Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a novel bitumen mixture
and a high performance prefabricated waterproofing membrane
useful for roofing which is obtained by impregnating differ-
ent layers of reinforcing material with the bitumen mixture.
More particularlyl the invention relates to a novel bitumen
mixture and a waterproofin~ membrane comprising a series of
reinforcing layers including a polyester ma~, a mat of
fiberglass and a fiberglass netO Each reinforcing layer is
im~regnated with bitumen mixed ~ith a thermoplastic polymer
wherein the polymer is selected from the group consisting of
an amo~phous copolymer of ethylene/propylene, atactic
polypropylene, polyisobutylene ar.d styrene-butadiene-stvrene
--1--
24141-A
block copolymer. The mixture has a minimum ring and ball
softening point of about 105C and preferablv 155C.
Preferably the bitumen contains amorphous ethylene/propylene
copolymer, a mixture of atactic polypropylene polymer and
ethylene propylene copolymer containing mineral acid and
isotactic polypropylene.
For almost a century bituminous roofing membranes
have been used in the United States to protect buildings,
their contents and the occupants from the weather. The most
common type of bituminous roofing membranes consist of two
to five layers of felt or fabric which during application to
the roof are made to adhere together with bituminous
material, such as tar, pitch or asphalt. The fabrics or
felts may contain organic material, asbestos or ~lass. In
general, these types of roofing membrane have been the
source of problems for manufacturers of the membrane r roof
designers, appliers and users. The incidence of failures in
flat roof waterproofing membranes has increased in the order
of 30 percent in that time period. The problems have been
~0 attributed in part to poor design, inadequate materials and
improper workmanship! but many believe that the problem is
more fundamental.
Conventional roofing membranes were originally
developed in order to cover concrete and wood roofs which
formed a relatively stable rigid base for the roofing mem-
brane. Today roofs are be;ng made of more flexible light-
weight material and are often formed from prefabricated
sheets or panels many of which have highly e~ficient thermal
insulationO These changes in the thermal properties of the
24141-A
building materials have completely altered the temperature
environment of the roofing membrane. This thermal change
coupled with resulting movement in the joints of the roof
and the insulation, places substantial local stress on con-
ventional roofing membranes which were originally designedwith relatively low tensile strength and elasticity.
An additional problem associated with traditional
roo~ing material is that it requires about 12 lbs/m2 of
bitumen or other petroleum based products. Due ~o the high
cost of petroleum and the efforts to conserve petroleum, it
is also desirable to decrease the amount of petroleum based
products used in roofing membranes.
Some attempts by others in the roofing field to
produce an improved roofing material are described in U.S.
Patent Nos. 3,741,856; 3,753,938 and 3,937,640. U~S. Patent
No. 3,741,856 to Hurst issued January 26, 1973, describes a
bitumen waterproofing sheet which has a polyethylene support
layer and a pressure sensitive adhesive backing. The
Montague patent, U.S. 3t753r938, issued August 21, 1973,
descri~es a special roofing material which contains a
mixture of bitumen, a synthetic elastomeric material which
is predominantly chlorosulphonated polyethylene and fibrous
material such as filaments of fiberglass or other synthetic
bituminous roofing membrane comprising a base sheet of a
synthetic polymer and one or more layers of bitumen. Tn
addition, another roofing membrane has been developed in
Europe in an attempt to meet the new requirements of modern
roof construction and is the subject of patents in Luxembourg
(No. 69480), France (NoO 7505703) and Italy (20554A/75).
(See also Impermeabilizzazione Delle Construzioni, Romolo
Gorgati, 1974 pp. 63-64). The preEabricated roofing membrane
developed in Europe contains a polyester mat and a fiber-
glass mat both impregnated with polymer modi~ied bitumen.
Although this roofing material has performed satisfactorily
in some applications, it does not have the necessary tensile
strength, dimensional stability, resistance to puncture,
oxidation and aging needed for demanding modern roofing
applications.
It would be desirable to provide a bitumen mixture
having superior mechanical and physical-chemical characteristics
which meet the preliminary performance criteria for bituminous
membrane roofing published by the United States Department of
Commerce/National Bureau of Standards and to achieve these
superior characteristics without substantially increasing the
total weight, cost of the roofing membrane or the amount of
petroleum based product used.
It is an object of this invention to provide a
novel bitumen mixture and a novel waterproofing membrane which
may mitigate at least some of the disadvantages previously
encountered.
