Experimental Investigation on Geopolymer Concrete:- Sustainable and Eco-Friendly Construction Material

Abstract

The research for the new environmental friendly construction material that will match the durability of ancient concrete has provoked interest into the study of alkali activated cementitious systems over the last two decades. It results in the development of Geopolymer Concrete. This paper represents the development of geopolymer mixes of various ratios of fly ash and GGBS and their mechanical properties were studied. aa Literature review on mechanical and durability properties of geopolymer concrete also been done. The ratio of sodium hydroxide to sodium silicate is 1:2 which is kept a constant to prepare the mix and alkaline liquid to binder ratio as 0.70, but changing the concentration of sodium hydroxide solution as 6M, 4M and 3M to prepare the mix Id. i.e. F75G25, F50G50 and F25G75, respectively (where F and G are Fly Ash and GGBS and the numerical value indicates the percentage of replacement of fly ash by GGBS) were prepared in AML laboratory, CSIR-SERC, Chennai. Ambient curing of concrete at room temperature was adopted.The compressive strength at age of 3, 7 and 28 days were determined. The strength of geopolymer concrete was increased with increase in percentage of GGBS in a mix. It was observed that the mix Id F25G75 gave maximum compressive strength for concentration of NaOH as 3M . Leaching of GPC reduces with increase in percentage of GGBS in a mix. Thus the geopolymer concrete have a relatively higher strength.

Full text

Experimental Investigation on Geopolymer Concrete:- Sustainable and
Eco-Friendly Construction Material
Amina Rafeek ,
1Sundar Kumar.S. and Indu Susan Raj3
1 PG Student, ,Mar Athanasius College of Engineering, Kothamangalam, Kerala-
686691;Email: aminarafq1999@gmail.com.
2 Principal Scientist, AML Lab, CSIR-SERC, Taramani,Chennai-
600113; Email: ssk@serc.res.in
3 Assistant Professor, Mar Athanasius College of Engineering, Kothamangalam, Kerala-
686691;Email: indususanraj@mace.ac.in
Abstract
The research for the new environmental friendly construction material that will match the durability of ancient
concrete has provoked interest into the study of alkali activated cementitious systems over the last two decades.
It results in the development of Geopolymer Concrete. This paper represents the development of geopolymer
mixes of various ratios of fly ash and GGBS and their mechanical properties were studied. aa Literature review
on mechanical and durability properties of geopolymer concrete also been done. The ratio of sodium hydroxide
to sodium silicate is 1:2 which is kept a constant to prepare the mix and alkaline liquid to binder ratio as 0.70,
but changing the concentration of sodium hydroxide solution as 6M, 4M and 3M to prepare the mix Id. i.e.
F75G25 , F50G50 and F25G75, respectively (where F and G are Fly Ash and GGBS and the numerical value
indicates the percentage of replacement of fly ash by GGBS) were prepared in AML laboratory ,CSIR-SERC,
Chennai. Ambient curing of concrete at room temperature was adopted.The compressive strength at age of 3, 7
and 28 days were determined. The strength of geopolymer concrete was increased with increase in percentage of
GGBS in a mix. It was observed that the mix Id F25G75 gave maximum compressive strength for concentration
of NaOH as 3M . Leaching of GPC reduces with increase in percentage of GGBS in a mix. Thus the
geopolymer concrete have a relatively higher strength.
Keywords: Geopolymer concrete, Compressive strength, mix, Alkaline solution,Ambient curing,
Groundgranulated blast furnace slag, Flyash.
1. Introduction
Concrete is the most commonly used construction material; it’s usage by communities across the globe is
second only to water. Ever grander building and infrastructure projects require prodigious quantities of concrete
with its binder of Portland cement whose manufacture, as we have seen, is accompanied by large emission of
carbon dioxide. Ranging from 0.66 to 0.82kg of CO2 emitted for every kilogram manufactured. The contribution
of the production of OPC is approximately 5-7% of global anthropogenic CO2emissions. The key cases of high
CO2 emissions arising from OPC manufacture have been attributed to i) Calcinations of lime stone, one of the
key ingredients, which leads to formation and release of CO2 and ii) High energy consumption during
manufacturing, including heating raw materials within a rotating kiln at temperatures greater than 14000°C.
The call for the day is, “Sustainable Development” which demands the new concrete technology which uses less
natural resource, energy and generates less CO2 without compromising on strength and durability aspects. This
burgeoning worldwide demand for concrete is a great opportunity for the development of geopolymer concrete
and geopolymer cements of all types, with their much lower tally of CO2. As of now, waste materials have
partly been used as aggregates and fillers in concrete. The research for the new environmental friendly
construction material that will match the durability of ancient concrete has provoked interest into the study of
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MATEC Web of Conferences 384, 02002 (2023) https://doi.org/10.1051/matecconf/202338402002
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© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0
(https://creativecommons.org/licenses/by/4.0/).

