Compositions and methods for manufacturing ettringite coated fibers and aggregates

Compositions and methods for the deposition of ettringite (3CaO-Al.sub.2 O.sub.3 .multidot.3Ca(SO.sub.4).multidot.30-32H.sub.2 O) onto the surfaces of fibers, aggregates, and other fillers. The ettringite is produced in situ within an aqueous suspension while in proximity to the fibers, aggregates, or other fillers to form a mineralized composite material comprising ettringite coated fibers, aggregates or other fillers. Ettringite treated fibers, aggregates, or other fillers are formed by adding chemical reactants such as calcium oxide and aluminum sulfate, which react together in the presence of water to form ettringite, which then precipitates onto the surface of the fibers or other substrates being treated. The ettringite treated fibers, aggregates or other fillers can be added to hydraulically settable materials to improve the chemical and mechanical bond between the fibers or other substrates within the resulting hardened hydraulically settable composite material, particularly a cementitious or concrete material.

BACKGROUND OF THE INVENTION 
1. The Field of the Invention 
The present invention relates to the treatment of fibrous and particulate 
substrates with a mineral coating. More particularly, ettringite crystals 
are precipitated in situ within an aqueous medium onto the surface of 
fibers and other substrates in order to improve their chemical and 
mechanical compatibility within a hydraulically settable matrix, 
especially a cementitious matrix. 
2. The Relevant Technology 
Discontinuous, discrete fibers and continuous fibers or filaments 
(hereinafter "fibers") may be incorporated into a variety of materials to 
form a fiber-reinforced composite material, which generally increases the 
toughness, flexibility, tensile strength, and flexural strength of the 
composite material and articles made therefrom. Such strengthening and 
toughening effect is significant whenever the tensile and flexural 
strength of the fibers exceeds the tensile and flexural strength of the 
otherwise non-fiber-reinforced material. One type of such material 
includes hydraulically settable composite materials, more particularly 
cementitious materials, which generally have high compressive strength but 
comparatively very low tensile and flexural strengths. The level of 
strength, flexibility, and toughness that is imparted by the fibers to the 
composite material or article corresponds to the degree of mechanical 
and/or chemical interaction between the fibers and the other components 
within the composite material. In the case of hydraulically settable 
materials, more particularly cementitious materials, an important variable 
is the degree of mechanical and chemical interaction between the fibers 
and the hydraulically settable binder, more particularly, the hydraulic 
cement binder. 
In general, fibers are able to strengthen and toughen a variety of 
hydraulically settable materials and articles made therefrom. 
Fiber-reinforced hydraulically settable materials are prepared by mixing 
fibers into a hydraulically settable mixture containing water and a 
hydraulically settable binder like hydraulic cement, gypsum, or calcium 
oxide (hereinafter "hydraulically settable," "hydraulic" or "cementitious" 
compositions, materials, or mixtures) and then allowing the mixture to 
harden into the desired shape of the article. Hydraulically settable 
materials also typically include one or more types of aggregates, which 
can improve the strength, flow properties, and cost effectiveness of the 
hydraulic cement composite, or concrete material. The hydrated 
hydraulically settable binder forms a structural matrix that holds the 
fibers and other components together. 
Fibers have been shown to greatly improve a variety of mechanical 
properties of the final hardened hydraulically settable composite 
material, including flexural strength, impact strength, toughness, 
fracture energy, fatigue strength, ductility, tensile strength, 
durability, and resistance to cracking. Nevertheless, the ability of the 
fibers to impart a substantial degree of the theoretical flexural and 
tensile strength based on the strength of the individual fibers to the 
hydraulically settable composite material is often reduced by the 
inability to form an adequate mechanical or chemical bond or interface 
between the fiber and the hydraulically settable structural matrix of the 
composite material. 
Many of the fibers that might be used to reinforce hydraulically settable 
materials are cellulosic or otherwise organic, which makes them relatively 
chemically incompatible with the hydraulically settable binder, which 
forms an inorganic, insoluble crystalline salt upon hydration. Whenever 
the bond or interface between the fiber and the hydraulically settable 
structural matrix is significantly weaker than the strength of the fibers, 
the fibers will generally experience "pull-out" upon the application of a 
strain on the composite article. If a pull-out of the fibers occurs at or 
only slightly above the stress necessary to cause the hydraulically 
settable structural matrix to first begin to rupture, it means that the 
fibers within the structural matrix are imparting little, if any, 
increased tensile or flexural strength to the hardened composite material. 
A pull-out effect may be desired in some cases over a better mechanically 
or chemically anchored fiber in order to improve the ductility, toughness, 
fracture energy, and flexibility of the article. However, in other cases 
it may be desirable to derive more of the tensile and flexural strength 
from the fibers by increasing the mechanical and/or chemical interaction 
or interface between the fibers and the hydraulically settable matrix. 
