimate the rate of corrosion, which is
becoming increasingly popular, is the linear polarization
resistance.
4.2. EQUIPMENT
Although other commercial devices like the less accurate
two probe system are also available, the Wenner four probe
technique is generally adopted for resistivity measurement
of in situ concrete. The technique was first used by
geologists to investigate soil strata. The technique can be
used to determine resistivities quickly and with little or no
damage to the concrete structures under study, Fig.
FIG. 4.1. Schematic of Wenner 4 probe resistivity meter.
The equipment consists of four electrodes (two outer current
probes and two inner voltage probes) which are placed in a
straight line on or just below the concrete surface at equal
spacings. A low frequency alternating electrical current is
passed between the two outer electrodes whilst the voltage
drop between the inner electrodes is measured. The apparent
resistivity (ρ) in “ohm-cm” may be expressed as:
ρ = 2πaV/I (12)
where
V is voltage drop,
I is applied current,
a is electrode spacing.
The calculation assumes the concrete to be homogeneous
and the inhomogeneity caused by the reinforcement network
must be allowed for by properly placing the probes to
minimize
its effect.
4.3. GENERAL PROCEDURE
Resistivity measurement is a fast, simple and cheap in situ
non-destructive method to obtain information related to the
corrosion hazard of embedded reinforcement.
The spacing of the four probes determines the regions of
concrete being measured. It is generally accepted that for
practical purposes, the depth of the concrete zone affecting
the measurement will be equal to the electrode spacing. If
the spacing is too small, the presence or absence of
individual aggregate particles, usually having a very high
resistivity, will lead to a high degree of scatter in the
measurement. Using a larger spacing may lead to
inaccuracies due to the current field being constricted by the
edges of the structure being studied. In addition, increased
error can also be caused by the influence of the embedded
steel when larger spacings are employed. A spacing of 50
mm is commonly adopted, gives a very small degree of
scatter and allows concrete sections in excess of 200 mm
thick to be measured with acceptable accuracy.
The efficiency of surface coupling is also important. In
order to establish satisfactory electrical contact between the
probes and the concrete, limited damage to the concrete
surface sometimes can not be avoided. In some commercial
devices, wetting or conductive gel is applied when the

probes are pushed against the concrete surface to get better
contact.
Prewetting of the surface before measurement is also
advised. Small shallow holes may also be drilled into the
concrete which are filled with a conductive gel. The probes
are then dipped into each hole. However, this procedure is
not practical for site use.
4.4. APPLICATIONS
The ability of corrosion currents to flow through the
concrete can be assessed in terms of the electrolytic
resistivity of the material. This resistivity can determine the
rate of corrosion once reinforcement is no longer passive.
The presence of ions such as chloride will also have an
effect. At high resistivity, the rate of corrosion can be very
low even if the steel is not passive. For example,
reinforcement in carbonated concrete in an internal
environment may not cause cracking or spalling due to the
very low corrosion currents flowing.
The electrical resistivity of concrete is known to be
influenced by many factors including moisture, salt content,
temperature, water/cement ratio and mix proportions. In
particular, the variations of moisture condition have a major
influence on in situ test readings.
Fortunately, in practice, the moisture content of external
concrete does not vary sufficiently to significantly affect the
results. Nevertheless, precautions need to be taken when
comparing results of saturated concrete, e.g. those exposed
to sea water or measurements taken after rain showers, with
those obtained on protected concrete surfaces. Another
important influence is the ambient temperature. Concrete
has electrolytic properties; hence, resistivity will increase as
temperature decreases. This is particularly critical when
measurements are taken during the different seasons, with
markedly higher readings during the winter period than the
summer period.
The principle application of this measurement is for the
assessment of the corrosion rate and it is used in conjunction
with other corrosion tests such as the half-cell potential
measurement or linear polarization measurement methods.
There are no generally accepted rules relating resistivity to
corrosion rate. However, a commonly used guide has been
suggested for the interpretation of measurements of the
likelihood of significant corrosion for non-saturated
concrete where the steel is activated, see Table .
