ASTM C39 Procedure
Compression test of moist-cured specimen should be done immediately after the removal from
moist storage. This is being done because the specimen should be tested in moist condition. All
the test specimens shall be broken within the prescribed test age (24h, 3d, 7d, 28d, 90d) and
permissible tolerance (---).
First, place the plain (lower) bearing block, on the platen of the testing machine directly under the
spherically seated (upper) bearing block. Make sure that the bearing surfaces of the machine are
clean and free of debris then place the specimen on the lower bearing block. If you are using
unbonded cap/caps, wipe the bearing surfaces of the retaining rings and center it on the cylinder.
Place the specimen and align its axis with the center of the upper bearing block.
Next, zero out the machine. Before applying the load, tilt the movable portion of the upper bearing
block to make the bearing face parallel to the top of the specimen.
If using unbonded caps, check the alignment of specimen after applying the load but before
reaching 10% of its anticipated strength. Check the cylinder's alignment making sure that the axis
doesn't depart from vertical by more than 0.5 degrees and ends are centered within the retaining
rings. If the cylinder is off center, remove the load and carefully recenter the specimen. Reapply
the load, recheck specimen centering, and if everything is good, proceed to the next step.
Continue applying the load without shock. The load shall be applied at a rate of movement
corresponding to a stress rate on the specimen of 0.25 +- 0.05 MPa/s [35 +- 7 Psi/s]. Maintain the
rate at least during the latter half of the loading phase.
It is allowed to increase the rate of loading during application of the first half but do it in a
controlled manner to avoid shock. Don't mess with the loading rate as the cylinder approaches its
peak load and stress rate drops. Then, apply compressive load until the indicator shows that the
load is decreasing steadily and shows a well-defined fracture pattern. Do not automatic shut-off a
testing machine equipped with a specimen break detector until the load has dropped to less than
95% of its peak load. When using unbonded caps, Type 5 or Type 6 fracture pattern may occur
before the ultimate capacity has been attained so continue compressing until you’re sure that the
ultimate capacity is attained. Determine the type of fracture and then record the carried load of
specimen during the test. If you see an unusual pattern, draw and described it briefly. If the
measured strength is lower than expected, look into the fractured concrete and note the presence
of large air voids, evidence of segregation, whether fractures pass predominantly around or through
the coarse aggregate particles, and verify end preparations were in accordance with Practice C617
or Practice C1 231/C1231M.
T22
In this test, you are allowed to use unbonded caps on one or both ends of the cylinder as
long as they meet the requirements. The pads to be used should be examined before testing, if there
are cracks with length exceeding 3/8 in (10mm), replace it. Then, insert the pads in the retainers
before placing on the cylinders. (Starch or talcum powder is recommended to be used in dusting
the pads) Take note that concrete cylinders will break more violently if unbonded caps are used in
the test. So, to avoid accidents, equipped the testing machine with protective cage. Be careful for
the possible sudden release of energy stored in elastomeric pads.
Center the unbonded caps or caps on the cylinder and place the cylinder on the lower bearing block
of the testing machine. Place the cylinder and align its axis by centering the upper retaining ring
on the spherically seated bearing block. To obtain uniform seating, rotate the movable portion by
hand while the spherically seated block is brought to bear on the upper retaining ring. Check the
alignment of specimen if it’s vertical within a tolerance of 1/8 in in 12 in (3.2mm in 300mm) after
applying the load but before reaching 10% of its anticipated strength and that the ends of cylinder
are aligned within the retaining rings. If the cylinder is off center, remove the load and carefully
recenter the specimen. If done, reapply the load again. Note that pausing the load is allowed when
checking the alignment.
Complete the load application, testing, calculation, and reporting of results in accordance with Test
Method C 39.