TM
5-818-6/AFM
88-32
regarded as suitable for use in grout. Ordinarily the presence of
harmful
impurities (e. g., alkalies, organic and mineral acids, deleterious
salts, or
large quantities of silt) is known in local water sources. If there
is reason
to suspect a water source, it should, be tested in accordance with
CRD-C 400
(see ref 9).
c. F i l l e r s . Fillers in portland-cement grout are used primarily for
reasons of economy as a replacement material where substantial quantities
of grout are required to fill large cavities in rock or in soil. Almost any
solid substance that is pumpable is suitable as a filler in grout to be used in
nonpermanent work. For permanent work, cement replacements should be
r e s t r i c t e d to mineral fillers. Before accepting any filler, tests should be
made in the laboratory or in the field to learn how the filler affects the set-
ting time and strength of the grout and whether it will remain in suspension
until placed. All aspects of the use of a filler should be carefully studied.
The economy indicated initially by a lower materials cost may not continue
throughout the grouting operation. Additional personnel and more elaborate
batching facilities may be needed to handle the filler. Some fillers make the
grout more pumpable and delay its setting time. Such new properties may
add to the costs by increasing both the grout consumption and the grouting
time.
(1) Sand. Sand is the most widely used filler for portland-cement grout.
Preferably it should be well graded. A mix containing two parts sand to one
part cement can be successfully pumped if all the sand passes the No. 16
sieve and 15 percent or more passes the No. 100 sieve. The use of coarser
sand or increasing the amount of sand in the mix may cause segregation.
Segregation can be avoided by adding more fine sand or using a mineral ad-
mixture such as fly ash, pumicite, etc. Mixes containing up to 3/4-in. aggre-
gate can be pumped if properly designed. Laboratory design of such mixes
i s recommended. Sanded mixes should never be used to grout rock contain-
ing small openings and, of course, should not be used in holes that do not
readily accept thick mixes of neat cement grout (water and portland cement
only).
(2) Fly ash. Fly ash is a finely divided siliceous residue from the com-
bustion of powdered coal, and may be used both as a filler and as an ad-
mixture. Most grades of fly ash have about the same fineness as cement
and react chemically with portland cement in producing cementitious proper-
t i e s . The maximum amount of fly ash to be used in grout mixtures is 30 per-
cent by weight of the cement, if it is desired to maintain strength levels
comparable to those of portland-cement grouts containing no fly ash.
( 3 ) Diatomite. Diatomite is a mineral filler composed principally of
s i l i c a . It is made up of fossils of minute aquatic plants. Processed diato-
mite is an extremely fine powder resembling flour in texture and appearance.
The fineness of the diatomite may range from three times to as much as
9
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