WO2013074296A1

WO2013074296A1 - Cmc/hec blends for cement slurries

Info

Publication number: WO2013074296A1
Application number: PCT/US2012/062900
Authority: WO
Inventors: Jolee M. Dominowski; Michael J. Radler
Original assignee: Dow Global Technologies Llc
Priority date: 2011-11-17
Filing date: 2012-11-01
Publication date: 2013-05-23

Abstract

The present invention provides dry mix compositions for use in a cement slurry comprising carboxymethyl cellulose (CMC) alone or in a blend with hydroxyethyl cellulose (HEC), one or more setting retardant, and hydraulic cement or lime wherein the carboxymethyl cellulose has a 1% solution viscosity ranging from 75 to 4400 cps measured as a 1.0 wt.% aqueous solution of the cellulose ether at 20°C, 2.55 s^-1 shear rate with a Haake Rotovisko viscometer, Model 550. In addition, the present invention provides methods of forming cement stabilized substrates comprising mixing the dry mix composition and water to form a cement slurry, adding the cement slurry to a substrate, mixing the cement slurry into the substrate, and grading and compacting the mixture of substrate and cement slurry. The compositions retard setting and stabilize cement slurries in use, especially with recycled asphalt substrates.

Description

CMC/HEC BLENDS FOR CEMENT SLURRIES The present invention relates to a composition which is useful as a rheology modifier for cement slurries. More particularly, it relates to compositions comprising carboxymethyl cellulose (CMC) alone or in a blend with hydroxyethyl cellulose (HEC), such as, for example, a setting retardant, such as a saccharide, and a hydraulic cement which can be a dry mix for use as a cement slurry in cement soil stabilization applications, in particular full-depth reclamation.

Cement slurries have been used in aqueous hydraulic cement compositions, particularly in well-cementing operations. Known hydraulic cement compositions may comprise a hydroxyalkyl cellulose ether as a fluid loss additive to lessen the fluid loss of the hydraulic cement composition to porous media.

In the construction industry, a stable rigid base is required for paving, building and parking structures, which requires the stabilization of the substrate soil. Such stabilization may be accomplished by combining cement with the soil in methods of forming compositions that include, but are not limited to, soil cements, cement treated bases, and cement stabilized soils.

Making soil cement comprises adding specified amounts of dry cement powder per cubic unit of soil. The resulting cement treated soil is then graded and compacted and allowed to cure whereby the cohesive material gains in strength and rigidity over time. In another method, preferred in populated areas, soil cement is formed from an aqueous cement slurry to avoid creating a large amount of dust from using fine cement powder. The cement slurry is placed over a substrate soil and then mixed in using mechanical means. However, cement slurry methods have proven to be very problematic in use because the slurry will harden in shipment if not removed in a timely manner. In addition, the cement itself will separate or fall out of solution almost immediately after mixing with water. Even in concentrations as low as 10% cement in water, the cement will begin to fall out of solution within a couple of minutes. The use of chemical retardation to prevent the premature setting of cement based materials, including cement slurry, is known throughout the industry. One common retarding compound is sugar. Employing chemical retardation in cement slurry tends to diminish the problems of setting prior to application. However, it additionally tends to lower the gelation temperature of cellulose ethers which may impair cement slurry stability.

As an alternative to making soil cement, a process called full depth reclamation can be used to provide a base for structures such as roads, parking lots, and other paved areas. This process involves grinding up and pulverizing the asphalt surface and blending it with the underlying base, sub base, and/or sub grade material.

Cement and water are added to the combined materials to stabilize them much in the same way that cement can be added to substrate soil to create stabilized soil cement. The mixture is then compacted in place to form a stabilized substrate for the new paving. However, this process, because it involves the addition of cement to stabilize the base, runs into the same settling and in-shipment hardening problems discussed above with respect to the application of cement for soil stabilization.

When using cement slurries for building a stable rigid base for paving, building and parking structures, it is critical to minimize the air entrapped in the hardened cement. Entrapped air reduces the stability of the hardened cement. However, previous known cement slurries tended to foam due to the continuous agitation which is necessary to keep the solid components of the slurry in suspension and due to additives like cellulose ethers incorporated in the cement slurry. Accordingly, there is a strong need to provide a new cement slurry wherein formed foam dissipates fast.

