Liquid hardeners for soil grouting formulations

Liquid hardeners for soil grouting formulations having an acid content no more than 0.1 mg KOH per gm in the form of dimethyl ester mixtures of dimethyl succinate, dimethyl glutarate and dimethyl adipate at a concentration in the mixtures lying within a bounded area in the graph of the drawing of the specification.

BACKGROUND OF THE INVENTION 
This invention relates to liquid hardeners and their preparation for use in 
soil grouting formulations. 
In constructing and repairing structures such as buildings, mines, dams, 
underground subway tunnels and the like, it is necessary to stabilize the 
soil adjacent excavation areas until the permanent structure is complete. 
To reinforce the soil, it is known to inject a liquid mixture of chemicals 
into the soil which react to form a precipitate which acts as a binder to 
rigidify the soil against collapse when excavated from below. The liquid 
mixture is dimethyl ester (DME), water and sodium silicate ("soil grouting 
formulation") which form the solid ester salt of sodium silicate ("silica 
gel"). The dimethyl ester (sometimes called dibasic ester) constituent 
("liquid hardener") is derived from C.sub.4 -C.sub.6 aliphatic dibasic 
acids and generally is a mixture of three C.sub.4 -C.sub.6 aliphatic 
dimethyl esters. C.sub.4 -C.sub.6 aliphatic dimethyl esters are typically 
a byproduct of the manufacture of adipic acid formed by esterifying the 
byproduct acid stream with methanol. Although the composition of the 
byproduct stream (and resulting dimethyl ester composition) varies, it is 
generally about 15 to about 30% succinic acid, about 50 to about 73% 
glutaric acid and about 6 to about 25% adipic acid. Dimethyl esters are 
commercially available from Monsanto Company, St. Louis, Mo. as 
Santosol.TM. and E. I. duPont Demours & Co., Wilmington, Del., U.S.A. or 
can be prepared by conventional methods known to those skilled in the art. 
The silica gel binder forms in the soil after a finite time interval after 
injection ("gel time") which is usually about 60 minutes. To the best of 
present knowledge before this invention, this gel time was pretty well set 
and could not be varied once the reactants were combined. It would be 
desirable to control gel time to facilitate the soil grouting process. 
SUMMARY OF THE INVENTION 
Now, improvements have been made in soil grouting formulations which permit 
controlling gel time by means of the dimethyl ester liquid hardener 
composition. 
Accordingly, a principal object of this invention is to reduce gel time of 
soil grouting formulations. 
Another object is to achieve this reduction by means of the particular 
dimethyl ester constituent of the soil grouting formulation. 
A further object is to achieve such reduction by manipulating the 
concentration of ester constituents in the dimethyl ester liquid hardener 
composition of the soil grouting formulation. 
Other objects will in part be obvious and in part appear hereinafter. 
These and other objects are accomplished by providing liquid hardeners for 
soil grouting formulations having an acid content no more than 0.1 mg KOH 
per gm and comprising dimethyl ester mixtures of dimethyl succinate, 
dimethyl glutarate and dimethyl adipate at weight % concentrations lying 
within the area bounded by ABCDEA in the drawing in this specification. 
Also provided is a method of preparing liquid hardeners for soil grouting 
formulations which comprises providing a dimethyl ester mixture of 
dimethyl succinate, dimethyl adipate and dimethyl glutarate having an acid 
concentration no greater than 0.1 mg KOH per gm and adjusting the 
components of the mixture so their weight % concentrations lie within the 
area bounded by ABCDEA in the drawing in the specification.

