CA1049708A - Shrinkage inhibition of cementitious systems through the addition of specially processed carbonaceous materials - Google Patents

Abstract

S P E C I F I C A T O N

SHRINKAGE INHIBITION OF CEMENTITIOUS SYSTEMS
THROUGH THE ADDITION OF SPECIALLY
PROCESSED CARBONACEOUS MATERIALS

Inventor: ROBERT W. GAINES

ABSTRACT OF THE DISCLOSURE

Naturally occurring particulate carbonaceous mater-ials are rendered capable of inhibiting shrinkage when added to cementitious systems by special processing including heat treatment at temperatures substantially higher than drying temperature. Further advantageous properties are obtained by contacting the material with a water spray at the heating temperature. The treatment enhances the properties of car-bonaceous materials which are already capable of inhibiting shrinkage in the cementitious systems. Shrinkage inhibition is also obtained by adding anthracite coal to a cementitious system. Bleeding is eliminated by the addition of a particu-late carbonaceous material which will inhibit shrinkage.

Description

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1049708 - : -BACKGROUND OF-THE_INVE~TION

Field Of The Invention , - . -- .
This inve~tion relates to an improved method and composition for inhibiting shrinkage in cementitious systems during setting and hardening. I
The term "cementitious systems", as used herein, is --¦
intended to include compositîons which generally possess the characteristic of hardening under water and includes, for -example, settable hydraulic cement, hydraulic lime, gypsum -and like materials, as well as mixtures of the foregoing with aggregates and water such as concrete, mortar, grout and 'products made therefrom.
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~ Description of The Prior Art : .
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- 1, Methods and means for inhibiting shrinkage o~
ii hydraulic cement mixtures during setting and hardening have 'previously been suggested. The prior art methods have included the addition, to such mixtures, o~ various expansion agents,~
such as aluminum powder and iron filings, which are generàllyc added at the mixing during the preparation of th~ cement mix-ture. These procedures have b~en impractical because of, -among other reasons, lack of adequate control of expansion.
It has also been found that certain unique materials can eliminate shrinkage in concrete due, it is theorized, to the - release of entrapped gas from porous particulate materials upon adsorption of water from the cementitious system.
Materials such as fluid coke, a combination of fluid coke and delayed coke, which are by-products of the petroleum industry, :. - ' ' -:

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and porous particulate materials, such as so called industrial adsorbents, have been used with various types of cementitious mixtures to successfull~ inhibit shrinkage Seefor example U. S. Patent Nos. 3,-503,767; 3,519,449; 3,794,544; and Re. 26,597.
The successful utilization of certain materials as shrinkage inhibitors in cementitious systems is unpredictable.
~For example, fluid coke is a carbonaceous material and there-fore its success as a shrinkage inhibitor without having deleterious effects on the CementltiOuS system is surprising. j~
,Thus, U. S. Patent No. Re. 26,597 states that no other type, --i.e., other than fluid coke, of coke or carbon has the effect of expanding cement in a controlled matter. The patent also I,~notes that coal clinkers may cause expansion but in a harmful land an uncontrolled amount with the expansion being related I,to the clinker suifur content. While clinker and coke breeze - Ithave been added to cementitious systems as aggregates, Concrete Technology", Vol. 1, John Wiley & Sons, ~ew York, l 1962, pp. 146-7, points out that the combustible matter, chiefly carbon, in these materials has led to failures due to excessive expansion when they have been used as a concrete , aggregate. The expansion may be exceptional, and is apparently uncontrollable due to moisture movement on wetting which can result in shrinkage on drying. -Carbonaceous materials have been added to cement - -compositions for very limited specific purposes in the oil well cementing environment. Thus, U. S. Patent No 2,609,8æ~
discloses adding activated carbon to a cement composition for cementing oil wells in order to offset the deleterious effects, ~ on the cement, of -the oil well drilling mud additives.

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U. S. Patent No. 3,376,146 discloses the addition of carbon including ground ligni!te coal, bituminous coal, anthracite coal, graphite,-petroleum coke and coke to a cement composi-tion for cementing oîl wells in order to provide a low den-sity composition. Nei~her o~ the aforementioned patents dealing with oil well cementing recognizes any advantage or disadvantage of the added carbon material other than that described. For general application it is still believed that the addition of carbon such as ~oa~ and liynite is detrLmental to concreteO See, for example, "Concxete Con-struction Handbook"~ Joseph J. Waddell, McGraw Hill, 2nd Ed., pp. 236-237 pointing out the limits for dele~erious substance~'in fine and coarse aggregates for concrete and identifying coal and lignite as deleterious additives.

