development of eco friendly concrete produced with rice
TRANSCRIPT
Advances in Concrete Construction, Vol. 9, No. 2 (2020) 139-147
DOI: https://doi.org/10.12989/acc.2020.9.2.139 139
Copyright © 2020 Techno-Press, Ltd. http://www.techno-press.org/?journal=acc&subpage=7 ISSN: 2287-5301 (Print), 2287-531X (Online)
1. Introduction
Development in civil engineering has enabled
urbanization and overall lifestyle enhancement. Production
of Ordinary Portland Cement (OPC) consumes massive
energy and raw materials while emitting a huge amount of
CO2 into the atmosphere (Ganesan et al. 2013).
Geopolymer technology was identified as an alternative to
OPC due to the consumption of lesser energy during
production and reduced CO2 emission compared to OPC
(Geraldo et al. 2017, Borges et al. 2014). Recently, the
inclusion of minerals to concrete becomes essential due to
the sustainability and environmental implications (Zerbino
et al. 2012). It would be much useful for the society if waste
materials like fly ash and rice husk ash are utilized as
pozzolanic substances in the preparation of eco-friendly
geopolymer concrete (Yang et al. 2016). Pozzolanic
materials like fly ash (Nath et al. 2015, Ganesan et al.
2014a, b), blast furnace slag, bottom ash (Matthes et al.
2018a, b). and other materials are also used in concrete
production. Rice Husk Ash (RHA) an agricultural deposit
generated during rice milling seems the correct option for
cementitious materials. Annual paddy production estimates
for 2010 was 678 million tons (MT), which produced
149.16 million tons (MT) of rice husk. Nearly 37 million
tons of RHA can be obtained from this (Rice Market 2009).
Corresponding author, Assistant Professor
E-mail: [email protected]
During milling, nearly 22% of the weight is received as
husk (Khan et al. 2012a, b).
Ungrained RHA produced is of poor quality and
contains residual carbon (which requires more water)
containing crystalline silica. The quality of residual RHA
can be enhanced by grinding it to the desired particle size at
a high cost. (Rodriguez et al. 2006a, b, Cordeiro et al.
2009a, b). During the burning of the husk, about twenty-
five percentage of the weight is transformed to ash,
notorious as Rice Husk Ash and the remaining 75%
contains organic volatile matter. It is well known that by
burning Rice Husk Ash in controlled conditions, non-
crystalline silica and highly reactive pozzolan are obtained
(Mehta 1977, Mehta 1994, RILEM committee 1988). Burnt
RHA contains approximately 85-90% silica, in an
amorphous state based on burning time and temperature.
The chemical composition of RHA differs from sample to
sample due to husk type and burning temperature. RHA,
when not used properly, turns into waste becoming a
massive threat to the environment and damaging the
surroundings when it is dumped. Use of RHA in concrete
reduces its impact during dumping and reduces CO2
emission to the atmosphere due to reduced cement
production (Nazari et al. 2011a, b, Ramasamy et al. 2012).
Geopolymer concrete is a polymer developed by
incorporating silica and alumina rich pozzalonic materials
(like RHA, Fly ash) with alkaline solutions (Combination of
potassium or sodium silicate and potassium/sodium
hydroxide) (Prabu et al. 2017a, b, Ganesan et al. 2015a, b).
