Engineering Material: Properties and Testing Methods

This document provides an overview of the properties of engineering materials, focusing on concrete. It discusses five different properties of concrete that can be tested, including strength, suitability, workability, and water tightness. The document also explains the working principles of rebound hammers, ultrasonic pulse velocity testing, and covermeters. It is a valuable resource for students studying engineering materials and professionals in the field.

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ENGINEERING MATERIALS (18CVA010)
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1. There is sometimes a need for the assessment of the in-situ properties of concrete.
Describe five different concrete properties that can be tested for, indicating an
appropriate test method for each.
Concrete is made of a mixture of sand, cement, aggregates and water that hardens to form a stone
like mass. This material is widely used as a construction material because it is more versatile. It
is a material of choice for many country due to its strength, durability, impermeability,
workability, water tightness, permanence, abrasion and fire resistance (Berndt, 2009).
Properties of concrete and the methods for testing
Strength
Compressive strength of concrete is one of the most essential properties of all. Therefore,
it is not surprising to test the strength of concrete on site before it is used for construction works.
However, there are also a number of factors that affect the compressive strength of concrete. The
major factors include water to cement ratio, curing and the degree of compaction (Cachim,
2009). Other factors that may influence the strength include the size of aggregates, volume, age
of loading and the type of cement.

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Source: (Corinaldesi, 2010)
Cut and Pull Out Test (CAPO) is the method used insitu to determine the compressive
strength of concrete mix. In most cases, the test is found to be within a range of 8% of the results
obtained. CAPO test is done in compliance with the ASTM C900 and EN-12504-3 (Muhit, et al.,
2013).
Suitability
A suitable concrete should be able to resist its decay and disintegration. A well-mixed
concrete should be durable with regard to weathering conditions which include moisture
changes, action of atmospheric gases, temperature variations. For concrete to maintain its
durability, water to cement ratio should be at the right measure to ensure a workable mix. A well
compacted concrete is one that has very few pores or voids that will make it more durable. To

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entrap air bubble in air bubbles on a mixture of concrete, admixture called vinsol resin is
sometimes added in the mixture (Cachim, 2009).
The chemical action in the cement should harden the concrete to enable it to resist the
lateral load the will be subjected to it in its service life. Concrete sustaining the damages of
weather can be attributed to thawing and freezing cycle. Thus increasing the water tightness in
water can help improve the resistance of damage in concrete. One of the best insitu methods to
determine the suitability of concrete and determine whether there is any form of damages is Ultra
Pulse Velocity (UPV) (Corinaldesi, 2010). This method has been traditionally used in quality
control of materials such as metals and welded connections. Advancement in transducer
technology has made it possible for testing of concrete to be widely accepted. The testing
procedures must comply with ASTM C 597 as the” Standard Test Method” (Muhit, et al., 2013).
The idea used in this technology is by measuring the time the acoustic waves get to travel
through a medium and comparing them with the density and elastic properties of a material.
Workability
This is the ease of working with concrete where by it can be easily placed and finished
without much energy involved. By workability we mean that concrete has achieved a certain
degree of consistency or fluidity which can be tested using slump test with in compliance with
ASTM C143. Slump test is the most common test that can either be done on laboratory on site, it
is done by collecting the sample of concrete mix and moulding the mixture in a frustum cone like
shape that is approximately 12 in high with a diameter of 8-in and 4-in at the base and top
respectively (Corinaldesi, 2010). When the mould is removed, the change in height of the sample
used as specimen is measured. When the change of height occurs, its regarded as the slump
value. The higher the water content in concrete the higher the slump value measured.

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Source: https://civilengineerspk.com/important-properties-of-concrete/
Water Tightness
Water tightness is a very essential in a concrete mix, concrete quality can be improved by
reducing the amount of water used in the mix. Excess water in concrete leaves cavities and voids
after evaporation and in case they are aligned together, water can pass through the concrete. The
use of air entrained admixtures and prolonged curing can be used to increase the water tightness
in the mix (Panda & Bal, 2013). It can also be increasing to achieve a more compacted concrete
during mixing by controlling the aggregate grading and using admixtures. This property can be
tested using penetration resistance to determine the time taken to penetrate into the concrete core.
The faster the velocity of penetration the lesser the water tightness or compaction of concrete and
the slower the velocity of penetration in concrete the higher the water tightness in concrete.