In practice, it is necessary to calibrate the technique, either
through exposing the steel to assess its condition, or by
correlating the resistivity values with data collected with
other techniques. For instance, the values given in Table 8.1
apply when the half-cell potential measurement shows that
corrosion is possible.
5. Half cell electrical potensial method
5.1. FUNDAMENTAL PRINCIPLE
The method of half-cell potential measurements normally
involves measuring the potential of an embedded
reinforcing bar relative to a reference half-cell placed on the
concrete surface. The half-cell is usually a copper/copper
sulphate or silver/silver chloride cell but other combinations
are used. The concrete functions as an electrolyte and the
risk of corrosion of the reinforcement in the immediate
region of the test location may be related empirically to the
measured potential difference. In some circumstances,
useful measurements can be obtained between two half-cells
on the concrete surface. ASTM C876 - 91 gives a Standard
Test Method for Half-Cell Potentials of Uncoated
Reinforcing Steel in Concrete.
5.2. EQUIPMENT FOR HALF-CELL ELECTRICAL
POTENTIAL METHOD
The testing apparatus consists of the following (Fig. 5.1):
FIG. 5.1. A copper-copper sulphate half-cell.
Half-cell: The cell consists of a rigid tube or container
composed of dielectric material that is non-reactive with
copper or copper sulphate, a porous wooden or plastic plug
that remains wet by capillary action, and a copper rod that is
immersed within the tube in a saturated solution of copper
sulphate. The solution is prepared using reagent grade
copper
sulphate dissolved to saturation in a distilled or deionized
water.
5.3. GENERAL PROCEDURE FOR HALF-CELL
ELECTRICAL POTENTIAL METHOD
Measurements are made in either a grid or random pattern.
The spacing between measurements is generally chosen
such that adjacent readings are less than 150 mV with the
minimum spacing so that there is at least 100 mV between
readings. An area with greater than
150 mV indicates an area of high corrosion activity. A direct
electrical connection is made to the reinforcing steel with a
compression clamp or by brazing or welding a protruding
rod. To get a low electrical resistance connection, the rod
should be scraped or brushed before connecting it to the

reinforcing bar. It may be necessary to drill into the concrete
to expose a reinforcing bar. The bar is connected to the
positive terminal of the voltmeter. One end of the lead wire
is connected to the half-cell and the other end to the
negative terminal of the voltmeter. Under some
circumstances the concrete surface has to be pre-wetted with
a wetting agent. This is necessary if the half-cell reading
fluctuates with time when it is placed in contact with the
concrete. If fluctuation occurs either the whole concrete
surface is made wet with the wetting agent or only the spots
where the half-cell is to be placed. The electrical half-cell
potentials are recorded to the nearest 0.01 V correcting for
temperature if the temperature is outside the range 22.2 ±
5.5oC.
Measurements can be presented either with a equipotential
contour map which provides a graphical delineation of areas
in the member where corrosion activity may be occurring or
with a cumulative frequency diagram which provides an
indication of the magnitude of affected area of the concrete
member.
Equipotential contour map: On a suitably scaled plan view
of the member the locations of the half-cell potential values
are plotted and contours of equal potential drawn through
the points of equal or interpolated equal values. The
maximum contour interval should be 0.10 V.
An example is shown in Fig. 6.2.
FIG. 5.2. Equipotential contour map.
Cumulative frequency distribution: The distribution of the
measured half-cell potentials for the concrete member are
plotted on normal probability paper by arranging and
consecutively numbering all the half-cell potentials in a
ranking from least negative potential to greatest negative
potential. The plotting position of each numbered half-cell
potential is determined by using the following equation.
The ordinate of the probability paper should be labeled
“Half-cell potential (millivolts, CSE)” where CSE is the
designation for copper-copper sulphate electrode. The
abscissa is labeled “Cumulative frequency (%)”. Two
horizontal parallel lines are then drawn intersecting the –
200mv and –350mv values on the ordinate across the chart,
respectively. After the half-cell potentials are plotted, a line
is drawn through the values. The potential risks of corrosion
based on potential difference readings are shown in Table
5.1.
