SOIL STABILIZATION
.
If the contractor attempts to pump the water from the caisson, he finds that he is removing sand with the water, often endangering adjacent buildings by undermining their foundations. Figure 12 shows how the chemical can be injected into the sand from the ground surface, in advance of caisson construction, thus preventing quicksand action. Chemical grouts would also be useful in expediting construction of open trenches throughout sandy soils before the water table. However, the cost of such treatment is generally large, so that the potential usefulness of the method for such work is limited. Figure 13 illustrates a pervious sand stratum extending beneath a dam foundation. Such a stratum often causes considerable loss of water from reservoirs, as well as endangering the stability of the dam in some cases. Cement grouts have been used for years in dam foundations, though chemical grouts, injected before or after construction of the dam in the pervious strata, would more effectively seal the strata, because of the difficulties encountered in grouting fine sand formations with cement. Chemical grouts would also be used in sealing fractured or cavernous rock formations, but there is a danger that the chemical would disperse and fail to polymerize should it encounter voids of any size in the rock. I n drilling water and oil wells, difficulties are often encountered because the expensive drilling mud is lost through pervious strata encountered a t various depths. Also, in drilling oil wells, it is often necessary to seal off the salt water encountered beneath
the oil in the oil-bearing sand stratum. It is believed that chemical grouts, used with special injection equipment and packers inside the wells, as pictured in Figure 14, could effectively prevent the loss of drilling mud, and could likewise prevent salt water from flowing into the well. Such grouting has been used successfully in a water well by the author, but no work has been done in the oil fields. Conclusions
There are numerous engineering problems concerning soil that could be eliminated by modifying the properties of the soil mass with the injection of chemicals. The cost of such treatment is in many cases reasonable, and with continuing development of injection techniques, some day it will be a valuable tool for the construction industry. Ac k n ow Ied gment
The author wishes to acknowledge the contributions of Clyde N. Baker of Soil Testing Services, Inc., and Robert J. Gnaedinger, Sr., engineering consultant. He is also indebted to J. G. Affleck of hmerican Cyanamid Co., V. C. Meunier of Rohm and Haas Co., and T. William Lambe of Massachusetts Institute of Technology for their cooperation in various aspects of the work. RECEIVED for review April 6, 1955.
ACCEPTED August 17, 1956.
Effect of Fatty Quaternary Ammonium Salts on Physical Properties of Certain Soils F R A N K X. GROSS1 A N D J O H N L. WOOLSEY UNION STARCH A N D REFINING CO.. GRANITE CITY. ILL.
T h e apparent limit t o t h e quantity of water adsorbable by a P u t n a m silt loam treated w i t h 0.1% dimethyldioctadecylammonium chloride (DDAC) i s directly responsible for its hydraulic stability. This alsoexplains t h e ability of the treated soil t o withstand rupture f r o m cyclic wetting and drying and also f r o m freezing and thawing. T h e effectiveness of t h e treatment of t h e soil will vary w i t h t h e concentration of DDAC, t h e magnitude of t h e electrokinetic potential of t h e soil, t h e p H of t h e soil, and t h e concentration of indifferent salts. Soils w i t h p H above 8 and w i t h abnormally high concentration of salts do n o t respond t o t h e described treatment. T h e capacity of t h e treated soil t o reaggregate on being reworked should prolong t h e duration of t h e treatment. T h e virtual lack of capillarity of t h e treated soil demonstrates t h e weakened forces of attraction between t h e treated soil particles and t h e water molecules. T h e compressive strength of t h e treated soil appears t o reach a constant value above a moisture content of 15% while t h e compressive strength for t h e untreated diminishes rapidly above t h e same moisture level.