Increasing the mechanical or chemical interaction between the fibers and 
the hydraulically settable matrix would be expected to result in more 
securely anchored fibers within the hydraulically settable structural 
matrix. This, in turn, would lessen the pull-out effect and increase the 
tensile and flexural strength of the composite material by increasing the 
magnitude of the stress required to break the bond interface and dislodge 
the fibers from the hydraulically settable matrix. In the case where the 
bond interface between the fibers and the hydraulically settable matrix 
approaches or exceeds the strength of the fibers, there will be little or 
no pull-out effect, and the hydraulically settable composite article will 
not fail until a stress that is greater than the tensile or flexural 
strength of the fibers is applied to the composite article. 
As stated above, the pull-out effect of fibers due to the generally weak 
bond or interface between the fiber and the hydraulically settable 
structural matrix of a hardened article is mainly the result of the 
chemical incompatibility between the fibers and the reaction products of 
the hydraulically settable binder and water that form the hydraulically 
settable structural matrix. Extremely smooth fibers also offer little 
mechanical anchoring because there is less for the hydraulically settable 
matrix to "grab onto" compared to rougher or more irregular fibers. The 
hydration reaction products of the hydraulically settable binder and water 
form structures which are mechanically and chemically complex but can be 
generally characterized as insoluble inorganic crystalline minerals having 
varying geometrical shapes. Fibers commonly utilized in hydraulically 
settable mixtures can be characterized as being larger than the crystals 
and having a surface chemistry which is chemically incompatible with the 
inorganic crystalline minerals, which inhibits the formation of a 
chemically integral bond. Moreover, the surface features of the fibers may 
also be so dissimilar to the crystalline structures of the hydraulically 
settable material that it is difficult to obtain a relatively strong 
mechanical bond between the fibers and the hydraulically settable 
materials. 
One way to increase the chemical and mechanical compatibility between the 
fibers and the hydraulically settable matrix would be to mineralize the 
surfaces of the fibers. One previously taught method of mineralizing the 
fiber surfaces involved the deposition of calcium carbonate (CaCO.sub.3) 
onto the fiber surfaces, which is disclosed in United Kingdom Patent 
Application No. 2,265,916 A (hereinafter "U.K. '916"). U.K. '916 teaches 
the deposition of calcium carbonate onto fibers by precipitating the 
calcium carbonate in situ from a suspension containing fibers and an 
aqueous phase containing the necessary reactants to precipitate calcium 
carbonate. More specifically, the method consists of contacting 
microfibrillated fibers held in suspension in an aqueous medium through 
moderate agitation with calcium ions (Ca.sup.2+) and carbonate ions 
(CO.sub.3.sup.2-) so as to effect crystallization of calcium carbonate in 
situ. The calcium ions are first introduced by way of lime (CaO) with 
moderate agitation, and carbonate ions are thereafter introduced 
indirectly by the injection of carbon dioxide into the aqueous solution by 
vigorous agitation. The resulting mineralized fibers have crystals of 
precipitated calcium carbonate organized in clusters of granules which are 
trapped by and between the microfibrils of the microfibrillated fibers. 
According to U.K. '916, the stated goal or advantage of precipitating 
calcium carbonate onto fibers is to increase the loading of calcium 
carbonate within paper without a decrease in strength which typically 
occurs as the loading of inorganic fillers such as calcium carbonate is 
increased. Although calcium carbonate provides an excellent filler in the 
manufacture of paper, particularly in its whitening effect, its usefulness 
in increasing the bond interface between fibers and a hydraulically 
settable matrix is limited. While the calcium carbonate would be expected 
to increase the chemical and mechanical compatibility of fibers treated 
according to U.K. '916, calcium carbonate itself forms a relatively weak 
crystalline structure, which would easily rupture upon application of a 
stress great enough to cause the pull-out of otherwise untreated fibers. 
In other words, treating fibers with calcium carbonate would only 
marginally increase the bond or interface between the fibers and the 
hydraulically settable matrix and would still result in substantial 
pull-out of the fibers from the hydraulically settable materials, while 
not significantly allowing the fibers to impart the upper limit of their 
tensile and flexural strength to the hydraulically settable composite 
material. 
In addition to fibers, hydraulically settable materials typically include 
one or more types of nonfibrous aggregates, which improve the strength 
(particularly compressive strength), flow properties, and cost 
effectiveness of the hydraulic cement composite or concrete material. 
Increasing the strength of the bond interface between the aggregate 
particles and the hydraulically settable binder would also be expected to 
increase the overall strength, particularly compressive strength, of the 
hardened hydraulically settable composite material. 
