TM
5-818-6/AFM
88-32
(3.) Other effects. Numerous other substances can be added to portland-
cement grout to obtain special effects, Bentonite or other colloids, or finely
powciered metal are added to grout to make it more viscous and stable.
powdered metals unite with hydration products of the cement and release
tiny bubbles of hydrogen, which, in addition to increasing the viscosity, cause
a slight expansion of the grout. Aluminum is the metal most often used. It
is added at the rate of about 1 teaspoonful of aluminum powder per sack of
c e m e n t . Very small amounts of carbohydrate derivatives and calcium
lignosulfonate may be used as retarders. Sodium chloride is used to brine
mixing water when grouting is performed in salt formations. This prevents
erosion of in situ rock salt and provides a degree of bonding of grout to salt.
Approximately 3 lb of dry salt for each gallon of water will provide a satu-
rated mixture and will result in some retardation of the grout set.
e. Effect of Groundwater. Alkalies, acids, or salts contained in ground-
water may cause more damage to portland-cement grouts placed in sandy
soils than to these placed in clays. This increase in damage is a result of
the sandy soils permitting rapid leaching as opposed to clays which tend to
retard groundwater movement. In most clays, sulfate salts are found in very
small quantities. Rich type V portland-cement grouts will not be damaged
by low or moderate concentrations of calcium sulfate salts (gypsum).
Portland-cement grouts should not be used in formations containing salts
that consist of high concentrations of magnesium and sodium sulfates. Where
such concentrations are found, the use of chemical grouts should be con-
s i d e r e d . Harmful chemicals in groundwater may come from a number of
s o u r c e s , e.g., manufacturing plant wastes, water from coal mines, leaching
from coal storage and waste areas, and leaching of sodium or magnesium
m a t t e r . Waters of some streams and lakes in the western United States are
very harmful to Portland- cement grouts because of their alkaline content.
f . Effect of Seawater. Crazing and hairline cracks occurring in hard-
ened--grouts because of shrinkage, temperature variations, and tension may
permit the infiltration of seawater , which causes chemical decomposition of
the grout. During hydration the higher silicates decompose into lower sili-
cates and calcium hydroxide. The calcium hydroxide crystals dissolve
slowly in water, resulting in subsequent decomposition of the clinker grains
and liberation of new quantities of calcium hydroxide thus causing the cement
to deteriorate. The free lime in the grout also reacts with magnesium sulfate
in seawater and forms calcium sulfate, causing swelling in the interstices.
Portland-cement grouts for use in the presence of seawater should contain
air- entraining portland cement (type IIA) and waterproofing agents and have
low water-cement ratios. Entrained air in grout increases the impervious-
ness of the grout. (Some modification of the usual mixing and dumping fa-
cilities may be required when using air- entraining cement to avoid having
the sump tank overflow with froth. ) Waterproofing compounds that have
been found to have a marked increase in promoting various degrees of im-
permeability in portland-cement grouts are lime, fine-grained soils, tars,
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