ASTM C 109 Compressive Strength of Hydraulic Cement Mortars(5)

P =total maximum load in lbf or [N],and A

=area of loaded surface in 2or [mm 2].

Either 2-in.or [50-mm]cube specimens may be used for the determination of compressive strength,whether inch-pound or SI units are used.However,consistent units for load and area must be used to calculate strength in the units selected.If the cross-sectional area of a specimen varies more than 1.5%from the nominal,use the actual area for the calculation of the compressive strength.The compressive strength of all accept-able test specimens (see Section 12)made from the same sample and tested at the same period shall be averaged and reported to the nearest 10psi [0.1MPa].12.Report

12.1Report the flow to the nearest 1%and the water used to the nearest 0.1%.Average compressive strength of all specimens from the same sample shall be reported to the nearest 10psi [0.1MPa].

13.Faulty Specimens and Retests

13.1In determining the compressive strength,do not con-sider specimens that are manifestly faulty.

13.2The maximum permissible range between specimens from the same mortar batch,at the same test age is 8.7%of the average when three cubes represent a test age and 7.6%when two cubes represent a test age (Note 9).

N OTE 9—The probability of exceeding these ranges is 1in 100when the within-batch coefficient of variation is 2.1%.The 2.1%is an average for laboratories participating in the portland cement and masonry cement reference sample programs of the Cement and Concrete Reference Laboratory.

13.3If the range of three specimens exceeds the maximum in 13.2,discard the result which differs most from the average and check the range of the remaining two specimens.Make a retest of the sample if less than two specimens remain after disgarding faulty specimens or disgarding tests that fail to comply with the maximum permissible range of two speci-mens.

N OTE 10—Reliable strength results depend upon careful observance of all of the specified requirements and procedures.Erratic results at a given test period indicate that some of the requirements and procedures have not been carefully observed;for example,those covering the testing of the specimens as prescribed in 10.6.2and 10.6.3.Improper centering of specimens resulting in oblique fractures or lateral movement of one of the heads of the testing machine during loading will cause lower strength results.

A

These numbers represent,respectively,the (1s %)and (d2s %)limits as described in Practice C 670.