Table 5.1 RISK OF CORROSION AGAINST THE
POTENTIAL DIFFERENCE READINGS
5.4. APPLICATIONS OF HALF-CELL ELECTRICAL
POTENTIAL TESTING METHOD
This technique is most likely to be used for assessment of
the durability of reinforced concrete members where
reinforcement corrosion is suspected. Reported uses include
the location of areas of high reinforcement corrosion risk in
marine structures, bridge decks and abutments. Used in
conjunction with other tests, it has been found helpful when
investigating concrete contaminated by salts.
5.5. RANGE AND LIMITATIONS OF HALF-CELL
ELECTRICAL POTENTIAL
INSPECTION METHOD
The method has the advantage of being simple with
equipment also simple. This allows an almost non-
destructive survey to be made to produce isopotential
contour maps of the surface of the concrete member. Zones
of varying degrees of corrosion risk may be identified from
these maps.
The limitation of the method is that the method cannot
indicate the actual corrosion rate.
It may require to drill a small hole to enable electrical
contact with the reinforcement in the member under
examination, and surface preparation may also be required.
It is important to recognize that the use and interpretation of
the results obtained from the test require an experienced
operator who will be aware of other limitations such as the
effect of protective or decorative coatings applied to the
concrete.
6. Pull out tests
Types of Pull Out Tests:
Depending upon the placement of disc/ring in he fresh
concrete, pull out test can be divided into 2 types,

a. LOK test
b. CAPO test (Cut and Pull out Test)
The LOK-TEST system is used to obtain a reliable
estimate of the in-place strength of concrete in newly cast
structures in accordance with the pullout test method
described in ASTM C900, BS 1881:207, or EN 12504-3.
A steel disc, 25 mm in diameter at a depth of 25 mm, is
pulled centrally against a 55 mm diameter counter pressure
ring bearing on the surface. The force F required to pullout
the insert is measured. The concrete in the strut between the
disc and the counter pressure ring is subjected to a
compressive load. Therefore the pullout force F is related
directly to the compressive strength.
LOK Test Process. H indicated the highest pullout force.
o CAPO test (Cut and Pull out Test)
The CAPO-TEST permits performing pullout tests on
existing structures without the need of preinstalled inserts.
CAPO-TEST provides a pullout test system similar to the
LOK-TEST system for accurate on-site estimates
of compressive strength. Procedures for performing post-
installed pullout tests, such as CAPO-TEST, are included in
ASTM C900 and EN 12504-3.
Cut and Pull out Test
When selecting the location for a CAPO-TEST, ensure
that reinforcing bars are not within the failure region. The
surface at the test location is ground using a planing tool and
a 18.4 mm hole is made perpendicular to the surface using a
diamond-studded core bit. A recess (slot) is routed in the
hole to a diameter of 25 mm and at a depth of 25 mm.
CAPO Test on Concrete Slab
Relationship between the pullout force and
compressive strength:
The relationship between the pullout force Fu in kN and
compressive strength Fc in MPa is given below,
Typical Pull out Force Calibration Chart
By measuring the pull-out force of a cast-in disc or
expanded ring, the compressive strength of in-situ concrete

can be determined from the relationship in fig.4 to a great
degree of confidence.
Pull off force compressive strength relationship
The pullout test produces a well defined in the concrete
and measure a static strength property of concrete. The
equipment is simple to assemble and operate.
The compressive strength can be considered as
proportional to the ultimate pullout force. The reliability of
the test is reported as good. It is superior to rebound hammer
and Windsor probe test because of greater depth of concrete
volume tested. However this test is not recommended for
aggregates beyond size of 38mm.
The major limitation of this test is that it requires special
care at the time of placement of inserts to minimize air void
below the disc besides a pre-planned usage.
Uses:
1. Determine in-situ compressive strength of the
concrete
2. Ascertain the strength of concrete for carrying out
post tensioning operations.
3. Determine the time of removal of forms and shores
based on actual in-situ strength of the structure.
4. Terminate curing based on in-situ strength of the
structure.
