WO2001036344A2

WO2001036344A2 - Low retarding, high fluidity producing lignin dispersant for concrete

Info

Publication number: WO2001036344A2
Application number: PCT/US2000/041808
Authority: WO
Inventors: Ashoke K. Sengupta; Jerry D. Gargulak; Lori L. Bushar; Vicky L. Zajakowski
Original assignee: Lignotech Usa, Inc.
Priority date: 1999-11-04
Filing date: 2000-11-02
Publication date: 2001-05-25
Also published as: WO2001036344A3; AU2749901A

Abstract

A lignosulfonate-based cement-dispersant that produces high fluidity in cement pastes, mortar, and the like, without causing excessive set-retardation. Cement compositions dosed with this dispersant harden rapidly, and therefore this dispersant is especially beneficial for use in pre-cast concrete where free flowing but fast-setting cement mixes are highly desirable. The lignosulfonates that can be used in making this dispersant are either sugar-lean, i.e. processed to eliminate most if not all of the otherwise existent sugars, or are modified, i.e. have been ammoxidized by a reaction with ammonia or an amine in the presence of an oxidant. The sugar-lean or the modified lignosulfonate, or a combination of such lignosulfonates, is blended with a ligand such as a carbonate, a bicarbonate, a silicate or a metasilicate that can precipitate multivalent cations, namely, calcium (Ca), magnesium (Mg), and aluminum (Al). The weight ratio of lignosulfonate and the precipitant or a combination of precipitants could vary in the range of 1:0.5 to 1:6, while the dosage of the lignin portion of the dispersant must be at least 0.1 % by weight of the cement.

Description

LOW RETARDING, HIGH FLUIDITY PRODUCING LIGNIN DISPERSANT FOR CONCRETE

FIELD OF THE INVENTION The present invention relates to lignosulfonate-based cement- dispersants that result in extended workability and /or high water- reduction, while offering the benefit of low set- time. More particularly, it relates to water reducers used wholly as, or as a component in, an admixture for concrete.

BACKGROUND OF THE INVENTION Cement dispersants, generally known as water reducers or superplasticizers, are used to increase the strength, and to improve the workability of concrete. When dispersants are added to cement compositions, the cement particles remain deflocculated. Thus, the amount of water that would be otherwise entrapped within the flocculated structures of particles is kept at a minimum, and so are any micro structural defects caused by aggregated particles. In effect, the concrete mix shows high fluidity and therefore good workability. Viewed differently, a dispersant added to a cement paste reduces the amount of water required to produce a given fluidity of the slurry. The outcome is a finished-concrete with high strength.

Many concrete applications set conflicting demands such as the cement composition must be free flowing after mixing, but should harden rapidly after placement, ideally with the rapid development of good strength. For example, in making pre-cast concrete, it is desirable that the cast objects have adequate early- strength so that the mold or form used to shape the concrete can be removed from the object within a day or less, ensuring high production rates. Clearly, in such concrete processing, the greater the fluidity of the concrete-mix, the easier it is to fill the molds with concrete. Lignosulfonate (LS) is a common water reducing agent used in the construction industry. High effectiveness, environmentally benign nature, and low cost make it an attractive additive for concrete admixtures. However, most lignosulfonate s tend to retard the set of fresh concrete. Therefore, to closely meet the foregoing demands faced in some concrete applications, it would be desirable to have a lignin-based dispersant with reduced set-retarding tendency.

A cement matrix presents a harsh environment for any dispersant to function adequately over a long time. High ionic strength and pH of the pore solution, as well as the constantly evolving surface properties of the hydrating cement particles are some of the elements that present such a challenging involvement. The dispersing ability of a polymeric additive depends on its affinity towards the particle surface, the dispersing medium, and itself, as well as on its ability to provide for interparticle repulsion via charge and /or steric mechanisms. For various reasons, these factors are likely to be affected by changes in the cement pore solution and/ or surface conditions. It is, therefore, a matter of considerable challenge to allow the dispersing functionality to last over an extended time in evolving systems such as cement slurries. Setting or hardening of cement is attributed to hydration reactions that cement particles undergo when wetted with water or an electrolyte. A direct outcome of these reactions is the dissolution of multivalent cations such as Ca, Mg, and Al from cement solids into the pore solution. Lignosulfonate, an anionic polymer, can utilize both electrostatic and steric mechanisms in stabilizing particles against aggregation. However, both these stabilization mechanisms are adversely affected by the presence of multivalent cations. The detrimental effects of multivalent cations on the dispersing ability of polyelectrolytes can originate from various phenomena such as the following: i) Surface charge imparted by ionic macromolecules adsorbed on the surface of particles is minimized, or the electrical double layer (EDL) that forms as a result of this surface charge is compressed spatially, resulting in a reduction in the EDL repulsion between the particles.

ii) Spatial expansion (in the form of loops and tails) of the adsorbed polyelectrolytes is reduced, thus lowering the interparticle steric repulsion.

iii) Adsorbed polymer chains on two adjacent particles are joined by a multivalent cation via complexation, thus bridging the particles.

iv) Solvency that water displays toward the polyelectrolytes is reduced, that in turn triggers an aggregating tendency among the adsorbed polymer chains, leading to the flocculation of cement particles and/ or precipitation of the polymer.

Therefore, one way to improve the cement dispersing power of lignosulfonate would be to use it in conjunction with a reagent that can precipitate the aforementioned multivalent cations. Besides, such precipitation of calcium may drive the equilibrium toward further solubilization of calcium. Since calcium-dissolution from cement solids is a basic requirement for cement hydration, the addition of a Ca- precipitant, therefore, may also accelerate the setting of concrete. Several attempts made in the past to produce lignosulfonates with reduced set- retarding property include:

i) Ultrafϊltration, resulting in partial or complete removal of sugars from lignosulfonate-containing liquors ii) Ammoxidation, a method for introducing nitrogen functionality in lignins (including lignosulfonates), that utilizes a reaction with ammonia or an amine and an oxidant, preferably air or oxygen-containing gas mixtures.

