Working as a concrete mason, I found that a well fitting, (but not so tight as to constrict crouching and bending) pair of Levi's under thin cotton coveralls was good for keeping certain cracks and orifices free of the fine sand and cement that can find it's way into everything through the course of a 50,000 square foot pour.
Only downside is that they retain a lot of body heat making one very uncomfortable on a 100 + degree day. However, this attribute of jeans worked well for me on my many treks through the Santa Anna, Rio Hondo, and especially UP the San Gabriel river ways as there is no way to negotiate the San Gabriel in Azusa Canyon without getting wet, but once you are wet, jeans are the next best alternative to wearing a wet suit for insulating and retaining body heat so long as you stay on the move or stay IN the water.
I have to agree with IG on the BDU's, but I would prefer the old thick cotton ones that were standard issue for all troops through (I believe the Viet Nam War) but are now only issued to CRT and BUDS volunteers. The only downside to these is that they are very heavy when wet, but this works as an excellent conditioning tool for the boys. Also staves off hypothermia much longer than the newer BDU's.
You'll probably laugh at this, and i know it sounds ridiculous, but the best all weather work outfit that I put together for large and small concrete pours, form setting, and rod busting, and even extreme treks was something very similar to the traditional desert dress of the Apaches.
However, I put it together with alternative options with my own little twists starting with a pair of cycling shorts (with the suede chamois), a long sleeve cotton pull over (tight fitting) and over these items I wore a Tae Kwon Doe "Do Bok" or Gee, but it was the more expensive thick (almost canvas like) type.
Humor me here guys... Now the top was essentially like wearing a smock, breathed very well in the heat but kept you warm enough in the early morning as long as you were working and not "gold bricking". Plus, one could easily wear their tool belt up high (preferred when wearing sharp trowels on ones back) instead of around the standard pant waist position. This allowed one to use the pant waist belt (usually cotton cloth) for hangin a little stash of almonds or a pack of smokes or whatever. And the wide sleeves worn down over ones rubber gloves provided further protection from the splashing concrete.
In the summer, after we were poured in, if it got too hot, I could easily roll up the sleeves and still have my skin protected from the concrete by my tight cotton long sleeve pull over, or just remove the top of the Gee all together on extremely hot days.
I could take it a step further and pull the pant legs out of my high top Irish Setters (always Red Wing) and simply roll them up when I was ready to go out and start swingin' a trowel and float. And the cool thing about the basic martial arts Gee is that if one has a wife with seamstress skills, it can be modified with your own pockets and loops.
With the wide folded bandana and a jungle hat or hemp knit coolie hat, I looked like a cross between Geronimo, Rai Den (Chinese Deity of lightning), and Luke Skywalker (with the high tops).
One can do it similarly with coveralls but I had a tendency to cook in those as opposed to the two piece "fold over front" Gee.
You certainly couldn't wear this get up to the local market or your kids ball game without a few stares but if your ego doesn't hurt you at work, I highly recommend it.
The only thing I would do different is get the Gee made from canibis hemp as it is significantly stronger, and will last longer than any other fiber available on the market, and it breathes just as well as cotton. Guess I rambled on like always... sorry