Development of geopolymer concrete using RHA with FA
and GGBS is novel and has not been investigated in
Development of eco-friendly concrete produced with Rice Husk Ash (RHA) based geopolymer
Shalini Annadurai1, Kumutha Rathinam2 and Vijai Kanagarajan3
1Department of Civil Engineering, Sona College of Technology, Salem-636005, Tamil Nadu, India 2Department of Civil Engineering, Sri Venkateswara College of Engineering, Sriperumbudur-602117, Tamil Nadu, India
3Department of Civil Engineering, St. Joseph’s College of Engineering, OMR, Chennai-600119, Tamil Nadu, India
(Received August 11, 2019, Revised November 21, 2019, Accepted November 27, 2019)
Abstract. This paper reports the effect of Rice Husk Ash (RHA) in geopolymer concrete on strength, durability and
microstructural properties under ambient curing at a room temperature of 25°C and 65±5% relative humidity. Rice husk was
incinerated at 800°C in a hot air oven. and ground in a ball mill to achieve the required fineness. RHA was partially added in 10,
15, 20, 25, 30 and 35 percentages to fly ash with 10% of GGBS to produce geopolymer concrete. Test results exhibit that the
substitution of RHA in geopolymer concrete resulted in reduced strength properties during initial curing. In the initial stage,
workability of GPC mixes was affected by RHA particles due to the presence of dormant particles in it. It is evident from the
microstructural study that the presence of RHA particles densifies the matrix reducing porosity in concrete. This is due to the
presence of RHA in geopolymer concrete, which affects the ratio of silica and alumina, resulting in polycondensation reactions
products. This study suggests that incorporation of rice husk ash in geopolymer concrete is the solution for effective utilization
of waste materials and prevention of environmental pollution due to the dumping of industrial waste and to produce eco-friendly
concrete.
Keywords: rice husk ash; microstructure; bond strength; strength; curing; carbonation
Shalini Annadurai, Kumutha Rathinam and Vijai Kanagarajan
(a) (b)
(c)
Fig. 1 SEM images (a) RHA, (b) Fly ash and (c) GGBS
ambient curing conditions. The strength and microstructure
of RHA, Fly ash and GGBS based geopolymer concrete
have not been discussed widely and hence it is the focus of
this investigation. This paper presents the strength and
micro structural characterization of RHA and Fly ash with
GGBS geopolymers to make a green geopolymer binder.
This study aims to formulate a new concrete mixture using
industrial waste products-fly ash, GGBS and RHA. These
materials are used as binder to produce geopolymer
concrete in this research. GGBS content was kept constant
while RHA and Fly ash were replaced at different
percentages to study its effect on mechanical properties like
tensile strength, modulus of rupture, compressive strength.
and bond strength, microstructural characterization by SEM
and EDX and properties like pH and carbonation.
2. Experimental investigation
2.1 Materials used
For this research Rice Husk was obtained from a Rice
mill and incinerated at 800oC in a microwave incinerator to
obtain Rice Husk Ash (RHA). To attain the required
fineness, RHA was ground in ball mill for 1000 cycles.
RHA’s physical properties and Oxide composition are
shown in Table 1 and 1(a). An SEM image of RHA is
presented in Fig. 1(a) and those of RHA are irregular in
shape with cellular porous surface. Fly ash (FA) was
obtained from the Mettur Thermal power station and
categorized as Class F Fly ash [ASTM 2006, IS 3812].
Physical and oxide compositions of FA are described in
Table 1 and 1(a). Fig. 1(b) shows the SEM image of FA and
the particles are in spherical shape. In this research, Ground
Granulated Blast furnace Slag (GGBS) [IS 12089] was
purchased from M/s. Quality Polytech, Mangalore.
The physical properties and Oxide composition of
GGBS are presented in Tables 1 and 1(a). Fig. 1(c) shows
the SEM image of GGBS which are in flakes shape and in
Table 1 Physical properties of fly ash, GGBS and rice husk
ash
Property Fly Ash GGBS Rice Husk Ash
Specific gravity 2.46 3.11 2.13
Blain Fineness 2351cm2/g 4580 cm2/g 5675cm2/g
Table 1 (a) Oxide composition of fly ash, GGBS and rice
husk ash
Oxides
Fly Ash GGBS Rice
Husk
Ash %
Requirement as
per IS 3812-
2003
%
Requirement
as per IS
12089-1987
SiO2 55.90 SiO2>35% 41.24 88.64
Al2O3 15.23 Total-70% 20.64 1.23
Fe2O3 21.78 - 7.28 1.19
CaO 0.17 - 25.45 1.09
MgO 2.45 < 5% 2.93 <17% 1.76
LOI 0.60 < 12% Nil - <6%
Table 2 Physical properties of fine and coarse aggregates
Property FA CA
Specific gravity 2.6 2.91
Bulk density 1675 kg/m3 1520 kg/m3
Fineness modulus 2.65 (Zone II) 5.4
aggloramation.
