When I was a kid these concrete cubes called ash pits were at the back of every home. Ashes from the coal burning furnaces were dumped into them. That was before my time.
Once gas furnaces were installed, these pits were used for burning rubbish and leaves until it was outlawed. Many people demoed them but there are a few complete ones still standing in Tower Grove South like this on on the 40 block of Potomac.