kasthurba aia-chicago21 may2014

Laterite Monuments of Malabar region, Western India

Dr Kasthurba A KVisiting Research Fellow, UIC, Chicago, IL

Associate Professor, Department of ArchitectureNational Institute of Technology, Calicut

APT-WGLC lecture21 May 2014, AIA Chicago

Background

The rich Architecture of India is a reflection of geological diversity of the nation. Indigenous architectural styles and construction techniques were evolved utilizing locally available building stones.

Objectives:• Laterite Monuments in W

India• Weathering issues• Conservation strategies

Outline of Presentation

• Laterite- Background• Laterite Monuments in India

– Prehistoric megaliths– Maritime Forts– Religious monuments– Traditional residences– Ancillary structures

• Laterite – Properties and weathering mechanisms

• Conservation Strategies• Summary & Conclusions

World wide distribution of laterite

– Laterite: weathered rock found in tropical and subtropical humid regions of the world.

– Major part of the Indian peninsula, which falls within Koppen’s ‘A’ climate, is subjected to formation of laterite

About laterite…

• Laterite, tropical weathered rock, defined for the first time by Buchanan(1807) as a versatile building material of Malabar region of India

• It is considered as metasomatic rock (different from other type of rocks) altered form of other rock types- igneous, sedimentary or metamorphic

• Laterite is treated as a weak rock for building applications; also as a soil group. Methods of testing-different from other rock types

• Cost effective, energy efficient and environment friendly building material in Malabar region of Kerala

• Good aesthetics, easiness to cut and hardening with age, makes it unique compared to other natural stones

Significance of Malabar laterite

National Geological Monument at Angadipuram, Kerala

Definition of Laterite in Malabar: later-ite meaning “brick-stone” by Buchanan in 1807

Laterite Quarrying

• Quarrying of laterite using rotary saw machine• Standard size specified by IS codes

Laterite Quarrying

Quarrying of laterite using mobile rotary saw machine

Obtaining laterite blocks of standard size from the same strata

Obtaining laterite specimens from quarry

Decrease in iron content with depth and increase in silica and aluminum (clay) content was seen in the profile.

Typical laterite profile: Characteristics

Prehistoric Megaliths( 2nd Cent B.C-1st Cent A.D.)

Pre-historic burial sites-lateritic zones

•Umbrella stones (kudacallu)

•Cap stones (Thoppicallu)

•Hood stones

•Caves ( muniyaras)

•Dolmens and menhirs

Protected monuments –Archaeological survey of India

Group of Umbrella Stones ( kodakkallu), Trichur (ASI Protected Monuments)

Prehistoric Megaliths ( 2nd Cent B.C-1st Cent A.D.)

Prehistoric Megaliths ( 2nd Cent B.C-1st Cent A.D.)

Maritime Forts of Malabar

• Bekkal Fort, Kasarkode (16th Century)

• Tellicherry Fort ( 18th century)

• Fort St. Angelo, Kannur ( 15th Century)

These heritage monuments and natural sites with its environmental settings has been recommended by ASI to include in the World Heritage list of UNESCO

Bekkal Fort – A Tourist Destination

BEKKAL FORT, KERALA, W.India- (16th Cent. A.D.)

Bekkal Fort, W.India

BEKKAL FORT, KERALA

Bekal Fort, Kasarkode

BEKKAL FORT, KERALA

Bastions and Fort walls facing sea

Bekkal Fort, Kasarkode, Kerala

Raised Bastion , Bekkal Fort, Kerala, India

Bekkal Fort, Kasarkode, Kerala

Main entrance from the road

Bekkal Fort, Kasarkode, Kerala

Tellicherry Fort- Entrance Structure

Tellicherry Fort ( British 18th Cent A.D.)

