Geopolymer

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As geopolymers inorganic be binder ( silicate technology ), respectively. Geopolymers can be used for sealing and reprofiling sewage systems.

history

Geopolymers were used as natural concrete by the chemist Joseph Davidovits as early as 1975 . At that time the term was used for the reaction of metakaolins in alkaline media to form aluminosilicate polymers. The addition "Geo" was intended to clarify the proximity to geological materials, ie natural rocks and minerals. Already at the end of the 1950s, Gluchovski was researching under the term Soil Cements how thermally activated clays , ashes , natural pozzolans and also slag could be used as latent hydraulic binders. This is generally referred to as an alkaline activation as a solidification reaction. Davidovits had already discussed a stone casting process for the construction of the Egyptian pyramids , which should be based on such binder systems. The thesis found both support and rejection in the natural sciences.

New developments in geopolymeric silicate binders were investigated by the Bauhaus University Weimar . In addition, innovative systems are based on one-component, highly chemical-resistant silicate systems that are implemented by alkaline activation of blast furnace slag with powdered water glass . The pressurized water-tight, shrink-free, environmentally friendly systems are free of calcium hydroxide and therefore have excellent acid and alkali resistance (pH 0-14).

In contrast to cement-bound building materials, an amorphous silicate gel (SiO 2 • nH 2 O) forms in the hardened matrix of the binder with alkali silicate mortars . In contrast to cement-based building materials, these alkali silicates, also known as hydrogels , are resistant to all inorganic and organic acids (except hydrofluoric acid ).

Due to the three-dimensional crosslinking of the silicate structures stable systems can produce very that already without fiber reinforcement compressive strengths of up to 95.3 N / mm² (7 days), 131 N / mm² (28 days) and flexural strengths of up to 10.41 N / mm² (7 days) or 11.67 N / mm² (28 days). Investigations at the University of Dresden have shown that this three-dimensional cross-linking is very well suited to binding even the very smooth carbon fibers very tightly (initial crack stress> 200 N / mm², stress-strain relationship at 13.3% elongation> 1,200 N / mm²). The SEM images also show the excellent edge fit to the embedded filler grain and the water pressure-tight silicate matrix.

Synthetic routes

A distinction can be made between two synthetic routes:

  1. In alkaline medium (Na + , K + , Li + , Ca 2+ , Cs + and the like)
  2. In an acid medium with phosphoric acid , fruit acids and humic acids .

Fruit acids can also be used to make minerals more reactive in alkaline media by leaching metals out of the minerals.

The extraction of clays with fruit acids to increase chemical reactivity is often used in the manufacture of fuller's earth .

use

These water pressure-tight and highly chemical-resistant structures can also be used for sealing and re-profiling sewage systems. It has been shown here that the geopolymer, silicate structures have a higher level of impermeability than corresponding cement-based or polymeric sealing systems.

The processing of the geopolymeric silicate binders is identical to the previously used polymer or cement systems. All existing coating processes and machines can be used. In contrast to cement mortars, however, due to their dense packing and excellent adhesion to mineral and metallic substrates, they can also be used as thin-layer coatings and scratch fillers. Due to the good water vapor diffusivity, there is no risk of moisture condensation behind the coating, as is often observed in polymeric coating systems on moist mineral substrates.

Due to the excellent chemical resistance and the inorganic, quasi- ceramic composite structure, no corrosion of the surface is to be expected.

The adhesion to mineral surfaces is excellent thanks to the liquid binding agent water glass. Very good adhesion can also be achieved on steel. A polymer hybrid primer is only required to promote adhesion for polymers .

Environmental sustainability

Through the use of slag sand or other latent hydraulic binders such as. B. Ashes and slag as the basic raw material, very environmentally friendly coatings and materials can be produced that have a very favorable CO 2 balance. These products are solvent-free and use water as an environmentally friendly solvent. Due to the low pH value (no Ca (OH) 2 ), it is easy and safe to process even for the processor without additional work protection.

There are different water glasses that differ in the metallic counterion . Sodium water glass is the cheapest, but unfortunately also plant-toxic variant. Lithium waterglass is the most reactive variant, but it is very expensive and also not plant-friendly. Potassium water glass is available inexpensively as a mass raw material, is the only representative with the plant fertilizer potassium as a counterion and is therefore very environmentally friendly.

Individual evidence

  1. ^ Joseph Davidovits: They built the pyramids . Institut Géopolymère, Saint-Quentin 2008, ISBN 2-9514820-2-7 .
  2. ↑ Sheila Berninger, Dorilona Rose: The Surprising Truth About How the Great Pyramids Were Built. In: Live Science. May 18, 2007, accessed July 29, 2017 .
  3. ↑ Dipayan Jana: Evidence from detailed petrographic examinations of casing stones from the great pyramid of khufu, a natural limestone from tura, and a man-made (geopolymeric) limestone . In: Proceedings of the Twenty-Ninth Conference on Cement Microscopy . May 2007 ( PDF ).
  4. ↑ M. Curbach, E. Lorenz: Investigations into the applicability of "Sinnodur-UHPC-casting mortar" as a high-strength fine concrete matrix for textile concrete. (PDF; 753 kB) Technical University of Dresden, Faculty of Civil Engineering, Institute for Solid Construction, Dresden 2010.
  5. ↑ J. Rathenow: Final report on HA project 181 / 09-11, silicate technology based on nanotechnology for coatings and pipeline construction. Sinnotec Innovation Consulting GmbH, Wiesbaden 2010.
  6. ^ Organic Acid Geopolymers. (No longer available online.) In: karls-geopolymers.proboards.com. Archived from the original on July 29, 2017 ; accessed on July 29, 2017 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / karls-geopolymers.proboards.com
  7. ^ Wet Activation of Clays instead of Calcination. (No longer available online.) In: karls-geopolymers.proboards.com. Archived from the original on July 29, 2017 ; accessed on July 29, 2017 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / karls-geopolymers.proboards.com
  8. ↑ B. Bosseler, M. Gillar, M. Liebscher: Rehabilitation of sewage shafts - investigation of materials and systems for sealing and coating. Part 2 Local sealing measures. In: Correspondence waste water. Volume 58, No. 9, 2011, pp. 814-824 (PDF; 608 kB).
  9. ↑ M. Liebscher, M. Gillar: Rehabilitation of sewer manholes, investigation of materials and systems for sealing and coating, final report on the research project rehabilitation of sewer manholes. (PDF; 15.8 MB) AZ: I-2-ZV-2.1-08 / 068 and I-2-ZV-2.1-08 / 068.1 (IV-7-041 105 0251), IKT, Gelsenkirchen 2011.

Web links

Commons : Silicates  - Collection of images, videos and audio files