5. It can be also used for testing repaired concrete
sections.
Post Test Process:
After the concrete has fractured by this test, the holes left
in the surface are first cleaned of the dust by a blower. It is
then primed with epoxy glue and the hole is filled with a
polymer-modified mortar immediately thereafter and the
surface is smoothened.
7. Abrasion test
There are different test methods to determine the abrasion
resistance of concrete subjected to number of various types
of abrasion. There are number of different tests used in
various countries and it is clear that there is no single test
that adequately measures the abrasion resistance of concrete
under all conditions.
7.1 Test Method for Abrasion Resistance of Concrete
by Sand Blasting (ASTM C 418)
This test method is based on the principle of producing
abrasion by sandblasting (Fig. 1). This procedure simulates
the action of waterborne particles and abrasives under traffic
on concrete surface. Controlling the pressure and the type of
abrasive allows the researcher to vary the severity of
abrasion. The blast cabinet is equipped with an injector type
blast gun with high velocity air jet (Figure 1.). The adjusting
parameters are gradation of sand, air pressure, rate of feed of
the abrasive charge and distance of the nozzle from the
surface.
7.2 Test Method for Obtaining and Testing Drilled Cores
and Sawed Beams of Concrete (ASTM C 944)
ASTM test method for abrasion resistance of concrete by
drilled cores and sawed beams of concrete gives an
indication of the relative abrasion resistance of mortar and
concrete based on testing of cored or fabricated specimens.
The test apparatus consists of rotating cutter and drill press
(Figure 2.). The difficulty in maintaining a constant load on
the abrading cutter when using the lever, gear and spring
system of a drill press has been eliminated by placing a
constant load of 98 N directly upon the spindle that turns the
cutter.
7.3 Test Method for Abrasion Resistance Of Concrete –
Underwater Method (ASTM C 1138)
ASTM Test method for abrasion resistance of concrete
(Underwater method) was originally developed by Liu
in 1980 for evaluating the resistance of concrete surface
subjected to abrasion action of water particles on
hydraulic structures such as stilling basin, spillways etc.
The apparatus consists of essentially a drill press, an

agitation paddle, a cylindrical steel container and 70
steel grinding balls of various sizes. Figure 6 shows the
cross section view of the test apparatus. The water in
the container is circulated by the immersion of agitation
paddle that is powered by drill press rotating at a speed
of 1200 rpm. The circulating water, in turn, moves the
abrasive charges on the surface on the concrete
specimen, producing the abrasion effects. The standard
test consists of six 12 hours test periods for a total of 72
hours.
8. Chloride content test
Chloride Content Test on Concrete Structures
Chloride content can be determined from broken samples or
core samples of concrete. Primarily the level of chloride
near the steel-concrete interface is of prime importance.
Chloride present in concrete are fixed (water insoluble) as
well as free (water soluble).
Though it is the water soluble chloride ions, which are
important from corrosion risk point of view, yet total acid
soluble (fixed as well as free) chloride contents are
determined and compared with limiting values specified for
the concrete to assess the risk of corrosion in concrete.
The total acid soluble chloride are determined in accordance
with IS:14959 Part – III – 2001, whereas for assessment of
water soluble chlorides the test consists of obtaining the
water extracts, and conducting standard titration experiment
for determining the water soluble chloride content and is
expressed by water soluble chloride expressed by weight of
concrete or cement.
The method gives the average chloride content in the cover
region. Further a chloride profile across the cover thickness
will be a more useful measurements as this can help to make
a rough estimate on chloride content diffusion rate.
One recent development for field testing of chloride content
includes the use of chloride ion sensitive electrode. This is
commercially known as “Rapid Chloride test kit-4”.
The test consists of obtaining powdered samples by drilling
and collecting them from different depths (every 5mm),
mixing the sample (of about 15.g weight) with a special
chloride extraction liquid, and measuring the electrical
potential of the liquid by chloride-ion selective electrodes.
With the help of a calibration graph relating electrical
potential and chloride content, the chloride content of the
samples can be directly determined.
