Note: Descriptions are shown in the official language in which they were submitted.
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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.
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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.
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hignosulfonates 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
~urfactants impart a strong negative charge which lowers
the surface tension of the surrounding water and greatly
enhances the fluidity of the system. Lignosul~onates 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 ~ormed 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
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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.
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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, aswell as other benefits will be readily ascertained from
the more detailed description of the preferred embodiments
which follow.
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pESCRIPTION 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~.
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se~ore 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 cro~s-
linking approach consists in taking lignin in alkaline
solution and reacting it with an aldehyde. When ~or
example formaldehyde is used, the reaction between the
lignin and formaldehyde is a methylolation reaction. The
lo 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.
15The 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 réaction 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~ 30 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
-
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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.
~xample 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.
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_g_
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
Startinq Liqnin 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
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Example III: Testinq 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 Dosaqe
Portland Cement (Type 10) 5000 grams
Water 2250 grams
Admixture Solids 0.3% by weight on
Cement
Table 2
Startinq Liqnin 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.
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Table 3
~iqnin Moles of Adduct per Liqnin Cs Unit
0.15 0.23 0.31
Torque 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.
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Exam~le IV: Testinq 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:
Com~onent Dosaqes (kq/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~.
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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- o 25.5 155 11.31
0.5 2 5.0 155 35.82
0.5 3 3.0 llo 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
(~) (mm)
Control 2.5 40
Sulfomethylolated 2.5 120
low molecular weight
ALCELL~ lignin +
~ 25 4~ TBP on lignin solids
Commercial 2.5 85
lignosulfonate based
admixture
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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 m3)
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 h 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 m3.
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The mixing procedure was in accordance with CSA
StandardCAN3-A266.6-M85. Fresh concrete was tested for
workability by measuring the slump in accordance with ASTM
specification C-143-9Oa. The time of setting was
determined by measuring the penetration resistance on
mortar extracted ~rom the concrete mixture in accordance
with ASTM specification C403-92. The compressive strength
of hardened concrete was measured in accordance with ASTM
specification C-192-9Oa, 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 o~ elasticity changes in concrete prisms exposed
to repeated cycles of ~reezing and thawing in accordance
with ASTM speci~ication C666-92.
Table 6 is a summary of the superplasticizing
admixture qualification tests for the non air-entrained
mix compositions.
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Table 6
Concrete property Non-Air Air CSA/CANS
Entrained Entrained A266.6-M85
Concrete Concrete Ty~e SPR
Water content,
~ of reference 87 87 max. 88
Slum~ 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 min. 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.l(CSA) 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.
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ExamPle VII: Testinq 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
(mL)
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
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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
e~bodiments.