C
ONTEMPORARY workers (3, 6, 7 , 8) in the field of soil aggregation have confined their efforts largely to aggregating agents of the polymeric anionic type and have emphasized the benefits to soil structure by their incorporation in the soil. Michaels (6) has studied the mechanism by which the anionic polyelectrolytes function as soil aggregants and has described how the effectjveness of polyacrylamide as a soil flocculant is related to the degree of hydrolysis. Michaels and Lambe (7) have also evaluated the use of a cationic polyelectrolyte, a copolymer of styrene and AT-methyl-2-vinylpyridine methosulfate, November 1955
on three widely separated soils, but the work of recent investigators with soil flocculants has dealt chiefly with polymeric soil additives with molecular weights as high as 200,000. The capacity of these compounds to aggregate soil particles is attributed ( 6 ) to their chain like structures, their adsorption on soil particles, and their ability to link to other soil particles. Attention has centered on hydrophilic polymers, the majority of which are negatively charged, and their effects on the physical properties of soils as they relate to crop response. This paper will deal with a markedly different type of soil
INDUSTRIAL AND ENGINEERING CHEMISTRY
2253
ENGINEERING, DESIGN, AND EQUIPMENT aggregant, a fatty quaternary ammonium salt, and the changes in soil-water relationships as the result of its incorporation in minute quantities in soils of a local character. The mechanism for its aggregating properties will be based on a study of the colloidal properties of the electrolyte, the charge of the soil additive, and the character of the substituent groups.
K
A 0 C
E w
9 -D
KEY DDAC VAMA PREGELATINIZED STARCH CMC-I20
Figure 1.
Aggregating property of some soil additives on Cisne silt loam
The interest o€the authors in the behavior of fatty quaternary ammonium salts towards soil colloids originated from initial observations of the effects of dilute solutions of these compounds when added to colloidal dispersions of caramel color and gelatinized starch. Negatively charged caramel colors and starch suspensoids were precipitated or flocculated by the fatty quaternary ammonium salts. After drying these amorphous precipitates under moderate conditions, they appeared to rewet very slowly and exhibited little or no tendency to swell to their original size. Changes of an irreversible nature had occurred in the physical properties of the treated colloids. No flocculation took place with positively charge caramel color or with a colloidal gelatin dispersion. On the basis of these preliminary observations it was decided to extend the study to the behavior of fatty quaternary ammonium compounds toward soil colloids. The flocculating power of a number of cations, including the ammonium ion, has been studied by Jenny and Reitemeier ( 4 )but only recently has the substituted ammonium ion and its effects on soils attracted attention. Michaels (6) has discussed and demonstrated the flocculation of soils with fatty quaternary ammonium compounds a t the Conference on Soil Stabilization a t Massachusetts Institute of Technology, Cambridge, Mass., June 1952. Hauser and Jordan (Z2) have made notable contributions by their treatment of colloidal silica and clays-mainly montmorillonite-with amines and fatty quaternary ammonium compounds to render such solids hydrophobic.
Table I.
Active Material, % 0.75 0.50 0.10
0.05
2254
Trimethyldodecvlammonium chloride, mean mol. wt. 264 Grams
... 0 ... ...
% ' '0
Experimental Work
This investigation can conveniently be divided into three phases. 1. An evaluation of a number of commercially available quaternary ammonium salts 2. A comparison in aggregating property between dimethyldioctadecylammonium chloride, the most effective soil aggregant, hereafter referred to as DDAC, and other synthetic aggregants 3. Observations of the changes in physical properties of the treated soil
Procedure in Determination of Percentage of Water Stable Aggregates. The method used is essentially that of Yoder ( 9 ) with minor modifications. Samples of Cisne silt loam and Herrick clay loam (surface soil 0 to 6 inches) were obtained from Hamel and New Douglas, Ill., regions, respectively, and allowed to dry thoroughly at room temperature for a t least a week. The soil was ground in a mortar and pestle and screened through a 60-mesh screen (0.25-mm. openings); 100 grams were treated with 100 to 750 mg. of the quaternary ammonium salt dissolved in sufficient water to bring the soil to an optimum moisture level (35 ml.) and thoroughly mixed by manipulation. The moist soil was then pressed through a sieve with 4.00-mm. openings and the crumbs air dried for a t least 2 days. Forty grams of the treated soil were placed in a sieve with 0.25-mm. openings (60 mesh). The sieve was slowly raised and lowered in water 120 times through a distance of 2.0 inches. The soil remaining on the sieve was transferred t o an evaporating dish and dried in an oven a t 105' C. for a t least 24 hours. The results are illustrated in Tables I and I1 and Figure 1.
Table I I.