In view of the foregoing, it would be a significant advancement in the art 
to provide compositions and methods for treating fibers to make them more 
chemically and mechanically compatible with hydraulically settable 
materials, particularly cementitious materials, thereby allowing the 
fibers to impart greater tensile and flexural strength to the 
hydraulically settable materials. 
It would be a further advancement in the art to provide compositions and 
methods for mineralizing the surface of fibers in order to provide the 
aforementioned increase in chemical and mechanical compatibility between 
the fibers and the hydraulically settable binder. 
It would be an additional advancement in the art if such compositions and 
methods yielded mineralized fibers in which the deposited minerals 
resulted in significantly increased mechanical anchoring of the fibers 
within the hydraulically settable matrix. 
Finally, it would be an advancement in the art to provide compositions and 
methods for treating aggregates in order to increase the strength of the 
bond between the aggregates and the hydraulically settable structural 
matrix. 
Such compositions and methods are disclosed and claimed herein. 
SUMMARY AND OBJECTS OF THE INVENTION 
The present invention provides compositions and methods for the deposition 
of minerals onto the surfaces of fibers and other particulate fillers. 
More specifically, the present invention provides compositions and methods 
for the mineralization of fiber and other filler surfaces with crystalline 
ettringite (or 3CaO.multidot.Al.sub.2 O.sub.3 .multidot.3CaSO.sub.4 
.multidot.30-32H.sub.2 O). 
Fibers and other particulate fillers treated with ettringite within the 
scope of the present invention can be utilized within any type of 
composition or mixture. Ettringite treated fibers and other substrates are 
particularly suitable for being utilized with hydraulically settable 
materials, especially cementitious materials. Because ettringite is an 
intermediate reaction product produced during the hydration of hydraulic 
cement binders, fiber and other filler surfaces treated with ettringite 
would be expected to become more chemically compatible and integrated into 
a hydraulically settable matrix. This in turn results in the ettringite 
treated fibers and other fillers being more securely anchored within the 
hydraulically settable structural matrix of hydraulically settable 
materials. The use of ettringite coated fibers and other fillers within a 
hydraulically settable composite material increases the tensile and 
flexural strengths of the resulting structural matrix of the composite 
material. 
Ettringite coated fibers and other substrates are prepared by introducing 
fibers or other substrates into water to form a slurry or suspension in 
which the aqueous phase includes calcium hydroxide (Ca(OH).sub.2) and 
aluminum sulfate (Al.sub.2 (SO.sub.4).sub.3 .multidot.18H.sub.2 O), which 
react together in the presence of water to form the insoluble precipitate 
mineral ettringite. The precipitated ettringite crystals tend to 
flocculate onto the surfaces of the fibers or other substrates, which 
provide crystallization points for the ettringite to form. In alternative 
embodiments, ettringite may be formed by: (1) reacting calcium 
sulpho-aluminate (4CaO.multidot.3Al.sub.2 O.sub.3 .multidot.SO.sub.3) with 
gypsum (CaSO.sub.4 .multidot.2H.sub.2 O) in the presence of water; (2) 
reacting lime (CaO) and ammonium alum (2AlNH.sub.4 (SO.sub.4).sub.2 
.multidot.12H.sub.2 O) in the presence of excess water; and (3) reacting 
monocalcium aluminate (CaO.multidot.Al.sub.2 O.sub.3) with calcium sulfate 
in the presence of water. In the latter two methods, it is necessary to 
include excess lime (CaO) or calcium sulphate in solution at the end of 
the reaction in order to create stable ettringite crystals that do not 
decompose to give alumina gel as a second solid phase. 
When the ettringite treated fibers and other substrates are added to a 
hydraulically settable mixture, a more integral bond interface is formed 
between the ettringite treated fibers and the hardened hydraulically 
settable structural matrix. The integral bond formed between the hardened 
hydraulically settable structural matrix and the fibers results from the 
increased chemical and mechanical compatibility of ettringite with the 
hydraulically settable structural matrix. It is within the scope of the 
present invention to deposit ettringite onto any type of fiber or 
substrate. Examples of fibers which are particularly suitable for being 
treated with ettringite include, but are not limited to, cellulosic 
fibers, wood fibers, plant fibers, protein fibers, organic polymer fibers, 
ceramic fibers, carbon fibers and metal fibers. More specific examples 
include, but are not limited to, polyvinyl alcohol fibers, polylactic acid 
fibers and steel fibers. 