Based on the chemical analysis, corrosion-prone locations
can be identified as per the guidelines given in table-below.
9. Penetration test
Windsor Probe is penetration resistance measurement
equipment, which consists of a gun powder actuated driver,
hardened alloy of probe, loaded cartridges, a depth gauge
and other accessories. In this technique a gunpowder
actuated driver is used to fire a hardened alloy probe into the
concrete. During testing, it is the exposed length of probe
which is measured by a calibration depth gauge. But it is
preferable to express the coefficient of variation in terms of
depth of penetration as the fundamental relation is between
concrete strength and penetration depth.
The probe shown in fig.1 has a diameter of 6.3mm, length of
73mm and conical point at the tip. The rear of the probe is
threaded and screwed into a probe-driving head, which is
12.6mm in diameter and fits snugly along with a rubber
washer into the bore of the driver. As the probe penetrates
into the concrete, test results are actually not affected by
local surface conditions such as texture and moisture
content. However damage in the form of cracking may be
cause to slender members. A minimum edge distance and
member thickness of 150mm is required. It is important to
leave 50mm distance from the reinforcement present in the
member since the presence of reinforcing bars within the
zone of influence of penetrating probe affects the
penetration depth.
A pin penetration test device (PNR Tester) which requires
less energy than the Windsor Probe system is given in fig.

Being a low energy device, sensitivity is reduced at higher
strengths. Hence it is not recommended for testing concrete
having strength above 28 N/sq.mm. in this a spring-loaded
device, having energy of about 1.3% of that of Windsor
probe, us used to drive 3.56mm diameter, a pointed
hardened steel pin into the concrete. The penetration of pin
creates a small indentation (or hole) on the surface of
concrete. The pin is removed from the hole, the hole is
cleaned with an air jet and the hole depth is measured with a
suitable depth gauge. Each time a new pin is required as the
pin gets blunted after use.
The strength properties of both mortar and stone aggregate
influence the penetration depth of the probe in a concrete,
which is contrastingly different than cube crushing strength,
wherein the mortar strength predominantly governs the
strength. Thus the type of stone aggregate has a strong effect
on the relation of concrete strength versus depth of
penetration as given in fig..
Fig. Effect of aggregate type on relationship between
concrete strength and depth of probe penetration.
For two samples of concrete with equal cube crushing
strength, penetration depth would be more in the sample
with softer aggregate than the one with harder aggregates.
Correlation of the penetration resistance to compressive
strength is based on calibration curves obtained from
laboratory test on specific concrete with particular type of
aggregates. Aggregate hardness is determined from standard
samples provided along with the instrument. Aggregate size
in the mix also influence the scatter of individual probe
readings. This technique offers a means of determining
relative strength of concrete in the same structure or relative
strength of different structures. Because of the nature of
equipment it can not and should not be expected to yield
absolute values of strength. This test is not operator
independent although verticality of bolt relative to the
surface is obviously important and safety device in the
driver prevents, if alignment is poor.
It is claimed an average coefficient of variation for a series
of groups of three readings on similar concrete of the order
of 4% may be expected. It has been observed that ±20%
accuracy may be possible in strength determination of
concrete. Fig.4 explains the approximate shape of failure
during the test.
Fig.: Approximate shape of failure zone in probe
penetration test

10. Breakoff test
10.1 BREAK-OFF TEST EQUIPMENT
The Break-Off tester, Fig. 3.1, consists of a load cell, a
manometer, and a manual hydraulic pump capable of
breaking a cylindrical concrete specimen having the
specified dimensions in Section 2. The load cell has two
measuring ranges: low range setting for low strength
concrete up to approximately 20 Mpa (3,000 psi) and high
range setting for higher strength concrete up to about 60
Mpa (9,000 psi), Fig. 3.2. A tubular plastic sleeve, with
internal diameter of 55 mm (2.17 in.) and geometry shown
in Fig. 2.1, is used for forming cylindrical specimen in fresh
concrete. A sleeve remover, Fig. 3.3, is used for removing
the plastic sleeve from the hardened concrete. A diamond
tipped drilling bit is used for drilling cores for the B.0 test in
hardened concrete, Fig. 2.2. The bit is capable of producing
a cylindrical core, along with a reamed ring (counter bore)
in the hardened concrete at the top with dimensions similar
to that produced by using a plastic sleeve. The manufacturer
also provides a calibrator for calibration and adjustment of
the B.0 tester, Fig. 3.4. The procedure of calibrating a B.0
tester is discussed in Section 10.2.
