Stone Flashcards
Natural stone used for building construction falls
within the following general classes
(a) Igneous rocks - these result from a molten
material which subsequently solidified, one of
the most common in this group is granite;
(b) Sedimentary rocks - these result from a breakdown
of igneous rock into small particles by
the changing climatic conditions. The particles
fall into low-lying areas to form layers which
over very many years become hardened by pressure. Among this group is sandstone and
Portland stone;
(c) Metamorphic rocks - these result from
igneous and sedimentary rocks which have
undergone a natural change by pressure or
heat, and in some cases, both. Among this
group is marble.
The types of stone principally employed in building
are
Granite
Sandstone
Limestone
Descibe one reaction of granite in a fire
Igneous
rocks, such as granite, contain free quartz, which
has the peculiar property of expanding very rapidly
at 575°C and completely shattering the rock.
Describe Limestone in a fire
Limestones are composed principally of
calcium carbonate, which decomposes at about
800°C into free lime and carbon dioxide. The
change is gradual with little alteration in volume,
and as heat is absorbed in the process, the interior
of a block of limestone may be protected by the
outer skin. Water used in firefighting will slake
away the quicklime so formed and will cause the
outer skin to fall away.
Describe Sandstone in a fire
Sandstone generally comes between granite and
limestone in fire behaviour and may shrink and
crack in a fire.
Why is stone inferior to brick in a fire situation
Stone is, in general, a good heat insulator, but is
inferior to brick when subjected to continuous
heat, because of its tendency to spall or split into
pieces, especially when water is suddenly applied
What control measure should be adopted if stonework is involved in a fire
Stonework should always be carefully watched for
signs of cracking when it is necessary to work
beneath or near it.
