Specifying Cement
Sustainability and factory-made cements:
Integration of sustainability into all its operations now sets
the UK cement industry's agenda. The implications for cements are
already clear; their embodied energy and carbon footprint must be
reduced over time but without jeopardising product performance. The
increasing availability of cements such as CEM II types for use in
concrete, mortar and grout plus the continued production of niche
Masonry cements for use only in mortar, will help the industry to
meet its social and environmental obligations and achieve necessary
economic objectives.
Until now, Portland cement CEM I, of strength classes 42,5 or
52,5, has been the 'traditional' cement in the UK. Looked at in
isolation, this may seem to be the least sustainable type of cement
as it has a high proportion of cement clinker, however, when used
as the essential activator of a mineral addition, such as fly ash,
slag or limestone within a mixer combination, its sustainability
credentials are significantly enhanced. Factory-made composite
cements incorporating intrinsically lower proportions of clinker
are now generally available in both bulk supply and packaged in
bags. Use of these non-CEM I factory-made cements should become
more widespread as specifiers become more familiar with their
specification criteria and appropriate usage.
Factory-made composite cements:
Used here, the expression, 'factory-made composite cements'
means any cement that comprises Portland cement clinker combined
(interground or blended) with one or more additional inorganic
constituents plus an optimised amount of set-regulator (gypsum).
The additional constituents are selected from materials such as
power station fly ash, blastfurnace slag and limestone, all already
familiar to UK concrete, mortar and grouting practice. Therefore,
in terms of the British/European standard for common cements, BS EN
197-1, factory-made composite cements, are collectively, types: CEM
II, CEM III, CEM IV and CEM V i.e. any 'non-CEM I' cement specified
in the standard. Such a use of the term aligns with the UK concrete
sector's traditional understanding but is wider than is implied by
the standard itself wherein two particular cements, CEM II/M and
CEM V, include the word 'composite' in their names. In general, the
appropriate use of factory-made composite cements delivers
performance equal to that of concrete containing CEM I cement and
under certain conditions, can improve on the durability performance
achieved. Furthermore, in the case of use in masonry mortars within
the generality of exposure conditions, factory-made composite
cements can achieve the same level of performance on a one-to-one
basis as a CEM I cement within the same traditional volume mix
proportions.
Portland cement cem I:
Formerly known as ordinary Portland cement (OPC), CEM I is
manufactured to conform to British Standard BS EN 197-1. CEM I is
the cement that has been most commonly used throughout the world in
civil engineering and building works. Concretes and mortars made
using CEM I are versatile, durable and forgiving of poor
construction practice. In addition, specific properties can be
enhanced by altering either the cement-making recipe or the size of
the particles and so producing different cements.
Sulfate-resisting cements:
The traditional sulfate-resisting cement used in the UK has been
sulfate-resisting Portland cement (SRPC), conforming to BS 4027.
SRPC is a special type of CEM I cement manufactured to contain a
high content of iron oxide in order to limit the amount of the
mineral phase tricalcium aluminate (C3A) and thereby increase its
sulfate resistance. Additionally, SRPC is normally a low alkali
cement which benefits concrete in resisting the alkali silica
reaction (ASR). However, it is not the only sulfate-resisting
cement available. Various factory-made composite cements are also
sulfate-resisting including the generally available CEM II/B-V type
of Portland-fly ash cement containing at least 25% of fly ash. Such
CEM II/B-V cements are permitted for use in the same wide-range of
sulfate exposure conditions as is SRPC and are also low in reactive
alkalis. Moreover, SRPC is no longer manufactured in the UK and is
becoming more difficult to source. Consequently, sulfate-resisting
composite cements will continue to grow in importance.