Aggregation of Herrick Clay Loam Aggregates >0.25 mm. Weight, grams 70 22.3 55.7
Soil Additive, 0.1% Canon. Control Vinvl acetate maleic an-
36.0
90.0
26.5 38.5 18.0 39.0
66.2 96.2 45.0 97.5
Effect of Moisture on Aggregating Power of VAMA and DDAC. A 100-gram sample of Putnam silt loam from Wentnville, Mo., had been thoroughly air dried and screened through a 60mesh screen (openings 0.25 mm. in diameter) was treated with 0.1% concentration of VAMA and DDAC a t various moisture levels. The treated soil was pressed through a screen with 4-mm. openings, the crumbs air dried for 2 days and the percentage of water stable aggregates determined. The results are shown in Table 111. Reworkability Studies. A sample of Putnam silt loam was treated with 0.1% concentration of VAMA and DDAC at
Aggregation of Cisne Silt Loam by Quaternary A m m o n i u m Salts
Trimethylhexadecslammonium chloride, mean mol. wt. 321 Grams
... 0
..
, . .
..
...
Trimethyloctadecylammonium chloride mean mol.'wt. 348
7%
Grams
.. 0 .. ..
...
8.5
... ...
'% 42:5
... ...
Soil Additives DimethylDimethyldidodecyldioctadecylammonium ammonium chloride, chloride mean mol.' wt. mean mol. wt. 585 480 Aggregates >0.25 mm. Grams % Grams % 12 30 40 100
...
..
...
..
...
..
...
39.5
'97
70
INDUSTRIAL AND ENGINEERING CHEMISTRY
I-Cetylpyridinium chloride, mol. wt. 339.5 Grams ...
...
20
3.2
4-ethyl: morpholiniu n. ethyl sulfate
%
Grams
3'%
... ...
...
..
50
8.0
... 0
0
...
..
Vol. 47, No. 11
-
~~
~
~
~~
~
~
~
~
moisture levels of 30 ml. and 40 ml. of water to 100-gram lots of soil and reworked twice by pulverizing the air-dried treated soil, screening it through a 60-mesh screen, reaggregating it, and wetscreening the dried aggregates. The results on the effect of aggregation are shown in Table IV. Aggregating Property of DDAC When Extended by Inert Materials. Five grams of DDAC (lOOyo active material) was dissolved in isopropyl alcohol. The solution was added t o and thoroughly mixed with 95.0 grams of dry coarse tailings, a cellulosic by-product of the corn wet milling industry. The mixture was then placed in a steam bath and the alcohol volatilized. The same procedure was used in depositing DDAC on spent carbon, that is, carbon that has been used t o decolorize corn sirups. The mixtures were pound in a mechanical mixer to pass a 60mesh screen (0.25-mm. openings). The aggregating property of DDAC when extended by coarse tailings and spent carbon was determined. The results are shown in Table V. Effect of Certain Chemicals Added to Soil on Aggregating Property of DDAC. One-hundred-gram samples of Putnam silt loam surface soil ground in a mortar to pass a sieve with 0.25mm. openings were treated with 0.2 gram of monobasic potassium phosphate, sodium bicarbonate, dibasic sodium phosphate, calcium carbonate, and ferric chloride, and then with 0.1% DDAC. The DDAC was added after first dispersing it in a small quantity of water. A total of 35 ml. of water was added to and thoroughly mixed with each sample. The moist samples were then pressed through approximately the same sized area of a 4-mm. sieve and the crumbs allowed to air dry a t least 2 days. The percentage of water stable aggregates (Table VI) was determined. Effect of Aggregation of Putnam Silt Loam with DDAC by Subjection of Treated Soil to Alternate Freezing and Thawing. Five hundred grams of air-dried Putnam silt loam were treated with 500 mg. of DDAC (100% active material) and 175 ml. of water; 75 grams of this paste was withdrawn for determination of percentage of water stable aggregates. The remainder was placed in a tared beaker and introduced