September 2006

MATERIALS OF CONSTRUCTION
The Amazing Acid Resistance of Potassium Silicate Concrete

   You may not even notice potassium silicate concrete’s most amazing performance feat.  Properly mixed and applied, you won’t notice any sign of weakening after it is exposed to some of the strongest acids for days, weeks, or months on end.  Unlike Portland Cement based concrete, potassium silicate based polymer concrete is resistant to immersion in all concentrations of nitric, hydrochloric, phosphoric acids, and sulfuric acids, including oleum.  And with compressive strengths hovering around 4,000 psi, with appropriate design, it can be used for structural applications such as footings and foundations in acid-contaminated “brownfield” sites.

   What makes potassium silicate concrete resistant to acid?  Let’s first examine why Portland Cement based concrete is not resistant to acid.  Portland Cement, the binder that holds the aggregate in concrete together is an alkaline material that reacts with acid.  This reaction between the Portland Cement and acid conveniently neutralizes the dangerous acid, but at a considerable expense to the concrete’s structural integrity.  Once weakened, the products of this neutralization reaction are susceptible to erosion, often leaving only the larger aggregate behind, remnants of the mighty concrete that once was.

   Potassium silicate concrete is a polymer concrete, meaning it contains no Portland Cement binder.  It relies on inorganic potassium silicate binder technology.  Once cured, potassium silicate polymer concrete does not react with acid in a way that leaves the material weaker.  Under certain conditions, potassium silicate concrete gains strength in the presence of acid.

   Of course, there are a few catches.  Potassium silicate concrete is not resistant to hydrofluoric acid, hydrofluorosilicic acid, or any other type of acid that attacks silica.  And, it is risky to use potassium silicate concrete in areas exposed to alkaline chemicals, even if the environment is acidic most of the time.  Though the material is fairly resistant to cool neutral water once it is fully cured, hot neutral water can erode potassium silicate concrete, particularly if it is exposed before full cure is reached.  For this reason, it is important to protect areas directly under steam traps with a steel plate or acid brick pad or to reroute the steam.
Copyright © 2006, Henkel Corporation. All rights reserved. You may reproduce this article by including this copyright and, if reproducing it electronically, including a link to www.tufchem.com.

Potassium Silicate Concrete
Chemical Resistance At-a-Glance

Chemical Exposure

Compatibility

Chromic Acid to 50%

RECOMMENDED

Hydrochloric Acid to 37%

RECOMMENDED

Hydrofluoric Acid to 70%

NOT  RECOMMENDED

Nitric Acid to 50%

RECOMMENDED

Oleum

RECOMMENDED

Phosphoric Acid to 85%

RECOMMENDED


Within its chemical resistance limitations, potassium silicate concrete can be a useful material of construction.  It can provide a durable, acid resistant wear course when used as an overlay on battery plant floors or in oleum storage dikes.  Floor slopes to promote positive drainage are always advisable for maximum service life.  Gunite formulations are frequently used to line sulfur pits in oil refineries and chimneys in coal-fired power plants.


Dished pump tank bottoms in sulfuric acid plants, which are not conducive to lining with acid brick, rely on cast-in-place potassium silicate concrete for corrosion protection

  

To balance economic and structural considerations, potassium silicate concrete is typically applied in a 2-inch layer.  Because this type of polymer concrete has a degree of absorption and, like Portland Cement based concrete, is subject to cracking, it is wise to use a chemical resistant membrane underneath for long-term corrosion protection.  Look for potassium silicate concrete formulations that utilize reinforcing fibers to reduce formation and propagation of shrinkage cracks.

   While potassium silicate concrete possesses many admirable qualities—suitability for large and small cast-in-place applications, low cost relative to other types of polymer concrete, very high temperature resistance, and quick turnaround for compressed installation schedules—its exceptional resistance to widely ranging concentrations of some of the strongest acids drives it specification as a corrosion barrier from oil and ore refineries to basic and specialty chemical plants.



Cast-in-Place Acid-Proofing Saves Time

Set equipment on potassium silicate concrete structures and overlays in 24-hours (at 70ºF).  Material is compatible with tools and equipment used to mix and finish Portland cement concrete.  Wet concrete cleans up with water.