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Processing and Activation of Supplementary Cementitious Materials (SCMs): Cement Replacement Materials and Clay Activation Technology

Supplementary cementitious materials (SCMs) are widely used cement replacement materials that substitute part of the limestone or traditional Portland cement clinker in cement and concrete. Using supplementary cementitious materials (SCMs) is one of the most effective levers for reducing CO₂ emissions because clinker production generates large amounts of CO₂: first from the chemical reaction during limestone calcination, and second from the energy demand of the high‑temperature kiln process. By replacing e.g. a portion of clinker with SCMs, less clinker is required, which directly lowers process‑related CO₂ emissions. In addition, many SCMs are industrial by‑products or locally available mineral resources, which can reduce virgin resource consumption and support circular‑economy principles.

Clinker Substitute Substitute for Portland Cement
Unburnt limestone Puzzolans
Seashells contain large amounts of lime and, once ground, can be used similarly to unburnt limestone. Slags: Waste materials from steel production are recycled. However, these industrial processes are becoming more efficient, reducing the availability of slag.
Fly ash: Due to the decreasing use of coal‑fired power plants, the availability of fly ash is steadily declining. Ash from food waste, such as rice husks, can be used to replace Portland cement.
Calcined clays can be calcined at 800 °C. Although CO₂ is released during calcination - similar to limestone firing - the required temperatures are significantly lower. -
Tailings from mining waste can even increase strength of cement depending on their composition. The advantage lies in resource conservation, as waste is reused, e.g. instead of natural sand.

By replacing clinker or Portland cement, significantly less CO₂ is released. In addition, less fuel is required for heating the rotary kiln.

Homogenization of Slags as Supplementary Cementitious Materials (SCMs)

Reliable laboratory characterization of slag based supplementary cementitious materials (SCMs) starts with consistent sample preparation. Slags are often highly inhomogeneous and may contain metallic residues, which is why magnetic components should first be removed before further processing. For crushing and homogenization, jaw crushers are typically used for pre crushing, followed by ball mills or the Cross Beater Mill SK 300 for fine grinding. When selecting the appropriate jaw crusher, the key factors are initial particle size, sample quantity, and the desired final fineness.

Kruszarki szczękowe

A two step pre crushing approach in the jaw crusher - first using a wide gap and then a narrow gap - is often faster than forcing material directly through a tight gap. Sample pieces up to approximately 20 mm can be efficiently processed in the SK 300, which achieves final fineness levels of about 700 µm and, thanks to its robust design and tungsten carbide baffle plates, is well suited for abrasive materials.

Młyn krzyżakowo bijakowy SK 300

Ball mills are suitable for fine grinding of slag sample pieces up to a maximum of 15 mm. Here again, the choice of mill type and operating parameters depends on initial particle size, sample amount, and target fineness. For small volumes up to 20 ml, the MM 400 is commonly used. For larger batches, the TM 300 can process around 500 g of slag with a particle size of 5 mm to a final fineness of 25 µm within a few hours and, with larger drums, can even handle more than 2 kg of sample.

Młyn bębnowy TM 300

Slag samples

120mm, 30 kg


BB 300

15 minuta | < 3 µm

15 mm, 250 g


PM 100

5 minuta | < 500 µm

15 mm, 200 g


SK 300

20 minuta | < 700 µm

5 mm, 500 g


TM 300

4 Godzin | < 25 µm

Processing Unburnt Limestone, Seashells, and Pozzolans as Cement Replacement Materials

Several mineral cement replacement materials can be processed with standard cement‑lab grinding equipment. Unburnt limestone is ideally processed using jaw crushers followed by ball mills. Seashells also consist mainly of CaCO₃ but are thinner than typical limestone samples and can therefore be efficiently pre‑crushed using cutting mills and finely ground in the Ultra Centrifugal Mill ZM 300; the 6‑disc rotor for cutting mills is suitable for this purpose, and wear‑resistant, tungsten‑carbide‑coated rotors as well as distance sieves can be used in the ZM 300. Softer supplementary cementitious materials e.g. pozzolans or volcanic materials like pumice are likewise processed using rotor mills such as the ZM 300 for volumes up to 5 l or the SR 300 for larger sample quantities. For sieve apertures below 1 mm, cyclones facilitate sample discharge and help prevent dust formation.

