Hydration of cubic tricalcium aluminate in the presence of calcined clays

Abstract

Calcium sulfates take an important role in the reaction of pozzolanic materials by forming ettringite with aluminum ions from the pozzolan. 1 Sulfate carriers like gypsum, bassanite, or anhydrite are used to retard the tricalcium aluminate (C 3 A) reaction in ordinary portland cement (OPC). 2 The latter mechanism is used to avoid flash set and to optimize strength development by preventing a superposition of the silicate and aluminate clinker reaction. 3 As calcined clay blended cements 4 or limestone calcined clay cements (LC 3 ) 5 are currently among the most promising solutions to address CO 2 emissions in cement industry 6 , their influence on cement hydration in general and on the aluminate reaction in particular is gaining attention. In calcined clay blended cements, where additional aluminum sources are present, awareness has been raised for extra sulfate demand, as the

Calcined Clays from Nigeria—Properties and Performance of Supplementary Cementitious Materials Suitable for Producing Level 1 Concrete

“…In comparison, no clear aluminate peak could be identified in the metasmectite-rich samples due to the further addition of gypsum, already indicating a too high sulfate dosage for these systems. The lower sulfate requirement for 2:1 compared to 1:1 meta-phyllosilicates is in line with previous studies [ 26 ].…”

“…The great potential of CC is based on physical effects such as the filler effect [ 22 , 23 ] and the adsorption of ions from the pore solution [ 24 ], as well as on the release of silicon and aluminum ions at an early time of hydration [ 15 , 25 ]. This is evidenced by a strong influence of the early clinker hydration in CC blended systems [ 26 , 27 , 28 ]. The released aluminum exploits its full potential, especially in the presence of LP [ 18 , 29 , 30 ].…”

Hydration and mixture design of calcined clay blended cements: review by the RILEM TC 282-CCL

“…Some studies suggest that other surfaces can contribute to the sulphate adsorption process. A recent study [106] reported the faster occurrence of the C 3 A hydration peak in C 3 Agypsum-calcined clay systems. Due to the lack of calcium silicate phases in this system, this cannot be attributed to sulphate uptake from C-S-H, or reaction of calcined clays (due to the lack of portlandite).…”

1:1 or 2:1 ‐ Does it matter for calcined clay as supplementary cementitious material?

“…When comparing 1:1 to 2:1 phyllosilicate dominated clays, the main difference lies in the availability of aluminum. At later hydration ages aluminum-rich clays can lead to higher amounts of AFm phases and the formation of strätlingite [44][45][46] as well as during the first day in systems without silicate clinker reaction [33].…”