Additives and Fillers in Concrete

Fillers and additives are fine-grained materials with a fineness similar to Portland cement.

Pozzolans and blast-furnace slag, used as cementitious additives, improve concrete qualities like workability and density while reducing bleeding and cracking.

Fillers can boost the hydration process of Portland cement by providing nucleation points forming calcium carbonate. These nucleation sites are observed in concrete with fly ash and titanium dioxide particles.

Calcium carbonate merges with the calcium silicate hydrate phase, favorably altering the structure of the cement paste once hydrated.

Fillers may also be derived from natural or processed inorganic substances, and they mainly exert a physical effect, such as hydrated lime or aggregate dust.

Typically, these filler materials serve as workability enhancers in grouts and masonry mortar. Color pigments are also considered inert additions.

When powdered zinc or aluminum is introduced in the presence of calcium hydroxide, it produces hydrogen gas. These materials, known as gas-forming admixtures, create aerated concrete.

Hydrogen peroxide, another example, releases oxygen bubbles retained within the sand-cement mixture to produce aerated concrete.