How soon can I pour grout equipment?

Assuming the concrete is properly cured, grout can be poured after all concrete laitance is removed.

How do I prepare my concrete foundation for grout?

A concrete foundation should be prepared for grout by removing all laitance with a chipping hamper with a chisel bit.

Can I sand blast a foundation to prepare the surface for gout?

It is unacceptable to sand blast a foundation in preparation for grout.  Preparation will need to be done with chipping hammers.  A chipping hammer will properly profile the foundation and remove the laitance layer.