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

• Published in: Construction & building materials 2010-05, Vol.24 (5), p.791-802
• Main Authors: Janotka, I., Puertas, F., Palacios, M., Kuliffayová, M., Varga, C.
• Format: Article
• Language: English
• Subjects: Analysis; Blend; Cement; Cement paste; Construction materials; Evolution; Hydration; Hydration (Chemistry); Mechanical properties; Metakaolin sand; Pastes; Pore structure; Portland cements; Rheology; Sand; Sands; Specific surface; Strength; Yield stress
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2009.10.028

In 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 2 h 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 6 h 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.