Masonry Magazine January 1970 Page. 36
Table 2. Comparison of Building Code Requirements
| Code Reference | Unprotected Minimum Air Temp. For Construction | Required Period of Protection against Freezing |
|---|---|---|
| BOCA Basic Building Code, 1965, page 183. | 28° F (rising) 36° F (falling) | 48 hours |
| Uniform Building Code | 40° F | 48 hours-Type I Cement 24 hours-Type III Cement |
| National Building Code, 1967, page 137. | 32° F (rising) 40° F (falling) | 48 hours |
| National Building Code of Canada, 1965, part 4, page 19. | 40° F | 48 hours |
| American Standard Building Code Requirements for Masonry USASI A411, 1953, page 18. | 32° F (rising) 40° F (falling) | 48 hours |
| Building Code Requirements for Reinforced Masonry USASI A41.2, 1960, page 7. | 40° F | 72 hours |
Table 3. Mortar Mixes, ASTM C 270
| Mortar Type | Parts by Volume of Portland Cement, or Portland Blast-Furnace Slag Cement | Parts by Volume of Masonry Cement | Parts by Volume of Hydrated Lime or Lime Putty | Aggregate, Measured in a Damp, Loose Condition |
|---|---|---|---|---|
| M | 1 | 1 (type II) | ¾ | Not less than 2¼ and not more than 3 times the |
| S | ½ | 1 (type II) | over ¼ to ½ | sum of the volumes of the cements and lime |
| N | 1 | 1 (type II) | over ½ to 1¼ | used. |
The effect of wind at low temperature, for example, that of a 15-mile-per-hour wind at an air temperature of 20 degrees above zero, is the same as that of still air at 10 degrees below zero. Called the wind chill factor, these combinations of of wind and temperature cause loss of heat from the body and therefore influence worker efficiency.
Expected air temperature influences planning and selection of protective devices to comply with the appropriate building codes. Air temperature is the single measureable index used as a criterion for the major building codes which affect construction of concrete masonry during cold weather. A summary of the provisions of several of these codes as shown in Table 2 illustrates a considerable variation in the minimum requirements. Frequently contractural specifications include the provisions of these codes. The source material for the various recommendations indicates that many of the requirements were developed from standards related to placing mass concrete in cold weather.
The data involved were obtained from work dating back to the 1920's as well as from recent investigations.
Many observers have reported the actual construction of masonry at temperatures below freezing with little or no auxiliary heating and no apparent adverse effect upon the masonry. Reports of construction in Canada and other countries indicate successful results in masonry built below freezing and in some cases below 0°F. In addition to observations of actual construction, recent analysis of laboratory experimentation indicates that the effect of freezing temperatures on masonry is not necessarily detrimental. The data reviewed suggest that neither the compressive strength nor the bond strength is significantly affected by affording a period of protection from freezing in a test program. From these observations it is evident that research and construction requirements relating to cold-weather concreting do not necessarily apply to masonry construction. Generally concrete is placed in forms which absorb little water from the concrete and prevent evaporation into the atmosphere. On the other hand, in masonry construction thin layers of mortar are placed between thicker absorbent units (concrete masonry blocks) which absorb water from the mortar and stiffen it. The degree of saturation of the mortar is therefore lowered and the water-cement ratio is reduced. Hence little water is actually left to freeze in the mortar and cause damage by expansion. As additional technical information is compiled, it is inevitable that some relaxation of requirements in building codes will occur and lead to more economical cold-weather concrete masonry construction.
Selection of Materials
The masonry unit itself influences the performance during the early period of construction due to the rate at which moisture is withdrawn from the mortar as discussed above. Where a choice is available and other factors of consideration such as aesthetics are equal, a unit having a high initial rate of absorption should be chosen in preference to one having low absorptive properties. And, all units should meet the requirements for Type I, moisture-controlled concrete masonry as listed in ASTM C 55 (brick), C 90 (hollow load-bearing), C 129 (nonload-bearing) and C 145 (solid load-bearing).
Mortar should conform to ASTM Specifications for Mortar for Unit Masonry C 270 (Table 3). The type of mortar selected should be dependent upon engineering requirements, but generally speaking mortars with slightly higher cement content are preferred for cold-weather construction because of the resultant superior bond and resistance to damage from freezing. The required protection period for recently-constructed masonry may be reduced by using high-carly-strength (Type III) portland cement as indicated below.
Admixtures or antifreeze agents in quantities which are high enough to lower the freezing point of mortars should not be permitted. The high content required would adversely affect mortar strength and other desirable properties. The use of calcium chloride as an admixture in masonry mortars for early strength development is permissible; however, providing that the amount added does not exceed 2 percent of the weight of the portland cement content. Calcium chloride should not be permitted for use in construction where metal objects such as ties, anchor bolts, etc., are imbedded in the mortar because the metal is thereby subjected to intensified corrosion. Care must be exercised to avoid combination of high temperature and concentration of calcium chloride.