UDK 625.042:549.621.

14 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(2)135(2023)

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 CO2
ZAKONITOSTI OLIVINSKEGA AGREGATA V APNU IN
CEMENTNIH MALTAH ZA ZAJEMANJE ATMOSFERSKEGA CO2

Sriram Pradeep Saridhe1, Hareesh M2, Shanmuga Priya T2,

Thirumalini Selvaraj3*
1VR Siddhartha Engineering College, Department of Civil Engineering, Vijayawada, Andhra Pradesh, India
2School of Civil Engineering, Vellore Institute of Technology, Vellore, Tamil Nadu, India
3CO2 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 To control the global CO2 emissions, carbon capture

and utilization (CCU) is one of the effective solutions.2 It
The significant growth in the urbanization and indus- comprises the sequestration of atmospheric CO2 and its
trialization of the world has triggered a drastic alteration
transformation into a valuable commodity either directly
in the climate of Earth and that may be the major reason
or after conversion. Direct utilization of CO2 is found in
behind the global warming. The intergovernmental panel
on climate change (IPCC), funded by the UN (United the pharmaceutical industry, enhanced oil recovery, and
Nations) concluded that the increase in global warming food and drink industries.3 The conversion of CO2 into a
occurred due to the rise in the atmospheric CO2 concen- product is found in the biofuel and chemical industry and
trations produced by humans.1 The burning of fossil fu- mineral carbonation.4 In case of mineral carbonation,
els like natural gas, coal and oils leads to a greater libera- CO2 interacts with metal oxides of calcium and magne-
tion of CO2 into the atmosphere, which further sium bearing compounds, producing stable calcium/mag-
significantly impacts the environment. According to the nesium carbonates. Its major shortcomings are mining,
Kyoto Protocol, the CO2 emissions from fossil fuels have transportation and production of metal oxides, requiring
been raised by 2.7 % annually over the previous ten a lot of energy, which may not be economical.2
years and are already 60 % higher than the levels in the At the same time, concrete is the most widely used
reference year 1990.2 material on Earth after water and it is primarily com-
posed of cement, aggregates and water.5 The production
*Corresponding author's e-mail: of cement necessitates the use of fossil fuels at tempera-
p.thriumalini@yahoo.in (Thirumalini Selvaraj) tures varying in a range of 1400–1500 °C and could en-

Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140 135

S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...

danger the environment due to the liberation of CO2.6 In Table 1: Oxide composition
general, the manufacture of one tonne of cement emits Percentage of oxides
an equivalent quantity of CO2 into the atmosphere, ac- Oxide components
Lime Cement
counting for 7 % of the world CO2 emissions.7 The con- CaO 63.2 66.67
struction sector also relies on non-renewable resources to MgO 0.161 0.87
generate aggregates, which account for around 60–75 % SiO2 19.94 18.91
of the total concrete volume.8 Al2 O3 4.315 4.51
Knowing from the past, lime mortars were the key Fe2 O3 1.833 4.94
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 2.2 Aggregates
calcium hydroxide with atmospheric CO2 to form a sta- Two types of aggregates are selected for the study,
ble compound, calcium carbonate (CaCO3).9 Hence the namely river sand and olivine aggregate. The river sand
carbonation is also called the natural way of sequestering is procured locally and the gradation of aggregates is
atmospheric CO2 from the environment and converting it done through a sieve analysis.13 Olivine is procured from
into a stable product and this technique is similar to the Industrial Minerals & Refractories, Tamil Nadu, India.
mineral carbonation in the CCU technique. The obtained olivine aggregates are ground into fine par-
In recent years, researchers have identified another ticles of a size not exceeding 65 μm.
important mineral, called olivine that could help to con-
vert atmospheric CO2 into stable carbonates. In general, 2.3 Mix proportions
olivine is a naturally occurring mineral with varying pro-
portions of magnesium to iron, combined with silicates. Two sets of samples are prepared to investigate the
It is usually identified in mafic and ultramafic igneous role of olivine aggregate in both lime and cement mor-
rocks. Based on the amounts of magnesium and iron, tars. Set 1 comprises lime sand (LS), lime olivine (LO)
they are named as forsterite (MgSiO4) and fayalite and Set 2 includes cement sand (CS), cement olivine
(Fe2SiO4). Fasihnikoutalab et al.10 studied the role of ol- (CO). For both sets of mortars, a 1:3 binder-to-aggregate
ivine aggregate in the stabilization of soils. The study ratio is adopted with 0.65 (lime) and 0.45 (cement) as the
concluded that an addition of olivine aggregates im- binder-to-water ratios. Initially, one part of binder
proved the unconfined soil strength by 120 % when com- (lime/cement) and three parts of aggregate (fine aggre-
pared with the reference one. They also stated that the gate/olivine aggregate) are weighed separately and
precipitation of magnesite was found, which could be the mixed thoroughly to attain a uniform state. The grinding
reason behind the improved strength. Westgate et al.11 of two sets of mortars are done in a separate paddle
discussed the role of olivine aggregate in lime mortars. mixer. Many researchers have discussed the chemical in-
The research confirmed that fine-sized olivine aggregates compatibility of lime and cement mortars. Hence, while
underwent dissolution in the lime alkaline environment mixing the mortars, proper care should be taken to avoid
and stable magnesium carbonate precipitated in compari- intermixing. After preparing the mortars as per IS 6932
son to references mortars. The authors also explained (Part VII): 197314 (Hydraulic lime) and IS 2550 : 198115
that the added olivine aggregate plays a dual role, replac- (Cement mortars), the mortar mix is shifted into moulds
ing fine aggregates and helping the sequestration of car- with a size of 50 mm × 50 mm in three layers with
bon dioxide from the atmosphere. Thus, in the current proper compaction to ensure the voids are reduced. Ce-
study the authors attempted to examine the carbon-cap- ment mortar is demoulded after 24 h and kept at a tem-
ture ability of both lime and cement mortar with olive perature of 27 ± 2 °C and 75 % relative humidity and
aggregates. Analytical techniques like XRD and TGA lime mortar is demoulded after 3 d and cured at the same
were conducted to identify the hydrated phases devel- conditions.
oped in the mortars.
2.4 Analytical techniques
2 EXPERIMENTAL PART After the curing period, the core portion of the cube
2.1 Binder is crushed thoroughly and passed through a 45 micron
sieve. The sieved (passed) material is examined with an-
Natural hydraulic lime and cement are chosen as alytical tests, X-ray diffraction (XRD) and TGA (thermal
binders for the proposed study. Both binders are pro- gravimetric analysis). The XRD of the samples is carried
cured from commercial suppliers from Vellore, India. out using BRUKER D8 Advance (Germany) with Cu Ka
Hydraulic lime conforms to class A according to IS 712: radiation (0.15406 nm), a Lynxeye detector (silicon-strip
1984;12 the chemical composition is presented in Ta- detector technology), and a Ni filter, detecting the crys-
ble 1. The lime exhibits nearly 24 % of clay impurities, talline phases present in the mortars. TGA is conducted
hence it is categorised as eminently hydraulic in nature. to identify the weight loss of various hydrated phases de-
Ordinary Portland cement (OPC) of grade 53 is used. veloped in both lime and cement mortars.16

