Seeding of the Hydration with Fine C-S-H particles

The VCCTL can also be used to explore unconventional means of modifying cement hydration kinetics and microstructure development. For example, the use of microfine C-S-H particles to seed the hydration of cement has recently been investigated [15]. Here, a simple comparison can be made between the predicted hydration and strength development of systems with and without the C-S-H seeding. Once again, Cement 135 is used, this time with a w/c of 0.40. The base system is compared to one with an addition of 0.0026 g C-S-H /g cement, a very low addition rate. Specifically, this required the addition of only 1717 one-pixels particles of C-S-H to the starting microstructure when specifying the input for Menu Selection 13, via the entry just beneath the "Inert filler" row in the middle of Figure 16. The phase ID used for C-S-H is 13, as indicated in the table in Figure 11.

Both systems were then hydrated under saturated/sealed conditions at 25 ºC for 1600 cycles (or about 32 d) of hydration using Menu Selection 13. The predicted degrees of hydration and compressive strength developments are shown in Figure 30. Because the C-S-H concentration affects the induction period in the CEMHYD3D model [1], addition of the C-S-H seeds is seen to shorten the induction period and increase the predicted degrees of hydration and compressive strengths at all times. After 4 days, the projected increase in compressive strength due to the C-S-H seeding is on the order of 5 MPa, while after 32 days it has decreased somewhat to about 3 MPa. Particularly, the hydration of the cement's silicate phases are increased by the seeding with microfine C-S-H particles. After 32 d, the degree of hydration of the C₃ S is increased from 0.8876 to 0.9088, while that of the C₂S is increased from 0.6198 to 0.6650. These degrees of hydration of specific phases were easily determined by using Menu Selection 9 to compute the phase counts before and after hydration for each of the two systems. This simulation study is very preliminary in nature, but does suggest that the benefits of increasing silicate hydration by the addition of "seed" C-S-H particles could be significant.

  

Figure 30: Predicted increase in hydration and compressive strength due to "seeding" microstructure with 1 µm C-S-H particles.