Naturally, available river sand was used as Fine
aggregate (FA) in this research. and its properties were
tested in accordance with IS: 2386 (Part-I)-1963. Fine
aggregate was dried in a hot air oven, to remove moisture.
Coarse aggregate (CA) of 12 mm was used in all mixes and
tested following IS 2386 (Part -I)-1963.
The physical properties of FA and CA are presented in
Table 2. Sodium hydroxide (NaOH) and Sodium Silicate
(Na2Sio3) solution were used as the alkaline solution part of
the mixture. 10M of Sodium hydroxide was kept as constant
for all mix preparations. The alkaline solutions were
prepared 24h before mixing to avoid excess heat in NaOH
solution during mixing.
2.2 Mix proportioning and curing
There is no standard code provision for mix design of
geopolymer concrete. The calculations of mix proportions
were arrived based on the report submitted by Wallah and
Rangan (2006). The density of geopolymer concrete was
assumed as 2400 kg/m3. In this study, seven mixtures, one
control mix with 90% of fly ash and 10% of GGBS and six
other mixtures with different proportions of RHA with
control mix were prepared. The content of GGBS was kept
as 10% constant for all mixtures. Percentage of fly ash and
RHA were varied by mass. The ratio of binder to the
alkaline solution was 0.4. The ratio of Na2Sio3 to NaOH
was kept as 2.5.
Additional water and superplasticizer (SP) were added
by 15% and 3% respectively, to the cementitious material to
140
Development of eco-friendly concrete produced with Rice Husk Ash (RHA) based geopolymer
Fig. 2 Test setup of accelerated carbonation chamber
enhance its workability properties. Total cementitious
material content was fixed at 394 kg/m3. The mixture code
and proportion of various materials for each designated
mixture are presented in Table 3. All specimens were cured
at room temperature till the testing period.
2.3 Test program
Workability of GPC and RHA based mixtures were
evaluated using the slump test. The slump of fresh concrete
was measured as per IS: 1199-1959. Cubes of 100 mm×100
mm×100 mm size were used for the compressive strength
test. The specimens were tested at 7, 28. and 56 days as per
IS 516:1959. The specimen samples were tested in a 2000
kN Compression testing machine. and the load was applied
up to failure. Three samples were used for each test. For the
evaluation of tensile strength of concrete, a cylindrical
specimen of 150 mm diameter and 300 mm height were cast and tested in a compression testing machine as per
IS: 5816- 1999. The plain beam specimen of size 100 mm× 100 mm× 500 mm was tested as per IS
516:1959 by Universal testing machine to obtain modulus
of rupture of geopolymer concrete. Similar to the
compressive strength, modulus of rupture and tensile
strength were evaluated at 7, 28. and 56 days.
The specimens bond strength was assessed by a pull-out
test as per IS: 2770 (Part-I)-1967. A cylindrical specimen
of 150 mm diameter and 300 mm height with a TMT bar of
12 mm diameter and 450 mm length were used to evaluate
the bond strength of geopolymer concrete. The specimens
were tested after 28 days in a Universal testing machine.
Bond strength was computed from the load at which the slip
was 0.25 mm. Tests were performed in triplicate specimens.
and average bond strength calculated.
It is well known that progress of carbonation in concrete
is a long-time reaction. However, for testing the carbonate
concrete samples a short-term accelerated carbonation
testing system was used. The test set up of carbonation
chamber is shown in Fig. 2 performed accelerated
carbonation tests for 56 days to calculate pH value with a
5% concentration of CO2, the relative humidity of 70±1%
and temperature of 20+1°C (Law et al. 2014a, b).
