Typical of the "white death ".The E coat has became knocked off allowing the exposed aluminum alloy to be subject to "galvanic " reaction .This condition will be more pronounced if the saw is allowed to come in contact with concrete for long periods of time .
One component of Portland cement is blue clay which contains alumina which is close to aluminum in atomic number .Aluminum is classified like zink,a sacrificing metal .It tries to become part of the concrete .