S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...
135–140
ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT
MORTARS FOR THE SEQUESTRATION OF ATMOSPHERIC CO
2
ZAKONITOSTI OLIVINSKEGA AGREGATA V APNU IN
CEMENTNIH MALTAH ZA ZAJEMANJE ATMOSFERSKEGA CO
2
Sriram Pradeep Saridhe
1
, Hareesh M
2
, Shanmuga Priya T
2
,
Thirumalini Selvaraj
3*
1
VR Siddhartha Engineering College, Department of Civil Engineering, Vijayawada, Andhra Pradesh, India
2
School of Civil Engineering, Vellore Institute of Technology, Vellore, Tamil Nadu, India
3
CO2 Research & Green technologies Centre, Vellore Institute of Technology, Vellore, Tamil Nadu, India
Prejem rokopisa – received: 2022-12-17; sprejem za objavo – accepted for publication: 2023-01-25
doi:10.17222/mit.2022.719
Construction industry is majorly criticised due to a great liberation of carbon dioxide (CO2) into the atmosphere. Researchers
have identified various techniques to capture the atmospheric CO2. Nevertheless, the recognised methods have both merits as
well as demerits. Thus, scientific communities are working on simple and easily exhibited ways of capturing atmospheric CO2.
One such technique is the conversion of gaseous CO2 into stable calcium/magnesium carbonates. The present study was con-
ducted to identify the carbon-capturing efficiency of olivine aggregate in cement and lime mortars. Olivine aggregate has a ten-
dency to change its mineral structure under alkaline environment and it is able to interact with atmospheric CO2 to form a stable
carbonate. Analytical techniques (XRD, TGA) were conducted to elucidate the formation of hydrated phases formed in both
lime and cement mortars. The study concluded that the addition of olivine sequestered atmospheric CO2 and converted it into
magnesium carbonate. Out of the lime and cement mortar, lime mortar captured a greater amount of CO2 and produced stable
compounds.
Keywords: carbon capture, carbon sequestration, olivine aggregate
Gradbena industrija se v glavnem kritizira zaradi velike svobode do izpustov ogljikovega dioksida (CO2). Raziskovalci so do
sedaj izna{li razli~ne tehnike za zajemanje atmosferskega CO2. Vendar pa imajo vse te do sedaj ugotovljene metode oziroma
postopki dolo~ene prednosti in pomanjkljivosti. Tako znanstvena skupnost {e naprej dela na poenostavitvah poti za zajemanje
atmosferskega CO2. Ena od tak{nih mo`nih tehnik je pretvorba plinskega CO2 v trdno obliko kot so karbonati na osnovi kalcija
in magnezija. Predstavljena je {tudija s katero so poizku{ali ugotoviti u~inkovitost agregatov olivina ((Mg,Fe)2SiO4)v
cementnih in apnenih maltah. Agregati olivina (pesek z delci velikosti pod 65 μm) imajo sposobnost reagiranja z atmosferskim
CO2 in tendenco pretvorbe svoje mineralne strukture v alkalnem okolju v trdni karbonat. S pomo~jo analiti~nih metod (XRD,
TGA) so razlo`ili nastanek hidratne faze, ki nastaja tako v apneni kot tudi v cementnih maltah. Ugotovili so, da dodatek olivina
izolira atmosferski CO2 in ga pretvori oziroma ve`e v magnezijev karbonat. Apnene malte ve`ejo ve~jo vsebnost atmosferskega
CO2 kot cementne in tvorijo trdne spojine.
Klju~ne besede: zajemanje atmosferskega ogljika, odstranjevanje atmosferskega ogljika, olivinski agregat
1 INTRODUCTION
The significant growth in the urbanization and indus-
trialization of the world has triggered a drastic alteration
in the climate of Earth and that may be the major reason
behind the global warming. The intergovernmental panel
on climate change (IPCC), funded by the UN (United
Nations) concluded that the increase in global warming
occurred due to the rise in the atmospheric CO
2
concen-
trations produced by humans.
1
The burning of fossil fu-
els like natural gas, coal and oils leads to a greater libera-
tion of CO
2
into the atmosphere, which further
significantly impacts the environment. According to the
Kyoto Protocol, the CO
2
emissions from fossil fuels have
been raised by 2.7 % annually over the previous ten
years and are already 60 % higher than the levels in the
reference year 1990.
2
To control the global CO
2
emissions, carbon capture
and utilization (CCU) is one of the effective solutions.
2
It
comprises the sequestration of atmospheric CO
2
and its
transformation into a valuable commodity either directly
or after conversion. Direct utilization of CO
2
is found in
the pharmaceutical industry, enhanced oil recovery, and
food and drink industries.
3
The conversion of CO
2
into a
product is found in the biofuel and chemical industry and
mineral carbonation.
