Work

Long-Term Hydration Study of Blended Cement: Calcined Kaolinite–Illite Composite Clays Compared to Fly Ash

Year: 2025

Type: article

Abstract: Calcined clays are a promising route to lower-carbon binders, but widescale adoption of limestone calcined clay cements (LC3) requires using low-kaolinitic resources due to the limited availability and pricing of high-grade sources. This study evaluates the long-term hydration of two locally available kaolinite–illite composite clays (kaolinite contents 18% and 13%) in binary (30% SCM) and ternary LC3-type (30% SCM + 15% limestone) binders, benchmarked against OPC and fly ash systems. Over 1 year, thermogravimetric analysis showed lower portlandite (CH) and increasing bound water in SCM systems relative to OPC, reflecting ongoing secondary hydration reactions of the SCMs. XRD/Rietveld confirmed formation of hemi- and monocarboaluminate, enhanced in LC3 versus the corresponding binaries. The degree of hydration (DoH) for clay blends exceeded OPC from 7 days onward and reached comparable hydration levels after 1 year, indicating a beneficial later-age contribution from illite. Mortar tests showed that binary clay mixes approximated the 42.5 N class target at 28 days, while all LC3 mixes exhibited lower early strength but additional strength gain from 28 to 90 days. Overall, low-grade kaolinite–illite clays combined with limestone deliver LC3 systems with hydration development and mechanical performance comparable to commonly used fly ash-based cements, supporting their feasibility as regionally sourced, low-carbon binders.

Source: Materials

DOI: 10.3390/ma18225123

Authors: Matea Flegar Pregernik, Marijana Serdar

Institution: University of Zagreb

Language: English

Topic: Concrete and Cement Materials Research

Subfield: Civil and Structural Engineering

Field: Engineering

Domain: Physical Sciences

SDGs: Responsible consumption and production, Climate action

Open Access status: gold

Estimated APC paid: $3,137