9.1 Data to establish precision statements for various testing
required by this standard were obtained in the Concrete
Proficiency Sample Program of the Cement and Concrete
Reference Laboratory.
9.2 The single-operator standard deviations for slump, unit
weight, air content, and 7-day compressive strength of trial
batches have been found to be 0.7 in., 0.9 lb/ft3, 0.3 %, and 203
psi, respectively; therefore the results of properly conducted
tests on two trial batches made in the same laboratory should
not differ by more than 2.0 in., 2.5 lb/ft3, 0.8 %, and 574 psi,
respectively. This precision statement is considered applicable
to laboratory trial batches proportioned to contain prescribed
quantities of materials and to have a constant water-cement
ratio. The values should be used with caution for air-entrained
concrete, concrete with slump less than 2 in. [50 mm] or over
6 in. [150 mm], or concrete made with other than normal
weight aggregate or aggregate larger than 1 in. [25 mm]
nominal maximum size