Geopolymers: Promising Materials For Underground Applications

By Carlos Montes, Trenchless Technology Center | November 2013, Vol. 68 No. 11
Geopolymer coated concrete pipes being subjected to a laboratory-scale Microbial Induced Corrosion test.

The high temperature and fire resistance of geopolymer binders is an important aspect of the product. Hydration based cements will contain bound water which explode out of the concrete matrix when exposed to temperatures above 800 degrees F. Geopolymers, on the other hand, possess a stable molecule with no “chemical” or bound water which provides stability up to 2,300 degrees F. Current research is being conducted at the TTC to further increase geopolymer stability limits to 2,800 degrees F and beyond. Test results have shown that geopolymer can withstand ablation significantly better compared with current refractories due to its toughness and strength. While some refractories may provide stability at higher temperatures, their brittle nature makes them fail under abrasion and ablation when exposed to aggressive environments such as rocket engine impingement (Figure 5).

Figure 5. Geopolymer refractory panel after a flame impingement exposure of up to 4,000 degrees F showing minimal erosion.

Finally, geopolymer’s ecological nature poses it as one of the most significant new materials to reduce the carbon footprint of projects. The utilization of geopolymer concrete could mean the reduction of up to 85 percent of these emissions when used in substitution for Portland cement along with 80 percent reduction in energy consumption.

Geopolymer applications
Geopolymer applications developed at the TTC include the aforementioned sprayed mortar, which recently reached a market ready development stage, in addition to a growing variety of products including mix and pour, precast, drycast and quick set products.

The initial idea of using geopolymer for manhole rehabilitation was followed shortly by the idea of producing pre-cast geopolymer concrete pipes and manholes. The TTC produced a geopolymer formulation suitable for mass production of pre-cast concrete pipe which has been subjected to D-load testing with satisfactory results (see Figure 6).

Figure 6. Geopolymer concrete pipe developed by the TTC have successfully passed industry standard D-load tests.

One particularly interesting test currently under way at the TTC is Microbial Induced Corrosion. Geopolymer can be used as an encapsulation agent for biocide agents that can be stored in a slow release to prevent bacterial growth and break the MIC cycle. Figure 7 shows the experimental setup with three geopolymer coated concrete pipes subjected to bacterial growth. Results will provide an important testimony as to the ability of geopolymer mixes to inhibit bacterial growth.