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Mechanical Properties Of Heated Concrete Of M100 Grade

Authors:
Dr Anduri Sreenivasulu at Gudlavalleru Engineering College
Dr Anduri Sreenivasulu
Srinivasa Rao Karumuri at Koneru Lakshmaiah Education Foundation
Srinivasa Rao Karumuri
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The present study investigated the effect of elevated temperatures ranging from 50 to 250 0 C on the compressive and splitting tensile strengths of Ultra strength concrete of M100 grade. Tests were conducted on 150 mm cubes, 150 mm diameter and 300 mm height cylindrical specimens. The specimens were heated to different temperatures of 50, 100, 150, 200 and 250 0 C for different durations of 1, 2, 3 and 4 hours at each temperature. After the heat treatment, the specimens were tested for both compressive and splitting tensile strengths. The results were analyzed and the effects of elevated temperature on these two properties were presented.
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A. Sreenivasulu, Dr. K. Srinivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue4, July-august 2012, pp.1944-1948
1944 | P a g e
Mechanical Properties Of Heated Concrete Of M100 Grade
A. Sreenivasulu1, Dr. K. Srinivasa Rao2
1. Associate Professor, Department of Civil Engineering, PVP Siddhartha Institute of Technology,
Vijayawada
2. Associate Professor in Civil Engineering, College of Engineering, Andhra University, Visakhapatnam.
Abstract:
The present study investigated the effect of
elevated temperatures ranging from 50 to 2500C on
the compressive and splitting tensile strengths of
Ultra strength concrete of M100 grade. Tests were
conducted on 150 mm cubes, 150 mm diameter and
300 mm height cylindrical specimens. The specimens
were heated to different temperatures of 50, 100,
150, 200 and 2500C for different durations of 1, 2, 3
and 4 hours at each temperature. After the heat
treatment, the specimens were tested for both
compressive and splitting tensile strengths. The
results were analyzed and the effects of elevated
temperature on these two properties were presented.
Keywords : Ultra strength concrete, split tensile
strength, Silica fume, Rheobuild, compressive strength.
1. Introduction:
Fire is one of the most severe conditions when
the structures are exposed for it. Mechanical properties
such as compressive strength, split tensile strength and
modulus of elasticity are considerably reduced during
exposure, potentially resulting in undesirable structural
failures. Therefore, the residual properties of concrete
are still important in determining the load carrying
capacity and the further use of fire damaged structures.
Previous investigations have shown that concrete type,
concrete strength, aggregate types, test types, maximum
exposure temperature, exposure time, type and amount
of mineral admixtures and type and amount of fibres
affect the residual properties of concrete after exposure
to high temperatures. When the concrete is subjected to
elevated temperature, the incompatibility of thermal
deformations within the constituents of concrete
initiates cracking.
Internal stress is also caused by microstructure
change due to dehydration and steam pressure build up
in the pores. Forecasting and obtaining information
about the physical, mechanical and transport properties
of concrete is crucial for determining the usability of
fire damaged structures.
Exposure to elevated temperatures causes
physical changes in Ultra strength concrete including
large volume changes due to thermal shrinkage and
Creep related to water loss. The changes in volume will
result in large internal stresses thus leading to micro
cracking. Elevated temperature also generates some
chemical and micro structural changes such as
migration of moisture and thermal incompatibility of
interface between cement paste and aggregate. All these
changes will have a bearing on the strength and
stiffness of concrete. Based on the limited amount of
experimental data available to date, it has been found
that the effects of elevated temperatures on the
mechanical properties of Ultra strength concrete vary
with a number of factors including the test methods,
permeability of concrete, the types of aggregate used
and moisture content.
1.1 Objective
The objective of this work is to understand the
behavior of M100 concrete when exposed to elevated
temperatures. The experimentation was carried out to
study the changes in compressive and splitting tensile
strengths of Ultra strength concrete subjected to
elevated temperatures for different durations of
exposure.
1.2 Research Significance
Concrete properties are changed by fire
exposure. The properties such as compressive and split
tensile strengths must be accurately predicted after the
fire as they are crucial for the further usage of concrete
structures affected by fire. Despite the fact that certain
models have already been proposed for the prediction
of compressive strength and split tensile strength loss,
they have limitations or lower statistical performances.
A unique and comprehensive empirical model is needed
to predict compressive and split tensile strength losses
with high statistical values for which the database of
test results is required. This study aims to fulfill the
need.
