Industrial Minerals · Buyer's Guide

Calcined Shale: Buyer's Guide to a Natural Pozzolan

Calcined shale is shale heat-treated in a rotary kiln until it becomes a reactive pozzolan. Concrete and cement producers use it to replace part of the cement and improve durability. It is specified as a Class N natural pozzolan under ASTM C618, and as burnt shale in European CEM II/T cements.

Calcined shale at a glance

Item	Typical value
Feed	Quarried shale or slate, crushed to about 38 mm maximum
Calcination	Rotary kiln, about 980–1,090 °C for roughly 45 minutes
Standard (US)	ASTM C618, Class N natural pozzolan
Class N chemistry	SiO₂ + Al₂O₃ + Fe₂O₃ at least 70%; loss on ignition at most 10%
Typical use in concrete	15–35% of the total cementitious material
European cements	CEM II/A-T: 6–20% burnt shale · CEM II/B-T: 21–35% burnt shale

Burnt shale in EN 197-1 refers to shale burnt in a special kiln at about 800 °C; check which material your specification means.

How calcined shale is produced

Shale or slate is quarried, crushed and calcined in a rotary kiln. The heat breaks down the clay minerals into a partly amorphous material that reacts with the calcium hydroxide released as cement hydrates, forming extra binder gel.

Do not confuse it with expanded shale: a lightweight aggregate made by firing shale until it bloats. It is a different product for a different use.

Where calcined shale is used

Concrete durability

As a pozzolan it lowers permeability and improves resistance to alkali-silica reaction, sulfate attack and chloride penetration.

Blended cements

European CEM II/A-T and CEM II/B-T cements blend Portland clinker with burnt shale.

Long-term strength

Pozzolanic reaction continues after the early days, adding strength gain over time.

Lower clinker use

Replacing part of the clinker or cement with a calcined pozzolan reduces the clinker a mix needs.

What to specify in your request for quotation

Standard: ASTM C618 Class N, or the EN 197-1 constituent your cement plant uses
Chemistry: SiO₂ + Al₂O₃ + Fe₂O₃ total and loss on ignition
Fineness: residue on a 45 µm sieve
Strength activity index at 7 and 28 days
Form: ground powder, or calcined granules for grinding at your plant
Quantity, packaging, Incoterm and destination port, plus a certificate of analysis per lot

Customs classification and shipping

Confirm the HS code before you ship. Classification depends on the exact processing and form, so check the tariff line with the HS Code Explorer and your customs broker.
Keep ground material dry and ship it in sealed bags; calcined granules can move in bulk.
Plan loads with the CBM calculator and the container specifications library, and compare FOB and CFR offers with the Incoterms® 2020 guide and the landed cost calculator.

About this guide

This is independent reference information for buyers and specifiers. IMPUTIX is published by Mada Trade Co. in Alexandria; the guide is not an offer to sell this material, and product availability should always be confirmed with your own suppliers.

Shipping a bulk mineral? See export packaging for FIBC bulk bags and export packaging options.

Market context: industrial minerals market research. Other mineral guides: Anhydrite · Metakaolin · Perlite.

Frequently asked questions

What is calcined shale?

Shale heat-treated in a rotary kiln, typically around 980–1,090 °C, so it becomes a reactive pozzolan for concrete and cement.

Which standard covers calcined shale?

ASTM C618 Class N in the US. In Europe, burnt shale is a cement constituent in EN 197-1 CEM II/A-T and CEM II/B-T cements.

How much calcined shale goes into concrete?

Natural pozzolans like calcined shale are typically used at 15–35% of the total cementitious material.

Is calcined shale the same as expanded shale?

No. Expanded shale is fired until it bloats and is sold as a lightweight aggregate; calcined shale is used as a pozzolan.

Sources

Last reviewed: September 2026.