Mapua University

School of Civil, Environmental, and Geological Engineering

CE133P – Structural Design I: RCD

CLASSWORK # 1

NAME: ROBIN, Charisse R. Date: Nov. 25, 2021

STUDENT NUMBER: 2015104917

1. What are the advantages (10) & disadvantages (10) of using Reinforced Concrete?
Concrete used for most construction projects use reinforcements, in which, this process is done by
embedding of deformed steel bars or welded wire fabric during casting of freshly made concrete (ACI,
2019). This is what we call as Reinforced Concrete.
Reinforced Concrete is widely used as it is economic and can be used in various types. But along with
advantages, this building material poses some disadvantages as well (Civil Today, 2018). Advantages are
as follows:
1) Compared to other building materials, it has higher compressive strength.
2) Reinforced concrete is able to withstand an adequate amount of tensile stress.
3) Has great fire and weather resistance.
4) Much more durable than other building materials.
5) As it begins from a fluid-like form, it can be molded economically into any shape.
6) Low maintenance cost.
7) Most economical building material for structures like footings, piers, dams, etc.
8) Minimum deflection.
9) Because of the minimum deflection, can be used in precast structural components.
10) Requires less skilled labor for structure building (Shojaedin, 2016).
Meanwhile, the disadvantages are as follows:
1) Tensile strength is about 0.1 of its compressive strength.
2) There’s uncertainty in the final strength as the main steps such as mixing, casting, and curing are
to be taken in as factor for the structure’s final strength.
3) Cost of forms used in casting is quite high.
4) Larger column section.
5) There is shrinkage which can cause crack development and loss in strength (Shojaedin, 2016).
6) Lack of attention during construction can cause durability issues.
7) Though it’s economical, it is not exactly environmentally friendly.
8) Does not gain strength once it’s poured. You will have to wait for it to harden and gain strength.
9) Requires more attention when pouring thick concrete.
10) Quite costly because it requires mockup test before start of construction (Prasad, 2015)

2. Explain the stress-strain diagram for a plain concrete.

Stress-strain relationship for plain concrete requires evaluation and definition as it graphically
represents behavior of concrete under load. It may not be possible to define the diagram using a single
approach and completely represent the concrete’s actual behavior with just ascending and descending
portion due to the fact that it has uniaxial shape. The diagram is greatly influenced by a number of factors
that affect the relationship of stress and strain of concrete (Ali, Farid, & Al-Janabi, 1990).
Below are several conditions that must be fulfilled in any mathematical model:
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 Mapua University
School of Civil, Environmental, and Geological Engineering
CE133P – Structural Design I: RCD

1) Point of origin, f = 0 at 𝜖 = 0.
df
2) Slope of the stress-strain curve at the origin, = Ec and 𝜖 = 0.
d𝜖
df
3) Point of maximum stress f = fo at 𝜖 = 𝜖0 , where = 0.
d𝜖
4) To show the ascending and descending portions, the analytical curve must satisfy the data.

3. Explain the stress-strain diagram for a steel reinforcement.

Stress-strain curve describes the behavior of steel reinforcement under load, created by testing steel
specimens. Stresses are plotted along the vertical axis, meanwhile, strains are plotted along the horizontal
axis. When the steel specimen is subjected to load, it behaves as an elastic material which means the
stresses and strains are proportional. But as the load is increased, the specimen starts to lose its
proportionality and ultimately fails or yields. When the load is increased beyond the yield point, the steel
bar goes through stress hardening and can sustain greater stress, after it reaches the fracture point. When
the steel specimen is subjected to load, it goes through several stages such as elastic stage, yield point,
and fracture (Hamakareem, 2015).
According to Ian McEnteggart’s interview (McEnteggart, 2016), strain measurement is a key element of
materials testing. The physical properties of materials are usually represented by a stress-strain curve and
knowledge of the curve allows engineering to compare different materials and predict the behavior of a
part or structure made from a particular material (e.g., stiffness and failure strength) during processing
operations (e.g., pressing and forging) and during service.

4. Explain the methods (at least 3) used for testing concrete strength and steel capacity. You
can provide steps, manuals, guidelines, etc.
(Hearns, 2019) says when choosing a method for monitoring the compressive strength of concrete, it’s
important for project managers to consider the impact each technique will have on their schedule. While
some testing processes can be done directly onsite, others require extra time for third-party facilities to
deliver strength data. Time is not the only factor that contributes to project managers’ decisions. The
accuracy of the testing process is just as important, as it directly effects the quality of the concrete
structure.
Field-cured cylinders are the most common method for monitoring the strength and durability of in-situ
concrete. These samples are cast and cured according to ASTM C31 and tested for compressive
strength by a third-party lab at various stages. Usually, if the slab has reached 75% of its designed
strength, engineers will give the go ahead to their team to move on to the next steps in the construction
process (Hearns, 2019).
Here are a few approaches to consider when choosing a method of strength testing.
1) Rebound Hammer or Schmidt Hammer (ASTM C805)
This method uses a spring release mechanism to activate a hammer that strikes a plunger to
drive into the concrete’s surface. The rebound distance from the hammer to the surface of the
concrete is given a value from 10 to 100. This measurement is then correlated to the concretes’
strength. This method is relatively easy to use and can be done onsite directly. But the pre-
calibration using cored samples is required for accuracy in measurements. The results of the test
can be skewed by surface conditions and the presence of large aggregates or rebar below testing
location (Hearns, 2019).

