Bio-inorganic composites as repair mortar for Heritage structures

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Bio-Inorganic Composites As Repair Mortars For Heritage Structures
Ammini College Of Engineering, Mankara, Palakkad
1. INTRODUCTION
Cement forms an integral part of the modern construction industry for past 100 years.
Though cement mortar offers early strength, faster construction, it has number of
disadvantages such as it is too strong for most of the building, the environmental impacts
during its manufacture, energy consumption during manufacture. Also the long term
durability and serviceability and behavior under seismic forces are under great question.
Traditional structures in India are contemporary of all ages and their synergic aspects can be
adopted by the people of all generation since the fundamental nature of construction is
always flexible and in tune with the rhythmic spatial forms to suit the taste of every
generation. Indian traditional structures built with lime mortar, which are more than 4000
years old like Mohanjedero is still a heritage monument of Indian civilization. It is more
appropriate to blend the traditional concept with modern structures. An increased attention is
paid for the Preservation of Cultural Heritage by National Institutes in the particular
countries, which mostly have the requirement that the materials used have to be identical or
as much as possible similar to the old materials. Hence, the repair of ancient historical
buildings, temples, monuments are of most important. The restoration and renewal of
historical buildings are of paramount importance. These works are generally based on
empirical experience with the traditional background of thousands of years. The major
drawback behind is the use of an unsuitable material and an incorrect method of applications,
having irrational approach. The mortars of historical buildings have been investigated mostly
in connection with a definite building. It is well known that quicklime is the basic binder
used for plasters from the ancient times. The quicklime in plaster reacts with carbon dioxide
to form Calcium Carbonate, which is the binder in lime plasters. Use of herbal extract as
admixture for the lime mortar preparation is introduced during ancient time and all the
monumental structures are built by using herbal extract as one of the major ingredient. Use of
herbal extract as admixture for the preparation of lime mortar produces energetic and good
repair mortar. However, this would be energetic by function, if adequate care is taken during
the preparation. Lime mortar can form a basic platform towards green or sustainable
retrofitting of heritage structures such as Vadakunnathan temple.

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2. VADAKUNNATHAN TEMPLE
The Vadakunnathan temple constructed during the 7th
century has proven its durability over
1300 years. The traditional lime mortar used in the temple is composed of hydrated lime,
sand and water. Besides these basic ingredients, it contains various admixtures which are of
herbal nature to improve their fresh and hardened properties.
Fig.2.1 Vadakunnathan Temple at Thrissur
The drawbacks of using raw lime mortar such as slow setting, low workability and low
compressive strength are counteracted by the addition of organic admixtures, which are
available regionally without causing any environmental effects in the place of chemical
admixtures. During the construction of this temple, different herbs namely Oonjalvalli
(CissusglaucaRoxb), Pananchikaai (Cochlospermumreligiosum), Kulamavu
(Perseamacrantha), Kadukai (Terminaliachebula) and Palm jaggery from Palm tree were
used along with lime as bio-admixtures to improve its functional properties. They are
available in central Kerala and are used as admixtures over centuries for the construction of
heritage structures such as temples and palaces. The whole preparation of herbal lime mortar,
which took 40 days, required skilled traditional craftsmen.

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The scientific assessment of using herbal admixture for the preparation of lime mortar can
form a basic platform towards green or sustainable retrofitting of heritage structures such as
Vadakunnathan temple. HEX-F mix with herbal extract, without control in water to lime
ratio, as followed in traditional practice. Since huge volume of work was involved in
retrofitting of the temple, a separate workshop had to be established and labours had to be
trained to make the special plaster. The consistency of the mortar is decided by the sthapathis
in such a way that the mortar on the back of trowel will not fall from 0.5 m height. No proper
water to lime ratio and the grinding period is maintained for the preparation of the mortar.
The traditional herbal mortar thus prepared at temple site is shown in Fig.
Fig.2.2 Herbal Lime Mortar prepared at the Temple