~ SUMMARY OF TEIE INVEN~ION

It has been found that, unexpectedl~, carbonaceous materials such as coal may be specifically processed ~o make -them suitable for use as additives in cementitious system~
and that when added to such systems the~ function ~o control lably inhibit the shrinkage that normally occurs upon settinl ¦
and hardening. -The processing according to this invention not only"energizes" carbonaceous materials, such as coal, previously I -unknown to possess advantageous characteristics useful for i shrinkage inhibition, but also enhances the results obtained with a known carbonaceous shrinkage inhibitor such as fluid coke. ~he effective results vary from carbonaceous material to carbonaceous material and thus a high degree of control of l-_4_ l ` !`.

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~-I shrinkage inhibition is obtained by this invention through ¦ the selection of the appropriately active material for a ¦ desired purpose. It is not known whether the variation in ¦ results among materials is due to the amount of carbon there-in although there is a variation among the various types of -coal which possess different amounts of carbon.
It is theorized, although I do not wish to be bound there~y, that the resulting shrinkage inhibition is due to l the release of gas from the surface and interstices of the ¦ carbonaceous materials when added to the cementitious systems l as particulate solids. Thus, the favorahle results obtained¦
¦ may be due to the desorption of gasses held to active surfacJ~
I of the material. ~his release occurs when water from the ¦ cementitious system is adsorhed on the particle surface and l replaces or displaces ~he gas. The precise manner in which this occurs, whether physical or chemical, is not fully unde _ stood. In particular, it is surprising that the carbonaceou materials pos~ess these advantages and enhanced properties -¦
When specially processed according to this invention since coal, for example, is generally ineffective as a shrinkage 1--inhibitor when added to cement and furthermore has heretofor ¦ been considered to have a deleterious ef*ect in normal appli I cations.
¦ Whether a physical or chemical change, or both, in !-the material occurs as a consequence of the special processi ng ¦
¦ of this invention is not known and need not be the criteria, ¦ it being sufficient to point out the manner in which the ¦ car~onaceous material is processed to achieve the advantageo s results obtained. The carbonaceous material is specially .
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` 1049708 traated according to this invention by heating it, as, for example, in an oven, in the presence of air to high tempera-tures and its shrinkage inhibition properties are further enhanced by contact with steam at these high temperatures.
The heating temperatures are substantially above ~ho~e a~
¦ which mere drying of the carbonaceous material occurs and ¦ while some physical devolatilization apparently takes place, it cannot be said for certain that the treatment results in I the occurrence of other calcining phenomenon such as pyrolysis, densification and crystallization.
The carbonaceous particulate material is added to I the cement mixture at a time prior to the addition o~ water ¦ thereto and discharges its gas during setting and hardening l of the cement mixture while in contact with water. A critex-ia for the material is that it release gas and ~hexefore it must possess a sufficient degree of dryness so ~hat i~ "holds' this gas and will adsorb water to release the gas. The carbonaceous par~iculate materials are advantageous for use f in a wide variety of cementitious systems having variou~
setting times. Thus, ~hey may be desirabl~ utilized in cement types which are fast setting and in tho~e w~ich set in regular time. consequently~ by selecting the proper carbon-aceous particulate material for a desired application, both the amount and time of shrinkage inhibition of the cementi~
¦ tious system can be much more effectively regulated.
Accordingly, a feature of this invention is the addition of carbonaceous materials to cementitious systems and the inhibition of shrinkage in such cementitious systems through such addition~ A further feature of this invention , `
¦ is the special processing of carbonaceous materials to make ¦ them useful or improve their use as shrinkage inhibitors in cementitious systems. ~
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` 104g708 -` ' -An unexpected property oE the carbonaceous materials added to cemen-itious systems according to this inven~ion is the reduction of undesirable bleeding, i.e., sedimentation of solid material with a concomitant rise of water to the surface. Bleeding is particularly undesirable in applica-tions such as the grouting of machinery and the like because -it results in water-fllled voids beneath baseplates and -reinforcing bars. Upon drying, these voids remain and ' ~ -bonding strengths are reduced. The release of gases from -the carbonaceous additives of the invention not only inhibits shrinkage but also serves to reduce the bleeding 'that would ', o`therwise normally occur. This is an observable fact, although it is not understood whether'it is due to the ex-pulsion of water from the mass upon expansion of the cement ~ against the restraining surface such as a baseplate or for ' other reasons.
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' Thus, it is a further ob~ect of this'invention to ' r provide a method and composition for reducing bleeding in ' setting cementitious systems.
' BRIEF DESCRIPTION OF THE DRAWI~GS
The accompanying drawings present, in the for~
of graphs, examples of the shrinkage inhibition ob~ained in ' cementitious systems over a period of time of curing for -various carbonaceous materials which have been specially processed according to this invention. Comparisons with the untreated material and a control, a cementitious system-having no shrinkage inhibiting carbonaceous material present, are shown. One graph presents results obtained with pro-cessing o-f a non-carbonaceous shrinkage control additive These graphs are illustrations only of the results obtained herein and for exemplary purposes the following materials are shown: ` ' ' 11 1049708 , I FIGURE 1 - An hracite FIGURE 2 - Lignite . .
FIGURE 3 - Fluid Coke I ~IGURE 4 - Delayed Coke .
FIGURE 5 - Activated Carbon .
FIGURE 6 - Bituminous Coal .
FIGURE 7 - Activated Alumina .-DESCRIPT~ON OF THE PREFERRED EMBODIMENTS I .

