In extremely cold temps, truck-mounted boom pump operators will swing the tip hose over the exhaust tip (pre-DPF emisions trucks) to use the heat from the exhaust to per-warm the pipe.  You have to be able to center the valve or leave the prime port or swing elbow open so the exhaust can flow through freely.  Perhaps you could use the exhaust from the line pump to do the same, but exhaust would exit the tip hose.  I've heard of some guys here mixing up magnesium chloride (It will produce it's own heat, at least initially) to give a bit of an anti-freeze solution in front of the grout.  Be sure to get rid of it all and a bit of the first concrete too, to be safe.  If using an anti-freeze, be sure it is environmentally friendly (RV plumbing antifreeze comes to mind) but be sure it is all clear of the system before placing the concrete too.

Dipstick  I sent you a p.m.

It is all about preheating EVERYTHING!

You could attach a heater (frost fighter) to the input end of the pipeline. Then wait until hot air blows from the discharge end. My guess is that with 60m of pipe (insulated) @ -12c you are probably looking at 45 min. of preheat.

I didn't see any pipe insulation on your boom.That works.

We only had 1/2 degree drop in temp. From hopper to discharge @ -28c I would consider that working we prime with hot water. once you are preheated you could prob. Do it with cold water not that I am willing to try

plenty of hot water and a little extra grout never failed me no matter how many stories i pumped and we never insulated our booms

you could connect your exaustpipe to your boom and so heat up your system