Final answer:
Micro spheres are microscopic, spherical air bubbles intentionally dispersed in concrete or mortar mix by an air-entraining agent. They act as void fillers and improve the workability and durability of the mixture.
Step-by-step explanation:
The microscopic, spherical air bubbles intentionally dispersed in concrete or mortar mix by an air-entraining agent are called micro spheres.
Micro spheres are void fillers that create air voids in the concrete or mortar mix. These air voids help improve the workability, freeze-thaw resistance, and durability of the concrete or mortar.
By incorporating micro spheres, engineers can adjust the air content of the mix and improve the overall performance of the concrete or mortar.