Ettringite can also be deposited onto aggregates to improve the 
compatibility and, hence, the chemical and mechanical bond between the 
aggregates and the hydraulically settable structural matrix. Ettringite is 
deposited onto the aggregate surfaces using the same reactions and methods 
described above for depositing ettringite onto fibers. Whether a 
particular filler material constitutes a "fiber" or an "aggregate" is 
often unclear, particularly if the fibers have a relative low aspect ratio 
(ie., &lt;10:1), or if the aggregate particles have a length that is 
significantly greater than the width. Regardless of whether a filler is a 
"fiber" or an "aggregate" if it has been coated or otherwise treated with 
ettringite as set forth herein it is certainly within the purview and 
scope of the present invention. Examples of aggregates which are 
particularly suitable for being treated with ettringite include, but are 
not limited to, natural rock and synthetic materials. Useful aggregates 
include, but are not limited to, slag, expanded clay, calcium carbonate, 
talc, chalk and shale. 
In light of the foregoing, an object of the present invention is to provide 
novel compositions and methods for treating fibers to make them more 
chemically and mechanically compatible with hydraulically settable 
materials, particularly cementitious materials, thereby allowing the 
fibers to impart greater tensile and flexural strength to the 
hydraulically settable materials. 
Another object is to provide compositions and methods for mineralizing the 
surface of fibers in order to provide the aforementioned increase in 
chemical and mechanical compatibility between the fibers and the 
hydraulically settable binder. 
An additional object is to provide compositions and methods for 
mineralizing fibers in which the deposited minerals result in 
significantly increased mechanical anchoring of the fibers within the 
hydraulically settable matrix. 
Finally, another object is to provide compositions and methods for treating 
aggregates in order to increase the strength of the bond between the 
aggregates and the hydraulically settable structural matrix. 
These and other objects and features of the present invention will become 
more fully apparent from the following description and appended claims, or 
may be learned by the practice of the invention as set forth hereinafter. 
BRIEF DESCRIPTION OF THE DRAWINGS 
In order that the manner in which the above-recited and other advantages 
and objects of the invention may be obtained, a more particular 
description of the invention briefly described above will be rendered by 
reference to a specific embodiment thereof which is illustrated in the 
appended drawing. Understanding that this drawing depicts only a typical 
embodiment of the invention and is not therefore to be considered to be 
limiting of its scope, the invention will be described and explained with 
additional specificity and detail through the use of the accompanying 
drawing in which: 
FIG. 1 is a scanning electron microscope photograph of the structure of 
ettringite bonded to the surface of hardwood fibers. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention relates to compositions and methods for the 
manufacture of mineralized fibers in which crystalline ettringite is 
deposited onto the exterior of the fibers. The present invention more 
particularly relates to methods for precipitating ettringite onto the 
surfaces of fibers in an aqueous suspension, followed by the isolation of 
the ettringite coated fibers. The compositions and methods may 
alternatively be employed in order to deposit ettringite onto the surface 
of any solid or particulate filler, such as aggregates, whenever greater 
chemical and mechanical interaction between the filler and the 
hydraulically settable matrix is desired. 
The fibers or aggregates utilized as a substrate for the deposition of 
ettringite are generally inert or nonreactive. That is, the fiber or 
aggregate substrate generally do not react with water within, e.g., a 
hydraulically settable mixture. Accordingly, a fiber or aggregate utilized 
as a substrate is collectively referred to in this specification and the 
appended claims interchangeably by the terms "inert filler", "nonreactive 
filler" or "nonreactive substrate material". The nonreactive substrate 
material includes discrete fibers or aggregate particles that will 
collectively be referred to as "individual substrate components." The 
ettringite is deposited on the surfaces of the nonreactive filler 
substrate material, particularly the exterior surfaces, as well as porous 
indentations or voids within the surface or interior of the substrates. 
After the nonreactive filler substrate material has been coated with 
ettringite it is referred to by the terms "coated", "mineralized" or 
"treated" nonreactive filler substrate material, "composite product," 
"mineralized composite material," or by a phrase such as a "ettringite 
coated nonreactive filler." The ettringite/substrate composites (i.e., the 
"mineralized composite material") manufactured according to the present 
invention should be distinguished from the theoretically possible 
formation of ettringite onto the surfaces of fibers, aggregates, or other 
fillers within cementitious compositions during hydration of the hydraulic 
cement binder. It is to be understood that the formation of ettringite 
onto the surfaces of the fibers and aggregate particles is a preliminary 
treatment process that yields ettringite coated fibers and aggregates 
(i.e., the "mineralized composite material") prior to their subsequent 
addition to, e.g., cementitious mixtures. 
I. GENERAL DISCUSSION 
The fibers or other filler particles treated according to the methods of 
the present invention are coated with the mineral compound ettringite 
(3CaO.multidot.Al.sub.2 O.sub.3 .multidot.3CaSO.sub.4 
.multidot.30-32H.sub.2 O). The ettringite is produced in situ while in 
proximity to the fibers or other fillers and deposited on the exterior of 
the fibers or filler particles to form an ettringite/fiber composite 
material (or ettringite/substrate composite). Because of the nature of how 
ettringite is deposited onto the fiber or other substrate surfaces, it 
forms a strong bond with the fibers or other substrate surfaces. When 
ettringite treated fibers or other substrates are incorporated into a 
hydraulically settable matrix, the ettringite crystals on the substrate 
surfaces are able to chemically and mechanically interact with the 
hydraulically settable binder, thereby creating more securely anchored 
fibers or particles within the hydraulically settable structural matrix, 
particularly a cementitious matrix. 