A sophisticated electronic apparatus was attached to the
chamber to calculate the temperature and relative humidity
in the system. A timer was used to control the system. The
timer switches on and switches of the system for 15 minutes
continuously. It ensures constant relative humidity in the
chamber. The Carbon di-oxide concentration was associated
comparative to the concentration of O2 in the chamber. Pore
water from concrete samples was got through a constructed
pore press. The pH value of each sample was measured
electronically using a water analyzer 371, with a sample
amount of 0.5 mg in 50 ml or 1000 ppm.
3. Results and discussions
Table 3 Details of mixture proportions
Mix
Code
RHA
content (%)
Proportion in kg/m3
Fly Ash GGBS RHA FA CA NaoH Mol/L Na2SiO3 Water SP
GPC 0 354.6 39.4 0 554.4 1294 45.1 10 112.6 59.14 11.83
R10 10 315.2 39.4 39.4 554.4 1294 45.1 10 112.6 59.14 11.83
R15 15 295.5 39.4 59.1 554.4 1294 45.1 10 112.6 59.14 11.83
R20 20 275.8 39.4 78.8 554.4 1294 45.1 10 112.6 59.14 11.83
R25 25 256.1 39.4 98.5 554.4 1294 45.1 10 112.6 59.14 11.83
R30 30 236.4 39.4 118.2 554.4 1294 45.1 10 112.6 59.14 11.83
R35 35 216.7 39.4 137.9 554.4 1294 45.1 10 112.6 59.14 11.83
Table 4 Strength development of RHA concrete
Mix Compressive strength (MPa) Tensile strength (MPa) Modulus of rupture (MPa) Bond strength
(MPa)
Slump
(mm) 7 d 28 d 56 d 7 d 28 d 56 d 7 d 28 d 56 d
GPC 21.20 31.30 32.32 1.62 2.25 2.64 2.12 3.26 3.42 5.32 40
R10 20.19 29.96 30.65 1.53 1.94 2.21 2.28 3.50 3.67 5.29 60
R15 19.33 25.80 27.12 2.21 2.51 2.69 2.11 3.25 3.48 5.99 50
R20 17.33 24.46 25.95 2.08 2.39 2.54 2.06 3.17 3.39 5.27 40
R25 18.23 27.80 29.17 1.94 2.19 2.38 2.19 3.37 3.57 5.01 15
R30 18.43 28.06 30.33 2.06 2.32 2.49 2.20 3.39 3.62 5.44 10
R35 18.10 24.26 26.93 1.51 2.06 2.19 2.05 3.15 3.32 4.63 5
141
Shalini Annadurai, Kumutha Rathinam and Vijai Kanagarajan
Fig. 3 Compressive strength results of RHA geopolymer
specimens
3.1 Workability of geopolymer concrete mix
Table 4 presents the slump values for the mixes. The
results of the slump test revealed that the increase in the
RHA in GPC mixes percentage revealed reduced
workability due to higher viscous and stiffness. Slump
values ranged from medium to very low. Reduction in
slump value is due to high water absorption capacity of
RHA resulting in increase in surface area and decrease the
water availability for the ingredients in the mix to flow.
3.2 Hardened properties
Earlier research revealed that GPC specimen’s hardened
properties were lesser in ambient temperature compared to
specimens exposed to heat curing. Reduction in strength
properties was due to the slower dissolution of Al and Si
monomers. In this research, 10% of GGBS was added to all
mixes. The final setting properties of all the mixes at 28
days of curing in room temperature are similar to the
conventional concrete. Alkaline activators (OH-) in
geopolymer concrete enhanced reactivity in GGBS,
promoting bond breaking in the structure and forming
dissolved species. It also generated the C-S-H matrix and C-
A-S-H, leading to denser microstructure (Patet and Shah
2014). Addition of RHA changed reaction process, physical
properties. and the matrix of geopolymer concrete. RHA,
which contains higher SiO2, can be used to fix the
Sio2/Al2O3 ratio in the source material. Fine-grained RHA
particles enhanced reactivity resulting in superior
geopolymerization. Table 4 gives the compressive strength
of GPC and RHA geopolymer concrete at different ages.
