Yes, pH of slurries is done. If you are just using the pH for process control,
you can do a dilution (say 10%) and measure the pH of the dilution.
A word of caution. Slurries tend to clog up pH electrodes, which normally
are somewhat porous. So at the very least, you need to clean the electrode often.
Also, you're getting to the pH where alkaline metal error can lead to
problems on some types of pH electrodes.