The document summarizes a study on the strength and durability characteristics of geopolymer concrete using ground granulated blast furnace slag (GGBS) and black rice husk ash (BRHA). GGBS was used as the base material for the geopolymer concrete and was replaced with 0-30% BRHA. The compressive strength of the mixtures was tested at various ages. The results showed that replacing GGBS with BRHA decreased the compressive strength due to the unburnt carbon content in BRHA. A 10% replacement of GGBS with BRHA provided adequate compressive strength while reducing the carbon footprint of the concrete.

1. Strength and Durability characteristics of
Geopolymer concrete using GGBS and RHA
S.Subburaj,T.Anantha shagar
VV college of Engineering,tisayanvilai
tutucorin
Abstract— Cement, the second most consumed product in the
world, contributes nearly 7% of the global carbon dioxide
emission. Several efforts are in progress to reduce the use of
Portland cement in concrete in order to address the global
warming issues. Geopolymer concrete is a cementless concrete. It
has the potential to reduce globally the carbon emission that lead
to a sustainable development and growth of the concrete
industry. In this study, geo-polymer concrete is prepared by
incorporating ground granulated blast furnace slag (GGBS) and
black rice husk ash (BRHA) as source materials. In India RHA is
used for cattle feeding, partition board manufacturing, land
filling, etc. RHA is either white or black in colour. If the rice
husk is burnt in controlled temperature and duration, it will
result the ash in white colour. This type of RHA has high
percentage of silica content. The ease availability of RHA is black
in colour due to uncontrolled burning temperature and duration
in various rice mills, so the resulting rice husk ash is called as
black rice husk ash (BRHA).
In this study GGBS used as a base material for geopolymer
concrete and it is replaced upto 30% by BRHA. The strength
characteristic of GGBS and BRHA based geopolymer concrete
has been studied. The suitable compressive strength test is
performed. The result shows that the replacement of BRHA
decreases the compressive strength of geopolymer concrete,
because of the unburnt carbon content present in the BRHA.
Keywords— Geopolymer concrete, GGBS, Black Rice Husk Ash,
Compressive strength
INTRODUCTION
Concrete is the second most used material in the world after
water. Ordinary Portland cement has been used traditionally
as a binding material for preparation of concrete. One tone of
carbon dioxide is estimated to be released to the atmosphere
when one ton of ordinary Portland cement is manufactured.
Also the emission by cement manufacturing process
contributes 7% to the global carbon dioxide emission. It is
important to find an alternate binder which has less CO2
emission than cement. Geopolymer is an excellent alternative
which transform industrial waste products like flyash, GGBS
and rice husk ash into binder for concrete. Al- Si materials
which are used as source materials undergoes dissolutions, gel
formation, setting and hardening stages to form geopolymers.
There are two main constituents of geo-polymers, namely the
source materials and the alkaline liquids. The source materials
for geo-polymers based on alumina-silicate should be rich in
silicon (Si) and aluminium (Al). These could be natural
minerals such as kaolinite, clays, etc. Alternatively, by-
product materials such as fly ash, silica fume, slag, rice-husk
ash, red mud, etc could be used as source materials. The
choice of the source materials for making geo-polymers
depends on factors such as availability, cost, type of
application, and specific demand of the end users. The
alkaline liquids are from soluble alkali metals that are usually
sodium or potassium based. The most common alkaline
liquids used in geo-polymerization are a combination of
sodium hydroxide (NaOH) or potassium hydroxide (KOH)
and sodium silicate (Na2SiO3) or potassium silicate (K2SiO3).
The alumino silicate material which is to be used in this study
is a combination of Rice husk ash and ground granulated blast
furnace slag (GGBS). RHA is either white or black in color. If
the rice husk is burnt in controlled temperature and duration, it
will result the ash in white color. This type of RHA has high
percentage of silica content. The ease availability of RHA is
black in color due to uncontrolled burning temperature and
duration in various rice mills, so the black color rice husk ash
is called as black rice husk ash (BRHA). The RHA used in
this study was black rice husk ash. This study aims to
synthesize geopolymer concrete using combination of GGBS
and BRHA. In this study GGBS used as a base material for
geoploymer concrete. GGBS is replaced up to 30% by BRHA
to understand the strength and durability characteristics.
MATERIALS
The materials used for making GGBS based geopolymer
concrete specimens are GGBS, Rice Husk Ash, aggregates,
alkaline liquids, water and super plasticizer. Ground
Granulated Blast furnace Slag was procured from JSW
cements in Bellari, Karnataka. Black Rice Husk Ash was
obtained from a Rice mill near Karaikudi and then it was
finely grounded. The properties of GGBS and BRHA are
given in Table I.
TABLE I. PROPERTIES OF GGBS AND RHA
Property GGBS BRHA
SiO2 31.25 % 93.96 %
Al2O3 14.06 % 0.56 %
Fe2O3 2.80 % 0.43 %
CaO 33.75 % 0.55 %
MgO 7.03 % 0.4 %
Specific gravity 2.61 2.11
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2. Aggregates
Coarse aggregate passing through 20mm sieve and fine
aggregate of river sand from a local supplier were used for the
present study and their properties are given in Table II.
