4 Materials
The main building block of the stupas is the burnt
brick, which has come in different sizes. Parker
[Parker 1909 ] has tabulated the sizes of bricks
used in many stupas. The bricks used in ancient
stupas are much larger than modern bricks, and
need the use of both hands to handle. Bricks of
different sizes have been used for different parts of
the same stupa, larger ones for the basal rings and
the dome, and smaller ones for the spire. Typical
sizes and masses of bricks used in Abayagiri stupa
are given in Table 3. Figure 15. Ground Plan of Abaygiri Stupa
(1-Platform, 2-Sand Terrace)
Location Dimensions
(LxWxT- mm)
Mass
(kg)
Basal rings 320x280x85 12.30
Dome 450x230x80 13.10
Square chamber 250x160x70 5.15
Spire 210x150x55 2.48
Table 3. Details of bricks of Abayagiri stupa
:
Property Value
Compressive strength 8500 kPa
Tensile strength 850 kPa
Young’s modulus 4.5 GPa
Poisson’s ratio 0.25
Specific weight 16.9 kN/m3
Table 4. Mechanical properties of Jetavana bricks
Laboratory tests have shown [Abeyratne 1982,
Ranaweera 2000] that the ancient bricks are more
stronger than modern factory made bricks used in
Sri Lanka, the strength of the former is around 8 -
12 MPa whereas that of the latter is around 4 - 7
MPa. Minerological studies [Siritunga ] have
shown that the ancient bricks from Jetavana have a
sand content of 55- 65% whereas the modern
factory made bricks have a sand content of 35 -
45%, and this may be the reason for the strength
difference. Typical mechanical properties of
Jetavana bricks are given in Table 4.
The mortar used in ancient stupa construction is a
very thin butter clay like a slurry. With this thin
mortar the bricks essentially sit one on top of the
other, the slurry filling the gaps (Fig. 16). This
gives a strong brickwork, unlike the modern
brickwork which uses a thick mortar which can
weaken the brickwork. At the outer surface
brickwork is water proofed using a thick plaster
(Fig. 7, 16). Mahawamsa also describes stringent
quality control of the materials used in ancient
stupas.