Castable additive?

[Josh Bernbaum]

I think I've heard it mentioned here before, but can't find in the search tab, about an additive to mix with castable to help ensure the chemical reaction takes place so it sets up properly. Is there such a product out there? I was just ordering some mortar from Harbison Walker and the guy with whom I spoke hadn't heard of such a thing as that 'additive'. And of course he reminded me that these castables have a limited shelf life. I'm hoping to use some Mizzou that's a little over a year old.