What is 'honeycombing' in concrete?

Honeycombing refers to areas of concrete where the mortar has failed to fill the spaces between coarse aggregates, leaving a coarse, stony surface with voids. It usually results from poor compaction/vibration during the pour or leakage of grout through formwork joints. While often cosmetic, deep honeycombing exposes reinforcement to air and moisture, accelerating corrosion. Repair involves cutting back to sound concrete and filling the voids with a flowable, high-strength repair grout.