WO1999044966A1 - Admixture for zero-bleed mixtures, grouts, and cements - Google Patents

Abstract

The present invention provides a process and product for introducing and dispersing a biopolymer such as Welan gum throughout a liquid cemental mixture. A carrier liquid of a superplasticizer high-range water reducer is used to suspend and maintain the biopolymer within a stericly hindered lattice structure and which maintains the biopolymer in a hydration-free state. Upon introduction into the aqueous cement-containing mixture, the carrier liquid uniformly distributes the unhydrated biopolymer. Upon continued mixing action of the slurry, the stericly hindered structure of the carrier liquid is physically degraded by the abrasive mixing action, thereby releasing the unhydrated biopolymer. Upon release the highly dipersed biopolymer subsequently hydrates. The thorough dispersion of the biopolymer, prior to hydration, provides an improved end product which cures with zero-bleed water.

Description

ADMIXTUR TOR ZERO-BLEED MIXTURES. qpnTTTR. AND CEMENTS

Rglatgfl applications

This application claims the benefit of and incorporates by reference U.S. provisional patent application Serial No. 60/076,845 filed March 5, 1998. sfc..fc_eιn_eτ.fc as to R ghts to inven Qps Made under Federally sponsored Research and Development The U.S. Government has rights in this invention pursuant to Contract No. DE-AC09- 96SR18500 between Westinghouse Savannah River Company and the U.S. Department of Energy. FnyttTr^T. ^{nf the} Invention This invention is directed towards improvements in cement-containing compositions. In particular, this invention is directed towards an admixture which produces a zero-bleed water cement- containing composition. T-ior Art nf the Invention

Admixtures are materials added to cemental mixtures such as concrete or mortar and which modify the properties so as to make the mixture more suitable for a particular purpose and/or to achieve a useful property at a more economical cost.

A variety of admixtures are commercially available in the form of water-soluble solids or powders. These materials are typically designed to be mixed at the job site into the mixer. Other admixtures include liquid formulations which are added at bulk blending stations. The amount of admixtures, whether solid or liquid, must be carefully controlled. For many admixtures, slight inaccuracies in the batching of the admixture may impair or defeat the original properties for which the admixture was selected.

Admixtures which are known within the art include accelerators, retarders, air detrainers, air-entrainers, alkali-reactivity reducers, bonding enhancers, water reducers, corrosion inhibitors, dampproffing additives, grouting agents, gas formers, permeability reducers, pumping aids, and reinforcing agents. One improvement to admixtures is taught in

U.S. Patent No. No. 5,203,629, incorporated herein by reference, and which teaches adding dry admixtures contained within a paper package to fresh concrete mixtures. The mechanical abrasion disintegrates the package and distributes the admixture contents throughout the fresh concrete.

Superplasticizers are a type of high range water reducing admixture used to make high-slump flowing cement-containing mixtures. The superplasticizers operate by reducing the water-to-cement ratio needed while still providing a mixture having a useful set time and other desirable properties. Various superplasticizers are known in the art as described in U.S. Patent No. 5,728,207 entitled "Cement Admixture Product having Improved

Rheological Properties and Process of Forming Same", and incorporated herein by reference.

It is also known in the art to use biopolymers such as Welan gum in cement-containing mixtures where the gum serves as a suspension agent. Such biopolymers serve to hydrate, expand and support the other materials within the mix as is taught in U.S. Patent No. 5,004,506 entitled "Welan Gum in Cement Compositions", and which is incorporated herein by reference.

One difficulty in the use of gum admixtures is the rapid hydration which occurs to the gum upon 99/44966 _. ,„_ιr,

PCT/US99/04915

exposure to liquids. Efforts to suspend the gum in a precursor liquid or to mix the gum with other dry ingredients have met with only limited success. As a result, the maximum benefit of gum admixtures has not been achieved in a cement-containing mixture. Accordingly, there remains room for improvement within the art of providing admixtures to cement containing mixes. gτnnιm_ry pf the invent ion Accordingly, one aspect of the present invention is to provide an admixture which provides for zero-bleed cured cement-containing mixes. It is a further object to provide for zero-bleed concrete mixes such as CLSM mixes, grouts, and concretes which maintain useful working properties including cohesiveness, flowability, self- compacting, and self-leveling. Further, it is an object to provide an admixture suitable for use with mixing equipment as well as more controlled batch production. It is a further object to provide a zero-bleed admixture and a resulting cement-containing composition having the admixture, which is useful for tank closings, mine closings, shaft closures, pipeline closings and non-shrink slabs.