Alkali metal carbonates, effective precipitants for Ca, are known to accelerate the setting of cement. Also in the prior art, carbonate and bicarbonate salts have been shown to improve the cement dispersing ability of lignosulfonate, although the reason for such dispersancy- enhancing role of carbonate additives has not been disclosed. Patent literature revealing the use of carbonate or bicarbonate salts in concrete admixture includes the following:

i) U.S. Patent 3, 118,779 to Leonard shows that sodium bicarbonate when added to a Portland cement- type III

(containing gypsum) acts as an accelerator.

ii) U.S. Patent 3,782,984 to Allemand et al. teaches that the addition of alkali bicarbonates in certain proportions to Portland cement accelerates the set-time even in the presence of hydroxylated organic acids (e.g., tartaric and gluconic acid) .

iii) U.S. Patent 2,646,360 to Phillips Petroleum Company teaches that blends of an alkali metal or alkaline earth metal lignosulfonate and an alkali carbonate may be added to a gypsum-containing cement slurry to reduce water loss and thus the amount of water initially needed.

iv) U.S. Patent 3,689,294 to Braunauer claims a method for producing free-flowing and low-porosity cement paste (gypsum-free) with high workability and with a low water-to- cement ratio. A combination of lignosulfonate and alkali carbonate is used. It is shown that the set-time tends to increase with increasing carbonate dosage.

v) U.S Patent 3,960,582 assigned to Westvaco Corporation shows that the set-time could be longer for lignosulfonate and alkali metal bicarbonate blend systems over lignosulfonate and alkali metal carbonate blend systems, claiming a method for making free-flowing cement pastes with the use of the former type of blends.

vi) U.S. Patent 4,019,918 to Martin Marietta Corporation reveals high strength, and low porosity Portland cement (containing gypsum) compositions containing mixtures of lignosulfonate and sodium bicarbonate. The cement compositions are shown to have an adequate plastic period of at least 90 minutes, as well as improved one and twenty-eight day strengths.

vii) U.S. Patent 4,264,367 to Sika Chemical Corporation shows that certain admixtures comprising of water-soluble carbonates and α-hydroxy carbonyl compounds (e.g. lactic acid) can accelerate the setting of Portland cement compositions.

viii) U.S. Patent 4,990, 191 to Westvaco Corporation teaches the use of an aminated lignosulfonate as a fluid loss control additive for hydraulic cement slurry. The slurry also contains sodium carbonate, sodium phosphate, sodium sulfite, sodium metasilicate, and napthalene sulfonate. ix) U.S. Patent 5,076,851 to Ceskoslovenska Akademie VED reveals a mixed gypsumless Portland cement of high initial and long-lasting strengths, that contains 0.1-3 weight percent of a sulfonated polyelectrolyte including lignosulfonate, and 0.5-6 weight percent of an alkaline carbonate.

x) U.S. Patent 5,350,450 to Sandoz Ltd. shows an improved method for applying a cementitious composition to a surface, for use in shotcreting applications where rapid hardening (set-time in the order of 15 minutes) of concrete is desirable.

The method involves adding to the cementitious composition an admixture comprised of the following: i) 0.001-5% (by weight of the cement) of a set retarding agent including a lignosulfonate, ii) 1.0- 10% of a cement quick-setting agent including alkali metal and alkaline earth metal carbonates, iii) 0.01-2% of a cement dispersant including a lignosulfonate, and iv) 0.01-0.2% of a slow release dispersing agent, that hydrolyzes under alkaline conditions to form a dispersant.

xi) U.S. Patent 5,792,252 assigned to MBT Holding AG reveals that carbonate, normally regarded as an accelerator, acts as a retardant in the presence of a tricarboxylic acid alkali metal salts such as trisodium or tripotassium citrates.

Unless subjected to a de-sugaring process, all commercial lignosulfonate products inevitably contain a considerable amount of sugars such as saccharides and/ or sugar acids that are known to function as retardants. The prior art on the use of a mixture of lignosulfonate and a water-soluble carbonate does not reveal nor seek any effects on performance properties, arising due to some compositional features and/ or chemical make-up of the lignosulfonate products used therein. As a result, it remains unknown whether any dispersancy- enhancement and set-acceleration effects achieved through the addition of carbonate in conjunction with lignosulfonate are greater for certain types of lignosulfonate products over others. For example, it is yet to be disclosed whether the set-accelerating influence of carbonate will be more pronounced for de-sugared lignosulfonate products or for some specifically modified ligno sulfonate s, as compared to ordinary lignosulfonate products. These voids provide the motivation for the investigation that led to the present invention.

SUMMARY OF THE INVENTION A dispersant in accordance with the present invention comprises a sugar-lean (also referred to herein as de-sugared) lignosulfonate (LS) and/ or a specifically modified (ammoxidized) lignosulfonate that is blended with a multivalent cation precipitant, or a combination of such precipitants that can precipitate calcium (Ca), magnesium (Mg), and /or aluminum (Al). When used in cement compositions, this dispersing agent results in substantially higher fluidity and much less set-retardation as compared to any ordinary lignosulfonate product or the lignosulfonate from which it is derived. Such increased fluidity is comparable to or greater than that produced by additives that are commonly known as superplasticizers. Also, with the proper selection of dispersant dosage and blend ratio, the enhanced dispersancy and therefore the increased workability can be retained over an extended time. Since high fluidity and low set-retardation of a concrete mix is highly desirable for pre-cast operations, it is an objective of the present invention to provide a lignosulfonate-based dispersant for such applications. Yet another object is to provide a dispersant of the above type, that is relatively inexpensive and environmentally benign. As noted, a sugar-lean lignosulfonate, or a modified lignosulfonate, or blends of sugar-lean and modified ligno sulfonate s may be used as the lignosulfonate component of the present dispersant. The sugar-lean lignosulfonate (LS) comprises a processed LS product, where all or substantially all of the otherwise existent sugars, for example saccharides and sugar acids, have been eliminated. The processed lignosulfonate used in the present invention is a de-sugared lignosulfonate (LS), that has been subjected to a mechanical, a physiochemical, or a chemical de- sugaring process. Examples of mechanical and physiochemical processes include: i.) ultrafϊltration where the de-sugared LS is obtained as the retentate after ultrafϊltration of LS-bearing liquors, ii) precipitation followed by filtration where the de-sugared LS is obtained after chemically precipitating the LS and then recovering the LS by filtration, and iii) chromatographic separation. Also included in the list of processed ligno sulfon ate s that could be used herein are lignosulfonate products that have been de-sugared chemically, for example, via strong oxidation, leading to the conversion of sugars to carbon dioxide. Methods for chemically de-sugaring lignosulfonate products may include ozone or hydrogen peroxide oxidation, high temperature destruction in combination with high pH and/ or bisulfite, as well as various fermentation methods. On the other hand, the specifically modified lignosulfonate used herein is obtained by the aqueous-phase reaction of lignin with ammonia or an amine in the presence of an oxidant, a process known as ammoxidation.

