Geology Reference
In-Depth Information
cation and type of cement
to use. For smaller projects or where the demands are less onerous,
then cost may be the controlling factor; aggregates and quarries have
place-value, which is a matter of the quality of aggregate at a particular
quarry together with the costs of transport to the project site. A useful
review of the factors to be considered in specifying concrete aggregate
is given by Smith & Collis (2001).
programme to optimise the aggregate speci
Armourstone is used to protect structures primarily from wave action
and is often made up of blocks of rock of several tonnes. Generally, the
rock must be durable and massive. If it softens or discontinuities open
up with time, then the function is lost. Massive crystalline limestone
often works well, as do many igneous and metamorphic rocks.
Usually, durability (and availability and cost) is all-important but see
the case history of Carsington Dam in
Chapter 7
where the choice of
limestone as riprap contributed to adverse chemical reactions and
environmental damage. Weak or fractured rocks are obviously not
appropriate. For many coastal defence works in the east of England,
large rock blocks are brought by barge from Scandinavia because of a
lack of suitable local rock. CIRIA (2005) provides useful guidance.
Where suitable rock is not available then concrete tetrapod structures
known as dolosse are used in the same way, piled on top of one another
and interlocked, to protect coasts and structures by dissipating wave
energy.
Aggregate is used in road construction in many different ways
-
as
general
fill or in the sub-base, as drainage material and in the wearing
course. There are many different standard tests to be applied in road
construction, and these are described in Smith & Collis (2001). The
most demanding speci
cation is for wearing course material. Rock must
be strong and durable but also must resist polishing as it is worn by
traf
c. This requires the rock used to comprise a range of different
minerals that are strongly bonded but wear irregularly. Rocks like
limestone are generally unsuitable (the polished stone value, PSV, is
too low). Rocks like Ingleton granite, which is really an arkose, have
excellent properties and therefore very high place values
-
worth
quarrying and transporting large distances
-
even from a National Park.
Dimension stone is quarried to be used directly in building, construc-
tion or even sculptures. Typical rocks quarried in this way include