Higher RHA amount resulted in reduced strength due to
slow geopolymerization at ambient curing caused by porous
and loose microstructure.
On the other hand, there was a slight increase in the
compressive strength of GPC with 30% of RHA due to an
enhanced quantity of reactive silica in RHA which leads to
superior density in the Si-O-Si bonds in the geopolymer
matrix (Zabihi et al. 2018a, b, Fan 2015). Another reason is
that a higher amount of RHA has higher surface area
compared to cement making stronger products by refining
the pores. Compared to Si-O-Al and Al-O-Al bonds, Si-O-
Si bonds are stronger. According to Fig. 3, replacement with
35% RHA based geopolymer concrete reduced compressive
Fig. 4 Tensile strength results of RHA geopolymer
specimens
strength caused by obstruction of Al and Si reorganization
due to an increased amount of soluble Si reducing the
skeletal density of geopolymer binder (Duxson et al. 2005a,
b), leading to a weaker geopolymer. Increased unreacted
RHA in the final product results in a less ductile and weaker
geopolymer causing it to suffer from lower strength.
Increase in RHA geopolymer concrete’s compressive after
28 days of curing reveals that as time increases, dissolution
of reactive aluminosilicate species and their
polycondensation strengthen the geopolymer gel matrix. To
wrap up, RHA geopolymer concrete’s compressive strength
at 28 days and 56 days varied from 28.06 MPa to 30.33
MPa, which is near the strength of M30 grade concrete.
The results provide an opportunity to use this type of
concrete in structural applications. RHA based geopolymer
concrete can be used as cementitious materials in civil
engineering constructions for building and roadways. Also,
geopolymeric binders immobilize radioactive waste and
toxic chemicals within the structures (Van Jaarsveld et al.
1997a, b, Hart et al. 2006a, b). Hence, the use of waste
containment and capsulation are the reasons for producing
RHA as a binder in geopolymer concrete. By utilizing the
RHA in geopolymer concrete, both economic and
environmental issues are resolved. The production of RHA
based geopolymer concrete, not only reduces problems in
waste disposal but it also reduces the production cost of
OPC. It also saves energy in cement manufacture and
diminishes CO2 emission into the atmosphere by firing
carbonates (Davidovit 1991). Utilization of rice husk ash in
geopolymer concrete mix is a good strategy to reduce its
harmful potential to affect human health and the
environment.
Tensile strength is an essential mechanical property used
in the different design guidelines for structures like
anchorage and shear reinforcement steel. The tensile
strength of different GPC mixes with RHA is presented in
Table 4. The test was carried out at 7, 28. and 56 days. The
GPC mix with 35% RHA exhibits lesser tensile strength
value at all curing periods. Tensile strength of 30% RHA
had 2.32 MPa at 28 days, which was higher compared to the
GPC mix. Test results disclosed that during ambient curing,
the rate of increase of tensile strength in increased amounts
of fly ash mix was slow as it was hard to break the Al and
Si monomers bond from fly ash particles to start the
reaction. There is a reduction in tensile strength with the
0
5
10
15
20
25
30
35
GPC R10 R15 R20 R25 R30 R35
Co
mp
ress
ive
stre
ngth
(MP
a)
Mix ID
7 days 28 days 56 days
0
1
2
3
GPC R10 R15 R20 R25 R30 R35
Ten
sile
str
ength
(M
Pa)
Mix ID
7 days 28 days 56 days
142
Development of eco-friendly concrete produced with Rice Husk Ash (RHA) based geopolymer
Fig. 5 Modulus of rupture results of RHA geopolymer
specimens
addition of RHA in geopolymer concrete.
