Humboldt H-4133 Acme Penetrometer - Manual (Page 4)

Number of Specimens
Prepare at least three separate batches for each test condition. One rate of hardening
test shall be made on each batch. An equal number of batches for each condition shall
be made on any given day. When it is impossible to make at least one test for each
variable on a given day, the mixing of the entire series of batches shall be completed in
a few days as possible and one of the mixtures shall be repeated each day as a standard
of comparison.
Penetration Test
Remove bleeding water from the surface of the mortar specimens just prior to making
a penetration test by means of a pipette or suitable instrument. To facilitate collection
of bleeding water, tilt the specimen carefully to an angle of about 12 degrees from the
horizontal by placing a block under one side 2 minutes prior to removal of the bleeding
water.
Insert a needle of appropriate size, depending upon the state of hardening of the mor-
tar, in the penetration resistance apparatus and bring the bearing surface of the needle
into contact with the mortar surface. Gradually and uniformly apply a vertical force
downward on the apparatus until the needle penetrates the mortar to a depth of 1 inch
(25 mm) as indicated by the scribe mark and take the maximum reading (lbs) indicated
on the gauge. The time required to penetrate to the 1 inch depth shall be approximately
10 seconds. Record the force required and the time of application, measured as elapsed
time after initial contact of cement and water. In subsequent penetration tests take care
to avoid areas where the mortar has been disturbed by previous tests. The clear distance
between needle impressions shall be at least two diameters of the needle being used,
but not less than 1/2 inch (13 mm). The clear distance between any needle impression
and the side of the container shall be not less than 1 inch.
Make penetration tests at hourly intervals for normal mixtures and normal temperatures,
the initial test being made after an elapsed time of 3 to 4 hours. For accelerated mix-
tures or high temperatures, it maybe advisable to make the initial test after an elapsed
time of 1 or 2 hours and subsequent tests at 1/2 hour intervals. For low-temperature
conditions or retarded concrete mixtures, the initial penetration test maybe deferred
for an elapsed time of 4 to 6 hours and perhaps longer. Subsequent tests maybe made
at intervals of 1 hour unless the rate of increase in penetration resistance indicates that
shorter intervals are desirable.
Not less than six penetration resistance determinations shall be made in each rate of
hardening test. And the time intervals between penetration resistance determinations
shall be such as to give a satisfactory rate of hardening curve, as indicated by equally
spaced points. Continue the test until one penetration resistance of at least 4000 psi
(27.6 MN/m
2 ) is reached.
Calculations
The gauge reading in each penetration test divided by the area of the bearing face of
the needle gives the penetration resistance corresponding to the gauge reading in
each test.