Digging in sand is unlikely to generate the really fine particles which cause the damage (smaller than are visible to the naked eye). Generally it’s using power tools (drills, grinders etc) which creates the fine dust. Breathing in cement dust is also a bad idea though.
If you do need a respirator (e.g. for a diy project!) then I recommend the JSP Force 8 half face ones:
Order online at Screwfix.com. Twin cartridge half-mask with Typhoon valve provides superior low breathing resistance. Features a fully adjustable, 4-point cradle suspension harness with quick-release buckles, ensuring an effective fit. Durable thermoplastic rubber for a superior fit to most face...
www.screwfix.com
They’re much more effective than the cheap paper masks. It’s worth being aware that you do need to be clean shaven for them to form a good seal though!
hth.