On large, commercial jobs, they typically take a sample of each batch of concrete and test it. The results take a bit, but it's often better to know before you've completed much more of the structure than at the end. Sometimes, the only way to verify what you have is to take a sample, mold it into a standard block, let it cure, and then test it. Other than that, you're at the mercy of the supplier and the crew, the weather (temperature has a big part in this) and often, the traffic in getting it to you if the truck was delayed, or there was a delay at the job site in getting things poured. We like to think that concrete and mortars are simple mixes, but that's simply not true, then throw in environmental conditions and the time it takes to place the materials, and there are a lot of ways to have a less than ideal result.
All sorts of things are used as the aggregate and fillers in both concrete and mortars...just depends on the characteristics you're looking for, what's available locally (it's expensive to ship concrete so they tend to use what's available locally to the plant), and cheapest for the job at hand. When I was on a tour at Mapei in September, they had samples of 12 different 'sand' sources from around the USA and Canada. They need to make all of their colored grouts look the same, but the color variations in the sand was significant from one source to the other...so, the same named product, built at a regional plant, each needed a different mix of ingredients to make them look and perform the same. Try getting your grout color to be consistent when you have 12 different colored sands to work with at the various plants. The same issue is true with cements and mortars. You buy a bag of X-brand, regardless of where you are, you expect them to function the same...this is not always simple, but one thing a good company has to deal with.
, as some will say . 
