Early hydration and mechanical strength of calcite–ettringite seeds added cement mixture for 3D printing

Cement mixture with calcite-ettringite seeds (CE seeds) was investigated in terms of early hydration and mechanical property. The ettringite crystals of ettringite seeds (E seeds) exhibited needle-like shapes with lengths of approximately 3 μm, and the ettringite crystals of CE seeds exhibited rodlike shapes with lengths less than 1 μm. A dense growth of network-structured ettringite and calcium silicate hydrate (C–S–H) was observed. The amount of cement hydrates was analysed by thermal analysis, and the weight loss of the hydrates was 1.62% (E seeds) and 1.79% (CE seeds) at approximately 104°C, indicating that the amount of hydrates was higher in the mixture with CE seeds. The average pore diameter and porosity of the mixtures decreased from 145 to 79 nm and from 14.88% to 13.89% with the addition of CE seeds. The initial and final setting times of the mixture with CE seeds were 20 and 21 min, which were 4.76% and 8.70% shorter than the setting times of mixture with E seeds. The compressive and flexural strengths of the mixture with CE seeds were 6% and 10% higher than those of the mixture with E seeds, respectively.