alkali activated cementitious systems over the last two decades. One effort to combat short fall is the
development of alternate binders to Portland cement aiming at to reduce the environmental impact of
construction, use of greater proportion of waste pozzolan, and also due to improve concrete performance.
Geopolymer is an ecofriendly material produced as a by-product from industrial wastes such as fly ash, ground
granulated blast slag, metakaolin, rice husk etc. The use of geopolymer reduces the carbon footprint. This
reduces the demand on conventional cements. Geopolymers have vast advantages over conventional cement in
view with mechanical and durability properties. Commercially geopolymers are used for fire and heat resistant
and as new binders for fire-resistant fiber composite toxics and at radioactive waste encapsulation and for
producing an alternative to conventional cements.
Geopolymers are more resistant to corrosion and fire and has high compressive and tensile strength. They gain
full strength faster and has less shrinkage than the conventional concrete. Geopolymer concrete is a viable
alternate to Portland cement concrete. The process of geopolymerisation has summarized in 3 steps such as
dissolution of silica and alumina from the source material through the action of hydroxide ions,transportation or
orientation or condensation of precursor ions into monomers.It essentially consists of covalently bonded (Si-O-
Al-O) sialiate monomers. It is an inorganic by product material which is rich in silicon (Si) and alumina
(Al),that react with alkali activators to from 3D polymeric chains of saliate and poly(sialiate).
Zhang and Wang(2013) studied the phenomenon of efflorescence of fly-ash geopolymers is mainly due to
sodium carbonate heptahydrate (Na2CO37H2O). The efflorescence has occurred in 3hrs in specimens which was
in contact with water at the bottom and it is faster in 25ºC sealed aged geopolymers. Therefore, hydrothermal
curing reduces the formation of efflorescence. The potential of efflorescence is compared by measuring cation
concentrations, pH value and electrical conductivity of geopolymer leaching solutions. The use of soluble
silicate present activator can achieve high strength as well as early age efflorescence under wet conditions and
restricts long term efflorescence potential. The pore solution analysis result shows that if soluble silicate content
increases, then the geopolymer mixture tends to decrease the alkali metal concentrations. And compressive
strength test for FA geopolymer concrete with 100% sodium silicate activator, FA geopolymer concrete with
100% NaOH solution as activator and geopolymer concrete of 80% FA and 20% slag are cured at 80ºC and
25ºC. The results show that geopolymer concrete containing slag’s strength has increased eloquently at 25ºC
compared to other mix. And the geopolymers cured at 80ºC, FA geopolymer concrete with 100% sodium
silicate activator has increased strength compared other geopolymer concrete. The addition of slag reduces the
alkali leaching and hence it reduces the leaching rate at initial stage only. From electrical conductivity it is found
that Na+, K+, OH- ions are the main contributors to leaching rate.Madheswaran and Gnanasundar(2013) has
done an experimental investigation on use of three different molarities of NaOH range 3M, 5M and 7M and
their influence on three different types of mixes in combination with FA and GGBS to study the effect of AAS
in geopolymer concrete. The mixes are 50% GGBS and 50% FA, 75% GGBS and 25% FA and 100% GGBS.
The result of compressive strength test of cube size 150 x 150 x 150mm shows that strength increases with the
molarity of NaOH. For the mix of 100% GGBS and 7M NaOH, it gives maximum compressive strength of
60MPa in 28 days. When the addition of GGBS increases then the compressive strength is also increased. From
the split tensile result of 150mmϕ 300mm height cylinders it has been observed that when the quantity of GGBS
increase the split tensile strength also increases.Chamila Gunasekara(2016) has studied the durability
characteristics of four different flyash geopolymer concretes and their permeation properties was carried out for
up to an age of 1 year. The flyash’s were taken from four different power plants in Australia. The AAS is a
mixture of sodium silicate and sodium hydroxide solution (15M). The aggregates used are river sand as fine
aggregate and 7mm & 10mm size coarse aggregates were used. The flyash geopolymer concrete has slightly
lower density than plain cement concrete and a collapsed type of slump. In these four types of flyash, gladstone
geopolymer has highest compressive strength of about 48.7MPa and Collie geopolymer has lowest value of
23.5MPa in 28days. From the compressive test they’ve found that there is an-going geopolymerization as the
compressive strength is increased with time in flyash geopolymer concrete. Gladstone, Pt. augusta and Tarong
geopolymers achieved a compressive strength more than 30MPa in 3days under exposure classification B1, B2.