The particulate material advanta~eously s~itable for this invention is a carbonaceous material which has under . i_ gone special processing and treatment according to this in-vention. The carbonaceous material may be one known to have I shrinkag~ inhibition characteristics, such as *luid coke, . ,.
¦ which may be enhanced according to this invention. Advan- ~.
tageou~ly, the carbonaceous material is one which is not generally known to possess shrinkage inhibition properties . -`:
¦of its own when added to cementitious systems in acceptable ..

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quantities, such as delayed coke, or which have even been - considered deleterious when added to cement, such as coal.
Fluid coke is made by a process described in U. S. Patent ; No. 2,881,130 while delayed coke is described in U. S.
Patent No. 2,835,605. The effects of these materials as -shrinkage inhibitors are set forth in U. S. Patent No. -~7 Re. 26,597. That patent discloses t~ while fluid coke is advantageously utilized in cementitious compositions to -inhibit shrinkage, delayed coke, although having a chemical -- 10 , composition very close to fluid coke, does not produce ex-- '. ' - ' -i pansion but behaves in the same manner as does an inert -- i additive, such as sand. In addition, it is described in -,U. S. Patent No~ Re. 26,597, that carbon, believed to be a -l'highly surface active material, does not cause expansion -15 , although it is readily wetted by water and might be expected to expand in view of the results with fluid coke. Thus, the ~ ' 'results herein are surprising and unexpected.
Coal is generally classified based on its value as !
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~ fuel, that is, on the percentage of carbon present and the .. . .
,;condition of the carbon. Part of the carbon in coal is fixed ~- and cannot be driven off by heating in a retort while part ; - -~
- of it is combined with hydrogen and nitrogen as volatile - ;
hydrocarbon compounds which can be vaporized. The proportion ~- of the volatile hydrocarbons to the fixed carbon in coal is called its fuel ratio and on this basis the type distinctions usually made are between lignite, bituminous, semi-bituminous, semi-anthracite and anthracite coal, in order oS increasing carbon content and increasing fuel ratio. Lignite or brown coal, is brown-black in color and has a specific gravity of .5 to 1~5. BituminouS or soft coal is blac~ and has a specific gravity of 1 25 to 1.4. Anthracite, also called - hard coal, is black with a speci,Sic gravity oE 1.3 to 1.75 ~-.
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Selection of a processed carbonaceous partlculate additive having substantially uniform or a selected range of particle sizes will aid in providing a controlled shrinkage inhibitor over an extended period during setting and harden-- ing of the cementitious system for various purposes. Since - the materials are al~ carbonaceous, they are compatible for blending for use. It will be understood by those s~illed -.. ,, . , . .
in the art that the selection of a specific carbonaceous-material, a particular trea~ment process therefor and~-j . . ~ ~ . particle sizes will be dependent upon the cementitious system ., ~, ' '. '.
used and the application desired~ The proper selection and amount to be added can be readily made based on routine '~observation and measurement of those parameters described - ! below, according to the teaching herein.
- 15 1 In carrying out the method of this invention, the , proper amount of processed carbonaceous material may be ,added to and mixed with cement or any type of cement mixture i, at any time prior to or during the addition of water to form aqueous cement mixtures. For exam21e, in preparing grout , or mortar, the additive may be mixed with cement or cement --and fine aggregates to form a dry cement mlxture which is subsequently mixed with the desired amount of water to form -, ~
grout or mortar. Similarly, in preparing ready-mixed con- -' - :' crete, the additive may be mixed with the cement and aggre-gates to form a dry mixture which is then used to form the ready-mixed concrete either in a stationary or in a truck - -mixer. On the other hand, it may be advantageous to mix all the ingredients, including the additi~-e, in the stationary and/or in the truck mixer to form the ready-mixed concrete.

