16-01-2013, 11:14 AM
Cold Weather Concreting Guide
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INTRODUCTION
The following policy reflects the standard of care required to place and cure concrete,
masonry mortar, and grout when temperatures drop below code and standard practice
temperatures as identified in the adopted building code and referenced guidelines. Every
effort shall be exerted by the builder or contractor to assure that ground, forms, and
reinforcement are at temperatures stated below for the requisite time to assure adequate
conditions for concrete, mortar, and grout placement are met to assure against undue
shock during the placement process. Every effort shall also be made to provide
protection and heat for the concrete, mortar, and grout to allow their proper cure to
assure that design strengths are achieved. The following guidelines state conditions and
policy of this office and are the basis for inspection, release to pour, and final approval
during cold weather conditions.
General
1. Concrete shall not be placed against or on frozen ground or surfaces. Frozen
materials in trenches and in forms shall be removed or heated to achieve appropriate
placement temperatures. Material that is heated shall meet the density and compaction
requirements of the code or shall be removed and replaced with suitable, non-frozen
material and re-compacted to meet 95 percent density.
2. Concrete shall not be placed against ice or snow. Ice or snow shall be removed and
area shall be heated to assure that foundation soils meet the temperature conditions for
placement and that material is of suitable density to meet the compaction requirements.
3. Concrete mixes may be created using heated ingredients. Such procedures shall
follow standard American Concrete Institute cold weather practices.
4. Tenting and heating shall be in place when temperatures drop below the stated
temperatures, before placement occurs, and shall be in place for a sufficient length of
time to assure that even temperature of ground, materials, forms, and the like are met.
5. Once concrete or grout has been placed or blocks laid with mortar, temperature
conditions shall be maintained to assure that adequate curing is achieved, as long as is
necessary to assure design strength is achieved.
6. Placement of tenting and subsequent heating must be done with protection of the
worker in mind, in addition to protection of project. Inadequate ventilation and poorly
operating heaters can produce carbon monoxide gas, which can injure workers and may
reduce the quality of the work, concrete, mortar, or grout.
7. Care must be used to assure against undesirable drying of concrete surfaces during
the curing process.
8. Placement of blankets may be an appropriate alternative when weather and
conditions permit. Temperature must be maintained and care must be exercised to
assure against loss of moisture.
9. Curing times stated below are designed to assure optimum strengths and prevent
potential for failure of materials once thawed and loaded. Allowance for reduction of
curing times depends entirely on proof of having achieved design strengths at an earlier
time and would require test backup on samples and engineering approval.
10. Stripping of forms, as long as it is done in a controlled environment, would follow
standard practices.
Masonry Placement and Grouting of Masonry in Cold Weather
1. The Building Code Official requires that an accessible tent or enclosure be built to
protect grout and mortar from freezing for 48 hours at a temperature of 40°F. The first 24
hours of the 48 hour period is used to cure the mortar and also the third day of concrete
curing, which is 3 days (see above.) The next 24-hour period is for the curing of the
grout. After this curing cycle is complete, the enclosure may be removed.
2. When air temperatures fall below 40°F, grout mixing water and aggregates shall be
heated to produce grout temperatures between 40°F and 120°F. (IBC 2104.3.2.1).
3. Masonry to be grouted shall be maintained above freezing during the grouting
placement and at least 24 hours after placement. (IBC 2104.3.2.4) This means that the
block must be brought up to appropriate temperatures before placement of the grout and
maintained throughout the placement and cure process.
4. When atmospheric temperatures fall below 20°F, enclosures shall be provided around
masonry during grout placement and for at least 24 hours after placement.