U.S. patent publication 2009/0044726, to Brouillette et al., discloses a cement slurry comprising from 45 to 65 wt.% cement, from 55 - 35 wt.% water, a retarder to prevent the cement from setting for a predetermined period of time and a thixotropic thickener to maintain cement in suspension for a predetermined period of time. Useful retarders are sucrose, carboxylic acids and others. Useful thixotropic thickeners include methyl hydroxyethyl cellulose. The cement slurry may comprise an anti-foaming agent. However, the cement slurries having a defoamer and a setting retardant are expensive to use and may require dosage rates in use that make them unattractive to end users.

Applicants have sought to solve the problem of providing cement slurries that do not prematurely set or settle out during transport and which at the same time avoid foaming problems in use while allowing for reduced dosages of additives in or to the cement slurry.

STATEMENT OF THE INVENTION

Herein, milliPascals^*second (mPa^*s) and centiPoise (cps) are interchangeable in reference to viscosity. Weight-percent, "wt%" and "wt.%" are interchangeable.

In accordance with the present invention, dry mixes for use as a cement slurry comprise carboxymethyl cellulose (CMC) alone or in a blend with hydroxyethyl cellulose (HEC), one or more setting retardant, such as, for example, a saccharide, and hydraulic cement or lime. The compositions form sedimentation resistant aqueous cement slurry compositions in water. The compositions find use in cement soil stabilization applications, in particular full-depth reclamation.

Suitable CMCs for use in the present invention have a 1 % solution viscosity ranging from 75 to 4400 cps, preferably, from 1600 cps to 4100 cps, or, more preferably, from 2000 cps to 4000 cps measured as a 1 .0 wt.% aqueous solution of the cellulose ether at 20 °C with a Haake Rotovisko viscometer, Model 550 (PSL Systemtechnik GmbH, Clausthal-Zellerfeld, DE) viscometer.

The one or more setting retardant preferably comprises a saccharide or carbohydrate, which may include oligosaccharides, reducing sugars, dextrans, gums, starches, dextrins, and is, more preferably, sucrose, raw sugar, and beet sugar by-products.

The composition of the present invention comprise a weight ratio of the total amount of CMC and HEC solids to setting retardant solids of from 0.13:1 to 0.65:1 , preferably, at least 0.25:1 , more preferably, 0.6:1 or less, or, particularly from 0.275:1 to 0.563:1 .

In the composition of the present invention, the total dosage of CMC and HEC solids ranges from 0.007 to 0.06 wt.%, based on the total solids of the cement slurry formulation, preferably 0.01 to 0.05 wt.%, or, more preferably, 0.020 to 0.04.

In the compositions of the present invention, the weight ratio of HEC to CMC may range from 0.0:1 .0 to 20:1 , or, preferably, from 0.2:1 to 1 .0:1 , or, more preferably from 0.4:1 to 0.8:1 . The formulation window of the composition of the present invention is much wider where the CMC viscosity is 1600 cps to 4100 cps, or, more preferably, from 2000 cps to 4000 cps measured as a 1 .0 wt.% aqueous solution of the cellulose ether at 20 °C, 2.55 s^"1 shear rate with a Haake Rotovisko viscometer, Model 550. If the viscosity of the CMC lies below this range, then more HEC than CMC should be used and the weight ratio of HEC to CMC should range from 1 .0:1 to 20.0:1 , to insure sedimentation stability as well as a desired slump which ensures efficient coverage when using a given amount of the cement slurry. If the CMC viscosity lies above 4400 cPs, then the water availability of the CMC is so small that resistance to sedimentation will be hampered.

In accordance with another aspect of the present invention, methods of forming a cement stabilized substrate comprise forming a cement slurry by mixing carboxymethyl cellulose (CMC) alone or in a blend with hydroxyethyl cellulose (HEC), one or more setting retardant, cement or lime and water, adding the cement slurry to the substrate, mixing the cement slurry into the substrate, and grading and compacting the mixture of substrate and cement slurry. The substrate may be any of asphalt, reclaimed asphalt, concrete, soil, sand and/or aggregate. Preferably, the methods further comprise grinding up and pulverizing a substrate chosen from asphalt, reclaimed asphalt and concrete and blending it with the underlying base to form an enhanced substrate, sub base, and/or sub grade material before adding the cement slurry to the enhanced substrate.