1.3 Admixtures used
Silica fume (Micro silica) as a mineral
admixture and Rheobuild 1100 as a chemical admixture
are used.
A. Sreenivasulu, Dr. K. Srinivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue4, July-august 2012, pp.1944-1948
1945 | P a g e
2. Review of Literature:
1. Klaus Holschemacher and Sven Klotz (2003)
[3] have studied about the ultra heigh strength concrete
under concentrated load and found that the
conventional reinforcement can be completely or partly
replaced by fibres, which are also effective in the
margin of the structural members. Furthermore they
have found that the tensile bearing behavior is uniform
2. Z.Wadud and S.Ahmad (2001) [4] have
carried out a parametric study on ACI method of
concrete mix design. Based on their study it was
concluded that the Inter particles voids, a function of
the coarse aggregate grading, is an important parameter
in the mix design. The ACI method has no adequate
paratmeter to take this aspect into account. This leads to
higher fine aggregate content, which consequently
increases the surface area of aggregates when coarse
aggregates of higher voids are used. The cement
content is determined even before the consideration of
any aggregate type, resulting in a lower cement/fine
aggregate ratio. This was responsible for the failure of
ACI method to gain desired strength when coarse
aggregates of higher voids are used.
3. H. Faghani Nobari and R.Ejlaly (2003) [5]
have studied about the punching shear Resistance of
high strength concrete slabs and found that the use of
high strength concrete improves the punching shear
resistance allowing higher forces to be transferred
through the slab column connection.
4. Eugen Brihwiler and Emmanuel Denarie
(2008) [6] studied about the rehabilitation of concrete
structures using Ultra-High Performance Fibre
Reinforced Concrete (UHPFRC) and found that it
combines efficient protection and resistance functions
of UHPFRC with conventional structural concrete. It
was also found that the rehabilitated structures
significantly improved structural resistance and
durability. The full scale realizations of the concept
under realistic site conditions demonstrate the potential
of applications and that the technology of UHPFRC is
mature for cast in-situ and prefabrication using standard
equipment for concrete manufacturing
5. V.K.R. Kodur and L.T Phan (1996) [7]
studied about the fire performance of High Strength
Concrete and found that High Strength Concrete is a
high-performing material and offers a number of
benefits over Normal Strength Concrete. However, it
was found that there is a concern on the occurrence of
spalling and lower fire endurance of High Strength
Concrete (as compared to Normal Strength Concrete).
The main parameters that were found influencing fire
performance of High Strength Concrete at material
level are: concrete strength, silica fume, concrete
moisture content, concrete density, fibre reinforcement,
and type of aggregate. At the structural level it was
found that, tie spacing, confinement, tie configuration,
load levels and size of the members play an important
role in determining fire endurance.
3. Experimental Program
Preliminary investigations were carried out to
develop M100 grade concrete. The mix proportion
arrived as per ACI 211.11 was 1:0.556:1.629 by weight
with w/c ratio as 0.25. The estimated batch quantities
per cubic meter of concrete were: cement, 671.81 kg;
fine aggregate, 373.33 kg; coarse aggregate, 1094.4 kg
and water, 167.95 litres. The optimum dosages of
Mineral and Chemical admixtures were identified as
6% and 1.5% of quantity of cement respectively from
the previous investigation.
3.1 Rheobuild 1100
The basic components of RHEOBUILD 1100
are synthetic polymers which allow mixing water to be
reduced considerably and concrete strength to be
enhanced significantly, particularly at early ages.
Rheobuild 1100 is a chloride free product. It allows the
production of very flowable concrete, with a low
water/cement ratio. Concrete with Rheobuild shows
strengths higher than concrete without admixture
having the same workability.
3.2 Silica Fume (Micro Silica)
It is a byproduct of producing silicon metal or
ferrosilicon alloys. Because of its chemical and physical
properties, it is a very reactive pozzolana. Concrete
containing silica fume can have very high strength and
can be very durable. Silica fume is available from
suppliers of concrete admixtures and when specified, is
simply added during concrete production. Placing,
finishing and curing silica fume concrete require special
attention on the part of the concrete contractor. Silicon
metal and alloys are produced in electric furnace. The
raw materials are quartz and wood chips. The smoke
that results from furnace operation is collected and sold
as silica rather than being land filled.
