Sorry red-dot, but what a load of pish! Portland based cement products set harder / stronger under water than they do in just the air. Portland cement was invented when they started building the London sewerage works and was used specifically because it set harder and faster under water ie below the water table.
You don't need any additive for concrete for an application like a kennel floor. A plain and simple mix of 5 ballast : 1 cement and adequate water to make it the right consistency will be just fine. I've laid 1000's of metres of concrete and apart from fibres or retarding additives nothing else has ever been added. Make sure the conc is at least 3" thick, don't lay it if the temp is likely to go below 2 degrees C and once it's been set for about 4 weeks paint it with a silicone based patio or brick sealer aka Thompsons water sealer. My current kennel floor has been laid for about 5 years since i moved to this house and it doesn't smell of p*ss and hasn't cracked.
Tom