That they do, well in block at least, heavies and lights. It is a lot like portland cement, a powder, a little lighter in weight, and grey in color, and is nothing like a cinder. They use a percentage of it in most cement if it's labeled cement rather than portland cement, even Quickcrete, not for weight but for price. It's a byproduct and cheaper, but not quite as strong, unless it's blended correctly. Cinder blocks have black spots where the cinders (charcoal) pieces of the aggregate are exposed. Block are about 80% aggregate, and about 20% cement. When fly ash is used, it's around 25% of the cement, or 5% of the block. Trust me, I got into this trade many years ago working for a mason who's father started and owned Wyoming Block, the biggest block manufacturing and masonry supply in Wyoming back in the day, with block plants in Torrington, Casper, Cheyenne, Riverton, Sheridan, and Rock Springs. My boss at the time even got a special family discount that made it easy for him to win bids. Where I live now, my 20 acres of North Platte River bottom, were once sand pits where the dad harvested sand, before they were reclaimed, and I bought it from him. He was a WWII D-Day vet, and a good friend of mine. I built the house I live in now for and with him -- It's split faced block. He's been gone for years, but old masons like me still joke about his lightweights not being so light. They are supposed to weigh under 27lbs, but his were more like 35, something a guy who handles them all day notices. But sand by the river is cheaper than all the light stuff, so he might of skimped some lol. I know block, but I wouldn't try to teach an old plumber about pipe, or herding turds, no matter what Wiki says.
