Note: Descriptions are shown in the official language in which they were submitted.
:1~'7~
METHODS OF MAKING C~MENTITIOUS
OMPOSITIONS FROM W~STE PRODUCTS
Technlcal Field
The invention relates to the use of various waste
produc-ts in cementitious compositions, such as cemen-ted mine
backfill, or other stabilized earths. Such waste products
may include non-ferrous slags, as well as fossil fuel
combustion residues.
Background Art
sy-products of metallurgical processes, such as slags
which result from the smelting of both ferrous and non-
ferrous ores, and combustion products of coal from fossilfuel powered generating stations, such as fly ash or
clinker, all represent the product of a significant
investment of energy which is normally lost upon the
subsequent disposal of these materials, heretofore
considered as waste.
The term 'slag' as used in this application refers to
the vitreous mass which remains after the smelting of a
metallic ore, a process which entails the reduction of the
metallic constituents in the ore to a molten state.
The terms 'ferrous slag' or 'blast furnace slag' refer
to that slag which remains after the smelting of iron ore.
Alternately, 'non-ferrous slag~ is that slag which remains
after the smelting of a non-ferrous ore such as copper,
75'~
- 2 -
nickel, lead, or zinc, whether it be done in a blast furnaceor otherwise. Therefore, a slag considered non-ferrous in
the metallurgical sense may contain appreciable amounts of
iron due t~ the presence of this compound as an impurity
within the ore.
Fly ash is a combustion product resulting from the
burning of coal which has been ground to a relatively fine
particle size. Coal which is not as finely ground produces
both fly ash and a coarse, incombustible residue known as
clinker.
Many countries, including the United States, ~anada,
Chile, South Africa, Australia and the Scandinavian
countries, produce or export a great deal of both ferrous
and non-ferrous metals. This results in the production of
significant quantities of slag, produced as a by-product of
the required smelting operations. Blast furnace slags are
currently used as additives in some low strength concretes
whereas, except for railway ballast and granular fill type
applications, the feasibility of potential utilizations of
non-ferrous slags and fly ashes has been comparatively
disregarded, leading to the disposal of substantial
quantities of these commodities with resulting large
accumulations in areas surrounding the smelters and power
stations.
The economic feasibility of sub-surface mining
techniquçs depends upon an ability to fill the cavities
created by the removal of the ore in order to establish and
retain safe ~Jorking conditions. One accepted technique for
performing this function involves the addition of Portland
~ ~ 7'~
cement to the fill to act as a bincler in crea~lng a hardened
cementitious composition.
The Portland cements used in this manner are specially
formula-ted to primarily comprise specific compounds, such as
tri-calcium silicates, di-calcium silicates and tri-calcium
aluminates which, on hydration, provide the desired
cementing or binding action. The principal constituents of
- these Portland cements, i.e. CaO and Sio2, are present in a
high ratio of about 3 : l to strongly promote the calcium
silicate reactions.
- 15 The difficulty and expense involved in transporting
large quantities of Portland cement to often isolated mining
locations has prompted a search for cheaper additives or
substitutes which can reproduce the cementitious effect of
Portland cement at a reduced cost. Thus, cemented fills
~ introduce a broad new flexibility into mine planning and
design; however, cost considerations limit potential
applications. Any means of reducing cemented fill costs for
a given fill duty, therefore, broadens the potential
application for the material.
In general, if a lower cost binder which allows the
formation of a slurry with mine tailings and/or sand at the
same viscosity as that of a Portland cement slurry and which
develops adequate compressive strength in adequate times to
prevent collapse was available, lower grade orebodies could
be mined economically. Applicants~ invention serves ~ust
such a function.
The class of materials described under the broad term
~'7~
- 4 -
of 'pozzolans' offers potential cost savings in cemented
fill practice. A pozzolan is any materlal which can provide
silica to react with calcium hydroxide in the presence of
water to form stable, insoluble cementitious hydrated
calcium siLicates, or related, more complex silicates. The
silicates formed by pozzolanic action are closely related to
some ol those formed by the hydration of Portland cement.
Iron blast furnace slag, fly ash and various 'natural~
slags and ashes have been known for some time to have
pozzolanic properties. Waste industrial slags, however, do
not contain the correct quantities of essential ingredients
of Portland cements. Iron blast furnace slag comes closest
with a CaO/SiO2 ratio of approximately l. To acquire such
pozzolanic properties, however, such slags must be cooled to
an amorphous (or highly vitreous) state by rapid quenching,
such as by immerslon in a large quantity of high pressure
water. It is well known for example, that granulated
blast-furnace slag obtained in the production of pig iron
can be mixed with Portland cement clinker and the mixture
finely ground to bring out the inherent hydraulic properties
of the slag.
~5
In most current applications wherein ferrous slag or
fly ash is used in backfilling, one finds a combination of a
small quantity of Portland cement providing some initial set
and strength, together with the slag or fly ash. The slag
or fly ash reacts with residual CaO from the cement
reactions to form a 'high-grade' pozzolanic material having
calcium silicates which provide the balance of the strength
required over a period of time.
