Aggregate

Aggregate is a medium for mortar and concrete, differentiated into Fine aggregate (-5mm) and coarse (+5mm), Crushed: angular particles from quarry with good bond strength low workability as it requires more water and cement, and uncrushed the opposite.

Aggregate types according to Specific Gravity are Lightweight, Normal weight, Heavyweight aggregate. LW 1200kg/m3 is porous, good thermal insulation produced from kiln and to be used in concrete blocks. Examples are Clay, Shale, and Blast Furnace Slag. NW 2300-2500kg/m3 is needed to be cleaned from impurities but it’s suitable for construction. HW 4000-8500 kg/m3 is low workability usually used as a protection against nuclear reaction.

Aggregate can resist physical (volume change, porosity, permeability, degree of saturation) and chemical attack.

Aggregate expansion is due to alkalis in cement react with Silica (8% cause maximum) in concrete forming Hydrous alkali silica gel that attracts water to form liquid solution (expand).
pH in pore solution must be controlled using fly ash, amount reactive of reactive silica and moisture too. We can test aggregates in 6 months sodium hydroxide solution which reach 0.1% expansion. Alternative way is to use lithium of barium salt to inactivate reaction of expansion.