Géopolymère: Fire Resistant Aluminosilicate Composites
Géopolymère: Fire Resistant Aluminosilicate Composites
Géopolymère: Fire Resistant Aluminosilicate Composites
géopolymère
Published in the journal "Fire and Materials, Vol. 21, 67-73 (1997)", USA
Richard E. Lyon
Fire Research Section
Federal Aviation Administration Technical Center
Atlantic City International Airport, NJ 08405
Usman Sorathia
Carderock Division, Naval Surface Warfare Center
Bethesda, MD
Keywords: Aluminosilicate, ceramic composite, cone calorimeter, fire, fire barrier, fire haz-
ard, flame spread, flammability, flexural strength, Geopolymer, heat release, smoke.
Geopolymer Institute
Geopolymer Institute
1997
© ALL RIGTHS RESERVED
02100 SAINT-QUENTIN - France
web: www.geopolymer.org
Fire Resistant Aluminosilicate Composites page -2-
Introduction
The flammability of organic polymer matrix, fiber-reinforced composites limits the use of
these materials in marine platforms and ships [1], ground transportation [2], and commercial air-
craft [3], where fire hazard is an important design consideration because of restricted egress. Al-
though carbon fiber and glass fibers are inherently fire resistant and significant progress has been
made in recent years to develop new, high temperature, thermo-oxidatively stable fibers from bo-
ron, silicon carbide, and ceramics [4], parallel work on high temperature/fire resistant matrix mate-
rials to bind the fibers has not kept pace. At the present time, affordable, low-temperature processable
matrix materials for fire resistant composites are unavailable since most organic polymers soften
and ignite at temperatures of 400-600°C characteristic of fuel fire exposure conditions.
The Federal Aviation Administration has recently initiated a research program to develop
aircraft cabin materials with an order-of-magnitude reduction in fire hazard compared to current
interior materials [5]. The flammability requirement for new materials is that they withstand a 50
kW/m2 incident heat flux characteristic of a fully-developed aviation fuel fire without releasing
significant amounts of heat or propagating an external fuel fire into the cabin compartment for
several minutes [6]. The goal of the program is to eliminate cabin fire as cause of death in aircraft
accidents. However, voluntary adoption of new fire resistant materials technology by aircraft and
cabin manufacturers requires that it be cost effective to install and use [7]. To this end a new, low-
cost, inorganic polymer derived from the naturally occurring geological materials is being evalu-
ated.
Materials
Aluminosilicate Resin: The Geopolymer matrix resin being evaluated for fireproof aircraft
cabin interior panels, marine structural composites, and infrastructure applications is a potassium
aluminosilicate, or poly(sialate-siloxo), with the empirical formula: Si32O99H24K7Al. A representa-
tive structure deduced from the elemental composition, x-ray diffraction, and 29Si magic angle
spinning nuclear magnetic resonance spectroscopy (29Si MAS-NMR) of the cured and dried
Geopolymer is a linear poly(metasilicate) with tetracoordinate aluminate crosslinks as illustrated
in Figure 1 [8]. This particular resin hardens to an amorphous or glassy material at moderate
temperatures with a density of 2.14 g/cm3 and is one of a family of inorganic Geopolymer materials
described previously [8,9].
