Concrete Cloth Stormwater Infrastructure

September 18, 2017
The Chemical Resistance of Geopolymers

Posted by: Joe Royer

Given enough time, use and environmental exposure, infrastructure in both the storm water and sanitary sewer markets are susceptible to deterioration. Rehabilitation is, of course, often an option but determining causation is usually the first step in understanding the best solution.  Failing or damaged infrastructure such as culverts, manholes or sewer lines all present different corrosion challenges that require specific repair methods.  

Completely replacing an item such as a large diameter pipe carries an extremely high price tag. Asset owners are wise to seek rehabilitation options first. However, these pipes must endure harsh environments, so asset owners also need a repair solution that can withstand the environmental conditions of these systems and can provide a longer lifespan for their infrastructure.

Piping used for sanitary sewers and storm water environments are both exposed to corrosive environments. Storm water applications, such as corrugated metal culverts, are generally prone to a simple deterioration process — exposure to flowing water and moist conditions over time leads to the inverts of these culverts rusting through or eroding from abrasion by harsh materials in the water flow.

In sanitary applications, due to the cementitious makeup of the infrastructure, these assets are subject to an entirely different corrosion mechanism, known as Microbial Induced Corrosion (MIC). MIC occurs on the top portion of the pipe. The specific composition of the cementitious material will ultimately dictate the severity of the MIC, but in general, it occurs in environments where the following circumstances take place:

  1. Hydrogen sulfide gas (H2S), commonly referred to as sewer gas, is released by the reduction of sulfates in the sewer effluent from anaerobic bacteria — generally living in a “slime layer” below the water line.
  2. Sulfuric acid (H2SO4) is formed on exposed surfaces through the oxidation of H2S by aerobic Thiobacillus bacteria.
  3. The sulfuric acid reacts most often with Ca(OH)2 found in many cements to form gypsum (CaSO4) which is water soluble and will wash away, leaving behind voids and damage in the cementitious pipe.

The results of this deterioration process have been the major impetus behind the growing demand for rehabilitation products that are increasingly resistant to chemical corrosion. Geopolymer repair products, such as Milliken Infrastructure’s GeoSpray® mortar, fit the bill in many applications — whether it’s repairing a weathered storm water culvert or a large diameter municipal interceptor.

What makes a geopolymer product like GeoSpray the preferred solution to these repair scenarios lies in its chemical makeup. Though resembling cement in its strength and durability, it contains very little calcium hydroxide. This composition makes the creation of gypsum far more difficult, which leads to a longer lifespan for the pipe.

While other internal pipe protection solutions such as spray-on polymer lining products might be considered a chemical-resistant alternative, a product like GeoSpray can produce a structural solution that is independent from the host structure and doesn’t require bonding to the existing structure. A plastic corrosion resistant coating requires a perfect bond, adopting a far greater risk of having a failure in the application when it is not applied to a perfect surface (i.e. when the pipe is initially manufactured). Asset owners concerned with chemical resistance in cement applications need to look no further than geopolymer mortar solutions.

To learn more about Milliken’s geopolymer mortar products such as GeoSpray™, and how they can improve the performance and strength of your storm and sanitary infrastructure, visit http://infrastructure.milliken.com/geopolymer-mortar-systems/.

 

FILED UNDER:
Category: GeoSpray Geopolymer

Comments

Leave a Comment