10.2 TEST PROCEDURE
10.2.1 Inserting Sleeves in Fresh Concrete
Sleeves should be at center to center and edge distance of
minimum 150 mm (6 in.). They are best pushed in-place by
a rocking and twisting action, Fig. 10.2.2. Concrete inside
the sleeve and the top of plastic sleeve itself should then be
tapped by fingers to insure good compaction for the B.O.
specimen. Sleeves should then be moved gently up and
down in-place and brought to the same level as the concrete
surface at its final position. For stiff mixes, i.e. low slump
concrete-, a depression may occur within the confines of the
sleeve during the insertion process. In such cases the sleeve
should be filled with additional concrete tapped with
fingers, and slightly jiggled from side to side. (On the -other
hand, for wet, high slump mixes, the sleeve may move
upward due to bleeding. For such cases, sleeves should be
gently pushed back in-place, as necessary, to the level of the
finished concrete surface. Some times this process may have
to be repeated until the uplift movement stops after the
initial setting has occurred. A small weight may be placed
on the sleeve in order to prevent its upward movement.
Heavy grease, or other similar material, should be used to
lubricate the plastic sleeves for easier removal after the
concrete hardens.
10.3 Preparation for Core Drilling from Hardened Concrete
The finished concrete surface should be evaluated for
sufficient smoothness in order Io fix the vacuum plate of the
core drilling machine. The core barrel should be
perpendicular to the concrete surface at all times. The
drilling process should be continued to the full depth
required to produce a cantilever cylindrical core of 70 mm
(2-76 in.) length, with a groove at the top of the core for
setting the B.O. tester load cell. A slightly longer drilled
core will not affect the B.O. reading, while a slightly shorter
drilled core will affect the B.O. reading, Fig..
10.4 Conducting the B.O. Test
At the time of the B.O. test, remove the inserted plastic
sleeve by means of the key supplied with the tester, Fig. 3.3.
Leave the plastic ring in-place. Remove loose debris from
around the cylindrical slit and the top groove, see Fig. 2.3.
Select the desired range setting and place the load cell in the
groove on the top of the concrete surface so that the load is
applied according to Fig. 2.3. The load should be applied to
the test specimen at a rate of approximately one stroke of
the hand pump per second. This rate is equivalent to about
0.5 MPa (7O psi) of hydraulic pressure per second. After
breaking off the test specimen, record the B.O. manometer
reading.
This manometer reading can then be translated to the
concrete strength using curves relating the B.C. reading to
the desired concrete strength (i.e., flexural and/or
compressive). 5.4 The B.O.
Tester Calibration Procedure The B.O. tester should be
calibrated preferably each time before
use, otherwise periodically. To calibrate the tester, follow
the following steps:
(1) Set the calibrator gauge to zero.
(2) Place the calibrator in the load cell, (Fig. 5.4.1).
(3) Set the load cell on the high setting.
(4) Apply the load to the calibrator by pumping the handle
until the load cell manometer reading is 100.
(5) Record the dial gauge reading and compare it with the
expected value obtained from the manufacturers calibration
chart, Fig. 5.4.2. The dial gauge value should be within 4%
of the manufacturer's chart value.
(6) Repeat the above procedure for the low range setting.
Adjustment of the B.O. tester is necessary if error in the
reading obtained is greater than +4 percent of the expected
value from the chart. For a well calibrated tester, the needle
on the manometer should move 5 bars per one hand stroke,
while the first and/or second strokes might not move it that
much. A good rate of applying the load would be one stroke
per second.
10.5 EVALUATION OF TEST SPECIMENS
Before accepting a particular B.O. reading, the B.O.
specimen tested should be examined to insure a "good" test.
