Many homeowners don't realize that ordinary Portland cement shrinks when it dries. The shrinkage is very little, however it does shrink. This means that if you patch a crack or a hole, a very tiny leak may form after the cement dries.
Hydraulic cements do the opposite. They expand as they dry. In new construction I use them to fill the void areas in foundations around water pipes, electric wire sleeves, foundation form holes, etc. The stuff works! Often it has a short 'pot' life. This means that you should only mix up enough material that you can comfortably use in 10 to 15 minutes.
There are numerous manufacturers of hydraulic cements. I have listed just a few. If you purchase a brand not listed, be sure the label says that it expands as it dries.
Author's Note: The following email comment was received from Art, a Cement Manufacturer's Representative in Southern California ...
I hope you take this in the spirit in which it is intended and that is to just help your site be better. Your definition of a hydraulic cement is misleading. According to ASTM (American Society for Testing & Materials), a hydraulic cement is a cement that creates a chemical reaction when it comes in contact with water (hydration) and will cure under water.
Being a hydraulic cement in itself has nothing to do with expansion, although some hydraulic cements will shrink less than others, but this is due to them being a sulfoaluminate based cement, not a Portland cement and has nothing to do with them being a hydraulic cement. Being a sulfoaluminate cement is also the reason you have the shortened working times.
Art / Cement Mfg. Rep.