-- 5 --
The p~operties of such ferrous slag-based pozzolanic
materials have been set forth ln great detail in varlous
reference works well known by those working in the field,
including, for example, Turriz:iani, R., "Aspects of the
Chemistry of Poz~olanas", Chapter 14, The Chemistry of
Cenents, H.F.W. Taylor, Ed. Vol. 2, Academic Press, 1964;
Nurse, R.W., "Slag Cements", Chapter 13, The Chemistry of
1 ements, H.F.W. Taylor, Ed., Vol. 2, Academic Press, 1964;
- Kramer, w., "Blast-Furnace Slags and Slag Cements", Paper
VII-2, Fourth International Symposium on the Chemistry of
Cement, Washington, D.C., pp. 957-981, 1960 and Biczok, I.,
"Portland Blast-Furnace Cements (Slag Cement)", pp. 50-58,
in Concrete Corrosion and Concr~te Protection", Chemical
Publishing Co., Inc., New York, N.Y. 1967.
Additionally, the general physical requirements for
S'acceptable" pozzolanic activity are set forth in the ASTM
Standard Specification for "Blended Hydraulic Cements", no.
C595. These requirements are reproduced below:
POZZOLAN
Fineness: Amount retained when wet sieved on
45 um ,No. 325) sieve, max. % 20.0
Pozzolanic
Activity
30 Test: With lime (8.16), strength,
minimum psi, (MPa) 800 (5.5)
or with portland cement, (8.17),
index, min. % 75
~7~ J~
S rJA-~
Slag
Activi-ty
Test: With lime (8.16), streng-th,
minimum psi (MPa) 800 (5.5)
or with portland cement ~8.19),
index, min. % 75
A pozzolan would therefore have acceptab]e pozzolanic
activity under these specifications if it meets either of
the two alternative limits.
The chemical composition of the non-ferrous slags,
however, is sufficiently different from that of the ferrous
slags to require modification as described below in order to
convert such non-ferrous slags from a 'low-grade pozzolan'
to a 'high-grade pozzolan'. That is to say, that, to enable
the use of non-ferrous slags as cement, their chemical
composition must generally be modified to produce a product
capable of competing with Portland cement, i.e., one
capable of achieving high early strength as well as a high
ultimate strength within an acceptable time frame.
Appli~ants have determined that a higher quality, less
expensive cemented backfill may be produced, without the use
of Portland cement, by adjusting the proportions of both CaO
and A1203 in non-ferrous slag. This adjustment then
converts the slag from a 'low-grade' pozzolan to a 'high-
grade' pozzolan wherein the necessary aluminate reaction can
be harnessed by adjusting the sulphate ion and-calcium
hydroxide concentrations. Further, the methods for making
~ ~ 7~t~L~
- 7 -
cement from non-ferrous slag may also be extra~olated and
used to prepare improved cements utilizing ferrous slags or
fossil fuel combustion residues.
Summary of the lnvention
The invention relates to a method for making
cementitious compositions from a residue of waste industrial
products such as non-ferrous slags, fossil fuel combustion
residue or ferrous slags. This method includes the steps of
grinding the vitreous waste residue whose composition may or
may not have been altered by the addition of Cao and/or
Al203, to a predetermined particle size, and adding calcium
hydroxide or CaO, and a compound containing a sulphate anion
to form a mixture with water, which is then allowed to cure
to the final cementitious compositions.
The Ca(OH)2 or CaO added after the waste residue has
been ground is to raise the pH, in the presence of the
water, to an alkaline value to activate the alumina
component and provide a hlgh early strength.
A preferr~d particle size is between about 2,500 and
5,000 Blaine, although larger or smaller particles will work
in this invention. A preferred pH range is between about lO
and 14 and this range i-s achieved by the addition of an
alkaline compound.
The curing of samples must be done under enclosed
conditions at saturated humidity.
The application of heat during mixing and curing of
3~
~ 7~
samples greatly enhances the strength/time relationship.
Tempe~ature is thus a very impor~ant parameter;in the
successful application of the invention.
In these methods, a predetermined amount of Portland
cement, aggregate, fillers, tailings, or other inert
material can be added to the mixture prior to adding -the
w~ter.
The compound containing CaO or Al203 may be added to a
furnace during the generation of the slag, or it may be
added to said slag after the slag has been formed and before
it is granulated. A preferred CaO containing compound is
lime for both composition modification and pH adjustment. A
preferred Al203 containing compound is fly ash. Also,
preferred compounds containing a sulphate anion include
¦ sodium sulphate or gypsum.
Finally, the invention relates to the cementitious
compositions produced by the previously described methods.
Detailed Description of the Preferred Embodiments
As one skilled in the art would realize, the chemical
analysis of various slags from either ferrous or non-ferrous
ore smelting operations as well as that of the fly ash or
clinker which results from fossil fuel combustion, can vary
over a wide range. Average typical analyses for such
materials are set forth in Table I. This table includes the
major components of the slags, but a minor amount of
additional components such as metal oxides, sulphides, etc.
may also be present.
