Humboldt H-2911 — H-2919 Compressometers / Extensometers - Manual (Page 3)

The Concrete Cylinder Compressometer-Extensometer is used to determine the static
modulus of elasticity (Young's Modulus) and Poisson‘s ratio of concrete in compression.
The instrument complies with the specifications of ASTM C469. Using the H-2912,
measurement of axial deformation and diametrical extension can be made on 6" dia
x 12" to 16" length, high-molded concrete cylinders and diamond-drilled concrete
cores, when longitudinal compressive stress is applied on the specimens. The device is
constructed of lightweight aluminum magnesium alloy. The mounting points and contact
points are of machine steel. The control (spacer rods) is stainless steel.
The axial and diametrical deformations can be read on the H-4460 & H-4461 dial
indicators by taking one-half of their indicated values. (The lever ratio of the instrument
multiplies the deformation by the factor 2*, therefore, actual deformation of the specimen
is one-half the indicated value).
The dial indicators have an operating range of 0.2 in. graduated in 0.0001 in. divisions
that are separated enough to read in between them to the nearest y, division or 0.000050
in. dividing this by 2 to account for the lever ratio gives 0.000025 in. deformation.
Strain is then computed by dividing by the effective specimen gage length, 6 in. for
diameter and 8 in. for axial, giving readability better than 5 micro in per in per in strain
required by ASTM C-469. Three metal blocks are recommended to enable the operator
to conveniently mount the instrument at mid height on the concrete cylinder.
For preparation of the specimen and detailed test procedure refer to ASTM C469.
Assembly
1 Place the concrete cylinder upright.
2 Assemble H-2912 as shown in the drawing. The H-4461 dial indicator with the stem
brake should be mounted in the vertical position. The other dial indicator H-4460
should be mounted horizontally.
3 Unscrew the seven contact screws (2 on the upper lock ring, 3 on the lower lock
ring and 2 on the middle ring) until the points are flush with the inside surface
of the rings.
4 Place the compressometer over the concrete specimen locating the specimen at
the center ofthe ring.
5 Place three equal length blocks under the lower ring. The length of the blocks
(cylinders) should be vertical to provide the correct height.
6 Hand-tighten the 3 contact screws in the lower lock ring. And the 2 contact screws
in the upper ring against the spedmen.
7 Also hand-tighten the 2 contact screws in the middle ring making sure that the
vertical stem of the axial strain dial indicator is midway between the two portions
of the middle ring.