Reporting the ancient green construction technology of limecrete slabs adopted in Udaipur, Rajasthan
Graphical abstract
Introduction
Ancient monuments are an essential part of cultural heritage, and it emphasizes the evidence of architectural and building techniques. The heritage structures comprise of the royal residence, religious worships, community meetings, military objects, etc. Hence it is our responsibility to safeguard the edifice for future generations. The adaptive reuse of these monuments can also be helpful for the economic and socio developments (Nikeghbali and Damavandi, 2018; Foster, 2020). Due to the rapid industrialization and lack of awareness about the ancient monuments, these are disappearing day by day. Hence the restoration of the old edifice is of paramount importance. The ancient monuments mainly compose stone, brick & timber as structural members and lime, clay & gypsum are used as plaster works. Among the binders, lime mortars are predominately used in major historical monuments. The invention of cement had depleted the usage of lime mortars due to the advantages like higher strength and faster setting. In recent years the revival of lime is observed for the restoration of heritage structures due to the adverse effect of cement mortar behaviour on the structural integrity of lime buildings (Van Hees et al., 2004).
On the other hand, the rapid urbanization of the world leads to the drastic change in earth’s climate which is responsible for global warming. The united nations sponsored Intergovernmental panel on climate change (IPCC), has confirmed that the rise in global warming is due to the increase in the atmospheric concentration of CO2, induced by humans (Mehta and Monteiro, 2017). The burning of fossil fuels like coal, oil and natural gas has a major effect on the environment. It is estimated that the emissions of CO2 from fossil fuels have been increasing by 2.7% annually over the past decade and are now 60% above the reference year 1990 levels, confining to Kyoto protocol (Cuéllar-Franca and Azapagic, 2015).
Concrete is the second most-consumed material on earth and it mainly composes cement, aggregates and water (Mindess, 2019). The production of one-ton cement leaves the liberation of an equivalent amount of CO2 into the atmosphere (60% due to calcium carbonate decomposition + 40% burning of fuel) that risks the global environment (Naqi and Jang, 2019). The cement manufacturers around the world are contributing nearly 5–7% of CO2 liberations (Singh and Subramaniam, 2019). Among the developing countries, China and India are in the top list. Due to the serious concerns about global CO2 emissions, researchers are looking for innovative ways to capture CO2. The CO2 sequestration is one of the trending research topics among the research communities across the world. It involves either the storing of atmospheric CO2 or converting into stable minerals. Among the techniques, carbonation one of the natural ways to convert CO2 into CaCO3/MgCO3 (Westgate et al., 2019).
Lime is one of the predominant binders which has been used in all the ancient structures. The production of lime requires low burning temperatures in the range of 900–1000 °C and it is a less energy-intensive process as compared with cement (1400–1500 °C), and that reduces the CO2 liberation from the burning of fuels, nearly 47–16% (Eriksson, 2015). Another significant benefit of the lime binder is, the hardening occurs through the interaction with atmospheric CO2. Hence, the revisiting of ancient construction techniques could be helpful for the restoration of ancient monuments that can be helpful to extend the service life of the structure, and also able to find the application of ancient construction techniques in the present construction field leads towards sustainability.
The authors have presented the application of lime binders in various ancient structures. Romans have greatly engineered the performance of lime mortars by adding a variety of pozzolanas in lime mortars. Jackson et al. (2017) have discussed the durability of ancient lime concrete near the seashore. She concluded the addition of lime blended with volcanic tuff ash with pyroclastic rocks had initiated the formation of Al-rich tobermorite, and that could be the reason behind the long-term durability. Vola et al. (2011) have investigated the ancient hydraulic concrete from roman piers at Sanra liberate, Italy and breakwater walls at the harbour of Caesarea Palestine, Israel. They found both the collected concrete samples have sanidine and clinopyroxene as pozzolana and calcareous stone with ceramic fragments are used as coarse aggregates. In their examination, they identified the binder matrix consists of amorphous gel-like CASH (Silica-rich).
In most of the Ottoman and Byzantine period, the structures are adopted with brickbats and powder are used as a pozzolan with lime. Pinter et al. (2011) have done the characterisation studies on Roman cement used in Budapest, Hungary. He justified the mortar are durable due to the formation of complex calcium aluminium silicates. Silva et al. (2011) have studied the lime mortars of military harbour walls in Portugal. He concluded the addition of ceramic fragments have initiated the pozzolanic activity and improved the structural durability. Uğurlu and Böke (2009) have stated the interaction mechanisms of brickbats and lime mortars. They characterised the lime mortar samples of Venice. They concluded the grater physio-chemical adhesion mechanism of lime and brick fragments is achieved due to the diffusion of calcium hydroxide into the porous of fragments brickbats and interaction with amphorous silica. Navrátilová and Rovnaníková (2016) discussed the role of brick powder as a pozzolan in lime mortars and stated the presence of brick powder had formed the hydraulic phases that help to improve the mechanical and durability properties of mortars.
Along with mineral admixtures, ancient also added chemical admixtures in the form of a plant, animal extracts. Egyptians have incorporated different natural admixtures like fruit juices, casein, egg whites, etc., (Sickels, 1981). Traditionally, people across the world have been using natural polymers to improve the fresh and hardened properties of lime mortar. Nene (2012) have discussed a variety of plant extracts like beal fruit (Aegle marmelos), black gram, jaggery (Unrefined sugar), tree barks, cotton fibres etc., used in ancient constructions of India.