Detailed Description It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary construction.

The present invention addresses some of the objects and needs discussed above by providing a process and material which permits the formation of a zero-bleed cement mixture. As used herein, the term "cement mixture" encompasses controlled low strength material (CLSM) mixes, grouts, and concretes.

The admixture comprises a superplasticizer such as a high range water reducer (HRWR) . An HRWR of an ASTM standard C494, type F, is provided by a polycarboxylic acid such as Advaflow or Adva Cast brands (W. R. Grace & Company, New York, N.Y.). This product has been found to work well and was used in the examples which follow. The HRWR was used to suspend the powdered biopolymer Welan gum (Kelco Crete, Kelco Company) . Welan gum is fully described in U.S. Patent No. 4,342,866, which is incorporated herein by reference. While not wanting to be limited by theory, it is believed that the Welan gum is attracted to certain short chain branch molecules present on the polycarboxylic acid. It is believed that through steric hindrance, such as formation of a micelle- type structure, a lattice structure, or some other stericly hindered placement, the polycarboxylic acid protects the associated gum particles from hydration.

In accordance with this invention, it has been found that an admixture of an effective amount of a Welan gum may be suspended, using a shear mixer at medium speed, within a solution of an HRWR polycarboxylic acid. Once suspended, the admixture is stable and protects the gum from hydration when exposed to agents which would normally cause hydration to occur. Upon introduction of the admixture to a cement slurry, the admixture is rapidly dispersed within the slurry. Continued agitation within the abrasive slurry releases the gum from the polycarboxylic acid where the gum is immediately hydrated. The hydration and enhanced dispersion of the gum, combined with the water- reducing activity of the HRWR, may provide a zero- bleed concrete material. Surprisingly, it has been found that the admixture is operative with a wide variety of varying concrete mixtures.

For instance, the admixture is useful for use with CLSM and grouts having reactive materials designed to interact with leachable components of mixed waste. Suitable reactive materials which may included within the cement mixtures includes ion exchange resins, zeolites (natural and synthetic) , clays, modified clays, cements, reducing agents, reactive blast furnace slag, reagent chemicals, sodium titanate, magnesium phosphate, amorphous silica, amorphous alumina, calcium hydroxide, kiln dust, and surface active refractories. The amount of reactive agent added to the

CLSM, grout or cement depends on the concentration, volume, and type of hazardous material. Additional factors include the volume of the reactive backfill to be added to the hazardous material storage area. Heretofore, concrete mixtures suitable for use in waste tank closures and backfill for waste stabilization would produce varying amounts of bleed water. Bleed water is the result of migration of water to a surface boundary of a freshly placed concrete composition and is attributed to the settlement of solid materials (cement, sand, or fly ash) within the composition. The percentage of bleed water is, in part, a function of the amount of mixing water and the amount of cement. Mixes with higher water content will generate a higher percentage of bleed water. Concrete composition mixes with higher cement content will generate a lower percentage of bleed water. However, efforts to reduce bleed water levels by adjusting the water ratio within the mix are largely unsuccessful in that the mixtures are difficult to work. Within the art of waste tank closures, the presence of bleed water results in the formation of a contaminated bleed water. The contaminated bleed water must then be properly handled and disposed of, increasing the cost and safety concerns associated with the cement usage. The present invention allows the complete elimination of any bleed water. As a result, safety and cost concerns associated with contaminated bleed water are eliminated.

The use of reactive materials within the cement compositions allows a single material to be provided which meets the chemistry requirements for encapsulating incidental waste found within used waste tanks and also meets performance requirements for a flowable fill which is self-leveling, self- compacting, cohesive, has no bleed water, has a low heat of hydration and exhibits a useful range of compressive strengths. In another preferred embodiment of the invention, a process for stabilizing a confined space container has the steps of mixing a concrete composition so that the concrete composition provides zero-bleed water, placing the concrete composition in a confined space, and sealing the confined space. This process can also include the step of mixing a reactive component with the concrete composition before placing it into the confined space. Examples of useful concrete compositions for use with the admixture are set forth in Table 1. For comparison, a control reducing grout (CTL) used for tank closures and which produces bleed water was also evaluated along with a CLSM formulation and reducing grout (RG) mixtures. The RG mixtures have reactive materials designed to stabilize and encapsulate incidental amounts of high level waste present in the closure tanks.

