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What is Geopolymer :

    A hardened cementitious paste made from fly ash without Portland cement. It has greater compressive and tensile strengths, high strength gain rate, lower porosity and permeability, and greatly enhanced resistance to chemical attack compared with ordinary Portland cement (OPC) concrete. It combines waste products into a useful product, conserving landfill space and promoting sustainability, and compared with Portland cement, it features a 90% or greater reduction in carbon dioxide emission.

     A solution of sodium hydroxide and potassium hydroxide (waste products from the chemical and petrochemical industries) must be prepared separately, then added to the liquid commercial sodium silicate; this solution may then be added to the powdered fly ash (waste product from coal and bio fuel combustion) in the same way as water is added for Portland cement.

    

     The big difference between geopolymers and regular Portland cement is that their setting mechanism does not depend on HYDRATION, but rather in a POLYMERIZATION, which happens in a short period of time, while cement's hydration is mostly completed within one month, and fully completed only until one year.


     Geopolymer paste can be combined with the same aggregates used for Portland cement, for its use as mortar or concrete.

Curing:

     An important difference between geopolymer and Portland cement is that the geopolymerization reaction requires the application of heat to take place. Curing temperatures ranged between 60 and 90 C depending on the properties of the fly ash used.

     In the lab, steam or oven curing may be used. Temperature times are usually 24 hrs. Shorter curing times are currently being researched.

Properties:


    
     Compressive strength: 3,000 – 16,000 psi (depending on the geopolymer formulation used).

     Flexural strength: Approximately twice that of OPC.

     Chemical resistance: Two to Five times greater resistance to sulfuric acid attack compared with OPC; virtually immune to sulfate attack.

     Porosity/Permeability: Ten times lower than OPC utilized in typical structural applications.

     Strength gain: Full strength is gained within 1 to 3 days; 80% of ultimate strength is gained within 1 day.

     Setting time: 15 to 120 minutes

     Fire Resistance: Non-flammable non-combustible.

     Carbon dioxide emission: 10% or less compared with OPC (i.e., 90% CO 2 emission reduction).

     Alkalis are incorporated in the geopolymer paste, therefore will not react with aggregates.

     Geopolymer does not have any phase that can lead to ettringite formation.

     Geopolymer's structure will allow much less ion penetration (Chlorine and Carbonate ions).

     Small drying shrinkage due to the geopolymer's smaller capillaries and its overall higher density.
 
 

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