136 Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140

 S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...

3 RESULTS 3.2 XRD analysis

Figures 2a and 2b depict the XRD patterns for LS
3.1 XRD of aggregates (lime + sand), LO (lime + olivine), CS (cement + sand)
and CO (cement + olivine) mortars for 28 d. The exami-
The crystalline phases of fine aggregate and olivine nation was initiated by comparing the crystalline phases
sand are compared with the XRD analysis as shown in of reference lime mortars with lime/olivine aggregate
Figures 1a and 1b. The majority of the peaks observed mortar. The significant peaks recognized in reference
in fine aggregate indicate quartz followed by feldspar mortars (Figure 2a) are calcite, portlandite, quartz, and
and zirconium. Quartz is a highly stable compound and it traces of tobermorite and gismondine. The dominant cal-
acts as an inert material in lime and cement mortars. On cite peaks are due to the conversion of portlandite to cal-
other hand, olivine is a natural mineral with variable cite through the process called carbonation. In general,
quantities of magnesium to iron, combined with silicates. carbonation is a natural phenomenon, in which atmo-
XRD interpolation confirms that the selected olivine ag- spheric CO2 reacts with calcium hydroxide in the pres-
gregate is a magnesium-rich forsterite mineral. Fasih- ence of pore water to from a stable compound, calcium
nikoutalab et al.17 discussed the dissolution mechanism carbonate. Cultrone et al.18 stated that carbonation is a
of olivine mineral in an aqueous solution. These authors slow process, prolonged from months to years. Hence,
also stated that olivine is a good candidate for CO2 se- the presence of portlandite could be the reason behind it.
questration because it originates from basalt rocks and it The traces of tobermorite and gismondine are also identi-
is a neosilicate mineral. The mechanism involves the dis- fied due to the presence of clay impurities in the binder.
solution of atmospheric CO2 in pore water and the for- In case of the LO mortar, Figure 2a depicts the majority
mation of carbonic acid, which keeps the pH at around of calcite peaks, followed by aragonite, magnesite, dolo-
5.7 and stimulates the dissolution of olivine aggregate so mite, tobermorite, gismondine and brucite. As discussed
that finally magnesium-bearing compounds are formed. before, the ground form of forsterite aggregate undergoes
The prime factors that affect the dissolution of olivine dissolution in water and converts into Mg and Si ions.
aggregate are pH, CO2 concentration, temperature and The magnesium ions interact with atmospheric CO2 and
grain size. The dissolution mechanisms of olivine aggre- form magnesite and dolomite. Magnesium ions can act
gates in the aqueous state are included in Equations (1), as catalysts for the precipitate aragonite phase in the lime
(2) and (3). mortars.19
Now the discussion will focus on the cement refer-
CO 2 + H 2 O ←⎯ ⎯⎯→ HCO −3 +
dissolution
ence mortar and cement/olivine mortar. For the reference
(1)
+H + ←⎯ ⎯⎯⎯⎯ ⎯→ CO −32 + H +2
formation of carbonites
mortar (Figure 2b), the major peaks observed indicate
quartz, calcite, ettringite, aragonite and portlandite. The
Mg 2 SiO 4 + 4H + ←⎯ ⎯⎯⎯⎯ ⎯→ occurrence of calcite is due to the presence of free
dissolution of forsterite (2) portlandite, which occurred during the hydration of ce-
2Mg 2 + + H 4 SiHO 4 ment. Tobermorite peaks are observed due to the interac-
tion of alite and belite with water. In comparison with
Mg 2 + + CO −2
3 ←⎯ ⎯⎯→ MgCO 3
carbonation
(3) reference mortars, cement/olivine mortar shows greater

