15 times that of cement. Small amounts of
diatomite may be used as admix-
tures to increase the pumpability of grout;
however, large amounts as fillers
will require high water- cement ratios for
pumpability. As a filler, diatomite
can be used where low strength grouts will
fulfill the job requirements.
( 4 ) Fumicite. Pumicite, a finely pulverized volcanic ash, ashstone,
pumice, or tuff, is also used as a filler in cement grout. Like fly ash and
diatomite, it improves the pumpability of the mix and has pozzolanic (hy-
draulic cementing) action with the portland cement.
( 5 ) Other fillers. Silts and lean clays not contaminated with organic ma-
t e r i a l s are sometimes used as fillers. Leess, a windblown silt containing
from 10 to 25 percent clay, is a suitable filler. Rock flour, a waste product
from some rock-crushing operations, is also used as a filler. Rock flour
produced during the manufacture of concrete sand is very fine but not al-
ways well graded. Grouts containing poorly graded rock flour are fre-
quently highly susceptible to leaching. Most finely divided fillers increase
the time required for the grout to set. It may be expedient to add an accel-
erator, described subsequently, to compensate for this.
d . A d m i x t u r e s . Admixtures as described herein are substances that
when added to portland-cement grout, impart to it a desired characteristic
other than bulking.
Accelerators. Accelerators cause a decrease in the setting time of
grout. These additives are used to reduce the spread of injected grout, to
reduce the erosion of new grout by moving groundwater $ and to increase the
rate of early strength gain. The most commonly used accelerator is calcium
c h l o r i d e . It can be added to the mixing water in amounts up to 2 percent of
the weight of the cement. Greater percentages of calcium chloride increase
the very real danger of having the mix set up in the grout plant. High alumina
cement and plasters having a calcined gypsum base may be proportioned with
portland cement to make a grout having various setting times. Other accel-
erators include certain soluble carbonates, silicates, and triethanolamine.
Small amounts of some accelerators are capable of producing instantaneous
or near instantaneous setting of the grout. Triethanolamine added to some
cements in the amount of 0.2 percent can produce such sets. When using ac-
celerators, competent technical advice should be sought and preliminary
tests conducted to determine the behavior of accelerators in the grout mix.
( 2 ) Lubricants. Fly ash and rock flour added to the grout mix increase
its pumpability. Fluidifiers and water- reducing admixtures improve the
pumpability or make possible a reduction in the water- cement ratio while
maintaining the same degree of pumpability. Most of these substances are
a l s o retarders. Laboratory or field trial mixes should be batched and all
pertinent effects observed and tested before adopting an unknown admixture
for any project.