Abstract
Retaining workability in blended cementitious systems containing calcined clays remains challenging. Here, the influence of calcined clay morphology on both fresh and hardened properties of blended cementitious materials is evaluated through flow and strength testing, comparing the performance of halloysite nanotubes, agglomerated halloysite spherical particles (obtained through spray drying), and conventional metakaolin sheets. In addition, calorimetry and quantification of portlandite content assess the influence of clay morphology on pozzolanic reactivity. All tests were performed at 10 % cement replacement by mass and benchmarked against ordinary portland cement (OPC) and OPC diluted with 10 % quartz. Calcined halloysite spheres were found to increase mortar flow by 30–75 %, produce a similar heat evolution profile, and moderately increase strength (up to 8 %) by 56 days, compared to 100 % OPC. This is achieved without a notable change in pozzolanic reactivity compared to halloysite nanotubes, beyond 7 days. Each of these performance metrics is equivalent to or an improvement over metakaolin sheets, demonstrating that the spherical morphology obtained through spray drying produces a calcined clay with advantages, particularly in workability.
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