The cause of many trough breakups is not the trough mixture but whether or not the soil mix allows instant drainage without any possibility of pooling. That is what happens in the ground where deeply froze soil thaws near the surface and water pool only to be refrozen. This will happen if you use a regular type soil mix. Just as a regular concrete planter can crack if regular soil is used in it. You must be using and alpine scree type mix which would be no more than 25% organic matter. The through itself needs to be capable of water flowing thru the sides. This also cools the roots in summer. When you have the trough partially cured the surface needs to be brushed or chisled to remove that thin layer of liquid cement that tends to make a seal on all surfaces. This also gives you the antique look right away. When you water, the water should go thru the mix as fast as you pour it on. And you absolutely have to have either chicken wire or preferably poly-mesh reinforcement. You need very large drainage holes like 1" with rubble over it. It needs to not be sitting on the ground because the drainage hole can seal itself up. The cement must not be old also. I have never had any winter damage on a trough in zone 5.