The B.O. test specimen must be perpendicular to the
concrete surface. A minimum center to center and edge
distance of 150 mm (6 in.) should be maintained. The failure
plane should be approximately parallel to the concrete
surface. It must be at a depth of 70 mm
(2.76 in.) from the finished surface. The presence of honey-
combed concrete, excessive air voids, and/or reinforcement
at the failure plane of test specimens could shift the rupture
plane from its intended place. Such test specimen results
should be rejected. The rejection criteria is somewhat
dependent on the engineering judgment of the user. Fig. 6.1
illustrates an example of irregular resistance mechanism to
the applied B.O. force. In this special case, two fairly large
aggregates exist in the rupture plane in such a way that the
combination of the two particles could create a resistance
couple. The rupture plane is forced to pass through the
tensile particle, as illustrated in

It is important to note that the inserted sleeve B.0 specimen
tends to be trapezoidal in shape rather than cylindrical (the
top diameter is 4 mm (0.16 in.) less than the bottom
diameter), while it is exactly cylindrical in the case of the
B.O. drilled core specimen.- However, inserted sleeve
B.O. specimen reading is not affected by the trapezoidal
shape because the bottom diameter at the failure plane
always remains 55 mm (2.17 in.) [13,14,15). In evaluating
inserted sleeve specimens, it is also reported that the drilled
core specimens give higher readings than the inserted sleeve
specimens [13,14,151. This is because in the case of the
inserted sleeve specimens, the accumulation of bleed water
under the bottom edge of the sleeve would tend to create a
weaker zone of concrete exactly where the failure plane for
the B.O. inserted sleeve test occurs.
10.6 APPLICATIONS
The potential of the B.O. test is promising. This method can
be used both for quality control and quality assurance. The
most practical use of the B.O. test method is for determining
the time for safe form removal, and the release time for
transferring the force in pre-stressed or post-tension
members. The B.O. method can also be used to evaluate
existing structures. It has been reported that the B.C. test
provides a more effective way in detecting curing conditions
of concrete than the Pull-out and the standard cylinder tests
(7,8,9,12,16).
In 1982 the B.0 tester was used to control the time for safe
form removal for a new "Bank of
Norway" building and an apartment building in Oslo. In
1983, the B.O. tester was used in
England. Recently the B.O. tester has been used by the
Norwegian Contractors Company, which is responsible for
building off-shore platforms for the oil fields in the North
Sea. The B.O. method can also be used to measure the
bonding strength of overlays or the bonding between
concrete and epoxy, but this usage has not been applied in
the field [12,16].
10.7 ADVANTAGES AND LIMITATIONS
The main advantage of the B.O. test is that it measures the
in-place concrete (flexural) strength.
The equipment is safe and simple; and, the test is fast to
perform, requiring only one exposed surface. The B.O. test
does not need to be planned in advance of placing the
concrete because drilled B.O. test specimens can be
obtained. The test is reproducible to an acceptable

.
REFERENCES
[1] ALEXANDER, A.M., THORTON, H.T., JR., “Ultrasonic pitch-catch
and pulse-echo measurements
[2] in concrete”, Non-destructive Testing of Concrete (Lew, H. S., Ed.),
ACI SP-112 (1989) 21.
[3] BOUNDY, C.A.P., HONDROS, G., Rapid Field Assessment of
Strength of Concrete by Accelerated
[4] https://theconstructor.org
[5] Curing and Schmidt Rebound Hammer, ACI J., Proc. 61 (9) (1964)
1185.
[6] CLIFTON, J.R., Non-Destructive Tests to Determine Concrete
Strength-A Status Report, NBSIR 75-
[7] 729, Natl. Bur. of Stand., Washington, D.C.
[8] JENKINS, R.S., Non-destructive testing - an evaluation tool, Concr.
Int., ACI (1985) 22.
[9] JONES, R., A method of studying the formation of cracks in a
material subjected to stress, Br. J.
[10] Appl. Physics (London) 3 (1952) 229
Notes by _ Imran B K

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