Investigation of C-S-H in ternary cement pastes containing nanosilica and highly-reactive supplementary cementitious materials (SCMs): Microstructure and strength

[Display omitted] •The C-S-H formed in cement pastes with SF or MK in conjunction with NS was characterized.•The SF or MK and NS shows a synergistic effect on the hydration of the cement pastes.•Pastes with NS and SF or MK presented higher content of C-S-H at 91 days.•NS potentiates the incorporation of Al, present in the MK, in the C-S-H structure.•Pastes with SF or MK and NS present the highest compressive strength and pore refinement at 91 days of hydration. This pioneering study reports on the investigation of C-S-H in as-produced ternary cement pastes while highly reactive supplementary cementitious materials, such as silica fume (SF) and metakaolin (MK), and colloidal nanosilica (NS) are included into the mixtures. Several techniques are used to evaluate the microstructure of the pastes containing colloidal NS (3%), SF (10%) and MK (10%): Consistency, compressive strength, thermogravimetric analyses, Fourier transform infrared spectroscopy, scanning electron microscopy (with energy dispersive X-ray spectrometry), 29Si-nuclear magnetic resonance, and mercury intrusion porosimetry. Ternary mixtures containing SF or MK require the highest superplasticizer (SP) consumption of 1.55% and 1.92%, respectively. Impressively, in late stage of aging, i.e 28 and 91 days of hydration, ternary mixtures reach compressive strength respectively above 90 MPa and 100 MPa, meaning an increase of about 30% above of the compressive strength of the reference paste. Moreover, the ternary MK-based paste shows increase C-S-H production, decreasing Ca/Si ratio and superior increasing mean chain length (MCL) of about 11.1 while compared with the MCL of the reference paste (about 4.6). Likewise, the highest relative reduction in mean porous size (56%) and the lowest total porosity (15.06%) is found in the ternary MK-based paste. Indeed, a strong synergistic effect was observed in the ternary mixture containing MK and NS.