Accordingly, the invention provides a prefabricated
waterproofing membrane which comprises a series of super-
posed reinforcing layers including a fiberglass mat, a
polyester mat and a fiberglass net, the layers being impregna-
ted with bitumen mixed with at least one thermoplastic
polymer selected from the group consisting of an amorphous
copolymer of ethylene/propylene, atactic polypropylene,
_. 4
polyisobu-tylene and styrene-butadiene-styrene block co-
polymer, the bitumen polymer mixture having a ring and ball
soEtening point of at least 105C wherein the bitumen poly-
mer mixture is further modified by the addition of at least
one polymeric material selected from the group consisting
of a mixture of atactic polypropylene and ethylene propylene
copolymer and a mixture of atactic polypropylene and ethylene
propylene copolymer containing mineral oil.
Preferably the ring and ball softening point
is at least 155C.
The invention also provides a novel bitumen mix-
ture which comprises bitumen mixed with amorphous copolymer
of ethylene and propylene modified by addition of at least
one of a mixture of atactic polypropylene polymer and
ethylene propylene copolymer and a mixture of atactic poly-
propylene polymer and ethylene propylene copolymer contain-
ing mineral oil.
A further aspect of the invention provides a
prefabrica-ted waterproofing membrane which comprises a
series of superposed reinforcing layers including a fiber-
glass mat and a bonded fiberglass net/polyester mat, the
layers being impregnated with bitumen mixed with at least
one thermoplastic polymer selected from the group consist-
ing of an amorphous copolymer of ethylene/propylene, atactic
polypropylene, polyisobutylene and styrene-butadiene-styrene
block copolymer, the bitumen polymer mixture having a ring
and ball softening point of at least 105~C.
The improved waterproofing membrane is formed
by the conventional method which is employed in Europe to
manufacture European type roofing membranes. The polymeric
i~
materials are melted and stirred in a heated au-toclave and
the bitumen is added and blended for about 1-2 hours. In
a second agita-ted autoclave additional bitumen and fillers
are mixed for about 5-10 minutes at about 100-150C~ At
the end of the mixing period the two mixtures are combined
and homogenized to form the bitumen polymer mixture. The
reinforcing layers are impregnated with the bitumen polymer
mixture by passing the reinforcing layers through the bitumen !
polymer mixture, at about 175C, whereby the reinEorcing
10. layers and the bitumen polymer mixture adhere and interact
with each other to form a single waterproofing membrane
with superior mechanical and physical-chemical
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I"
24141-~
characteristics over known waterproofing membranes~ The
reinforcing layers are preferably positioned together at a
point above the median point of the membrane close to the
upper surface of the membrane in order that the bulk of the
bitumen polymer mixture in the membrane which acts as the
adhesive for the membrane is below the reinforcing layers
and is thereby shielded from the sun's ultraviolet rays.
The bitumen polymer layer under the reinforcing layers is at
least 1.5-2.5 mm thick. The preferred order of the re-
in~orcing layers within the membrane is to have the fiber-
glass mat closest to the surface, the fiberglass net in ~he
center and the polyester mat beneath it.
The polyester mat, the inner most reinforcing
layer weighs from about 50-250 y/m2 and (1) distributes
internal tensions in the membrane and (2) improves the
impact resistance of the membrane. Moreover, the polyester
mat permits the membrane to remain impermeable to water even
if the outer fiberglass mat and fiberglass net are ruptured
by an external force. The fiberglass mat weighs about ~0~
125 g/m and, as the top reinforcing layer, provides thermal
stability to the membrane both during manufacture and in
application. It also serves to screen the membrane from
ultraviolet rays and minimizes tearing due to the foo~
traffic associated with installation and maintenance.
The middle fiberglass net weighs about 60-100 y/m2
and adds additional stability to the waterproofing membrane
without significantly increasing the thickness or weight of
the membraneO The additional stability provided by the
fiberglass net is needed in order to mlnimize movemen~ in
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the membrane due to thermal changes. The open weave of the
net is from about 1 mm to 5 mm, and preferably about 3 mm,
which allows the bitumen polymer mixture to flow through the
net and provide good contact between the polyester mat below
and the fiberglass mat above~ The addition of the fiber-
glass net which has definite structure and rigidity as
compared to the fibergla s mat improves tensile strength,
but does not decrease the elongation at the break of the
resulting membrane. Rather surprisingly, the presence of
the fiberglass net tends to increase the elongation at break
of th~ membrane.
