Fire Resistance of FRP Reinforced Concrete

This assignment delves into the crucial topic of fire resistance in structures reinforced with Fiber-Reinforced Polymers (FRP). It explores the complex interplay between elevated temperatures, FRP material properties, and concrete behavior. The analysis encompasses the impact of various factors such as FRP type, bonding mechanisms, and environmental conditions on the overall fire resistance of FRP-reinforced concrete elements. Furthermore, it discusses relevant design considerations and guidelines for ensuring the structural integrity of FRP-reinforced concrete structures in fire scenarios.

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Performance based review of available fire protection system for FRP
Introduction
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Fibre-reinforced polymer also known as (FRPs) fiber-reinforced plastics, (FRP) is a composite
material, which is usually made of a polymer matrix that is reinforced with fibers (Huang, 2009).
The common fibers which are used are usually glass, carbon, aramid or basalt. The FRPs are
gaining a lot of recognition and increasing their usage in these industries. The polymers are
designed to meet some specific condition and this has led to their increased usage. Nevertheless,
these materials also require some special attention which will ensure that they are able to
mitigate their available defects. One of the key defects when it comes to the FRPs is their ability
to withstand fire for a long time (Firmo, Correia, and França, 2012). This means that these
materials have poor fire resistivity. Their inability to withstand fire has led to research on
different mechanisms which can be adopted to make the materials better used in fire prone zones.
Fire protection is usually defined as the practice taken to mitigate the unwanted effects and
destruction due to fire occurrence (Katz, Berman and Bank, 2010). The common areas where the
FRPs are applied are prone to fire and this causes the key requirement to ensure that the
structures build using these materials are safe and stable. This paper will be able to analyze the
different fire protection mechanisms and their performance when FRPs are applied.
First, the properties of FPRs are able to make them suitable to resistant to fire and high
temperatures. ii
Application of FRPs
The FRPs have found their application on different industries such as the aerospace, automotive,
marine and even the construction industry (Mallick, 2017). The construction industry, and more
specifically the members are highly affected by fire. Their strength is able to reduce with
increase in fire effects. FRPs have been gaining popularity a lot in the past decades. Fire
iiiprotection systems have been enhanced a lot in relation to the adoption of the fibre-reinforced
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polymer in different industries. The construction industry has in the past years seen a lot of
efforts in increase of fire protection of the FRPs (Ahmed and Kodur, 2011). In civil engineering
and structures, the consideration for the fire exposure has become a key element. Performance of
structures under fire is a key element which structures are able to focus on (Barros and Fortes,
2006). The introduction of FRP is able to enhance the strengthening of fire resistance on such
structures. Although the documentation of FRPs is not common, the use of FRPs has been in
application since 1980s. Bond properties and mechanical characteristics to enhance the resistance
on fire has been some of key areas of focus in relation to the FRPs. The increased use of FRPs in
this industry has led to various reviews on the available mechanism for the fire protection on
such structures. The different mechanisms has been able to perform differently with combination
with the FRP ( Katz, 2009). This facture has led to the increased adoption of the material in
many construction activities ranging from slab, beams and even the columns. iv
According to Benichou at al., (2010), many FPRs have designed insulation which is made to
resist the increase on temperature when buildings and structures are under fire. The behavior of
the FRPs under fire has raised the need of the fire protection mechanisms on the structures.
nevertheless, there have been lack of proper address of the limitations on the use of FRPs at
different segments. Th FRP characteristics has raised the need to have the fire protection
mechanisms considering its combination with fire spreading.
In construction industry, the FRPs have found their way and they are gaining popularity at a high
rate. The need to mitigate the fire spread effect of the FRPs and their inability to withstand the
fire for a long time has raised the need for innovations on the fire protection mechanisms on
these materials. Use of insulation has become a common norm for the structure elements such as
the beams, columns and slabs in the construction industry (Fib bulletin 14, 2011). Proper
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materials such as cementitious materials and gypsum have been used as coatings in these
elements to enhance the fire resistance. In addition, the materials used for the fire protection have
been able to enhance the structural capacity of the construction elements. These mechanisms are
used to lower the heat penetration in case of fire or absorb the fire effects (Maraveas, Miamis and
Vrakas, 2012). This effect is able to increase the fire resistivity thus taking longer to reach the
FRP material. There is need therefore to control the fire effect when the FRPs are used in the
different industries.