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 Mapua University
School of Civil, Environmental, and Geological Engineering
CE133P – Structural Design I: RCD

The tests can be performed in horizontal, vertically upward, vertically downward or any
intermediate angled positions in relation to the surface (Figures 1 and 2). The devices are furnished
with correlation curves by the manufacturer. ASTM C805 now states that these references to the
relationship between the rebound number and compressive strength provided by the manufacturer
“shall be used only to provide indications of relative concrete strength at different locations in a
structure.” To obtain greater accuracy of test results, it is recommended that the user develop a
correlation for the device on each concrete mixture design to be tested and at the intended test
angle (CEMEX USA, 2013).

Figure 1 and 2 – Horizontal orientation of hammer during a measurement

ASTM C805 states that the relationship must be established by correlating the rebound numbers
obtained for a given area of concrete to the results of cores obtained from the corresponding
locations. The reason stated for the required use of cores is that “The use of molded test
specimens to develop a correlation may not provide a reliable relationship because the surface
texture and depth of carbonation of molded specimens are not usually representative of the in-
place concrete.” (CEMEX USA, 2013)
ASTM C805 requires a minimum of two cores obtained from at least six locations with different
rebound numbers. The test locations should be selected so that a wide range of rebound numbers
are obtained. The ASTM standard also states that the locations where it is intended to estimate
strength based on the correlation data shall have a similar surface texture and have been exposed
to similar conditions as the locations used to develop the correlation data. (CEMEX USA, 2013)
There is an advantage in using the rebound hammer as a means of evaluating concrete to
assess the in-place uniformity, to delineate regions in a structure of poor quality or deteriorated
concrete, and to estimate in-place strength. The unit is easy to use, and a large number of readings
can be obtained in a relatively short amount of time. The method is for the most part non-
destructive and typically more economical than other methods. However, with these advantages
come disadvantages related to limitations on accuracy, and the need for proper calibration and
correlation with cores for evaluation of an existing structure. (CEMEX USA, 2013)
The rebound hammer can be a valuable tool for evaluating the uniformity of concrete in the
field provided that the concrete is under the same conditions related to age, moisture content,

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 Mapua University
School of Civil, Environmental, and Geological Engineering
CE133P – Structural Design I: RCD

surface carbonation, and temperature. It should not be used as a substitute for performing normal
specified quality control procedures. (CEMEX USA, 2013)
Of most importance is that the current version of ASTM C805 states “This test method is not
suitable as the basis for acceptance or rejection of concrete.” As stated previously when ASTM
C805 is followed, it will provide an estimation of the in-place compressive strength; however, it is
not a direct measurement, and the data obtained should not be used to accept or reject the
concrete in place. (CEMEX USA, 2013)
2) Penetration Resistance Test (ASTM C803)
To complete a penetration resistance test, a device drives a small pin or probe into the surface
of the concrete. The force used to penetrate the surface, and the depth of the hole, is correlated to
the strength of the in-place concrete. ASTM C803 is relatively easy to use and can be done directly
onsite, just like ASTM C805. But data is significantly affected by surface conditions as well as the
type of form and aggregates used. Requires pre-calibration using multiple concrete samples for
accurate strength measurements (Hearns, 2019).
This method is conducted on concrete structures using Windsor Probe test machine, using a
steel probe fired on the concrete surface by a sudden explosion. The penetration is inversely
proportional to the strength of concrete. The result of the test is influenced by aggregate strength
and nature of formed surfaces of concrete (Hearns, 2019).
The purpose of the penetration resistance test is used to determine the uniformity of concrete,
specify the poor quality or deteriorated concrete zones, and evaluate the in-place strength of
concrete. It is sometimes necessary to estimate the strength of concrete on-site for early form
removal or to investigate the strength of concrete in place because of low cylinder test results
(Hamakareem, 2015).
Due to the nature of the equipment, it cannot and should not be expected to yield absolute
values of strength.
Testing Considerations:
1. If the probe is sloped with respect to the surface of the concrete, take four measurements
equally spaced around and parallel to the probe and average them to get the measurement.
2. If the probe is not firmly embedded, then the test is not valid and hence it should be
repeated.
3. Similarly, the test should be repeated if the range of depth of penetration for three tests is
more than 8.4mm in concrete made with 25mm maximum aggregate size, and 11.7 in
concrete made with 50mm maximum aggregate size.
4. When tests are to be made on concrete having a density of approximately 2000 kg/m3 or
less, and on all concrete with strengths less than 17 MPa, decrease the amount of energy
delivered to the probe by the driver or use a larger-diameter probe, or both.
The penetration resistance of concrete is computed by measuring the exposed length of probes
driven into concrete. In order to estimate concrete strength, it is necessary to establish a
relationship between penetration resistance and concrete strength.
Such a relationship must be established for a given test apparatus, using similar concrete
materials and mixture proportions as in the structure.
3) Ultrasonic Pulse Velocity (ASTM C597)
An ultrasonic pulse velocity (UPV) test is an in-situ, nondestructive test to check the quality of
concrete and natural rocks. In this test, the strength and quality of concrete or rock is assessed by

