1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
28
BEHAVIOUR OF ALKALI ACTIVATED FLY ASH-BASED GEOPOLYMER
CONCRETE ON THERMAL ACTIVATION
Sameer Vyas1
, Neetu Singh2
, RP Pathak3
, Pankaj Sharma4
, NV Mahure5
, SL Gupta6
(CSMRS*, Olof Palme Marg, Hauz khas, N. Delhi, India)
* Central Soil and Materials Research Station
ABSTRACT
Fly ash based geo-polymers are finding a wider range of applications as construction as well
as repairing materials due to their strength and durability under aggressive environment. Present
study focusses on understanding the behavior of geo-polymer on exposure to elevated temperatures.
These samples were subjected to thermal activation at 200 ºC, 400 ºC and 650ºC. The results of
Fourier transform infrared spectroscopy reveal that most of the molecular water gets removed from
the sample at 200ºC, while crystalline –OH remains in the sample even at 650ºC. The X- ray
diffraction pattern of thermally activated samples shows retention of mineralogical composition even
at 650ºC. The geopolymer concrete shows good compressive strength inspite of thermal activation
upto 650ºC. Owing to their capability to maintain dimensional stability at very high temperatures,
these possess good compressive strength even on extreme thermal exposure, which make them
suitable materials capable of withstanding high thermal stresses.
Keywords: Alkali Activator, Cementitious Material, Compressive Strength, Geopolymer,
Thermal Activation.
I. INTRODUCTION
Fly ash is a bulk industrial byproducts which consistently pose disposal problem [1].
Productive and effective management of this resource necessitates evolving eco-friendly
technologies. Among various uses of fly ash, its bulk utilization is possible in geotechnical
engineering applications [2, 3]. Development of alkali activated fly ash based geopolymer concrete
(GPC) is proving to be green substitute for ordinary Portland cement (OPC) in the construction
industry [4, 5]. Its adequate compressive strength [6], durability under adverse conditions like
sulphate attack [7], acid resistance [8, 9, 10] and heat endurance capability [11, 12] make it a more
versatile construction and repair material. The chemical composition of the geopolymer material is
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 4, April (2014), pp. 28-36
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
www.jifactor.com
IJCIET
©IAEME

2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
29
similar to natural zeolitic materials, but the microstructure is amorphous [13]. Present study focusses
on understanding the behavior of GPC on exposure to elevated temperatures. These samples were
subjected to thermal activation at 200 ºC, 400 ºC and 650ºC. The results of Fourier transform
infrared (FTIR) spectroscopy reveal that most of the molecular water gets removed from the sample
at 200ºC, while crystalline –OH remains in the sample even at 650ºC. The X- ray diffraction pattern
of thermally activated samples shows retention of mineralogical composition even at 650ºC. The
GPC shows good compressive strength inspite of thermal activation upto 650ºC. It possesses a high
degrees of fire resistance, because the intrinsic chemistry of the geopolymer binder does not require
the retention of water or hydration within gel phases to maintain structural integrity of the binder.
Owing to their capability to maintain dimensional stability at high temperatures [14, 15] these
possess good compressive strength even on extreme thermal exposure, which make them suitable
materials capable of withstanding high thermal stresses [16].
II. SYNTHESIS OF GPC
2.1 Materials
2.1.1 Fly Ash
Chemical composition of Low calcium based type F fly ash used for synthesis of GPC is
presented in Table-1
Table 1: Chemical composition of used fly ash
Parameters % by weight
Silica, SiO2 57.95
Alumina ,Al2O3 31.78
Iron Oxide , Fe2O3 4.30
Lime,CaO 1.10
Magnesia,MgO 0.51
Sodium Oxide, Na2O 0.15
Potassium .Oxide, K2O 0.28
Loss on ignition, LOI 2.65
Sul.anhydride,SO3 0.075
2.1.2 Alkaline Activator (AA)
Activator concentration affects the residual strength of alkali activated FA pastes
subjected to thermal load [17]. For present study AA was prepared by mixing a sodium silicate
(Na2SiO3) and 10 M NaOH solution in the ratio of 2.5.
2.2 Methodology
2.2.1 Geopolymerisation
GPC is synthesized by polycondensation reaction of FA (geopolymeric precursor), and alkali
polysilicates [18]. The process of alkali activation of fly ashes produces a material with similar
cementing features as that of OPC [19]. The geopolymerisation mechanisms proceeds in four
stages [20].