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3. MATERIALS
The details of the constituent materials used in the present study for preparation of the lime
mortar cubes are described below:
3.1. Lime
Lime is versatile building material used in traditional temples and monuments Lime allows
the building to “breathe”. Water can escape by evaporation, unlike cement where the only
way the water can escape is by being absorbed into the bricks and therefore, risking damp
and erosion of the building substrate. Lime is soft and flexible. It allows the building to move
without cracking and unlike cement it has been stated as “self-healing” because of this
ability. Lime also has considerable economic advantages over Portland cement. The cement
is relatively expensive to produce and critically for developing countries, often requires
expensive imported technologies and fuels. Lime has none of these disadvantages and is
normally considerably cheaper to produce, needs much lower or even negligible capital
inputs to get started, and requires far less imported technology and equipment.
Lime mortar is carbon neutral. Lime mortars are classified as non-hydraulic and hydraulic,
the former is produced by mixing slaked lime with aggregates and harden by evaporation and
carbonation. The later is prepared either by mixing lime with pozzolans containing
amorphous active silicates and aluminates or by developing hydraulic phases through the
calcination of silica rich limestone. High early strength is gained for hydraulic lime mortar
during the hardening process and produces Calcium Silicate Hydrates and Calcium
Aluminate Hydrates. Like cement it gives off carbon dioxide during manufacture. Yet, unlike
cement, lime mortar actually re-absorbs carbon dioxide when it sets. It has many other
benefits, such as:
 Lime mortar is easy to remove from bricks and blocks allowing the reuse of
the bricks.
 During manufacture lime produces 20% less carbon dioxide than cement
production.

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 Lime is essential in the building of any natural house (any house built using
straw bales, timber, earth etc).
 Lime is biodegradable and recyclable.
 Lime is burnt at a lower temperature than cement in the production process
(900°C as opposed to 1300°C), therefore making lime production not only
more eco-friendly but also more economic as well.
Lime stone and shell lime in equal proportion are used as binder, called as lime powder. The
chemical composition of lime powder is determined by using atomic absorption spectroscopy
and results of gravimetric analysis are presented below.
Table3.1.Percentage of various components present in lime samples
Sample CaO MgO SiO2 Al2O3 Fe2O3 LI HI CI
Lime stone 62.10 1.21 14.3 2.14 2.29 14.9 0.5 1.18
Shell lime 66.00 0.543 19.5 0.63 0.27 17.11 0.6 1.60
The quicklime in plaster reacts with carbon dioxide to form calcium carbonate, which is the
binder in lime plasters. The reaction follows the equation
Ca (OH)2 + CO2------ CaCO3 + H2O
3.2. Aggregate
Well graded washed river sand, which is free from organic matters, is used as fine aggregate.
Sand may be categorized as a well graded aggregate with the specific gravity of 2.61 as used
in the traditional lime mortar.
3.3. Herbs
Different herbs, namely Oonjalvalli, Kulamavu, Kadukai, Pananchikaai and Jaggery are used
as source for preparation of herbal extract. All the herbs are polysaccharides in nature and
produce carbon-dioxide on fermentation, which helps in the early carbonation and
accelerated initial setting of the lime mortar leading to the early formation of calcite crystals.

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Oonjavalli, Kulamavu and Kadukai alter the workability of the lime mortar. Pananchikaai,
the cotton fibres imparts gleaming whiteness and texture to the base. Jaggery accelerates the
initial hardening of the mortar and significantly improves the weather resistance by many
folds. Jaggery and kadukai are widely used across the country for weather proof construction.
Fig.3.1 Raw materials used for preparation of herbal extract lime mortar

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4.METHODOLOGY
4.1. Herbal Extract preparation
To understand the different stages in the preparation of herbal extract and about the nature
and preparation of traditional lime mortar used in Vadakunnathan temple, discussions were
held with the sthapathis through Archeological Survey of India, Thrissur circle. The HEX-F
mix proportion is worked out with the help of the sthapathis and the same proportion is used
for HEX-L mix, but with optimized water to lime ratio. The herbal extract is prepared by
taking approximately the particulars given below
Table.4.1 Particulars of herbal extract
Particulars Amount (Kg)
Pananchikaai fruit 7.5
Oonjalvalli stem 2
Kulamavu leaves 0.5
Kadukai 1
Jaggery 3
They are crushed and mixed with 10 litres of water in a separate container and fermented for
a minimum period of 7 days. The prepared herbal extract is used for mortar preparation.
4.2. Mortar preparation
In the traditional lime mortar, HEX-F, one part of binder (lime powder consisting of
lime stone and shell lime) with 3 parts of sand (1:3 ratio by weight) are mixed with herbal
extract arbitrarily, grounded and kept for 15 days at temple site. The consistency of the
mortar is decided by the sthapathis in such a way that the mortar on the back of trowel will
not fall from 0.5 m height. No proper water to lime ratio and the grinding period is
maintained for the preparation of the mortar.
In the laboratory preparation of traditional lime mortar, HEX-L, lime powder passing through
850 μm sieve, is mixed with herbal extract in equal proportion. The contents are mixed with
a stirrer for 5 minutes and left aside for one day. It is then mixed with 3 parts of sand by

