Performance evaluation of reactive powder concrete with polypropylene fibers at elevated temperatures

Construction and Building Materials 169 (2018) 499–512

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Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat

Performance evaluation of reactive powder concrete with polypropylene
fibers at elevated temperatures
Parameshwar N. Hiremath, Subhash C. Yaragal ⇑
Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575025, India

h i g h l i g h t s
 Performance of RPC with different fiber dosages at elevated temperatures is investigated.
 RPC with at least 0.1% polypropylene fiber dosage, checks spalling at elevated temperatures.
 0.5% fiber dosage, has shown superior fire endurance characteristics.

a r t i c l e

i n f o

Article history:
Received 31 July 2017
Received in revised form 18 February 2018
Accepted 1 March 2018

Keywords:
Reactive powder concrete
Polypropylene fibers
Elevated temperature
Mechanical properties

Microstructure

a b s t r a c t
Reactive Powder Concrete (RPC) is a type of ultra-high strength concrete. Due to its dense microstructure,
is vulnerable to explosive spalling at elevated temperatures. Remarkable application of RPC in special
structures throughout the world has drawn the attention to understand the performance of RPC at elevated temperatures, which has not been investigated extensively yet. The main objective of this work
was to evaluate the performance of RPC at elevated temperatures from 200 °C to 800 °C, by obtaining
residual mechanical properties after exposure. The study aims to find an optimum fiber dosage for spalling protection of RPC. To improve the mechanical properties, RPC incorporating fiber dosage from 0.1% to
0.9% is studied. The thermal deterioration of RPC is assessed using ultrasonic pulse velocity, water
absorption and sorptivity. Results shows that 0.1% fiber dosage is enough to control spalling of RPC up
to 800 °C. To enhance the residual properties of RPC exposed to elevated temperatures, it is recommended to use fiber dosage of 0.5%. The study also includes microstructural analysis of RPC subjected
to elevated temperatures, to assess and evaluate the formation of pores and cracks.
Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction
Concrete is a composite material consisting of various ingredients, that are entirely different in their properties from each other.
It is very difficult to assess the fire resistance of concrete, due to
different thermal characteristics of each ingredient. The most
vencher part is presence of moisture and porosity of the concrete.
The utilization of High Strength Concrete (HSC) for last few decades, throughout the world, has proved itself to be promising construction material [1]. But in case of fire performance, some
research studies have shown that HSC has disadvantage to resist
fire, i.e., it is more prone to explosive spalling, due to low permeability and high brittleness when compared to normal strength
concrete [2]. The same observation was made in case of High Performance Concrete (HPC) due to dense microstructure and very

⇑ Corresponding author.
E-mail address: (S.C. Yaragal).
/>0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

low permeability seems to be a disadvantage, in the situations
where HPC is exposed to fire [3]. From earlier studies, it is proven

that HPC, is susceptible to spalling or even explosive spalling when
subjected to rapid rise in temperature during fire exposure. Spalling of concrete depends on many parameters such as ingredients
of mix, type of aggregate, rate of temperature exposure, thermally
induced mechanical stress, density of concrete, moisture content
etc. The main two reasons for explosive spalling of HPC are, thermal stress induced by rapid temperature rise and water vapour
which may cause high pore vapour pressure. To overcome spalling
of concrete, addition of fibers, especially polypropylene fibers to
concrete is well known fact in the field of construction. Addition
of polypropylene fiber has been proved to be very efficient in
reducing spalling of concrete at elevated temperatures. Polypropylene fibers melt at temperature of 170 °C, whereas spalling occurs
between 190 °C and 250 °C [4]. Presence of polypropylene fibers
reduces the internal vapour pressure and eliminates the chances
of spalling under fire. The length of fibers has significant effect in


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P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512

preventing explosive spalling of concrete. Using 12 mm length of
polypropylene fibers efficiently mitigates the explosive spalling
when compared to 6 mm length [5]. This is in agreement with findings of [6] who reports that as length of fiber increases such as 12,
19 and 30 mm, it proves to be more effective in preventing spalling
when compared to shorter polypropylene fibers of length 3 mm
and 6 mm. From literature, it is learnt that adding polypropylene
fiber in HSC was good to reduce chances of spalling, but however
some of researchers have reported that this has an adverse effect
on strength.
RPC is a new emerging construction material in the modern era.
RPC with its high strength and durability properties, has been gradually replacing HSC and HPC, especially in special structures like

long span bridges, tall structures and nuclear power plants. As it
is becoming commonly used, the chances of being exposed to high
temperature also increases in the event of accidental fires. However, so far only a few researchers have reported on its performance at elevated temperatures. RPC has dense microstructure
this seems to be a disadvantage in the situation where the fire
endurance is a necessity. The absence of voids does not relieve
the internal stress that creates a major problem. This problem
can be solved by addition of polypropylene fibers to the mix. However only a few studies have been carried out on RPC subjected to
elevated temperatures and they also revealed contrary results,
necessitating further research.
An experimental investigation made in 2015 [7,8] found that,
plain RPC spalled under high temperature and spalling starts at
360 °C, whereas RPC with polypropylene fibers shows no spalling.
The reason behind spalling and performance of RPC prepared with
different fiber dosages under elevated temperatures remains to be
investigated. Furthermore, mechanical properties including compressive strength, split tensile strength and weight loss of RPC,
exposed to elevated temperatures are also of great concern from
the serviceability requirements. Experiments indicate that, despite
the positive effects of polypropylene fibers in enhancing the residual strength of the heated RPC, an overdose of fiber could have an
adverse influence on the RPCs thermomechanical properties. A
proper dosage of fibers to improve the spalling resistance of RPC
depends on the mix proportion and the geometry of the fibers. In
case of elevated temperatures resistance performance, of RPC
remains a concern, more so in relation to explosive spalling. Earlier
researchers have investigated that RPC is vulnerable to explosive
spalling under elevated temperatures, which seriously jeopardizes
the safety of RPC applications. Yang et al. [9] studied performance
of RPC under elevated temperature in the range of 400 °C–800 °C.
Results show considerable reduction in strength and elastic modulus values due to elevated temperatures.
Liu and Huang [10], have reported that the residual strength of
RPC at elevated temperatures decreases significantly at temperature beyond 300 °C when compared that of RPC at room temperature. The reduction in strength is mainly because of the pore