+
O OH O K O +
K
Si O Si O Si O Al O
O +
17 OH 12 O K 3
O
The Geopolymer potassium aluminosilicate resin was prepared by mixing 100 g of an aque-
ous silica + potassium oxide solution with 135 g of a silica powder having SiO2/AlO2 in a mole
ratio of 27/1. The liquid and solid com- 1x105
ponents were mixed for one minute at
room temperature in a food processor. 1x104
The as-mixed viscosity of the
VISCOSITY, kPa-s
Geopolymer resin was measured at
1x103
room temperature (20°C) in a dynamic
rheometer (Rheometrics RDA-II) using
1x102
parallel plate mode with 25 mm diam-
eter stainless steel plates. Figure 2 is a Room Temperature
1
plot of the room temperature viscosity 1x10
of the Geopolymer resin versus time af-
ter mixing. The initial mix viscosity of 1x100
0 2 4 6 8 10 12 14 16 18 20
the Geopolymer resin is about 2 Pa-s (20
TIME, hours
Poise) and the resin remains workable Figure 2: Room temperature (20°C) viscosity of
for about 4-5 hours at room temperature. Geopolymer resin versus time after mixing
Differential scanning calorimetry studies were conducted to determine the extent of reaction
of the Geopolymer resin during the 3 hour, 80°C composite cure cycle. The isothermal conversion
of the Geopolymer resin as a function of time at 80°C was determined using a Perkin Elmer DSC-7
Differential Scanning Calorimeter on resin samples of approximately 50 mg which were mixed and
immediately placed in sealed stainless steel sample pans. Heat flow versus time for the cure exotherm
was recorded and the instanta-
neous extent of reaction was cal- 100 700
culated from the cumulative heat 90 Percent
evolution divided by the total Reacted 600
80
PERCENT REACTED
Analyzer to determine the weight loss history of the cured Geopolymer resin at elevated tempera-
tures. Samples of 10 mg were heated at 10°C per minute in an inert environment (99.99% nitrogen)
and the mass of the sample recorded versus temperature. Figure 4 shows the residual mass and its
first derivative versus temperature for the cured Geopolymer resin in the TGA experiments. It is
observed that the resin is thermally stable up to about 250°C, at which temperature a seven percent
102 0.016
Residual Mass Mass Loss
Derivative
0.008
0
Residual Mass, %
98
-0.008
96
-0.016
94
-0.024
92 -0.032
90 -0.04
0 200 400 600 800 1000
Temperature, deg.C
Figure 4: Thermogravimetric data for Geopolymer resin heated at 10°C/min.
Heavy line ( ) is the mass loss derivative and doted line (J)is residual mass .
weight loss occurs over the range 250-625°C. The mass loss at temperatures >250°C is assumed to
occur through a dehydration reaction which yields gaseous H2O according to
∆
2(SiO3-2.2M+)-OH ⇒ (SiO3-2.2M+)2O + H2O(↑) (1)
The dehydration reaction produces steam at many times its liquid volume and pressure result-
ing in an unconstrained volume expansion of the resin of 488 ± 48% at 850°C. The resulting
morphology is a microcellular amorphous material at room temperature. At temperatures above
850°C a small secondary weight loss occurs producing a strong, fused, glassy resin. The secondary
weight loss temperature is near the melting point (976°C) of potassium metasilicate (K2SiO3 in
Figure 1) and may be final dehydration of the molten resin.
Composite Fabrication: Cross-ply fabric laminates were made by hand rolling the deaerated
Geopolymer liquid resin into a 0.193 kg/m2 (5.7 oz/yd2), 3K plain weave, Amoco T-300, carbon
fabric and air drying 30 seconds at 80°C to remove residual moisture and develop tack. Unidirec-
tional tape was used to fabricate cross-ply laminates for off-axis tensile testing of inplane shear
properties. In all cases hand impregnated plies were cut, stacked, and cured in a vacuum bag at
80°C in a heated press with 0.3 MPa pressure for three hours. The panels were then removed from
the vacuum bag and dried for an additional 24 hours at 100°C or until constant weight was achieved.
Approximately 22% of the as-mixed liquid resin is water, about half of which is removed during
Fire Resistant Aluminosilicate Composites page -5-
Final thickness of the 25 layer fabric laminates was a uniform 5.6-mm and the density was
1.85 g/cm3. Warp direction tensile specimens were cut from 4 layer fabric laminates. Visual
inspection of cut edges revealed that the laminates were substantially free of large voids. Hand
impregnation and layup resulted in a fiber volume fraction of approximately 50-55% and void
fraction of less than 5% in the Geopolymer laminates.
Organic matrix crossply laminates of polyester (PE), vinylester (VE), epoxy (EP), cyanate
ester (CE), bismaleimide (BMI), PMR-15 polyimide (PI), and phenolic (PH), thermoset resins as
well as thermoplastic polyphenylene sulfide (PPS), polyetheretherketone (PEEK),
polyetherketoneketone (PEKK), polyarylsulfone (PAS), and polyethersulfone (PES) resin matrices
were prepared from commercial S-glass, E-glass or carbon fabric prepregs. The details of material
composition and fabrication have been described elsewhere [10-12]. Some of the phenolic lami-
nates were hand impregnated [13] and contained only about 34 volume percent fiber compared to
a nominal 60 percent fiber volume for all of the commercial prepreg materials. The density of these
cured laminates ranged from about 1.55 to about 1.98 g/cm3 at the nominal 60 volume percent
carbon and glass fiber loading, respectively.