As seen in Fig.4, the tensile strength of GPC mix with
RHA ranges from 1.62 MPa to 2.21 MPa at 7 days, 2.25
MPa to 2.51 MPa at 28 days and 2.64 MPa to 2.69 MPa at
56 days. Increase in RHA percentage in GPC mix decreases
tensile strength. A similar statement was reported by
(Venkatesan and Pazhani 2016, Liu et al. 2014 a, b) in
geopolymer concrete made with palm oil fuel ash as a
binder. RHA particles acquire various structures. and when
the ratio between SiO2 to Al2O3 is high, the kinetics of
polymerization is slowed due to differences in the solubility
of Fly ash, GGBS. and RHA. Therefore the production rate
of geopolymer gel is reduced as reported by (Kusbiantoro et
al. 2012a, b) Appreciable tensile strength in a lower
percentage of fly ash and RHA based GPC was achieved in
7 days due to the premature precipitation of C-S-H and
geopolymeric gel.
The test results of modulus of rupture of GPC mixes
with different proportions of RHA are presented in Table 4
and Fig. 5. Comparable to compressive strength, the
addition of RHA in the GPC mix resulted in increased
modulus of rupture of RHA based geopolymer concrete.
Enhancement in the strength of RHA concrete is due to the
excellent interfacial bond between the aggregate and paste.
It increased by 30% RHA, but beyond it, strength was
reduced. However, modulus of rupture with 30% of RHA
geopolymer concrete was higher than that of GPC mix
without RHA. Fig. 4 shows that the modulus of rupture
increases with an increase in the age of concrete. The
highest modulus of rupture of 3.50 MPa was obtained for
the mix R10 at 28 days. and the lowest modulus of rupture
was observed for the R35 mix. Modulus of rupture of mix
R35 was 3.15 MPa at 28 days.
Higher mechanical properties were achieved using a
higher ratio of silica to alumina in the geopolymer mix with
higher elasticity. The temperature in ambient curing is
insufficient to dilute the particles of binders of SiO2 in the
alkaline solution resulting in superior unreacted particles
which obstruct geopolymerization and weaken the density
of the geopolymer matrix. When applying the load, such
weaker geopolymer concrete specimens cannot transfer the
load which induces cracks and reduces its strength. It was
pragmatic that percentage increase in strength decreased as
RHA content increased from 10% to 35% in the mixes
irrespective of age. This is due to the enhanced ratio of
Fig. 6 Bond strength results of RHA geopolymer specimens
Table 5 pH of RHA geopolymer concrete specimens after
Carbonation
Mix pH
0 d 3 d 7 d 28 d 56 d
GPC 11.43 11.20 11.17 11.10 11.04
R10 11.20 10.91 10.86 10.75 10.72
R15 10.58 10.23 10.17 10.12 10.08
R20 11.08 10.82 10.76 10.69 10.61
R25 11.18 10.88 10.83 10.79 10.71
R30 11.03 10.77 10.69 10.61 10.58
R35 10.98 10.64 10.61 10.58 10.54
silica to alumina and the difference in the solubility of fly
ash, GGBS. and RHA which produce a weaker geopolymer
matrix; the reason is the same as mentioned in the
compressive strength discussion.
Past research reports on Geopolymer concrete state that
it acts as an excellent corrosive environment for steel
reinforcement in concrete. This research revealed that the
pH of Geopolymer concrete ranged from 10.58-11.43, but it
varied slightly for OPC concrete where pH value ranges
from 12 to 13. Hence this research aims to confirm the null
contribution of Geopolymer concrete with rich husk ash for
corrosion of reinforcement steel due to the substituted
cementitious materials. Corrosion of steel reinforcement
mainly affects the bonding capacity of reinforced steel with
concrete. Load transformation inside the concrete will be
affected. and reinforced steel might slip out due to
inadequate friction between the reinforced steel and
geopolymer concrete. Bond strength of Geopolymer
concrete with different percentages of rice husk ash was
found out by pull out test.
