Geoscience Reference
In-Depth Information
ASBESTOS CEMENT PRODUCTS
a flintlime brick is illustrated in Figures 249-251 . Both of
these examples are old calcium silicate bricks that are fully
carbonated.
Calcium silicate brickwork is more prone to expansion
and shrinkage than clay brick masonry and in certain
circumstances this may cause significant masonry
cracking. This has caused some to regard calcium silicate
bricks as potentially deleterious and, consequently, there
is often a requirement to identify their presence during
building surveys. This identification is routinely done by
petrographic examination of small lump samples, which
is regarded as the definitive method.
Asbestos cement products are the most common
asbestos-containing materials in use and their
manufacture consumes 70% of world asbestos
production. The range of products includes wall and roof
sheet (corrugated and flat), roof tiles, rainwater goods,
sewerage pipe, and pressure pipe. Asbestos cement
products are manufactured using mechanized processes
with 10-20% asbestos fibre being mixed with Portland
cement slurry. After forming into the desired shape they
are usually steam cured with low pressure steam at 80°C,
249
250
249 General view of flintlime brick showing crushed
flint (white/brown), quartz (white) fine aggregate
(white), lime/calcium silicate hydrate binder (brown).
Some of the flint aggregate particles appear to have
been calcined prior to brick manufacture (mottled
brown); PPT, ×35.
250 Same view as 249 in cross-polarized light
showing crushed flint (grey), quartz (white) fine
aggregate particles, and carbonated lime/calcium
silicate hydrate binder (light brown); XPT, ×35.
251
251 Close view of flintlime brick showing flint (grey)
and quartz (black/grey/white) fine aggregate particles
bound by a matrix of carbonated lime/calcium silicate
hydrate (light brown); XPT, ×150.
 
 
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