It's a chemical reaction caused by one component of Portland cement .The blue clay slurry contains alumina a couple of valance electrons away from aluminum that causes it, the concrete eating away at anything with aluminum in it .Chainsaws are not the only thing that can get gobbled up because over time it can get window cases , screen doors etc .Stihl for one used E coat to try to prevent this which from my observation has worked .The older saws such as my avatar saw ,a 2100S Homelite do get messed up .Fact on that one I had to repair the front of the oil tank with JB Weld .