The compatibility of the ettringite coating and the hydration reaction 
products in the structural matrix of a hardened hydraulically settable 
article enables the ettringite crystals to chemically react with or, at a 
minimum, to interlock with the hydration reaction products to form a more 
integral bond. This is especially true in the case of a hydrating 
hydraulic cement, such as portland cement, in which ettringite is formed 
as an intermediate reaction product. Thus, the ettringite on the fiber 
surfaces will be virtually indistinguishable from the intermediate 
ettringite products and, hence, serve to chemically incorporate the fibers 
or other ettringite-treated substrates into the hardened structural 
matrix. The ettringite crystal structure within an ettringite/fiber 
composite is shown in FIG. 1, which is a scanning electron microscope 
photograph of ettringite crystals bonded to hardwood fibers. The 
ettringite crystals are generally hexagonal prismatic or acicular 
crystals. 
Adding ettringite treated fibers to hydraulically settable mixtures during 
any stage of the hydration of hydraulically settable materials will result 
in a chemically and/or mechanically integral bond between the treated 
fibers and the resulting hardened hydraulically settable structural 
matrix. Although ettringite is generally formed during the early hydration 
of hydraulically settable materials, particularly portland cements, it is 
not necessary to add the ettringite treated fibers during this stage of 
the hydration reaction of the hydraulically settable materials to form an 
integral bond between the ettringite treated fibers and the hydraulically 
settable structural matrix, as the ettringite treated fibers are 
compatible with the hydration materials throughout the hydration reaction. 
It is believed that the concentration of ettringite within a hydraulically 
settable structural matrix may be present in higher concentrations near 
the ettringite treated fibers, which would further increase the 
compatibility between the ettringite treated fibers and the hydration 
reaction products within the structural matrix of a hydraulically settable 
composite material. In support of this theory, it has been observed that 
when ettringite forms in concrete it typically grows in open spaces such 
as the interfacial zone between aggregates and cementitious matrix. In 
addition, it is possible that the ettringite coated fibers and other 
substrates constitute reactive nucleation sites for the further formation 
of ettringite crystals. 
It is within the scope of the present invention to cover at least a portion 
of the exterior surface of any type of fiber with ettringite. The fibers 
can be either hydrophilic or hydrophobic. Examples of fibers which are 
particularly suitable for being treated with ettringite include, but are 
not limited to, cellulosic fibers, wood fibers, plant fibers, protein 
fibers, organic polymer fibers, ceramic fibers, carbon fibers, and metal 
fibers. More specific examples of organic polymer fibers include, but are 
not limited to, polyvinyl alcohol fibers, polylactic acid fibers and steel 
fibers. The percentage of the exterior surface of an individual fiber 
covered with ettringite can range from about 0.01% to about 100%. In 
addition, crevices or other depressions or voids within the fiber or 
substrate interior can also become coated or filled with ettringite using 
the processes of the present invention. 
Ettringite can be precipitated onto fibers within an aqueous mixture by 
adding various combinations of chemical reactants to the water and fiber 
slurry. The basic steps involve forming a suspension or slurry by adding 
together fibers, water, and at least two chemical reactants which form 
ettringite while in the presence of water and then isolating the 
ettringite coated fibers from the suspension. 
According to one method of the present invention, ettringite may be formed 
by the following chemical equation: 
EQU 6Ca(OH).sub.2 +Al.sub.2 (SO.sub.4).sub.3 .multidot.18H.sub.2 O+6-8H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.30-32H.sub.2 O 
wherein calcium hydroxide (Ca(OH).sub.2) is first added to a mixture of 
fibers and water; thereafter aluminum sulfate (Al.sub.2 (SO.sub.4).sub.3 
.multidot.18H.sub.2 O) is mixed into the aqueous mixture including 
Ca(OH).sub.2. Stoichiometric equivalent amounts of calcium hydroxide and 
aluminum sulfate are weighed to yield ettringite according to the above 
formula (water is included in excess). In other words, approximately six 
equivalents of Ca(OH).sub.2 are added for every equivalent of 
Al(SO.sub.4).sub.3. Ettringite is formed thereby and, being in close 
proximity to the fibers, it is deposited onto the fiber surfaces. The 
deposition of ettringite onto the fiber surfaces is primarily due to the 
absorption of dissolved calcium hydroxide (Ca(OH).sub.2) into the surface 
of the fibers when the calcium hydroxide is mixed into the fibrous slurry. 