t o the freezer compartment of a refrigerator (0’ F.) and left there overnight to ensure solidification. The frozen soil was allowed to thaw at room temperature; any loss in weight due to evaporation was compensated for; and an additional 75-gram aliquot of the treated soil was removed for determination of percentage of water stable aggregates. This procedure was repeated four more times. The results are demonstrated in Table VII. The last phase of this work deals 11 ith changes in the physical properties of the soil when treated with O.lyoof DDAC. The first under consideration is the moisture equivalent. Moisture Equivalent of Putnam Silt Loam Surface Soil. Briggs and McLane ( 1 ) developed the moisture equivalent as an expression of the ability of a soil to hold water under a centiifugal force 1000 times that of gravity. This value was considered to represent the moisture in the smaller capillary pores and was determined by calculating the percentage moisture retained, based on dry soil weight, after removing surplus moisture from saturated soil by suction in lieu of centrifugation. Air-dried soil, previously treated with 0.02, 0.05, and 0.1% DDAC, 0.02, 0.05, and 0.1% VAMA and control (Table VIII) Rere sieved through a screen with 2.00-mm. openings. Soil was then placed in Buchner funnels (5.0 X 2.5 cm.). The funnels were completely filled. Care was taken to compact the samples by tapping the lower end of the funnel gently against the table top. The funnel was then placed in a beaker and water was added until i t reached the upper level of the soil. The soil was allowed to soak for 24 hours. Excess moisture was removed by suction for 15 minutes. The weight of moist soil was determined by subtracting the weight of funnel from the total weight of the funnel with the moist soil. The soil was placed in a 105’ C. oven to dry to constant weight November 1955
SOIL STABILIZATION
~ ~ ~ _ _ _ _ _ _ ~ _ _ _ _ ~
Table 111.
Effect of Moisture Content of Soil on Aggregating Property of V A M A and DDAC
(Concentration of VAMA and DDAC = 0.1%) Aggregates >0.25 Mm. Grams % M1. H20/100 Grams Soil VAMA DDAC VAMA DDAC 30 35 40
30.0 32.2 35.8 36.8
35.0 38.8 38.0 38.9
75.0 80.5 89 , 5 92.0
87.5 97.0 95.0 97.3
...
92.3
...
...
Table IV. Effect of Aggregation of P u t n a m Silt Loam Treated w i t h O.lyo of V A M A and DDAC When Reworked a t Various Moisture Levels Aggregates >0.25 Mm. Grams % DDAC VAMA DDAC VAMA Moisture Leyel30 R.11. HzO/100 Grams Soil No. times reworked 0 1 2
36.0 36.8 36.5
30.0 6.2 2.1
90.0 92.0 91.3
75 0 15 5 5.3
Moisture Level 40 M1.Hz0/100 Grams Soil 38.8 38.7 38.2
0
1
2
Table V.
35.0 10.2 4.0
97.0 97.8 95.5
87.5 25.5 10.0
Aggregating Property of DDAC When Extended
Coarse Tailing on Cisne Silt Loam 39.5 30.5 28.0
0.1 0.075 0.05
98.8 76.8 70.0
Spent Carbon on Putnam Silt Loam Soil 37.2 36.4 33.7
0.1 0.075 0.05
93.0 91.0 84.3
Table VI. Effect of 0.270 Concentration of Certain Inorganic Chemicals Added t o P u t n a m Silt Loam on Aggregating Property of DDAC a t Concentration of O.lyo Salt Added,
Aggregates >0.25 Mm. Grams %
0.2% 0
35.8 36.0 36.1 35.5
NaHCO: KHsPOa NarHPOi NHdNOa (i”a)zSO4 KC1
89.5 90.0 90.3 88.8 90.0 89.8 91.8 89.8 91.0 90.0
36.0 35.9
36.7 35.9 36.4 36.0
KnSOa
FeCla KNOs
Tab1e V I I . Percentage of Water Stable Aggregates (Putn a m Silt Loam) Treated w i t h O.lyoDDAC after Alternate Freezing and Thawing Freese-~haw Cycle
Grams Aggregates 2 0 . 2 5 Mm. in Diameter Grams % 39.5 39.0 38.3 38.7 37.0 37.4
Table V I I I.
98.7 97.5 95.7 96.7 92.5 93.5
Moisture Equivalent of Treated P u t n a m Silt Loam
Soil Additive, %
Control
DDAC
0.05
,..
