portland cement?

Quoted text begins.The early history of hydraulic limes, natural cements, and their
artificial cement successors could well do with a proper study from a
modern perspective - though anyone who takes it on should take care not to
be chauvinistic! Soon after the time that Smeaton was working in England
(2nd half of 18th C), Vicat (one of Napoleon's engineers) was making
similar studies in France. Vicat's accounts are available in translation
(Nick mentioned the Building Limes Forum Book Sales; look up the limey
publisher Donhead; they produce great facsimiles). The state of the art
in the early 19th C is summarised in Pasley's book - also Donhead.
End of quote.

Aspdin was awarded his patent in 1824 following early trials in Yorkshire
and used the term Portland Cement because he thought that it looked similar
to Portland Stone (ha!). It was indeed a lot paler than the Natural
Cements obtained from burning septaria such as Parker's Roman Cement. But
quality control and standardisation were a great problem in the early
decades. To start with, burning temperatures were too low to produce the
trisilicates that form such an important part of the strength of modern
OPC, and the proportions of clay and limestone (=chalk) that went into the
kiln were very variable. Also the significance of obtaining a clinker (of
the right sort) and then grinding it very fine were not appreciated. But
Aspdin's material was nevertheless promising enough for his son to open a
larger plant for manufacture in East London in order to meet demand that
was hitherto being met by Parker's Cement and Frost's Cement. There were
rumours that ground clinker from blast-furnaces were being added to the mix
(to add iron as in modern cement manufacture) and there were also some
high-profile failures. The improvements that came with correct mixes and
the right temperature to produce the optimum clinkering came from another
firm, Whites (also in southeast London).

Tim

Dr Tim Palmer C.Geol., F.G.S.
Executive Officer, The Palaeontological Association
I.G.E.S., University of Wales
Aberystwyth SY23 3DB
Wales, U.K.

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