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Title:
LIGNIN-BASED CONCRETE ADMIXTURES
Document Type and Number:
WIPO Patent Application WO/1997/013733
Kind Code:
A1
Abstract:
The invention provides for an admixture for reducing the water content of a concrete mix. The admixture comprises an alkaline solution of a lignin in a sulfomethylolated form. The admixture further comprises an air detrainer. Also provided are novel cement compositions comprising the admixture of the invention.

Inventors:
Bremner, Theodore Zhor Jiri Goyal Gopal C.
Lora, Jairo H.
Application Number:
PCT/US1995/013836
Publication Date:
April 17, 1997
Filing Date:
October 11, 1995
Export Citation:
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Assignee:
ALCELL TECHNOLOGIES INC
Bremner, Theodore Zhor Jiri Goyal Gopal C.
Lora, Jairo H.
International Classes:
C04B24/16; C04B24/18; C04B28/02; C04B103/30; C04B103/50; C04B; (IPC1-7): C04B24/18
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Claims:
1. 97/13733 19 We claim : An admixture for reducing the water content of a concrete mix comprising an alkaline solution of a lignin in a range of from about 30% to about 45% on a solids weight basis with said lignin solution The admixture of claim 1 wherein said lignin is in sulfomethylolated form.
2. The admixture of claim 2 further comprising an air detrainer.
3. The admixture composition of claim 3 wherein said air detrainer is tributyl phosphate.
4. The admixture of claim 4 wherein said air detrainer is from about 0.3% to about 5% on a weight basis with said lignin.
5. A cement composition comprising a cement and an admixture for reducing the water content of said cement composition, said admixture in a range of from about 0.2% to about 1% on a solids weight basis with said cement.
6. The composition of claim 6 wherein said admixture comprises an alkaline solution of a lignin in a range of from about 30% to about 45% on a solids weight basis with said lignin solution.
7. The composition of claim 7 wherein said lignin is in sulfomethylolated form.
8. The composition of claim 8 wherein said admixture comprises an air detrainer.
9. The composition of claim 9 wherein said air detrainer is tributyl phosphate.
10. The composition of claim 10 wherein said air detrainer is from about 0.3% to about 5% on a weight basis with said lignin.
11. A method for reducing the water content of a cement mix comprising the step of adding an admixture to said concrete mix in a range of from about 0.2% to about 1% on a solids weight basis with said cement.
12. The method of claim 12 wherein said admixture comprises an organosolv lignin.
13. The method of claim 13 wherein said organosolv lignin is in sulfomethylolated form.
14. The method of claim 14 wherein said admixture further comprises an air detrainer.
15. The method of claim 15 wherein said air detrainer is tributyl phosphate.
16. The method of claim 16 wherein said air detrainer is from about 0.3% to about 5% on a weight basis with said lignin.
Description:
LIGNIN-BASED CONCRETE ADMIXTURES

BACKGROUND OF THE INVENTION

Cement compositions are brought into a workable form by mixing the solid components with an amount of water which is greater than that required to hydrate the cement components therein. The mixed mineral binder composition is poured into a form and allowed to harden at atmospheric temperature. During the hardening, some of the excess water remains, leaving cavities in the formed structural unit and, thus, reduces the mechanical strength of the resultant unit. It is well known that the compressive strength of the resultant structure generally bears an inverse relationship to the water-cement ratio of the starting mix. The need to use smaller quantities of water is limited by the required flow and workability properties of the fresh mixture.

In structural cement compositions, it is highly desirable to maintain very low water content in order to achieve high strength in the final product. However, since the amount of water needed for adequate workability of the cement exceeds that required by the chemistry of curing, this excess water results in weaker concrete.

Concrete admixtures refer to compounds and compositions added to concrete mixtures to alter their properties. Water-reducing agents have been used as concrete admixtures. They are generally used to improve workability while decreasing water addition so that a stronger and more durable concrete is obtained. Water- reducing agents are classified by their ability to reduce water content as superplasticizers or high-range water reducers and plasticizers or normal-range water reducers.

Plasticizers and superplasticizers are made using chemicals with surface-active characteristics. One of the traditional resources for the manufacture of water- reducing admixtures for concrete are the waste products from the pulp and paper industry, namely lignin and its derivatives. Traditionally, sulfite pulping has been the major source of lignosulfonates which after extended purification are used as normal range water-reducing and retarding admixtures for concrete.

The chemical structure and composition of water- reducing admixtures influence their surfactant properties which generally determine their effectiveness in cement- water mixtures.