Gladstone geopolymer concrete has enough 50MPa compressive strength of maritime structure in sea tidal
zones under exposure classification C1, C2. From SEM data it has been observed that there is an increase in the
aluminosilicate gel in the concrete matrix and a decrease in the quantity of micro cracks for all geopolymers.
From UPV test it has been found that only gladstone geopolymer concrete has categorised being in good
condition. Gladstone and Pt. Augusta shows reduction in water absorption with time and are classified as low
permeable concrete and as well as low air permeability index with time. But Tarong is significantly performing
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well with respect to water absorption, AVPV, strength test, UPV, permeability data’s observed over a period of
1year. A salt ponding test has been done for a term of 90days to observe its resistance to corrosion. Gladstone
and Pt. Augusta geopolymer concrete showed high surface chloride concentration at early age which was higher
than plain cement concrete and blended cement concrete but the surface chloride concentration of all four
geopolymer concretes reduced with age of concrete and varied between 0.34 to 0.39% chloride by weight of
concrete at 1 year. The chloride diffusion coefficient of all four flyash geopolymer were between 15.8 x 10-11
and 21.5 x 10-11 m2/s at 28days but these were decreased with age of concrete. Hence an improvement in the
durability properties of all four flyash geopolymer concrete with time. Zengqing Sun(2020) three types of
geopolymers were tested for leaching, they are flyash geopolymer (FAG), metakaolin geopolymer (MKG) and
commercial geopolymers (CG) are used. The horizontal dynamic surface leaching of Na, K, Al, Si, Ca, Ba, As,
Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, Tl, V, Zn were studied and was done for samples that are cured for 56days
before leaching. FAG has lower reaction and the unreacted alkali in FAG has higher pH value and releases more
Na because of using sodium-based activators. Si is more easily leached than Al in FAG and CG. The results
show there’s strength loss after leaching in deionized water of FAG, MKG and CG samples of about 11.8%,
9.4% and 14.9%. The 56day compressive strength of MKG is 68MPa, which more compared to FAG and
CG.Rachit ghosh(2018) investigated leaching on three flyash collected from Tata Power Jojobera Plant, Rawan
Plant and Ennore Plant and named as FA1, FA2 and FA3 resp. GGBS were collected from Tata Steel and
bottom ash (BA) from Tata power plant. The flyash based geopolymer concrete is a mixture of flyash, GGBS,
bottom ash as fine aggregate and crushed stone aggregate. The AAS used were NAOH and NA2SiO3 (1:1) as
alkali-1 (6M), alkali-2 (8M) and alkali-3 (10M). From XRD it is observed the flyash’s from different plants are
quartz, mullite, hematite and magnetic. In Toxicity characteristic leaching procedure (TCLP), 1M sodium
acetate buffer was used as an extraction liquid at pH 4.99 for TCLP and for batch leach test the pH value is 7.2.
Mn, Cu and Mg were leached out at higher amount in all Flyash samples and Ni, Fe, Pb were leached out at a
lower concentration. It is also found that metals concentration in TCLP was higher than batch leach test since
the solubility of metals decreases with increasing pH value, because of insoluble hydroxides at high pH values.
From mercury intrusion, the pores are uniformly distributed and the variation in number of pores is less in
6MFA3GC when compared to 6MFA1GC and 6MFA2GC. From the compressive strength test, the 6MFA3GC
reported the maximum strength which is then followed by 6MFA2GC and 6MFA2GC but when compared with
different concentration of alkali, the maximum strength is achieved by 6MFA3GC and minimum strength by
10MFA1GC. This is because the 1 day to 7days strength was slow due to alkali’s reaction but it was totally
reverse after 28day strength. The leaching out and efflorescence behaviour and its effect were studied for up to
180 days, it has been found that leachates of heavy metals and trace elements were below the permissible limits
as per IS code. And also there was no visual deterioration of geopolymer concrete specimens when exposed to
weathering condition up to 180 days.
2. Materials and Methods
The materials used in the study are class F fly ash (FA) and ground granulated blast slag (GGBS). The
concentration sodium hydroxide (SH) solution in this study was 6Molar, 4 Molar and 3 Molar. The ratio of
sodium hydroxide to sodium silicate (SS) is maintained at 1:2. The specific gravity and bulk density of low
calcium class F fly ash was 2.8 and 995 kg/m3 respectively. The specific gravity and bulk density of GGBS was
2.9 and 1250kg/m3 with a fineness of 400 m2/kg.
The oxide composition of fly ash and GGBS was obtained from XRF analysis is given in table 1.Sodium
hydroxide was used in the form of flakes and sodium silicate in liquid form. M sand is used as fine aggregate
and coarse aggregate of 10mm and 20mm down size is used in 60% and 40% of total weight.