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¦ Since the amount of additive to ~e used in any .
¦ cementitious system can ~e best calculated based on the ¦ amount of cement in ~he system, it is advantageous to incor-¦ porate the additive directly in the cement prior to its ¦ shipment to the user.
¦ Further to illustrate this invention, specific -¦ examples are described hereinbelow. In these examples, the performance of the additive was judged by the expan~ion and :
¦ contraction of the cementitious system as soon as it was l mixed with water and cast in a cylindrical mold in a 3 1/2 ¦ inch deep casting with approximately 10% of exposed surface.
- ¦ The expansion and contraction of the cast was deteLmined by the vertical movement of the top surface. ~or the purpose I of higher ac~racy, a light test, submitted to the C-9 ¦ committee of the ASTM for approval, waq used to ~ea~ure the ¦ movement of the top surface. ~he test consists o u~ing a focused light beam to project a shadow of the top surface onto a screen eouipped with a vertical graduation in "inch"
units. The ma~nification is 88 times. The movement of the top surface on the screen is recorded in inches at frequent intervals for each cast until final set, which usuall~ takes about 3 to 4 hours with longer setting materials and less tha ~ --60 minutes with a fast setting cementitious composition.
A thin layer of oil was added on top of the cast cementitious material in the mold to prevent evaporation for ~-setting under'~ noevaporation" condition. To facilitate the detection of the movement of the top surface, a sphere was placed on top of the surface and the expansion or cont~raction of the cast was determined by the movement of the apex of the shadow projected on the screen.
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In each example run, a cementitious system was prepared by mixing, in ~eight ratios, 42.5 parts Type I
cement, 50 parts sand and 7.5 parts carbonaceous additive, processed according to the invention by heating to between 1300 F and 1500 F and also, further by spraying with water at that temperature. The treatment times are not critic 1 - 1 to 2 hours heating being sufficient~ Runs with unprocessed material, as received and as dried, were also made to serve as a control for comparison purposes. In addition example I -runs using activated alumina in place of the carbonaceous additive were also made to determine the effect of the speciai ~ -. - . ; .
processi~g of this invention on a non-carbonaceous material.
Each of the compositions was thoroughly mixed with water, about nine quarts per 100 pounds of mix, cast as described jabove and the expansion or contractions observed.
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EXAMPLE 1 - A throuqh H
, The carbonaceous materials, ground to pass a ~o. 16-sieve and added in the proportions given abovej were:
A. Fluid coke ~ ~
, B. Delayed coke , - '': ~ ',: . . !
C. Anthracite coal .
D. Ft. Union lignite coal . Pittsburg seam - bituminous coal F. Activated carbon -The results are set forth in Table 1 showing the light test measurements in "inch" units resulting from use of carbonaceous materials having undergone different processing treatments according to this invention and demonstrate the efficiency of these materials as shrinXage inhibitors when so processed The results using (G ~ actlvated alumina, a non-carbonaceous shrinkage control additive, are also sho~,~n , ~:
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The dry heat treatment comprises heating the carbonaceous material or other non-shrink additive or contro in an electric oven such as a Type 1400 Furnacé made by ¦ Thermolyne of Dubuque~ Iowa having resistance heaters built I into the walls controlled by on-off cycling timers to ~he temperature desiredO Heating occurs in a sparse presenc2 of air due to slight leakage around the oven door, for ex-ample the seal is not so tight that a paper sheet chn not I be drawn therethrough. However, it is theorized that the ¦ internal oven atmosphere soon contains car~on monoxide and ¦ dioxide and less oxygen due to oxidation of the carbon.
~oreover, not only does the presence of air not adversel~
affect the results of the processes but actually enhances .
them as described in greater detail below. Steam heat treat~
ment comprises the dry heating followed by spra~lng with a water vapor jet forming steam at that temperature.
In contrast to the results set forth in Table 1, an aqueous ceme!nt mixture identical to the above but wi~h -l 7.5 parts (H.) sand added, as a control, in place of the l carbonaceous material underwent a shrinkage measured~ in the l id~ntical manner as above~ as -3.375 inchesO The activated 1--- I alumina, while a shrinkage inhibitor in its untreated state, does not improve i~ effectiveness when undergoing the ~pecia I ,~
¦ processing herein suggestin~ that the special processing ¦ of the invention is particularly advantageous for carbonaceo~ s materials. - -' `
Although it is still widely believea that the addition of carbonaceous material such as coal and lignite is undesirable in concrete, I have found that the compressiv~