Standard mixing protocols were followed using a continuous auger batch plant. The admixtures used the indicated proportions of the Welan gum powder suspended within the indicated volume of the polycarboxylic reducer (Advaflow) . A mix time on the order of several minutes was found sufficient to disperse the reducer and achieve hydration of the gum.

Set forth in Table 2 is test data conforming to the mixtures made according to Table 1. Flow determinations for the CLSM and RG mixtures conform to ASTM reference D-6103. For tank closures, a minimum flow of 10 inches is desired. The CTL grout flow was determined by the Kordan flow cone method.

Other ASTM measurements include: Bleed water, reference C-232; Air content, reference C-231; Unit weight, C-138; and compressive strength, C-39. The ASTM standards are well known within the industry.

Test mix formulation RG3 was further field tested in waste tank closure operations. In field use, the RG3 mixture proved workable and resulted in multiple tank closures with zero-bleed.

Set forth in Table 3 is a formulation for a CLSM zero-bleed formulation also found to be useful. Set forth in Table 4 is a comparison of a control grout using a type V cement in reference to the RG3 grout having a type I Portland cement. Ideally, the ratio of the superplasticizer to the biopolymer thickener is in the range of about 65- 130 grams per liter superplasticizer. The individual amounts of superplasticizer to polycarboxylic acid vary depending on the type of concrete composition in which the admixture is to be placed.

In general, a zero-bleed composition for a controlled strength material comprises about 50-600 pounds per cubic yard cement, about 2000-2500 pounds per cubic yard sand, about 0-600 pounds per cubic yard fly ash, about 0-600 pounds per cubic yard ground blast furnace slag, about 55-75 gallons cubic yard water, about 220-350 grams per cubic yard gum thickener, about 70-140 ounces per cubic yard superplasticizer and about 2-10 pounds per cubic yard reactive component.

An example of a zero-bleed, CLSM mix is about 150 pounds of cement per cubic yard, about 2300 pounds of sand per cubic yard, about 500 pounds of fly ash per cubic yard, about 63 gallons of water per cubic yard, and about 275 grams of gum thickener per cubic yard which is preblended in about 90 ounces of the HRWR superplasticizer per cubic yard of mix. The zero-bleed, controlled low strength material is ideal for filling containers where there will be relatively low compressive forces upon the concrete composition.

In every instance, use of the admixture as mixed and used as described above resulted in a zero-bleed product. As seen in the data, the compressive strength exceeds the requirements for a CLSM mix. Further, versatile mixtures (not separately reported) were obtained in which the sand component of the concrete mixtures was replaced with various grades of coal ash. With slight increases in the cement and water proportions and the inclusion of a fly ash, a workable CLSM mix with zero-bleed was obtained. The present invention represents a needed improvement with respect to the formation of a zero-bleed concrete mixture. In particular, the invention provides a solution to the difficulty of using biopolymers. Gums and related biopolymers have proven very difficult to thoroughly mix into the concrete. Addition and dispersion of the small amount of biopolymer or gum (about 6.75 pounds) into about 31,500 pounds of concrete, has heretofore limited practical use of gum admixtures in concrete, particularly in a powdered form. By adding the gum in a protective liquid carrier to the slurry, the gum is more throughly dispersed prior to hydration. As a result, better performing, zero-bleed concrete-containing compositions can be provided.

HRWR having polycarboxylic acids were found to work best in the present invention. Other water reducers including melamine-based materials, lignosulfonate-based materials, and surfactants were evaluated but were not found to eliminate bleed water formation. Without undue experimentation, the admixture described above is believed compatible with other conventional concrete mixtures. As a result, it would be a simple matter to provide an admixture to reduce or eliminate the bleed water formation in standard concrete-containing mixtures. Even where bleed water formation is not a concern, the present invention provides an improved dispersion of a biopolymer. As a result, the invention provides improvements which result from the increase in suspension and hydration properties of the cement mixtures.

While the above examples make use of Welan gum, other biopolymers are believed to offer similar results. Other gums may be compatible with other types of plasticizers. Any cellulosic or polysaccarite gum which binds to the plasticizer, and is afforded some level of steric protection 10 from hydration, should be operative within the scope of the present invention.

It should be noted that the cement type can vary in each of these formulations. It can be any one from type I, type II, type III, type IV, type V or any Portland cement. Different cements are selected for different needs, the selection, production, and use of which is well known in the art. Minor modifications to the formulations may be made depending on the type of cement that is used and the desired compressive strength of the concrete composition.