Accordingly, the present invention provides uses of the above-mentioned polymer composition of the invention for modifying the rheology of a cement slurry.

Further, the present invention provides uses of the above-mentioned cement composition of the invention for stabilizing a substrate.

All ranges recited are inclusive and combinable. For example, a disclosed proportion of from 0.13:1 to 0.65:1 , preferably, at least 0.25:1 , more preferably, 0.6:1 or less, or, particularly from 0.275:1 to 0.563:1 would include the ratios of from 0.13:1 to 0.65:1 , from 0.13:1 to 0.6:1 , from 0.13:1 to 0.563:1 , from 0.25:1 to 0.65:1 , from 0.25:1 to 0.6:1 , from 0.25:1 to 0.563:1 , from 0.275:1 to 0.6:1 , from 0.275:1 to 0.563:1 , and from 0.275:1 to 0.65:1 .

Unless otherwise indicated, all temperature and pressure units are room temperature and standard pressure. All phrases comprising parentheses denote either or both of the included parenthetical matter and its absence.

Unless otherwise stated, all percentages are wt.% based on the total dry weight of the hydraulic setting composition, including the dry weight of any liquid additives, such as polyacrylamides.

Unless otherwise stated, the term "EN" stands for European Norm and designates a test method as a prefix to the test method number. European Norm is a standard published by the European Technical Committee for Standardization CEN/TC 67 'Ceramic tiles', Brussels, Belgium. Unless otherwise stated, the test method is the most current test method as of the priority date of this document.

As used herein, the term "weight average molecular weight" means the

molecular weight of a polymer or copolymer as determined by gel permeation chromatography against a polyacrylic acid standard.

The cement slurry formulations comprising CMC either alone or in a blend with HEC allow for up to a 50% reduction in admixture (CMC, HEC + setting retardant) dosage rate to achieve a stable, suspended, cement slurry without compromising slurry rheology and end-use performance criteria. CMC also enables cost

reduction as it is cheaper to manufacture compared to HEC, and does not

contribute any foam to the manufacturing process.

Suitable carboxymethyl celluloses (CMCs) for use in the present invention may include, for example, carboxymethyl hydroxyethyl cellulose (CMHEC),

carboxymethyl cellulose (CMC), hydrophobically modified

carboxymethyl hydroxyethyl cellulose (hmCMHEC), hydrophobically modified carboxymethylmethyl cellulose (hmCMMC), carboxymethylsulfoethyl cellulose

(CMSEC).

Suitable hydroxyethyl celluloses (HECs) for use in the present invention may include, for example, a hydrophobically modified hydroxyethyl cellulose such as one hydrophobically modified by substituting the hydroxyethyl cellulose with one or more hydrocarbon substituents, preferably with acyclic or cyclic, saturated or unsaturated, branched or linear hydrocarbon groups, such as an alkyl, alkylaryl or arylalkyl group having at least 8 carbon atoms, generally from 8 to 32 carbon atoms, preferably from 10 to 30 carbon atoms, more preferably from 12 to 24 carbon atoms, and most preferably from 12 to 18 carbon atoms. Suitable

hydroxyethyl celluloses may be formulated with a polyglycol anti-foamant in the amount of 0.2 to 2 wt.%, based on the total solids of the HEC product.

The viscosity of a suitable carboxymethyl cellulose (CMC) may range from 1000 to 4400 cps, preferably, from 1600 cps to 4100 cps, or, more preferably, from 2000 cps to 4000 cps as measured as a 1 .0 wt.% aqueous solution of the cellulose ether at 20 °C, 2.55 s^"1 shear rate with a Haake Rotovisko viscometer; Model 550 (PSL Systemtechnik; GmbH). CMC of too high a viscosity has such a low water availability that it dissolves slowly, so that cement slurries made with higher viscosity CMC grades would not flow as well in use, thereby requiring larger batch sizes to do the job. Conversely, with use of CMCs of too low a viscosity give an undesirable slump size and more water availability that may lead to a very runny slurry which when applied to a road bed would have the potential of running off the road grade.