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strengths o~ exemplary comp~sitions prepared in accordance with the procedures described abo~e still fall ~Jithin acceptable limits. When-one considers the expansion obtained, . the fact that these compressive s~rengths, per identical unit volume, are somewhat lower than tha_ of a sand-cement ;
mixture alone without any additive is not o~ significant consequence compared to the use and result desired Example 2 ` In this example, the effect of heating in the presence of an increased amount of air was ascertained.
Heating of (B.) delayed coke and (C) anthracite coal took . . place as previously described with the exception that instead of being shut, the oven door was permitted to remain open 1/4 inch. Cementitious systems were prepared and light test ' measurements made as described for Example 1. The cemen- .
o titious system containing anthracite coal heated at 1300 F
i ! -in the presence of this increased air expands~13.2 "inch" : -. uni~ as compared to ~14 "inch" uni.ts,shown in Table 1, when ' :
heated in sparse air, no significant change.. However, the ~ .-cementitious system containing delayed coke heated at 1300F
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in increased air expanded +17.5 "inch" unit compared to only +8.8 "inch" units, shown in Table 1, when heated in sparse air, a highly effective energization of this material as a shrinkage inhibiting agent.
As an aid to a better understanding of the results obtained with the special processing of this invention, certain results selected merely as exemplary are set forth in illustrative graph form in FIGURES 1 through 7. FIGURES
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1 through 7 pre~ent the expansion or shrinkage reading ob-¦ tained according to the light test described above, plotted ¦ as the ordinate, as a function of curing time, in minute.
I after casting, of ~he cementitious system plotted on the abscissaO The legends appearing on the individual plot ¦ lines are explanatory of the treatment which the material has undergone. The term "dried" refers to heating to 250F
only, to remove moisture.
In interpreting the graphs of FIGURES 1 through 7, as well as the results presented in Table ~ it must he remembered that the expansion or shrinkage is pre~ented in ¦ "inch" units which correspond to graduations on the ch~rt ¦ used in the light test to reflect changes in elevations in ¦ the cast surfaces. This test is highly sensitive to changes ¦ in the cast surfaces and magnifies those changes 8~ times.
As a consequence, differenc~s of one or two units may not be ~ I particularly significant in comparing results of various - I trea~ments or various materials.
¦ Nevertheless, FIGURES 1 through 6 shows the con-20 ` ¦ trollability of shrinkage inhibitors, in some case~ actual expansion, through the appropriate selection of materials l proces-qed according to this invention. Many combinations are ¦ possib1e to control not only the amount o~ shrinkage inhibi-¦ tion or expansion but also the time at which it is initiated ¦ and the period for w~ich it lasts. This is advantageous in ¦ view of the many different types of cements with var~ing ¦ characteristics such as setting time. For example, the plott~
lines with arrows at their ends signify that the material re ¦ mained effective to cause expansion or shrinkage inhibition ¦ beyond the abscissa limit. That is, entrapped gas continues to be released. r .
The results presented in FIGURES 1 through 6 are un~
expected and unpredictable. As can be seen,even within this¦
group of materials, i.e. carbonaceous, the results var~. Thesle are described further with reference to the specific materia~
¦ used.
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¦ The foregoing demon~trate~ that carbonaceouq - ¦ materials can be rendered effective oementitious sy~tem ¦ shrinkage inhibitors by treatment with heat and with heat ¦ plus steam or water spraying. Where the carbonaceous mater-1 ial already poqsesse_ shrinkage inhibition propen~ities, ¦ these are vastly enhanced by the ~reatment of this invention ThiQ is surprising and unexpected since there does not appea~ .
to be any p~ysical similarity between the various successful I carbonaceous materials when in an untreated state. Thus, -¦ fluid coke has a hailstone-like, built-up concentric sphere ¦ structure resulting from an accretion o~ blisters while de-¦ layed coke is sponge-likeO and not layered or spherical ¦ Coal, however, is different from both fluid coke anddelayed cokeO being layered or laminar in structure. ch~mically, ¦ the materials may be considered simil~r to ~he extent ~hat they all contain carbon. ~et, all function differently, although successfully, when treated. Untreated, the shrink~ , inhibiting behaviour is radically different among the ma-terials. ~
The shrinkage inhibition properties of fluid coke ~ -increa~e with heating, a heating which is more than merel~ 3 -~hat ~hich is sufficient to drive off water for the purpose of dr~ing the material. -Delayed coke as received from the refinery is in-effective for shrinkage inhibition when added to cementitiouc ~ystems in acceptable quantitiesO Thus, it has been found jthat delayed coke willresult in expansion when added to cementitious systems only in an amount approximately ten times that amount normally required to achieve the same re-sult with fluid cokeO