Fig. 6 depicts the bond strength of Geopolymer concrete
specimens. Test results of bond strength revealed that
addition of RHA does not enhance strength in the pull-out
test. Other factors influencing bond strength are reactivity
of source material used, curing temperature. and the
alkaline activator solution used. Due to the quick
dissolution of Si-O bond from rice husk ash contributes to
polycondensation of Geopolymer gel and enhances the
bond capacity of Geopolymer concrete with reinforced
steel.
The pH concentration of blended, fresh. and Ordinary
Portland Cement concrete was more than 13. The
carbonated concrete had a pH value of less than 9, due to
0
1
2
3
4
GPC R10 R15 R20 R25 R30 R35
Mo
du
lus
of
Ru
ptu
re (
MP
a)
Mix ID
7 days 28 days 56 days
0
1
2
3
4
5
6
7
GPC R10 R15 R20 R25 R30 R35
Bo
nd
str
ength
(M
Pa)
Mix ID
143
Shalini Annadurai, Kumutha Rathinam and Vijai Kanagarajan
Fig. 7 EDX profiles of RHA geopolymer specimens; (a)
10% of RHA, (b) 15% of RHA, (c) 20% of RHA, (d) 25%
of RHA, (e) 30% of RHA and (f) 35% of RHA
calcium carbonate formation. C-S-H and Ca(OH)2 gel
supports buffering to preserve pH value more than 13 in
Ordinary Portland cement concrete. However, in
geopolymer concrete, such buffering is not supported by the
(Mz(AlO2)x(SiO2)y.nMOH.mH2O) gel. Carbonation in
geopolymer concrete is hypothesized as the chemical
process of NaOH with carbon-di-oxide making sodium
carbonate hydrates. The output of this is a lesser
minimization of pH value, which ranges from 10.58. The
obtained results compared to earlier reports for alkali-
activated slag concretes reported no harmful effects due to
carbonation (Deja 2002, Shi et al. 2006a, b). The pH value
proves that it can provide safety to steel reinforcement after
carbonation.
3.3 Microstructural properties
Fig. 7 presents the energy dispersive X-ray spectrometry
(EDX) profile of RHA based geopolymer concrete.
Different percentages of RHA added concrete were selected
after 28 days of curing for the EDX analysis. Table 6
presents the test results of EDX analysis under ambient
curing conditions. They reveal that elements like O, Al, Si,
Na and Ca are common elements in the RHA based
geopolymer framework. At 28 days of curing, the ratio of
silica to alumina detected is 1.96 for fly ash and the GGBS
based specimen. and the ratio varied from 3.08 to 4.46 for
rice husk ash-based geopolymer concrete specimens. The
variation was due to the presence of unreactive silica
particles and dissolution of silica particles on RHA
surfaces. Observations from earlier literature on RHA based
geopolymer concrete with fly ash reveals that increase in
(a) (b)
(c) (d)
(e) (f)
Fig. 8 Morphological changes of RHA geopolymer
specimens; (a) 10% of RHA, (b) 15% of RHA, (c) 20% of
RHA, (d) 25% of RHA, (e) 30% of RHA and (f) 35% of
RHA
Table 6 EDX element weight percentage analysis of
ambient cured specimens
Element Mix
GPC R10 R15 R20 R25 R30 R35
O 46.03 55.75 53.24 55.22 56.58 54.47 54.82
Na 6.70 5.73 5.69 4.23 5.22 4.21 5.45
Al 10.34 8.26 6.98 7.57 6.35 6.99 6.62
Si 27.42 25.45 28.25 28.06 27.02 31.22 28.90
K 1.54 0.52 0.47 0.93 3.47 0.43 0.49
Ca 6.00 3.14 4.12 2.80 0 2.68 2.61
Fe 1.96 1.15 1.24 1.19 1.36 0 1.11
Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00
age reduces reactive silica particles in the specimen due to
the instantaneous reaction of silica and alumina precursor’s
dissolution- polycondensation progression of the framework
in the geopolymer and the steady low down rate diffusion of
residual ions in fly ash particles to attain equilibrium.