Methods
Ignitability, Heat Release, and Smoke (ASTM E-1354): Peak heat release rate, 300-second
average heat release rate, total heat release, mass loss during burning, ignitability (time-to-igni-
tion), and the specific extinction area of smoke produced were measured in an oxygen consumption
calorimeter employing a conical radiant heater to provide 50 kW/m2 of radiant energy to the
surface of a 10-cm by 10-cm sample having a nominal thickness 6-mm. The sample is positioned
horizontally on a weighing device with a spark igniter 2.54-cm above the surface to ignite combus-
tible vapors (piloted ignition). The mass flowrate of air past the burning sample is measured as
well as the amount of oxygen consumed from the air stream by the combustion process and these
measurements are used to calculate the heat release rate (HRR) of the burning material using a
factor of 13.1 kJ of heat produced per gram of oxygen consumed [14].
Flame Spread Index (ASTM E-162-83): Flame spread across a surface is one measure of
the propensity of a material to propagate a fire. Downward flame spread was measured after igni-
tion of a 15-cm by 46-cm sample by a radiant heat source. Only the combustible organic matrix
composites were tested in this procedure as the Geopolymer sample would not support flaming
combustion.
Residual Flexural Strength (ASTM D-790): Specimens were tested for flexural strength
before and after the fire test to determine the residual strength of the composite panels after fire
exposure. Specimens having dimensions 7.6-cm by 7.6-cm were exposed to a 25 kW/m2 radiant
heat source for a duration of 20 minutes according to ASTM E-662 protocol for smoke generation
in a flaming mode. The panels were reclaimed and 5 coupons, 1.27-cm wide by 7.6-cm long were
Fire Resistant Aluminosilicate Composites page -6-
cut from each for flexural testing on a universal testing machine. The Geopolymer composites
were not subjected to the ASTM E-662 protocol because they would not burn. Instead panels were
tested at room temperature (22°C) or subjected to temperatures of 200, 400, 600, and 800°C for
more than 60 minutes in a forced air oven. The oven exposure at 400°C is comparable to the
equilibrium surface temperature of a vertically oriented, unit-emissivity surface exposed to25 kW/m2 of
radiant energy in quiescent air for the same time period [15]. The original sample thickness was
used to calculate a nominal flexural strength after the fire (organic resins) or thermal exposure
(Geopolymer) test.
Tensile Properties (ASTM D3039-76): Tensile strength and modulus of cross-ply fabric
laminates were measured in the warp fiber direction using four (4) ply specimens.
Inplane Shear Properties (ASTM D3518-76): The inplane shear strength and stiffness of a
unidirectional Geopolymer laminate was determined by measuring the tensile stress-strain response
of ±45-degree laminates fabricated from unidirectional carbon fiber tape.
Interlaminar Shear Properties (ASTM D3846): Interlaminar shear tests were conducted on
Geopolymer-carbon fabric laminates by applying direct shear over an area of approximately 80
mm2 on an 80 x 12 mm double-notched compression specimen which was 6 mm thick. Failure
occurred between the notches in all cases and the failure plane was interlaminar. Tests were con-
ducted at ambient temperature (22°C) on samples which were subjected to a one hour (or more)
exposure at 200, 400, 600, 800, and 1000°C in a forced air oven. The interlaminar shear strength of
a phenolic resin/T-300 carbon fabric laminate was determined using a short beam shear specimen
according to ASTM D2344 and the specimen was a [0/±45/90] quasi-isotropic layup of phenolic
resin impregnated Hercules IM-7 carbon fabric.
Table 1 lists the inplane shear, interlaminar shear, warp tensile, and flexural properties of the
Geopolymer-carbon fiber/fabric crossply laminates. The room temperature strengths of the
Geopolymer-carbon fiber/fabric laminates are 343, 245, and 14 MPa for warp tensile, flexure, and
interlaminar shear, respectively. The corresponding values for a phenolic resin-T-300 carbon fab-
ric crossply laminate are 436 and 290 MPa for warp tensile and flexural strength, respectively, and
24 MPa for interlaminar (short beam) shear strength (13). Moduli for the Geopolymer resin crossply
fabric laminate in the warp tensile and flexure tests are 79 GPa and 45 GPa, respectively, compared
to 49 GPa and 29 GPa for the corresponding moduli of a phenolic resin composite (13).