The sugar- lean lignosulfonate or the modified lignosulfonate, or a combination of sugar-lean and modified lignosulfonates, is blended with a multivalent cation-precipitant that includes ligands such as carbonates, bicarbonates, silicates or metasilicates used either singly or in combinations. These reagents by themselves do not show any cement dispersing ability toward Portland Type 1 cement. The weight ratio of the sugar-lean LS or the modified LS to the precipitant reagent may vary from 1:0.5 to 1 :6, and more preferably from 1 : 1 to 1 :2. To achieve the desired effects or results, the dosage of the active portion (the sugar-lean LS or the modified LS) of the dispersant must be at least 0.1% by weight of dry cement, and may be as high as 1.5% by weight, while the dosage of the multivalent cation precipitant may be from 0.1% to 3% by weight of dry cement.

DETAILED DESCRIPTION OF THE INVENTION The term "lignin", as is used herein, refers to the substance typically recovered from the organosolv process, or from alkaline black pulping liquors, such as those produced in the kraft, soda, and other alkaline pulping operations, as well as the lignosulfonates. The term "lignosulfonate" used in this specification, refers to the product that is obtained by the introduction of sulfonic groups into the lignin molecule, i.e. sulfonated lignins as well as sulfite lignins. Lignin may be sulfonated by the reaction with sulfite or bisulfite compounds via the well-known sulfonation or sulfoalkylation processes such as high temperature sulfonation, oxidative sulfonation at ambient temperature, or sulfoalkylation involving a reaction of lignin with sodium sulfite and an aldehyde. Sulfite lignin, inherently obtained during sulfite pulping of wood, straw, corn stalks, bagasse, and the like, and that is a principal constituent of the spent sulfite liquor obtained from that process, is also included in the phrase "lignosulfonate". Also included in the term "lignosulfonate" are spent sulfite liquors that may be used "as is" or may be further reacted, purified, fractionated, and the like.

The preferred "sugar-lean" or "de-sugared" lignosulfonate is an ultrafiltered lignosulfonate. The terms "sugar-lean" or "de-sugared" are meant to encompass lignosulfonate products containing 2% or less of sugars, and preferably 1% or less of sugars. The method of calculating the percentage of sugar is determined by the reducing sugars method practiced in the industry (Brown, C.A., and Zerban, F.W. "Sugar Analysis," 3^rd Edition, John Wiley & Sons, Inc., 1941). The term "sugars" is meant to include any of various water-soluble carbohydrates normally referred to as sugars in this industry and typically contained in lignosulfonates, including but not limited to saccharides such as mono- or di-saccharide sugars like sucrose, manose, arabinose, rhamnose, galactose, glucose and xylose, as well as polymerized sugars or sugar acids such as gluconic acid and mono- or di-carboxylic acid decomposition products of the above sugars. Lignosulfonates, both of hardwood and softwood origin, may be utilized herein in the "as is" or whole liquor condition, or in a purified form, partially or fully devoid of sugars as noted previously herein, or additionally of inorganic constituents such as sodium chloride, sodium sulfate, sodium sulfite, and various other ionic species or salts. In addition, lignosulfonates in various salt-forms including sodium lignosulfonates, calcium lignosulfonates, sodium/ calcium lignosulfonates, ammonium lignosulfonates, potassium lignosulfonates, magnesium lignosulfonates, potassium/ calcium lignosulfonates, and mixtures or blends thereof may also be utilized herein. Examples of processed lignosulfonates suitable for use in making the disclosed dispersant include Ultrazine NA, Ultrazine NAC (manufactured by Borregaard LignoTech), Ultrafine (manufactured by Georgia Pacific), Marasperse N3 (an ozone-oxidized product made by Borregaard LignoTech), and Marasperse AG (a sulfoalkylated product manufactured by Borregaard LignoTech) .

Specifically modified lignosulfonates of use in the present invention are those which have been ammoxidized, i.e. reacted with ammonia or an amine in the presence of an oxidant. Lignosulfonates to be used in making ammoxidized products may be obtained from any number of commercial sources. Some typical lignosulfonates that may be used in this reaction include: sodium lignosulfonate such as Lignosol SFX-65 and Borresperse NA (manufactured by Borregaard LignoTech); calcium lignosulfonate such as Lignosite 50 (manufactured by Georgia Pacific); sodium/ calcium lignosulfonate such as Norlig 24C; ultrafiltered sodium and calcium lignosulfonates such as Ultrazine NA and Ultrazine CA (all manufactured by Borregaard LignoTech), respectively.