Table 1 Oxide Composition of Fly Ash and GGBS
While preparing Alkali activator solution (AAS), first the SH flakes were dissolved a day before casting due to
rise in temperature during addition of flakes in water then SS solution was added 2mins before casting of
Materials SiO
2
Al
2
O
3
Fe
2
O
3
CaO MgO Na
2
O
3
K
2
O TiO
2
Mn
2
O
3
SO
3
Fly Ash 62.1 27.44 4.57 0.83 0.55 0.04 1.17 1.09 0.04 0.04
GGBS 43.4 12.5 - 40.3 1.5 0.9 0.6 - - -
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concrete. Slump value was found for all the mixes.
Table 2 Composition and Properties of Sodium Silicate
Na
2
O
(%)
SiO
2
(%)
Total Solids
(%)
Viscosity
(Ns/m2)
Specific
gravity
14.2 31.2 45.4 900 1.4
The specific gravity and bulk density was 2.65 and 1550kg/m3 respectively for M sand and for coarse aggregate
its 2.71 and 1600kg/m3. The ratio of Fly ash to GGBS in this study is 75:25, 50:50 and 25:75, three mixes were
developed for this ratio for 6M, 4M and 3M respectively. FA, GGBS, fine and coarse aggregates were mixed
dry in 50Kg mixer pan for few minutes the AAS is added little by little looking at the consistency of the
concrete. The addition AAS can lesser or more than the calculated value. The geopolymer concrete cubes of all
the mixes were cured under ambient temperature. The details of the 3 mixes are given in the table 3 .
Table 3 Quantity of Mixes
The slump test is shown in Fig 1 and its values for various mixes are depicted in table 4.
Figure 1 Slump test
Mixes GGBS
Fine
Aggregate
Coarse
Aggregate Activators
10mm 20mm AAS Molarity
GM1 300 100 655 606 404 260 6
GM2 200 200 645 594 396 260 4
GM3 100 300 640 588 392 260 3
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Table 4 Slump Value
Mix ID Slump Value
(mm)
GM1
195
GM2
198
GM3
190
2.1 Tests on Concrete
2.1.1 Compressive strength of concrete
The compressive strength of concrete was done to determine the strength of 100mm cube on 3rd day, 7th day
and 28th day in UTM (Universal Testing Machine) shown in Fig 2. The compressive strength results are
depicted in table 5.
Figure 2 Compression Test
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Table 5 Compressive strength results
3. Results and Discussions
The detailed analysis has been carried out for,and the results are described in the following.
 A total of three geopolymer mixes were studied.
 The geopolymer mixes achieved a very good workability in terms of slump values. The mixes also had
sufficient workability retention time. Though slump retention was not measure, the mixes started
hardening only after 30-40 minutes after initial mixing.
 Comparative Compressive Strength Graph is shown in Fig3. The highest strength was achieved by the
Mix GM3.
 All the geopolymer concrete mixes had a faster rate of strength gain when compared to the rate
normally one would anticipate from Portland cement concrete.
 Initial stages leaching was observed, but it decreases with age and Leaching of GPC reduces with
increase in percentage of GGBS in a mix.
 Hence geopolymer concrete of nominal strength can be produced with relative mild activators. These
mixes can be handled easily, produced in situ and in large quantities with existing infrastructure itself.
Figure 3 Comparative Compressive Strength Graph
References
1) Ghosh, R., Gupta, S. K., Kumar, A., & Kumar, S. (2018). Leaching and efflorescence effects in
geopolymer concrete. Journal of Metallurgy and Materials Science, 60(2), 79-88.
2) Gunasekara, C., Law, D. W., &Setunge, S. (2016). Long term permeation properties of different fly ash
geopolymer concretes. Construction and Building Materials, 124, 352-362.
https://doi.org/10.1016/j.conbuildmat.2016.07.12
3) Madheswaran, C. K., Gnanasundar, G., &Gopalakrishnan, N. (2013). Effect of molarity in geopolymer
concrete. International Journal of Civil & Structural Engineering, 4(2), 106-115.
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Comp. Strength (MPa)
Time (days)
GM SERIES
GM1
GM2
GM3
MIX ID
3
rd
days
strength,
MPa
7
th
day
strength,
MPa
28
th
day
strength,
MPa
GM1 8.93 15.02 28.48
GM2 14.56 29.68 46.25
GM3 28.23 38.12 53.5
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4) Sun, Z., &Vollpracht, A. (2020). Leaching of monolithic geopolymer mortars. Cement and Concrete
Research, 136, 10616
5) Z. Zhang, H. Wang, J.L. Provis, & A. Reid, (2013). Efflorescence: a critical challenge for geopolymer
applications In Concrete Institute of Australia's Biennial National Conference 2013 (pp. 1- 10)
. Concrete Institute of Australia.
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