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.

Some of the reasons behind the lack of acceptance of previous geopolymer technology were the poor workability, fast setting and hardening times and inability to produce ambient cured geopolymer mixes. The TTC has begun a comprehensive research study on the mechanisms behind the setting and hardening process of geopolymer and has found that current ASTM standards are not adequate to measure it in geopolymer systems. Work is under way to modify these standards to enable adaptation to geopolymer binders, including the incorporation of emerging ultrasonic shearwave technology. A technical report on this research thrust is expected to be released soon.

Regarding corrosion resistance, the TTC’s patented sprayable geopolymer offers corrosion resistance up to eight times greater than that of Portland cement-based sprayed mortars. Extensive research regarding geopolymer corrosion resistance against several acids reagents as well as sea water was recently completed at the TTC with excellent results demonstrating the ability of the material to be used in applications ranging from chemicals and wastewater storage facilities, to industrial sewers and saline lines in desalination plants.

Another interesting feature regarding geopolymers is the protection it offers to carbon steel rebar. Its denser and less permeable structure decreases chlorine intrusion up to 90 percent providing more effective protection to the steel rebar (Figure 3). This is enhanced by geopolymer’s chemical adhesion in addition to the mechanical interlock to steel surfaces which increase pull out strength by up to three times compared with these observed for Portland cement. Surprisingly, geopolymer concrete also exhibited greatly enhanced pull-out strength for embedded smooth stainless steel rebar, further indicating a possible chemical adhesion (Figure 4).

Figure 3. Corrosion on steel rebar inside Portland cement concrete after an accelerated chlorine intrusion test (left), its counterpart embedded in geopolymer concrete shows no signs of corrosion.

Figure 4. The pull out force on stainless steel rebar embedded in geopolymer concrete is up to three times of that of steel bars in Portland cement concrete.

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