Generally, the ammoxidation reaction is carried out by dissolving the lignosulfonate in water to a solids level of 10 to 60%, more preferably to a level of 30%, adjusting the pH to 6- 10, adding the desired amine and oxidant, and heating for 0.25 to 20 hours at 90-180 C. The reaction is most easily carried out in a pressure reactor. Sulfonated lignin used for this process may be obtained either from lignosulfonate or from sulfonation of Kraft or organosolve lignin. Oxidizing agents such as oxygen, air, hydrogen peroxide, ozone are considered as acceptable oxidants. The amines that may be reacted with lignosulfonate include ammonia, and other primary and secondary alkyl amines such as pentaethylenehexamine, hexamethyleneamine and the like. In particular, organic amines that may be reacted with lignosulfonate are primary amines such as methylamine, ethylamine, ethylenediamine, benzylamine or aniline, secondary amines such as dimethylamine, diethylamine, diisobutylamine, methylphenylamine and ethylbenzylamine, and tertiary amines like trimethylamine, triethylamine or tributylamine. The amount of oxidant used is between 0.01 to 2 moles per 100 g of lignosulfonate, more preferably between 0.15 to 0.25 moles per 100 g of lignosulfonate. The lignosulfonate or the sulfonated lignin can be treated with oxidizing agents such as hydrogen peroxide and the like prior to ammoxidation. A set of typical reaction conditions for ammoxidation includes 28% lignin solids by weight of the reaction mixture, 3% ammonia by weight of the lignin, 3-6% hydrogen peroxide by weight of the lignin, heating at 165°C under 200 psi of oxygen or air pressure for 1 hour.

The multivalent cation-precipitant used in the dispersant disclosed herein is selected from the group of a water-soluble sodium, potassium, lithium or ammonium carbonate, bicarbonate, silicate or metasilicate and the like, used either singly or in combinations. The weight ratio of lignosulfonate and the foregoing precipitant-reagent in the blend may vary from 1 :0.5 to 1 :6, and more preferably between 1 : 1 and 1:2. The two reagents in the blend may be mixed together (either by dry blending or preferably by blending in solution form) prior to addition in cement compositions or they may be added separately to a carrier such as water used in mixing the cement composition. In the latter case, either of the two reagents may be added prior to the other. When the two reagents are mixed together while they are in solution, forming a liquid dispersant additive to be added to cement or concrete, the total amount of solids (the combined weight of the two reagents) in this liquid product could vary between 10% and 50%.

The dosage of the active part (the sugar-lean LS or the modified LS) of the dispersant can vary in the range of 0.1% to 1.5% by weight of dry cement, while the most preferred dosage is 0.5%. The multivalent cation precipitant may be present in the range of 0.1% to 3% by weight of dry cement. This yields a free-flowing cement paste or a mortar composition with considerably reduced set-times as compared to any ordinary lignosulfonate used alone or the original lignosulfonate. The dispersant is generally added all at once at the time of mixing of the cement composition, although it may be added incrementally as well.

Cement is a material that binds together solid bodies such as sand and gravel (aggregate) by hardening from a plastic state. An inorganic cement, used for construction, functions by forming a plastic paste when mixed with water and develops rigidity (sets) and then steadily increases in compressive strength (hardens) by chemical reactions with water (hydration).

The type of cements that this dispersant would be effective in include, but is not limited to, Portland cements, combined Portland cements (e.g. combined with pulverized flyash), Pozzolanic cements, white cements, and oil well cements. It may also be used in mortar, as well as in gypsum pastes (or slurries) used in making gypsum board, and thus it is specifically intended that the term "cement" also include mortar, and gypsum pastes. Other potential dispersion applications for this additive include, but are not limited to, carbon black, clays, mineral slurries, and pigments. Concrete is a composite material made with cement, water, and aggregates such as sand and gravel. A typical example of how these materials are proportioned for concrete are 2: 1 :4:6. This may vary widely depending on a number of factors, including strength, cost and other specifications. Upon hydration of this mixture concrete is formed. A typical concrete composition comprises from about 5% to 25% by weight cement, from about 3% to 12% by weight water, and from about 60% to 90% by weight aggregate. If the composition includes cement, water and sand, but no gravel, the material is typically referred to as mortar.

The practice of this invention may be seen in the following section where dispersancy and set- time performances of the disclosed dispersant(s) in various brands of Potland Type I cement are illustrated.

EXAMPLE 1

Illustration of dispersancy enhancement effect of carbonate An ammoxidized lignosulfonate or a mixture of an ammoxidized lignosulfonate and sodium carbonate is added to a cement paste comprising of 250 g of Type I Portland cement, and 200 g of water (w/c = 0.8). The viscosity of the resulting slurry is recorded at various times measured from the instant cement is mixed with water containing a dispersant. A Brookfield viscometer is used for recording the slurry- viscosity. A set of such slurry-viscosity tests is carried out varying the type of lignosulfonate and the carbonate dosage. All slurry-viscosity measurements are carried out at 20 rpm using a #2 spindle. The slurry is mixed thoroughly to re-suspend any settled mass of cement just before the slurry-viscosity is measured. Enhancement in cement dispersing ability of the lignosulfonates achieved by the addition of carbonate is quantified using an enhancement-factor that is the ratio of slurry-viscosity in the presence of a mixture of lignosulfonate and carbonate, and in the presence of the lignosulfonate alone. The lower the slurry-viscosity, the stronger is the dispersancy. Therefore, an enhancement-factor of < 1 implies an increase in dispersancy; the smaller the value, the greater is the enhancement. The results of these tests are presented in Table I for ammoxidized Ultrazine NAC (ultrafiltered sodium lignosulfonate of softwood origin), and in Table II for ammoxidized Lignosite 50 (calcium lignosulfonate of softwood origin), where all dosage values are by weight of the cement.

Table I (Lignosulfonate: Ammoxidized Ultrazine NAC)

Lignosulfonate Carbonate Elapsed Time, Enhancement

Dosage, % Dosage, % min Factor

^~05 05 5 0.06

10 0.06

15 0.06

20 0.07

25 0.08

30 0.13

0.5 0.75 5 0.06

10 0.06

15 0.06

20 0.06

25 0.08

30 0.13 Table II (Lignosulfonate: Ammoxidized Lignosite 50)

Lignosulfonate Carbonate Elapsed Time, Enhancement

Dosage, % Dosage, % min Factor

0.5 0.25 5 0.06

10 0.21

15 0.76

20 1.1

0.5 0.3 5 0.06

10 0.06

15 0.31

20 0.64

25 1.1

0.5 0.5 5 0.06

10 0.05

15 0.04

20 0.04

25 0.04

30* 0.08

*The slurry viscosity was 320 cps after 45 minutes as compared to 570 cps after 30 minutes in the absence of 0.5% sodium carbonate.