In a preferred embodiment, the fiberglass net is
made with fiberglass fibers containing about 20-25% poly-
vinyl chloride threads and the glass net is heat fused
directly to the polyester mat at a temperature of about
100C to form a single fiberglass net/polyes~er mat layer.
The polyvinyl chloride threads melt and serve to fuse the
layers together. The resulting single layer is thinner than
the combined thickness of the unfused polyester mat and
fiberglass net. The single fused fiberglass net/polyester
mat layer is then used as described above witEl the fiber-
glass mat to form the waterproofing membrane.
Regardless of how the reinforcements are pre-
pared, the resulting waterproofing membrane is about 4 cm
thick. However, since the fused fiberglass net/polyester
mat is thinner than when each layer is combined separately~
the resulting waterproofing membrane can contain more of the
bitumen mixture below the reinforcing layers and still be
about 4 mm thick. In addition the use of the fuse~ fiber-
24141-A
glass net/polyester mat allows for faster manufacturing
speeds since the fusion step helps to eliminate the forma-
tion of air bubbles between the fiberglass mat and the
polyester mat during impregnation with bitumen.
Bitumen as used in making the novel waterproofing
membrane is a solid or viscous semisolid mixture of hydro-
carbons which is obtained from petroleum by distillation of
the lighter hydrocarbons at atmospheric pressure. The ring
and ball softening point of the bitumen can vary, but the
most common range is between 30C and 110C. The ring and
ball softening test is a standard test described in
Impermeabilizzazione Delle Costruzione, Romolo Gorgati,
1974, pp. 13-14. The ring and ball softening poin~ of
bitumen is the temperature at which a standard steel ball
placed on a standard ring filled with bitumen penetrates
into the bitumen. It is also known as asphalt and may also
be obtained from the acid sludge produced by treating the
heavy distillates of asphalt based petroleum with concen-
trated sulfuric acid~
In or~er to improve the elasticity, flexibility,
homogeniety, cold cohesion and aging of the resulting water
proofing membrane, the bitumen is modified by mixing with a
thermoplastic polymer such that the bitumen polymer mixture
has a ring and ball softening point of at least 105C, and
preferably about 155C.
Examples o~ suitable polymers or modifying
bitumen are amorphous ethylene/propylene copolymers, atactic
polypropylene, polyisobutylene and styrene-butadiene-styrene
block copolymer~ Preferably, amorphous ethylene/propylene
24141-A
;3~
block copolymer is used because of its high resistance to
oxidation and its elasticity. Ethylene/propylene copolymer
is usually, but not necessarily, a by-product of the produc-
tion of polypropylene~ The preferred copolymer ha~ a
S viscosity o~ about 0.3-25 million CPS (centipoise) at about
180C and contains from 0-40~ ethylene, preferably 20-30%,
and may contain some atactic and isotactic polypropylene.
Prior to this invention, amorphous ethylene/propylene co-
polymer had been considered to be of no industrial value
because of the high viscosity and resulting fusion problems.
This invention takes these previously undesirable properties
and utilizes them to prepare a bitumen mixture and a water-
proofing membrane with superior mechanical and physical
characteristics.
In the preferred embodiment, additional modifiers
selected from the group consisting of atactic polypropylene,
powdered rubber, isotactic polypropylene, a mixture of
atactic polypropylene polymer and ethylene propylene co-
polymer and a mixture of atactic polypropylene polymer and
ethylene propylene copolymer containing mineral oil are
added to the bitumen polymer mixture to further improve its
characteristics. The mixture of atactic polypropylene
polymer and ethylene polypropylene copolymer containing
mineral oil, a by-product of the process for separating
atactic and isotactic polypropylene, is the preferred
additional modifier and is often used in the bitumen in
combination with isotactic polypropylene. The mineral oil
in the preferred modifier can be, for example, paraffin or
one of its homologs. Powdered rubber which can also be used
24141-A
as an additional modifier in this invention is obtained from
natural or synthetic rubber, or a mixture thereo~, and has a
particle size of about 20-50 microns. Atactic polypro-
pylene, another modifier, is obtained as a by-product of the
process for producing isotactic polypropylene.
The preferred bitumen polymer mixture may also
contain a plasticizer, for example, a paraFfin lubricating
oil having an Engler viscosity lower than 10 at 50C. If
the mixture of atactic polypropylene polymer and ethylene
copolymer containing mineral oil is used, the plasticizer is
not needed.
