Concrete
Our 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 National Silicates' 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.)