EXAMPLE 2

Illustration of set-time benefit of blends of carbonate and a ultrafiltered Na-LS

A mixture of sodium carbonate and ammoxidized Ultrazine NAC is added to a mortar mixture consisting of 450 g of Type 1 Portland cement, 1350 g of sand, and 184.5 g of water. To an identical mortar mixture is added individually i) a mixture of sodium carbonate and Ultrazine NAC, ii) Ultrazine NAC, and iii) ammoxidized Ultrazine NAC. The blend ratio (1 : 1) of carbonate and lignosulfonate (LS) is identical for the two mortar compositions receiving carbonate-LS mixture, and the lignosulfonate dosage is the same for the four mortar compositions. Two additional mortar compositions were prepared, that received carbonate-LS mixture at a blend ratio of 1 : 1.5.

For all mortar compositions, the cement dispersing ability of the lignosulfonate samples is determined following a procedure described in ASTM C87, which uses a flow table such as the one described in ASTM C230. Entrained air may contribute to flow; therefore, tributyl phosphate, a defoamer, is added to keep the air content of mortar compositions low. The set-time is determined by monitoring the transient variation of temperature of a mass of mortar taken in an insulated cup, using a thermocouple probe. As the mortar undergoes the initial set, the liberated heat of hydration of cement causes a sharp rise in temperature of the mortar mass. The time at which the temperature vs. time plot

(obtained by joining the data points with straight lines) shows a change in slope is taken as the set- time. The results of such performance testing are shown in Table III.

Table III

Sample Flow, Set Time, cm Hour

0.5% Ultrazine NAC 16 1 1.4

0.5% Ultrazine NAC + 0.33% Na₂CO₃ 18.9 10.5

0.5% Ultrazine NAC + 0.5% Na CO₃ 19.9 9.8

0.5% Ammoxidized Ultrazine NAC 17.6 9.6

0.5% Ammoxidized Ultrazine NAC + 0.33% 1 199..66 9.2

Na C0₃

0.5% Ammoxidized Ultrazine NAC + 0.5% 19.9 8

Na₂CO₃ It may be seen that the addition of carbonate improves the dispersing ability of both Ultrazine NAC and its ammoxidized form. Also, carbonate is found to act as an accelerator in the presence of both lignosulfonates. Furthermore, while there is a considerable reduction in set-time after ammoxidation, the addition of carbonate reduces the set- time still further.

EXAMPLE 3

Illustration of set-time benefit of blends of carbonate with an ammoxidized softwood Na-LS.

To illustrate the set-time benefit of a mixture of ammoxidized lignosulfonate and carbonate over a similar mixture of unmodified lignosulfonate and carbonate, mortar compositions similar to the ones described in Example 2 were prepared and tested, using Lignosol SFX-65 and its ammoxidized form individually as the dispersant. The results of these mortar tests are shown in Table IV.

Table IV

Sample Flow, Set Time, cm Hour

0.5% Lignosol SFX-65 Ϊ β fl

0.5% Lignosol SFX-65 + 0.33% Na₂C0₃ 21.2 16.7

0.5% Lignosol SFX-65 + 0.5% Na₂C0₃ 20.5 14.5

0.5% Ammoxidized Lignosol SFX-65 17.1 10.1

0.5% Ammoxidized Lignosol SFX-65 + 0.33% 21.4 12.5

Na₂C0

0.5% Ammoxidized Lignosol SFX-65 + 0.5% 21.3 10.1

Na C0₃

0.5% Ammoxidized Lignosol SFX-65 + 0.75% 21.7 9.1

Na₂C0₃ Apparently, carbonate acts as a retardant in the presence of Lignosol SFX-65, a product that contains a considerable amount of sugar and sugar acids. However, this retarding effect of carbonate is minimized as the carbonate dosage is increased. As evident from Table IV, a lower set-time is achieved with certain blends of ammoxidized Lignosol SFX-65 and carbonate, as compared to similar blends of the unmodified lignosulfonate and carbonate, or the unmodified lignosulfonate itself.

EXAMPLE 4 Illustration of set- time benefit of blends of carbonate and an ammoxidized hardwood Na/Ca-LS

Mortar compositions similar to the ones in Examples 2 and 3 were prepared and tested for flow and set time. The cement used, Portland Type 1 , however, is made by a different manufacturer as compared to the cement used in the previous examples. The lignosulfonate product from which the ammoxidized sample was prepared is Norlig 24C (sodium/ calcium lignosulfonate of hardwood origin). The results of these mortar tests are shown in Table V, demonstrating that blends of the ammoxidized lignosulfonate and carbonate result in set-times that are considerably lower than that found with the unmodified lignosulfonate.

Table V

Sample Flow, Set Time, cm Hour

0.5% Norlig 24C 14.6 11.5

0.5% Ammoxidized Norlig 24C 15.4 10.1

0.5% Ammoxidized Norlig 24C + 0.5% 19.6 9.3

Na₂CO₃

0.5% Ammoxidized Norlig 24C + 0.75% 20.1 9.1

Na₂CO₃

0.5% Ammoxidized Norlig 24C + 1% Na₂CO₃ 20.3 9

0.5% Ammoxidized Norlig 24C + 1.5% 20.1 7.9

Na C0₃ EXAMPLE 5

Illustration of set-time benefit of blends of carbonate and an ammoxidized softwood Ca-LS

Mortar compositions similar to the ones in Examples 2 through 4 were prepared and tested for flow and set time. The same brand of cement as in example 4 is used herein, although the cement had longer storage-period as compared to the one used in example 4. The lignosulfonate product from which the ammoxidized sample was prepared is Lignosite 50 (calcium lignosulfonate with softwood origin). The set- time benefit achieved from blends of the ammoxidized LS and carbonate is shown in Table VI.

