Lehigh
The Texas, US-based building materials manufacturer - a unit of
Lehigh Hanson says that the introduction of portland-limestone cement (PLC) by the industry in the last few years represents a significant step forward, especially when used in conjunction with supplementary cementitious materials (SCM) such as slag cement.
Portland-limestone cements are specially formulated cements that are claimed to provide comparable performance to ordinary portland cements (OPC) while delivering a more environmentally sustainable product. While OPCs may contain up to 5% limestone, PLCs are manufactured with up to 15% micro-sized limestone. By diverting a portion of the limestone past the pyro-processing stage, Lehigh Hanson says that the release of CO2 from both combustion and calcination can be avoided by incorporating it into the cement. It states that, in addition, the inclusion of optimally sized limestone enhances the cement’s properties due to improved particle packing, the creation of nucleation sites enhances hydration, and the formation of carbo-aluminates helps to stabilise and densify the reaction products.
PLCs are accepted in the United States and Canada and have been adopted by CSA A3000 (Cementitious Materials Compendium), CSA A23.1 (Concrete Materials and Methods of Concrete Construction), and the National Building Code of Canada. In the US, the ACI 318-14 building code references ASTM C595 and C1157 and AASHTO M240 specifications for PLCs and concrete made with PLC are similar to those of regular portland cements in that they must both meet the same performance requirements.
Lehigh Hanson says that the use of both PLCs and SCMs results in an enhanced product performance and a significant reduction to greenhouse gas emissions, energy consumption, and quarried material consumption. It adds that concrete finishability and pumpability are generally improved, as are the hardened concrete’s durability and late age strength.
“The sustainability of our products and ability to offer long-term solutions for the construction industry are a significant part of our strategy to meet our responsibilities to the industry and our communities,” said Lino Dinis, sales manager for Lehigh Cement.
In 2018, the Hanson Ready Mix operations in Ontario, Canada were able to run a mix portfolio with approximately 66% PLC, 14% OPC, and 20% slag achieving a claimed more than a 26% reduction in greenhouse gas emissions, or a saving of more than 24,000 tonnes of CO2. With amendments made to CSA mid-2018, Hanson Ready Mix says it has been able to convert entirely to PLC cement and is anticipated to now achieve an approximate 30% reduction in CO2 emissions.