20.65
0.10
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
9,62
VAMA 25.41
23.78
25.73
2255
ENGINEERING, DESIGN, AND EQUIPMENT
Figure 2. Compressive strength of P u t n a m s i l t loam w i t h 0.1% DDAC as function of water immersion time Initial water content 0.9%
and the loss of moisture was calculated as the difference in the weight of dry soil from the damp soil. Capillarity of Putnam Silt Loam Treated with 0.1% DDAC. A small quantity of cotton batting was placed above the stopcock in a 20-ml. buret. It was then filled to the mark with airdried Putnam soil that had been screened through 60-mesh screen. The soil was well packed by gently tapping the walls of the buret with a glass rod. The piece of cotton prevents the soil from running out and acts also as a wick. Another buret of similar capacity also supplied with a piece of cotton was filled with Putnam soil of the same mesh treated with 0.1% DDAC. The weights of the soil were obtained by the difference in weight between the filled buret and the empty buret.
Table IX.
Test Duration, Days 2 7 16 23
Increase in Weight (yo)of Column of Soil by Ca pi I larit y Weight Pu_tnam Silt Grams Wet soil 28.46 39.57 39.85 ... 39.46 ... 39.87
3
Loam
%
Gain 39.04 40.02 38.65 40.09
Weight Putnam Silt Loam Ty_ea_ted-with 0.1% U U A C , Grams'" Dry Wet % soil soil Gain 29.13 29.72 2.03 ... 29.90 2.64 ... 29.88 2.58 29.68 1.89
carved from a large aggregate of Putnam silt loam treated with 0.1% DDAC. The dry weight of the block was obtained and then the block was immersed in a beaker of tap water for one hour. The block was withdrawn, excess moisture on the faces was blotted, and the dimensions and weight were taken. The block was allowed to dry a t room temperature for 48 hours, its weight taken, and then reimmersed for a longer period. This process of recording changes, Table X, in weight and dimensions with cyclic wetting and drying was repeated five times. Compressive Strength of Putnam Silt Loam Treated with 0.1 % DDAC. Columns of soil with a square base of 1 cm. on the side and a height of 2.54 cm. (1 inch) were carved from a large aggregate of Putnam silt loam that had been treated with 0.1% DDAC. The columns were immersed in a beaker of water for periods ranging from 1 to 336 hours (2 weeks) and the compressive strength was determined by the load in grams per square centimeter the column was able to withstand before rupture (Figure 2). The graph shown in Figure 3 represents the relation of compressive strength to percentage of water edsorbed. Relation of pH of Putnam Silt Loam to Aggregating Efficiency of DDAC. A 100-gram sample of air-dried Putnam soil sieved through 60-mesh screen (0.25-mm. openings) was treated with 1N sodium hydroxide and 1N sulfuric acid in varying quantiBies to raise or lower its pH. The soil was dried in moderate oven (50' C.), pulverized, and screened through the 60-mesh sieve. The samples of soil were aggregated with 0.1% DDAC and the percentage of water stable aggregates was determined. Results are shown in Table XI.
Table X I .
Effect of p H of P u t n a m Silt Loam on Aggregation When Treated w i t h O . l ~ oDDAC pH of Putnam Soil, pH 2.7 4.3 5.2 6 . 3 (as is) 8.9 9.8 10.5
Aggregates >0.25 Mm. in Diameter Grams % 37.9 94.70 35.4 88.60 38.4 96.00 39.0 97.50 37.9 94.75 31.7 79.25 20.1 50.25
Discussion of Results
In the evaluation of the fatty quaternary ammonium compounds as soil aggregants with the Cisne silt loam, the dimethyl... dialkylammonium chloride in which the dialkyl groups were unbranched CI8 hydrocarbon chains was the most effective. The aqueous dispersion of this compound was a colloid or hydrophobic sol in contrast to the clear solutions of the salts of lower molecThe tips of the burets were dipped in a water reservoir so that ular weight. the cotton wicks were barely wetted. Increase in weights of the Michaels (6) states that flocculation of soil suspensions occurs columns of soil (Table I X ) were taken a t intervals of 48 hours, by reduction of the electrokinetic potential to permit particle 1 week, 16 days, and finally 23 days. The column of untreated aggregation. Similarly the mechanism for flocculation of a soil soil was completely wetted after 24 hours. by the colloidal fatty quaternary ammonium salt can be deExpansion and Contraction of Putnam Silt Loam Treated with scribed as the result of interaction between oppositely charged 0.1 DDAC. Rectangular block with following dimensions colloidal systems-i.e., the complex formed when the colloid 2.56 X 2.83 X 2.99 cm. as measured with a vernier caliper was cation of the a u a t e r n a r y ammonium salt associates with the colloid anion of the soil Table X. Changes in Weight and Volume w i t h Cyclic Wetting and Drying of Block of It is logical to exP u t n a m Silt Loam Treated w i t h 0.1% DDAC % Change after Immersion pect that the hydrophilic porTime Initial Initial and Drying, Expansion + tion of the cation is adsorbed Contraction Block IsHr. VolumeC c . Block Weight, by the soil particles and the Cycle Immersed, of Block, Grams Volume Weight 1 1 21.66 35.661 -2.03 +0.03 h y d r o c a r b o n chains would 2 2 21.22 35.673 fO.OO +0.04 associate, thus aggregating the 3 3 21.22 35 689 +0.71 -0.02 4 61/2 21.37 35.683 " -0.70 -0.21 particles. The water stability 5 24 21.22 35.608 -0.33 -0 19 6 48 21.29 35.540 4-1.45 -0.15 of the aggregates of the soil particles is attributable to the