The viscosity of a suitable hydroxyethyl cellulose may range from 3500 to 8000 cps or, preferably, from 4000 cps to 7000 cps, measured as a 1 .0 weight percent aqueous solution of the cellulose ether at 25°Cwith a Brookfield LVF viscometer equipped with a #4 spindle (Brookfield Engineering Laboratories; Middleboro, MA), at 30 rpm.

The composition of the present invention further comprises one or more setting retardant. The setting retardant prevents cement from prematurely setting during transport or otherwise before a cement slurry is mixed into a substrate. Various materials that can be used as a setting retardant include, for example, saccharides, such as carbohydrates, dextrans, starches, dextrins, gums, and pectins;

lignosulfonates and their salts; polybasic carboxylic acids; whey protein, oxides of lead and zinc; metal or ammonium phosphates, polyphosphates, magnesium salts of organic and inorganic acids; borates, and clays, such as bentonite. Useful saccharides may include, for example, sucrose, raw sugar, beet sugar, and reducing sugars, such as dextrose. Useful starch compounds may include, for example, starch ethers, such as hydroxypropyl starch or carboxymethyl starch. Useful guar gums may include, for example, guar and xanthan gums,

carboxymethyl guar, hydroxypropyl guar, carboxymethyl hydroxypropyl guar or cationized guar. Preferred hydroxypropyl guars and the production thereof are described in U.S patent No. 4,645,812, columns 4-6. Useful xanthan gums may include those, such as are described in more detail in European patent

EP0504870B, page 3, lines 25-56 and page 4, lines 1 -30. Preferred carbohydrates include sucrose as table sugar, cane or beet sugar, raw sugar (98.5% purity or higher), corn syrup powder or beet sugar by-products.

The compositions of the present invention may further comprise an anti- foaming agent, preferably in a solid form. When the active component is liquid at 25 °C and atmospheric pressure, such as liquid oxyalkylene antifoaming agents, preferably a polypropylene glycol, the agent is preferably supported by a solid carrier, such as talc, diatomaceous earth, amorphous, colloidal, or crystalline silica, silica dioxide or a silicate, preferably calcium silicate. Such a liquid antifoaming agent can be mixed with the carboxymethyl cellulose and/or hydroxyethyl cellulose and spray dried, or simply sprayed thereon.

Examples of useful liquid anti-foaming agents may include , for example, petroleum hydrocarbon oils, non-silicone acetylenic materials; and polyoxyalkylene glycols. Examples of useful solid anti-foaming agents may include, for example, tributyl phosphate or a metallic stearate. Suitable antifoaming agents may include Agitan™ P-823 (a blend of liquid hydrocarbons and polyglycols on an inorganic carrier, Munzing Chemie, GmbH, Heilbronn, DE), Dee Fo™ 97-3 (a metallic stearate on a mineral oil carrier from Munzing Chemie GmbH, Surfynol™ DF 1 10L (a nonionic, nonsilicone, acetylenic material from Air Products and Chemicals, Allentown, PA), Axilat™ 770DD (polypropylene glycol, petroleum distillates, butylated hydroxytoluene and calcium silicate from Hexion Specialty Chemicals Incorporated; Columbus, OH) Axilat™ 727DD (silicon dioxide, colloidal silica, and an antioxidant), Axilat™775DD (talc, petroleum hydrocarbon oil, silicon dioxide, and crystalline silica).

The present invention further relates to methods of modifying the rheology of a cement or lime slurry which comprises the step of incorporating compositions comprising carboxymethyl cellulose (CMC) alone or in a blend with hydroxyethyl cellulose (HEC), and one or more setting retardant into a slurry of cement or lime in water to form the cement slurry. The carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), and one or more setting retardant can be added individually to the cement or the components can be pre-mixed before adding them to the cement. Some or all of the

components can be added to the cement or lime during or after, but preferably before the addition of water to the cement or lime to form a cement slurry.

Lime slurries and hydraulic cements may be used in accordance with the compositions and methods of the present invention. A variety of hydraulic cements are suitable for use in accordance with the methods and compositions of the present invention including those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include, but are not limited to, Portland cements, pozzolanic cements, gypsum cements, aluminous cements, silica cements and alkaline cements. Portland cements are generally preferred for use in accordance with the present invention.

