Displaying items by tag: Limestone calcined clay cement
Natural pozzolan use in the US
03 July 2019Charah Solutions has been steadily building up its fly ash distribution business in recent years with an eye on the supplementary cementitious materials (SCM) market. This week it opened the third of its new series of SCM grinding plants, at Oxnard in California, US. The unit sticks out because it is focusing on grinding natural pozzolans. The plant will receive natural pozzolan by truck and rail and then use Charah’s patented grinding technology to produce pozzolan marketed under its MultiPozz brand. The previous plants in this series mentioned natural pozzolans but this is the first to promote it explicitly.
The change is potentially telling because global demand for granulated blast furnace slag (GBFS) outstrips supply. Both performance benefits and environmental regulations are pushing this. It’s a similar situation for fly ash, also driven by trends to close coal-fired power stations in some countries. As Charles Zeynel of SCM trading firm ZAG International explained in the March 2019 issue of Global Cement Magazine, “...volcanic pozzolans are a potential SCM of the future. This is gaining traction, but it’s slow progress at the moment. This will be the answer for some users in some locations.”
The problem though is that natural pozzolans are down the list of preferred SCMs for their chemical properties after silica fume, GBFS and fly ash. The first is expensive but the latter two were traditionally cheap and easy to obtain if a cement or concrete producer had access to a source or a distribution network. Natural pozzolans are very much subject to variations in availability.
It’s no surprise then that Charah is promoting natural pozzolans in a Californian plant given that state’s environmental stance. It’s unclear where Charah is sourcing their pozzolan from but they are not the only company thinking about this in the US. Sunrise Resources, for example, is working on the environmental permits for a natural pozzolan mine near Tonopah in Nevada. As it described in its company presentation, California and Nevada are the most affected states in the fly ash supply crisis because they are, “...at the end of the line when it comes to rail deliveries from power stations in central and eastern USA.” It also estimated that California used 0.9Mt of pozzolan in its cement production of which about 90% is fly ash. The state produced 9.6Mt in 2015. Other companies are also mining and distributing natural pozzolans in the US as the website for the National Pozzolan Association (NPA) lists. Although, if this line-up is comprehensive, then the field is still fairly select. Most of these companies are based in the west of the country.
One last thing to consider is that various groups are tackling a potential future lack of SCMs for the cement industry by making their own pozzolanic materials through the use of calcined clay. These groups include the Swiss-government backed LC3 project and Cementir’s Futurecem products. Using clay should bypass the supply issues with natural pozzolans but the cost of calcining it requires at the very least an investment to get started.
As concrete enthusiasts often point out, a variant of pozzolanic concrete was used by the Romans to build many of their iconic structures, some of which survive to the present day. To give the last word to the NPA, “What is old is new again: natural pozzolan is back!” If environmental trends continue and steel and coal plants continue to be shut then it might just be right.
Cuba: The University ‘Marta Abreu’ of Las Villas (UCLV) has started operating a 7t/day limestone calcined clay cement plant. The unit will be run by the Geominera del Centro Company, according to the Cuban News Agency. Building materials produced at the plant will be used locally.
Fernando Martirena Hernández, director of the Centre for Research and Development of Structures and Materials (CIDEM), said it was the first plant producing low carbon cement in the world. The project is a collaboration between the university and the Swiss Agency for Development and Cooperation as part of the LC3 project. Similar plants are planned for 18 countries including India, China, Indonesia, Thailand, Guatemala, Mexico, Ecuador, Colombia, Peru, Ivory Coast, Cameroon and Senegal.
New LC3 cement mixture developed
24 September 2014India: Swiss, Indian and Cuban researchers have come together to develop limestone calcined clay cement (LC3), which can help reduce the carbon dioxide emissions of cement by almost 30%.
"The LC3 project is an example of scientific and technical collaboration between Switzerland and India. The innovative cement production process on which these institutions are working is of great economic and environmental significance," said Switzerland Ambassador to India Linus von Castelmur.
The LC3 is a synergetic hydration of clinker, calcined clay and crushed limestone to achieve the performance required from commercial cements, with clinker factors as low as 0.40. It also costs less than traditional types of cement.
"The testing and application phase is over, now it has to pass through standardisation committee before it is accepted by the industries. The research that has been done will not be patent protected but available to everyone," said Castelmur.