Chinese have engineered the properties of ancient lime mortars by adding sticky rice, Tung oil, egg white, animal blood, etc., Fang et al. (2015) have done interaction studies on animal blood with quick lime. He concluded the protein structure in blood has controlled the crystal growth and attained compacted structure that could be the reason behind the improved properties like water resistance, compressive strength etc. Peng Zhao et al., 2015 studied the significant role of Tung oil in lime mortars. He discussed the unsaturated fatty acids in Tung oil interacted with lime and acted as a waterproof material. Yang et al., 2010 have addressed the role of sticky rice in ancient lime mortars of Chinese structures. He found the amylopectin in sticky rice have yielded the organic-inorganic composites in lime mortars, and that could be the reason behind the long durability of Chinese structures. Organic Sanhetu Concrete (OSC) is another type of concrete that originated in China. It composes calcium hydroxide, sand and kaolin with organic extracts sticky rice, egg white, blood, brown sugar etc as chemical admixtures. The construction of OSC is adopted in major important structures like bridges, fork houses and dams etc. Min Dai et al. (2019) have characterised the ancient OSC obtained tomb of Qing dynasty belongs to 1644–1911 AD. They found the concrete has performed greater strength and durability properties and also concluded the addition of calcium hydroxide absorbs atmospheric CO2 while hardening and that makes OSC as environment-friendly material.
Many authors have discussed the role of different plant and animal extracts in lime mortars. But only a few authors have stated the usage of fermented plant extracts in the construction of ancient structures. Ravi and Thirumalini (2019) studied the addition of fermented Cissus glauca Roxb in the lime mortar to understand the mechanical and durability properties. He concluded during the fermented process, complex compounds are dividing into simple compounds by liberating CO2, and that could be encouraged the process carbonation in lime mortars. Thirumalini et al. (2018) analysed the effective role of fermented jaggery (Unrefined sugar), kadukkai (Terminalia chebula), kulamavu (Persea macrantha) in lime mortars and achieved the addition of plant extracts leads to the formation of weddellite element in lime mortar, that drastically improved the physical and mechanical properties. Along with fermented plant extracts, ancients also used plant and animal-derived fibres in lime mortars. Plant extracts include hemp, jute, bassage and animal fibres comprises, wool, silk and hairs (Nene, 2012). These type of fibres are readily available and economy. The idea behind their addition is to improve the tensile and flexural strength of lime mortars (Stefanidou et al., 2016). Singh et al. (2015) have found the addition of hemp fibres in 6-11th century AD in lime plaster of Ajanta caves, India. He also stated the addition could be the reason behind the improved tensile strength of base coat, lime mortars.
Hence the present study is focussed on the characterisation of ancient limecrete samples collected from Bichili haveli, Udaipur, Rajasthan, India (Fig. 1 Location of Bichili haveli & Fig. 2 Inside view of Bichili Haveli) constructed by ancestors of the Mehta family located in Udaipur, India. The collected samples are undergone for acid loss analysis to estimate binder to the aggregate ratio and organic tests to find the percentage of biomolecules present in the sample. Analytical techniques like XRF (X-Ray Fluorescence Spectroscopy), XRD (X-ray diffraction), TGA-DTA (Thermo Gravimeter- Derivate of TG (DTG), FESEM (Field Emission Scanning Electron Microscopy), FT-IR (Fourier Transform – Infrared) is also carried out to identify the oxide compositions and mineralogical phases present in the samples. A semi-formal interview was conducted across the vicinity of structure, forgetting the important information about the construction techniques and raw materials used. After concluding the characterisation studies and a brief discussion with local architects, full-scale production of limecrete preparation is presented. At last, the authors are discussed the applications of limecrete usage towards sustainability. The structure of the article as follows, the collection of limecrete samples, semi-formal interviews with local architects, characterization of limecrete, discussion on the production of limecrete and its application.
Section snippets
Haveli background
Haveli is constructed in the 18th century by the ancestors of the Mehta family. The structure composes different building materials ranging from stones, bricks, timber and binding materials like clay and lime. The present investigation is focussed on the characterisation of haveli roof slabs (Fig. 3). These are in solid-state without any visible cracks. The surface is exposed to different environmental actions hence while taking the sample, the top surface is scrapped and the material is
Binder to the aggregate ratio
From the acid loss analysis, the ratio of binder to the aggregate is in the range of 1:1:3 (Binder: Brickbats (Coarse aggregate): sand (Fine aggregate)) as presented in Table 2 and shown in Fig. 5a. The variation in B/A of all the three samples is minimal, and that resembles the ancient production technology of limecrete. The size of brick aggregates is covered from fine to coarse aggregates. Hence the crushed bricks of varying sizes are incorporated in the ancient production of limecrete. It
Conclusions
The characterisation of ancient limecrete samples is undergone to identify the raw materials incorporated and the state of their deterioration. The major outcomes are.
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Calcite is the dominant mineral with other polymorphs of calcium carbonate.
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Quick lime has used a binder, sand as fine aggregate and brickbat as coarse aggregates.
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The binder to aggregate ratio has 1:1:3 (Lime: Coarse aggregate: Fine aggregate).
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The addition of brick powder and bats have originated the pozzolanic activity and
Credit author statement
Sriram Pradeep Saridhe: Investigation, Data acquisition, Writing - original draft, Writing - review & editing. Thirumalini Selvaraj: Project administration, Conceptualization, Investigation, Data curation, Methodology, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors are thankful to restoration works International, USA and Ar. Malvika Mehta for helping in collecting the samples and providing funds for the project.
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