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2. The rebound hammer is a non-destructive testing device that can be used to assess
the properties of in-situ concrete.
i. Explain briefly how the rebound hammer works.
This instrument is used to test the compressive strength of concrete. A rebound hammer
is made of elastic material and it works on the principal that any elastic mass will have a rebound
which is directly dependent on the hardness of the surface struck which in turn is determined by
compressive strength of concrete the surface is made of.
The rebound hammer test is a non-destructive, convenient and quick method of testing
concrete strength. It consists of a spring-controlled elastic mass, which slides on a tube encased
plunger (Sulaeman, 2012). It has a plunger which is pressed at constant energy upon the concrete
surface, making the pring-controlled mass to rebound to an extent the value of which is
determined by the hardness of the surface (Sulaeman, 2012). The value of rebound is red from a
calibrated scale and is read as a rebound number or index. Weakness and stiffness in concrete
makes it absorb a lot of energy leaving little to make the mass rebound. This test is best carried
out on a flat surface which includes horizontal, vertical and diagonal surfaces, as long as the
plunger is kept perpendicular to the surface (Sulaeman, 2012). Holding the hammer at an angle
will result in different readings on the same concrete surface. Therefore a rebound hammer can
be applied to determine whether a surface is of acceptable quality or not.
Objective
The instrument is primarily built to measure concrete strength by relating it to the
rebound index. The concrete strength however can be measured to compare the strengths of

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different surfaces, assess uniformity of a concrete surface and to assess if concrete made
conforms to standard specifications (Sulaeman, 2012). In general, the harder a concrete surface
is, the larger the rebound value.
Procedure
Before a rebound hammer is put to use, it is tested against the test anvil so that reliable
results are gotten. On the anvil are values which are suitable for different types of rebound
hammers, and the range between which each hammer falls is indicated by the manufacturer.
Applying pressure lightly on the plunger unlocks it, enabling it to extend into a position in which
they can carry out the test (Mishra, 2018b). While perpendicularly holding the hammer to the test
surface, press the plunger using subsequently increasing pressures until the hammer hits the
surface. The button is pressed until a suitable position from which to take the reading is reached.
At least 15 readings are taken and their average calculated. The compressive strength is read
from a graph located on the outer surface of the hammer.
ii. Explain why, within a concrete member, the rebound number obtained by
testing at different locations can vary significantly.
Concrete strength is determined by factors like surface condition and moisture content of
concrete, and carbonation of the concrete surface. The same concrete when applied to areas of
different climates will dry at different rates and this could cause a wide disparity in the measured
values because concrete gets stronger as it dries (Mishra, 2018b). When concrete surface is
smooth, clean and dry, the reading gotten from it will be different from that obtained from a

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similar surface which is dirty or not dry. This is because rough and moist surfaces absorb a lot of
energy and this could cause differences in the rebound.
Although rebound number only applies for a thin surface layer of concrete, varying
thickness of concrete could cause a slight difference in readings.
iii. Can the rebound hammer be used to assess the strength of the concrete in a
structure, and how reliable is such an assessment likely to be?
Compressive strength of concrete has been experimentally proved to be correlated to rebound
number. This conclusion is arrived upon testing the same surface simultaneously with a
compression tester and a rebound hammer (Mishra, 2018b). On concrete surfaces that have
already dried, the rebound hammer is found to be efficient when many measurements of the
same surface are done and an average value is calculated. For wet surfaces or those with
moisture in them, a rebound hammer is not advisable for testing.
3. The Proceq PUNDIT apparatus (portable ultrasonic non-destructive insitu test)
measures the velocity of an ultrasonic pulse travelling through the concrete from a
transmitting transducer to a receiving transducer.
i. Explain briefly how the process of UPV works.
A material’s pulse velocity depends on its elasticity and density. The process of testing
ultrasonic pulse velocity is used to determine sonic properties of concrete which in turn defines
the strength, evenness and quality of concrete. This test can be carried out with various goals
such as to determine the homogeneity of concrete, internal voids and cracks and overall
imperfections in the concrete, strength of the concrete, concrete quality compared to that