Table VI

Sample Flow, Set Time, cm Hour

0.5% Lignosite 50 21.5 14.2

0.5% Ammoxidized Lignosite 50 19.7 1 1.1

0.5% Ammoxidized Lignosite 50 + 0.5% 21.4 9.9

Na₂COs

0.5% Ammoxidized Lignosite 50 + 1% 20.3 5.1

Na₂C0

0.5% Ammoxidized Lignosite 50 + 1.5% 20.5 3.1

Na C^Q ₃

EXAMPLE 6

Illustration of the beneficial effects of blends of metasilicate and an ammoxidized softwood Na/Ca-LS

Mortar compositions similar to the ones in the previous examples were prepared and tested for flow and set time. The cement used is the same as the one in Example 4. Lignosite 50 is the lignosulfonate product from which the ammoxidized sample was prepared. Sodium metasilicate obtained from Aldrich Chemicals contained 44-47% SiO₂. The results of the mortar tests are shown in Table VII, demonstrating dispersancy- enhancement as well as set-time gains achievable from certain blends of metasilicate and the ammoxidized LS.

Table VII

Sample Flow, cm Set

Time, Hour

0.5% Lignosite 50 15.5 11.1

0.5% Ammoxidized Lignosite 50 17.2 7.6

0.5% Ammoxidized Lignosite 50 + 0.75% Na- 18.9 10.3 metasilicate

0.5% Ammoxidized Lignosite 50 + 1.5% Na- 19.2 12.4 metasilicate

0.5% Ammoxidized Lignosite 50 + 2.3% Na- 18.2 10.2 metasilicate

0.5% Ammoxidized Lignosite 50 + 3% Na- 19.2 7.6 metasilicate

EXAMPLE 7

Examples 2 through 5 demonstrate that in the presence of carbonate, a de-sugared lignosulfonate such as ultrafiltered lignosulfonate, or an ammoxidized lignosulfonate, would result in set- times that are considerably lower than that seen in the absence of carbonate, or that found typically with ordinary or unmodified lignosulfonates. Apparently, therefore, the removal of sugar and sugar acids from lignosulfonate products facilitates set-acceleration by carbonate. The present example provides an additional confirmation of these findings based on the results of mortar tests performed using a Type I Portland cement made by a different manufacturer as compared to the cements used in the previous examples. The test results are presented in Table VIII, where Norlig 12 is a full-sugared hardwood product, and Marasperse N3 an ozone-oxidized softwood product where sugars have been mostly converted to carbon dioxide. Table VIII

Sample Flow, cm Set

Time, Hour

0.5% Ultrazine NAC 16.2 13.5

0.5% Ultrazine NAC + 0.75% Na₂C0₃ 17 12.3

0.5% Ultrazine NAC + 0.8% Na₂C0₃ 20.1 8.0

0.5% Norlig 12 16.4 14.5

0.5% Norlig 12 + 0.75% Na₂CO₃ 19.7 16.9

0.5% Marasperse N3 19.4 12.4

0.5% Marasperse N3 + 0.75% Na C0₃ 20.5 13.4

0.5% Ammoxidized Lignosite 50 16.9 8.1

0.5% Ammoxidized Lignosite 50 + 0.75% 20.7 8.9

Na₂C0₃

0.5% Ammoxidized Lignosite 50 + 1% Na₂CO₃ 18.3 7.1

As evident from Table VIII, carbonate acts as a strong retardant in the presence of the full- sugared lignosulfonate product Norlig 12, while it acts as an accelerator in the presence of de-sugared lignosulfonate Ultrazine NAC. Also, the set-retarding effect of carbonate is much less with Marasperse N3 than with Norlig 12. It may be noted that for the cement used in examples 5 and 6, a mortar mass containing a mixture of 0.5% Norlig 12 and 1% Na C0₃ did not set, i.e. did not show the characteristic temperature rise (following an induction period) even after an extended time. Also, note that even for Lignosol SFX-65 that contains considerable amounts of sugars and sugar acids, the set times increased considerably as a result of carbonate addition, as shown in Table IV.

EXAMPLE 8

For the purpose of comparison, this example illustrates the effect of carbonate addition on dispersancy and set-time in the presence of a synthetic dispersant (polynapthalene sulfonate, PNS). Mortar tests were carried out similarly as in the previous examples, whose results are shown in Table IX. The cement used is the same as the one used in Example 5.

Table IX

Sample Flow, cm Set Time, Hour

0.5% PNS 16.5 5.5

0.5% PNS + 0.5% Na₂CO₃ 21.8 5.5

0.5% PNS + 1% Na₂COs 19.8 3.9

The set-acceleration effect of carbonate is evident; however, it was found separately that the dispersancy-enhancement effect lasts over a much shorter time with PNS than with lignosulfonate, as shown in Table X.

Table X

Dispersant, Carbonate Elapsed EnhanceDosage, % Time, min ment Factor

0.5% Ammoxidized Lignosite 0.5 5 0.16 50 10 0.06

15 0.04

20 0.03

25 0.02

30 0.02*

0.5% Polynapthalene 0.5 5 0.04 sulfonate

10 0.02

15 0.02

20 0.02

25 0.04

30 0.54** *The slurry viscosity was 18 cps after 60 minutes in the presence of carbonate as compared to 830 cps after 30 minutes without the carbonate.

** The slurry viscosity was 760 cps after 35 minutes in the presence of carbonate as compared to 800 cps after 30 minutes without the carbonate.

Claims

CLAIMS We claim:

1. A cement dispersant comprising a blend of a lignosulfonate selected from the group consisting of a de-sugared lignosulfonate, a modified lignosulfonate, and mixtures thereof, and a precipitating agent for multivalent cations.

2. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate contains 2% or less of sugars.

3. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from ultrafiltration.

4. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate precipitated from a lignosulfonate-containing liquor.

5. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from oxidation of sugars to carbon dioxide.

6. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained by fermentation of sugars to carbon dioxide.

7. The cement dispersant of claim 1 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from chromatographic separation.