Structure of FRPs and relation to fire
In terms of structure, the FRPs have high-strength fibers which are embedded in a polymer
matrix. This makes them suitable for consideration in fire prone structures. Moreover, the
adoption of the FRPs in the construction industry has been promoted due to the high strength of
the material, corrosion resistance and its ease of application (Kodur and Ahmed, 2010). The
FRPs have been also applied in the strengthening of concrete structures such as beams, columns
and slabs. Nevertheless, the strength of the FRPs with the temperature increase is able to affect
the strength of the materials. This raises the need to have fire protection mechanisms for the
FRPs (Green, 2014). The most common materials which are used for the FRP include the
Aramid, Carbon and Glass FRP. Their bond strength is able to vary differently when the
structure is exposed to fire. This makes the need to have the fire protection mechanism to have a
key say. The graph below is able to show the behavior of the FRPs when exposed on heat. The
FRPs behavior as show, is able to raise the need of the fire protection mechanisms to enhance
fire resistance. v
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Behavior of FRP under fire
Low transition temperature, which is denoted as Tg is one of the main characteristic of the FRP.
Tg is defined as the midpoint of the range of temperature over which the FRP undergoes its
changes from a hard and brittle material to a viscous and rubbery material (Bisby, Green and
Kodur, 2008). The low temperature means that the materials will be unable to withstand fire and
therefore raising the needs to have fire protection. The fire protection will be able to work as an
insulator which will increase the fire resistance of the FRP. The glass transition temperature of
many of the FRPs is able to range between 60oc and 100oc (Gates, 2011). This means that the
change of the FRP will be able to occur within a short time after tye exposure on heat. In
addition, without the fire protection, FRPs will be able to ignite, emit smoke and also support fire
spread on the structure. This statement means that in case of fire outbreak and the FRPs are not
insulated, the spread of the fire will be much sever and dense. For this reason, the fire protection
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mechanisms has been key area which is required when the FRPs are being used in different
structures. Moreover, the FRPs are able to experience melting, delamination, charring, cracking
and even deformation when exposed to fire (Yu and Kodur, 2014). Also, lose of strength is
another key change which is experienced when the FRPs are exposed to fire. The increase in
temperature is able to lose the structural strength of the material and therefore making them
weak. These are more added reasons to have the fire protection mechanisms on the FRPs.
Fire protection mechanism and resistance
Different fire protection mechanisms are usually applied on FRPs considering the cons being
experienced without the fire protection mechanisms (Sen, Mariscal and Shahawy, 2013). As
noted earlier, the fire protection mechanisms are usually provided in terms of insulations on the
available FRP structures. Columns, beams and slabs are some of the key structural elements
where the FRPs are applied and fire protections are exercised on them. Gypsum insulation and
cementitious insulations are some of the key fire protection mechanisms which are applied on the
structural members to enhance their fire resistance. The following figure is able to show different
stages at which the investigation on the protection mechanism of a column is able to pass in the
investigation (Chowdhury et al., 2011). After moulding the column, the FRP mechanism is
installed. Then the fire protection mechanism is then insulated on the FRP material. Lastly, the
testing on the behavior of the fire protection mechanism in terms of the fire resistance is
measures. It has to be noted that the fire resistance is the time at which a structural member will
be able to withstand the effects of fire without lose of the structural strength of the material.vi
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Bare reinforced
concrete column
Column with FRP
installed
Column with FRP wrap and
spray-on insulation in text
chamber
Column after fire
resistance testing
After installation of the reinforcement, the FRP is installed and appropriate fire protection
mechanism is put in place. The exposure of the column to fire at different stages is able to show
that the fire resistance is able to depend on different parameters. In the insulation part, the
thickness of the insulation material is a critical parameter on the fire resistance (Barnes and
Fidell, 2006). Changing the different parameters on the fire protection mechanism was carried
out and it was able to show that the insulation plays a critical role in fire protection. the
following tabulated results where carried out to investigate the key parameters which are able to
play a role when it comes to fire protection mechanisms on columns (Palmieri, Matthys and
Taerwe, 2012). This test method is a clear indicator that whichever insulation method achieved,
fire protection against FRPs is achieved to some key levels. vii
Column
No.
