Geopolymer concrete ( A Concrete without Cement)

Concrete is the most used construction material. As the demand of concrete as a construction material increases, so also the demand of cement. Since Cement manufacturing industry is responsible for around 5-7% of total CO2 emissions in the world. 

The Global warming and climate change are the major concern of the modern society.

There is a major problem of dumping fly ash; a waste product of thermal power plant and Blast furnace slag; a waste product of metal industries.

Geopolymer concrete is a type of concrete in which cement can be replaced up to 100 %.

Components of Geopolymer Concrete:

The major components of geopolymer concrete are :-

  • Low Calcium (Class F) Fly Ash
  • GGBS (Ground Granulated Blast Furnace Slag)
  • Sodium Hydroxide (NaOH)
  • Alkaline Sodium Silicate (Na2SiO3)
  • Aggregates

Binding Action of Geopolymer concrete:

As we all know that cement act as a binder in concrete to bind aggregates . Although Fly ash is a pozzolanic material but in geopolymer  concrete, it does not undergo pozzolanic reaction.

In Geopolymer concrete the binding action is due to the activation of fly ash by highly alkaline solution of Sodium Hydroxide and Sodium Silicate, the reaction is called polymerisation reaction.
The reaction is fast and can be accelerated by providing extra heat.

 We cannot use Class C fly ash as it hinders the reaction.

Mix design:

A general mix design of geopolymer concrete is as follows:

•    Density = 2400 Kg/m3

•    Cementatious material : fine aggregate : coarse aggregate=1 : 1.3 : 3.1
(Cementatious materials=Fly ash + GGBS)

•    Alkaline liquid: Cementitious material =0.35
(Alkaline liquid= Sodium Hydroxide +Alkaline Sodium Silicate

•    Fly ash : GGBS=7:3
•    NaOH:Na2SiO3=2.5
•    w/c ratio=0.35
•    Molarity of NaOH = 12M

This is a general mix design. Various parameters of this design can be varied to get better results.

Curing of Geopolymer Concrete:

As no hydration reaction is taking place so water is not used in the polymerization reaction.
We opt for dry curing to drain out excess water and to accelerate polymerization reaction.

Advantages of Geopolymer Concrete:

•    Geopolymer concrete attains its ultimate strength quickly ,can be used for manufacturing precast members.
•    Geopolymer concrete does not generate any deleterious alkali-aggregate reaction even in the presence of high alkalinity.
•    Geopolymer concrete  has very low creep and shrinkage.
•    Geopolymer concrete can withstand heat and cold better than OPC cement concrete .
•    Geopolymer concrete cost analysis shows that it is economic than OPC cement concrete.

Disadvantages of Geopolymer Concrete:

•   Geopolymer concrete requires external heat for curing.
•    The polymerization reaction is sensitive to many factors so the products lack uniformity.
•    Geopolymer concrete requires skilled labour for its batching and mixing.
•    Geopolymer concrete is still under study and research.

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