pressure mechanism in RPC that prevents water vapour from free
transport within and its escape from the matrix, when exposed
to elevated temperatures. Pore pressure mechanism is caused
due to dense microstructure and mainly due to disconnected pores.
Explosive spalling occurs when the pore pressure in the matrix
accumulates to a threshold, exceeding the tensile strength of concrete. Kalifa et al. [11] suggested that mixing polypropylene fibers
could reduce the pore pressure of concrete and decreases the risk
of spalling and also as fiber content increases pore pressure
decreases. Essential problem associated in understanding, spalling
of RPC including pore characteristics, pore size distribution, pore
pressure and factors related to explosive spalling are yet, not
exhaustively studied. However, dense microstructure of RPC prevents evaporation and escape of free water from the interior portion of RPC specimen at elevated temperatures. Due to its low

permeability and discontinuous pore network, the risk of explosive
spalling has jeopardized the safety of RPC structure. This hinders
the commercial development and application of RPC in the field
of modern constructions. Therefore, the physical parameters like
weight loss, colour change, crack development, mechanical properties such as compressive strength, split tensile strength and water
absorption of RPC at elevated temperatures is required to be
investigated.
The effect of different fiber dosage on spalling has not been
reported for RPC. Since, the RPC is more likely to spall than HSC,
it is necessary to investigate and understand the spalling behavior
of RPC and recommend optimum fiber dosage to prevent spalling
without compromise on fresh and hardened properties. The effect
of elevated temperatures up to 800 °C on fiber reinforced RPC has
been the scope of this study. Mechanical properties such as compressive strength, split tensile strength and physical parameters
like weight loss, crack development at different temperatures were
determined. Durability properties like water absorption and sorptivity have also been studied. This study also investigates the
degradation of microstructure and its effect on residual mechanical

properties of RPC after exposure to elevated temperatures. To identify the deuteration portion at microstructural level, RPC specimens were subjected to Scanning Electron Microscope (SEM)
analysis. The SEM results strengthen and reinforce the reason
behind reduced mechanical properties after exposure. The previous researcher’s results on mechanical properties of RPC containing polypropylene fibers are not in agreement with each other.
This is due to differences in curing condition of specimen, material
used for RPC production and the way of experimentation. The optimum fiber dosage to prevent explosive spalling and simultaneously maintaining the residual strength to the expected range for
RPC is yet to be investigated in detail. Therefore, the focus of present investigation is to determine minimum dosage of polypropylene fibers required to mitigate spalling and to possess acceptable
residual strength levels.

2. Experimental program
2.1. Materials
RPC is composed of cement, silica fume, quartz powder and silica sand with very low w/b ratio to achieve required workability.
High range water reducing admixtures are used. RPC is cement
based concrete mixture. In the present study, Ordinary Portland
Cement of 53 grade was used which complies with IS:122692013. The chemical and physical properties of cement are shown
in Tables 1 and 2 respectively. Silica fume is the second basic
important ingredient of RPC which fills the voids of micro particulates in the cement. It also produces secondary hydrates products
by pozzolanic reaction from the results of primary hydration.
Undensified silica fume was used in the present study, which complies with ASTM C1240-03 a and IS:15388-2003. Chemical composition of undensified silica fume is presented in Table 1. The
particle size of silica fume is extremely very fine of size 0.1 mm.
The physical properties of silica fume are tabulated in Table 2.
Quartz powder is the finest material compared to cement. The particle size of quartz powder ranges from 10 mm to 45 mm. It acts as a
filler material in the mix proportion of RPC. The chemical and
physical properties of quartz powder are tabulated in Tables 1
and 2 respectively. Silica sand is largest particle size material in
mix proportion of RPC. In the present study silica sand was used
with particle size ranging from 150 mm to 600 mm. The sand confirms to zone IV grading requirement as per IS: 383-2016. To maintain the required workability, a second generation polycarboxylic
ether polymer, high range water reducing superplasticizer Master


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P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512
Table 1
Chemical composition of RPC ingredients.
Constituents

Cement
Silica Fume
Quartz Powder

Chemical compositions (%)
CaO

SiO2

Al2O3

MgO

Fe2O3

TiO2

SO3

59.67
0.16
–

20.21

95.89
>99

9.08
0.22
0.17

2.02
0.11
–

3.64
0.10
0.56

0.45
–
–

2.41
–
–

Table 2
Physical properties of RPC ingredients.
Mix Constituents

Physical properties
Specific surface area/Particle size

Cement
Silica Fume
Quartz Powder
Silica Sand

2

330 (m /kg)
20,000 (m2/kg)
10–45 mm
150–600 mm

Specific Gravity

Density (kg/m3)

Colour

LOI

3.15
2.26
2.60
2.60

3210
300
700
1630

Light grey
Dark grey
Milky white
Yellowish-white

1.45
1.10
–
–

Glanium Sky 8276 was used in the present study which meets the
requirements of IS: 9013-1999. Polypropylene fibers of length 12
mm were used in the present study.
2.2. Mix proportion and specimen preparation
The mixing method adopted in producing RPC is quite involved
when compared to conventional concrete production [12,13]. The
only change is the addition of polypropylene fibers and increment
of superplasticizer dosage to maintain required flowability. Mix
proportion of RPC adopted is presented in Table 3.
The mixing sequencing of RPC as followed is, dry mixing of all
ingredients in first stage, later in the second stage addition of half
volume of water containing half the amount of superplasticizer. In
the present study, same mixing sequence was adopted [12] with
one more value-added ingredient that is polypropylene fibers.
These fibers were added at the end of third mixing stage with
increased mixing time by two minutes in total mixing duration.
The entire mixing process is completed within 14 min. Normal
pan mixer with mixing speed of 80 RPM was used. After completion of mixing, fresh mix of RPC was poured in 100 mm cube
moulds and compacted on vibration table to remove air voids.
After one day of setting, cubes were removed from moulds and

kept for curing under water for 28 days.
2.3. Parameters studied
Effect of different dosages of polypropylene fibers in preventing
explosive spalling of RPC has been focused in the present study.
The polypropylene fibers content is varied from 0.1% to 0.9%. The
performance of RPC prepared with different fiber dosages at elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C, are investigated using digitally programable electric muffle furnace as
shown in Fig. 1. The rate of heating was 5 °C/min. The retention
period at elevated temperature, is taken as 30 min for all temperature levels. The microstructural investigation was carried out on
RPC samples exposed to different temperature levels. Physical
parameters, such as colour change and crack development at different elevated temperatures were recorded by physical
observation.