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
30
(i) Dissolution of Si and Al from the solid aluminosilicate materials in the strongly alkaline
aqueous solution,
(ii) Formation of oligomers species (geopolymers precursors) consisting of polymeric bonds of
Si-O-Si and/or Si-O-Al type,
(iii) Polycondensation of the oligomers to form a three-dimensional aluminosilicate framework
geopolymeric framework)
(iv) Bonding of the unreacted solid particles and filler materials into the geopolymeric framework
and hardening of the whole system into a final solid polymeric structure.
III. CASTING AND CURING OF CUBES
3.1 Geopolymer Concrete Cubes (GPCC)
FA-AA composite was mixed with sand in the ratio 1:1 (Fig. 1a) and casted in metallic
prismatic moulds having Cube Area of 14.44 cm2
(Fig. 1b). In order to achieve optimum
compressive strength the cubes were cured at different temperature (Fig. 1c) and for different time
intervals. Polymerization and condensation reactions transformed the glassy constituent of the FA
into well compacted cementitious material. Cubes cured at 1200
C for 72 hours attained the maximum
compressive strength of 36.50 Mpa.
a b c
Figure 1: Mixing-casting-curing of GPCC
3.1.1 Internal Transformations during Geopolymerisation
3.1.1.1 FTIR Study
The FTIR spectrum of fly ash and GPC presented in fig. 2 shows shift of the band
attributed to the asymmetric stretching vibrations of Si-O-Si and Al-O-Si [21]. The broad band at
around 1067.18 cm-1
for FA transformed into a sharper band at 1021.87 cm-1
(marked as Zone A)
during geopolymerisation to GPC. This indicates the formation of amorphous aluminosilicate gel
phase which is associated with the dissolution of the amorphous fly ash phase in strong AA
solutions. Appearance of new bands at 777.73 cm-1
(marked as Zone B) attributed to symmetric
stretching of Si-O-Si and Al-O-Si indicating structural reorganization i.e. formation of amorphous to
semi-crystalline aluminosilicates. Broad IR bands are noticed at 3462.29 cm−1
(marked as Zone C)
and 2360.76 cm−1
(marked as Zone D) due to stretching/deformation vibration of OH and H-O-H
groups respectively. Bands at 1653.90 cm−1
(marked as Zone E) represent the bending vibration of
H-O-H. After the treatment increase in the intensity and the broadness of the stretching

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
31
Figure 2: FTIR spectrum of FA and GPC
v(O-H) band at 3462 cm−1
(marked as Zone C) is observed which is attributed to an increase in
hydrated products due to the reaction between amorphous silicates (i.e., glass) and the alkali.
Substitution of Si 4+
by Al 3+
in some of the tetrahedral framework of the primary building units of
the alumino-silicates and their external linkage with the Na+
ions during geopolymerisation process
illustrated by shift of asymmetrical strong stretching band of TO4 (SiO4 or AlO4) from 1067.18 to
1021.87 cm−1
(marked as Zone A) confirms synthesis of silicates.
3.1.1.2 XRD Study
The XRD pattern of original fly ash and GPC is presented in fig. 3. The pattern shows that
besides crystalline phase composed of quartz and mullite, FA is primarily
Figure 3: The XRD pattern of original FA ash and GPC

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
32
composed of amorphous material. On geopolymerisation the peaks which represents the amorphous
phase of FA appears slightly shifted toward higher theta values which indicates transformation of
FA amorphous phase into new GPC amorphous phase. These new diffraction peaks are mainly due
to formation of new crystalline zeolitic phases like hydroxysodalite, analchime and herschelite.
3.2 OPC Cubes (OPCC)
OPCC specimens were prepared using 43 grade OPC. The concrete cubes were allowed to set
for 24 hours, demoulded and placed in water pond for 28 days for effective curing.
IV. EFFECT OF ELEVATED TEMPERATURES ON BEHAVIOR OF GPCC and OPCC
In order to evaluate the effect of elevated temperature the GPCC and OPCC were subjected
to thermal activation at 200 ºC, 400 ºC and 650ºC (Fig. 4).
Figure 4: Thermal activation of OPCC and GPCC
4.1 Observations
Following observations were made on used FA, GPCC, OPCC, thermally activated GPCC
(TGPCC) and thermally activated OPCC (TOPCC)
• Determination of Compressive strength (CS) of GPCC, OPCC, TGPCCs and TOPCCs using
Universal Testing Machine (UTM).
• FT-IR study on FA, GPCC and TGPCCs using Nicolet IR-200 spectrometer in order to
evaluate the intrinsic chemistry involved during different phase transformations.
• XRD analysis of FA, GPCC and TGPCCs using EMMA 125 diffractometer to study the
changes in the mineralogical compositions.