The preferred bitumen mixture also contains
fillers to decrease oxidation and slow the aging of the
waterproofing membrane. Suitable fillers have a particle
size of about 10 to 75 microns, and may include, for
example, spent lime (calcium hydroxide oxide), talc
tmagnesium silicate Mg3Si4OlO(OH2), ground sand, ground
slate, ground cement, diatomaceous earth, clay and
titanium dioxide. Preferably, the filler is any inert
absorbant material such as spent lime.
The novel bitumen mixture used to impregnate t.he
reinforcement layers, and thereby to form the waterproofing
membrane, contains about 50-70% bitumen, about 10-50%
- polymer and about 0-20~ fillers. The preferred bitumen
mixture contains about 67% bit~men, about 24% polymers, and
about 9~ fillers and additives~
The composition of the bitumen mixture can be
adjusted in order to adapt to local climate conditions. In
colder climates, for example, the bitumen mixture preferably
--10--
24141-A
contains about 65% bitumen, about 28% polymer and about 7~
other fillers and additives. In warmer climates the mixture
preferably contains, for example, about 62~ bitumen, about
22% polymer and about 16% other additivesO
S The wa~erproofing membrane which results from the
impregnation of a fiberglass mat, a fiberglass net and a
polyester mat with the bitumen polymer mixture is abou~
4-7 mm thick, preferably 4-5 mm, and weighs about 4~3-5.4
Kg/m . In the embodiment containing the single layer fused
fiberglass net/polyester mat, the thickness and weights are
normally the same.
The surface of the resulting waterproofing mem-
brane is dusted lightly with talc or some other suitable
material to prevent sticking, covered with a protective film
lS such as polyethylene and rolled up and packaged in rvlls
about 100-110 cm high and 7-10 meters long. The water~
proofing membranes are placed loose on the roof surface or
are fused in place on the roof using a gas burner or similar
equipment. In applyin~ the membrane to the surface, the
membrar.es are overlapped at the edges and fused to insure
complete waterproofing.
In general, the una9ed waterproofing membrane of
about 4 mm thickness has superior physical-mechanical
characteristics as listed in Table I and can be expected to
give at least 20 years of service under normal conditions.
24141-A
, 5~
TABLE I
Physical Mechanical Properties of an
unaged 4 mm waterproofing membrane
PropertY Value
Creep due to heat
(DIN 53.123/181gO)
(AIB 4687.02) 120C
Low temperature flexibility
(AIB 4224) -10C
Permeability to water
under pressure (DIN 16935~ none (131' column of water)
Vapor permeation Index (23C) 11.2934 g~m2/24 hrs) (24 hrs)
10.2714 g/m /24 hrs) t72 hrs)
Permeance = 0~0246 meters perms
Solubility in water (25C) 0.019 mg/cm2
Tensile Strength (ASTM 2523) 200 lbs/in
Elas~icity modulus 0.13
Coefficient of thermal
expansion (30-O~F) 20 x 10 6
Longitudinal elongation at
break* 0F (ASTM 2523) 3
Transver~al Elongation at
break 0F (ASTM 2523) 3%
* Percent elongation at break is
equivalent to the percent strain.
The waterproofing membrane also has high impact
strength when tested according to ASTM D-2643 6O7~
At 3.9C no damage to the membrane was observed
and at -13C only a slight crack at the point of impact was
observed when the sample was bent. Visible crackin~ occurred
at the point of impact when a standard weight was dropped :
from a height of seven feet.
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24141 A
DETAILED DISCUSSION OF THE INVENTION
This invention will be more fully understood
through the following examples which are used only for
illustration and are not meant to limit this invention in
S any way.
Example 1
A waterproofing membrane was prepared by impreg-
nating three reinforcing layers, that is a fiberglass mat
which weighed 70 g/m2, a fiberglass net whic~ weighed 80
g/m2, and polyester mat which weighed 150 g/m2 with a bitu-
men polymer mixture which contained 66.7 bitumen, 1~.7%
ethylene/propylene copolymer, 9.5~ atactic polypropylene,
2.4% isotactic polypropylene and 8.7% fillers (spent lime
and talc). In order to prepare the bitumen polymer mixture,
~00 kg of copolymer of ethylene/propylene, 600 kg atactic
polypropylen~ and 150 kg isotactic polypropylene were melted
in an agitated autoclave at 190C allowing a minimum time
for the operation. 2100 kg of bitumen were added keeping
the blend at 150C for one and one-half hours~ The temper-
ature should not be allowed to exceed 195C~ In another
stirred autoclave, 2100 kg bitumen, 150 kg talc and 400 kg
lime were mixed for lG minutes at 150C. At the end of the
operation, the second blend was homogenized with the first
blend at about 175C for 6 hours~ At this point, the
bitumen polymer mixture had acquired the characteristics of
an entirely new substance having a ring and ball softening
point of 150C and good flexibility down to -8C.