... ~~
2256
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47 No. 11
SOIL STABILIZATION hydrophobic groups of the colloid cation or to its virtual irreplaceability by a more hydrophilic cation. The variables in the flocculating property of DDAC are classified as: 1. Mixing proportions of the fatty quaternary ammonium salt and the soil 2. pH of the soil 3. Concentration and type of inorganic salts in the soil The percentage of water stable aggregates of the soil treated with DDAC increased as the percentage of soil additive increased. When the concentration of aggregant reached 0.170, 1 0 0 ~ aggregation o was approached. Dosages in excess of 0.1% gave values only slightly greater than the 9i’.5y0 aggregation at 0.1% concentration by the method for wet screen analysis employed (9). Herrick, Cisne, and Putnam soils gave very close agreement. The fatty quaternary ammonium salt was diluted with inert materials, that is, materials possessing no aggregating capacity, without impairment to its aggregating activity. The salt was dissolved in isopropyl alcohol, the solution mixed with coarse tailings or spent carbon from the corn wet milling industry a t a ratio of 1 part by weight of DDAC to 19 parts of the inert, dried, and ground into a fine powder. The extended material was effective as the undiluted-an indication that no appreciable dissipation of the positive charge of DDAC had occurred. If, however, a polysaccharide like gelatinized starch is used as an extender in the same ratio, the dried powder showed poor aggregating qualities. The complex formed by the association of the colloid cation and the colloid anion (gelatinized starch) would not redisperse and the aggregating property inherent in either component failed to manifest itself. A marked difference in the aggregating property of DDAC and the anionic polyelectrolyte, VAMA, was noted when the treated soil was reworked. The explanation for this observation is as follows: Both DDAC and VAMA (or any other polyelectrolyte) are adsorbed on soils from aqueous solution; hence it is likely that water must be present in sufficient quantity a t or near soil particle surfaces to provide the medium for either adsorption or desorption to occur. DDAC, by rendering the soil particle surfaces hydrophobic, displaces a good part of the water necessary for this purpose, while the water soluble polyelectrolytes, bei‘ng hydrophilic, do not. Hence under shear such as occurs in reworking there is greater opportunity for aggregant-desorption and aggregate breakdown in highly hydrated polyelectrolytetreated soil than in the necessarily “drier” DDAC-treated soil. This effect of reduced aggregation by pulverizing VAMAtreated soil was pointed out by Hedrick and Mowry (3)but they explained it as a mechanical breaking of the polymer-stabilized aggregates when the dry soil was pulverized. While the polymer is still adsorbed, it is now on individual particles rather than binding soil particles together. The flocculability of a hydrophobic sol, represented by an aqueous dispersion of DDAC, is drastically affected by the pH of the hydrophilic sol or the soil in an aqueous environment. If flocculation is pictured as a process which is allied to salt formation between the cation of the fatty quaternary ammonium salt and the colloid anions of the soil it will be clear how variations in pH values affect, the stability of the floccule. At p H values below 8.0 there appears t o be no appreciable deviation in the additive behavior of the colloid cation and the colloid anion. The complex formed is still hydrophobic and the aggregates formed retain a high degree of hydraulic stability. At high pHs and a t low water contents in soil, the alkali metal ion concentration in the water phase can become extremely high-in the order of 0.2N; under these circumstances, competition between the alkali and fat,ty cations may be great enough to suppress adsorption of the latter. The other is that, in alkaline mediums, appreciable quantities of both silica and alumina are solubilized 1
-
November 1955
from clays, and appear in solution as polyanions; these polyanions might well preferentially complex with the fatty cations, leaving none for adsorption on the particle surface. The presence of large quantities of an indifferent salt in the soil can prevent flocculation with DDAC. For example, poor results were obtained with a Cisne silt loam containing 1%ammonium chloride when treated with 0.1% DDAC. Aggregation can be inhibited, therefore, with a soil containing an abnormally high concentration of inorganic salts. However, a t a level of 0.2% concentration of certain inorganic salts, some of which contain polyvalent cations and anions, D D S C exhibited good salt resistance.