DETAILED DESCRIPTION OF THE INVENTION 
Liquid hardener dimethyl ester compositions of this invention comprise 
dimethyl succinate (DMS), dimethyl glutarate (DMG) and dimethyl adipate 
(DMA) at weight percent concentrations equivalent to those lying within 
the area bounded by curved line ABCDEA of the drawing. 
Soil grouting formulations are injected under pressure into and permeate as 
liquid through a predetermined layer of usually loose soil below ground 
level. During a brief finite time interval called gel time the components 
react in the soil to form solid silica gel. The relatively hard silica gel 
has a consistency of candlewax and binds the soil together sufficiently as 
not to collapse when soil below without silica gel is removed. If the soil 
grouting formulation is too thick before setup, i.e. just before silica 
gel precipitates, it may not permeate the outer reaches of the soil region 
desired to be reinforced. On the other hand, if gel time is too long, the 
liquid mixture may laterally permeate through more soil than intended 
which is wasteful of the formulation and expensive. 
This invention relates concentrations of the particular dimethyl ester 
components of the liquid hardener dimethyl ester mixture to gel time and, 
more particularly, are chosen to provide a gel time of about 15 to about 
35 minutes. The liquid hardener mixtures of this invention are a species 
of dimethyl ester compositions commercially available from Monsanto 
Company under the trademark Santosol. 
To avoid influencing gel time, byproduct acid in the liquid hardeners of 
the invention is purposely kept low at a concentration no greater than 0.1 
mg of potassium hydroxide (KOH) per gm. Liquid hardeners of the invention, 
therefore, are relatively pure and stable, the ester component 
concentrations being tailored to promote hydrolysis in a controlled manner 
when mixed with water and sodium silicate components of the soil grouting 
formulation. 
The desired concentration of each specific dimethyl ester component in the 
three-component dimethyl ester liquid hardener mixture is readily obtained 
by conventional blending. In a commercial system associated with a 
distillation column providing the three-component mixture, column 
operating conditions may be set to provide a stream containing two of the 
three components and the third metered in at a predetermined appropriate 
rate to provide the desired concentration of each component in the three 
component mixture. 
The invention is further described in the following illustrative examples 
which are not intended to limit the invention. Percentages listed are by 
weight. 
EXAMPLE 1-7 
Simulate gel time with the following laboratory test conducted at room 
temperature (23.degree. C.). Add 45 g sodium silicate and 48 g H.sub.2 O 
to a glass container and shake gently. Then add 7 gm of dimethyl ester 
liquid hardener and hand shake for about 10 sec. Set the container with 
contents aside undisturbed and, using a stop watch, note the time interval 
until white precipitate is first visually noticed between the interfaces. 
This is gel time. 
Determine acid concentration of the liquid hardeners by autotitration using 
a standard solution of 0.1N tetrabutyl ammonium hydroxide, toluene and 
acetonitrile in the presence of methanol. Concentration in units of mg KOH 
per gm of sample is provided when the reaction between standard solution 
and DME is complete. 
Using the gel time test, liquid hardeners with varying component 
concentrations are prepared and gel times noted. The acid concentration of 
each liquid hardener is less than 0.1 mg KOH per gm sample. Results are as 
follows. 
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Example 
1 2 3 4 5 6 7 
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% Component Conc. 
DMA 32 4 44 16 2 15 10 
DMS 36 40 53 44 80 31 52 
DMG 32 56 3 40 18 54 38 
Gel Time (min.) 32 25 33 21 16 27 20 
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The compositions of Exs. 1-7 identified with the example number are shown 
within the area bounded by ABCDEA in the graph of the drawing. All such 
compositions have gel times between about 15 and about 35 min. 
EXAMPLES C1-C3 
These control examples are not according to the invention since the gel 
times for the compositions which are not within the boundary line ABCDEA 
are too long or short. 
The procedure of Exs. 1-7 is repeated with the following results. Each 
control composition is identified in the drawing by its control example 
number. 
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Example 
Component Conc. (wt. %) 
DMA 2 68 17 
DMS 81 19 16 
DMG 17 13 67 
Gel Time (min.) 12 70 55 
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The preceding description is for illustration only and not to be taken in a 
limited sense. Various modifications and alterations will be suggested to 
persons skilled in the art. The foregoing, therefore, is exemplary only 
and the scope of the invention is to be ascertained from the following 
claims.