Fig. 1. Electric Muffle Furnace.

2.4. Parameter evaluated
In this study an attempt was made to study the performance of
plain RPC at elevated temperature. RPC after exposure to elevated
temperatures, under goes changes in physical and chemical properties. Generally assessment of fire damaged structure, usually
starts with visual observation of colour change, crack development
and spalling of concrete [14]. Changes in physical properties
including colour change and crack development have been considered here for assessment after exposure. The variation in colour
change and initiation of crack for RPC mixes prepared with different fiber dosages have been evaluated by careful inspection. The
weight loss at a given temperature was measured from three specimens. Average percentage of weight loss were determined for RPC
specimen prepared with various fibers dosages. The weights of
samples were taken before and after exposure to elevated temperatures for weight loss evaluation. Portable Ultrasonic Nondestructive Digital Indicating Tester (PUNDIT) measurement is one of the
quick methods that indicates, the qualitative degree of damage.
Deterioration of RPC after exposure to elevated temperatures, is
assessed by using PUNDIT. The UPV test is conducted on 100 mm
cubes as per IS:13311 (Part 1):1992. Compressive strength test
was conducted on cubes of 100 mm as per IS: 516-1959. The resid-

Table 3
Mix proportion of RPC.
Cement

Silica fume

Quartz powder

Water/binder ratio

Superplasticizer dosage

900 kg/m3

20%

20%

0.18

1.5 to 2.5%


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P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512

ual compressive strength is evaluated for each temperature level.
Compression testing machine of capacity 2000 kN was used in

the present study. Split tensile test was conducted on exposed
100 mm RPC cube specimen. The testing procedure as per IS:
5816-1970, was fallowed. The most important essential parameters governing the concrete durability is penetration of water,
gas and ions which mainly depends upon micro structure and
porosity of concrete. It is well known that RPC consists of dense
microstructure. The development of pores and micro cracks under
elevated temperatures has a major impact on durability properties
like water absorption and sorptivity. The water absorption test was
carried out on exposed 100 mm RPC cubes as per BS 1881-122. RPC
cubes after exposure to elevated temperature were cooled down to
room temperature. Later weight of the cubes were taken and
immersed under water for 24 h. After 24 h, the cubes were
removed and kept outside till it reaches to surface saturated condition then weight of cubes were taken. The same procedure was followed for all RPC cubes with different fiber dosages, which were
subjected to elevated temperature exposure.
Sorptivity test determines the rate of capillary rise in absorption
of water as a function of time when only one surface of the specimen is exposed to water ingress by capillary suction, during initial
contact with water. Before conducting sorptivity test, four side surfaces of exposed RPC cubes were sealed with paraffin wax to
ensure free water movement only through the bottom surface.
Then RPC specimen were kept on plastic strip in a tray such that
the free water level was about 5 mm above the bottom surface of
specimen in contact with water. The mass of water absorbed per
unit area before immersion and subsequently after intervals of 5
min, 10 min, 20 min, 30 min, 60 min, 180 min, 360 min and 1440
min was determined. Test setup of sorptivity is as shown in
Fig. 2. Three cubes were used for each test.

2.5. Microstructure analysis
In the present study SEM was used to understand the morphology of RPC after exposure to different elevated temperatures. The
presence of polypropylene fiber in RPC at low temperature exposure, that created channels through melting process of polypropylene fiber was confirmed by secondary electron images at high
magnification using SEM. The SEM was aided with Energy Dispersive X-ray Spectroscopy (EDS) which facilitates understanding the

elemental composition and atomic weight of chemical compounds
developed in RPC, when exposed to elevated temperatures. Based
on the presence of chemical compounds such as Ca, Si, Al and S
and their atomic weight, the ratio of Si to Ca was determined. A
detailed microstructural investigation was carried out to understand the structural arrangements of hydrated and unhydrated
products when RPC specimen were exposed to different elevated
temperature levels.

Fig. 2. Water sorptivity Setup.

3. Results and discussion
3.1. Performance of plain RPC at elevated temperatures
Current study includes performance of plain RPC at elevated
temperatures. The results are as shown in Fig. 3 and Table 4.
From results, it can be observed that as temperature increases
strength also is observed to increase. The increase in strength
observed from 100 to 350 °C is around 20%. The increase in
strength may be due to rapid hydration of unreacted cement and
silica fume which produce large amounts of hydrated products.
Thermoactive nature of quartz powder also participates in the
hydration process when RPC is exposed to elevated temperatures,
that leads to formation of dense hydrated products. When plain
RPC is exposed to 400 °C, explosive blasting of RPC was observed
as shown in Fig. 4. Therefore, the results of residual strengths of
RPC, have been reported in the above Table up to 350 °C.
3.2. Physical observation
The damage to the fiber reinforced RPC, after being exposed to
elevated temperature can be roughly detected by observing the
RPC surface. Fig. 5(a)–(c) shows RPC surface with different fiber
dosage exposed to various elevated temperature levels (200 °C,

400 °C, 600 °C, 800 °C), along with the one at ambient temperature.
From Fig. 5(a)–(c) it can be observed that, at 200 °C, there is no
colour change and visible crack development on RPC surface. At
400 °C, formation of light micro cracks was observed on RPC surface composed of 0.1% fiber dosage. The RPC cubes composed of
0.5% and 0.9% have not shown any crack development at 400 °C
of exposure. RPC exposed to 600 °C has shown visible cracks on
surface of all RPC cubes composed of different fiber dosages.
Among three different fiber contents, the RPC prepared with
low fiber dosage (i.e. 0.1%) has shown considerable surface cracks,
compared to other RPC prepared with high fiber dosages. From
Fig. 5 it can be observed that as fiber content increases number
of cracks appears to get reduced. The presence of small pores were
observed on the surface of RPC specimen composed of 0.1% fiber
content at 600 °C. The presence of these pores were less in number
on surface of RPC specimen composed of 0.5 and 0.9% fiber
dosages. The slight colour change was observed in this temperature range. Colour of cubes turns to slight pink reddish and the
intensity of colour decreases as fiber dosage increases.
When RPC cubes were exposed to 800 °C, the development of
crack was more pronounced, especially for RPC cubes produced
with 0.1% fiber as shown in Fig. 5(a). The RPC specimen have

Fig. 3. Compressive strength of plain RPC at elevated temperatures.