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
33
4.2 Results and Discussion
4.2.1 Compressive Strength
The CS of OPCC, TOPCC, GPCC and TGPCC is presented in figure 5. Percent change in CS
of TOPCC as well as TGPCC upto 650 o
C is presented in figure 6. Beyond 200 o
C the decrease in
CS for TOPCC is more pronounced while TGPCC shows better endurance to temperature. Upto a
temperature of 300 o
C the CS of TGPCC showed increasing trend. There is about 9-10% decrease in
CS upto 400 o
C. At 500 o
C it ranged between 24-25%. At 650 o
C the decrement in CS was of the
order of 44%.
0
10
20
30
40
50
0 100 200 300 400 500 600 700
Temperature
o
C
CompressiveStrength(Mpa)
GPCC
OPCC
)
Figure 5: Compressive strength of OPC, GPC, TOPCCs and TGPCCs
-80
-60
-40
-20
0
20
40
100 200 300 400 500 600 700
Temperature
o
C
%ChangeinCompressiveStrength
GPCC
OPCC
Figure 6: Percent variation in compressive strength of TOPCC and TGPCC on thermal exposure

7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
34
4.2.2 FT-IR Spectrum Analysis
FTIR spectrum of tests conducted on GPCC and TGPCCs at 200 o
C, 400 o
C and 650 o
C is
presented in figure 7. The infrared bands are recorded for wavelengths between 3500 cm−1
to 400
cm−1
. It was observed that there are significant changes in the intensities and the width of various
bands on thermal activation.
A decrease in the intensity corresponding to the bending v(O-H) band from 1653.90 cm-1
, (F
to G) reveals loss of adsorbed water and the water of hydration.
Figure 7: FTIR spectrum of GPCC and TGPCCs at 200 o
C, 400 o
C and 650 o
C
The broadness of band at 3462.29 cm-1
indicates the presence of strong hydrogen bonding
The band is attributed to surface –OH groups of silanol groups (-Si-OH) and adsorbed water
molecules on the surface, shows gradual decrement in the intensity and broadness (H to I for
TGPCC-200 o
C, H to J for TGPCC-400 o
C and H to K for TGPCC-650 o
C. This confirms loss of
water during thermal activation.
4.2.3 XRD analysis
XRD patterns of fly ash and GPC are shown in Fig. 7. New crystalline zeolitic phases like
hydroxysodalite, analchime and herschelite formed during geopolymerisation contribute in
improvement in CS. XRD pattern of TGPCC-200 o
C, TGPCC-400 o
C clearly shows that the
mineralogical composition remains almost unaltered while there are signs of alterations in TGPCC-
650 o
C. Thus GPCC do not show substantial loss of CS on thermal exposure upto 400 o
C.

8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
35
Figure 7: XRD pattern of Fly ash, GPCC and TGPCCs
V. CONCLUSION
Geopolymer concrete provides an ecofriendly alternative for constructive use of Fly Ash. At
normal temperature Geopolymer concrete cubes possess almost equivalent compressive strength as
that of OPC cubes. Magnitude of the loss in compressive strength of Geopolymer concrete cubes is
much less than that of OPC cubes. The observations in Fourier transform infrared spectroscopy and
X- ray diffraction pattern of GPC before and after thermal activation clearly indicate that GPC could
maintain their dimensional stability even on high thermal activation. Prevalence of crystalline
zeolitic phases in GPC even on thermal exposure contributes to retention of compressive strength. As
compared to simple OPC, GPC thus provides much better thermal endurance. This makes GPC as a
suitable construction/repair material to resist mild to medium fire where temperature of the order of
400 – 500 ºC may be achieved.
VI. ACKNOWLEDGEMENTS
The authors extend their sincere gratitude to Director Central Soil and Materials Research
Station for his constant guidance and encouragement. We also extend our sincere gratitude to all the
authors whose publications provided us directional information from time to time.
VII. REFERENCES
[1] Narasimhan, M. C, B. T. Patil and Shankar H. Sanni, Performance of Concrete with Quarry
Dust as fine aggregate – An Experimental Study, Civil Engineering and Construction
Review, 1999, 19-24.
[2] Bumjoo Kim, Monica Prezzi and Rodrigo Salgado, Geotechnical Properties of Fly and
Bottom Ash Mixtures for Use in Highway Embankments, Journal of Geotechnical and
Geoenvironmental Engineering, Vol.131 (7), 2005, 914-924.
[3] N. S. PANDIA Fly ash characterization with reference to geotechnical applications,
J. Indian Inst. Sci., 2004, 84, 189–216.