8. The cement dispersant of claim 1 wherein said modified lignosulfonate comprises an ammoxidized lignosulfonate.

9. The cement dispersant of claim 1 wherein the weight ratio of said lignosulfonate and the multivalent cation precipitating agent comprises from 1 :0.5 to 1:6.

10. The cement dispersant of claim 1 wherein said lignosulfonate is selected from the group consisting of a sulfonated lignin and a sulfite lignin.

1 1. The cement dispersant of claim 1 wherein said lignosulfonate is selected from the group consisting of calcium lignosulfonate, sodium lignosulfonate, ammonium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, sodium-calcium lignosulfonate and potassium- calcium lignosulfonate.

12. The cement dispersant of claim 1 wherein said multivalent cation precipitating agent is selected from the group consisting of a water- soluble carbonate, a bicarbonate, a silicate and a metasilicate.

13. The cement dispersant of claim 12 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

14. A concrete composition comprising an admixture of the following components:

(a) from about 5% to 25% by weight cement;

(b) from about 3% to 12% by weight water; (c) from about 60% to 90% by weight aggregate; and

(d) from about 0.2% to 4.5% by weight of a cement dispersant comprising a blend of a lignosulfonate selected from the group consisting of a de-sugared lignosulfonate, a modified lignosulfonate, and mixtures thereof, and a precipitating agent for multivalent cations, said components totaling 100% by weight of the composition.

15. The concrete composition of claim 14 wherein said de-sugared lignosulfonate contains 2% or less of sugars.

16. The concrete composition of claim 15 wherein said de- sugared lignosulfonate comprises a purified lignosulfonate obtained from ultrafiltration.

17. The concrete composition of claim 15 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate precipitated from a lignosulfonate-containing liquor.

18. The concrete composition of claim 15 wherein said de- sugared lignosulfonate comprises a purified lignosulfonate obtained from oxidation of sugars to carbon dioxide.

19. The concrete composition of claim 15 where said de-sugared lignosulfonate comprises a purified lignosulfonate obtained by fermentation of sugars to carbon dioxide.

20. The concrete composition of claim 15 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from chromatographic separation.

21. The concrete composition of claim 14 wherein said lignosulfonate comprises from 0.1% to 1.5% by weight of dry cement.

22. The concrete composition of claim 14 wherein said multivalent cation precipitating agent comprises from 0.1% to 3% by weight of dry cement.

23. The concrete composition of claim 14 wherein the weight ratio of said lignosulfonate and the multivalent cation precipitating agent comprises from 1:0.5 to 1:6.

24. The concrete composition of claim 14 wherein said lignosulfonate is selected from the group consisting of a sulfonated lignin and a sulfite lignin.

25. The concrete composition of claim 14 wherein said lignosulfonate is selected from the group consisting of calcium lignosulfonate, sodium lignosulfonate, ammonium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, sodium-calcium lignosulfonate and potassium-calcium lignosulfonate.

26. The concrete composition of claim 14 wherein said multivalent cation precipitating agent is selected from the group consisting of a water- soluble carbonate, a bicarbonate, a silicate and a metasilicate.

27. The concrete composition of claim 26 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

28. A cement composition comprising an admixture of the following components:

(a) from about 40% to 80% by weight cement;

(b) from about 20% to 60% by weight water; and

(c) from about 0.2% to 4.5% by weight of a cement dispersant comprising a blend of a lignosulfonate selected from the group consisting of a de-sugared lignosulfonate, a modified lignosulfonate, and mixtures thereof, and a precipitating agent for multivalent cations, said components totaling 100% by weight of the composition.

29. The cement composition of claim 28 wherein said de-sugared lignosulfonate contains 2% or less of sugars.

30. The cement composition of claim 28 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from ultrafiltration.

31. The cement composition of claim 28 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate precipitated from a lignosulfonate-containing liquor.

32. The cement composition of claim 28 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from oxidation of sugars to carbon dioxide.

33. The cement composition of claim 28 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained by fermentation of sugars to carbon dioxide.

34. The cement composition of claim 28 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from chromatographic separation.

35. The cement composition of claim 28 wherein said lignosulfonate comprises from 0.1% to 1.5% by weight of dry cement.

36. The cement composition of claim 28 wherein said multivalent cation precipitating agent comprises from 0.1% by 3% by weight of dry cement.

37. The cement composition of claim 28 wherein the weight ratio of said lignosulfonate and the multivalent cation precipitating agent comprises from 1 :0.5 to 1.6.

38. The cement composition of claim 28 wherein said ligno sulfoante is selected from the group consisting of a sulfonated lignin and a sulfite lignin.

39. The cement composition of claim 28 wherein said lignosulfonate is selected from the group consisting of calcium lignosulfonate, sodium lignosulfonate, ammonium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, sodium-calcium lignosulfonate and potassium-calcium lignosulfonate.

40. The cement composition of claim 28 wherein said multivalent cation precipitating agent is selected from the group consisting of a water- soluble carbonate, a bicarbonate, a silicate and a metasilicate.

41. The cement composition of claim 40 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

42. The cement composition of claim 28 wherein said cement is selected from the group consisting of Portland cement, combined Portland cement, Pozzolanic cement, white cement, oil well cement, mortar, and gypsum paste.

43 A method of reducing the set-retarding tendency of a ligno sulfonate -based cement dispersant, comprising the steps of: removing sugars from a lignosulfonate to form a de-sugared lignosulfonate containing 2% or less of sugars; and mixing with said de-sugared lignosulfonate a precipitating agent for multivalent cations to form a blend.

44. The method of claim 43 wherein the step of removing sugars comprises ultrafiltering said lignosulfonate to obtain said de- sugared lignosulfonate as a retentate.

45. The method of claim 43 wherein the step of removing sugars comprises oxidizing the sugars to carbon dioxide.

46. The method of claim 45 wherein said oxidizing step utilizes an oxidizing agent selected from the group consisting of oxygen, air, hydrogen peroxide and ozone.