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11 , ' ,' - ' - -Yet, while delayed coke as received from the re-finery is ineffective, it becom~s equal to or superior to fluid coke when it is treated by heating and subjecting to a fine spray of water or steam. Hard coal appears to provide a benefit when used even as received and becomes a superior shrinkage inhibitor when heated and contacted with - a fine spray of water. The ability of hard coal to inhibit shrinkage in its natural state was verified by observing that ground anthracite coal released gas when placed in water.
IAlso surprising is the fact, as found by me, that the addition ~-,of 1% anthracite coal which has been ground and treated by l,heating to 1500F and steam spraying is more effective, as ' ;,~an expansion-agent in a cementitious system, than is fluid llcoke added in the amount of 1%, aithough both are satisfactory ,'Soft coal is essentially ineffective as received but becomes , ,effective when treated. In surprising contrast lignite pro-~vides somej apparent benefit in its untreated state which is ! enhanced upon treatment. These variations make possible llselected combinations of the different carbonaceous materials ~to yield an additive with the desired degree of shrinkage compensating properties for particular requirements. Conse-quently, a-greater degree of selectivity and control, based on differing rates of expansion and volumes of expansion, is now possible. Other carbonaceous materLals, such as cannel coal, charcoal and the like are contemplated for use and treatment herein.
Moreover, the compressive strengths obtained are unexpectedly satisfactory in view of the belief in the art tha-t coals adversely affected the same in cement. Here, the ,~ .
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benefit of shrinkage inhibition far outweighs any change that .necessarily accompanies expansion and/or the addition o~ a soft material to the cement. . .
The surprising ability of the carbonaceous materials which inhibit shrinkage by gas release to also minimize bleeding in cementitious systems is illustrated by Example 3 ~ ¦

