Note: Descriptions are shown in the official language in which they were submitted.
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SULFOMETHYLOLATED 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 r~m~i~s, 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. Attempts to use lignin-based methylsulphonates as
water-reducing admixtures is known in the art as shown by
"Effect of Chemical Characteristics of Alcell~ Lignin-Based
Methylsulphonates on Their Performance as Water-Reducing
Admixtures", Superplasticizers and Other Chemical Admixtures in
Concrete by J. Zhor, T. W. Bremner and J. H. Lora, 1994,
incorporated by reference herein.
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 entr~inment may
be desirable in certain applications such as the manufacture of
concrete blocks.
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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
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poly-acrylate in combination with an alkali metal or alkaline
earth metal poly-naphthalene sulfonate-formaldehyde or an alkall
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 ~m~n~s 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
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superplasticizing and water-reducing admixture composition. The
superplasticlzer 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.
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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 EM~30DIMENTS __
The lignin which can be employed in this invention is
a high purity lignin, particularly an organosolv lignin. The
purity of the llgnin in the present invention is from about 85
to about 100%. 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 cont~min~nts.
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
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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 crosslinking 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 crosslinking approach consists in taking lignin in
alkaline solution and reacting it with an aldehyde. When
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~O to about 13Qo on
a lignin weight basis. The methylolation reaction can be carried
3 0 out at from about 60~C to about 95~C for from about 1 to about 3
hours.
~ A sulfomethylolated lignin can be prepared in variousalternative methods including the following. The lignin can be
reacted with a salt of hydroxymethane sulfonic acid such as its
sodium salt. The latter is also known as "adduct" and is
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available ~ommercially. 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 lO0~C.
The lignin can also be sulfomethylolated in a two-s~ep
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 lO to about 30% formaldehyde on
lignin weight. This methylolation step is generally followed by
reaction with from about lO to about 25% sodium sulfite on a
weight basis with lignin, at from about 120~C to about 160~C for
from about l to about 4 hours.
An alternative method to modify the molecular weight
of the concrete admixtures of the present invention consists of
crosslinking a sulfomethylolated product with a crosslinking
agent such as epichlorohydrin. The epichlorohydrin can be added
in a range from about 0.05 to about 0.5 moles of epichlorohydrin
per sulfomethylolated lignin C-9 unit or of from about l.5~ to
about 16.5% on a sulfomethylolated lignin weight basis. The
crosslinking reaction can be carried out at from about 60~C to
about 100~C for from about l 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 about 15% resulting
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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.
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-10-
Example II Manu~acture of A~mixtures
A series of lignin-based admixtures were prepared by
sul~omethylolation using as starting materials low molecular
weight organosolv lignin, organosolv lignin and their
methylolated counterparts. Initially, the lignins were dissol'ved
in an aqueous solution of sodium hydroxide cont~ining 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
methylo~ated were treated with 0.5 moles of formaldehyde per
lignin C-9 unit for 2 hours at 70~C. The sulfomethylolation was
carried out at a temperature o~ about 95~C and ~or 6 hours with
adduct prepared as in Example I and using the levels described
in Table 1.
Table l _
Starting LigninAdduct Sodium Hydroxide
(Mole per Lignin C-9 Unit)
Low Molecular Weight 0.15 0.59
Low Molecular Weight 0.23 0.67
25 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
30 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: 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
10 Water 2250 grams
Admixture Solids 0.3~ by weight on
cement
Table 2 shows the initial set retardation on cement
slurries. In general, the retardation decreases when the
molecular weight increases and the level of adduct used
decreases.
Table 2
Starting Lignin Moles of Adduct per Lignin C-9 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
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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.
5 Table 3 ,. ---
Lignin Moles of Adduct per Lignin C-9 Unit
0.150.23 0.31
Torque Decrease (Nm)
Low Molecular 3.58 4.18 4.28
Weight
15 Regular 3.74 3.60 3.51
Methylolated2.95 4.06 ---
Low Molecular
Weight
Methylolated3.32 3.36 4.06
Regular
Example IV: Preparation of Crosslinked Sulfomethylolated
Lignins
Sulfolmethylolated lignins were prepared using as
starting materials low molecular weight organosolv and
organosolv lignin as outlined in Example II. The
sulfomethylolation reaction took place at a temperature of about
95~C and for about 6 hours using the levels described in Table
4. The regular sulfomethylolated organosolv lignin was further
crosslinked by reacting the sulfomethylolated lignin with 12.6%
by weight of epichlorohydrin at about 95~C for 140 minutes.
Upon cooling, the resulting solution had a pH of ll.89,
contained 41% solids by weight and had a viscosity of 3,600 cps.
