Sunday, June 16, 2024

Geopolymers and wastewater technology

By Dipl.-Ing. Jörg Brunecker Managing Director of Swietelsky Faber GmbH Kanalsanierung

Sustainability awareness also plays a key role today and will continue to do so in the future for construction products used in sewer renovation. Due to their energy-intensive production and enormous CO2 release, traditional cement products are now even classified as climate killers by experts. This is because, depending on the cement used, the enormous amount of CO2 released can only be partially absorbed again. The construction industry therefore urgently needs solutions. Anyone looking into this cannot avoid the term geopolymer, but what is a geopolymer, and is it also used in the wastewater network?

Swietelsky Faber GmbH Kanalsanierung has found what it was looking for in its search for geopolymers for sewers in America and is now launching the GeoKrete system for the trenchless lining of sewer pipes and structures exclusively in the German-speaking market.

Geopolymers are inorganic, non-hydraulic binders. In contrast to polymer concrete, they can be used to produce geopolymers with a drastically reduced proportion of cement.

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The play on words “geo” symbolically refers to the three-dimensional polymer cross-linking structure of the building material, which results in outstanding material strength and high resistance to temperature and chemicals under external pressure. The reason for this was insufficient fabrication of the liner, which took place without static proof. It was therefore not a Class A liner and consequently received the overall rating INADEQUATE, regardless of performance against all other criteria.

Basically, geopolymers are two-component systems that contain a reactive silicon and aluminum oxide component as well as a basic activation solution of alkali hydroxides. As with classic cement, the solid component consists of natural minerals. The concrete-like strength of the inorganic polymer is then achieved by mixing the ground solid mixture with the so-called activation solution.

An innovation from Vortex

 Geopolymers already appeared on the market in the 1970s. However, the breakthrough in the classic construction sector has not yet been achieved due to the price disadvantage compared to cements and the two-component processing. One of Vortex’s innovations is that they were able to bypass the two-component variant to create a single-component product that is soluble in water on the construction site by adding powdered aluminosilicate.

This means that the GeoKrete geopolymer can now simply be mixed with water and processed. Unlike conventional cements, which bind additives through hydration, GeoKrete simply uses water as a catalyst to trigger a chemical reaction. This reaction results in very high early and long-term strength, exceptional binding properties and ideal conditions for precise mixing, pumping and spraying on the construction site.

How Geopolymerisation works

In contrast to polymer concrete, where only synthetic resins are added to the cement products as a binder, the way geopolymers work is very different. The term geopolymerisation refers to the chemical reaction of geopolymeric materials, and the reaction mechanism initially involves the nucleophilic attack of hydroxide ions on the partially positively charged aluminium compounds and silicon crystals of the material. This leads to the breakage of the silica and aluminum oxide chains. At the same time, oligomer structures are formed, which polymerise to form a three-dimensional chain scaffold. The hydroxide ions undergo multiple chain scission.

Due to their structure, kaolinite and metakaolin dissolve in layers and release adsorbed water, which significantly reduces the viscosity of the not yet hardened geopolymer. Cement is still the most used building material in the world, but geopolymers can quickly overtake it for special applications. This is because they also have technical advantages: they are more heat-resistant than concrete – the bound water in concrete builds up vapor pressure in the event of fire, which leads to cracks or spalling. And they are more resistant to chemicals, as they do not contain lime, which dissolves on contact with acids and aggressive substances. After just one day, geopolymers develop compressive strengths like high-strength concrete. They can be stripped quickly and are suitable for the mass production of prefabricated parts.

Various manufacturers are currently experimenting with chemical-resistant wastewater pipes made from geopolymers. Although they are currently still more expensive than cement or concrete pipes… the sustainability and durability is a very good argument for the use of geopolymer pipes.

For trenchless sewer rehabilitation, the employees of Swietelsky Faber GmbH Kanalsanierung are convinced that geopolymers are ideally suited for use in manhole rehabilitation, the lining of accessible and non-accessible sewers and special structures of all kinds. For this reason, Swietelsky Faber GmbH is initially offering sewer rehabilitation with GeoKrete from Vortex exclusively in German-speaking countries. The first projects are already being planned and we will be happy to report back.

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