Because of our screwy laws designed to protect businesses at the expense of the people what you did would be considered stealing. Even if someone is throwing something out in the trash it is their owned trash and you are taking their property. However you did a good deed and you should continue acts like that. Saving stuff from going to landfills where it won't get used again and just rot away is a good thing and we as humans throw away so much useful stuff, it is ridiculous. We have laws that say perfectly good food needs to be thrown away because of an arbitrary date that may not be when the food will actually spoil. It is all ridiculous.

Now probably your average construction worker doesn't give a care about stuff they threw out intentionally but I know some supermarket employees do care for whatever reason and some supermarkets care to the point they use compactors instead of donating the food or leaving it for people to pick. I have gotten almost full boxes of brand new food that maybe had a jar break or they just got too much and couldn't keep it. I literally took at least 50 bottles of extra virgin olive oil from a dumpster once because some bottles had broken and the rest just needed to be rinsed off. I gave some away to charity stuff and friends and still have a bottle around. There were more bottles as well that I didn't take because I just simply didn't have the space in the vehicle. It was good olive oil too not the crap.