The reinforcing layers were passed through the
bitumen polymer mixture and allowed to adhere togethre to
form the waterproofing membrane which had a total weight of
4.4 Kg/m2, a thickness of 4 mm. The bitumen polymer layer
under the reinforcing layer was 1.5 mm thick.
The superior physical properties of the water-
proofing membrane described in Example 1 were tested ac-
cording to Recommended Practice for Testing Load-Strain
Properties of Roof Membranes, ASTM-D-2523-70, Part 11, ASTM
Annual Book of Standards, 1973 which is incorporated herein
by reference. Each test was performed six times, three
times on transverse samples and three times on longitudinal
samples. The results of those tests appear in Tables II
and III, respectively.
Image
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24141-A
TABLE I I I
LONGITUDINAL SAMPLES
Average
Test Value
Average coefficient oflxlO ~3xlO` 66xlO 6 3.3xlO 6
5. expansion (73~30~F)
Average coefficient of24xlO 626xlO 626xlO 625.3xlO 6
expansion (30-0F)
Tensile strength 210 238 232 226.6
lbs~in (0F)
Percent elongation at3.~6 3.10 3.31 3~22
break (0F)
Load Strain modulus 0~3217 0.3836 0.3502 .3518
x 104 lbs/in (0F)
Modulus of Elasticity - - - 0~13
(lb~/in)
I~ can be se~n from these test results that the
novel waterproofin~ membrane as described in Example 1 has a
superior thermal expansion coefficient and high elasticity.
The average modulus of elasticity of ~he improved water-
proofing membrane described in Example 1 is 0.13 in both thelongitudinal and transverse directions of the membrane.
Comparisons have shown that the longi~udinal mod-
~lus of elasticity for Example 1 is about 1.8 times higher
~ than the average modulus of elasticity obtained for three
leading roofing materials and about 2.7 times higher than
the value for th~ least popular of the three materials and
about l.S times higher than the leading material.
Comparisons have also shown that the transverse
modulus of elasticity for the material described in Example 1
~ ; 24141-A
was about 2.2 times higher than the average value for the
three leading materials; about 2.7 times higher than the
value for the least popular materials and about 1.86 times
higher than the leading material.
Example 2
~ waterproofing membrane was prepared by impreg-
nating three reinforcing layers, tha~ is a fiberglass mat
which weighed 95 g/m2, a fiberglass net which weighed
80 g/m2, and polyester mat which weighed about 120 g/m2 with
a bitumen polymer mixture which contained 66.7~ bitumen,
11.5% ethylene/propylene copolymer, 11.5% of a mixture of
atactic polypropylene polymer and ethylene propylene
copolymer containing mineral oil obtained from separa~ing
atactic and isotactic polypropylene, 1.5~ isotactic
polypropylene and 8.7% fillers ~spent lime and talc). In
order to prepare the bitumPn polymer mixture, 72~ kg of co-
polymer of ethylene/propylene, 725 kg atactic polypropylene
and 95 kg isotactic polypropylene were melted in an agitated
autoclave at 190C allowing a minimum time for the
operation. 2100 kg of bitumen were added keeping the blend
at 150C for one and one-half hours. The temperature should
not be allowed to exceed 195C. In another stirred
autoclave, 2100 kg bitumen, 150 kg talc and 400 kg spent
lime were mixed for 10 minutes at 150C~ At the end of the
operation, the second blend was homogenized with the first
blend at about 175C for 6 hours. At this point, the
bitumen polymer mixture had acquired the characteristics of
an entirely new substance having a ring and ball softening
point of 155C and good flexibilit~ down to -10Co
-16-
~ ; 24141-A
The three reinforcing layers were passed through
the bitumen polymer mixture and allowed to adhere together
to form the waterproofing membrane which had a total weight
of 4.4 Kg/m2 and a thickness o~ 4 mm. The bitumen polymer
layer under the reinforcing layer was 1.5 mm thick.
