Achieve rapid setting and great early strength of shotcrete by using ettringite carriers to disperse nano-SiO2

The poor dispersion of nano-SiO₂ in shotcrete systems limits its effectiveness and can even lead to detrimental effects. To address this issue, ettringite suspension was introduced as a novel dispersion carrier. Nano-SiO₂ was found to physically adsorb onto ettringite crystals, significantly improving its spatial distribution without organic dispersants. Compared to direct nano-SiO₂ addition, the incorporation of ettringite—especially via premixing—markedly enhanced performance. With premixed nano-SiO₂ and ettringite, and nano-SiO₂ content ranging from 0.25 % to 1 %, the 6-hour compressive strength increased by 93∼600 %, while the initial and final setting times were reduced by 46∼79 % and 47∼91 %, respectively, compared to the control. Isothermal calorimetry, quantitative X-ray diffraction (QXRD), and thermogravimetric analysis (TG) confirmed that the well-dispersed nano-SiO₂ accelerates early cement hydration by providing abundant nucleation sites facilitating rapid formation of hydration products, mainly calcium silicate hydrate (C–S–H). Simultaneously, ettringite acts not only as a dispersant but also strengthens the early-age framework, enhancing load transfer within the shotcrete matrix.