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P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512
Table 4
Compressive strength results at elevated temperatures.
Temperature (°C)

100

150

200

250

300

350

Mean (MPa)

105

111

115

119

123

126

fiber dosage inefficient to reduce spalling of concrete. The vapour
pressure created inside the concrete at elevated temperature leads
to formation of micro cracks. These small width cracks grew to

large widths at higher elevated temperatures.

3.3. Weight loss

Fig. 4. Explosive blasting of plain RPC at elevated temperatures.

shown, major colour change when exposed to 800 °C. From Fig. 5
(a), it can be observed that colour of cubes turns to grey reddish.
The presence of more surface voids was observed on RPC composed of low fiber dosages. Spalling was not observed in entire
exposure condition at elevated temperatures. This indicates that
0.1% of polypropylene fiber is sufficient to prevent explosive spalling of RPC up to 800 °C.
From the above observation, it can be concluded that, as fiber
content increases, leading to decreases in surface cracks and pores.
The thick cracks were observed on RPC samples composed of low
fiber dosage at elevated temperatures. This is may be due to low

27 ˚C

200 ˚C

Fig. 6 shows the variation of average percentage loss in weight
with elevated temperature for RPC specimen of different fiber
dosages. From Fig. 6, it can be observed that as temperature
increases, there is an increase in percentage weight loss in all
RPC specimen prepared with different dosages. In case of RPC prepared with 0.1% fiber dosage show, lower percentage of weight loss
at elevated temperatures compared to other RPC mixes prepared
with 0.5% and 0.9%. This is because at temperatures above 170
°C, polypropylene fibers melt and create channels inside the concrete. RPC with high dosage of fiber, suffer more weight loss due
to fiber evaporation at high temperatures.
At temperatures, above 600 °C, these fibers turn to molten state

and evaporates. As fiber content increase, the rate of evaporation
also increases. Therefore, there is an increase in percentage weight
loss with increase in fiber dosage at elevated temperatures. The
weight loss predominantly occurs, due to loss of water in all three
forms, namely free water, adsorbed water and chemically bounded
water. From results, it can be observed that there is no significant
difference observed between RPC mixes prepared with different
fiber dosages at elevated temperature of 200 °C.

400 ˚C

600˚C

800˚ C

(a)

27 ˚C

200 ˚C

600˚C

400 ˚C

800˚ C

(b)

27 ˚C

200 ˚C

400 ˚C

600˚C

(c)
Fig. 5. Fiber dosage (%) (a) 0.1 (b) 0.5 (c) 0.9.

800˚ C


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P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512

Fig. 6. Average percentage weight loss at different elevated temperatures.

At 400 °C the percentage weight loss, is more for RPC mix prepared with 0.9% fiber dosage. As fiber content increases the percentage weight loss is also increasing with temperature [15]. The
same trend can be observed at 600 and 800 °C. At 800 °C, maximum variation in weight loss was observed between RPC mixes
prepared with different fiber dosages. There seems to be approximately 5% and 7% variation in weight loss with 0.5% and 0.9% fiber
dosage when compared to 0.1% fiber dosage.
There is a sudden increase in weight loss beyond 400 °C. The
rate of weight loss increase drastically as fiber dosage increase
beyond 400 °C. From the above observations, it can be stated that
the apparent bulk mass loss occurs between 400 °C and 800 °C.
This loss may be due to evaporation of water and in addition
beyond 400 °C there may be decomposition of hydrated and unhydrated compounds. The process of dehydration starts beyond 400
°C, which release considerable amount of chemically bound water

creating the interior pores. At higher temperature levels,
polypropylene fibers have been completely vaporized. Hence
cumulative effects of these parameters make RPC specimen to suffer considerable amount of weight under elevated temperatures.

3.4. Ultrasonic pulse velocity
This test is a qualitative one, used to evaluate the quality of concrete and this technique is sensitive to degradation phenomena
including internal cracking and other deuteration due to thermal
treatment. UPV test was carried out to determine the severity of
damage, when RPC specimen were exposed to elevated
temperatures.
Fig. 7 shows results of RPC specimen prepared with various
fiber dosages subjected to elevated temperatures. From Fig. 7 it
can be observed that, as fiber dosage increase, the UPV also
increases at room temperature. In case of 0.1% fiber dosage, the
UPV results show sudden drop in velocity beyond 200 °C.
For the case of 0.1% fiber dosage, the value of UPV decreases
continuously with increase in temperature up to 400 °C. The smaller the relative UPV value, more is the severity of the damage. The
reduction in UPV value in 0.1% fiber dosage, is due to insufficient
fiber content which is unable to release vapour pressure from core
of concrete, that leads to micro-cracks. As number of cracks
increases there will be chances of discontinuous matrix and formation of voids. This leads to reduction in UPV values.
The RPC mixes, prepared with 0.5 and 0.9% fiber dosages have
shown higher UPV values compared to RPC mix prepared with

0.1% fiber dosage for 200 °C and 400 °C. Values for the case of
0.1% fiber dosage, shows reduction in velocity from 4.78 to 2.00
km/s with increase, in temperature from 27 °C to 800 °C and consequently gradual deterioration in the quality of concrete. It is
observed that, beyond 200 °C the UPV values decrease rapidly,
due to sharp deterioration in the physical state of exposed RPC.
Beyond 400 °C the UPV values of RPC mixes prepared with 0.5%

and 0.9% fiber dosages have shown a large decrease. This is may
be due to evaporation of fibers that create channels which leads
to increase of internal micro cracks. As number of microcracks
increase, the quality of concrete decreases directly. This leads to
higher reduction in UPV values for cases of 0.5% and 0.9% fiber
dosage when compared to the case with 0.1% fiber dosage for
600 °C and 800 °C.
The lowest UPV value, was observed for RPC specimen prepared
with 0.9% fiber dosage, and at 800 °C. Formation of pores and
cracks through melting of fibers in case of higher dosage of fibers,
under elevated temperatures leads to physicochemical changes in
cement paste and thermal incompatibility between cement paste
and aggregate which is, believed to be responsible for the deterioration in mechanical properties.
At 800 °C, the UPV values for 0.1% dosage, is quite higher than
for the specimen prepared with 0.9%. This is due to less number
of cracks developed inside the concrete after evaporation but in
case of 0.5% and 0.9% fiber dosage, the number of microcracks in
specimen seems to be more, hence there is sharp decrease in
UPV values at 800 °C. From the above discussion, it was observed
that as fiber dosage increases, UPV value also increases at room
temperature as well as at 200 °C. Beyond 200 °C there is a sharp
decrease in UPV values for 0.1% and 0.9% fiber induced RPC specimen. After 400 °C, also 0.5% fiber embedded RPC specimen have
shown better UPV values, that fall in the range of good quality of
concrete as per Table 5.

