ORIGINAL PAPER
Pozzolanic reactivity and specific surface area of thermally treated clay materials: comparative study of smectite, illite and kaolinite-based compositions
1
AGH University of Krakow, Poland
2
University of Applied Sciences in Tarnow, Poland
Submission date: 2025-11-05
Final revision date: 2026-04-01
Acceptance date: 2026-04-15
Publication date: 2026-09-28
Gospodarka Surowcami Mineralnymi – Mineral Resources Management 2026;42(3):67-84
KEYWORDS
clay-based materialsthermal treatmentpozzolanic activityraw material characterizationsupplementary cementitious materials (SCMs)
TOPICS
ABSTRACT
Ten clay mineral samples from currently exploited deposits in Poland were examined to determine how mineral composition and thermal transformations affect specific surface area and pozzolanic reactivity. The raw materials exhibited wide mineralogical variability, including clays dominated by illite, smectite, kaolinite, and halloysite, along with minor crystalline phases rich in Ca, Fe, Mg, and alkalis. Phase composition and its evolution during firing were determined using X-ray diffraction (XRD), while changes in specific surface area were measured by the Brunauer–Emmett–Teller (BET) method. Pozzolanic activity was assessed through dissolution tests in alkaline solutions. Firing caused dehydroxylation, amorphization, and structural collapse of layered minerals, leading to the formation of highly reactive aluminosilicate phases. The highest reactivity was observed in materials containing kaolinite and smectite. In kaolinite, it resulted from the formation of metakaolinite – a highly reactive pozzolanic phase. In smectite-rich materials, the activity was attributed to dehydroxylation and amorphization of the 2:1 layers and to the presence of amorphous silica (opal-A), which enhances CaO fixation. Additionally, fine particle size increased the specific surface area and accessibility of reactive tetrahedral layers. However, the results showed that surface area alone did not determine reactivity – the key factors were chemical composition and the nature of thermally transformed phases. This study elucidates the interrelations between mineralogy, microstructural evolution, and pozzolanic properties, providing insights for optimizing clay raw materials as sustainable pozzolanic additives and functional components in ceramic and environmental technologies.
FUNDING
Research project supported by the program “Excellence Initiative – Research University” at the AGH University of Krakow, project no. 10388.
CONFLICT OF INTEREST
The Authors have no conflict of interest to declare.
METADATA IN OTHER LANGUAGES:
Polish
Reaktywność pucolanowa i powierzchnia właściwa termicznie obrobionych materiałów ilastych: badanie porównawcze kompozycji na bazie smektytu, illitu i kaolinitu
materiały ilaste, obróbka termiczna, aktywność pucolanowa, charakterystyka surowcowa, uzupełniające materiały cementowe (SCM)
Dziesięć próbek minerałów ilastych z obecnie eksploatowanych złóż w Polsce przebadano w celu określenia, w jaki sposób skład mineralny i przemiany termiczne wpływają na powierzchnię właściwą oraz reaktywność pucolanową. Surowce wykazywały szeroką zmienność mineralogiczną, obejmującą iły z dominacją illitu, smektytu, kaolinitu i haloizytu, a także mniejsze ilości faz krystalicznych bogatych w Ca, Fe, Mg i alkalia. Skład fazowy oraz jego zmiany podczas wypalania określono metodą dyfrakcji rentgenowskiej (XRD), natomiast zmiany powierzchni właściwej oznaczono metodą Brunauera–Emmetta–Tellera (BET). Aktywność pucolanową oceniono za pomocą testów rozpuszczalności w roztworach alkalicznych. Proces wypalania powodował dehydroksylację, amorfizację i załamanie struktury minerałów warstwowych, prowadząc do powstania wysoko reaktywnych faz glinokrzemianowych. Największą reaktywność wykazywały materiały zawierających kaolinit i smektyt. W przypadku kaolinitu wynikała ona z tworzenia metakaolinitu – wysoce reaktywnej fazy pucolanowej. W smektytach natomiast aktywność przypisano dehydroksylacji i amorfizacji warstw 2:1 oraz obecności amorficznej krzemionki (opal-A), sprzyjającej wiązaniu CaO. Dodatkowo drobne uziarnienie zwiększało powierzchnię właściwą i dostępność reaktywnych warstw tetraedrycznych. Wyniki wykazały jednak, że sama powierzchnia właściwa nie decyduje o reaktywności – kluczowe znaczenie mają skład chemiczny i charakter termicznie przekształconych faz. Badanie to wyjaśnia współzależności między mineralogią, ewolucją mikrostrukturalną a właściwościami pucolanowymi, dostarczając wskazówek dotyczących optymalizacji surowców ilastych jako zrównoważonych dodatków pucolanowych oraz funkcjonalnych komponentów w technologiach ceramicznych i środowiskowych.
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