The calcium hydroxide added to the fibrous slurry will be fully dissolved 
into the aqueous phase depending on the amount of water present, since 
calcium hydroxide has a solubility of about 1 g per liter of water. After 
the ettringite has been formed onto the fiber surfaces, the excess water 
and solutes are removed from the suspension by filtration of the 
ettringite-treated fibers to yield the ettringite/fiber composite. 
Before adding the ettringite forming reactants, the mixture of fibers and 
water are moderately mixed to disperse the fibers to be treated. It may be 
preferable for the fibers to be subjected to minimal shear and stress 
during the dispersion of the fibers in water to avoid rupturing and 
fibrillating the fibers. Rupturing and/or shortening of the fibers 
decreases the toughness of articles formed from such fibers as the fibers 
can be weakened and/or anchored over a shorter length of the hydraulically 
settable structural matrix of the article. Excessive fibrillation of the 
fibers weakens the tensile strength of the fibers and should generally be 
minimized. Nevertheless, to the extent that fibrillation occurs without 
substantially decreasing the tensile strength of the fibers it may be 
beneficial as the microfibrilated fibers have an increased surface area 
for the bonding of the ettringite onto the fibers. 
The dispersion of the fibers in water is generally necessary to 
disagglomerate the fibers. Additionally, when using hydrophilic fibers the 
mixing of the fibers in water causes the surface area of the fibers to 
increase as the fibers expand. After the fibers are sufficiently dispersed 
in water, calcium hydroxide (Ca(OH).sub.2) is added and dissolved into the 
aqueous phase. The aluminum sulfate (Al.sub.2 (SO.sub.4).sub.3 
.multidot.18H.sub.2 O) is thereafter mixed and dissolved within the 
aqueous solution. The calcium hydroxide and aluminum sulfate react in the 
presence of water to cause the generation and subsequent precipitation of 
the relatively insoluble ettringite. The fibers provide crystallization 
points for the ettringite to form and grow crystals. The excess water is 
then removed by filtration. Dispersants can be added to the aqueous slurry 
after the formation of ettringite to prevent agglomeration of the 
individual ettringite treated fibers. The term "dispersants" includes 
those substances which are commonly referred to in the cement industry as 
"superplasticizers". It is also within the scope of the present invention 
to add a rheology modifier, a binder, or a filler to the ettringite 
treated fibers. 
According to another method of the present invention, ettringite may be 
formed by the following chemical equation: 
EQU 4CaO.multidot.3Al.sub.2 O.sub.3 .multidot.SO.sub.3 +2CaSO.sub.4 
.multidot.2H.sub.2 O+31 H.sub.2 O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+2Al.sub.2 O.sub.3 
.multidot.3H.sub.2 O 
The preferred method for forming ettringite according to the above equation 
involves preblending the solid reactants, calcium sulpho-aluminate 
(4CaO.multidot.3Al.sub.2 O.sub.3 .multidot.SO.sub.3) and gypsum dihydrate 
(CaSO.sub.4 .multidot.2H.sub.2 O), and then mixing the fibers and water to 
form a fibrous suspension. The preblended solid reactants are then 
intermixed with the fibrous suspension to form a suspension comprising an 
aqueous phase and fibers. The solid reactants are dissolved into the 
aqueous phase, where they react to form ettringite according to the above 
equation. Thereafter, the excess water is drained from the suspension to 
yield ettringite treated fibers. Due to the relatively low cost of the 
calcium sulpho-aluminate (4CaO.multidot.3Al.sub.2 O.sub.3 
.multidot.SO.sub.3) it is useful for industrial scale production of 
ettringite. 
In another embodiment, ettringite is formed by the following chemical 
equation: 
EQU 6CaO+2AlNH.sub.4 (SO.sub.4).sub.2 .multidot.12H.sub.2 O+20H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+(NH.sub.4).sub.2 SO.sub.4 
The preferred method of forming ettringite according to the above equation 
involves preblending the solid reactants, (CaO) and (2AlNH.sub.4 
(SO.sub.4).sub.2 .multidot.12H.sub.2 O), and forming a separate slurry of 
fibers and water. The preblended solid reactants are then intermixed with 
the slurry of fibers and water to form a suspension. The preblended solid 
reactants react in the presence of water to form ettringite, which is 
deposited onto the fiber surfaces. The ettringite treated fibers are 
isolated from the suspension by draining the excess water. 
In yet another embodiment, ettringite is formed by the following chemical 
equation: 
EQU 3CaO.multidot.Al.sub.2 O.sub.3 +3CaSO.sub.4 +35H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+2Al(OH).sub.3 
The preferred method of forming ettringite according to the above equation 
involves preblending the solid reactants, (3CaO.multidot.Al.sub.2 O.sub.3) 
and (CaSO.sub.4), and forming a separate slurry of fibers and water. The 
preblended solid reactants are then intermixed with the aqueous fiber 
slurry to form a suspension. The preblended solid reactants react in the 
presence of water to form ettringite, which is deposited onto the fiber 
surfaces. The excess water is then drained from the suspension to yield 
ettringite treated fibers. 
