GEOPOLYMER CONCRETE

Generally Optimum temperature for curing is adopted as 60°C and period of curing is 24 hrs.

Studies showed that beyond 24 hrs period, heat curing is not required.

Alkaline chemicals are mixed before ½ hr of concrete making. Many researchers opined that it should be

mixed 1 day before using in concrete.

Compressive strength increases as temperature of oven curing increases from 30°C to 90°C.

Many researchers opined that: Longer curing times will increase compressive strength (generally 4 to 96

hrs).

Initial setting of geopolymer is very high, so GGBS should be added to reduce setting time.Only with

fly-ash addition will not set for even 2 days.

Rest period is the period before keeping in oven for curing.

Always Seal and keep it in oven Or Give rest period of 1- 3 days and keep in oven without seal.

Bond strength of round bar/HYSD bars and Geopolymer paste were higher than conventional concrete

(1.05-1.12 times for mild steel/1.60 for HYSD bars).

FA+SF/FA+GGBS combination allows GPC to set quickly.

16M or18M NaOH gives maximum compressive strength.

NaOH or KoH/ Na2Sio3 or K2So3 are the alkaline liquids used.

Formation of Geopolymer binder has basic reaction mechanism in three stages

1. Dissolution of Si and Al from the source material (fly ash) into concrete

2. Hydrolysis or gelation

3. Condensation

After 3 stages of reaction, 3D network of silica-aluminates are formed

In GPC-no hydraulic binder is required

Si-Al source + silicates+ water+ alkaline liquid forms Geopolymer precursor

Maintain Na2Si03/NaOH=2.5

Maintain Sio2/Na20 in Sodium silicate =2.00 (2.00-2.40)

Geopolymers are shapeless to semi-crystalline 3D alumina-silicate polymers like zeolites.

Geo-polymers are composed of polymeric silicon-oxygen-aluminum framework with silicon and

aluminum tetrahedral linked in three directions by sharing all the oxygen atoms

Geopolymerization process involves reaction between alumina-silicate oxides under alkaline conditions

yielding polymetric Si-O-Al-O bonds

The negative charge created by aluminum is balanced by the presence of positive ions such as Na+, K+

and Ca+

Water is released from the geopolymer matrix during chemical reaction. This water expelled from the

geopolymer matrix leaves discontinuous nano-pores in the matrix which are beneficial to the

performance of geopolymers.

Microstructure of geopolymers depends on the ratio of Si/Al

High pH is deleterious for geopolymer concrete and safe for OPC in reducing corrosion.

More molarity (of NaOH) gives high compressive strength.

Higher Na2Sio3/NaOH (2.0 to 3.5) higher compressive strength (as per researcher’s maximum@2.5).

Quality and reactivity of FA through mechanical chemical reaction.

Crystalline fly ashes should be grinded to sub-microcrystalline or Nano crystalline particles will enhance

reactivity.

Sub-bituminous coal on combustion gives fly ash with more calcium and less iron ex. ASTM Class C fly

ash (>20% CaO).

Bituminous coal and anthracite coal gives fly ash with less calcium and more iron ex. ASTM Class F fly

ash or alumina-silicate glass or (<10% CaO).

LOI gives presence of unburnt carbon.

Geopolymer concrete inorganic polymer- similar to natural zeolite materials – where microstructure

is amorphous instead of crystalline.

Presence of high calcium effects the polymerization process and consequently its microstructure.

Molar ratio of Si/Al should be =2.0 for GPC

1. Si/Al=1 Bricks/ceramics/fire protection

2. Si/Al=2 Concrete/low co2 cements

3. Si/Al=3 foundry Equipments

4. Si/Al>3 Sealants

Any material with Si and Al in amorphous forms can be used to manufacture of geo-polymers

If 16M NaOH, 16x40=640 gms of NaOH solids/litre of water

Where Molecular weight of NaOH=40

Total solution, 1000+640=1640 gms

For1640 gms of total solution, 640 gms is NaOH

So for1000 gms of total solution, the NaOH is 444 gms/litre

NaOH+Na2Sio3 solution should be kept for 20 min before preparing concrete making.

Maintain Na2Sio3+NaOH/Fly ash ratio=0.5

Maintain Na2Sio3/NaOH=2.5

Maintain Sio2/Na20=2.0