A. Sreenivasulu, Dr. K. Srinivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue4, July-august 2012, pp.1944-1948
1946 | P a g e
3.3 Casting and curing specimens
The test specimens were demoulded after a lapse of
24 hours from the commencement of casting and
submerged in water until the time of testing.
3.4 Exposing the specimen to elevated
temperatures An oven with a maximum temperature
of 3000C was used for exposing the specimens to
different elevated temperatures. It was provided with
a thermostat to maintain constant temperatures at
different ranges. The specimens were kept in the
oven as shown in fig.2 for a specified duration after
the temperature in the oven reached the defined
temperature. The specimens were heated to different
temperatures of 50, 100, 150, 200 and 2500C for
different durations of 1, 2, 3 and 4 hours at each
temperature. The specimens were tested for their
strengths with minimum delay after removing from
the oven in a hot state under unstressed condition.
3.5 Testing the specimens
3.5 Testing the specimens
The cubes and cylinders after heating in the oven
were tested by using compression testing machine of
capacity 400 tons and the values of compressive and
split tensile strengths are as shown in Tables 1 and 2.
Table 1 : Compressive and % Residual compressive strengths of cubes after exposing to elevated temperature
Temperature
(0C)
Compressive Strength (N/mm2)
% Residual Compressive strength
1 hour
duratio
n
2 hours
duratio
n
3 hours
duratio
n
1 hour
duratio
n
2 hours
duratio
n
3 hours
duratio
n
27
131.67
131.67
131.67
100.0
100.0
100.0
50
140.39
146.93
134.29
106.62
111.59
101.99
100
148.24
136.47
143.01
112.58
103.65
108.61
150
144.75
134.94
138.43
109.93
102.48
105.13
200
136.25
131.24
135.16
103.48
99.67
102.65
250
120.77
144.32
130.58
91.72
109.61
99.17
Fig. 1 Cubes on
Vibrating table during
Compaction
Fig. 2 Cube in
Oven while heating
Fig. 3 Testing of Cylinder
during split tensile strength test
Fig. 4 Tested
Concrete cube
A. Sreenivasulu, Dr. K. Srinivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue4, July-august 2012, pp.1944-1948
1947 | P a g e
Table 2 : Split tensile and % Residual split tensile strengths of cylinders after exposing to elevated temperature
Temperature
(0C)
Split Tensile Strength (N/mm2)
% Residual Split Tensile strength
1 hour
duratio
n
2 hours
duratio
n
3 hours
duratio
n
1 hour
duratio
n
2 hours
duratio
n
3 hours
duratio
n
27
30.79
30.79
30.79
100.00
100.00
100.00
50
38.50
36.83
35.72
125.04
119.62
116.01
100
44.62
26.83
36.28
144.92
87.14
117.83
150
35.38
29.89
27.87
114.91
97.08
90.52
200
26.41
28.50
20.71
85.77
92.56
67.26
250
20.43
18.63
17.38
66.35
60.51
56.45
4. Results and Discussions
4.1 Compressive strength
The factors that influence the compressive
strength of Ultra strength concrete when exposed to
elevated temperatures are temperature and time of
exposure. The test results are presented in Table 1.
The variation of % Residual Compressive strength
with temperature for different exposure durations is
shown in Fig.5. The compressive strength at any
temperature is expressed as the % of Compressive
strength at room temperature. The heated
specimens are tested in hot condition for
compressive strength according to IS: 516-19592
4.2 Split Tensile strength
Residual splitting tensile strength of
concrete was found to be influenced by the
temperature to which it was exposed and the
duration of exposure. Residual splitting tensile
strength of all heated specimens at any exposure
time was expressed as the percentage of 28 days
split tensile strength of unheated concrete
specimens. The test results are presented in Table
2. The variation of % Residual Split tensile strength
with temperature for different exposure durations is
shown in Fig.6. The Split tensile strength at any
temperature is expressed as the % of Split tensile
strength at room temperature.
4.3 Effect of temperature on residual
Compressive strength
The variation of Compressive strength
with the increase in temperature is studied in terms
of the percentage residual compressive strength for
different durations of 1, 2, 3 and 4 hours. Initially,
the strength increased with temperature 50 to 1000C
for different durations and beyond that it was
reduced. The maximum Compressive strength was
noticed when the cube was heated at1000C for 1
hour duration.
4.4 Effect of temperature on residual Splitting
tensile strength
The variation of splitting tensile strength
with the increase in temperature is studied in terms
of the percentage residual Splitting tensile strength
for different durations of 1, 2, 3 and 4 hours.
