How a portland cement get fast set without loss its strenght?
Your best bet might be to use a different type of cement, for example one with pozzolan or a greater C3A content. Changing the w/c ratio will have a effect on the strength of the concrete, and so you could be getting yourself into a world of trouble. Perhaps if you used a lower w/c ratio and a plasticizer, since obviously if you lower the ratio it will become difficult to work and place around reinforcement. This could be problematic!