4
In case of mineral carbonation,
CO
2
interacts with metal oxides of calcium and magne-
sium bearing compounds, producing stable calcium/mag-
nesium carbonates. Its major shortcomings are mining,
transportation and production of metal oxides, requiring
a lot of energy, which may not be economical.
2
At the same time, concrete is the most widely used
material on Earth after water and it is primarily com-
posed of cement, aggregates and water.
5
The production
of cement necessitates the use of fossil fuels at tempera-
tures varying in a range of 1400–1500 °C and could en-
Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140 135
UDK 625.042:549.621.14 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(2)135(2023)
*Corresponding author's e-mail:
p.thriumalini@yahoo.in (Thirumalini Selvaraj)

danger the environment due to the liberation of CO
2
.
6
In
general, the manufacture of one tonne of cement emits
an equivalent quantity of CO
2
into the atmosphere, ac-
counting for7%ofthew orld CO
2
emissions.
7
The con-
struction sector also relies on non-renewable resources to
generate aggregates, which account for around 60–75 %
of the total concrete volume.
8
Knowing from the past, lime mortars were the key
materials used over the centuries for the ancient struc-
tures. The hardening of lime mortars occurs through the
process called carbonation. It involves an interaction of
calcium hydroxide with atmospheric CO
2
to form a sta-
ble compound, calcium carbonate (CaCO
3
).
9
Hence the
carbonation is also called the natural way of sequestering
atmospheric CO
2
from the environment and converting it
into a stable product and this technique is similar to the
mineral carbonation in the CCU technique.
In recent years, researchers have identified another
important mineral, called olivine that could help to con-
vert atmospheric CO
2
into stable carbonates. In general,
olivine is a naturally occurring mineral with varying pro-
portions of magnesium to iron, combined with silicates.
It is usually identified in mafic and ultramafic igneous
rocks. Based on the amounts of magnesium and iron,
they are named as forsterite (MgSiO
4
) and fayalite
(Fe
2
SiO
4
). Fasihnikoutalab et al.
10
studied the role of ol-
ivine aggregate in the stabilization of soils. The study
concluded that an addition of olivine aggregates im-
proved the unconfined soil strength by 120 % when com-
pared with the reference one. They also stated that the
precipitation of magnesite was found, which could be the
reason behind the improved strength. Westgate et al.
11
discussed the role of olivine aggregate in lime mortars.
The research confirmed that fine-sized olivine aggregates
underwent dissolution in the lime alkaline environment
and stable magnesium carbonate precipitated in compari-
son to references mortars. The authors also explained
that the added olivine aggregate plays a dual role, replac-
ing fine aggregates and helping the sequestration of car-
bon dioxide from the atmosphere. Thus, in the current
study the authors attempted to examine the carbon-cap-
ture ability of both lime and cement mortar with olive
aggregates. Analytical techniques like XRD and TGA
were conducted to identify the hydrated phases devel-
oped in the mortars.
2 EXPERIMENTAL PART
2.1 Binder
Natural hydraulic lime and cement are chosen as
binders for the proposed study. Both binders are pro-
cured from commercial suppliers from Vellore, India.
Hydraulic lime conforms to class A according to IS 712:
1984;
12
the chemical composition is presented in Ta-
ble 1. The lime exhibits nearly 24 % of clay impurities,
hence it is categorised as eminently hydraulic in nature.
Ordinary Portland cement (OPC) of grade 53 is used.
Table 1: Oxide composition
Oxide components
Percentage of oxides
Lime Cement
CaO 63.2 66.67
MgO 0.161 0.87
SiO2
19.94 18.91
Al2
O
3
4.315 4.51
Fe2
O
3
1.833 4.94
2.2 Aggregates
Two types of aggregates are selected for the study,
namely river sand and olivine aggregate. The river sand
is procured locally and the gradation of aggregates is
done through a sieve analysis.
13
Olivine is procured from
Industrial Minerals & Refractories, Tamil Nadu, India.
The obtained olivine aggregates are ground into fine par-
ticles of a size not exceeding 65 μm.
