Hydration of blended cement with halloysite calcined clay

A. TIRNONI, F. CRAVERO, A. SCIAN, E.F. IRASSAR

Calcined Clays for Sustainable Concrete

Springer

Año: 2018; p. 455 - 460

The effects of calcined kaolinitic clays as supplementary cementitiousmaterials (SCMs) on the performance of pastes and mortars have been wellstudied. Less attention has been paid to the thermal transformation of halloysitethan that of kaolinite and its possibility to be used as SCMs. Halloysite andkaolinite have identical chemical composition, except that halloysite may havetwo molecules of H2O, as interlayer water. The content of additional water in theinterlayers of halloysite has a decisive influence on the crystal morphology, whichis generally curled rather than platy as in kaolinite. Common forms are elongatedtubes and spheroids. The aim of this investigation is to study the hydration ofblended cements with 25% of different calcined clays to evaluate the influence ofthe content and the morphology of halloysite in the development of the hydratationcompounds, and compressive strength of mortars. Three clays with differenthalloysite/kaolinite content, and different morphology were analyzed. Thehydrated phases present in pastes at 2, 7, and 28 days were identified by X-raydiffraction (XRD), and the content of CH by differential thermal analysis (DTA/TG). The compressive strength of mortars was tested at 2, 7, and 28 days. Thepozzolanic reactivity of the calcined clays was influence by the kaolinite contentand morphology of halloysite in natural clays. This results in different crystallineand amorphous aluminic phases obtained at different ages, and that the ensembleresults differ, this affects the porosity and the compressive strength.1