Further, the cement composition of the present invention optionally comprises fillers, such as calcium carbonate, fly ash, blast furnace slag, fumed silica, bentonite, clay, natural minerals based on hydrous aluminum silicate, for example kaolinite or halocite. These powders can be used alone or in combination thereof. Further, sand, ballast and mixtures thereof may be added if necessary as aggregate to these powders.

The water in the cement compositions of this invention can be fresh water, unsaturated salt solutions including brines and seawater and saturated salt solutions. Generally, the water can be from any source provided it does not contain an excess of compounds that adversely affect other components in the cement compositions. However, the cement composition preferably comprises no or not more than 5 percent of sodium chloride, based on the weight of water. The water is present in the cement compositions of this invention in an amount sufficient to form a pumpable slurry. More particularly, the water is present in the cement

compositions in an amount in the range of from 0. 3 to 2 weight parts of water, preferably 0.5 to 1 weight parts of water, per weight part of cement.

The cement slurry can be used in a method of forming a cement stabilized substrate which comprises the steps of adding to the substrate a cement slurry produced by mixing the carboxymethyl cellulose, with or without hydroxyethyl cellulose, and the setting retardant with cement or lime, and water to form a cement slurry, adding the cement slurry to the substrate, mixing the cement slurry into the substrate, and grading and compacting the mixture of substrate and cement slurry.

In preferred methods, full depth reclamation comprises grinding up and pulverizing a substrate chosen from asphalt and concrete and blending it with the underlying base, sub base, and/or sub grade material to form an enhanced substrate. The cement slurries of the present invention are added to the enhanced substrate to stabilize it much in the same way that the cement slurries can be added to substrate soil to create stabilized soil cement. The mixture is then compacted in place to form a stabilized substrate for the new paving or flatwork.

The substrate can be soil, aggregate, asphalt, reclaimed asphalt, and mixtures thereof. Aggregates include ballast from river, land, mountain or sea, lime ballast, rubble thereof, blast furnace slag coarse or fine aggregate, ferronickel slag coarse aggregate, artificial and natural light-weight coarse aggregate, and regenerated aggregate.

Examples: The present invention is further illustrated by the following examples which are not to be construed to limit the scope of the present invention. Unless otherwise indicated, all percentages and parts are by weight.

The following components are used in the examples:

CMC A is a Walocel™ CRT 30000 P (The Dow Chemical Company, Midland, Ml) powder of sodium carboxymethyl cellulose (CMC) having an estimated 1 wt.% aqueous (aq.) solution viscosity of 4,000 milliPascals^*seconds (mPa^*s) (Haake Rotovisko @ 20 C, 2.55 s-1 , Thermo Fisher Scientific, converted from Brookfield viscosity that was measured with a Brookfield LVT, 25°C, 30 rpm, Spindle #3 (Brookfield Engineering Laboratories; Middleboro, MA by using a Visco

NavigatorTM chart (The Dow Chemical Company).

CMC B is a Walocel™ CRT 20000 PV fine powder CMC having a 1 wt.% aq. solution viscosity of 2500 mPa^*s (Haake Rotovisko @ 20 C, 2.55 s-1 , converted from Haake 2 wt.% viscosity). CMC C is a Walocel™ CRT 40000 PV fine powder CMC having a 1 wt.% aq. solution viscosity of 5077 mPa^*s (Haake Rotovisko @ 20 C, 2.55 s-1 , converted from Haake 2 wt.% viscosity).

CMC D is a Walocel™ CRT 10000 GA granular CMC having a 1 wt.% aq.

solution viscosity of 1 ,460 mPa^*s (Haake Rotovisko @ 20 C, 2.55 s-1 reported as 1 wt.% solution viscosity).

CMC E is a Walocel™ CRT 10000 PV fine powder CMC having a 1 wt.% aq. solution viscosity of 1 128 mPa^*s (Haake Rotovisko @ 20 C, 2.55 s-1 , converted from Haake 2 wt.% viscosity).

CMC F is a Walocel™ CRT 1000 GA granular CMC having an estimated 1 wt.% aq. solution viscosity of 83 mPa^*s ((Haake Rotovisko @ 20 C, 2.55 s-1 , estimated from relation of Haake to Brookfield viscosity).