Table 2 summarizes all of the cone calorimeter data for the composite specimens. Individual
values for percent weight loss during the fire test, time to ignition, peak heat release rate, 300-
second average heat release rate, total heat released per unit area, and specific extinction area of
smoke are reported for each material. Average values of these fire parameters were calculated for
families of the organic materials grouped together according to chemistry (condensation/phenolics,
addition/thermosets), physical properties (engineering thermoplastics), or end-use applications (high
Fire Resistant Aluminosilicate Composites page -7-
temperature/advanced thermosets). It is seen that this somewhat arbitrary grouping leads to varia-
tions within groups which can be greater than the variation between groups. However, the aver-
ages are fairly representative of each type of material, and it is clear that the Geopolymer composite
is non-combustible while all of the organic polymer matrix composites support flaming combus-
tion. It was noted that the Geopolymer resin became white after fire exposure but did not ignite or
smoke even after ten minutes in the cone calorimeter.
MAX.
PROPERTY TEMP. n MODULUS STRENGTH
(°C) (GPa) (MPa)
It is important to try to understand how or if the fire parameters in Table 2, measured in a small
scale bench test, relate to the actual fire hazard of a composite material in the use environment.
This is a very difficult task and it is necessary to realize that no single parameter will provide the
best estimation of the fire hazard of a material in all situations because the hazard depends to a large
extent on where and how the material is used (e.g., enclosed space, open space, structural, non-
structural, etc.).
It has been suggested that heat release rate of a material measured in small scale tests under
simulated radiant exposure conditions is the single most important parameter in characterizing the
hazard of a material in a fire [16]. Recently, it was shown that a combined parameter which is the
ratio of the peak heat release rate to the time to ignition, also known as the flame propagation index
(FPI) or flashover parameter, is a more accurate predictor of time-to-flashover in both room and
aircraft compartment fires because it more accurately accounts for thickness effects of the material
[17]:
Peak Heat Release Rate (kW/m2)
Flame Propagation Index (FPI) = (2)
Time-to-ignition (seconds)
Fire Resistant Aluminosilicate Composites page -8-
Table 2: Fire Calorimetry Data for Crossply Laminates at 50 kW/m2 Irradiance [10-12]
GEOPOLYMER Carbon 0 ∞ 0 0 0 0
Equation 3 is an empirical equation which correlates EURIFIC full scale fire test data [18] for
13 different lining materials (r2 = 0.94) obtained according to ISO 9705 corner wall/room fire test
using the 100/300 ignition option (100 kW fire for 10 minutes + 300 kW fire for additional 10
minutes) in the corner of a room 3.6-m long x 2.4-m wide x 2.4-m high. For comparison to the
predicted behavior of the composite materials in Figure 5, materials in the ISO 9705 test with 10-12
minute flashover times include a melamine high pressure laminate on non-combustible board, steel
faced polymeric foam with mineral wool backing, fire-retardant PVC on gypsum wallboard, fire
retardant particle board, and a fire retardant textile on gypsum wallboard.
The calculated values for time-to-flashover of organic and Geopolymer composites in a full
scale room test shown in Figure 5 provide a qualitative ranking of the fire hazard of these materials
in a compartment. The engineering thermoplastics are predicted not to reach flashover during the
20 minute ignition period but could generate appreciable smoke, while the Geopolymer composite
will never ignite, reach flashover, or generate any smoke in a compartment fire. It is possible that
the actual time to flashover of the continuous fiber reinforced composite laminates listed in Table 2
would be significantly different from the calculated values displayed in Figure 5 and full-scale
validation tests of these materials are required to design for fire protection.
Poor Fair Good Excellent
Composite Resin
GEOPOLYMER
ENGINEERING
THERMOPLASTICS
Figure 5: Predicted time to
PHENOLICS flashover in ISO 9705 corner/
room fire test with various
structural composites as wall
ADVANCED
materials.
THERMOSETS
THERMOSETS
0 10 20 30 40 50 ∞60
Time to Flashover, minutes
The flame spread index provides a relative measure of the speed at which the flame front of a
burning composite travels. Consequently the flame spread index provides a qualitative ranking of
the rate of fire growth in an open environment. Figure 6 shows a plot of the ratio of the peak heat
release rate / time-to-ignition (FPI) from Table 2 for selected materials which were also tested for
flame spread index. The correlation is seen to be very good between the flame propagation index
determined in the bench scale cone calorimeter test and the measured ASTM E-162 flame spread
index for these cross-ply composite laminates. According to this plot, the Geopolymer composite
would have a flame spread index of zero, indicating that the Geopolymer composite would be an
excellent fire barrier.