:[ 1 7
V -
f\ 6 -
-
(I Y
A
$5-
I)
KEY TREATED UNTREATED
z w E4Y
2 i 3 0 K
s0z II
,
,
,
6 9 12 15 18 21 24 % WATER ADSORBED BY BLOCK (I CM.X I CM.XZ.54CMJ
Figure 3. Relation of compressive strength of block of P u t n a m soil treated w i t h 0.1% DDAC t o % water adsorbed I n i t i a l water content 0.9%
Aggregation of DDAC with the soils studied varies with the mixing proportions of the fatty quaternary ammonium salt and the soil. Almost maximum aggregation is obtained a t a concentration of 0.1% DDAC and a minimum a t 0.01%. If one can visualize the complex brought about by the union of colloid cation and the colloid anion as a floccule with the hydrophobic groups oriented away from the hydrophilic portion of the floccule one can comprehend the alteration in physical properties of the treated soil aggregates with respect t o changes in soil-water relationships. Observations with treated soil particles less than 0.25 mm. in diameter show almost complete loss of capillary conductivity. This may be explained by the fact that by rendering the soil particle surfaces hydrophobic, DDAC increases the contact angle between soil and water in the presence of air. This change in contact angle greatly reduces or may actually eliminate the tendenry of water to migrate into the microscopic pores of a soil by capillarity and also make entry of water into the macroscopic pores by gravitational forces more difficult. Therefore, it becomes easier t o displace water from the soil voids by air. Thus, absence of large capillary imbibition pressures, and ease of water displacement by air, would account for low moisture pick up, low moisture retention, and high hydraulic. stability. Thus a 61.7% reduction in the moisture equivalent of the Putnam silt loam was realized by the 0.1% treatment with DDAC. And, in another instance, an aggregate or clod of similarly treated Putnam silt loam with an initial weight of 188.6 grams gained 21.9% in weight when immersed in water for a period of 44 days. I n comparison,
INDUSTRIAL AND ENGINEERING CHEMISTRY
2257
ENGINEERING, DESIGN, AND EQUIPMENT the same soil (untreated) gained 39.3% in weight by capillarity in a relatively short time. The reduced capacity of the treated soil to adsorb water has resulted in two other changes in the physical properties of the mil. 1. A lowered tendency to expand and contract with alternate wetting and drying 2. A greater compressive strength when the treated soil is soaked in water for prolonged periods of time
Repeated wetting and drying of soil is accompanied by alternate contraction and expansion. The effect of volume changes is to cause disruption of soil aggregates or clods into smaller units when the dried soil is wetted. The rapid intake of water causes unequal swelling throughout the clod which produces fracture and fragmentation along the cleavage planes. Then, too, the penetration of water into the capillaries results, first in a compression of the occluded air and finally in a virtually explosion within the clod as the pressure of the entrapped air exceeds the cohesion of the particles. Yoder (9) has shown that slow wetting by capillarity does not cause violent disruption of the clod but if the clod is immersed in water, disintegration into smaller fragments takes place as the air is expelled. With a soil treated with DDAC the capacity to adsorb water has been reduced, its rate of water adsorption lowered and consequently its tendency to expand minimized. The air occluded in the pores is free to escape as its place is occupied by the slowly entering water. An examination of the data accumulated in Table X will show the increased resistance of a treated Putnam soil to volume and weight changes concomitant with cyclic wetting and drying. I n the experiment with blocks of treated Putnam silt loam it has been demonstrated how the compressive strength is a function of the moisture adsorbed by the treated soil when immersed. Prolonged periods of immersion indicate that treatment with 0.1% DDAC imposes a limit on quantity of water adsorbable a t about 21%. Since this is lower than the value for untreated soil, the treated soil aggregate remains intact by virtue of the decreased water adsorption. Theoretically, if the immersed block of treated soil does not
soak up moisture any further, and if it is not subject to forces greater than the bresk point, it should resist disintegration indefinitely in its aqueous surroundings. I n actual practice, other forces created by the turbulence of water will naturally affect the length of time an aggregate of immersed treated soil will remain intact. Figures 2 and 3 show that the compressive strength is inversely related to the time of immersion or percentage of water adsorbed. The values for the compressive strength of the treated and untreated Putnam soil are somewhat parallel to a moisture content of roughly 15y0,above this figure the compressive strength of the untreated falls off rapidly while that of the treated appears to reach a constant value.