3.5. Compressive strength
RPC belongs to HSC category, the dense microstructure of RPC
does not allow release of pressure, created by vapour under elevated temperatures. This may lead to development of internal
cracks in the cement matrix zone of RPC. Which in turn may cause
spalling of concrete, so to reduce this event from happening, different polypropylene fiber dosages were added to RPC mixes to study

their performance at elevated temperatures. Compressive strength
at room temperature and residual compressive strengths at differ-


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Fig. 7. UPV results of RPC exposed to different elevated temperatures.

Table 5
Velocity criterion for concrete quality grading [IS:13311 (Part 1):1992].
Sl. No

Pulse velocity (km/s)

Concrete quality grading

1
2
3
4

Above 4.5
3.5–4.5
3.0–3.5
Below 3.0

Excellent
Good

Medium
Doubtful

ent elevated temperatures, for RPC with different fiber dosages, are
presented in Table 6 and in Fig. 8. Normalized residual strength
variation of RPC at elevated temperatures is also shown in Fig. 9.
Increase in fiber dosage has shown increase in compressive
strength at room temperature. At 200 °C, polypropylene fiber
dosage of 0.1, 0.5 and 0.9% has shown 3, 4 and 4% higher compressive strength compared to RPC at room temperature respectively.
The increased compressive strength is due to strengthened
hydrated cement paste after evaporation of free water at 200 °C,
which leads to greater Van der waals forces that cause cement
gel layer to come closer to each other [16].
At 400 °C exposure, the compressive strengths have increased
drastically for all RPC mixes as seen from Fig. 9. RPC mix prepared
with 0.1, 0.5 and 0.9% fiber dosage have shown 6, 13 and 13%
increase in compressive strengths respectively when compared
to RPC at room temperature. Increase in strength is mainly attributed to further hydration process, with catalyzed hydration
through non-reacted cement products, in the presence of steam
upshot under autoclaving effect formed in pastes, which is considered as advancement in chemical bonding process [17]. Among

three different fiber dosages, 0.5% and 0.9% have shown considerable higher compressive strengths up to elevated temperature of
400 °C. From Fig. 8 it can be observed that up to 400 °C as fiber content increases strength is also observed to increase. Porosity of concrete has a significant impact on pore vapour pressure.
Polypropylene fibers melt at temperature less than 300 °C, which
results in an increase in concrete porosity and creation of more
escape routes leading to reduction in bond water vapour pressure.
However, melting of polypropylene fibers causes thermal incompatibility between the aggregate and cement paste which leads
to increase in free space and creates a thermal shock absorber.
The melting of polypropylene fibers is beneficial for evaporation
of water vapour and improves the compressive strength of RPC,

up to 0.5%. Fiber dosage of 0.5% in RPC has shown best performance
at elevated temperatures.
Beyond 600 °C the residual compressive strength decreases significantly for all RPC mixes prepared with different fiber dosages.
This decrease is due to the transformation of calcium hydroxide
to calcium oxide in the range of 400 °C to 500 °C and reduction
and disintegration of Calcium Silicate Hydrated between 400 °C
and 600 °C [17]. Among three fiber dosage, RPC with 0.5% fiber content has shown highest residual compressive strength. This may be
due to right fiber dosage addition leads to proper and proportionate channels for release of vapour pressure there by reducing the
chances of spalling. However, at higher fiber dosage than optimum,
due to more pores, the strength suffers more.
The residual strength of RPC with 0.1% fiber dosage after exposure to 600 °C was 77.3% of its original strength at 27 °C, that is
22.7% reduction in compressive strength. For RPC with 0.5% fiber

Table 6
Compressive strength results of RPC at elevated temperatures.
Temperature (°C)

Fiber dosage (%)
0.1

27
200
400
600
800

0.5

0.9

Strength MPa

Normalized Strength

Strength MPa

Normalized Strength

Strength MPa

Normalized Strength

105
108
111
82
71

1.00
1.03
1.06
0.78
0.68

108
112
122
98
82

1.00
1.04
1.13
0.91
0.76

113
118
128
88
68

1.00
1.04
1.13
0.77
0.60


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Fig. 8. Compressive strength results of RPC at elevated temperature.

Fig. 9. Normalized compressive strength of RPC at elevated temperature.

dosage, the residual strength was 90% of its original strength at 27
°C, which was much more than residual strength obtained for RPC
with 0.1% fiber dosage. The reduction in compressive strength was

about 10% for RPC composed of 0.5% dosage at 600 °C. RPC with
0.9% fiber dosage at 600 °C has shown 22% reduction in compressive strength which is almost same as that of 0.1% fiber dosage at
600 °C. This shows that minimum fiber dosage 0.1% is not efficient
to maintain residual strength within acceptable range as well as
0.9% fiber dosage seems to be over dosage for RPC under elevated
temperatures. Results indicate that, 0.5% fiber dosage effectively
serves the purpose of reducing explosive spalling as well as maintain reasonable residual strength. The same observation was made
in the study of polypropylene reinforced concrete at elevated temperature [18].
RPC mixes exposed to 800 °C have shown considerable strength
loss. The residual compressive strength obtained for RPC with 0.1%
fiber dosage at 800 °C was around 68% which indicates 32% loss in
strength. However, for 0.5% fiber dosage, the residual strength
being 76% of its original strength at room temperature. For 0.5%
fiber dosage, there was only 24% reduction in strength which is
comparatively better than 0.1% fiber dosage.
The drastic reduction in residual compressive strength (40%)
was observed for RPC with 0.9% fiber content. This may be due to
adverse effect of over dosage of fibers that leads to creation of large

number of channels due to evaporation of fibers at high temperature. These channels propagate and enlarge in size causing early
failure of concrete. The reduced strength at 800 °C is due to transformation of quartz from a to b form that cause the volumetric
expansion of the RPC at approximately 571 °C, which results in
reduction of bonding between the aggregate and cement paste
[19]. The other strong reason for reduced strength at 800 °C is
the decomposition of calcium hydrate gel that causes severe deterioration of RPC [20].