In general, the initial matrix dominated strengths (i.e., inplane shear, interlaminar shear, trans-
verse tension, compression) of addition cured thermoset or thermoplastic organic matrix compos-
Fire Resistant Aluminosilicate Composites page -10-
Differences in the initial strength of organic matrix and Geopolymer resin composites can be
compensated in the design phase of a component or structure by simply modifying the dimensions
of the structural element. However, the residual strength of a fire exposed composite structure is
determined not only by its physical dimensions but also by thermal transport properties, material
chemistry, and thermal stability of the composite. Comparison of the composite resin categories on
the basis of percent residual flexural strength retained after the fire exposure is shown in Figure 7.
The values represent a combined average for the thermoset (vinylester, epoxy), advanced thermoset
(BMI, PI), phenolic, and
Composite Resin
engineering thermoplastic
GEOPOLYMER, 75kW/m2
(PPS, PEEK). The
Geopolymer-carbon fabric
GEOPOLYMER, 25kW/m2
crossply laminate which
was subjected to a 400°C
ENGINEERING THERMOPLASTIC
oxidizing (air) environ-
ment for one hour instead
PHENOLIC
of the 25 kW/m2 radiant
ADVANCE THERMOSET
exposure retains 67% of its
original 245 MPa flexural
THERMOSET
strength. The failure mode
in the 400°C exposed
0 10 20 30 40 50 60 70 80 90 Geopolymer composite
Residual Flexural Strength, Percent
flexural test was a shear
Figure 7: Residual warp-direction flexural strength of crossply
laminates after fire/thermal exposure delamination near the neu-
tral axis corresponding
Fire Resistant Aluminosilicate Composites page -11-
to a maximum shear stress at failure of about 6.5 MPa, in close agreement with the value of 6.8
MPa obtained for the interlaminar shear strength of the notched compression specimen after 400°C
aging in air.
Specific Maximum
MATERIAL Tensile Specific Flexural Flexural Temperature
Density Modulus Modulus Strength Strength Capability
kg/m3 GPa MPa-m3/ MPa MPa-m3/ °C
kg kg
Fiber-Reinforced
Concrete 2300 30 13.0 14 0.006 400
Structural
Steel 7860 200 25.4 400 0.053 500
7000 Series
Aluminum 2700 70 25.9 275 0.102 300
Phenolic-Carbon
Fabric Laminate [13] 1550 49 31.6 290 0.187 200
Phenolic-E Glass
Fabric Laminate [13] 1900 21 11.0 150 0.074 200
Geopolymer-Carbon
Fabric Laminate 1850 76 41.0 245 0.132 ≥ 800
Specific flexural strength is the flexural strength of the material divided by the bulk density
and is the figure of merit for weight-sensitive applications such as aerospace and surface transpor-
tation vehicles. Similarly, specific modulus is defined here as the tensile (Young’s) modulus of the
material divided by its bulk density. In the case of the anisotropic crossply laminates the warp
tensile modulus is used for the calculation. The Geopolymer composite is superior to all of the
materials listed with regard to specific modulus and is second only to the phenolic-carbon crossply
laminate in specific strength. However, the Geopolymer-carbon fabric laminate is unique in its
high temperature structural capability and fire resistance.
Fire Resistant Aluminosilicate Composites page -12-
Conclusions
Carbon fiber reinforced potassium aluminosilicate resin (Geopolymer) composites are non-
combustible materials which are ideally suited for construction, transportation, and infrastructure
applications where a combination of fire endurance, non-combustibility, and specific flexural strength
is needed. Carbon fabric reinforced Geopolymer crossply laminates have comparable initial strength
to fabric reinforced phenolic resin composites but have higher use temperatures and better strength
retention after fire exposure. In comparison to structural steel the Geopolymer composite falls
short in flexural strength, modulus, and cost but the temperature capability is superior. Conse-
quently in applications requiring fire endurance, replacement cost or the added cost of a fire barrier
must be figured into the material cost for metallic structures.
Aircraft manufacturers and operators are sensitive to fuel costs so that the figure of merit for
this application remains specific strength (strength/density). The high specific flexural strength,
flexural modulus, temperature capability, and non-combustibility of the Geopolymer composite
make it ideally suited for fire resistant aircraft components. The capability for hand layup or fila-
ment winding and low temperature curing suggests applications in seismic retrofit of bridge and
building interior columns where upgraded fire resistance and good adhesion to concrete is required.
Load bearing capability during severe fire exposure, where temperatures reach several hundred
degrees Centigrade, will be significantly higher than organic resin composites, steel, and aluminum
Fire Resistant Aluminosilicate Composites page -13-
which soften and lose nearly all of their compressive and flexural strengths well below these tem-
peratures. Consequently, applications in the chemical industry for fireproof pipe, tanks, and deck-
ing are also being considered.