~ 7~
. g
TABLE I
~OMPOSII'ION OF TYPI~AL SLAGS
Weight Percent
_.______________.________ ____
10 Ni,ckel Reverbe~atory Slag 2-10 32-36 2-10 4~-56
Copper Reverberatory Slag 1-8 33-40 2-10 47-50
Iron Blast Furnace Slag 35-50 28-38 10-20 3-5
Non-Ferrous Blast Furnace
Slag 15-20 32-38 2-10 30-40
Fossil Fuel Combustion
Residue ~Fly Ash) 2-15 38-67 15-38 3-13
20 The present invention relates to a composition and a
method for obtaining useful cementitious products comprised
of such waste residues by adjusting and balancing various
important components to control the cementitious reactions
in the final compositions. As shown in Table I, non-ferrous
slags typically have relatively low calcium oxide and
alumina contents. Such amounts of calcium oxide and alumina
are often insufficient to provide for the required calcium
sulpho-aluminate and calcium silicate reactions and thus,
such slags are not suitable for use on their own as cements
unless their chemistry is appropriately modified.
A minimum amount of about 8% CaO and about 3 1/2 - 4% of
A12O3 is required to be present (in a preferred ratio of
3~
~L~ 7~L'~
- 10 -
approximately 2:1 CaO:A12O3) within the waste material
utilized to form the cementitious composition of the present
invention. These levels are necessary in order to provide a
starting material whose alumina component may be activated
upon the s~bsequent addition of a composition containing
additional Ca(~l)2 or CaO to react with a sulfate--containiny
composition and form a cementitious material capable of
p~oviding a high early strength.
Such a modification of the calcium oxide content can be
carried out using a variety of methods. During the
formation oF slag in a furnace, additional lime or limestone
may be added during the smelting process, with a
corresponding increase in the final calcium oxide content of
the slag. Similarly, a modification of the aluminium oxide
content can be achieved by the addition of, for example, fly
ash, during the smelting process.
Once a slag of the correct composition has been made and
granulated to a high glass content, it must be ground,
together with the gypsum if necessary, to a predetermine
fineness, preferably between about 2,500 and 5,000 ~laine.
Thus, the addition of water and an alkaline material,
preferably lime, serves to activate this composition.
Differentiation is necessary, however, between lime used as
an activator and lime added to the furnace feed to increase
the CaO content of the slag, this being the lime which
subsequently plays a major role in the cementitious
reactions. It is necessary that this CaO be incorporated
into the amorphous structure of the slay to enhance its
disordered chemical state and increase its reactivity.
The alkaline materlal, added in order to activate the
mlxture, adjusts the p~I upwardly to about twelve and allows
the formation of gels and ~l2 ions. Unless gypsum
(C~S04-2H2O) or some other sulphate ion containing materials
are added, however, the alumina component remains
unreactive. In order for the cementitious compound to be
successful, its alumina component chemistry must approach
t~at of the compound Ettringite, a calcium monosulpho-
aluminate compound with the approximate formulaCa6Al2(S04)3(OH)l2 26H20. The traditional 'pozzolonic~
slay-lime-water system is generally deficient in sulphate
radical and unless this is added from some extraneous
source, the desired cementitious reactions will not occur.
It is possible that in certain ores, the sulphate radical
may exist in the mill tailings in a form in which it would
be available for the cementitious reactions but for most
cases, additional sulphate ions must be added to the slag.
Thus, it is critical to adjust the sulphate content to a
range which, when combined with the other ingredients,
provides the approximate stoichiometric ratio found in the
mineral ettringite. The sulphate anion can be added as
either gypsum or sodium sulphate or other.
The pH of the mix may be raised to the required alkaline
value by addition of an alkali metal hyroxide or other base,
or by the addition of alkaline materials such as sodium
carbonate, sodium bicarbonate or potash, provide they are
accompanied by the addition of free lime.
By adjusting all of these components within the
parameters stated above, a cementitious composition is
formed, having a portion which forms ettringite-like
3~
- ].2 -
structures, thus obtaining sufficient strength and stabi].ity
in the final cementitious product.
With respect to ferrous slags, a similar procedure could
be followed. Such slags, however, usually contain a much
higher calcium oxide and alumina content than non-ferrous
slags and their compositions would not need adjusting. The
o~her steps described above would be followed in an
- essentially identical fashion to those for non-ferrous slags
in order to achieve the desired cementitious compositions.
Fly ash or other fossil fuel combustion residue would be
treated in the same manner as ferrous slags.
As would be clearly understandable to one skilled in the
art, the cementitious compositions of the present invention
may be used alone, or they may be mixed with a wide variety
of fillers, aggregate, accelerators, r.eOtarders or other
additives. Also, such cementitious compositions can be
substituted for all or a portion of the Portland cement
component of ordinary cementitious compositions or concrete.
Such cements can also be mixed with high aluminous cements,
pozzolans or other materials to form specialty cements for
specific applications.
While it is apparent that the invention disclosed herein
~ is calcu~ated to provide an improved cementitious system
over those described in the prior art, lt will be
appreciated that alternate embodiments may be devised by
those skilled in the art. It is therefore intended that the
appended claims cover all modifications or embodiments as
fall within the true spirit and scope of the present
invention.
3~