-
Acknowledgment
Gratitude is expressed to Armour Chemical Division, Chicago, Ill., The Mathieson Co., Inc., Joliet, Ill., and Atlas Powder Co., Wilmington, Del., for working samples of fatty quaternary ammonium compounds. The authors are especially indebted to A. S. Michaels of the Department of Chemical Engineering, MIT, for his valuable assistlance in the preparation of this paper, and to George R. Bauwin, formerly of Union Starch & Refining Co., for some of the experimental data. Literature Cited
(1) Briggs, J., and McLane, J. W., U. S. Dept. Agr. Bull. 45, 1907. (2) Hauser, E. A., and Jordan, J. W., Silicates ind., 17, 9-10 (1952). (3) Hedrick, R. M., and Mowry, D. T., Soil Sci., 73, 436, 472 (1952). (4) Jenny, Hans, and Reitemeier, R. F., J . Phys. Chem., 39, 593604 (1935). (5) Michaels, A. S., Proceedings, Soil Stabilization Conference, MIT, Cambridge, Mass., June 1952. (6) Michaels, A. S., IND. ENQ.CHEM.,46, 1485-90 (1954). (7) Michaels, A. S., and Lambe, T. W., J . Ag. Food Chem., 1, 836 (1953). ( 8 ) Ruhrwein, R. A., and Ward, D. W., Soil Sci., 73, 485 (1952). (9) Yoder, R. E., J. Am. SOC.Agron., 28, 337 (1936). RECEIVED for review April 5 , 1955.
ACCEPTED September 1, 1955.
Acrylate Salts of Divalent Metals ROBERT P. H O P K I N S ROHM
Be
H A A S CO.. P H I L A D E L P H I A 37. PA.
M i l i t a r y interest in t h e possible use of acrylate salts of divalent metals--e.g., calcium acrylate-as soil solidifiers and t h e need of basic information for general development of t h i s new class of vinyl monomers were responsible for t h i s work, T h e polymers of these bifunctional salts exploit t h e water or moisture equilibrating property of salts t o a unique degree. Moreover temperature-water-polymer interrelationships influence mechanical properties greatly and are sufficiently characteristic t o merit description of such products as “inverse t h e r m o hydroplastics.” Practical applications involving t h e use of these acrylic salts--e.g., as soil binders-require attention t o both the equilibrating behavior and related mechanical strength of t h e polymers produced. This is demonstrated i n soil solidification studies on these salts, a n application discovered by workers a t MIT working under t h e Soil Solidification Project of t h e U. S. Army.
M
OST research on acrylic monomers has centered around the ester and nitrile derivatives and, to a lesser degree, amide derivatives of acrylic and methacrylic acids. A smaller amount of attention has been given to the acids themselves and to the salts of monovalent cations. The bifunctional acrylic monomers represented by the acrylate salts of divalent metals are the newest members of the acrylic family undergoing research and commercial development. These salts are represented by the general formula 2258
0
II
O-C-CH=CHs
/
X
\
O-C-CH=CHe
I1
0
where X is the divalent cation.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vel. 47, No. 11