HEC G is a CELLOSIZE™ QP 100 MHV (The Dow Chemical Company) hydroxyethyl cellulose (HEC) that contains trace amounts of propylene glycol, having a 1 wt.% aq. solution viscosity of 6,141 mPa^*s 4400 mPa^'s, measured using Brookfield LVF, spindle #4, 30 rpm at 25 °C.

Setting retardant H is sucrose (CAS # 57-50-1 ); extra fine granulated 99.9+% sucrose; melting point 185 C; solubility in water 200gm/1 OOgm @ 20 C; Bulk density 784 - 896 kg/m³; Specific gravity 1 .59. Percent moisture by weight 0.05.

Cement I is Portland cement.

The following test methods were used to evaluate the example formulations:

Quick Foam Test: A 200g solution of the CMC, HEC and setting retardant in water was prepared according to each formulation composition listed in the formulation Tables 1 A and 1 B, below. Once hydrated, the solution was added into a mixing bowl, and mixed for 5 minutes with a Kitchen Aid Professional mixer Model KSM50P (Kitchen Aid; St. Joseph, Ml) at a speed as high as possible such that the solution still stayed in the bowl, usually a speed setting of 4. When mixing was stopped, the time it took for the foam to reach 80% dissipation was recorded. A foam dissipation time of < 10 minute is preferred. Foam dissipation time of < 20 minutes is acceptable.

Slump/Flow Test: The target amount of cement (approximately 342.86 grams) was added to each Example mixture from the foam test to make approximately 518 grams of a mixture that was mixed in a Kitchen Aid Mixer for 5 minutes at a speed setting of 4-6 so that the mixing speed did not throw material out of the bowl when mixing, when slaked for 5 more minutes to make a cement slurry. The slurry was poured (100ml) to the fill line of a Nalgene funnel 10.8 cm top diameter, 12.0cm total height, and 1 .0 cm spout diameter (Thermo Fisher Scientific; Rochester, NY) connected to a ring stand and arranged 25 cm above a Mylar™ plastic film (Grafix; Cleveland, OH) Then the time for the slurry to empty the funnel was recorded within one minute after the funnel was emptied and the diameter of the slump was recorded. Slump is measured at the longest length and width of the corresponding "circle" that forms by the slurry deposited on the film and the average slump

(average of length and width in cm) is recorded.

An acceptable result in slump is 12.7 to 30.5cm (5 to 12 in), with preferred results ranging from 15.2 to 22.9cm (6 to 9 in.). A result in slump lower than this range can be accepted. A higher result in slump size is never acceptable.

(Heated) Slurry Suspension Test: Slurry samples were made in a Kitchen Aid mixer according to the formulation compositions listed in the formulations Tables 1 A and 1 B, below. Each sample was prepared according to the procedure listed under the Quick Foam test method listed above. A 236.6 ml (8 oz) jar was filled approximately half full with the sample. The jar was then oven heated at 67°C (152.6 °F) for 12 hours. After the heating, samples were visually inspected for slurry separation. To check settling of cement and sedimentation, a tongue depressor was inserted into the slurry. If the depressor could be inserted to the bottom of the jar and stirred by hand so as to reform a slurry, the sample passed the test.

Table 1 A: Formulations of HEC-CMC Slurry Blends (wt.% of total wet formulation)

Denotes Comparative Example

Each of the formulations set forth in Table 1 A and Table 1 B was evaluated in the tests summarized in Tables 2A and 2B.

As shown in Table 2A, below, in Examples 2 to 14A, the carboxymethyl celluloses CMC A and B provide a wide formulation window to enable cement slurries that are resistant to sedimentation, provide a suitable slump or flow and do not foam. In fact, each of CMC's A and B, respectively, having a viscosity of a 1 wt.% solution in water of 4,000 mPa*s and 2500 mPa*s (Haake Rotovisko Model 550 @ 20 C, 2.55 s-1 , PSL Systemtechnik GmbH, Clausthal-Zellerfeld, DE) provide acceptable and low foaming cement slurries at as low as a 3:7 weight ratio with hydroxyethyl cellulose in Examples 6 and 1 2 and also when used all by themselves in Examples 2 and 7, which exhibit no foaming at all. The optimal CMC B in Example 14 can be formulated in a ratio as low as 1 :20 with HEC. On the whole, the above Examples 2-14A show that CMC as well as HEC and their blends provide useful cement slurry compositions with an added saccharide setting retardant. However, in slurries shown in Examples 27 and 29 when too much of the CMC or CMC/HEC blend is used relative to the amount of setting retardant, the compositions lose their resistance to sedimentation. Example 28 appears to have been an anomaly and when repeated in Example 14A gives good results.