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weight and grounded mechanically for a period of 10 minutes in order to have uniform mix
of binder and sand. The mortar as prepared is kept in a container for 24 hours for the process
of fermentation to control the drying shrinkage of the mix. After fermentation period, water
to lime ratio of the mix is adjusted to 0.65 based on workability test by using the flow table
as per IS: 6932 (VIII)-1973, which is calculated according to the number of bumps required
to attain the spread value of 190 mm. In same way, the laboratory made reference mix
(LM–R) is prepared by using lime powder to sand ratio of 1:3 by weight. The results
obtained from the workability test carried out for LM-R and HEX- L are shown in Table 4.2.
It is observed that the water to lime ratio of the LM-R mix can be fixed as 0.7 based on the
workability and the spread ability index. In the case of HEX-L mix, the number of bumps
required to attain the spread value of 190 mm is found to be 2 at water to lime powder ratio
of 0.65. Mixes passing this test is a mandatory requirement for lime mortar as per
IS: 6932(VIII)-1973. Further, in the case of HEX-F mix, over flow or spread has occurred
due to uncontrolled lime powder to water ratio.
Table.4.2 Results of workability (no. of bumps for a spread of 190 mm)
SAMPLES
WATER TO LIME RATIO
0.6 0.65 0.7
LM-R 7 6 5
HEX-F - - -
HEX-L 5 2 2
4.3. Compressive strength
Mortar cubes of size 50 x 50 x 50 mm are cast for LM-R, HEX-F and HEX-L mixes and
demolded after three days and left in atmospheric condition for 28 and 90 days for curing.
The results are shown below,

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Table.4.3 Results of compressive strength
Description 28th
day (N/mm2
) 90th
day (N/mm2
)
LM-R 1.28 1.78
HEX-F 1.56 2.76
HEX-L 2.46 4.52
4.4.Bulk Density and Porosity
The bulk density is defined as the ratio of the mass of the mortar to its bulk volume. It is
calculated as ratio of 28th day weight of the sample to its volume. Porosity is indirect
measure of water absorption and easy measure of carbonation. Porosity is defined as the
fraction of the total volume of a solid that is occupied by pores or empty spaces or voids. The
unit weight and porosity of samples are given below,
Table.4.4 Unit weight and porosity
Description Unit weight (KN/mm2
) Porosity %
LM-R 16.50 15.00
HEX-F 17.50 21.10
HEX-L 20.00 13.40
4.5. Carbonation
On exposure to atmosphere, lime reacts with carbon dioxide (CO2) to form Calcium
Carbonate. This process is known as carbonation and it is responsible for hardening of the
mortar. During carbonation, the change in pore volume takes place due to the attachment of
calcite crystals to the surface of aggregates particles. With the use of Phenolphthalein
(C20H14O4), carbonation can be assessed by pouring dye on the broken surfaces of the mortar
samples, which turns colorless in acidic or neutral solution and pink in basic media. The
colorless region indicates carbonation, while pink region (dark shaded) indicates the
uncarbonation of mortars as shown in Fig.

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HEX-L HEX-F (Exterior)
HEX-F (Interior)
Fig.4.1 Carbonation of lime mortars
4.6. Mineralogical Analysis
XRD is carried out by using Bruker’s D2-PHASER Desktop XRD. The detector used is 1D
LynxEye, with operating voltage of 30 KV, 10 mA and Nickel based filters are used to filter
the monochromatic radiation. The XRD spectra of the raw materials of lime powders i.e.
shell lime and lime stone and the hydration of lime mortars such as LM-R, HEX-F and HEX-
L at 90th day are carried out towards mineralogical analysis.

