For the past 120 years, Portland cement manufacture has
been undertaken on the shores of the Whangarei Harbour in northern New Zealand.
Through a serendipitous conjunction of geo-chemistry, the argillaceous marl
found on Limestone
Island in the harbour and
Tikorangi Hill provides a perfect mix of the various elements required for
strong and durable cement.
Golden Bay
Cement, and its predecessors, have been the guardians and managers of the use of
these minerals. As the demands of the concrete industry have increased, so have
the needs of the manufacturing process. Careful mapping of the resource at both
Portland and
Wilsonville Quarries has been undertaken. This has allowed the Company to change
the Quarry operation from a purely volume basis to one of selection and blending
of constituent minerals.
Within the manufacturing process, change has also been
introduced. Analytical techniques, using x-ray fluorescence spectrometry,
microscopy and the application of modem data collation, has allowed fine tuning
of the process. The Company now produces an increasing diverse range of products
for both the domestic New
Zealand market and exports to various South
Pacific countries.
This paper discusses the processing of limestone and
cement rock' into cement clinker, an intermediate synthetic mineral ground into
cement. It examines control and blending regimes, and some methods used in
determining process efficiency.
An important technique rediscovered' has been the
application of microscopy to clinker. Examination of the major silicate
minerals enables interpretation of the kiln processing and feedback to process
operators. It also enables a prediction of indicated performance when ground
into cement. Examples this paper give an insight into the use of minerals from
Northland in some of the more important construction projects in modem
New
Zealand.