Segregation
Segregation turns up in 2 fields: concrete, asphalt. Here is what it means to the people in each one.
Segregation in concrete
Separation of coarse aggregate from the mortar in fresh concrete, leaving rock-heavy and paste-heavy zones.
Stone and paste stop traveling together when concrete free-falls onto rebar, leaves a chute at a bad angle, is mixed too wet, is overvibrated or is pushed sideways with a vibrator. The result is honeycomb and rock pockets in one spot and weak, shrink-prone paste in another. Drop chutes, sensible slump and placing concrete close to its final position keep it in check.
"Quit dumping it off the end of the chute from six feet up, you're getting segregation all over that footing."
Segregation in asphalt
Separation of coarse and fine aggregate, or of hot and cold mix, that leaves open, low-density spots in the mat.
Non-uniformity in the mat, either gradation segregation, where coarse stone separates from the fines and binder, or thermal segregation, where cold lumps of mix sit next to hot material. It shows as open, rocky patches in a pattern: at the end of each truckload, in a center streak, or along the edges. Segregated areas cannot reach density and ravel early, so crews fight it with proper silo loading, steady augers, MTVs and restraint with the hopper wings.
"Truck-end segregation every load, coarse spots right where the tailgate opens, have the plant drop the load in three piles."