Crushing Limestone and ClayMłyn tnący SM 300
Młyn ultra odśrodkowy ZM 300Młyn bijakowy SR 300

Seashells & Puzzolans

50 mm, 100 g


BB 50


1 minuta | < 2 mm

80 mm, 1 kg


Pre-crushing SM 200
Fine-grinding ZM 300

3 minuta | 0,3 µm

5 mm, 200 g


SR 300


45 s | < 500 µm

2 mm, 90 g


ZM 300


2,5 minuta | 0,1 mm

Plant‑Based Supplementary Cementitious Materials (SCMs) and Ash‑Derived Cement Replacement Materials


Ash‑derived plant materials - especially those originating from food‑industry waste such as rice husks - can serve as supplementary cementitious materials (SCMs) and cement replacement materials. They can be homogenized in the same way as slags or limestone. The wear resistant SK 300 is particularly suitable for abrasive samples, while for fine grinding below 500 µm, ball mills (for small to medium sample quantities) or drum mills (for larger quantities) are used. The plant‑based raw materials themselves (e.g., rice husks, sunflower‑seed‑hull pellets, or straw residues) must also be analyzed; cutting mills are used for preliminary size reduction, followed by the ZM 300 or, for larger volumes, the SR 300 for fine grinding. For fibrous samples, cyclones should always be considered, as they cool the material, improve sample discharge, and prevent dust formation; slow, steady feeding or the use of distance sieves also helps reduce heat buildup. The DR 100 feeding system enables easier and more consistent sample introduction. 

Fineness of the particles in the pellets depends on the type of mill used

If the fiber content of the ground sample needs to be reduced, the sieves in cutting mills or the SR 300 can be installed in reverse orientation, or the rotor speed in rotor mills can be reduced. For XRF analysis, very fine grinding - often below 50 µm - is required; whether ball mills or rotor mills are more suitable depends on the downstream analysis, since ball mills provide finer results but take longer and may generate more metal abrasion [3]. If abrasion is not critical, the general rule for reproducible XRF results is: the finer, the better.

Plant samples

Rice husks 8 mm, 200 g


ZM 300

8 minuta | 0,5 mm

Ash from rice husks 15 mm, 450 g


SK 300

2 minuta | 1 mm

Sunflower seed husk pellets 30 mm, 500 g


ZM 300

15 minuta | 0,5 mm

Straw 20 mm, 300 g


SR 300

7 minuta | < 200 µm

Mechanochemistry Meets Cement:
Clay Calcination Alternatives and Activation Technology for Clays

Aktywowane gliny należą do najbardziej obiecujących dodatków mineralnych do cementu (SCM), ponieważ są powszechnie dostępne na całym świecie, mogą być pozyskiwane lokalnie i umożliwiają znaczną redukcję udziału klinkieru. Tradycyjnie reaktywne gliny wytwarza się poprzez kalcynację, jednak aktywacja mechanochemiczna jest rozwijającą się technologią, która w określonych zastosowaniach może stanowić atrakcyjną alternatywę. Aktywacja mechanochemiczna glin — szczególnie z wykorzystaniem młynów kulowych, takich jak PM 100 lub PM 300 — polega na wykorzystaniu energii mechanicznej do modyfikacji struktury krystalicznej, inicjowania amorfizacji oraz zwiększenia reaktywności, co pozwala na wykorzystanie szerokiego zakresu lokalnych typów glin jako materiałów zastępujących cement. Młyny PM 100 i PM 300 są optymalnie przystosowane do realizacji tego procesu w skali laboratoryjnej i półtechnicznej. Badania pokazują, że gliny aktywowane mechanicznie są drobniejsze, mają zmodyfikowaną strukturę oraz wykazują wyższą reaktywność chemiczną niż gliny kalcynowane, szczególnie w przypadku materiałów o wysokiej zawartości miki. Kluczowym elementem kontroli procesu aktywacji jest system GrindControl, który umożliwia ciągły pomiar temperatury i ciśnienia wewnątrz naczynia mielącego, pomaga zapobiegać przegrzewaniu oraz dostarcza istotnych informacji na temat przebiegu reakcji mechanochemicznych. Czujniki są kompatybilne z różnymi pojemnościami naczyń mielących. Podczas aktywacji glin obserwuje się znaczący wzrost temperatury i ciśnienia, co wskazuje na wydzielanie gazów oraz przemiany mineralne; monitorowanie tych parametrów jest kluczowe dla kontroli reaktywności oraz zapewnienia stałej jakości produktu SCM. Uzyskane dane mogą również wspierać wnioskowanie na temat składu glin — na przykład materiały o wyższej zawartości dolomitu generują wyższe ciśnienie w wyniku wydzielania CO₂ [1].