3.6. Split tensile strength
The split tensile strength results of RPC with fiber dosage of 0.1,
0.5 and 0.9% at room temperature and at elevated temperatures are
presented in Table 7. The variation of split tensile strength is also

shown in Figs. 10 and 11. At 200 °C the split tensile strength of
RPC increases considerably when compared to RPC at 27 °C. From
Fig. 10 it can be observed that, as fiber content increases strength
is also increasing up to 400 °C. This shows positive impact of
polypropylene fibers in strength enhancement of RPC under tensile
loading. All three-different fiber dosage i.e. 0.1, 0.5 and 0.9% have
shown 26, 28 and 18% increase in split tensile strength at 200 °C
respectively.


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Table 7
Split tensile strength results of RPC at elevated temperatures.
Temperature (°C)

Fiber dosage (%)
0.1

27
200
400
600
800

0.5

0.9

Strength MPa

Normalized Strength

Strength MPa

Normalized Strength

Strength MPa

Normalized Strength

4.14
5.25
6.30
3.62
1.70

1.00
1.26
1.50
0.87
0.41

7.56
9.80
11.85
6.90
3.42

1.00
1.28
1.56
0.91
0.45

9.25
10.99
13.45
7.27
2.86

1.00
1.18
1.45
0.78
0.30

Fig. 10. Split tensile strength of RPC after exposure to elevated temperature.

Fig. 11. Normalized split tensile strength at elevated temperature.

The increased split tensile strength was also observed when RPC
specimen exposed to 400 °C. There was about 50, 56 and 45%
increase in tensile strength observed for fiber dosage of 0.1, 0.5
and 0.9% respectively. The drastic increase of strength of RPC for
all fiber dosages is due to development of secondary hydrated
and conversion of remaining unhydrated cement grains that
rapidly hydrated producing secondary hydrated gel with active
participation of silica fume at this temperature.

The increase in strengths is may be due to bonding effect
between fiber and matrix as we can observe from Fig. 10 with
increase in fiber dosage strength is also observed to increase. This
indicates positive influence of fiber effect on tensile strength
enhancement of RPC up to 400 °C. The tensile strength of RPC at

400 °C increases due to autoclave effect and the creation of shorter
and stronger siloxone elements that causes an increase in strength
in temperature range of 250–350 °C [19].
The drastic decrease in tensile strength of RPC after 600 °C was
observed for RPC mixes with various fiber dosages. The RPC with
0.5% fiber dosage has shown less deterioration in tensile strength.
The residual tensile strength is around 91% of its original strength
at 27 °C [21]. For RPC with 0.9% fiber dosage the residual strength
is less when compared to 0.5% fiber dosage and it is around 78% of
its original strength at 27 °C. The lowest tensile strength of RPC
with high dosage of polypropylene fibers is possibly be due to
dense network of melted channels created through evaporation
of fibers under elevated temperature that accumulate at a single


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place, initiating cracks. That leads to sudden failure of RPC specimen under tensile loading.
The similar strength deterioration trend was observed when
RPC specimen were exposed to 800 °C. The reduction in strength
is mainly because of chemical degradation and microcracking
due to excessive pore pressure and thermal incompatibilities

between aggregate and cement paste. The other reason for large
strength deterioration is phase changes of quartz aggregates. At
high temperature more than 600 °C transformation of quartz from
a to b form causes the volumetric expansion of RPC at approximately 571 °C, which results in reduction of bonding between
the aggregate and cement paste [22].
RPC with 0.5% fiber dosage has shown good residual strength
when compared to RPC with 0.1% and 0.9% fiber dosages. The mean
high strength is due to proper bonding between aggregate and
cement paste without major cracks developed due to channels created through melting of polypropylene fibers. However, after exposure to 800 °C, still the residual strength is around 45% of its
original strength at 27 °C. RPC with 0.9% fiber dosage has shown
reduced split tensile strength (30%) compared to RPC with 0.5%
fiber dosage. The addition of higher content of fibers creates continuous and dense channel that leads to propagation of micro
cracks to large scale. This phenomenon causes deterioration of concrete under low tensile loading condition.
Th reduction of tensile strength at 600 °C and 800 °C due to
pores and channels created due to evaporation of bond water
and melting of fibers, which increase the internal defects of RPC
matrix and also weaken the bonding between cement paste and
aggregate. This is considered as adverse effect of over dosage of
polypropylene fibers. On the contrary polypropylene fiber has positive effect, if and only when optimum fiber content is embedded
in RPC. The maximum reduction of tensile strength at 800 °C is
due to phase change of quarzitic material. As temperature
increases, the tetrahedral chains of quartz molecules gets elongated and reorient, leading to significant volume increase, that
causes radial cracking around the perimeter of the particle in
heated specimen [23].
3.7. Water absorption
The most important essential parameters governing the concrete durability is penetration of water, gas and ions which mainly
depends upon micro structure and porosity of concrete. It is well
known that RPC consists of dense microstructure. The development of pores and micro cracks under elevated temperatures has
a major impact on durability properties like water absorption
and sorptivity. Hence water absorption studies on exposed RPC

specimen were carried out, to assess the properties like intrinsic
porosity and permeability of concrete. RPC cubes after exposure
to elevated temperatures were cooled down to room temperature.
Later weight of the cubes were taken and immersed under water
for 24 h. After 24 h, the cubes were removed and kept outside till
it reaches to surface saturated condition then weight of cubes were
taken.
The quantity or volume of moisture, that enters concrete,
depends on the concrete permeability and interconnectivity
between pores. Results of water absorption of RPC specimen with
different fiber dosages, and exposed to elevated temperatures are
presented in Fig. 12.
It is observed that, as temperature of exposure increases water
absorption is also increasing. At 200 °C, there is no much difference
between water absorption values obtained for RPC with different
fiber dosages. At 400 °C percentage of water absorption for RPC
specimen with 0.9% fiber dosage has shown a little higher value
compared to RPC specimen with 0.5% and 0.1%. The increase in
water absorption, is may be due to penetration of more water

