The building was built entirely without steel
reinforcing rods to resist tensile cracking, so necessary in concrete members,
and for this concrete dome with a long span to last centuries. It is the largest dome in Europe with its domes
diameter and height is 43.3 meters’ special concrete was used in construction
of building. The stone in the rotunda is primarily volcanic or shaped concrete,
honeycombed with hidden arches to add strength to the entire structure.
The dome is heavier and thicker at the
bottom than at the top, and the center of the dome has an 8-meter-wide opening
called an oculus. Its structure is further lightened at the top by using more
lightweight volcanic rock in the concrete aggregate, with heavier granite-based
concrete aggregate used toward the dome's base. Arches are used throughout the
structure to add strength without adding too much weight to the foundation.
The 8.3-meter oculus forms a structural balance with the surrounding
circumference, which helps both to enter the light inside and to carry the
weight of the dome. Pantheon is carried in pink-gray color with 16 original granite
columns. Interior spaces were covered with red, yellow color antique marble and
other marbles. The insertion of a large round room attached to the portico of a
classical temple is an innovation in Roman architecture. The model circular
space covered by a vault had already been used in large thermal rooms, but it
was a novelty to a temple.
References:
https://www.reference.com/art-literature/materials-were-used-build-pantheon-f7469fcedaed2f5d#