Lignin-type water-reducing agents are well known for use in preparing concrete mixes. Such agents serve to reduce the amount of water that would ordinarily be required to make a pourable mix, without however disturbing most of the other beneficial properties of the mix. On various occasions, however, the use of such water-reducing agents may entrain air into the mix.

Entrained air (from any source) tends to reduce compressive strength. As a general rule, with every one volume percent air in the concrete, 5% of strength is lost. Thus, 5% air means about 25% strength loss. However, air entrainment maybe desirable in certain applications such as the manufacture of concrete blocks.

Lignosulfonates are also known to slow down the curing of concrete thus causing what is known in the art as set retardation. Set retardation is particularly increased when the lignosulfonate contains impurities such as wood sugars.

Lignosulfonates are classified as anionic surfactants since the hydrophilic groups associated with the organic polymers are sulfonates. It has been reported that when absorbed onto cement particles, these surfactants impart a strong negative charge which lowers the surface tension of the surrounding water and greatly enhances the fluidity of the system. Lignosulfonates also exhibit set retarding properties. Lignosulfonates, when used in an amount sufficient to furnish the desired water reduction in a mix, normally entrain more air than desired and retard the setting time of concrete far beyond the ranges for a high-range water-reducing admixture.

Lignosulfonate-based concrete admixtures are usually prepared from the waste liquor formed by the production of sulfite pulp. By neutralization, precipitation and fermentation of this liquor a range of lignosulfonates of varying purity, composition and molecular weight distribution is produced. A number of researchers have reported several attempts to enhance the lignosulfonates so that they would meet the requirements of a superplasticizer as a high range water-reducing admixture. To date no purely lignosulfonate based superplasticizer for concrete has been placed on the market .

For example, in U.S. Pat. No. 4,239,550 is disclosed a flowing agent for concrete and mortar based on lignin sulfonate and on ring-sulfonated or sulfomethylolated aromatic substances. According to the invention, the flowing agent imparts to concrete or mortar high fluidity without leading to undesirably long setting times. In U.S. Pat. No. 4,460,720 is disclosed a superplasticizer cement admixture for portland cement based compositions formed from a low molecular weight alkali metal poly-acrylate in combination with an alkali metal or alkaline earth metal poly-naphthalene sulfonate- formaldehyde or an alkali metal lignosulfonate or an

alkaline earth metal lignosulfonate or mixtures thereof. In U.S. Pat. No. 4,623,682 is disclosed cement mixes having extended workability without substantial loss in rate of hardening when containing an admixture combination of a sulfonated naphtalene-formaldehyde condensate and fractionated sulfonated lignin such as ultra-filtered lignosulfonate. In U.S. Pat. No. 4,351,671 is disclosed an additive for lignin type water-reducing agent which reduces air entrainment in the concrete mix and in U.S. Pat. No. 4,367,094 is disclosed an agent for preventing deterioration in the slump properties of mortar concrete, containing as a main ingredient a lignin sulfonate.

Environmental considerations present an important aspect in the development of pulping technologies . Due to increasing environmental demands during the last three decades, traditional sulfite pulping has almost completely been replaced by the kraft pulping process. Both sulfite and kraft pulping processes are noted for their contribution to air and water pollution, which requires costly pollution control equipment to bring kraft and sulfite pulping operations into environmental compliance. These pulping technologies can now be economically replaced by more environmentally friendly processes. One of these processes is the organosolv pulping process which has minimal impact on the environment and produces a pure lignin as one of the coproducts to the pulp. Unlike the traditional sulfite process, the new organosolv pulping process allows for the recovery of a pure, non-sulfonated form of lignin. This organosolv lignin can be suitable as a raw material for the preparation of a superplasticizer water-reducing admixtures for concrete .

By the methods of the present invention is provided an environmentally friendly organosolv lignin- based superplasticizing and water-reducing admixture composition. The superplasticizer admixture compositions of the invention can impart a high degree of fluidity to cement compositions, can cause retention of the fluidity over extended time and can achieve these results at low dosages. By manipulation of the conditions for the manufacture of the admixture, it is possible to obtain products that do not have an adverse effect on set retardation. Unlike lignosulfonates, the lignin-based admixtures of this invention are high in purity and free of sugar contamination.

SUMMARY OF THE INVENTION

The invention provides for a novel lignin-based admixture produced from derivatized organosolv lignin. This lignin-based admixture uses a coproduct from an environmentally friendly process while fulfilling a need in the construction industry. The novel lignin-based admixture is produced by derivatizing organosolv lignin by treating the lignin in a sulfomethylolation step. The derivatized lignin can be formulated with an air detrainer and the resulting admixture when added to concrete mixes effectively functions as a superplasticizer and as a high- range water reducer.