Addition of GGBS with fly ash and RHA accelerated
polycondensation and dissolution of aluminosilicate gel in
the geopolymer.
The absorption of H+ (hydrogen ion) by the Al-Si-rich
layers results in the further dissolution of silica particles
from RHA surfaces due to an increase in the pH in solution.
The RHA and fly ash based specimen face dissolution of
144
Development of eco-friendly concrete produced with Rice Husk Ash (RHA) based geopolymer
silica particles from RHA particles continuously to increase
the ratio of Si and Al development. Configuration of the Si-
O based geopolymer networks results in denser geopolymer
paste, with good bonding at interfacial transition zones and
the nanopores structure of the geopolymer matrix.
The absorption of H+ (hydrogen ion) by the Al-Si-rich
layers results in the further dissolution of silica particles
from RHA surfaces due to an increase in the pH in solution.
The RHA and fly ash based specimen face dissolution of
silica particles from RHA particles continuously to increase
the ratio of Si and Al development. Configuration of the Si-
O based geopolymer networks results in denser geopolymer
paste, with good bonding at interfacial transition zones and
the nanopores structure of the geopolymer matrix.
Progression of morphological changes in geopolymer
concrete with additions of 10%, 15%, 20%, 25%, 30% and
35% RHA at 28 days is seen in Fig. 8. Investigation of
SEM analyses images revealed that RHA particles added to
geopolymer concrete had a dense and compact matrix with
a high geopolymerization, whose dominant elements were
Si, Al. and Na. It was seen from SEM images that fly ash
particles were not recognized denoting that chemical fusion
in the dissolution of the alkaline environment was
proficient, particularly in RHA geopolymer concrete from
28 days.
Fig. 7 shows that RHA based geopolymer concrete
samples contained micro voids with a non-homogeneous
and porous microstructure on the surface. These cracks are
due to the following two reasons: (1) shrinkage cracks
developing due to water evaporation during curing of
geopolymer specimens; (2) Load based cracks during
compression testing. Voids may also be due to two
inferences: (i) due to residual air bubbles created in the
geopolymer precursor during the first stage of mixing; (ii)
initially the gap engaged by water and then remained as
void later on it evaporated. Earlier studies state that in early
ages, the geopolymer matrix contains insolubilized
particles. RHA contains unreactive particles and impurities
and influences geopolymerization (Duxson et al. 2007a, b,
De Vargas et al. 2011a, b). It is a significant factor that
influences the strength properties of RHA geopolymer
concrete, making them inconsistent and complicated. It is seen from Fig 8(e), at 28 days, the matrix’s
morphology is denser without particles of the geopolymer matrix. Morphology change implies that polymerization of the geopolymer matrix is reliable at 28 days and supports a strength increase in geopolymer concrete samples. This is due to the involvement of organic molecules present in rice
husk ash which eliminates the steric hindrance between the reacting species and assists development of the sialate-siloxo link which enhances its nature of amorphous and densifies the bonding of the matrix to be flexible, strong and homogeneous with better properties.
4. Conclusions
The study focuses on the influence of Rice Husk Ash
(RHA) in addition to GGBS and Fly ash in geopolymer
concrete on the strength properties. Test results exhibit that
the substitution of 30% of RHA in the geopolymer mix
shows better mechanical, durability. and microstructural
properties. RHA geopolymer concrete’s bond strength was
higher compared to other mixes due to good friction caused
by RHA’s higher fineness. Test results of microstructural
study revealed that, the presence of RHA in the geopolymer
mix densifies the concrete and makes it as homogeneous
and enhances its strength properties. Carbonation results
revealed that the pH value of RHA geopolymer concrete
was similar to that of conventional concrete. This research
suggests that RHA can be used to prepare eco-friendly
geopolymer concrete. It also reduces environmental
pollution caused by dumping of industrial by-products as
wastes in landfills.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest
with respect to the research, authorship. and/or publication
of this article.
Funding
The author(s) received no financial support for the
research, authorship. and/or publication of this article.
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