Metakaolin sand–blended-cement pastes: Rheology, hydration process and mechanical properties: Fid-Bau Portal

Metakaolin sand–blended-cement pastes: Rheology, hydration process and mechanical properties

Janotka, I. / Puertas, F. / Palacios, M. / Kuliffayová, M. / Varga, C.

AbstractIn the present work, the use of three Slovak poor metakaolin sands with different metakaolin content (36.0% (MK-1), 31.5 (MK-2) and 40.0% (MK-3)) and specific surface has been deeply studied as mineral addition for Portland cement. The percentage of metakaolin sands in the blended cements was 10%, 20% and 40%.The pozzolanic tests confirm that the three metakaolin sands show a high pozzolanic activity, comparable to a commercial metakaolin and silica fume. With respect to the rheological behaviour, metakaolin sand–blended-cement pastes fit to Herchel–Bulkley model and their yield stress increases as the metakaolin content increases. MK-3 sand with the highest pozzolanic activity and highest specific surface induces the highest increase of the yield stress.From the calorimetric results it is concluded that the addition of MK-1 and MK-2 sands to Portland cement induces a delay up to 2h of the precipitation of the main hydration products in the blended-cement pastes and decreases the maximum heat evolution rate. On the contrary, the incorporation of 40% of MK-3 sand shortens 6h its apparition and increases significantly the maximum heat evolution rate. Additionally, the presence of the metakaolin sands reduces the heat released during the hydration process with respect to non-blended-cement pastes.The incorporation of metakaolin sand induces a decrease of the mechanical strength, being the decrease higher as the metakaolin sand content increases although they also produce a refinement in the pore structure and a decrease of the permeability.