Geoscience Reference
In-Depth Information
Concrete products
6
mould. Lightweight aggregate blocks, manufactured using
clinker aggregate, are used extensively for internal
masonry building partitions. Another form of lightweight
concrete is 'aircrete' which is an aerated cement mortar.
This has been used for semistructural masonry blocks and
floor/roof panels since the 1950s.
Calcium silicate units differ from the other concrete
products, as they do not contain Portland cement.
Instead, they are manufactured from siliceous aggregate
and lime; there is a range of products, the most important
being masonry bricks. Invented and patented in Britain
in 1866, calcium silicate bricks are now used extensively
throughout Europe and are the dominant brick type in
Holland and Germany (Bowley, 1993/4).
Fibre reinforcement is used in some concrete products
to enable the production of building elements of reduced
minimum dimensions and increased flexural and impact
strengths. Asbestos was first used in widely manufactured
concrete products in the late 19th century and, since then,
other fibres made from glass, steel, polymers, carbon, and
vegetable matter have all been utilized.
The principal uses of petrographic examination for
investigations of concrete products are:
• Quality assessment during product development and
manufacture.
• Identifying the type of concrete product in existing
structures.
• Identifying the ingredients used and the
manufacturing process.
• Screening the product for inherent defects including
potentially deleterious ingredients.
• Identifying the presence of hazardous materials such
as asbestos.
• Diagnosing the causes and significance of decay and
deterioration in service.
Concrete products are concrete construction units or
modules that are built into structures after they have
fully hardened. They cover a wide range of products that
are often 'precast' in that they are cast in moulds, usually
in a factory, providing economies of scale and improved
quality control. Concrete products form a significant
portion of the construction materials industry and may
be divided into the following groups:
• Architectural cast stone and other types of
ornamental concrete.
• Load-bearing structural units such as piles, lintels,
beams, railway sleepers, pipes, and water tanks.
• Concrete steps, paving flags, block pavers, and kerbs.
• Concrete blocks and slabs.
• Roofing tiles.
Architectural cast stone is used as a substitute for natural
stone on buildings where cost savings are required. It
comprises concrete units made from ingredients that are
carefully chosen to simulate the appearance of natural
stone. It is rarely seen on buildings dated before 1900
but is now widely used for external masonry in areas
with planning restrictions, which require a stone-like
appearance.
Precast concrete products have been in use since the
mid-19th century and they now comprise a major
proportion of the concrete industry. They include various
load-bearing units which are used either alone to form
concrete structures, or in combination with
in situ
concrete.
Many of these units are prestressed and in some cases the
appearance is of secondary importance. Other precast units
are not load-bearing and these include items which are
required to resist wear by foot and other traffic by having
a strong dense wearing surface. The manufacture of load-
bearing and wear-resistant units is often conducted in
accordance with normal concrete practice. In contrast,
precast concrete units for masonry wall construction are
usually turned out from machines in which a semi-dry mix
is heavily rammed or pressed into a compressible steel
For most concrete products, the petrographic techniques
and examples presented in Chapter 5 (Concrete) will apply
and these should be referred to. To avoid repetition, four
of the more specialized types of concrete product have
been chosen for detailed discussion in the following pages.