The superior physical properties of the water~
proofing membrane described in Example 2 were tested as de-
scribed ~or Example 1. Three samples were tested. The
average of those three test results appear in Tables IV
and V.
TABLE IV
TRANSVERSE SAMPLES
Average
Test Value
Average coefficient of 1.34 x 10 6
expansion (73-30F)
Average coefficient of 5.3 x 10 6
expansion (30-0F)
Tensile strength 244
~0 lbs/in (0F)
Percent eLongation 2.8
at break ~0F)
Load Strain modulus 0.879
x 104 lbs/in (0F)
Modulus of Elasticity 0.14
(lbs/in)
TABLE V
LONGITUDINAL SAMPLES
Aver age
Test Value
Average coefficient of 1.48 x 10 6
expansion (73-30F)
Average coefficient of 3.0 x 10 6
expansion (30-0F)
Tensile strength 252.5
lbs/in (0F~
Percent elongation at 2.8
break (0F)
Load Strain modulus O.gl6
x 104 lbs/in (0F)
Modulus of Elasticity 0.14
(lbs/in)
It can be seen from these test results that the
novel waterproofing membrane as described in Example 2 has a
lower and, therefore, superior thermal expansion coefficient
as well as high elasticity. The average modulus of elas-
ticity of the improved waterproofing membrane described inExample 2 is 0.14 in both the longitudinal and transverse
directions of the membrane.
Comparisons have shown that the longitudinal mod-
ulus of elasticity for Example 2 is about 1.9 times higher
~5 than the average modulus of elasticity obtained for three
leading roofing materials and about 2.7 times higher than
the value for the least popular of the three materials and
about 1.6 times higher than the leading material.
Comparisons have also shown that the transverse
modulus of elasticity for the material described in Example 2
was about 2.4 times higher than the average value for the
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` 24141-A
three leading materials; about 2.9 times higher than the
value for the least popular materials and about 2.0 times
higher than the leading material.
Example 3
A waterproofing membrane was prepared as described
in Example 2 except that a fiberglass net is made with fiber-
glass fibers containing about 25% polyvinyl chloride threads
and which weighed 80 g/m was fused at about 100C with a
polyester mat which weighed about 50 g/m2. The fused poly-
ester mat/fiberglass net single layer and a fiberglass mat
which weighed 95 g/m2 were passed through the bitumen poly-
mer mixture and allowed to adhere together to fQrm a water-
proofing membrane which has a total weight of about 4.3 kg/m2
and a thickness of about 4 mm.
In preliminary testing, the membrane was found to
permit excellent tensile strength and percent elongation at
break when proper impregnation was achieved, as shown below
in Table VI.
TABLE VI
Longitudinal
Tensile Strength (lbs/in) 288 318 205 191* - 183*
Pescent elongation at break 3.5 3.9 ?.3 2.2 - 1.9
Transversal
_
Tensile strength (lbs/in) 171* 225 177* 172* 165* 226
Percent elongation at break 2.2 2.9 2.3 2.2 2.1 3~0
* samples not adequately impregnated
--19--
24141~A
As will be seen from Table VI, the material must be properly
impregnated with the mixture to achieve homogeneity and
optimum properties on a consistent basis.
Exam~e 4
A conventional waterproofing membrane was prepared
by impregnating a ~iberglass mat which weighed 50 y/m2 and a
polyester mat which weighed 150 g/m2 with a bitumen mixture
which contained 65.0% bitumen, Z3.5% atac~ic polypropylene,
2.5% isotactic polypropylene and 9.0% fillers (talc and spent
lime).
The bitumen mixture was prep~red as in Example 1
and the reinforcing layers were passed through the bitumen
mixture to form the conventional waterproofing membrane.
The tensile strength and the percent strain at 0F of this
membrane were measured by the same procedure used in Example 1
The sample had a longitudinal tensile strength of
132 lbs/in and a percent strain of 3. The transverse
tensile strength was 94 lbs/in and the transverse percent
strain was 2%. It should be noted that not only are tbe
2Q tensile strengths and percent strain values for Examples 1,
2 and 3 significantly better than those for Example 4, but
there is greater consistency in the transverse and longi-
tudinal values for Examples 1, 2 and 3 than for Example 4.
These results demonstrate that not only do the novel mem-
branes described in Example 1, 2 and 3 give superior values
over conventional membranes, but those values are also more
consistent throughout the membrane regardless of test
direction.
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