Additionally, a reactive component may be added to any of these concrete compositions. Examples of such reactive components are sodium thiosulphate, calcium sulfite and sodium sulfite. These chemicals are useful to react with sludge left in a confined space so that even though the concrete hardens and there is zero-bleed water, the reactive chemicals react with hazardous material inside the sludge found in the bottom of a confined space. The chemical reaction ensures that the harmful chemicals in the sludge are precipitated out into a less harmful form. For example, ASTM blast furnace slag, when mixed in the chemically reactive concrete composition, reacts with the alkalis in the waste and calcium from the cement to chemically reduce protechnetate (Tc⁺⁷) to Tc⁺⁴ which is then precipitated as a hydroxide and/or sulfide in the basic environment of the concrete composition.

Additional chemically reactive substances which may be included in a concrete composition are disclosed in a U.S. patent application, bearing Attorney Docket No. WSR-19, filed on March 5, 1999 entitled "Reactive Composite Compositions and Mat 11

Barriers" , which is incorporated herein by reference.

It should be understood by those of ordinary skill in the art that the foregoing presently preferred embodiments are exemplary only and that the intended description thereof is likewise by way of words of example rather than words of limitation, and their use does not preclude inclusions of such modifications, variations and/or additions to the present invention as would be utterly apparent to one of ordinary skill in the art, the scope of the present invention being set forth in the appended claims.

--O

Table 1

CΛ CTL

§ CΛ Ingredients Reducing HP-ZB

H Grout CLSM RG1 RG2 RG3 RG4 RG5 RG6

H

Cement, Type I, Ibs/cyd 1353* 150 50 150 75 150 120 75

H

W Slag, Grade 100, Ibs/cyd 209 — 210 210 210 210 275 210

CΛ

Fly Ash, Ibs/cyd — 500 300 200 375 300 165 325 N>

Sand, Ibs/cyd 1625 2300 2300 2300 2300 2300 2300 2300

H Water, gals/cyd 86 4 63 60 60 60 60 60 60

Advaflo , l oz/cyd — 90 90 90 90 90 90 90

Kelco-crete, gm/cyd — 275 275 275 275 275 275 275

Silica Fume, Ibs/cyd 90 — — — -.» — — —

Sodium Thiosulfate, Ibs/cyd 2 1 — — — -- — — 2 1

HRWR, fl oz/cyd 250 — — ~ — — — —

Retarder, 11 oz/cyd 150 — — ~ — — — ~

Type V Cement

o

CΛ

©

Table 2

Ingredients RGA1 RGA2 RGAF1 RGAF2 RGAF3 RGD1 RGD2 4-.

\©

Cement, Type I, 165 200 200 200 200 100 100 9 Ibs/cyd

Slag, Grade 100, 210 — — — 210 210 Ibs/cyd

Pond Ash, 600* 1200* 1200* 1200* 1500* 340** 1705**

§ Ibs/cyd

H Fly Ash, Class F, — — — — 400 — — H Ibs/cyd

Sand, ASTM C-33. 2190 1400 1400 1400 ~ 2500 —

CΛ Ibs/cyd

Water, 92 105 7 105 111 5 80 67 8 115 5

H gals/cyd

Maxflow Air, — — 20 5 15 5 30 — — Ibs/cyd

Maxflow RMA, -- — — — 90 — — fl oz cyd

Advaflow, 180 180 — — — 180 180 fl oz cyd

Kelco-crete, — 275 — — -- 275 275

gms/cyd

H n

Shading indicates the mix selected for field testing

IS v©

Table 3

Bleed Unit- Air Compressive Strength

CΛ Flow Water Wt. Content Temp, (psi)

§ CΛ Mixes On) (%) (lbs/eft) (%) (°F) 7-day 28-day 56-day

H

Reducing Grout 10 0 80 N/A 90 50 500 500 w Acceptance Criteria min min max min. min min.

CTL Reducing Grout 4' 0 128 4 85 6570 9725 10,700 seconds *-

H HP-ZB CLSM 1050 0 ** 230 710

TEST MIXES

RG1 1113 0 1204 66 84 ** ** 1230

RG2 1200 0 1205 66 76 ** ** 1550

RG3 1150 0 1209 5.8 78 360 1085 1300

RG4 1175 0 1222 55 78 420 1420 1620

RG5 1188 0 1196 70 78 670 1465 1580

RG6 1150 0 1210 57 77 380 1080 1320

n

CΛ

Table 4

Ingredients RG3

10

Reducing HP-ZB -© A--.