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4.7.Microstructure Analysis
Microstructure analysis of LM-R, HEX-F and HEX-L mortar is performed by using SEM.
The morphological images of the hydrated phases for these lime mortars are shown below,
Fig.4.2 Gismondine

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5. RESULTS AND DISCUSSIONS
5.1. Compressive Strength Test of Mortar Mixes
From the compressive strength of mortar cubes it can be observed that strength is increased
for HEX–L mix compare to HEX–F and LM–R mixes. The three fold increment of
compressive strength for the mix HEX-L, with respect to LM-R, at 90 days is mainly due the
interaction of the mixes with organic admixtures. In the case of lime mortars prepared by
using the herbal extract, the strength gain is mainly by the formation of Gismodine
(CaAl2Si2O8.4H2O) and Calcium Alumino hydrate (Ca3Al2O6.6H2O). Hence, in the present
study also the same effect is expected for HEX-L mix as it contains herbs as admixture. The
effects of herbal extract on HEX-L mix towards the precipitation of Gismodine and Calcium
Alumino Hydrate during the hydration are assessed through XRD and SEM analysis.
5.2. XRD Analysis
From the analysis of XRD spectra of the all the three mixes, it is confirmed that the highest
strength gain by HEX-L mix at 90 days is due to the formation of Gismondine and Gehlenite,
which are rich in the mixed hydrates of calcium, silica and alumina and is influenced by
polysaccharides. Also the CO2/H2O ratio is controlled in the HEX-L mix, which is proven by
the controlled formation of calcite and CSH.
The reduced compressive strength for the mix HEX-F is due to the absence of the major
strength giving phases such as Gismondine and Gehlenite. The formation of calcite is
because of the uncontrolled CO2/H2O ratio and improper grinding, it affects the CSH
formation due to the disturbance caused to the structurally bounded water.
For LM-R mix, the formation of Gismondine and Gehlenite are not activated during
hydration. This could be due to the absence of polysaccharides, which are hydroxyl and
carboxyl linked organic molecules present in the herbal extract. The hydrates of Calcium
Silicate and Calcium Aluminates modify the microstructure of lime mortar mix such as size,
shape and structure of carbonate crystals and hence increased hydraulic properties, which
ultimately results in enhanced mechanical strength. Moreover, CAH imparts more
compactness and high flexibility to the mix.

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5.3. Porosity Analysis
The order of the porosity of the mixes are found to be as HEX - F> LM-R> HEX- L. The
highest porosity of HEX-F resulted in higher carbonation depth. This greater depth of
carbonation indicates the higher amount of calcite formation as detected by XRD of HEX- F
mix and proves the self healing process. However, the mixes LM-R and HEX-L have shown
a decreased porosity compare to HEX -F. In general, the degree of carbonation is influenced
by the solubility of calcium compounds as the solubility of Ca(OH)2 being about 100 times
higher than that of all three CaCO3 polymorphs. Therefore, self-healing will preferentially
occur in partially carbonated lime mortar, where the uncarbonated part will provide Ca(OH)2
to fill thin cracks thereby enhancing durability. The polymorphs of CaCO3 namely Vaterite,
Aragonite and Calcite are found in XRD pattern. These combinations influence the
dissolution and the subsequent recrystalization process and thereby contribute to the self-
healing nature of mortars.
5.4. SEM Analysis
The SEM images of all the mixes taken at 90 days of hydration are shown in Fig. The SEM
images of LM-R show the denser microstructure with evenly distributed phases. The
morphology of HEX- L refers the presence of compacted and well refined phases in their
microstructure, which indicates the formation of highly ordered minerals during hydration.
This also indicates the formation of calcite crystals of irregular morphology in white layer
heaped on top, which also combines the effect of silica rich fibrous morphology and
texturally the pores in the mortar are irregular in shape. The controlled addition of herbal
extracts reduces the porosity; either the carbonation or the breathability (self-healing) of the
lime mortar is not significantly affected. In the case of HEX -F mix, the anhydrate phases are
detected, which indicate the anhydrate of Larniteas confirmed by XRD. The deposition of
secondary precipitates is noticed, which indicate the highest porosity of the mix. This was
also confirmed by the analysis of porosity and carbonation depth of the mix and supports for
the high open porosity of the HEX-F mix.

