This test method covers determination of the compressive strength of hydraulic cement mortars, using 2-in. or
[50-mm] cube specimens
The mortar used consists of 1 part cement and 2.75 parts
of sand proportioned by mass. Portland or air-entraining
portland cements are mixed at specified water/cement ratios.
Water content for other cements is that sufficient to obtain a
flow of 110 6 5 in 25 drops of the flow table. Two-inch or
[50-mm] test cubes are compacted by tamping in two layers.The cubes are cured one day in the molds and stripped and
immersed in lime water until tested.
Significance and Use
4.1 This test method provides a means of determining the
compressive strength of hydraulic cement and other mortars
and results may be used to determine compliance with specifications. Further, this test method is referenced by numerous
other specifications and test methods. Caution must be exercised in using the results of this test method to predict the
strength of concretes.
Apparatus
Weights and Weighing Devices, shall conform to the
requirements of Specification C1005. The weighing device
shall be evaluated for precision and accuracy at a total load of
2000 g.
Glass Graduates, of suitable capacities (preferably large
enough to measure the mixing water in a single operation) to
deliver the indicated volume at 20°C. The permissible variation
shall be 62 mL. These graduates shall be subdivided to at least
5 mL, except that the graduation lines may be omitted for the
lowest 10 mL for a 250-mL graduate and for the lowest 25 mL
of a 500-mL graduate. The main graduation lines shall be
circles and shall be numbered. The least graduations shall
extend at least one seventh of the way around, and intermediate
graduations shall extend at least one fifth of the way around.
Specimen Molds, for the 2-in. or [50-mm] cube specimens shall be tight fitting. The molds shall have not more than
three cube compartments and shall be separable into not more
than two parts. The parts of the molds when assembled shall be
positively held together. The molds shall be made of hard metal
not attacked by the cement mortar. For new molds the
Rockwell hardness number of the metal shall be not less than
55 HRB. The sides of the molds shall be sufficiently rigid to
prevent spreading or warping. The interior faces of the molds
shall be plane surfaces and shall conform to the tolerances of
Table 1.
Cube molds shall be checked for conformance to the
design and dimensional requirements of this test method at
least every 2½ years.
Mixer, Bowl and Paddle, an electrically driven mechanical mixer of the type equipped with paddle and mixing bowl,
as specified in Practice C305.
5.5 Flow Table and Flow Mold, conforming to the requirements of Specification C230/C230M
Tamper, a nonabsorptive, nonabrasive, nonbrittle material such as a rubber compound having a Shore A durometer
hardness of 80 6 10 or seasoned oak wood rendered nonabsorptive by immersion for 15 min in paraffin at approximately
392°F or [200°C], shall have a cross section of 0.5 (60.06) by
1-in (60.06) [13 (61.6) by 25 (61.6) mm] and a length of 5 to
6 in. or [120 to 150 mm]. The tamping face shall be flat and at
right angles to the length of the tamper.
5.6.1 Tampers shall be checked for conformance to the
design and dimensional requirements of this test method at
least every six months.
Testing Machine, either the hydraulic or the screw type,
with sufficient opening between the upper bearing surface and
the lower bearing surface of the machine to permit the use of
verifying apparatus. The load applied to the test specimen shall
be indicated with an accuracy of 61.0 %. If the load applied by
the compression machine is registered on a dial, the dial shall
be provided with a graduated scale that can be read to at least
the nearest 0.1 % of the full scale load (Note 3). The dial shall
be readable within 1 % of the indicated load at any given load
level within the loading range. In no case shall the loading
range of a dial be considered to include loads below the value
that is 100 times the smallest change of load that can be read
on the scale. The scale shall be provided with a graduation line
equal to zero and so numbered. The dial pointer shall be of
sufficient length to reach the graduation marks; the width of the
end of the pointer shall not exceed the clear distance between
the smallest graduations. Each dial shall be equipped with a
zero adjustment that is easily accessible from the outside of the
dial case, and with a suitable device that at all times until reset,
will indicate to within 1 % accuracy the maximum load applied
to the specimen.
5.9.1 If the testing machine load is indicated in digital form,
the numerical display must be large enough to be easily read.
The numerical increment must be equal to or less than 0.10 %
of the full scale load of a given loading range. In no case shall
the verified loading range include loads less than the minimum
numerical increment multiplied by 100. The accuracy of the
indicated load must be within 1.0 % for any value displayed
within the verified loading range. Provision must be made for
adjusting to indicate true zero at zero load. There shall be
provided a maximum load indicator that at all times until reset
will indicate within 1 % system accuracy the maximum load
applied to the specimen.
5.9.2 Compression machines shall be verified in accordance
with Practices E4 at least annually to determine if indicated
loads, with and without the maximum load indicator (when so
equipped), are accurate to 61.0 %.
The upper bearing assembly shall be a spherically
seated, hardened metal block firmly attached at the center of
the upper head of the machine. The center of the sphere shall
coincide with the surface of the bearing face within a tolerance
of 65 % of the radius of the sphere. Unless otherwise specified
by the manufacturer, the spherical portion of the bearing block
and the seat that holds this portion shall be cleaned and
lubricated with a petroleum type oil such as motor oil at least
every six months. The block shall be closely held in its
spherical seat, but shall be free to tilt in any direction. A
hardened metal bearing block shall be used beneath the
specimen to minimize wear of the lower platen of the machine.
To facilitate accurate centering of the test specimen in the
compression machine, one of the two surfaces of the bearing
blocks shall have a diameter or diagonal of between 2.83 in.
[70.7 mm] (see Note 4) and 2.9 in. [73.7 mm]. When the upper
block bearing surface meets this requirement, the lower block
bearing surface shall be greater than 2.83 in. [70.7 mm]. When
the lower block bearing surface meets this requirement, the
diameter or diagonal of upper block bearing surface shall be
between 2.83 and 31⁄8 in. [70.7 and 79.4 mm]. When the lower
block is the only block with a diameter or diagonal between
2.83 and 2.9 in. [70.7 and 73.7 mm], the lower block shall be
used to center the test specimen. In that case, the lower block
shall be centered with respect to the upper bearing block and
held in position by suitable means. The bearing block surfaces
intended for contact with the specimen shall have a Rockwell
harness number not less than 60 HRC. These surfaces shall not
depart from plane surfaces by more than 0.0005 in. [0.013 mm]
when the blocks are new and shall be maintained within a
permissible variation of 0.001 in. or [0.025 mm].
5.9.3.1 Compression machine bearing blocks shall be
checked for planeness in accordance with this test method at
least annually using a straightedge and feeler stock and shall be
refinished if found to be out of tolerance
