Admixture

Admixture is used to change composition of the mix proportion when the desired modification properties of fresh or harden concrete cannot be achieved.

Types of admixture are accelerating admixture Ca(Cl)2 mainly for compressive strength at 3 days earlier which is not recommended for hot weather and excessive usage causes corrosion, creep, rapid stiffening and drying shrinkage, Retarding admixture NH4 or zinc mainly for delaying setting and hardening during hot weather, Superplasticizer containing sulfonic acid group to neutralize surface charges on cement mainly to increase compressive strength by increasing dispersion of cement particles reducing viscosity of concrete, Air-Entraining admixture mainly to increase workability, reduce segregation, bleeding, shrinkage and compressive strength, Pozzolans (Mineral admixture) which is non cementitious but replacing cement mainly to increase ultimate strength, workability and lower heat of hydration, permeability, and cost.

Superplasticizer families are SMF: Sulfonated melamine-formaldehyde condensates, SNF: Sulfonated naphthalene-formaldehyde condensates, MLS: Modified lignosulfonates and Polycarboxylate derivatives.

Hydration process and Pozzolanic reaction:
Cement + H2O→ C-S-H gel + Ca(OH)2 , SiO2 + Ca(OH)2 → C-S-H gel

Examples of pozzolans are GGBFS: Ground Granulated Blast Furnace Slag, PFA: Pulverised Fuel Ash, SF: Silica Husk Ash, POFA: Palm Oil Fuel Ash. Among all, Slag is a non metallic product added up to 80% to mixture as it’s cementitious plus pozzolanic
Polyproplene Fiber is added to improve, mix cohesion, freeze-thaw resistance, impact, plastic and explosive resistance.