Novel features and aspects of the invention, as well as other benefits will be readily ascertained from the more detailed description of the preferred embodiments which follow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lignin which can be employed in this invention is a high purity lignin, particularly an organosolv lignin. The lignin is separated as a by-product of the pulping and chemical delignification of plant biomass with organic solvents, for example ethanol. Organosolv lignin is a nontoxic, free-flowing, powder. It is soluble in aqueous alkali and in selected organic solvents. It is generally characterized by its hydrophobicity, high purity, melt flow and a low level of carbohydrates and inorganic contaminants.

An example of the lignins which are suitable to accomplish the objectives of the invention are organosolv lignins such as regular ALCELL ® lignin or low molecular weight ALCELL ® lignin. The regular ALCELL ® lignin can be characterized by a number average molecular weight of about 700 to 1500 g/mol and the low molecular weight ALCELL ® lignin can be characterized by a low average molecular weight in the range of less than 600 g/mol.

Alternatively to organosolv lignins, it is believed that high purity lignins such as steam explosion or soda lignins can be suitable to accomplish the objectives of the invention.

The organosolv lignins of the invention can be derivatized using a sulfomethylolation procedure. Before carrying the sulfomethylolation procedures described below, the lignin is solubilized into an alkaline solution. The amount of alkali used can vary depending on the type of lignin and the reaction conditions. For example, with ALCELL ® lignin or low molecular weight ALCELL ® lignin, from about 8% to about 20% caustic based on lignin solids can be used. The amount of water used was adjusted to obtain a solids content in the final admixture of from about 30% to about 45%.

Before sulfomethylolation, the molecular weight of the lignin can be increased by cross-linking reactions. This can be accomplished by heating the lignin in alkaline solution for from about 1 to about 4 hours at from about 60°C to about 95°C. An alternative cross¬ linking approach consists in taking lignin in alkaline solution and reacting it with an aldehyde. When for example formaldehyde is used, the reaction between the lignin and formaldehyde is a methylolation reaction. The aldehyde can be added in a range of from about 0.3 to about 0.8 moles of aldehyde per lignin C-9 unit or of from about 5% to about 13% on a lignin weight basis. The methylolation reaction can be carried out at from about 60°C to about 95°C for from about 1 to about 3 hours.

The lignin in alkaline solution can be sulfomethylolated in a number of ways. The lignin can be reacted with a salt of hydroxymethane sulfonic acid such as for example its sodium salt. The latter is also known as "adduct" and is available commercially. It is the addition product resulting from the reaction of formaldehyde with either sodium bisulfite or sodium sulfite. Preferably, the amount of adduct used for sulfomethylolation can be from about 8% to about 30% adduct solids based on a weight basis with the lignin and the sulfomethylolation reaction time is from about 2 to about 6 hours. Sulfomethylolation is generally performed at from about 70°C to about 100°C.

The lignin can also be sulfomethylolated in a two-step process by initially reacting the lignin solution with excess of an aldehyde such as formaldehyde to methylolate the lignin thus introducing reactive aliphatic hydroxyl groups. This is done by following a similar procedure as described above to increase molecular weight

but using higher levels of aldehyde such as for example of from about 10 to about 30% formaldehyde on lignin weight. This methylolation step is generally followed by reaction with from about 10 to about 25% sodium sulfite on a weight basis with lignin, at from about 120°C to about 160°C for from about 1 to about 4 hours.

The lignin-based admixtures can be mixed with a concrete mix in a range of from about 0.2% to about 1% on a weight basis with the cement in the concrete. The admixture causes a water reduction of from about 5% to bout 15% resulting in higher concrete strength and improved resistance to freeze and thaw.

In certain applications, it may be desirable to control the entrained air in the resulting mix. An air detrainer such as tributyl phosphate, dibutyl phthalate, octyl alcohol, water-insoluble esters, carbonic and boric acids and silicones can be used. Tributyl phosphate (TBP) can be added to the derivatized lignin in a range of from about 0.3% to about 5% weight basis based on lignin solids resulting in a reduction in the air content of from about 9% to about 32% to as low as from about 2% to about 3% while maintaining reasonably high slump values.

Example I : Preparation of Sulfite Adduct

The adduct can be prepared by addition of about 60 grams of 50% formaldehyde to a solution of about 126 grams sodium sulfite in about 700 milliliters of water.

