Masonry Magazine January 1972 Page.19
ogy but again emphasizes the need for understanding mortar technology.
Illustration 10 shows the effect of cure environment on the compressive strength of masonry cement mortars subjected to freezing during the early periods after fabrication. Although it is impossible to water-cure masonry and realize the increase in unused strength shown between air and water cured cubes, any naturally or artificially provided water will reinitiate the portland cement hydration and increase the masonry strength.
Illustration 13 shows the rapidity with which the water migrates from the mortar joint. Three masonry mortar systems, each with low and high air contents, were investigated by placing a mortar bed on a masonry unit of known suction, severing the joint into 10 horizontal sections and determining the mortar moisture content. Contact period between mortar and masonry equalled 1 to 2 minutes. Significant findings include a very rapid migration (loss of 20% of water in 1 to 2 minutes) relatively unaffected by mortar air content and composition. The portland cement-limestone mortar system of research interest, singly, showed the greatest water loss, which is attributed to difference in fineness between limestone and hydrated lime.
Illustration 11 introduces the remaining illustrations where our interest is directed to water migration and evaporation and the effect of water on masonry performance. This wall cross-section shows brick veneer over wood frame construction without water being present.
Illustration 14 shows that masonry assemblages freeze in a relatively short period of time. Mortars mixed and assemblages fabricated at 73°F. freeze in approximately 1½ hours, the same period when mortars containing calcium chloride admixtures showed retardation. During this period, 0 to 12 hours, the mortar may lose sufficient water to prevent expansion on freezing, and compressive strength development is now perhaps 50% to 70% of that measured at 28 days. Colder temperature, winds and saturated and frozen units would reduce the time of freezing. Conversely, higher mortar temperatures, heated units, windbreaks and enclosures with heat extend the period before masonry freezes.
Illustration 12 shows water distribution immediately after wall construction. Water migrates to the masonry unit and evaporates to the collar joint and to the atmosphere. The masonry mortar is very susceptible to freezing in this condition, especially if water-saturated and frozen masonry units prevent the water migration to the masonry unit.
Illustration 15 shows the relative humidity instrumenta-