Twittern

The quantified course of setting of binder pastes and mortars

• 1 Definition of stiffening, setting and hardening...

• 2 Instruments for testing the stiffening and...

• 3 Measuring the course of setting

• 4 Setting of a cement paste (linear diagram left,...

• Haste makes waste

Summary: The terms “stiffening” and “setting” mentioned in the gypsum and cement standards are elaborated and combined into “course of setting”. In general terms the course of setting consists of the sequence of initial stiffening, final stiffening, final setting, 6.5 Newton time and 10 Newton time. Defined resistances to penetration by the standardized Vicat needle can be allocated to these five criteria. These values can also be measured on walls, ceilings and floors on the building site under practical conditions with the easy-to-operate units described here or with a digital dynamometer. This makes it possible to combine previously separate test criteria for the initial development of the microstructure of binder pastes and mortars to form a continuous course of setting that can be proved with measured values and displayed graphically. The particular setting speed can also be calculated in the context of an increase in strength.

After conclusion of the rheological processes in pastes and fresh mortars made of cement and other binders the required transition from the liquid to the solid state always takes place in the three successive phases of stiffening, setting and hardening. The cement handbook [1] cites and updates some fundamental work from 1981 on the “Stiffening and setting of cement and concrete” [2]. There is a standardized test method, the Vicat needle test, for assessing the stiffening and setting of cement. Information about the course of the stiffening and setting with time is...