Example II: Manufacture of Admixtures

A series of lignin-based admixtures were prepared by sulfomethylolation using as starting materials low molecular weight organosolv lignin, organosolv lignin and their methylolated counterparts. Initially, the lignins were dissolved in an aqueous solution of sodium hydroxide containing the alkali levels specified in Table 1. The amount of water used was adjusted to obtain a solids content in the final admixture of approximately 35% by weight. Those samples that were methylolated were treated with 0.5 moles of formaldehyde per lignin C-9 unit for 2 hours at 70°C. The sulfomethylolation was carried at a temperature of about 95°C and for 6 hours with adduct prepared as in Example I and using the levels described in Table 1.

Table 1

Starting Lignin Adduct Sodium Hydroxide

(Mole per Lignin C-9 Unit)

Low Molecular Weight 0.15 0.59

Low Molecular Weight 0.23 0.67

Low Molecular Weight 0.31 0.74

Methylolated Regular 0.15 0.67

Methylolated Regular 0.23 0.71 Methylolated Regular 0.31 0.78

Regular 0.15 0.58

Regular 0.23 0.66

Regular 0.31 0.73

Methylolated Low 0.15 0.55 Molecular Weight

Methylolated Low 0.23 0.63 Molecular Weight

Example III: Testing on Cement Slurries

The sulfomethylolated organosolv lignin-based admixtures were tested in cement slurries. The mixes were prepared by mixing together the following ingredients:

Component Dosage

Portland Cement (Type 10) 5000 grams

Water 2250 grams

Admixture Solids 0.3% by weight on Cement

Table 2

Starting Lignin Moles of adduct per lignin C9 unit

0.15 0.23 0.31

Set Retardation (min)

Low Molecular 200 380 380

Weight

Regular 40 60 20

Methylolated 240 320

Low Molecular

Weight

Methylolated 0 120 120

Regular

Table 2 shows the initial set retardation on cement slurries. In general, the retardation decreases when the molecular weight and the level of adduct used decreases .

Table 3

Lignin Moles of Adduct per Lignin C9 Unit

0.15 0.23 0.31

Torσue Decrease (Nm)

Low Molecular 3.58 4, .18 4.28

Weight

Regular 3.74 3, .60 3.51

Methylolated 2.95 4. .06

Low Molecular

Weight

Methylolated 3.32 3, .36 4.06

Regular

Table 3 shows the fluidifying effect of the lignin admixtures on cement slurries as determined by decrease in torque resistance. In general, lower molecular weight and high levels of adduct resulted in a greater fluidifying effect.

Example IV: Testing on Concrete Mixes

Sulfomethylolated low molecular weight lignin is obtained with a ratio of 0.31 moles per C-9 unit using the procedure of Example II was evaluated as an admixture in concrete mixes. The effect of tributyl phosphate as an air entrainer agent was also evaluated. The proportions of the concrete mixes were as follows :

Component Dosages (kg/m3)

Portland Cement (Type 10) 307 Fine Aggregate 862

Coarse Aggregate 935

Water 187

Admixture 4.87 (0.5% solids on a weight basis with cement)

The proportion of cement in the mixes conformed to the requirements of ASTM specification C-494.

Table 4 shows the plasticizing effect of the low molecular weight sulfomethylolated organosolv lignin on concrete as shown by the high slump numbers relative to the case where no admixture is used. If an air detrainer is not used, a high air content can be observed which causes a decrease in concrete strength. Tributyl phosphate can be added to reduce the air content while maintaining a high slump and high strength. As can be seen, by adjusting the amount of detrainer agent added, a wide variety of air contents can be attained, including air contents for non- air entrained concrete (below 3.5%) and air contents for typical air entrained concrete of 4 to 8%.

Table 4

Low Molecular Tributyl Air Slump Compressive weight phosphate content mm strength sulfomethylolated % MPa lignin (% solids based on cement)

0 0 2.5 40 37.77

0.5 0 25.5 155 11.31

0.5 2 5.0 155 35.82

0.5 3 3.0 110 37.3

0.5 4 4.0 120 37.1

Example V:

In this example, sulfomethylolated low molecular weight organosolv lignin formulated with an air detrainer showed a higher plasticity over a commercial lignosulfonate such as for example PDA-25XL from Conchem.

The results are shown in Table 5.