The ettringite treated fibers formed by the above methods are novel 
composite products and may be used in any desired application. As stated 
above, they are useful as a strengthening aid within hydraulically 
settable composite materials. They have been shown to increase the tensile 
strength and flexural strength of such composite materials compared to 
where ordinary fibers are used. 
Ettringite can also be deposited onto the surface of any solid or 
particulate filler, such as aggregates, to improve the mechanical and 
chemical compatibility of the aggregates and a hydraulically settable 
matrix. Ettringite can be deposited on aggregates using the same 
compositions and methods set forth herein for treating fibers. The 
aggregate surfaces, in the same manner as the fibers, provide 
crystallization points for the ettringite to form and grow into crystals. 
A composite product is formed by coating at least a portion of the 
exterior surface of an aggregate material with precipitated ettringite. 
Whether a particular filler material constitutes a "fiber" or an 
"aggregate" is often unclear, particularly if the fibers have a relatively 
low aspect ratio (i.e., &lt;10:1), or if the aggregate particles have a 
length that is significantly greater than the width. Regardless of whether 
a filler is a "fiber" or an "aggregate", if it has been coated or 
otherwise treated with ettringite as set forth herein it is certainly 
within the purview and scope of the present invention. Aggregates which 
are suitable for being treated with ettringite include aggregates 
comprising either naturally occurring material or synthetic material. More 
specific examples include aggregates such as sand, gravel, rocks, 
limestone, silica, alumina, slag, expanded clay, calcium carbonate, talc, 
chalk, and shale. 
The ettringite coated inert fillers have many applications in different 
industries. As s discussed above, the fillers are very useful in fiber 
reinforced concrete as well as in fiber reinforced ceramics. Additionally, 
the fillers are useful in the manufacture of sheets and foamed products 
which are chemically or also structurally compatible with the ettringite 
treated filler such as those formed from hydraulically settable mixtures.

II. EXAMPLES OF THE INVENTION 
Below are specific examples of the treatment of fibers with ettringite 
according to the present invention. These examples are illustrative only 
and not the definitive manner for obtaining ettringite treated fibers, 
aggregates or fillers. The examples involve the treatment of wood fibers; 
however, the same steps can also be used to treat aggregates or any other 
types of fibers. 
Example 1 
In this example, fibers were treated with ettringite according to the 
following equation: 
EQU 6Ca(OH).sub.2 +Al.sub.2 (SO.sub.4).sub.3 .multidot.18H.sub.2 O+6-8H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.30-32H.sub.2 O 
Ettringite treated fibers were obtained by first dispersing 1000 g of dry 
Hard Wood fiber in 10,000 g water using a WELBILT Vaimixer at 200 rpm for 
30 minutes. To this mixture, 180 g of Ca(OH).sub.2 were added and the 
resulting aqueous slurry mixed at 200 rpm for 20 minutes. 
A second aqueous solution was prepared by dissolving 270 g of Al.sub.2 
(SO.sub.4).sub.3 .multidot.18H.sub.2 O in 2000 g of water and then mixing 
the solution at 150 rpm in a WELBILT Vaimixer for 30 minutes into the 
aqueous slurry of fibers and aqueous Ca(OH).sub.2. The excess water was 
filtered from the received suspension until the total net weight was 5500 
g, which included 1000 g of fiber, 500 g of ettringite, and 4000 g of 
water. 
After filtration of the ettringite treated fibers, 400 g of Methocel 240 
was added to the wet batch of ettringite treated fibers and mixed at 250 
rpm for 30 minutes. The Methocel 240 was utilized as a rheology modifier 
and a binding agent. Then, 3500 g Gamma Sperse CaCO.sub.3 was added to the 
mixture and mixed at 150 rpm for 20 minutes. The CaCO.sub.3 was utilized 
as a filler. 
Example 2 
In this example, fibers were treated with ettringite according to the 
following equation: 
EQU 4aO.multidot.3Al.sub.2 O.multidot.SO.sub.3 +2CaSO.sub.4 2H.sub.2 O+3H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+2Al.sub.2 O.sub.3 3H.sub.2 O 
Ettringite treated fibers were obtained by first dispersing 1000 g of dry 
Hard Wood fiber in 10,000 g water using a WELBILT Vaimixer at 200 rpm for 
30 minutes. To this mixture, a preblended solid was introduced that 
comprised 243 g of 4CaO.multidot.3Al.sub.2 O.sub.3 .multidot.SO.sub.3 and 
137 g of CaSO.sub.4 .multidot.2H.sub.2 O. The preblended solid and the 
mixture were mixed at 150 rpm for 30 minutes to form a suspension. The 
excess water was filtered from the received suspension until the total net 
weight was 5500 g, which included 1000 g of fiber, 500 g of ettringite, 
and 4000 g of water. 