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(a)LM-R (b)HEX-L
(c)HEX-F
Fig.5.1 Texture analysis of lime mortar using SEM

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6. CONCLUSION
A detailed scientific assessment has been carried out to gain the full potential of the herbal
extract admixed lime mortars as repair material for the retrofitting of heritage structures such
as Vadakkunnathan temple situated in Kerala. Three types of lime mortars as reference
(without herbal extract), controlled (as per repair material standard) and uncontrolled (field
prepared) addition of herbal extracts, are prepared to assess their performance in terms of
strength. It is concluded that among all the mix HEX-L performed better in all respects as
proven by XRD, SEM and strength analysis.
Compressive strength for the prepared mixes follows the order of HEX-L>HEX-F>LM-R.
The strength of HEX – L mix has improved by 64% and 154% compared to HEX-F and LM-
R mixes. This is due to the addition of optimum water to lime ratio and by adopting proper
grinding technique as per code.
XRD and SEM studies prove the presence of major strength gaining phase Gismondine, one
of the required phase in repair material to satisfy the repair criteria, is formed in HEX -L mix
and their absence is also noticed in HEX-F and LM-R mixes. It can be concluded that the use
of Herbs in lime mortar under controlled condition shows the enhanced properties.

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REFERENCES
1) S. Thirumalini, S. K. Sekar, B. Bhuvaneshwari, and Nagesh R. Iyer (2015), A
study on “Bio-inorganic composites as repair mortar for heritage structures”, Journal
of Structural Engineering Vol. 42.
2) Cristiana Nunes, ZuzanaSlížková, and Dana Křivánková, (2013) A study on
“Lime-based mortars with linseed oil: sodium chloride resistance assessment and
characterization of the degraded material”, An International Journal of Mineralogy,
Crystallography, Geochemistry, Ore Deposits, Petrology, Volcanology And Applied
Topics On Environment, Archeometry And Cultural Heritage.
3) Eunice Salavessa, Said Jalali, Luís M.O. Sousa, Lisete Fernandes, Ana Maria
Duarte (2013),A study on “Historical plasterwork techniques inspire new
formulations”, Construction and Building Materials 48, 858–867.
4) P Thirumalini, Dr S K Sekar (2013), A study on “Review on Herbs used as
Admixture in Lime Mortar used in Ancient Structures”, Indian Journal Of Applied
Research.
5) Athuman M. K. Ngoma (2009), A study on “Characterization and Consolidation of
Historical Lime Mortars in Cultural Heritage Buildings and Associated Structures in
East Africa”.
6) Naji N. Khoury, Musharraf Zaman, and Joakim G. Laguros (2005), A study on
“Use Of XRD Patterns To Evaluate Compressive Strength Of Stabilized
Aggregates”, International Centre for Diffraction Data, Advances in X-ray Analysis,
Volume 47.

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APPENDIX-I
1. Oonjalvalli
Oonjalvalli (CissusglaucaRoxb), they are available in central Kerala and are used as
admixtures over centuries for the construction of heritage structures. It alters the workability
of the lime mortar.
2. Pananchikaai
Pananchikaai (Cochlospermumreligiosum), the cotton fibers imparts gleaming whiteness and
texture to the base. They are available in central Kerala and are used as admixtures over
centuries for the construction of heritage structures.
3. Kulamavu
Kulamavu (Perseamacrantha), which alters the workability of the lime mortar and they are
locally available in central Kerala.
4. Kadukai
Kadukai (Terminaliachebula), which alters the workability of the lime mortar. They are
widely used across the country for weather proof construction. And they are locally available
in central Kerala.
5. Palm jaggery
Palm jaggery from Palm tree was used along with lime as bio-admixtures to improve its
functional properties. They are available in central Kerala and are used as admixtures over
centuries for the construction of heritage structures such as temples and palaces. They are
widely used across the country for weather proof construction. Jaggery accelerates the initial
hardening of the mortar.
6. Gismondine
Gismodine (CaAl2Si2O8.4H2O), which gain the strength of mortar. It is one of the required
phase in repair material to satisfy the repair criteria. They are rich in the hydrates of calcium,
silica and alumina and are influenced by polysaccharides.

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