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 Mapua University
School of Civil, Environmental, and Geological Engineering
CE133P – Structural Design I: RCD

measuring the velocity of an ultrasonic pulse passing through a concrete structure or natural rock
formation (Wikipedia, 2015)
This test is conducted by passing a pulse of ultrasonic through concrete to be tested and
measuring the time taken by pulse to get through the structure. Higher velocities indicate good
quality and continuity of the material, while slower velocities may indicate concrete with many
cracks or voids.
This is a non-destructive testing technique which can also be used to detect flaws within the
concrete, such as cracks and honeycombing. However, it is highly influenced by the presence of
reinforcements, aggregates, and moisture in the concrete element. It also requires calibration with
multiple samples for accurate testing.
Ultrasonic Pulse Velocity can be used to:
• Evaluate the quality and homogeneity of concrete materials
• Predict the strength of concrete
• Evaluate dynamic modulus of elasticity of concrete,
• Estimate the depth of cracks in concrete.
• Detect internal flaws, cracks, honeycombing, and poor patches.
The test can also be used to evaluate the effectiveness of crack repair. Ultrasonic testing is an
indicative and other test such as destructive testing must be conducted to find the structural and
mechanical properties of the material (Wikipedia, 2015).
The basic idea on which the pulse velocity method is established is that the velocity of a pulse
of compressional waves through a medium depends on the elastic properties and density of the
medium (Naik, Maholtra, & Popovics, 2004).
The transmitting transducer of the pulse velocity instrument transmits a wave into the concrete
and the receiving transducer, at a distance L, receives the pulse through the concrete at another
point. The pulse velocity instrument display indicates the transit time, ∆t, it takes for the
compressional wave pulse to travel through the concrete. The compressional wave pulse velocity V,
therefore, is
L
V=
∆t
The compressional pulse transmitted through the concrete undergoes scattering at various
aggregate–mortar boundaries. By the time the pulse reaches the receiving transducer it becomes
transformed into a complex waveform, which contains multiply reflected compressional waves and
shear waves. Of course, compression waves traveling the fastest arrive first at the receiver (Naik,
Maholtra, & Popovics, 2004)

Works Cited
ACI. (2019). Retrieved from American Concrete Institute:
http://www.concrete.org/topicsinconcrete/topicdetail/Reinforcement%20in%20Concrete?search=Reinf
orcement%20in%20Concrete

Ali, A. M., Farid, B. J., & Al-Janabi, A. M. (1990). Stress-Strain Relationship for Concrete in Compression Made
of Local Materials.

Carreira, D. J., & Chu, K. H. (n.d.). Stress-Strain Relationship for Plain Concrete in Compression. ACI Journal.
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 Mapua University
School of Civil, Environmental, and Geological Engineering
CE133P – Structural Design I: RCD

CEMEX USA. (2013). Proper use of the Rebound Hammer (ASTM C805). Retrieved from CEMEX USA:
https://www.cemexusa.com/documents/27329108/45560536/proper-use-of-the-rebound-
hammer.pdf/1417ecb8-2a04-1b8a-48aa-
853149c76936#:~:text=The%20Rebound%20Hammer%20has%20been,surfaces%20using%20the%2
0rebound%20principle.

Civil Today. (2018). Modulus of Elasticity of Concrete: Advantages and Disadvantages of Reinforced Concrete.
Retrieved from Civil Today: https://civiltoday.com/civil-engineering-materials/concrete/23-advantages-
and-disadvantages-of-reinforced-concrete

Hamakareem, M. I. (2015). Stress-strain Curve for Steel Bars. Retrieved from The Constructor:
https://theconstructor.org/structural-engg/stress-strain-curve-steel/3514/

Hearns, A. (2019, June 11). 7 Methods for Testing Concrete Strength. Retrieved from For Construction Pros:
https://www.forconstructionpros.com/concrete/article/21072546/7-methods-for-testing-concrete-
strength

McEnteggart, I. (2016, January 6). The Importance of Strain Measurement in Materials Development. (S.
Milhe, Interviewer)

Naik, T. R., Maholtra, V. M., & Popovics, J. S. (2004). The Ultrasonic Pulse. CRC Press LLC.

Prasad. (2015). Advantages and Disadvantages of Reinforced Concrete. Retrieved from Structural Guide:
https://www.structuralguide.com/advantages-and-disadvantages-of-reinforced-concrete/

Shojaedin, R. (2016, July 19). Advantages and Disadvantages of Reinforced Concrete. Retrieved from
Linkedin: https://www.linkedin.com/pulse/advantages-disadvantages-reinforced-concrete-reza-din

Wikipedia. (2015, June). Ultrasonic Pulse Velocity Test. Retrieved from Wikipedia:
https://en.wikipedia.org/wiki/Ultrasonic_pulse_velocity_test

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