12m High Wall in laterite Tellicherry Fort

Tellicherry Fort, Malabar, India

Tellicherry Fort: Adjoining Areas

The Fort was built by the Portuguese in 1505

Fort St Angelo, Kannur : Main Entrance

View towards the Sea from the Fort- Cannons pointing towards sea

Fort St Angelo, Kannur 15th Century

Fort St Angelo, walls abutting the Arabian sea

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Vaulted Structures in Laterite, Fort St Angelo

Fort St. Angelo- Horse stables within the fort

The Vaulted structure- Horse stables

Fort St Angelo, Kannur

Fort St. Angelo- The Prison cells within the Fort

Thick Fort Walls – Laterite Ashlar Masonry

Fort walls- Laterite Ashlar masonry

Church Within the Fort. St Angelo

Fort St Angelo- Church building within the Fort

Maintenance work by ASI- Fort St. Angelo

Fort St Angelo- Removal of vegetation

Fort St Angelo- Maintenance

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Fort St Angelo, Kannur

After

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Fort St Angelo, Kannur

Fort St Angelo, KannurWeathering of Laterite due to aggressive sea environment

Temples of Malabar

Trikkaikunnu Temple, Kottayam

Siva Temple at Ferooke, Calicut

Siva Temple at Calicut

Wide Projecting Eaves

Granite Door Frames

Granite Plinth Protection

Traditional Conservation Practices

Traditional residences in Malabar, Kerala

Traditional residences in Malabar, Kerala

Ancillary structures –temple entrance

Ancillary structures –temple entrance

Traditional ancillary structures

Bathing ponds attached to temples and residences Temple enclosure wall-(elephant form)

World heritage monuments: Churches and convents of Goa

Church of St. Francis of Asissi, Goa

DETERIORATION TO LATERITE: BASILICA OF BOM JESUS , GOA

Mosque , Goa

Traditional Bungalow, Goa

Bungalows in Goa

Laboratory Studies at IIT Madras-

Preparation of specimens

Engineering properties: compressive strength

Engineering Properties

Density Dry 1.80- 2.78 Saturated 2.36-3.04

Specific gravity - 2.84-3.58 Porosity % 20-40 Water absorption % 10- 18 Compressive strength ( MPa)

Parallel to bedding plane Wet 1.29-4.45 Dry 6.0-9.60

Parallel to bedding plane Wet 1.29- 4.54 Dry 4.41- 8.29

Modulus of Elasticity (Flexure) MPa

Wet 2.09-4.66 Dry 4.41-5.96

Weathering Studies

• Field studies- classification of weathering forms• Laboratory weathering studies

– Slake durability– Salt crystallisation– Wetting and drying

• Natural weathering trials• Weathering process

Field Study: Classification of weathering forms

1

4

2

5 6

3Granular

disintegration Biodegradation Vegetation growth

Human intervention

EfflorescenceSalt attack

Laboratory weathering studies

Salt crystallisation test (RILEM test No: IV)

Wetting and drying test (ASTM D 5313)

Slake durability test (ASTM D 4644)

Laboratory studies

Salt crystallisation test Slake durability test

Salt weathering Mechanism – Schematic model

Phase 1Leaching

Phase 2Salt crystallisation

Phase 3Debonding

Vesicules

Clay filled cavities Salt crystals

Fragments of debonded laterite

Honeycomb

•Field weathering forms matched with the laboratory findings

•Salt crystallisation attack was severe form of decay in laterite

•Salt and moisture were the mechanisms of salt attack

Summary

• Salt attack and biodegradation were the main cause for weathering in laterite (as determined from the field studies on monuments)

• Salt crystallisation test proved that dampness and salt were the agents for the decay mechanism

• Slake durability study established the corrosive action of acidic rains on laterite

• Strong laterite (high compressive strength) offered good resistance to weathering (salt attack and rainwater slaking)

Conclusions

• Laterite is sensitive to attack by salt crystallisation; salts migrate into the structure mainly from the ground

• Deferential weathering of laterite in the same environment suggests need for protection of weak laterite in damp environment

• Laterite with dense iron formation are found more durable and can be used in exposed conditions

• Decline in strength of laterite due to saturation suggests protection from dampness

• Protection from dampness can prevent deterioration to a large extent

THANK YOU