Initially, the strength increased with temperature
upto 1000C for different durations and beyond that
it got reduced. The maximum splitting tensile
strength was noticed when the cylinder was heated
at1000C for 1 hour duration.
80
85
90
95
100
105
110
115
120
125
050 100 150 200 250 300
Temperatrue (Degree Celsius)
% Residual Compressive Strength
1 Hour Duration
2 Hours Duration
3 Hours Duration
4 Hours Durartion
Fig. 5 Variation of % Residual Compressive
strength with temperature
Fig. 6 Variation of % Residual Split tensile strength
with temperature
20
40
60
80
100
120
140
160
180
050 100 150 200 250 300
Temper ature (De gree Celsius)
% Residual Split T ensile Strength
1 Hour Duration
2 Hours Duration
3 Hours Duration
4 Hours Duration
A. Sreenivasulu, Dr. K. Srinivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue4, July-august 2012, pp.1944-1948
1948 | P a g e
5. Conclusions
On the basis of the experimental work with
ranging temperature from 50 to 2500C, the
following conclusions are drawn.
a) The compressive and split tensile strengths of
M100 concrete are increased initially upto a
temperature of 50 - 1000C and beyond that
they got reduced rapidly with increasing the
temperature
b) It was observed that major part of loss in split
tensile strength is taking place in the first 1
hour exposure.
c) The compressive and Split tensile strengths are
lost very much when they are heated at 2500C.
References:
1. ACI 211.1-91 - Standard Practice for
Selecting Proportions for Normal,
Heavyweight and Mass Concrete.
2. IS : 516-1959 - Indian Standard Methods
of tests for Strength of concrete
3. Klaus Holschemacher and Sven Klotz
(2003); “Ultra High Strength Concrete
under Concentrated Load”, Department of
Civil Engineering, HTWK Leipzig.
4. Z. Wadud and S. Ahmad (2001); “ACI
method of concrete mix design- A
parametric study”, The Eighth East Asia-
Pacific Conference on Structural
Engineering and Construction, Nanyang
Technological University, Singapore.
5. H.Faghani Nobari and R.Ejlaly (2003);
“Punching Shear Resistance of High
Strength Concrete slabs”, Department of
Civil Engineering, Iranian Science and
Technology University, Tehran.
6. Eugen Brihwiler and Emmanuel Denarie
(2008), “Rehabilitation of concrete
structures using Ultra-High Performance
Fibre Reinforced Concrete”, Department
of Civil Engineering, Lausanne,
Switzerland.
7. V.K.R.Kodur and L.T. Phan (1996); “Fire
performance of high-strength concrete”,
National Institute of Standar
andTechnology,Gaithersburg.
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Full-text available
  • Nov 2013
An original concept is presented for the durable rehabilitation and strengthening of concrete structures. The main idea is to use ultra-high performance fibre reinforced concrete (UHPFRC) complemented with steel reinforcing bars to protect and strengthen those zones of the structure that are exposed to severe environmental influences and high mechanical loading. This concept efficiently combines the protection and resistance properties of UHPFRC and significantly improves the structural performance of the rehabilitated concrete structure in terms of durability. The concept has been validated by means of field applications, demonstrating that the technology of UHPFRC is now well developed for cast in situ and prefabrication using standard equipment for concrete manufacturing. This novel technology is a step forward towards more sustainable structures.
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Factors governing the fire performance of high strength concrete systems
Article
  • Sep 2007
  • FIRE SAFETY J
High strength concrete (HSC), is being increasingly used in a number of building applications, where structural fire safety is one of the major design considerations. Many research studies clearly indicate that the fire performance of HSC is different from that of normal strength concrete (NSC) and that HSC may not exhibit same level of performance (as NSC) in fire. This paper discusses the material, structural and fire characteristics that influence the performance of HSC under fire conditions. Data from earlier experimental and numerical studies is used to illustrate the impact the concrete (material) mix design and structural detailing (design) has on fire performance of HSC systems. An understanding of various factors influencing fire performance will aid in developing appropriate solutions for mitigating spalling and enhancing fire resistance of HSC members.
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ACI method of concrete mix design-A parametric study
  • Jan 2001
  • Z Wadud
  • S Ahmad
Z. Wadud and S. Ahmad (2001); "ACI method of concrete mix design-A parametric study", The Eighth East Asia-Pacific Conference on Structural Engineering and Construction, Nanyang Technological University, Singapore.