Note: Descriptions are shown in the official language in which they were submitted.
106Z830
This invention relates to novel lightweight aggregate-containing,
hydraulic cement compositions having improved properties. More particularly,
this invention concerns novel compositions containing hydraulic cement as a
binder and additionally a lightweight aggregate such as expanded vermiculite
or perlite to which have been added a polymer of ethylene oxide to enhance
certain properties thereof.
In the construction of in-ground swimming pools wherein a water-
impermeable membrane such as a plastic film is employed as a liner, it is
highly desirable to protect the membrane from being punctured by irregular-
ities in the surface of the cavity, e.g. rocks or shale, against which the
membrane is placed. One method of providing such protection is by pouring
and screeding a layer of sand on the bottom or horizontal surface adjacent
the liner. In another method, a layer of lightweight, inert foraminous part-
iculate material such as expanded vermiculite, perlite, etc., is employed
which not only covers the surface irregularities but also provides a more
"cushioned" and less abrasive surface for the easily-perforated liner. On
the non-horizontal surfaces of the cavity formed to receive the liner in in-
ground pool construction, it has been the practice to trowel a layer of wet
sand to provide the necessary protection. The applied sand, however, when
dried has a tendency to fall off of the surface, exposing the liner to the
rocks or other surface irregularities. To avoid this problem, a binder such
as Portland cement can be mixed with the sand. A more advantageous protective
coating can be prepared from a mixture of such a binder with the aforemention-
ed lightweight foraminous material, for example, expanded vermiculite aggre-
gate. Such a coating is less abrasive to the liner than sand and also has
insulating properties that the sand coating does not. The foraminous material
in the coating renders it porous thus permitting water which has seeped be-
tween the liner and the coating to drain through the coating. The highly
porous nature of the coating also protects it from being washed out by rising
water tables during wet months of the year. The composition containing the
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foraminous aggregates have however, been found to be difficult to trowel onto
the non-horizontal surfaces of the cavity. Attempts at trowelling such com-
positions on other than horizontal surfaces often results in severe tearing,
sagging and general unmanageability of the applied product.
Accordingly, the invention provides a dry, settable, composition
with a density after setting of less than 50 pounds per cubic foot containing
a hydraulic cement, a lightweight, inert, low density, foraminous particulate
aggregate selected from the group consisting of expanded vermiculite, expanded
perlite and expanded shale in an amount of from about 1 to 25 parts by volume
per part by volume of said cement, and from about 0.01 to about 2 percent by
weight of a polymer of ethylene oxide based upon the weight of said particulate
material.
Thus, it has been found that the trowelability of such cementing
compositions containing a hydraulic binder and lightweight foraminous aggre-
gates such as expanded vermiculite, perlite, shale, etc., is enhanced by the
incorporation therein of relatively small amounts of high molecular weight
polymers of ethylene oxide. The presence of a small amount of such polymers
was found to enable placement and trowelability of compositions having ratios
of such aggregates to cement either too difficult or impossible to produce or
place on non-horizontal surfaces.
Another aspect of the invention provides the method of constructing
in-ground structures comprising the steps of: (a) forming a cavity in the
ground having a desired configuration; (b) trowelling a smooth, wet mixture
containing a hydraulic cement, a lightweight, inert, low density, foraminous,
particulate aggregate selected from the group consisting of expanded vermicu-
lite, expanded perlite and expanded shale in an amount of from about 1 to 25
parts by volume per part by volume of said cement, water, and from about 0.01
to about 2 percent by weight of a polymer of ethylene oxide based upon the
weight of said aggregate to enhance the trowelability of the wet mix over the
interior surface of said cavity; and (c) thereafter placing a water-impermeable
membrane over the trowelled mixture.
The compositions to which the ethylene oxide polymers are added
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according to the invention comprise a hydraulic cement binder such as Port-
land cement to which is added the desired proportion of inert lightweight
foraminous particulate aggregate, and sufficient water to give the desired
fluidity to the wet mix. Expanded vermiculite is the preferred inert
foraminous aggregate for use in the present invention. The exact proportion
of foraminous aggregate employed will vary according to the desired degree
of "cushion" wanted in the set coating but in general between about 1 and
25, preferably about 4 and 16 parts by volume of vermiculite will be employed
per part by volume of cement. Also, the precise amount of water to be
employed will also vary according to the degree of fluidity desired in the
mix. Workable mixtures will, however, normally require the use of between
about 2 and 5 gallons of water for each cubic foot of foraminous aggregate
present. In addi~ion to expanded vermiculite, other inert lightweight
foraminous particulate materials such as expanded perlite and expanded shale
can be employed. The set compositions will generally have a dry density of
less than about 50 lbs. per cubic foot, more often about 15 to 35 lbs. per
cubid foot. Additional ingredients such as sand, air-entraining agents, etc.,
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can be employed in the compositions of the invention.
The ethylene oxide polymers useful in the invention are the well
known water-soluble organic polymers having a molecular weight ranging from,
e.g. lO0,000 to 6,000,000 or more. The polymers are preferably incorporated
in the composition in finely divided form in an amount of from about 0.01 to
about 2 percent, preferably from about 0.05 to about 1 percent by weight
based on the inert lightweight foraminous aggregate present in the composit-
ion. The preferred polymers for use in the invention have a molecular weight
of less than 1,000,000 with polymers having a molecular weight in the range
of about 100,000 to 400,000 being especially preferred.
The following examples serve to illustrate the invention.
Example
To a paddle type mixer are added 25 gallons of water followed by
one cubic foot of Portland cement. Eight cubic feet of expanded vermiculite
to which had previously been added 100-110 cubic centimeters of a polymer of
ethylene oxide having an approximate molecular weight of 200,000 is then
slowly added while the mixer is rotated. After approximately one minute,
the mixture is conveyed to an excavation in the ground formed to receive the
lining element of an in-ground swimming pool. Following application of the
wet mix by trowel, a smooth, porous, nonabrasive coating is formed having a
compressive strength in the range of 90 to 125 pounds per square inch and a
dry density of less than 50 pounds per cubic foot, the liner can be installed
over the coating when either wet or dry.
The lightweight, low-density compositions of the invention have
obvious utility in applications other than in-ground swimming pool construct-
ion, for instance, as lightweight insulating concretes in roof, wall, etc.,
construction.