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specified by standard requirements, and to track any changes that would occur in the concrete
with time due to contact with excessive heat, chemicals and moisture (PCTE Associate, 2017).
Other properties like thickness of one side of a concrete component can also be calculated. The
test essentially involves projecting an ultrasonic wave from an ultrasonic source to an ultrasonic
receiver on the other side of the concrete material.
The time which this ultrasonic wave takes to get to the opposite side is used to calculate
velocity and determine several’ other properties of concrete. The ultrasonic wave used in this
case is a p-wave as known as a compression wave. The velocity in question here is gotten by
dividing the distance between the source and receiver by the time the wave takes from the
transducer to antenna.
The standard transducers have a frequency of 54 KHz but there are options with
frequencies varying between 25-150 KHz. This can pass through a wide variety of concrete
thicknesses and densities (Pine Technical Support, 2019).
A calibrated bar matches the velocities to different densities of concrete. This equipment is very
convenient since readings are taken on a screen and it is a fast method because sound in general
travels very fast. It is also non-invasive and caters for rough surfaces. For this reason it can be
used for on-site measurements.
ii. Explain why, within a concrete member, the UPV obtained by testing at
different locations can vary significantly.
The speed of sound in solids is faster than that in liquids and gases. When a concrete
component has a crack or a void in its structure, the air in the voids will slow down the sound
making it reach the receiving transducer within longer time period (Pine Technical Support,

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2019). When a sound wave is passed through the concrete of similar thickness and strength but
without voids, the time taken will be shorter.
For a concrete component that is not homogeneous, there will be definite differences in
the time taken for the sound beam to go through it. The less homogeneous it is, the larger the
variation between values of velocity.
Challenges
 When measuring depths of cracks, the results might be erroneous if the crack is filled
with water.
 The process even thigh it can be used on rough surfaces is quite unreliable for very rough
surfaces.
 When the device is not handheld, it is necessary to prepare the surface before the test so
that the transducers stick to the surface.
iii. Can the UPV be used to assess the strength of the concrete in a structure, and
how reliable is such an assessment likely to be?
Yes, ultrasonic pulse velocity can be applied in the assessment of concrete strength.
Strength of concrete is determined by its hardness, and this is a property which is accurately
measured by UPV (Pine Technical Support, 2019). The pulses are optimally shaped to give
maximum transmission even at low voltages. The voltage of the transmitter is directly

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proportional to the receiver gain. On the equipment, these two have been related such that there
is optimal signal transmission and for this reason measurements are accurate and have stability.
On the other hand, if there are imperfections in the concrete and they are filled with water
which has closer velocity of sound to solids than air, the test could lead to incorrect conclusions.
4. A covermeter is a hand-held device that measures the depth of the reinforcement
i. Explain briefly how the covermeter works.
Reinforcements in concrete structures are included to add ductility and tensile strength. A
covermeter is a device that can detect the exact concrete cover and as find out the depth of
metallic enhancements (Mishra, 2018a). Only non-destructive methods can be used to carry out
such a test. This particular device is handheld, as well as fast and accurate and is a means of
measuring, locating and identifying orientation of concrete and metal bars within concrete. Some
of the technologies used to make covermeters are Ultrasonic, ground-penetrating radar, concrete
resistance, potential field, and the eddy current method which has been implemented in new
models (Mishra, 2018a).
A magnetic covermeter locates bars inside concrete using magnetism. The handheld
device is laid on a concrete surface and moved in different directions in an attempt to get a
reading. A beep will indicate the presence of a metallic bar in the ground below. This operates on
the principal that metals like steel affect the magnetic field of the areas where they are located.
All magnetic metals are removed from the vicinity so that the test is not interfered with. The
magnetic field will be stronger for a steel reinforcement closer to the surface (Mishra, 2018a).
The device is graduated such that the location of the Meta can be read from it. Some of these

