1. A STUDY ON THE COMPRESSIVE STRENGTH AND MINERALOGICAL PROPERTIES OF FLY ASH AND RED MUD BASED GEOPOLYMER MORTAR
Dr. B HANUMANTHA RAO, IIT BHUBANESWAR, ODISHA, INDIA –
Introduction
Chemical Composition of Fly ash & Red mud
Compressive Strength & Mineralogical Properties
Material
Oxide Compositions (In weight %)
SiO2
Al2O3
Fe2O3
CaO
Na2O
K2O
Other oxides
LOI*
Fly ash
61.9
28.10
4.15
0.89
0.37
0.80
3.3
0.48
Red mud
14.6
25.26
45.31
1.19
4.80 -
2.7
6.5
Compressive strength is decreasing with the increase in the red mud proportion in the mix.
With the increase in red mud, the total silica content is reducing which could be the reason for decrease in the strength.
Also decrease in the strength with time is noticed when the red mud content is 20% or more.
FLY ASH
RED MUD
1 tonne of cement production leads to emission of equal amount of CO2
Generation of huge amount of industrial wastes such as fly ash, red mud. Storage area construction and its maintenance are highly cost-intensive.
Geopolymers have the potential to use industrial wastes and completely avoid cement usage. Utilization of fly ash, and red mud through geopolymers as an environmental protection material would be big step towards green revolution.
Mix Proportioning of Fly ash-Red mud Mortar
Increase in the red mud content is inhibiting the geopolymerization.
With an increase in the red mud content, the increase in the amount of unreacted particles can be seen.
This could be causing decrease in strength of the mortar specimens.
Mix
Na2SiO3 /NaOH
AAS to BS
Fly ash
(kg/m3)
Red mud (kg/m3)
Sand
NaOH
Na2SiO3
Remarks FA
1.5
0.5
714
1286
143.8
214.2 Na O H
14M M1
709 37
1353
149.3
224 M2
671 75
1354
149.2
223.8 M3
633
112
1355
149.1
223.6 M4
596
149
148.9
223.4 M5
558
186
1356
148.8
223.2 M6
520
223
1357
148.6
222.9 M7
483
260
1358
148.4
222.7
OPC Binder vs Geopolymer Binder
SEM images of geopolymer mortars of various mixes after
28 days of curing
leaching of sodium and ferrous ions are increasing with time, where the red mud content in the geopolymer mixes is exceeding 15%.
This could also be another reason for the decrease in the strength with time.
FA: 100% Fly ash; M1- 95% FA + 5% RM; M2- 90% FA + 10% RM;
M3- 85% FA + 15% RM; M4-80% FA + 20% RM; M5- 75% FA + 25% RM; M6: 70% FA + 30% RM; M7: 65% FA + 35% RM
Cubes cast with different FA & RM combination
MATERIALS
USED
Elemental compositions at 28 days
SUMMARY
Fly ash alone based geopolymer mortars showed better compressive strength, as high as 51 MPa, over its counter parts and it found to increase with time.
With increase in the red mud content in the mix, the compressive strength decreases.
Red mud content above 15% is unacceptable because of strength properties.
Increase in the leaching of sodium and ferrous ions with time takes place when the red mud content in the geopolymer mixes is above 15%.
Specimens prepared for experimental investigation