Increasing Cold-Weather Masonry Construction Productivity
CHARLES J. KORHONEN, ROBERT D. THOMAS, AND EDEL R. CORTEZ
used in concrete (Korhonen et al. 1994). Since ma-
INTRODUCTION
sonry mortars are also portland-cement-based, it
Background
seems reasonable to investigate the application of
Since 1970, the International Masonry Indus-
antifreeze admixtures to masonry mortar as well.
try All-Weather Council (IMIAWC) has provided
However, there are significant differences be-
guidance for cold weather masonry construction
tween concrete and mortar that must be consid-
(IMIAWC 1988). Among other things, IMIAWC
ered. As little water as possible is used in the
recommends that fresh mortar not be placed on
preparation of concrete. In contrast, high water
snow- or ice-covered surfaces, and that it be
contents in mortar are not of concern during mix-
maintained above freezing for 16 to 24 hours after
ing because the concrete masonry units on which
placement. Low temperatures can slow the
the mortar is placed draw free water out of the
strength gain of mortar, and sufficiently low tem-
mortar. This suction of water from mortar results
peratures can permanently damage it. Though
in a rather open pore structure in the hardened
fresh mortar can develop apparent strength while
mortar. The aggregates used in concrete are also
frozen, this strength dramatically degrades when
much coarser than those used in mortar. For these
the mortar is thawed.
and other reasons, while positive experiences
In its guide specifications, the Council requires
with admixtures in concrete provide promise for
that the moisture content of newly placed mortar
their use in masonry mortar, testing is certainly
be reduced to a maximum of 6% prior to discon-
required to demonstrate their effects on masonry
tinuing heating. The guide specification does not
mortar.
provide guidance on the time needed for typical
Objectives
masonry mortars to reach the required moisture
The intent of this project was to develop im-
content. In addition, heating mortar ingredients,
especially water, up to 50C (122F) is recom-
proved cold-weather masonry criteria, construc-
tion procedures, and guide specifications that
mended to assist in frost protection.
minimize excessive protection requirements for
The recommendations contained in the guide
newly installed masonry, thus resulting in im-
specification were based on the experience and
proved long-term freezethaw durability and
empirical data available at the time it was writ-
economy. The specific objectives were:
ten. As a result of limited experimental data, the
guidance is quite conservative. It constitutes a
1. Evaluate cold-weather performance of
safe approach to uncertainty, but results in signif-
masonry,
icant cost penalty. This research project has pro-
2. Evaluate antifreeze admixtures for masonry
duced experimental data that can lead to a safe
mortars, and
reduction in thermal protection.
3. Update guide specifications for cold-
The minimum cold weather protection is no
weather masonry.
thermal protection at all. This can only be
To evaluate the cold-weather performance of
achieved with the help of antifreeze admixtures.
conventional masonry systems, experiments
Antifreeze admixtures have been successfully
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