References
1. Demarco, R.A. (1991).»Composite Applications at Sea: Fire Related Issues,» Proc. 36th Int’l. SAMPE Sym-
posium, April 15-18, pp. 1928-1938
2. Hathaway, W.T. (1991). «Fire Safety in Mass Transit Vehicle Materials,» Proc. 36th Int’l. SAMPE Sympo-
sium, April 15-18, pp. 1900-1915
3. R.G. Hill, T.I. Eklund, and C.P.Sarkos (1985) «Aircraft Interior Panel Test Criteria Derived from Full-Scale
Fire Tests,» DOT/FAA/CT-85/23
4. Engineered Materials Handbook, Vol. 1. , COMPOSITES, ASM International, Metals Park, OH, 1987
5. Lyon, R.E. (1995). «Fire Safe Aircraft Cabin Materials,» in Fire and Polymers, ACS Symposium Series Number
599, G.L. Nelson, ed., American Chemical Society, Washington, D.C., p. 618
6. Lyon, R.E. (1994). «Advanced Fire Safe Aircraft Materials Research Program,» Technical Report DOT/FAA/
CT-94/60
7. R.E. Elliot, «Aircraft Interior Integration,» Aerospace Engineering, May 1995
8. Davidovits, J. (1991).»Geopolymers: Inorganic Polymeric New Materials,» J.Thermal Analysis, 37, pp.1633-
1756
9. Davidovits, J., and Davidovics, M (1991). «Geopolymer: Ultra-High Temperature Tooling Material for the
Manufacture of Advanced Composites,» Proc. 36th Int’l SAMPE Symposium, pp. 1939-1949
10. Scudamore, M.J. , Briggs, P.J. and Prager, F.H. (1991). «Cone Calorimetry-A Review of Tests Carried Out on
Plastics for the Association of Plastics Manufacturers in Europe,» Fire and Materials, 15, pp. 65-84
11. Sorathia, U, Dapp, T., and Kerr, J. (1991). «Flammability Characteristics of Composites for Shipboard and
Submarine Internal Applications,» Proc. 36th Int’l SAMPE Symposium, pp. 1868
12. Sorathia, U, Rollhauser, C.M., and Hughes, W.A. (1992).»Improved Fire Safety of Composites for Naval
Applications,» Fire and Materials, 16, pp. 119-125
13. Sorathia, U., Telegadas, H, and Beck, C. (1994). «Mechanical and Flammability Characteristics of Phenolic
Composites for Naval Applications,» Proc. 39th Int’l SAMPE Symposium, pp. 1940
14. Babrauskas, V. (1992) «Heat of Combustion and Potential Heat,» in Heat Release in Fires, Chapter 8, Elsevier
Applied Science, New York, pp. 207-223
15. Foden, A. J., Lyon, R.E., Balaguru, P.N., and Davidovits J.(1996) «High Temperature Inorganic Resin for Use
in Fiber Reinforced Composites,» Proceedings of the First International Conference on Composites in
Infrastructure (ICCI 96), Jan. 15-17, Tucson, Arizona, pp. 166-177
16. Babrauskas, V. and Peacock, R.D. (1992).»Heat Release Rate: Single Most Important Variable in Fire Haz-
ard,» Fire Safety Journal, 18, pp. 255-272
17. Hirschler, M. M. (1995) in Fire and Polymers, ACS Symposium Series Number 599, G.L. Nelson, ed., Ameri-
can Chemical Society, Washington, D.C.
18. Sundstrom, B. (1991). «Classification of Wall and Ceiling Linings,» Proceedings of the EURIFIC Seminar,
Copenhagen, Denmark, September 11-12
19. Balaguru, P. N. , and Surendra, P. S., (1992). Fiber Reinforced Cement Composites , McGraw-Hill, Inc., New
York
20. Harmathy, T.Z., (1988). «Properties of Building Materials,» in SFPE Handbook of Fire Protection Engineer-
ing , Chapter I-27, pp.378-391, Society of Fire Protection Engineers, Boston, MA
21. CRC Handbook of Tables for Applied Engineering Science (1979). «Engineering Materials and Their Proper-
ties,» Section 1, pp. 3-137, CRC Press, Inc. Boca Raton, FL
22. MIL-HDBK-5F (1990). Military Handbook, Chapter 3, pp. 348, Department of Defense, Washington, D.C.