Table 1 B: Formulations of HEC-CMC Slurry Blends (wt.% of total wet formulation)

Denotes Comparative Example

Table 2A: Test Results for Hiqher Viscosity CMC

1 . Slump time through funnel.

As shown in Table 2B, below, in Examples 15 to 22 and comparative Examples 23 to 26, the carboxymethyl celluloses CMC D, E and F which have below preferred viscosities all provide cement slurries that are resistant to sedimentation and do not foam. The slump size results in Examples 15-26 are acceptable but low. Accordingly, such CMCs D, E and F are preferably formulated with a large proportion of HEC. The viscosity of CMC C in Example 30 is too high to give a sedimentation resistant cement slurry. On the whole, the above Examples 15 to 26 show that CMC/HEC blends provide useful cement slurry compositions with an added saccharide setting retardant even when using a CMC having a viscosity of from 75 to 1600 mPa^*s when measured as a 1 .0 wt.% aqueous solution of the cellulose ether at 20 °C with a Haake Rotovisko viscometer, Model 550 at 2.55 s^"1 shear rate. In comparative Example 29, the CMC/HEC blend composition with a CMC A at a higher proportion than the inventive dry mix set more quickly than is desired. In comparative Example 30, the CMC/HEC blend composition with high viscosity CMC C set more quickly than is desired.

Table 2B: Test Results for Lower Viscosity CMC and Comparatives

^*Denotes Comparative Example; 1 . Slump time through funnel.

Claims

CLAIMS:

1 . A dry mix composition comprising carboxymethyl cellulose alone or in a blend with hydroxyethyl cellulose, one or more setting retardant, and hydraulic cement or lime.

2. The composition as claimed in claim 1 , wherein the carboxymethyl cellulose has a 1 % solution viscosity ranging from 75 to 4400 centiPoise measured as a 1 .0 weight-percent aqueous solution of the cellulose ether at 20 °C, 2.55 s^"1 shear rate with a Haake Rotovisko Model 550.

3. The composition as claimed in claim 2, wherein the viscosity ranges from 1600 centiPoise to 4100 centiPoise.

4. The composition as claimed in claim 1 , wherein the one or more setting retardant comprises a saccharide or carbohydrate.

5. The composition as claimed in claim 4 comprising a weight ratio of the total amount of carboxymethyl cellulose and hydroxyethyl cellulose solids to setting retardant solids ranging from 0.13:1 to 0.65:1 ,

6. The composition as claimed in claim 5, wherein the weight ratio of the total amount of carboxymethyl cellulose and hydroxyethyl cellulose solids to setting retardant solids ranges from 0.25:1 to 0.6:1 .

7. The composition as claimed in any one of claims 1 to 6, wherein the total dosage of carboxymethyl cellulose and hydroxyethyl cellulose solids ranges from 0.007 to 0.06 weight-percent, based on the total solids of the composition.

8. The composition as claimed in any one of claims 1 to 6, wherein the weight ratio of hydroxyethyl cellulose to carboxymethyl cellulose ranges from 0.0:1 .0 to 20:1 .

9. A method of forming a cement stabilized substrate comprising forming a cement slurry by mixing the dry mix composition as claimed in any one of claims 1 to 6 and water to form a cement slurry, adding the cement slurry to a substrate, mixing the cement slurry into the substrate, and grading and compacting the mixture of substrate and cement slurry.

10. The method as claimed in claim 9, wherein the substrate is chosen from asphalt, reclaimed asphalt, concrete, soil, sand and/or aggregate.

1 1 . The method as claimed in claim 9, further comprising grinding up and pulverizing the substrate and blending it with an underlying base to form an enhanced substrate, sub base, and/or sub grade material before adding the cement slurry to the enhanced substrate.

12. The use of the composition as claimed in any one of claims 1 to 6 for modifying the rheology of an aqueous cement slurry or for stabilizing a substrate with the aqueous cement slurry.