Bentonite-based LC3 low carbon cement and activation by C-S-H nucleation seeding

Abstract

This study explores the feasibility of using calcined bentonitic clays in LC3-50 binders. Four commercially available bentonite rocks were thermally activated and milled to a Dv,50 of 12 ± 2 μm. Their pozzolanic activities were assessed using the R3 method, yielding total heat released values between 190 and 378 J/g-SCM, exceeding the minimum requirements for supplementary cementitious materials (SCMs). The incorporation of superplasticisers (SP) in bentonitic LC3 mortars was optimized, requiring dosages between 0.7 and 1.1 wt% (by the weight of binder) to achieve an initial slump of 200 ± 20 mm, with flow maintained for 1 h in three of them. These results dispel concerns regarding the use of SP in LC3 containing calcined bentonites. Early-age hydration reactions were accelerated using C-S-H nucleation seeding technology, which increased bentonite LC3 mortar compressive strength by 50 % at one day. The compressive mechanical strengths at 28 days of the seeded mortars were also enhanced by 15 %. To elucidate the effects of C-S-H nucleation seeding, LC3 pastes were analysed, confirming the occurrence of pozzolanic reactions at one day of hydration. The portlandite contents, determined by Rietveld quantitative phase analysis and thermal analysis, were lower than expected based on the alite hydration degree at the analysed times. Furthermore, the strength enhancing admixture systematically increased the formation of AFm-type phases, such as hemicarboaluminate, and refined the pore microstructure at one day of hydration.