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Penetrating sealant
Accelerating admixture
Alkali-activator for fly ash and slag
Component for refractory materials and specialty cements
PQ® silicate products are used both as penetrating
sealants and as admixtures for cement and concrete. Concrete sealants may be
formulated from either sodium or potassium liquid silicates.
As the
silicate solution penetrates the concrete surface, the soluble SiO2
species react with portlandite (Ca(OH)2) and/or Ca2+ in
the pore solution to form calcium silicate hydrate (C-S-H). Portlandite is an
undesirable phase in concrete because it precipitates as platelets near
aggregates. The result is a porous paste/aggregate interface that increases
concrete permeability and reduces compressive strength. Portlandite is also
subject to acid attack and carbonation.
In contrast, C-S-H is the
desirable, space-filling glue phase. Applying a silicate sealant causes C-S-H to
replace portlandite. The results are enhanced abrasion resistance (that is,
dust-proofing), chemical resistance, and durability of the concrete surface.
Instructions on how to formulate and apply silicate-based sealants are
available through PQ’s Technical Service Group. Care should be taken to avoid
circumstances that promote efflorescence, or blooming, of the concrete after
silicate application. In some cases, potassium silicate can be used to avoid
blooming problems.
As an admixture, silicates can be added to cement or
concrete mixes either as liquid, hydrous powder, or even glass powder. Soluble
silicates accelerate cement set. The degree of acceleration will depend on the
form of the silicate added. For example, a liquid will cause the fastest set
because the silica is already in solution. For powders, however, the silicate
must dissolve first. Because hydrous powders dissolve more quickly than glass
powders, they will accelerate the set faster than glass. (Other factors, such as
ratio and particle size, also will affect dissolution rates.) A typical example
of silicate use is shotcreting, in which a liquid silicate causes the cement to
set immediately.
Set accelerators can have a detrimental effect on
compressive strength. In smaller doses, however, silicates may provide higher
compressive strength and improved durability because of the reduction in
portlandite formation. (This technique is similar to adding pozzolans or other
silicas to concrete.)
The use of a soluble silicate admixture is
especially helpful when fly ash or slags are blended with cements. Large
additions of these products can significantly retard set unless some
counter-measure, like silicate addition, is used. Soluble silicate can also
serve as an alkali-activator for fly ash and slag, and thereby turn waste
products into useful materials.
In the composition of refractories and
chemically resistant materials, sodium and potassium silicates serve as binders
and as sources of alkali and silica. Air-setting specialties that contain
soluble silicates are used as refractory mortars and as ramming, gunning, and
patching mixes in virtually all refractory or chemically resistant construction.
Among examples are:
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Boilers |
Chimney Construction |
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Incinerators |
Sulfite Digesters |
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Furnaces and Ovens |
Electrolytic Cells |
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Ladle Linings |
Acid Manufacturing |
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Catalytic Cracking Chambers |
Soaking Pits |
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Sewage Works |
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