What causes early stiffening and what is the difference between false set and flash set?
Early stiffening is a premature loss of workability or plasticity of cement paste, mortar, or concrete. This includes both false and flash set. False set (plaster set) is evidenced by a significant loss of plasticity without the evolution of much heat shortly after mixing. From a placing and handling standpoint, false-set tendencies in cement will cause no difficulty if the concrete is simply mixed for a longer period of time or remixed without additional water before being transported or placed. False set occurs when too much gypsum dehydrates in the cement mill forming too much plaster (some plaster in the cement is desirable). This leads to stiffening due to the rapid reformation of secondary gypsum with interlocking needle-like crystals. Additional mixing without added water breaks up these crystals to restore workability. Ettringite precipitation can also contribute to false set. Flash set (quick set) is evidenced by a rapid and early loss of workability in paste, mortar, or concr
