Why does concrete made with plain gravel crumble quickly?
Concrete made with plain gravel crumbles quickly because the gravel lacks the ability to cleave, or bond properly, with the cement. Washed sand is needed for a durable mix; without it, even the best cement cannot hold together and soon starts crumbling.
Les explains from his farming experience that before farmers mixed concrete with washed sand, they used any gravel they could get their hands on. If you mix even the best cement with just gravel, it will not last long; it starts crumbling because it lacks the ability to cleave. He uses this as an illustration of the iron and clay toes of the Western Europe consortium of nations. Europe has many nations that have hated each other for centuries, and those deep hatreds mean they cannot bond together any better than plain gravel can bind with cement.