TABLE III. PROPERTIES OF AGGREGATES
Property Coarse
Aggregate
Fine
Aggregate
Specific gravity 2.73 2.60
Fineness modulus 7.36 2.63
Bulk density 1533 kg/m3
1254 kg/m3
B. Alkaline solution
A mixture of Sodium hydroxide and Sodium Silicate was used
as the alkaline solution in the present study. Commercial
grade Sodium Hydroxide in pellets form (97%-100% purity)
and Sodium silicate solution having 7.5%-8.5% of Na2O and
25% -28% and water of 67.5%- 63.5% were used in the
present study. The ratio of Sodium Silicate to Sodium
Hydroxide was kept as 2.5. In this study the compressive
strength of geo-polymer concrete is examined for the mix of
8M of NaOH solution. The molecular weight of NaOH is 40.
For example to prepare 8M of NaOH solution 320g of NaOH
flakes are weighed and they can be dissolved in distilled water
to form 1 litre solution. For this, volumetric flask of 1 litre
capacity is taken, NaOH flakes are added slowly to distilled
water to prepare 1litre solution.
In order to improve the workability of fresh concrete, high-
range water-reducing naphthalene based super plasticizer was
used. Extra water nearly 15% of binder is added to increase
the workability of the concrete.
METHODOLOGY
C. Mixing, Casting and Curing
The mix proportions were taken as given in Table. III. As
there are no code provisions for the mix design of geopolymer
concrete, the density of geo-polymer concrete was assumed as
2400 Kg/m3
and other calculations were done based on the
density of concrete [4]. The combined total volume occupied
by the coarse and fine aggregates was assumed to be 77%.
The alkaline liquid to binder ratio was taken as 0.40. GGBS
was kept as the primary binder in which BRHA was replaced
in 0, 10, 20 and 30% by weight. The normal mixing procedure
was adopted. First, the fine aggregate, coarse aggregate and
GGBS & BRHA were mixed in dry condition for 3-4 minutes
and then the alkaline solution which is a combination of
Sodium hydroxide and Sodium silicate solution with super-
plasticizer was added to the dry mix. Then some extra water
about 15% by weight of the binder was added to improve the
workability. The mixing was continued for about 6-8 minutes.
After the mixing, the concrete was placed in cube moulds of
size 150mm X 150mm X 150mm by giving proper
compaction. The GPC specimens were then placed in a hot air
oven at a temperature of 60o
C for 48 hours and then the
specimens were taken out and cured under room temperature
till the time of testing.The cubes were then tested at 3, 7 and
28 days from the day of casting.
TABLE IIIII. MIX PROPOTIONS OF GEOPOLYMER CONCRETE
Materials Mass(Kg/m3
)
Mix1
(0%
RHA)
Mix2
(10%
RHA)
Mix3
(20%
RHA)
Mix4
(30%
RHA)
GGBS 394 355 315 276
RHA 0 39 79 118
Coarse
Aggregate
647 647 647 647
Fine
Aggregate
1201 1201 1201 1201
Sodium
Hydroxide
45 45 45 45
Sodium
Silicate
113 113 113 113
Super
Plasticizer
8 8 8 8
Extra
Water (15%)
59 59 59 59
RESULTS AND DISCUSSION
The cubes were tested in the compressive testing machine to
determine their compressive strength at the age of 3, 7 and 28
days from the day of casting. The Table IV and figure 1 shows
the compressive strength variation with percentage
replacement of BRHA. The table4 shows that GGBS based
geopolymer concrete attained compressive strength of 69
MPa. 10 % replacement of GGBS by RHA gives compressive
strength of 58 MPa.
The figure1 shows that there is an increase in compressive
strength if the curing time increases. The percentage of
increase in strength is approximately 16 to 20 for the curing
time of 3days to 28days. The percentage increase in strength
from 3 to 28 days curing time is approximately 24% for mix1.
The graph shows that the replacement of BRHA in GGBS
based geopolymer concrete decreases the compressive
strength. Because of the unburnt carbon content present in
BRHA, decreases the compressive strength. The average 28
days compressive strength of mix2 and mix3 is decreases by
20% and 46% compared to mix1.
TABLE IVV. COMPRESSIVE STRENGTH TEST RESULTS
Mix Compr
essive
strength
at 3rd
day(MPa)
Compr
essive
strength
at 7th
day(MPa)
Compre
ssive
strength at
28th
day(MPa)
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3. Mix 1 (100%
GGBS, 0% RHA)
55.9 60.5 69.2
Mix 2 (90%
GGBS, 10% RHA)
48.6 54.3 57.46
Mix 3 (80%
GGBS, 20% RHA)
40.75 44.72 47.36
Mix 4 (70%
GGBS, 30% RHA)
20.8 23.54 27.36
Fig.1 Variation of compressive strength at 3rd
, 7th
and 28th
days with replacement of BRHA
CONCLUSIONS
From the limited experimental study conducted on the
geopolymer concrete made with GGBS and BRHA, the
following conclusions are made.
1. The GGBS based geopolymer concrte gives higher
strength.
2. The replacement of GGBS by BRHA decreases the
compressive strength because of the unburnt carbon
content.
3. The percentage replacement of BRHA in GGBS based
geo-polymer concrete is significant only in 10%.
4. Due to the presence of high silica content in BRHA
(94%) there is a fast chemical reaction occurred resulting
quick setting of geo-polymer concrete.
5. In this study, the Si / Al ratio is not maintained due to low
alumina content in the source materials resulting in lesser
compressive strength .
6. I feel that GGBS with 10% of RHA will be well and eco
friendly when compared with OPC
ACKNOWLEDGMENT
The author would like to acknowledge his Research
supervisor mr.p.muthuraman for his meticulous guidance and
constant motivation. The author would also like to thank the
faculty members of Division of Structural Engineering, vv
college of Engineering University, tisayanviai for their
consent encouragement and support during the project work.
The author would also like to thank his family and friends for
their complete moral support.
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