through surface voids and channels created by melted polypropylene fibers. Strength enhancing chemical compounds starts to
decay from 450 °C. The decomposition of these compounds creates
porosity in internal matrix. RPC specimen after exposure to 600 °C
has shown considerable amount of water absorption. The results
also show that as fiber content increases, the percentage of water
absorption is also observed to increase. This is obvious as fiber content increases, the rate of fiber evaporation also increases at elevated temperatures, which leaves more number of channels and
enhances interconnected voids through which water easily penetrates into the body of concrete, thus increasing the water absorption value. The presence of molten fiber and channels created by
melting of fibers are confirmed through SEM images at different
magnifications which is discussed in Section 3.9.
Among the three fiber dosages, RPC with 0.9% fiber content has

shown higher percentage of water absorption after exposure to
elevated temperatures. Also, the rate of water absorption increased
rapidly beyond 400 °C for all fiber contents. The percentage of
water absorption till 400 °C was lower than 4%, this may be due
to the presence of molten polypropylene fibers blocking the channels and not allowing water to enter the concrete core. However, at
higher temperatures, due to melting of fibers more channels are
created through which water has easy access into the body of concrete. At 800 °C, the RPC with 0.9% fiber dosage has 9.7% of water
absorption, which is comparatively higher than RPC specimen prepared with 0.5 and 0.1% fiber dosages. The bunches of inter connected channels created through melting of fibers, makes the
concrete much more porous, which is the reason for higher water
absorption values.
3.8. Water sorptivity
After RPC exposure to elevated temperatures, the water sorptivity of the specimen were assessed to determine the inner concrete
properties, since the test is directly related to the formation of
pores and cracks in the heated RPC specimen. Fig. 13, shows results
of water absorption per unit area for RPC with 0.1% fiber dosage at
different elevated temperatures. The rate of water sorptivity
increased sharply with increase in temperature. From Fig. 13 it
can be observed that, at 200 °C the rate of sorptivity increases up
to 20 min and then on it gradually decreases. In case of 400 °C
the rate of sorptivity increases till 30 min.
This is likely due to more surface damage of RPC at 400 °C that
leads to propagation of surface cracks. These cracks allow water to
penetrate inside the body of concrete increasing sorptivity. When
RPC specimen were exposed to 600 °C there is colour change and
formation of visible hair cracks on surface of RPC specimen.
The sorptivity results at 600 °C, show decrease in rate of sorptivity after 20 min. This is because the heated RPC specimen absorb
more water to fill the voids and pores, and also shrinkage cracks
created due to thermal effect within short period of time. Later
the rate of water absorption reduces due to saturation condition
attained inside the body of concrete. From the Fig. 13 it is further

observed that, the high rate of sorptivity was obtained for the
RPC exposed for 800 °C. It reaches to 29.11 Â 10À4 mm/min0.5
within 10 min duration, after which sorptivity sharply drops. From
the overall sorptivity results it can be concluded that, the rate and
total sorptivity of RPC specimen after exposure can be attributed to
the effect of moisture loss and crack development which in turn is
due to thermal incompatibility between cement paste and aggregate under elevated temperatures.
Fig. 14 shows sorptivity results of RPC with 0.5% fiber dosage,
after exposure to elevated temperatures. At 200 °C, the sorptivity
value is gradually increasing till 30 min where it attains maximum
value of sorptivity 1.22 Â 10À4 mm/min0.5, which is comparatively
less than RPC with 0.1% fiber dosage at 200 °C. This is due to the


P.N. Hiremath, S.C. Yaragal / Construction and Building Materials 169 (2018) 499–512

Fig. 12. Water absorption for RPC at elevated temperatures.

Fig. 13. Sorptivity results of RPC with 0.1% fiber dosage at different elevated temperature.

Fig. 14. Sorptivity variation of RPC (0.5% fiber dosage) with temperature.

509


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presence of high percentage of fiber dosage at the exterior portion

of cubes, that creates dense matrix not allowing the moisture
ingress inside. As temperature increases, sorptivity is also observed
to increase. At 400 °C the rate of sorptivity increases up to 20 min
and attains maximum sorptivity value of 3.96 Â 10À4. Then rate of
sorptivity decreases gradually. The increased rate of sorptivity at
initial duration is due to melting and evaporation of fibers located
on the exterior portion of specimen, leaving maximum number of
channels on the surface. These surface channels created by fibers
allow water to ingress to some more extent with passage of time.
Later the dense matrix of RPC with its interface connectivity with
remaining fibers and molten fibers that block the channels from
outside to inside there by arresting water ingress. This is the likely
reason for slowdown of rate of sorptivity after 20 min of duration.
At 600 °C, the rate of sorptivity increased to 5.67 Â 10À4 mm/
min0.5 within 10 min. This value is comparatively higher than sorptivity at 400 °C with 10 min duration. The possible reason for this
is, presence of large number of channels on the surface and interior
cracks created by melting of fibers that allow moisture at a faster
rate so that, the maximum value of sorptivity was attained within
a short duration of time. The same observation was made in case of
800 °C. Among all, the maximum sorptivity was obtained for 800
°C at duration of 10 min. The total sorptivity value for RPC with
0.5% fiber dosage has shown comparatively reduced value than
that for the RPC with 0.1% fiber dosage. This observation indicates
that 0.5% fiber dosage is relatively better than, that for the case of
0.1% fiber dosage, as far as durability is concerned.
Fig. 15, shows sorptivity results of RPC with 0.9% fiber dosage. It
is observed that at 200 °C, the rate of sorptivity is very slow and it
has reached 0.73 Â 10À4 mm/min0.5 with long duration of 60 min.
This is due to dense fiber matrix interface on the surface of the
specimen that control moisture ingress. But in case of 400 °C the

sorptivity value increases suddenly up to 2.52 Â 10À4 mm/min0.5
with in short duration of time 10 min. Later, it has shown gradual
decrease in rate of sorptivity. At 600 °C, the maximum sorptivity
value was 6.86 Â 10À4 mm/min0.5, which is comparatively higher
than the sorptivity value for RPC with 0.5% fiber dosage at 600
°C. This is due to high percentage of fiber dosage, that leads to
evaporation of fibers and creates maximum number of melted
channels. These channels permit moisture ingress. Hence the maximum sorptivity results were obtained for RPC with 0.9% fiber
dosage. Finally, at 800 °C the initial rate of sorptivity is observed
11.36 Â 10À4 mm/min0.5 which is higher than sorptivity results of
RPC with 0.5% fiber dosage and less than RPC with 0.1% fiber