9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 4, April (2014), pp. 28-36 © IAEME
36
[4] Panias D., Giannopoulou I. P. Development of inorganic polymeric materials based on fired
COAL FLY ASH, Acta Metallurgica Slovaca, 2006, 321 – 327, (12).
[5] V. M. Malhotra, High performance high volume fly ash concrete, ACI Concrete
International, vol.7 (24), 2002, 1-5.
[6] Wallah, S.E., Low-calcium fly ash based Geopolymer concrete: Long term properties,
Research report GC2, Curtin University of Technology Perth, Australia, (2006).
[7] Rajamane, N. P et al., Sulphate resistance and eco-friendliness of geopolymer concrete, The
Indian Concrete Journal, Jan., 2012, 13-22.
[8] Neetu Singh et al., Effect of Aggressive Chemical Environment on Durability of Green
Geopolymer Concrete, International Journal of Engineering and Innovative Technology,
vol. 3, (4), 2013, 277 - 284
[9] Suresh Thokchom, Dr. Partha Gosh and Dr. Somnath Gosh, Acid resistance of fly ash based
geopolymer mortars, International Journal of Recent Trends in Engineering, 1(6), 2009,
36-40.
[10] Manu Santhanam et al., Durability Study of low calcium fly ash geopolymer concrete,
Proceedings of third ACF International conference-ACF/VCA, 2008, 1153-1159.
[11] Davidovit. J., Geopolymers: Inorganic polymeric new materials, Journal of Materials
Education,Vol. 16, 1994, 91 – 139.
[12] Davidovits, J., Properties of geopolymer cements, Proceedings of first International
conference on alkaline cements and concretes, 1, SRIBM, Kiev, Ukraine, (1994), 131-149.
[13] Shankar H. Sanni1, Khadiranaikar, R. B Performance of geopolymer concrete under severe
environmental conditions, International Journal of Civil and Structural Engineering Volume
3, (2), 2012, 396 -407
[14] Omar A Abdulkareem et al., Alteration in the Microstructure of Fly Ash Geopolymers upon
Exposure to Elevated Temperatures, Advanced Materials Research, Vol. 795, 2013, 201-205.
[15] Kong, D.L.Y.; Sanjayan, J.G. Effect of elevated temperatures on geopolymer paste, mortar
and concrete. Cem. Concr. Res. 40, 2010, 334–339.
[16] Omar A Abdulkareem et al., Mechanical and Microstructural Evaluations of Lightweight
Aggregate Geopolymer Concrete before and after Exposed to Elevated Temperatures,
Materials, Vol. 6, (10), 2013, 4450-4461.
[17] Rashad, A.M.; Zeedan, S.R. The effect of activator concentration on the residual strength of
alkali-activated fly ash pastes subjected to thermal load. Contsr. Build. Mater. 2011, 25,
3098–3107.
[18] Abdullah, M.M.A.B. et al., Fly ash porous material using geopolymerization process for high
temperature exposure. Int. J. Mol. Sci. 2012, 13, 4388–4395.
[19] Avidovits J., Geopolymer, green chemistry and sustainable development, Proceedings of the
world congress Geopolymer, 2005, 9-17.
[20] Hua Xu, J.S.J.van Deventer, The Geopolymerisation of Alumino-Silicate Minerals,
International Journal of Mineral Processing, 59(3), 2000, 247-266.
[21] Stuti Katara et al., Surface Modification of Fly Ash by Thermal Activation: A DR/FTIR
Study International Research Journal of Pure & Applied Chemistry, vol. 3(4), 2013, 299-307.
[22] Sitiradziah Abdullah, Ahmad Shayan and Riadh Al-Mahaidi, “Assessing the Mechanical
Properties of Concrete Due to Alkali Silica Reaction”, International Journal of Civil
Engineering & Technology (IJCIET), Volume 4, Issue 1, 2013, pp. 190 - 204, ISSN Print:
0976 – 6308, ISSN Online: 0976 – 6316.
[23] N. Krishna Murthy, N. Aruna, A.V.Narasimha Rao, I.V.Ramana Reddy and M.Vijaya Sekhar
Reddy, “Self Compacting Mortars of Binary and Ternary Cementitious Blending with
Metakaolin and Fly Ash”, International Journal of Civil Engineering & Technology (IJCIET),
Volume 4, Issue 2, 2013, pp. 369 - 384, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.