What is the difference between between silicates and colloidal silica?
Sodium, Potassium, and Lithium are known silicate materials. Sodium silica dates back to 1930’s Germany, and has been used extensively worldwide, as an inexpensive hardener and densifier. It effectively minimizes dusting and efflorescence, and increases abrasion resistance and surface water repellency.
As of late, there has been much ado about the improved performance of colloidal silica –which means the silica is amorphous, spherical in shape, minute in size, and remains suspended into an aqueous base. It outperforms silicates, simply because it is a finer solids then a non-colloidal silicate.
All colloidal silica solutions on the market are made using known silica materials. The “glass-like” alkali reactive gel (C-S-H) formed at the surface and sub-surface levels of a concrete mass is what creates the added abrasion resistance, stops dusting and decreases surface permeability.
How is DRYCRETE different from other colloidal silica or silicate compounds?
DRYCRETE Moisture Stop is a proprietary, catalyzed colloidal silicate –and not colloidal silica.
Although similar in chemical composition, DRYCRETE Moisture Stop contains a proprietary catalyst which changes its physical properties, so that is remains suspended in colloidal form, into an aqueous base. It does not compare to colloidal silica, as the effects of the catalyst changes the chemical structure and physical properties of DRYCRETE Moisture Stop in liquid form. The molecular level demonstrates spherical cells of minute proportion, each consisting of a conglomerate of spine-like smaller cells, clumped together to form a single cell.
As the product reacts with free alkali, it further breaks down to the smallest of the cells which form the nucleus, and create a 100% solids Calcium Silicate Hydrate (CSH) gel which then exudes all of the properties of a solidified silica.
How can Drycrete products be used as a curing medium, while conventional silicates cannot?
The American Concrete Institute (ACI), states that conventional silicate solutions simply cannot act as a curing medium because they do not:
"... maintain moisture and temperature conditions in a freshly placed cementitious mixture to allow hydraulic cement hydration and (if applicable) pozzolanic reactions to occur so that the potential properties of the mixture may develop.“
They further state that conventional silicates could improve concrete durability if applied after proper curing.
On this point, both ACI and the manufacturers of conventional silicate solutions agree - silicate solutions "should not be applied on fresh concrete."
Since conventional silicate solutions are more viscous than the water filling the surface pore structure of fresh concrete, silicate solutions cannot "penetrate properly and will not chemically react as intended.
Concrete samples treated with DRYCRETE™ products have been tested and compared to water cured samples, and demonstrate equal or superior performance on the following tests:
• Compressive Strength (7% Increase)
• Flexural Strength (15% Increase)
• Abrasion Loss (50% Reduction)
• Surface Dusting (31% Reduction)
• Water Permeability - Tested over 100-foot Head Pressure (89% reduction)
• Water Permeability - USACOE C48 @ 100-foot Head Pressure (0 Leakage)
• Water Permeability - DIN 1048 @ 72.9-psi Pressure (94% Reduction)
• Freeze-Thaw Resistance (85% Improvement)
Over the past two decades, DRYCRETE Products have consistently demonstrated, through testing and field observations, that they achieve the intent of ACI's definition for curing even though no surface membrane is formed.
What are the chemical / physical differences between Drycrete Products and conventional silicate sealers?
Upon application, DRYCRETE Products forms colloidal silica within the capillaries and pores of the concrete.
Colloidal silica is essentially a suspension of dense, amorphous Si02 particles dispersed in a liquid phase. These particles are so small (i.e. approximately 30 to 100 nanometers) that gravity will not cause them to settle out of suspension. In addition, DRYCRETE Products exhibit a viscosity close to water and a pH in the range of 11 to 12. These attributes give DRYCRETE Products superior concrete penetrating characteristics.
Conventional silicate sealers, on the other hand, are water-soluble crystals that exhibit viscosities closer to syrup when in solution and have a pH range of 12 to 13. This indicates that for a given concrete substrate, the penetrating ability of DRYCRETE Products are much greater than conventional silicate sealers.
Why are silicates and DRYCRETE Products used for waterproofing, and why should they not be considered equal?
Both are widely marketed as penetrating reactive sealers because they react with unbound, free alkalis in the concrete capillary and pore space to form Calcium Silicate Hydrate (CSH) – the “glue” that holds concrete together. However, the degree of surface penetration, completeness of the reactions, and long-term performance are very different.
Conventional silicates, in addition to being more viscous than DRYCRETE Products, react quickly with alkalis upon contacting the concrete surface. The poorly distributed and formed thixotropic crystalline gel at the surface hinders the penetration of the viscous solution, thus limiting its waterproofing effectiveness and longevity.
The thixotropic crystalline gel is also not of uniform composition and can contain variable-sized pores, ranging from very small to very large. This causes the thixotropic crystalline gel to be temporary, at best. As water migrates through the larger gel pores, the thixotropic gel can erode and eventually fail at a rate dependent on the volume of water and its driving force passing through the concrete.
“DRYCRETE Products allow for deeper penetration before the CSH-forming reactions take place.”
Therefore, the depth of penetration is greater and more consistent when compared to conventional silicates.
In addition, since the colloidal silica particles that form within the concrete capillaries and pores are of uniform size – not the product of uncontrolled precipitation like the silicates – the CSH gel formed in the capillaries and pores is much more uniform without the inconsistent voids found in silicate gels.
Can ion chromatography be used to determine the presence of DRYCRETE Products like conventional silicates?
NO, because DRYCRETE Products are not in the same category as sodium, potassium, and lithium silicates that precipitate out of solution. DRYCRETE Products revolve around a catalyzed colloidal silicate that forms reactive colloidal silica within the capillaries and pores, which is substantially different.
Conventional silicate sealers are known to contribute to concrete deterioration if they are subjected to repeated wetting / drying cycles (i.e. – exterior concrete, floor cleaning, etc.). In addition to any unreacted conventional silicate solution that is trapped within the pore space, the ionic salts that are used to stabilize the sealers’ chemistry also form compounds within the concrete porosity that are moisture sensitive and can create expansive forces. Eventually, this results in a type of craze cracking on the concrete surface. Continued wetting / drying cycles eventually lead to surface pitting and shallow potholes.
Ion chromatography is used to identify conventional silicate-based concrete surface hardeners, but it does not look for silicates per se. Instead, it looks for the ionic salts associated with their chemistry (i.e. – sodium, potassium, lithium, etc.)
Since DRYCRETE Products are based on catalyzed colloidal silicates that contain little to no ionic salts to stabilize its chemistry, the lab testing does not reveal much of anything.