SEATTLE — After months on strike, some Seattle-area concrete mixer drivers could return to work this week. But they still have not reached a deal with their employers. Teamsters Local 174 offered to return to work as soon as Tuesday at three of the six Seattle concrete suppliers where workers are on strike. Negotiations would continue. A spokesperson for the concrete suppliers issued a statement saying only that “the Union can return to work at any time and does not require Company approval for this return. The companies remain legally obligated to continue bargaining with the Union for a new …