Mortar moisture loss tests
The mortar was used to fabricate two prisms
The rate of water loss from mortar can be affect-
each with two units separated by a single full mor-
ed by a number of different variables. Those vari-
tar bed joint. The mortar was placed on the top of
ables investigated as part of this research include:
the bottom brick using a mortar template to
unit type, unit moisture content, unit temperature,
achieve a uniform joint thickness and to reduce
mortar type, mortar temperature, and air tempera-
workmanship variations between prisms. The sec-
ture. Among those properties not evaluated are the
ond brick was then carefully placed onto the mor-
relative humidity of the air surrounding the units
tar joint and the joint was compacted using a 1.8-kg
and the effects of wind. The testing was not struc-
(4-lb) drop hammer to apply an impact force to the
tured to distinguish between mortar moisture loss
top brick. Using the same mortar, the second prism
attributed to absorption from the units and mois-
was then fabricated in the same manner. Prism fab-
ture loss attributed to evaporation to the air. To re-
rication was completed within 10 minutes after
duce the number of tests required and to facilitate
mortar mixing.
laboratory constraints, most of the testing was per-
Five minutes after the first prism was fabricat-
formed using a single unit type (concrete brick)
ed, the top unit was removed from the prism and
and a single mortar type (type M masonry cement
the exposed mortar joint was cut into a grid. One of
mortar).
the grid segments was sampled using a spatula
All mortar was proportioned using 2880 g of
and measured for moisture content. Approximate-
masonry sand. Batch weights of other materials
ly 30 g of mortar was sampled, placed on a ceramic
(portland cement, masonry cement, and lime)
plate, and dried in a microwave oven. The mois-
were determined based on the volume propor-
ture content was calculated based on the difference
tions included in Table 1. Mortar was mixed in the
between the initial weight of the mortar compared
laboratory using a Hobart mechanical mixer. With
with its final dry weight. The top brick was placed
the exception of the type of mixer used, mixing
back on the exposed mortar joint, and the prism
was performed to simulate field conditions. In the
remained undisturbed until the next sampling
field, the mason is allowed to adjust the water con-
time. This procedure was repeated at 5, 15, 30, 45,
tent of the mortar by eye to achieve the necessary
60, 120, 240, and 1440 min.
mortar workability to accommodate the existing
These procedures were used to evaluate the ef-
conditions at the job site. For example, on hot,
fects of unit temperature, unit moisture content,
windy days, the mason may use additional water
mortar type, mortar temperature, and air tempera-
in mixing to prevent premature drying of the mor-
ture on the rate of mortar water loss. Similar proce-
tar. Less absorptive units may require the mason
dures were used with several different concrete
to reduce the amount of water in the mix. Various
masonry units to investigate the effects of unit
mortar admixtures may also require the mason to
manufacturing. The matrix of combinations used
adjust the mortar. Because some of the variables in
to achieve this information is listed in Table 6. Two
these tests may affect water demand, the mason
prisms were fabricated for each of the combina-
was allowed to adjust the water content as neces-
tions shown.
sary to achieve the desired mortar consistency.
Different mortar temperatures were achieved
Tests were performed on the fresh mortar to docu-
by heating or cooling the mortar materials (ce-
ment its air content, unit weight, and consistency
ment, sand, water) before the mortar was mixed.
by cone penetration (ASTM C 780).
Unit temperatures were achieved by the same
For all mixes involving the primary mortar type
method. Two different air temperatures were used,
5 and 20C (41 and 68F). Those prisms that were
in this program, type M masonry cement mortar,
kept at 20C (68F) were stored in the open lab air
no adjustments of water content were found to be
necessary despite variations in the temperature of
for the duration of the test. Those prisms kept at
the mortar materials from 5 to 20C (41 to 68F).
5C (41F) were placed within an environmental
The resulting tested moisture contents for these
chamber maintained at that temperature. Because
mortars were therefore rather consistent (13.9 to
the chamber requires air circulation to maintain
15.9%), as were the cone penetrations. It was
specified temperatures, the prisms were sealed in
found that more water was required to obtain a
plastic bags to prevent wind effects from influenc-
similar mortar consistency in the portland cement
ing the loss of moisture from the mortar. At the
and lime mortars--particularly for the PCL type
specified sampling times, the prisms were re-
M mortar, which contains a greater proportion of
moved from the chambers, the bags were opened,
cementitious materials than the other mortars.
the mortar sample was taken, and the prisms were
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