CLSM ι© Ov

Cement, Type I, Ibs/cyd 75

Slag, Grade 100, Ibs/cyd 210

Fly Ash, Ibs/cyd 375 Λ Sand, Ibs/cyd 2300

Coal Ash, Ibs/cyd —

CΛ

H Water, gals/cyd 60

Advaflow, fl oz/cyd 90

M Kelco-crete, gm cyd 275 Λ

Table 5

H Ui

3 Set Time Temp. Thermal Lin Height Cost per

Mix Flow (hr.) (^CF) Cracking Restriction cyd*

C TL Reducing 4 sec * 24-35 350 °F Yes One foot *=$450 Grout

HP-ZB Reducing Grout/CLSM 11 5 in ** 24-30 110 °F Very No lift «$80

Mix RG3 Minimal Restriction

* Kordan Flow Cone Method H n ** ASTM D-6103 Method CΛ ι©

* Data from the SRS Tank 17- and 120-F closures are the basis of these estimates ;© © 4-> v©

Claims

16WHAT IS CLAIMED IS:

1. A process of forming a zero-bleed admixture comprising: providing a liquid polycarboxylic acid water reducer; and, suspending an effective amount of a biopolymer within the liquid; wherein, the resulting admixture provides a stable carrier for introducing and distributing the biopolymer into a concrete containing slurry.

2. The process according to claim 1 wherein said biopolymer is a Welan gum powder.

3. The process according to claim 1 wherein said step of suspending an effective amount of a biopolymer further comprises the steric positioning of the biopolymer within a lattice structure defined by the polycarboxylic acid water reducer.

4. An admixture for a zero-bleed concrete- containing composition comprising: a liquid polycarboxylic acid water reducer having an effective amount of a biopolymer positioned within a lattice structure of the polycarboxylic acid in a stericly hindered configuration, wherein the biopolymer is resistant to hydration while in said stericly hindered configuration.

5. The admixture according to claim 4 wherein said biopolymer is a Welan gum.

6. The admixture according to claim 4 wherein said liquid pόlycarboxcylic acid water reducer is an ASTM C494, type F, water reducer.

7. An additive for concrete, grout, or CLSM prepared by: providing a first admixture comprising a polycarboxylic water reducer; suspending a second admixture comprising a biopolymer within the water reducer, the resulting W wOυ 9 ^y9/449v6o6o PCT/US99/04915

17 suspended biopolymer being resistant to hydration and thereby providing a zero-bleed admixture.

8. The additive according to claim 7 wherein said biopolymer is a Welan gum.

9. A process of preparing a cementitious mixture including: providing a first admixture comprising a polycarboxylic water reducer; suspending a second admixture comprising a powdered biopolymer within the water reducer, the suspended biopolymer being resistant to hydration and thereby providing a zero-bleed admixture; introducing the zero-bleed admixture into a cementitious composition having a liquid; distributing the zero-bleed admixture throughout the cementitious composition through mechanical agitation; providing additional mechanical agitation to the cementitious composition and distributed zero- bleed admixture, said mechanical agitation exposing the biopolymer to hydrating conditions; and, hydrating the biopolymer within the cementitious composition; wherein said cementitious composition cures to a zero-bleed product.

10. The process according to claim 9 wherein said biopolymer powder is a cellulosic gum.

11. The process according to claim 9 wherein said biopolymer is a xanthum gum.

12. A process for stabilizing a confined space container comprising the steps of: mixing a concrete composition wherein the concrete composition has about zero-bleed water; placing the concrete composition in a confined space; and sealing the confined space. W wOw 9 ^y9^y/^/4^49v6o6o PCT US99/04915

18

13. A process for stabilizing a confined space container according to claim 12 , wherein the step of mixing the concrete composition further comprises adding a reactive component.

14. A process for stabilizing a confined space container according to claim 12, wherein the step of adding a reactive component includes adding at least one of sodium thiosulfate, calcium sulfite, or sodium sulfite.

15. A zero-bleed admixture comprising about 60 to about 130 grams of biopolymer thickener suspended within about one liter of superplasticizer.

16. A zero-bleed admixture according to claim 14, wherein the biopolymer thickener is Welan gum.

17. A zero-bleed admixture according to claim 14, wherein the superplasticizer is polycarboxylic acid.