Hello Norew,

Yes, even quarried shales may possess pozzolanic properties if they are of the correct lithological type (eg opaline shales) and are not significantly weathered. However most natural pozzolans need to be heat treated (ie dried or calcined) to enhance their pozzolanic properties.

Even if the shale does not possess any natural pozzolanic properties, it is still okay to use it as a mineral additive, as long the cement performance is acceptable in your marketplace. One thing to note is that cement colour will probably be different (darker) using shale compared to limesone.

 

Regards,

Ted.

What is the common practice in the industry in calcining shale when incorporated in the process line?

Hello Norew,

It depends on the availability of the shale and the cost of calcination.

Calcined shale is best utilised if it is the waste product of another beneficial process, rather than consuming energy just to calcine the shale with no other benefit than that of increasing it's pozzolanic properties.

Where they are locally available, carboniferous shales (e.g. oil shales) are a good example of this. These shales can be burnt to provide heat energy for various applications, and the resulting waste product, calcined shale, can be used in cement. The cement company itself may actually burn the shale or it might be burnt by an independent company. In either case, the resulting calcined shale waste is utilised by the cement plant, in a manner similar to the way electricity generating companies supply flyash to cement producers.

Some oil companies also produce burnt shale as a waste product during the process of extracting and purifying oil from oil shale deposits. Depending on the temperature used in the process, this could also be a rich source of pozzolanic shale for cement  manufacture.

If you have a source of non-carboniferous shale and simply wish to calcine it to produce a pozzolanic shale for use in cement, you would have to evaluate the costs versus the benefits to see if the process is economically viable. e.g. you might have enough spare heat capacity in the kiln to calcine the shale and reduce or eliminate the need for additional fuel for calcination.

 

Regards,

Ted.

 

what is the required temperature for calcining shale?