Comparative Assessment of Calcined and Mechanically Activated Muscovite Clay as Supplementary Cementitious Material

Abstract

This study evaluates activated a high‐grade muscovite clay as a Supplementary Cementitious Material (SCM). This sample is an archetype to understand the behaviour of muscovite‐containing clays. The high‐grade clay was: (i) thermally activated (CMs) and (ii) mechanochemically activated (MMs). The pozzolanic activity of both activated clays was assessed using R ³ tests (ASTM C1897‐20). MMs showed higher pozzolanic properties than CMs (Heat‐7d: 484 vs. 413 J/gSCM; BW: 10.1 vs. 7.4 g/100g of dried activated clay). LC ³ ‐50 mortars were prepared using CMs and MMs. The sulfate content was optimized to 2 wt% of additional gypsum for both LC ³ binders. Two admixtures were used in pastes and mortars: a PCE‐based superplasticizer (SP) and a C‐S‐H seeding admixture. LC ³ ‐MMs mortar required slightly less SP (0.8 wt%) than LC ³ ‐CMs mortar (0.9 wt%) to achieve the same slump spread (200±20 mm) at w/b = 0.40. At 1 day, both unseeded mortars showed similar compressive strength values of ∼16 MPa. However, the strength increase after seeding was higher for LC ³ ‐MMs, which reached 28 MPa, compared with 22 MPa for LC ³ ‐CMs. In addition, LC ³ ‐MMs mortar developed higher 28‐day strengths, indicating higher pozzolanic activity, in agreement with the R ³ results. The strength enhancing effect of C‐S‐H seeding was also larger for LC ³ ‐MMs mortars.