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Portland-limestone cements (PLCs) are produced at numerous plants across the UK(1). They have strong positive environmental credentials. This cement type accounted for more than 24% of the European cement market (approximately 40 million tonnes) in 2000(2). However, these cements have not been used to any great extent in the UK. The objective of this article is to update an earlier article in CONCRETE, explaining the properties and uses of factory-produced Portland-limestone cements. It is hoped that they will become more widely used as a consequence(3).
What is PLC?
Factory-produced PLC is produced by inter-grinding Portland cement clinker with limestone. They are covered by the cement standard BS EN 197-1: 2000 Composition, specifications and conformity criteria for common cements(4) where they are given the following designations:
* CEM II/A-LL where limestone content is 6-20% of cement mass
* CEM II/B-LL where limestone content is 21-35% of cement mass
* an LL suffix is replaced by L when the limestone has a total organic content (TOC) greater than 0.20%, yet below 0.50% by mass.
The only PLC currently manufactured in the UK is CEM II/A- LL (or A-L), containing between 6% and 20% limestone. It is available in both the 42,5 and 52,5 characteristic cement strength classes. The factory-produced cement conforms to BS EN 197-1: 2000 and is both quality assured and CE-marked(4). Prior to the introduction of BS EN 197-1: 2000, PLC containing up to 20% limestone was covered by BS 7583: 1996 Specification for Portland limestone cement.
It is important to distinguish between true PLC and Portland cement containing a small proportion of limestone as a minor additional constituent (MAC). BS EN 197-1: 2000(4) permits incorporation of 5% MAC by mass in a Portland cement. This may be finely ground limestone. If Portland cement contains limestone MAC, it is still classified as a Portland cement (CEM I in BS EN 197-1: 2000). Codes and Standards across Europe classify the mechanical properties and durability of concrete containing CEMI with a limestone MAC as identical to concrete containing CEM I without a MAC. The two cement types should not be confused. PLC is a unique cement type with different properties to CEM I, specifically manufactured to...