dosage. The higher sorptivity compared to 0.5% fiber dosage is
because of more number of melted channels that allows water to
penetrate in the body of concrete. While the lower sorptivity
results compared to 0.1% fiber dosage is because of less deterioration of interior structure of concrete due to reduced spalling mechanism and pore pressure.
3.9. Microstructure analysis
The microstructure of RPC with different fiber dosages at various temperatures from 200 °C to 800 °C are shown in Figs. 16–
19. The RPC specimen have shown dense microstructure with
closed arrangements of hydrated compounds at 200 °C, which
can be seen in Fig. 16. The same dense matrix have been observed
for all RPC specimen with different fiber dosages. The SEM images
of RPC with 0.5% and 0.9% have shown presence of polypropylene
fibers and these fibers are closely knit with cement paste at 200 °C.
The high strength was observed for all RPC specimen with different
fiber dosages at 200 °C. The increase in compressive strength is due
to unreacted silica fume that reacts with cement and hydrates: SO2
serves as a catalyst and accelerates the hydration reaction by producing C-S-H, which enhances the compressive strength of RPC
[24].
At temperature of 400 °C the microstructure of RPC is as shown

in Fig. 17. RPC prepared with 0.5% and 0.9% have shown molten
channels created by melting of polypropylene fibers. The compressive strength of RPC at 400 °C has shown increase in strength when
compared to 200 °C. This may be due to dense internal structure of
RPC and at this temperature quartz powder serves as a catalyst and
accelerates the reaction, which results in formation of dense C-S-H
structure. This observation is confirmed through EDS analysis i.e.,
Si/Ca ratio of RPC exposed to 400 °C has shown higher value compared to RPC at room temperature. Hence increased compressive
strength was observed at this temperature.
Microstructure of RPC cubes are exposed to 600 °C, revels that
there is decomposition of CH and considerable number of cracks
occurs due to thermal expansion of the cement paste which causes
local break down of bond between cement and aggregate. Hence
the reduction in compressive strength was observed for RPC at
600 °C. The presence of channels and cracks developed due to thermal expansion was observed in SEM images of RPC at 600 °C as
shown in Fig. 18. From figure, it is observed that RPC with 0.1%
fiber dosage has shown deuteration of interface zone between
aggregate and cement paste. The presence of micro cracks devel-

Fig. 15. Sorptivity variation of RPC (0.9% fiber dosage) with temperature.


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0.1%

0.5%

Polypropylene fiber

Polypropylene fiber

0.9%

Fig. 16. Microstructure of RPC at 200 °C with different fiber dosages.

0.5%

0.1%

Melted fiber channels

0.9%

Melted fiber channels

Melted fiber channels

Fig. 17. Microstructure of RPC at 400 °C with different fiber dosages.

0.1%

Cracks in ITZ

0.5%

Micro cracks in interface

0.9%

Bunch of melted fiber channels

Fig. 18. Microstructure of RPC at 600 °C with different fiber dosages.

0.1%

Weak ITZ

0.5%

0.9%

Interaction of channels

Fig. 19. Microstructure of RPC at 800 °C with different fiber dosages.

oped due to vapour pressure were more. In case of RPC with 0.5%
fiber dosage has shown less number of microcracks and dense
structure of cement and aggregate interface as shown in Fig. 18.
This may be the reason for high residual strength of RPC with

0.5% fiber dosage after 600 °C. The microstructure of RPC with
0.9% fiber dosage has shown good interface between aggregate
and cement paste, but number of microcracks in channels created
by melting of fibers are more. However, this may be possible rea-


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son for reduced residual strength of RPC with 0.9% fiber dosage
compared to 0.5% fiber dosage at 600 °C.
As temperature increases microstructure leads to deterioration
continuously, in RPC with 0.1% fiber dosage has shown porous and
weak interface zone between aggregate and cement paste at 800 °C
as shown in Fig. 19. This leads to reduction in compressive strength
of RPC.
The minimum cracks and dense microstructure with limited
number of melted channels were observed in case of RPC with
0.5% fiber dosage at 800 °C. This may be the reason for considerable
residual strength obtained with 0.5% fiber dosage. The microstructure of RPC with 0.9% fiber dosage has shown more number of
melted channels and cracks on the boundaries of melted channels
at 800 °C as shown in Fig. 19. At this temperature, the microstructure of RPC becomes quite disintegrated with rough grains. The
reduced strength at 800 °C is due to increase in width and number
of cracks. And, due to presence melted channels and cracks
through boundaries of channels that deteriorates RPC rapidly,
resulting in very low residual compressive strengths at 800 °C.
4. Conclusions
In the present study, residual properties and prevention of spalling of RPC subjected to elevated temperature by using different
polypropylene fiber dosages, is investigated. Following, important
conclusions are drawn from this study.
1. Spalling of RPC can be protected by using minimum fiber
dosage of 0.1% and as fiber dosage increases risk of spalling
reduces. The increase in fiber dosage reduces the surface cracks
and pores at elevated temperatures.
2. Weight loss of RPC increases as fiber content increases at elevated temperatures. The UPV results show higher values for
RPC with high percentage of fiber up to 400 °C. Further as temperature increases beyond 400 °C, the velocities are decrease, as
fiber dosage increases.
3. The residual mechanical properties such as compressive

strength has shown increase in strength up to 400 °C and later
there is sudden drop in strength. As fiber dosage increases
strength is also increasing up to 400 °C. After 600 °C, the residual strength of RPC decreases as fiber dosage increases.
4. Split tensile strength of RPC has shown considerable increase in
strength with increase of fiber dosage up to 400 °C. However
sudden drop in strength was observed after 600 °C.
5. The durability properties such as water absorption and sorptivity has shown RPC prepared with 0.5% fiber dosage, perform
better in durability aspects compared to other fiber dosages.
6. Microstructural analysis of RPC revealed that, formation of
dense microstructure and quantity of hydrated products
increase up to 400 °C. Later as temperature increases to 600
°C concrete starts to deteriorate by decomposition of hydrated
products.

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