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devices feature data storage which makes them very convenient. The size of the reinforcement
can only be found after its location has been found.
If the test is being done during maintenance, a drill may be used to chip away at the
concrete so that the metal rod sizes are measured.
ii. Explain how accurate the covermeter is, and what problems may occur with
its use.
This instrument is used to find out exact values of the depth of concrete cover and exact
locations of rebar in the concrete. It is generally considered to be very accurate. To get precise
values of things like bar diameter, it is imperative to ascertain that there are no interfering factors
that could tamper with the value (Mishra, 2018a). These are more reliable than rebar detectors
which only detect metallic bars from shallow depths.
Problems
Readings are affected when the device is operated within radio frequencies of certain
magnitudes. The magnetic method is not suitable for highly reinforced surfaces. Flawed results
may be obtained if the concrete thickness has the same value as the spacing between bars. The
measurements vary with different strengths of concrete and therefore the instrument should be
calibrated at the manufacturers to cater for these differences (Mishra, 2018a). This instrument
gives more precise measurements with shallow depths, with precision reducing with increasing
depth. For a magnetic covermeter, the presence of magnetic materials will interfere with
measurements.

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iii. When might the covermeter be used, and why?
This method is used to describe and analyse internally concrete surfaces to determine
whether concrete cover is healthy or not and to assess metal reinforcements for possible
problems such as corrosion. This helps to lessen risks that are unwanted and could have been
avoided and therefore in a way ensure the long life of the structure. Providing enough depth of
reinforcements as recommended by construction codes minimizes corrosion. Knowledge about
the depth of cover is crucial so that durability standards of a construction are adhered to.
Diameter and location of bars is necessary information so that bars and their spacing can be
understood, especially when no drawing of this additions are available. in situations where parts
of concrete are to be removed from a mass, knowing the location of rebars will ensure that none
of them are cut through in the process (Mishra, 2018a). This information is mostly used in
maintenance processes, when cutting through any bars could make a structure weak and damage
tools used for drilling. The cover is connected to the longevity and the environmental conditions
of the structure.

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References
Berndt, M.L., 2009. Properties of sustainable concrete containing fly ash, slag and recycled
concrete aggregate. Construction and building materials, 23(7), pp.2606-2613.
Cachim, P.B., 2009. Mechanical properties of brick aggregate concrete. Construction and
Building Materials, 23(3), pp.1292-1297.
Corinaldesi, V., 2010. Mechanical and elastic behaviour of concretes made of recycled-concrete
coarse aggregates. Construction and Building materials, 24(9), pp.1616-1620.
Mishra, G., 2018a. Magnetic Rebar Locator (Covermeter) Test. [Online] Available at:
https://theconstructor.org/practical-guide/magnetic-rebar-locator-covermeter-test/5736/
[Accessed 13 April 2019].
Mishra, G., 2018b. Rebound Hammer Test on Concrete - Principle, Procedure, Advantages &
Disadvantages. [Online] Available at: https://theconstructor.org/concrete/rebound-hammer-test-
concrete-ndt/2837/ [Accessed 13 April 2019].
Muhit, I.B., Haque, S. and Alam, M.R., 2013. Influence of crushed coarse aggregates on
properties of concrete. American Journal of Civil Engineering and Architecture, 1(5), pp.103-
106.
Panda, K.C. and Bal, P.K., 2013. Properties of self compacting concrete using recycled coarse
aggregate. Procedia Engineering, 51, pp.159-164.

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PCTE Associate, 2017. Pundit Lab - Ultrasonic Pulse Velocity Tester. [Online]
Available at: https://www.pcte.com.au/pundit-lab-ultrasonic-tester [Accessed 13 April 2019].
Pine Technical Support, 2019. Proceq Pundit Lab Ultrasonic Pulse Velocity Concrete Hardness
Tester. [Online] Available at: https://nerdyturtlez.com/tutor/order.php?id=934828 [Accessed 13
April 2019].
Sulaeman, A., 2012. Rebound Hammer Test. [Online] Available at:
https://www.engineeringcivil.com/rebound-hammer-test.html [Accessed 13 April 2019].