Table 5

Admixture Air Content Slump ill (mm)

Control 2.5 40

Sulfomethylolated 2.5 120 low molecular weight

ALCELL ® lignin +

4% TBP on lignin solids Commercial 2.5 85 lignosulfonate based admixture

Example VI :

In this example, a low molecular weight lignin- based admixture prepared as in Example II with a 0.31 moles of adduct per lignin C-9 unit was subjected to superplasticizing admixture qualification tests. The admixture contained about 1.5% TBP as an air detrainer. Two basic mix proportions were used, one for the non-air- entrained concrete and one for the air-entrained concrete. The following concrete mix proportions were used.

Component Dosages (per m 3 !

Non Air Entrained Air Entrained

Portland Cement 307 Kg 307 Kg

(Type 10)

Fine Aggregate 734 Kg 694 Kg

Coarse Aggregate 1150 Kg 1128 Kg

Water 175 Kg 160 KG

Admixture 4 L 4 L

(at 35% solids)

Air Entraining None 362 mL

Admixture

Reference mixes were prepared without the superplasticizer admixture. Reference air entrained mix was prepared using 147 mL of air entraining agent per m 3 .

The mixing procedure was in accordance with CSA Standard CAN3-A266.6-M85. Fresh concrete was tested for workability by measuring the slump in accordance with ASTM specification C-143-90a. The time of setting was determined by measuring the penetration resistance on mortar extracted from the concrete mixture in accordance with ASTM specification C403-92. The compressive strength of hardened concrete was measured in accordance with ASTM specification C-192-90a, ASTM specification C-39-86 and ASTM specification C-617-87. Length change was measured in accordance with CAN/CSA-A23.2-3C and CAN/CSA-A23.2-14A. Durability factor was calculated from relative dynamic modulus of elasticity changes in concrete prisms exposed to repeated cycles of freezing and thawing in accordance with ASTM specification C666-92.

Table 6 is a summary of the superplasticizing admixture qualification tests for the non air-entrained mix compositions.

Table 6

Concrete property Non-Air Air CSA/CANS

Entrained Entrained A266.6-M85

Concrete Concrete Type SPR

Water content, % of reference 87 87 max. 88

Slump retention, % 76 63 min. 50

Time of initial set retardation h:min 2:40 2:45 1:00 to 3 :00

Compressive strength,

% of ref x 1.05 (CSA)

1 day 137 150 mm. 130

3 days 131 155 min. 130

7 days 143 142 min. 125

28 days 124 137 min. 120

180 days 130 145 min. 100

Length Change

(shrinkage) % of 119 106 max. 135 ref. or increase over reference 0.005 0.002 max. 0.010

Relative durability factor not required 109/99 % of ref. xl.KCSA) min. 100

When length change of reference concrete is 0.030% or greater % of reference limit applies; increase over reference limit applies when length change of reference is less than 0.030%.

As can be observed, the admixture met the requirements of the standard and resulted in concrete with higher strength than the reference. The admixtures can therefore be classified as a superplasticizer.

Example VII: Testing on Concrete Masonry Blocks

Sulfomethylolated low molecular weight lignin with 35% solids content by weight was tested in concrete blocks production, both as a water reducer and as replacement for an air entrainer agent . Each mix was prepared with 172 kg of cement and 1814 kg of fine aggregate. The amount of water per mix was adjusted to obtain the desired workability of concrete. The admixture and quantities were as follows:

Admixture Quantity (Mhl

Control Airex L 120

Mix 1 Sulfomethylolated 1500

Low Molecular Weight Lignin + 1.2% TBP

Mix 2 Sulfomethylolated 750

Low Molecular Weight

Lignin Mix 3 Sulfomethylolated 1500 Low Molecular Weight

Lignin Mix 4 Sulfomethylolated 2000

Low Molecular Weight

Lignin Mix 5 Sulfomethylolated 3000

Low Molecular Weight

Lignin

A total of 110 standard hollow masonry units

(blocks) were prepared from each concrete mix. All blocks were prepared and cured using standard procedure.

Subsequently a randomly chosen sample from each batch was tested for compressive strength. Table 7 summarized the

- 18 -

results of testing of standard hollow concrete masonry units. As can be seen, the use of the lignin-based admixtures of the invention resulted in higher strength. In general, as the admixture level increases, the concrete strength increases.

Table 7

Concrete Mix Block Age Gross Stress

(days) (%)

Control 8 100 Control 15 100 Mix 1 8 115 Mix 2 15 98 Mix 3 15 107 Mix 4 15 108 Mix 5 15 118

The invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various modifications and changes can be made without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the compositions and processes hereinbefore described being merely preferred embodiments.