ASPHALT GROUTS. Large subsurface flows of water are at times diffi-
cult to stop by grouting with cement, soil, or chemical grouts. For these
conditions asphalt grouting has sometimes been used successfully, particu-
larly in sealing watercourses in underground rock channels (see ref 54
and 57). Asphalt grout has `also been used to plug leaks in cofferdams and in
natural rock foundations. Asphalt is a brown-to-black bituminous substance
belonging to a group of solid or semisolid hydrocarbons. It occurs naturally
or is obtained as a comparatively nonvolatile residue from the refining of
s o m e petroleums. It melts between 150 and 200 F. When used for grout-
ing it is generally heated to 400 or 450 F before injection. Asphalt emul-
sions have also been used for grouting. These are applied cold. In the
emulsion the asphalt is dispersed in colloidal form in water. After injection
the emulsion must be broken so that the asphalt can coagulate to form an ef-
fective grout. Special chemicals are injected with the emulsion for this
p u r p o s e . Coal-tar pitch is not a desirable material for grouting since it
melts more slowly and chills more quickly than asphalt grout. When heated
above its melting point, coal-tar pitch also emits fumes that are dangerous
CHEMICAL GROUTS. In 1957 there had been some 87 patents issued
for processes related to chemical groutings (see ref 43). Since then there
undoubtedly have been more. These processes cover the use of many
different chemicals and injection processes. The primary advantages of
chemical grouts are their low viscosity and good control of setting time.
Disadvantages are the possible toxic nature of some chemicals and the rela-
tively high cost. Only a few of the more widely known types of chemical
grouts are discussed in the following paragraphs. Because of the variety of
the chemicals that can be used and the critical nature of proportioning,
chemical grouts should be designed only by personnel competent in this field.
Commercially available chemical grouts should be used under close consul-
tation with the producers.
-- . Precipitated Grouts.
(1) In this process the chemicals are mixed in liquid form for injection
into a soil. After injection, a reaction between the chemicals results in pre-
cipitation of an insoluble material. Filling of the soil voids with an insoluble
material results in a decrease in permeability of the soil mass and may, for
some processes, bind the particles together with resulting strength increase.
( 2 ) The most common form of chemical grouting utilized this process
with silicates, usually sodium silicate, being the primary chemical. Sodium
silicate is a combination of silica dioxide (Si0 2 ), sodium oxide (Na 2 0), and
w a t e r . The viscosity of the fluid can be varied by controlling the ratio of
S i 0 2 to Na 2 0 and by varying the water content. Silicate can be precipitated
in the form of a firm gel by neutralizing the sodium silicate with a weak
a c i d . The addition of bivalent or trivalent cations will also produce gelation.