2.3 Mix proportions
Two sets of samples are prepared to investigate the
role of olivine aggregate in both lime and cement mor-
tars. Set 1 comprises lime sand (LS), lime olivine (LO)
and Set 2 includes cement sand (CS), cement olivine
(CO). For both sets of mortars, a 1:3 binder-to-aggregate
ratio is adopted with 0.65 (lime) and 0.45 (cement) as the
binder-to-water ratios. Initially, one part of binder
(lime/cement) and three parts of aggregate (fine aggre-
gate/olivine aggregate) are weighed separately and
mixed thoroughly to attain a uniform state. The grinding
of two sets of mortars are done in a separate paddle
mixer. Many researchers have discussed the chemical in-
compatibility of lime and cement mortars. Hence, while
mixing the mortars, proper care should be taken to avoid
intermixing. After preparing the mortars as per IS 6932
(Part VII): 1973
14
(Hydraulic lime) and IS 2550 : 1981
15
(Cement mortars), the mortar mix is shifted into moulds
with a size of 50 mm × 50 mm in three layers with
proper compaction to ensure the voids are reduced. Ce-
ment mortar is demoulded after 24 h and kept at a tem-
perature of 27±2° Ca n d7 5%relative humidity and
lime mortar is demoulded after 3 d and cured at the same
conditions.
2.4 Analytical techniques
After the curing period, the core portion of the cube
is crushed thoroughly and passed through a 45 micron
sieve. The sieved (passed) material is examined with an-
alytical tests, X-ray diffraction (XRD) and TGA (thermal
gravimetric analysis). The XRD of the samples is carried
out using BRUKER D8 Advance (Germany) with Cu K
 radiation (0.15406 nm), a Lynxeye detector (silicon-strip
detector technology), and a Ni filter, detecting the crys-
talline phases present in the mortars. TGA is conducted
to identify the weight loss of various hydrated phases de-
veloped in both lime and cement mortars.
16
S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...
136 Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140

3 RESULTS
3.1 XRD of aggregates
The crystalline phases of fine aggregate and olivine
sand are compared with the XRD analysis as shown in
Figures 1a and 1b. The majority of the peaks observed
in fine aggregate indicate quartz followed by feldspar
and zirconium. Quartz is a highly stable compound and it
acts as an inert material in lime and cement mortars. On
other hand, olivine is a natural mineral with variable
quantities of magnesium to iron, combined with silicates.
XRD interpolation confirms that the selected olivine ag-
gregate is a magnesium-rich forsterite mineral. Fasih-
nikoutalab et al.
17
discussed the dissolution mechanism
of olivine mineral in an aqueous solution. These authors
also stated that olivine is a good candidate for CO
2
se-
questration because it originates from basalt rocks and it
is a neosilicate mineral. The mechanism involves the dis-
solution of atmospheric CO
2
in pore water and the for-
mation of carbonic acid, which keeps the pH at around
5.7 and stimulates the dissolution of olivine aggregate so
that finally magnesium-bearing compounds are formed.
The prime factors that affect the dissolution of olivine
aggregate are pH, CO
2
concentration, temperature and
grain size. The dissolution mechanisms of olivine aggre-
gates in the aqueous state are included in Equations (1),
(2) and (3).
CO H O HCO
H
22
dissolution
formation of carbo
+←→ ⎯⎯⎯+
+
−
+
3
nites
CO H ←→ ⎯⎯⎯⎯⎯ ⎯+
−+
3
22
(1)
Mg SiO H
Mg
2 dissolution of forsterite
2
4
4
2
+← → ⎯⎯⎯⎯⎯ ⎯ +
+
+
HS i H O
44
(2)
Mg CO MgCO
2+
3
carbonation
+←→ ⎯⎯ ⎯
−2
3
(3)
3.2 XRD analysis
Figures 2a and 2b depict the XRD patterns for LS
(lime + sand), LO (lime + olivine), CS (cement + sand)
and CO (cement + olivine) mortars for 28 d. The exami-
nation was initiated by comparing the crystalline phases
of reference lime mortars with lime/olivine aggregate
mortar. The significant peaks recognized in reference
mortars (Figure 2a) are calcite, portlandite, quartz, and
traces of tobermorite and gismondine. The dominant cal-
cite peaks are due to the conversion of portlandite to cal-
cite through the process called carbonation. In general,
carbonation is a natural phenomenon, in which atmo-
spheric CO
2
reacts with calcium hydroxide in the pres-
ence of pore water to from a stable compound, calcium
carbonate. Cultrone et al.
18
stated that carbonation is a
slow process, prolonged from months to years. Hence,
the presence of portlandite could be the reason behind it.
The traces of tobermorite and gismondine are also identi-
fied due to the presence of clay impurities in the binder.
In case of the LO mortar, Figure 2a depicts the majority
of calcite peaks, followed by aragonite, magnesite, dolo-
mite, tobermorite, gismondine and brucite. As discussed
before, the ground form of forsterite aggregate undergoes
dissolution in water and converts into Mg and Si ions.
The magnesium ions interact with atmospheric CO
2
and
form magnesite and dolomite. Magnesium ions can act
as catalysts for the precipitate aragonite phase in the lime
mortars.