After filtration of the ettringite treated fibers, 400 g of Methocel 240 
was added to the wet batch of ettringite treated fibers and mixed at 250 
rpm for 30 minutes. The Methocel 240 was utilized as a rheology modifier 
and a binding agent. Then, 3500 g Gamma Sperse CaCO.sub.3 was added to the 
mixture and mixed at 150 rpm for 20 minutes. The CaCO.sub.3 was utilized 
as a filler. 
Example 3 
In this example, fibers were treated with ettringite according to the 
following equation: 
EQU 6CaO+2AlNH.sub.4 (SO.sub.4).sub.2 .multidot.12H.sub.2 O+20H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+(NH.sub.4).sub.2 SO.sub.4 
Ettringite treated fibers were obtained by first dispersing 1000 g of dry 
Hard Wood fiber in 10,000 g water using a WELBILT Vaimixer at 200 rpm for 
30 minutes. To this mixture, a preblended solid was introduced that 
comprised 234 g of CaO and 361 g of AlNH.sub.4 (SO.sub.4).sub.2 
.multidot.12H.sub.2 O. The preblended solid and the mixture were mixed at 
150 rpm for 30 minutes to form a suspension. The excess water was filtered 
from the received suspension until the total net weight was 5500 g, which 
included 1000 g of fiber, 500 g of ettringite, and 4000 g of water. 
After filtration of the ettringite treated fibers, 400 g of Methocel 240 
was added to the wet batch of ettringite treated fibers and mixed at 250 
rpm for 30 minutes. The Methocel 240 was utilized as a rheology modifier 
and a binding agent. Then, 3500 g Gamma Sperse CaCO.sub.3 was added to the 
mixture and mixed at 150 rpm for 20 minutes. The CaCO.sub.3 was utilized 
as a filler. 
Example 4 
In this example, fibers were treated with ettringite according to the 
following equation: 
EQU 3CaO.multidot.Al.sub.2 O.sub.3 +3CaSO.sub.4 +35H.sub.2 
O=&gt;3CaO.multidot.Al.sub.2 O.sub.3 
.multidot.3Ca(SO.sub.4).multidot.32H.sub.2 O+2Al(OH).sub.3 
Ettringite treated fibers were obtained by first dispersing 1000 g of dry 
Hard Wood fiber in 10,000 g water using a WELBILT Vaimixer at 200 rpm for 
30 minutes. To this mixture, a preblended solid was introduced that 
comprised 189 g of CaO.multidot.Al.sub.2 O.sub.3 and 163 g of 
Ca(SO.sub.4). The preblended solid and the mixture were mixed at 150 rpm 
for 30 minutes to form a suspension. The excess water was filtered from 
the received suspension until the total net weight was 5500 g, which 
included 1000 g of fiber, 500 g of ettringite, and 4000 g of water. 
After filtration of the ettringite treated fibers, 400 g of Methocel 240 
was added to the wet batch of ettringite treated fibers and mixed at 250 
rpm for 30 minutes. The Methocel 240 was utilized as a rheology modifier 
and a binding agent. Then, 3500 g Gamma Sperse CaCO.sub.3 was added to the 
mixture and mixed at 150 rpm for 20 minutes. The CaCO.sub.3 was utilized 
as a filler. 
III. SUMMARY 
From the foregoing, it will be appreciated that the present invention 
provides novel compositions and methods for treating fibers to make them 
more chemically and mechanically compatible with hydraulically settable 
materials, particularly cementitious materials, thereby allowing the 
fibers to impart greater tensile and flexural strength to the 
hydraulically settable materials. 
The present invention provides compositions and methods for mineralizing 
the surface of fibers in order to render the fibers more chemically and 
mechanically compatible with a hydraulically settable binder. 
The present invention also provides compositions and methods for yielding 
mineralized fibers in which the deposited minerals result in significantly 
increased mechanical anchoring of the fibers within the hydraulically 
settable matrix. 
Finally, the present invention provides compositions and methods for 
treating aggregates in order to increase the strength of the bond between 
the aggregates and the hydraulically settable structural matrix. 
The present invention may be embodied in other specific forms without 
departing from its spirit or essential characteristics. The described 
embodiments are to be considered in all respects only as illustrated and 
not restrictive. The scope of the invention is, therefore, indicated by 
the appended claims rather than by the foregoing description. All changes 
which come within the meaning and range of equivalency of the claims are 
to be embraced within their scope.