Type of
FRP
Type of insulation
and thickness
Test load
ratio1
Fire
resistance
(min)
Predicted strength (at
room temperature) (kN)
1 1 layer
Carbon Tg=
Gypsum-based,
57mm
0.50 >3002 5,094
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930C
2
1 layer
Carbon Tg=
930C
Gypsum-based,
32mm
0.50 >3002 5,094
3
2 layers
Carbon Tg=
710C
Cementitious, 53mm 0.56 >3002 4,720
4
2 layers
Carbon Tg=
710C
None 0.56 210 4,720
One of ther key parameters which is critical in the fire protection mechanism is the layer
thickness of the protection material (Burke, 2008). From analysis, it has been concluded that a
layer of gypsum is able to offer more fire resistance to the FRP material than 2 layers of
cementitious insulation. In addition, lack of use of any fire protection mechanism is able to
increase the fire intensity and therefore making the member to fail within the shortest time
possible (Nanni, & Jawaheri, 2014). FRP material increases the fire intensity and therefore
increasing the failure chances for the materials. In order to analyze the effects of fire protection
systems, it is good enough to look from the effects of strength of materials aft6er their exposure
on fire. Research has been able to show that gypsum insulation and fire protection mechanism is
much better than cementitious material insulations (Williams et al., 2008). An insulation
thickness of 32 mm of Gypsum is able to offer a maximum of 5094 kN for a structural column
when exposed on fire. Insulating the same column with cementitious material of 53 mm
thickness produces a maximum strength of 4720 kN. this analysis shows that the gypsum
insulation is able to offer a better fire resistance to protect the FRP material.
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Another key area which can be used to analyze the effect of fire protection materials and
mechanisms on structural members is the fire resistance. The fire resistance is measured in terms
of the minute at which the structural members are able to fail under fire exposure. the insulation
materials of gypsum and cementitious materials have been used effectively in the FRP fire
protection (Firmo, Correia and Bisby, 2015). The uninsulated column is able to show that the
fire protection mechanism are critical in fire resistance. Lack of insulation on the column means
that the column is able to fail in lesser time that the insulated column regardless of the material
used. ULC S101 states that the accepted fire resistance rating for any material should be about 5
hours even with variation of Tg. Both gypsum and cementitious materials regardless of their
thickness are able to achieve this specification. The uninsulated column fails at 3.5 hours and this
shows that the insulation mechanisms are critical to enhance the members to be in position and
retain their structural strength. viii
In addition, minimum thickness for the fire insulation material is critical to ensure that the fire
resistance is maintained at the required standards. For instance, a gypsum insulation of 19 mm is
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able to produce a fire resistivity of 147 mins in slabs. Changing the thickness of the gypsum
insulation to 38 mm for the slabs is able to produce a fire resistance of more than 240 minutes. In
this case, it means that some key specific fire insulation material thickness is required to ensure
that the FRPs are well protected against fire (Adelzadeh, Green and Benichou, 2012). The
thickness is able to play a key role when it comes to fire protection. There are different standards
which are accepted for the fire protection regardless of the mechanism employed. This ensures
that fire resistance measures are well met at the different moments. The protection layer is able
to play a key role not only to the gypsum and cementitious material but to all FRP protection
mechanismsix.