19
Now the discussion will focus on the cement refer-
ence mortar and cement/olivine mortar. For the reference
mortar (Figure 2b), the major peaks observed indicate
quartz, calcite, ettringite, aragonite and portlandite. The
occurrence of calcite is due to the presence of free
portlandite, which occurred during the hydration of ce-
ment. Tobermorite peaks are observed due to the interac-
tion of alite and belite with water. In comparison with
reference mortars, cement/olivine mortar shows greater
S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...
Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140 137
Figure 1: a) sand, b) olivine aggregate

intensive peaks of aragonite, dolomite, calcite and traces
of brucite. The reason behind the domination of crystal-
line phases compared to amorphous phases could be the
natural carbonation of mortars (CS, CO) (a temperature
of 28 °C and RH of 65 %). Cizar et al.
20
discussed the
competition of hydration and carbonation in hydraulic
mortars under standard conditions. These authors con-
cluded that hydration is followed by a carbonation pro-
cess. Based on the above discussion, the final conclusion
is that lime mortars have a natural CO
2
sequestration
ability, but an addition of olivine improves the sequestra-
tion process, which is evident due to the greater intensity
peaks observed in the mortars with added olivine. The
olivine mortars also show the major strength giving com-
pounds due to the presence of magnesium ions.
3.3 TGA analysis
Combined TGA and DTA graphs of lime and cement
mortars are depicted in Figures 3a and 3b; the weight
losses of both mortars are presented in Table 1.Inthe
temperature range below 120 °C, weight losses of
0.27 % and 0.3 % are observed for lime and olivine mor-
tars, representing a low level of hygroscopic water.
Weight losses of 4.36 % and 4.44 % (120–420 °C) are
identified in lime reference and lime/olivine mortars.
This could be due to the weight loss of the clay impuri-
ties present in lime, while the slight increase in the
weight loss of olivine mortars could be attributed to the
presence of brucite. In the temperature range of
400–600 °C, weight losses of 2.62 % and 2.96 % are ob-
served in LS and LO mortars. The weight loss in both
S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...
138 Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140
Figure 2: a) LO, LS, b) CO, CS; P: portlandite; G: gismondine; B: brucite; T: tobermorite; C: calcite; M: magnesite; A: aragonite; D: dolomite;
Q: quartz; E: ettringite
Figure 3: a) LS – 28, b) LO – 28

mortars is due to the decomposition of uncarbonated
portlandite present in the samples. In addition, the
greater weight loss in LO mortar is due to the decompo-
sition of magnesite. The fall in weight at 600–800 °C is
due to the release of CO
2
from the polymorph of calcium
carbonate (aragonite, calcite) in LS mortars.
16
The
greater weight losses in LO mortars are due to the forma-
tion of dolomite along with calcium carbonate poly-
morphs. The XRD results also depict the presence of ad-
ditional minerals like brucite, magnesite and dolomite in
the lime/olivine mortar.
Significant mass losses of 7.6 (CS) and 7.7 % (CO)
are observed in the range of 120–420 °C due to the loss
in the surface water, dehydration of C-S-H and decompo-
sition of ettringite and brucite (Table 2). The weight
losses in cement olivine mortars are greater than in lime
mortars due to a greater decomposition of calcium sili-
cates and aluminates along with brucite. DSC depicted
an exothermic reaction in the temperature range of
400–600 °C, which can be attributed to the dehydration
of portlandite and magnesite. A weight loss of 5.01 % is
found in CO mortars compared to 3.27 % in CS mortars
in the temperature range of 600–800 °C. The increase in
the weight loss of CO mortars is due to the decomposi-
tion of calcium carbonate along with dolomite. DSC
curves show endothermic reactions in the same tempera-
ture range. The decomposition of calcium carbonate is
shifted before 800 °C, which can be due to the formation
of metastable calcium carbonates (Figures 4a and 4b).
Hence, the increased weight loss in both LO and CO
mortars is due to the interaction of finely ground forster-
ite compounds with atmospheric CO
2
, confirming that
olivine-based mortars have a greater ability to capture at-
mospheric CO
2
.
4 CONCLUSIONS
An addition of olivine aggregates greatly improves
the properties of both lime and cement mortars. The
strength gains in both mortars are due to the formation of
magnesium-bearing compounds magnesite and dolomite,
which is confirmed with analytical techniques, XRD and
TGA. These compounds are formed due to the interac-
tion of carbonate ions with dissolute magnesium ions in
both mortars. During the process of hardening of olivine
mortars (lime, cement), olivine sequesters atmospheric
CO
2
and forms a stable compound. Hence, the adoption
of olivine aggregate in binding mortars is highly advis-
able as it improves the properties of both mortars and re-
duces the carbon footprint on the environment, acting as
a carbon capture and sequestration unit.
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Figure 4: a) CS – 28, b) CO – 28
Table 2: Percentage of weight loss
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