GrindControlMłyn planetarno-kulowy PM 100
Mechanochemia

Reactivity of different clays after thermal and mechanical activation; GrindControl pressure increase reflects dolomite content

A study [2] examines how energy input during mechanochemical activation influences the chemical reactivity of clays, with a focus on planetary ball mills. The planetary ball mill is a preferred laboratory tool because it enables precise adjustment of key parameters such as rotational speed, ball to powder ratio, and milling duration. By analyzing nearly 100 data points, the researchers identified a strong correlation between energy input and resulting clay reactivity. Chemical reactivity increases rapidly with rising energy input up to about 100 kJ/g, while further increases show only minor additional effects. In practical terms, the PM 300 planetary ball mill - operated at high speeds such as 850 rpm - offers significant advantages by maximizing energy input and accelerating the activation process for clay based supplementary cementitious materials (SCMs).

Planetarny młyn kulowy PM 300

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FAQ

What are supplementary cementitious materials (SCMs)?

Supplementary cementitious materials (SCMs) are cement replacement materials that substitute a portion of limestone and/or traditional Portland cement clinker in cement and concrete.

Why do supplementary cementitious materials (SCMs) help reduce CO₂ emissions?

They reduce the amount of clinker required. Clinker production is CO₂‑intensive due to the calcination reaction of limestone and the high energy demand of the kiln process, so replacing clinker with SCMs directly lowers process‑related emissions and can support circular‑economy resource use.

Which materials can be used as SCMs and what affects their availability?

Examples include slags, fly ash, pozzolans/volcanic rocks (e.g., pumice), unburnt limestone, seashells (CaCO₃‑rich), ash from food‑industry waste such as rice husks, calcined clays, and mining tailings. Availability can change with industrial trends - for example, more efficient steel production can reduce slag availability, and reduced coal power generation can limit fly ash supply.

How does clay activation work, and how is it different from clay calcination?

Tradycyjnie reaktywne gliny są wytwarzane poprzez kalcynację w temperaturze 800°C, natomiast aktywacja mechanochemiczna jest technologią zwiększającą reaktywność glin poprzez ich mielenie (np. w planetarnych młynach kulowych PM 100 lub PM 300). Energia mechaniczna modyfikuje strukturę krystaliczną, sprzyja amorfizacji oraz może umożliwić wykorzystanie szerszego zakresu lokalnych glin. Kontrola procesu może być wspierana przez system GrindControl (monitorowanie temperatury i ciśnienia).

References

1] Tole, I., Delogu, F., Qoku, E., Habermehl-Cwirzen, K., & Cwirzen, A. (2022). Enhancement of the pozzolanic activity of natural clays by mechanochemical activation. Construction and Building Materials, 352, 128739.  

[2] Alastair T.M. Marsh, Sreejith Krishnan, Suraj Rahmon, Sisan A. Bernal and Xinyuan Ke; Relationsship between milling input energy and chemical reactivity for mechanochemical activation of clays; Royal Society of Chemistry 2025, DOI: 10.1039/d5mr00088b

[3] Permission for picture usage by Rigaku Europe SE