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Alkali Activated Binder | Alkali Activated Cement





What's wrong with cement which is a highly used material in the construction industry.  cement has good binding properties than other binding materials like if we compare with lime. so let's go to know two major regions which insist us to find out other alternatives.

CO2   Emission : 

About 1.35 billion tons made per year Ordinary Portland cement (OPC) is typically used in the production of concrete as a binder. In the production of OPC carbon dioxide (CO2) is also produced.  OPC is responsible for approximately 7% of the total CO2 emissions released into the atmosphere per year worldwide. so due to many environmental concerns, the need to develop a new, sustainable alternative for OPC is needed.

Workability : 

Another problem faced by OPC concrete is related to its durability issues. OPC has a relatively high permeability, thus allowing water and other harmful media to penetrate concrete, causing corrosion and carbonation problems.

So what would be Alternative?

In this blog, I am gonna explain about Alkali Activated Binder

Why: Alkali Activated binders have shown to be a potential solution to OPC concrete concerns. Alkali – activated binders are seen to be a more sustainable choice due to its use of waste by-products, such as slag from the production of iron or fly ash from the burning of coal.



HOW TO GET alkali-activated binder

Davidovits, when he used to work in the industry, proposed that an alkaline liquid that can react with the silicon (Si ) and aluminum (Al) in a source material of geological origin or in by-product material can be used to produce binders.

  Exp.  Fly ash, when combined with an alkaline activator such as sodium hydroxide (NaOH) or           sodium silicate has been seen to produce not only a strong concrete binder but also more durable,     in comparison to OPC when exposed to harsh environments

       
        Source material         +              Alkaline liquid 

Alkali activated cement constitutes of two main compounds namely source materials and alkaline liquids.

What could be the source material?

  Generally, we take those waste materials having aluminum content more to minimize the CO2
  emissions.
 &
  Depending on aluminum and calcium contents we can classify GEO-POLYMER, SOIL CEMENT,    INORGANIC-POLYMER  CALCIUM SULFO-ALUMINATE, and  ORDINARY PORTLAND        CEMENT 



So, we are gonna use waste material having a low content of calcium and high content of aluminum. for example: fly ash, granulated blast furnace slag, rice husk ash, silica fume, red mud, municipal solid waste, metakaolin, or other alumina-rich materials 

What could be  Alkaline liquid?
  The alkaline liquids are from soluble alkali metals which are sodium or potassium-based. 
  Sodium hydroxide (NaOH) or Potassium Hydroxide (KOH) and Sodium silicate or Potassium 
  silicate are most widely used alkaline liquid.


Alkali-activated cement (AAC), also broadly termed as geopolymers (mainly for those systems with low content of calcium).

       the application of inorganic polymers as construction materials is unfavorable due to the high price of commercially available raw materials. For example, the price of metakaolin has risen during the last years due to its high demand. Therefore, in recent years, there is a trend to investigate alternative prime materials to be revalorized for the development of alkali-activated binders. In recent literature, other raw materials than metakaolin, mainly waste products from different industrial origins, are increasingly studied to be processed to synthesis an alkali-activated binder or geopolymer binder, and very promising results have been found, but also indicate that further research is needed. the synthesis of geopolymers out of waste ceramics which were activated by alkali hydroxides and/or sodium/potassium silicate solutions. compressive strength measured after 28 days was 71.1 MPa and favorable thermodynamically stable properties were observed. The results approve the approach of recycling ceramic wastes for the production of value-added alkali-activated composites.

      The greatest effect on strength characteristics is made by soluble sodium silicates. The alkali-activated cement concretes made using sodium silicates have high compressive strength reaching 120–140 MPa. 

Producing binders using low basic calcium or calcium-free aluminosilicates (clays) and solutions containing alkali metals. the binders called "soil cement" and the corresponding concretes "soil silicates".



 Composition of Waste material or source material 
 In the below table, we have taken compositions of fly ash and ground granulated blast-furnace slag



GRADE OF ALKALI-ACTIVATED FLY ASH CONCRETE AND RATIO




CORRESPONDING COMPRESSIVE STRENGHT



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Location: India

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