EXAME~LE 3 - : - ¦
i' . ' ' I' ' ~ , The characteristic of bleeding was observed by pre~
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'paring three cementitious compositions by mixing, in weight `
'ratios, 42.5 parts Type I cement and 57.5 parts sand and ,thoroughly mixing 100 pounds of each of the compositions with nine, eight and seven quarts of water, respectively. ~o ,~carbonaceous additive was used. Each of the cementitious systems exhibited bleeding, with the "nine quart" system - : -',bleeding more than the "eight quart" system which in turn texhibited more bleeding than the "seven quart" system, al- :
,though the latter underwent less shrinkage. The bleeding, ~ .
'.as well as shrinkage, was eliminated by replacing 3 parts : .sand with 3 parts fluid coke. It was found that 2 5 parts ~ :
of fluid coke will also eliminate the bleeding while an amount . .
as small as 2 parts does not do so, although this lesser amount is sufficient to inhibit shrinkage. The amount re-quired to eliminate bleeding is thus quickly ascertainable by observation, since bleeding is recogni~ed by the appearance of water on the surface of the casting, and may be readily selected according to the cement type, water content and carbonaceous material used. The carbonaceous material must, however,.be one capable of inhibiting shrinkaye.
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Claims (14)

The embodiments of the Invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for inhibiting the shrinkage of an aqueous hydraulic cementitious system prior to hardening comprising selecting a particulate naturally occurring carbonaceous material, incorporating the particulate carbonaceous material in the cementitious system, in an amount effective to counter-act the shrinkage tendency of the cementitious system but ineffective to reduce the compressive strength of the system appreciably below that strength obtained without the particulate carbonaceous material, the carbonaceous material being one which is effective to inhibit shrinkage by causing expansion of the system compared to no incorporation of carbonaceous material.

2. A method for inhibiting the shrinkage of an aqueous hydraulic cementitious system prior to hardening as claimed in Claim 1 further comprising incorporating particulate anthracite coal in the cementitious system, in an amount effective to counteract the shrinkage tendency of the cementitious system, but less than about 25 percent, by weight, of the cement in the system, causing the system to expand, as compared to no such corporation, while allowing it to set and harden.

3. A method for inhibiting the shrinkage of an aqueous hydraulic cementitious system prior to hardening as claimed in Claim 1 further comprising wherein the particulate carbonaceous material need not be naturally occurring but may be selected from the group consisting of delayed coke and naturally occurring coal, treating the material by heating it to a temperature substantially in excess of that temperature at which moisture is driven out of the material, incorporating the treated particulate carbonaceous material in the cement-itious system, in an amount effective to counteract the shrinkage tendency of the cementitious system, the carbonaceous material being one which when so treated is effective to inhibit shrinkage by causing expansion of the system compared to no incorporation of carbonaceous material.

4. A method as claimed in Claim 3 wherein the heating temperature is in excess of that temperature at which devol-atilization of constituents in the carbonaceous material occurs.

5. A method as claimed in Claim 3 wherein the heating is primarily carried out in an essentially closed system.

6. A method as claimed in Claim 3 wherein the heating is carried out in the presence of air.

7. A method as claimed in Claim 3 wherein the heating temperature is in excess of 900°F.

8. A method as claimed in Claim 3 further including following the heating by contacting the carbonaceous material with a water spray at the heating temperature.

9. A method as claimed in Claim 3 wherein the naturally occurring carbonaceous material is selected from the group consisting of anthracite coal, bituminous coal and lignite coal or combinations of the same.

10. In a cementitious composition for forming an aqueous hydraulic cementitious system, the improvement comprising the inclusion therein, in an amount effective to inhibit the shrinkage of the system prior to hardening but ineffective to appreciably reduce the compressive strength of the system, of a particulate naturally occurring carbonaceous material, the carbonaceous material being one which is effective to inhibit shrinkage by causing expansion of the system compared to no inclusion of carbonaceous material.

11. A cementitious composition for forming an aqueous hydraulic cementitious system as claimed in Claim 10 further containing solids including aggregate for structural use, the further improvement resulting in inhibition of shrinkage of the system while maintaining sufficient compressive strength for structural use comprising the inclusion therein in addition to the aggregate of particulate anthracite coal, as the naturally occurring carbonaceous material, in an amount less than about 20 percent, by weight, of the total solids in the system.

12. A cementitious composition for forming an aqueous hydraulic cementitious system as claimed in Claim 10 wherein the particulate carbonaceous material need not be naturally occurring but may be selected from the group consisting of delayed coke and naturally occurring carbon-containing mat-erials specially processed by heating the material to a temperature substantially in excess of that temperature at which the material is merely dried, the carbonaceous material being one which when so processed is effective to inhibit shrinkage by causing expansion of the system compared to no inclusion of carbonaceous material.

13. A composition as claimed in Claim 12 wherein the carbonaceous material has been water sprayed at the heating temperature.

14. A composition as claimed in Claim 12 wherein the naturally occurring carbonaceous material is one selected from the group consisting of anthracite coal, bituminous coal, and lignite coal or combinations of the same.