47. The method of claim 43 wherein the step of removing sugars comprises precipitating said lignosulfonate from a lignosulfonate- containing liquor.

48. The method of claim 43 wherein the step of removing sugars comprises fermenting said lignosulfonate to convert sugars to carbon dioxide.

49. The method of claim 43 wherein the step of removing sugars comprises chromatographically separating said lignosulfonate.

50. The method of claim 43 wherein the weight ratio of said de- sugared lignosulfonate and the multivalent cation precipitating agent comprises from 1:0.5 to 1 :6 in said blend.

51. The method of claim 43 wherein said lignosulfonate is selected from the group consisting of a sulfonated lignin and a sulfite lignin.

52. The method of claim 43 wherein said lignosulfonate is selected from the group consisting of calcium lignosulfonate, sodium lignosulfonate, ammonium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, sodium-calcium lignosulfonate and potassium-calcium lignosulfonate.

53. The method of claim 43 wherein said multivalent cation precipitating agent is selected from the group consisting of a water-soluble carbonate, a bicarbonate, a silicate and a metasilicate.

54. The method of claim 53 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

55. The method of claim 43 further including the step of mixing said blend with a cement selected from the group consisting of Portland cement, combined Portland cement, Pozzolanic cement, white cement, oil well cement, mortar and gypsum paste.

56. A method of reducing the set-retarding tendency of a lignosulfonate-based cement dispersant comprising the steps of: ammoxidizing a lignosulfonate to form a modified lignosulfonate; and mixing with said modified lignosulfonate a precipitating agent for multivalent cations to form a blend.

57. The method of claim 56 wherein ammoxidizing said lignosulfonate comprises reacting the lignosulfonate with an amine and an oxidizing agent under oxidizing conditions.

58. The method of claim 57 wherein said amine is selected from the group consisting of primary alkyl amines, secondary alkyl amines and tertiary alkyl amines.

59. The method of claim 57 wherein said amine is ammonia.

60. The method of claim 57 wherein said oxidizing agent is selected from the group consisting of oxygen, air, hydrogen peroxide and ozone.

61. The method of claim 56 wherein the weight ratio of said modified lignosulfonate and the multivalent cation precipitating agent comprises from 1:0.5 to 1 :6 in said blend.

62. The method of claim 56 wherein said lignosulfonate is selected from the group consisting of a sulfonated lignin and a sulfite lignin.

63. The method of claim 56 wherein said lignosulfonate is selected from the group consisting of calcium lignosulfonate, sodium lignosulfonate, ammonium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, sodium-calcium lignosulfonate and potassium-calcium lignosulfonate.

64. The method of claim 56 wherein said multivalent cation precipitating agent is selected from the group consisting of a water-soluble carbonate, a bicarbonate, a silicate and a metasilicate.

65. The method claim 64 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

66. The method of claim 56 further including the step of mixing said blend with a cement selected from the group consisting of Portland cement, combined Portland cement, Pozzolanic cement, white cement, oil well cement, mortar and gypsum paste.

67. A method of making a pre-cast concrete structure comprising the steps of:

(a) providing a concrete composition containing a dispersant comprised of an admixture of a lignosulfonate selected from the group consisting of a de-sugared lignosulfonate, a modified lignosulfonate, and mixtures thereof, and a precipitating agent for multivalent cations; and

(b) filling a mold with said concrete composition.

68. The method of claim 67 wherein the step of providing a concrete composition includes the step of mixing said dispersant directly into said concrete composition.

69. The method of claim 67 wherein said concrete composition includes cement, and the step of providing a concrete composition includes the step of mixing said dispersant with said cement and subsequently mixing said cement and dispersant with water and aggregate to form said concrete composition.

70. The method of claim 67 further including the step of blending said admixture so that the weight ratio of said lignosulfonate and the multivalent cation precipitating agent comprises from 1 :0.5 to 1:6.

71. The method of claim 67 wherein said de-sugared lignosulfonate contains 2% or less of sugars.

72. The method of claim 67 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from ultrafiltration.

73. The method of claim 67 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate precipitated from a lignosulfonate-containing liquor.

74. The method of claim 67 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from oxidation of sugars to carbon dioxide.

75. The method of claim 67 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained by fermentation of sugars to carbon dioxide.

76. The method of claim 67 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from chromatographic separation.

77. The method of claim 67 wherein said modified lignosulfonate comprises an ammoxidized lignosulfonate.

78. The method of claim 67 wherein said multivalent cation precipitating agent is selected from the group consisting of a water-soluble carbonate, a bicarbonate, a silicate and a metasilicate.

79. The method of claim 78 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.

80. A method of making a concrete composition having relatively high fluidity that lasts over an extended time, and relatively low set retardation, comprising the steps of:

(a) providing a concrete composition; and

(b) mixing with said concrete composition a dispersant comprised of an admixture of a lignosulfonate selected from the group consisting of a de-sugared lignosulfonate, a modified lignosulfonate, and mixtures thereof, and a precipitating agent for multivalent cations.

81. The method of claim 80 further including the step of blending said dispersant so that the weight ratio of said lignosulfonate and the multivalent cation precipitating agent comprises from 1:0.5 to 1:6.

82. The method of claim 80 wherein said de-sugared lignosulfonate contains 2% or less of sugars.

83. The method of claim 80 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from ultrafiltration.

84. The method of claim 80 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate precipitated from a lignosulfonate-containing liquor.

85. The method of claim 80 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from oxidation of sugars to carbon dioxide.

86. The method of claim 80 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained by fermentation of sugars to carbon dioxide.

87. The method of claim 80 wherein said de-sugared lignosulfonate comprises a purified lignosulfonate obtained from chromatographic separation.

88. The method of claim 80 wherein said modified lignosulfonate comprises an ammoxidized lignosulfonate.

89. The method of claim 80 wherein said multivalent cation precipitating agent is selected from the group consisting of a water-soluble carbonate, a bicarbonate, a silicate and a metasilicate.

90. The method of claim 89 wherein said carbonate is selected from the group consisting of sodium, potassium, lithium and ammonium carbonate.