-
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Table 4
Starting Lignin Adduct Sodium Hydroxide
(% on a lignin weight
basis)
Low molecular weight 16.1% 12.0%
Regular 36.8% 20.5%
Example V. Testing on Cement Slurries
~ The crosslinked sulfomethylolated lignins in Example
IV were incorporated into cement slurries in the quantities set
forth in Example III (with the exception of the fact that only
1,750 grams of water were used in this case) and the slurries
were tested for torque decrease and set retardation. The
results of those tests are provided in Table 5.
Table 5
Lignins Torque Decrease (Nm) Set Retardation
(min)
Low molecular weight 29.9 330
Regular after 28 130
25 crosslinking with
epichlorohydrin
Table 5 shows that the admixture obtained after
crosslinking the regular sulfomethylolated lignin with
epichlorohydrin had approximately the same fluidity (torque
3û dec~ea~e) as the low molecular welght sulfomethyioiated product,
but had considerably less set retardation.
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-14-
Example VI: Testing on Concrete Mixes
Sulfomethylolated low molecular weight lignin obtained
with a ratio of 0.31 moles per lignin 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:
lO Component ~Dosages (kg/m3)
Portland Cement (Type lO) 307
Fine Aggregate 862
Coarse Aggregate 935
15 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 6 demonstrates the beneficial plasticizing
effect of the low molecular weight sulfomethylolated organosolv
lignin of Example VI on concrete mixes as shown by the high
slump numbers of such mixes relative to a concrete mix
containing no admixture; see the first entry of Table 6. The
second entry of that table further reveals that if an air
detrainer is not used, a high air content can be observed which
causes a decrease in concrete strength. Tributyl phosphate (TBP)
can be added to reduce the air content while maintaining a high
slump and high strength. As can be seen in the third through
fifth entries, 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 6
Low Molecular Tributyl Air Slump Compressive
weight pho~phate 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 VII:
In this example, sulfomethylolated low molecular
weight organosolv lignin of Example VI formulated with an air
detrainer showed a higher plasticity over a commercial
lignosulfonate such as PDA-25XL from Conchem. The results are
shown in Table 7.
Table 7
Admixture Air Content Slump
(%) (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
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-l6-
Example VIII: r
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 and an air-entrained reference mix were
subjected to superplasticizing admixture qualification tests.
The admixture contained about l.5% TBP as an air detrainer. The
reference mix was prepared without the superplasticizer
admixture and included 147mL of air entraining agent per m3. The
following concrete mix proportions were used.
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Component Dosages (per m3)
Non-Air-Entrained Air-Entrained
5 Portland Cement 307 Kg 307 Kg
~Type lO)
Fine Aggregate 734 Kg 694 Kg
Coarse Aggregate 1150 Kg 1128 Kg
Water 175 Kg 160 Kg
10 Admixture 4 L 4 L ---
(at 35~ solids)
Air Entraining None 362 mL
Admixture
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-143-9Oa. 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-192-9Oa, 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 of elasticity changes in concrete
prisms exposed to repeated cycles of freezing and thawing in
accordance with ASTM specification C666-92.
Table 8 is a summary of the superplasticizing
admixture qualification tests for the non-air-entrained and the
air-entrained reference mix compositions.
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Table 8
Concrete property Non-Air Air -- CSA/CANS
Entrained Entrained A266.6-M85
Concrete Concrete Type SPR
Water content, q
% of reference 87 87max. 88
Slump retention, ~ 76 63 min. 50
Time of initial
set retardation
h:min 2:40 2:451:00 to 3:00
Compressive strength,
% of ref x 1.05 (CSA)
1 day 137 150min. 130
3 days 131 155min. 130
7 days 143 142min. 125
28 days 124 137min. 120
180 days 130 145min. 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 min. 100
% of ref. xl.l(CSA)
When the length change of the 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 invariably met the
requirements of the superplasticizing standards and resulted in
concrete with higher strength than the reference. Hence,
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--1 9--
admixtures formulated in accordance with the present invention
can be classified as a superplasticizer.
,,
Example IX: 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
(mL)
Control Airex L 120
Mix 1 Sulfomethylolated 1500
Low Molecular Weight
Lignin + 1.2~ TBP
Mix 2 Sulfomethylolated 750
Low Molecular Weight
Lignin
25 Mix 3 Sulfomethylolated 1500
Low Molecular Weight
Lignin
Mix 4 Sulfomethylolated 2000
Low Molecular Weight
Lignin
Mix 5 Sulfomethylolated 3000
Low Molecular Weight
~ Lignin
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-20-
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 9 summarized the 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 9
Concrete Mix Block Age Gross Stress
(days) (g)
Control 8 lOO
Control 15 100
Mix 1 8 115
Z0 Mix 2 15 98
Mix 3 15 107
Mix g 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.