Figure 1: a) sand, b) olivine aggregate

Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140 137

S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...

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

intensive peaks of aragonite, dolomite, calcite and traces 3.3 TGA analysis
of brucite. The reason behind the domination of crystal-
Combined TGA and DTA graphs of lime and cement
line phases compared to amorphous phases could be the
natural carbonation of mortars (CS, CO) (a temperature mortars are depicted in Figures 3a and 3b; the weight
of 28 °C and RH of 65 %). Cizar et al.20 discussed the losses of both mortars are presented in Table 1. In the
competition of hydration and carbonation in hydraulic temperature range below 120 °C, weight losses of
mortars under standard conditions. These authors con- 0.27 % and 0.3 % are observed for lime and olivine mor-
cluded that hydration is followed by a carbonation pro- tars, representing a low level of hygroscopic water.
cess. Based on the above discussion, the final conclusion Weight losses of 4.36 % and 4.44 % (120–420 °C) are
is that lime mortars have a natural CO2 sequestration identified in lime reference and lime/olivine mortars.
ability, but an addition of olivine improves the sequestra- This could be due to the weight loss of the clay impuri-
tion process, which is evident due to the greater intensity ties present in lime, while the slight increase in the
peaks observed in the mortars with added olivine. The weight loss of olivine mortars could be attributed to the
olivine mortars also show the major strength giving com- presence of brucite. In the temperature range of
pounds due to the presence of magnesium ions. 400–600 °C, weight losses of 2.62 % and 2.96 % are ob-
served in LS and LO mortars. The weight loss in both

Figure 3: a) LS – 28, b) LO – 28

138 Materiali in tehnologije / Materials and technology 57 (2023) 2, 135–140

 S. P. SARIDHE et al.: ROLE OF OLIVINE AGGREGATE IN LIME AND CEMENT MORTARS ...

Figure 4: a) CS – 28, b) CO – 28

Table 2: Percentage of weight loss

Description < 120 °C 120–420 °C 400–600 °C 600–800 °C

LS – 28 0.27 4.26 2.62 13.11
LO – 28 0.3 4.34 2.92 15.37
CS – 28 2.14 5.47 4.23 3.27
CO – 28 2.27 5.52 4.61 5.01

mortars is due to the decomposition of uncarbonated olivine-based mortars have a greater ability to capture at-
portlandite present in the samples. In addition, the mospheric CO2.
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 CO2 from the polymorph of calcium 4 CONCLUSIONS
carbonate (aragonite, calcite) in LS mortars.16 The
greater weight losses in LO mortars are due to the forma- An addition of olivine aggregates greatly improves
tion of dolomite along with calcium carbonate poly- the properties of both lime and cement mortars. The
morphs. The XRD results also depict the presence of ad- strength gains in both mortars are due to the formation of
ditional minerals like brucite, magnesite and dolomite in magnesium-bearing compounds magnesite and dolomite,
the lime/olivine mortar. which is confirmed with analytical techniques, XRD and
Significant mass losses of 7.6 (CS) and 7.7 % (CO) TGA. These compounds are formed due to the interac-
are observed in the range of 120–420 °C due to the loss tion of carbonate ions with dissolute magnesium ions in
in the surface water, dehydration of C-S-H and decompo- both mortars. During the process of hardening of olivine
sition of ettringite and brucite (Table 2). The weight mortars (lime, cement), olivine sequesters atmospheric
losses in cement olivine mortars are greater than in lime CO2 and forms a stable compound. Hence, the adoption
mortars due to a greater decomposition of calcium sili- of olivine aggregate in binding mortars is highly advis-
cates and aluminates along with brucite. DSC depicted able as it improves the properties of both mortars and re-
an exothermic reaction in the temperature range of duces the carbon footprint on the environment, acting as
400–600 °C, which can be attributed to the dehydration a carbon capture and sequestration unit.
of portlandite and magnesite. A weight loss of 5.01 % is
found in CO mortars compared to 3.27 % in CS mortars
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