In addition, another key material which is used for the fire protection mechanism is the Tyfo VG
insulation. A range of between 25 and 38 mm is usually acceptable to offer a fire resistance of
more than 4 hours when this material and mechanism is used (Kodur and Baingo, 2008).
According to ASTM E119 definition, the thickness range is able to meet the required standards
and ensure that fire protection is achieved on the different structures. the Tyfo VG insulation is
able to protect the FRP from heat by simply blocking the heat penetration. Moreover, the
insulation thickness of 38 mm of this mechanism is able to offer and maintain the Tg temperature
of less than 54 minutes. Another key element which is important when it comes to fire protection
is the control of the temperature around the structure which is exposed to fire. The insulation
mechanism through this material is able to maintain a low temperature to the FRP structure
(Kumahara et al., 2009). This ensured that the failure of the structural element did not occur
under the service load level during the fire incidents. Extended fire endurance timeline is a key
element to ensure that the structures are able to maintain their strength. Proper fire resistance of
the materials used is able to enhance the fire resistance and thus the better. This means that the
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failure of the structures will be prolonged and thus offering better chances for the fight against
the fire.
In comparison with other materials, it is clear that the thickness requirement of the protection
materials is able to vary from one material to another (Bisby and Green, 2005). Nevertheless, a
range of between 25and 40 mm of thickness of the insulation materials is able to offer the
required standard fire protection standards. Proper application of these standards is able to
enhance endurance range of concrete structures of up to 40 percent when they are exposed to
fire. The materials are able to affect the heat transfer to the FRP material (Wang, Young and
Smith, 2011). These key mechanisms are able to prevent the heat penetration from the fire source
to the FRP material. The solution methods are able to enhance the heat resistivity and therefore
absorbing a lot of heat.
The FRPs are combustible and are able to enhance the fire spread over the places where they are
applied (Foster and Bisby, 2008). For this reason, the need to have the fire protection
mechanisms is key min order to enhance the protection os the structures. Some of the key defects
of the FRPs in relation to the fire are the evolution of smoke and spreading of fire. These raises
the needs to have proper fire protection mechanisms in the different sections. In order to properly
apply the FRP fire protection mechanisms, the classification of the buildings and the FRP
systems used must be defined well (Manoochehr, Manoochehr and Zoghi, 20. K13). The
manufacturers of the FRP materials are therefore able to recommend the coating mechanisms to
be used of any other fire protection mechanisms, which will be able to suit the smoke and flame
spread requirements.
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Spray-applying of cementitious fireproofing material and gypsum are some of the common
mechanisms which are used in fire protection in FRPs. In addition to the increase of the fire
resistivity on the members, the materials are able to enhance the strength (ASTM E119-08a
2008). The mechanisms applied in addition has to meet the specification which are found in ULC
S101 and ASTME119 in terms of the service load carriage.
Conclusion
FRPs have been in the market for a long time. Review on the fire protection mechanisms is a
critical process which will ensure that the available flaws of the FRPs are mitigated well. First, as
noted earlier, the FRPs are able to lead to an increase in fire intensity and therefore it is key to
adopt proper fire protection mechanisms. This will ensure that ample time is provided for the
firefighters to tackle the fire incidents. The Insulation of both cementitious and gypsum have
been used in the construction industry has part of the fireproofing materials for the FRPs. These
materials have been able to enhance the fire resistivity for the FRPs in the industry and
enhancing the fire resistivity of to up to more than 4 hours. The thickness of the insulating
materials, which acts fire protection material is a key element in achieving the required fire
resistivity. In many cases up to 40 mm of these materials thickness is usually sprayed on the
FRP material to achieve the required standard of the fire protection. In addition, the
manufacturers of the FRPs are able to play a critical role on which material will be able to
enhance the fire protection of the material and the thickness factor. In addition, the different
materials for the fire protection must be able to meet the standards as stated on ULC S101 and
ASTME119. This ensures that the failure during loading when the structures are under fire are
not achieved easily until the fire resistivity period elapses.
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