2. 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 formation
• Weathering issues
• Conservation strategies
• Laterite buildings
3.
4.
5.
6.
7. LATERITE STORY
Of the various soil types that occur in the tropics and sub-tropics,
laterites are
of special interest in conjunction with building construction. These
are highly
weathered soils, which contain large, though extremely variable,
proportions
of iron and aluminium oxides, as well as quartz and other minerals.
They are found abundantly in the tropics and sub-tropics, where they
generally
occur just below the surface of wide grasslands or forest clearings in
regions
with high rainfall. The colours can vary from ochre through red,
brown, violet to
black, depending largely on the concentration of iron oxides
8. • Soft occurrences tend to harden on exposure to air, which is why
blocks have traditionally (eg in India) been cut in situ, allowed to
harden and then used for masonry wall construction (hence the
name was derived from “later”, the latin word for “brick”).
• The darker the laterite, the harder, heavier and more resistant to
moisture it is.
• Some laterites are found to have a pozzolanic reaction when mixed
with lime (which can be explained by the high clay content),
producing hard and durable
building materials (eg stabilized blocks).
9. 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
10. 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
11. 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
12. Significance of Malabar laterite
National Geological Monument at
Angadipuram, Kerala
Definition of Laterite in
Malabar: later-ite meaning
“brick-stone” by Buchanan in
1807
19. 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
20.
21. Decrease in
iron content
with depth
and increase
in silica and
aluminum
(clay) content
was seen in
the profile.
Typical laterite profile: Characteristics
22.
23.
24. 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
25. Group of Umbrella Stones ( kodakkallu), Trichur
(ASI Protected Monuments)
Prehistoric Megaliths ( 2nd Cent B.C-1st Cent A.D.)
26. 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
27. Bekkal Fort – A Tourist Destination
BEKKAL FORT, KERALA, W.India-
(16th Cent. A.D.)
85. 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
86. Weathering Studies
• Field studies- classification of weathering forms
• Laboratory weathering studies
– Slake durability
– Salt crystallisation
– Wetting and drying
• Natural weathering trials
• Weathering process
87. Field Study: Classification of weathering
forms
1
4
2
5 6
3
Granular
disintegration Biodegradation Vegetation growth
Human
intervention
EfflorescenceSalt attack
88. Laboratory weathering studies
Salt crystallisation test (RILEM test No: IV)
Wetting and drying test (ASTM D 5313)
Slake durability test (ASTM D 4644)
90. Salt weathering Mechanism – Schematic model
Phase 1
Leaching
Phase 2
Salt crystallisation
Phase 3
Debonding
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
91. 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)
92. 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