Moisture growth
Clay fired brick masonry will never be dryer than the moment it is removed from the kiln. After that moment, the masonry will begin to absorb atmospheric moisture, as well as moisture from weather events until the masonry reaches equilibrium. BIA Tech Note 18 recommends using a moisture expansion coefficient range of between 3 x 10-4 and 5 x 10-4 mm/mm (in./in.), depending on the brick’s porosity.
Concrete shrinkage
Concrete theoretically cures forever; and during this cure process, some water is evaporating from the concrete, while majority of the water is reacting with the cement particles. Both evaporation and reaction cause the concrete to shrink, however, most of the shrinkage occurs within the first year after concrete is placed. This mode of movement is not relevant to mass masonry structures. Transitional and cavity wall masonry buildings with a concrete structure experience movement due to this phenomenon. ACI 209.1-05, Report on Factors Affecting Shrinkage and Creep of Hardened Concrete, gives a shrinkage coefficient range of between 2 x 10-4 and 8 x 10-4 mm/mm (in./in.). The shrinkage will vary based on the concrete mix design and environmental conditions.
There are additional sources of movement that can occur in masonry, most of which can be considered negligible. For the sake of this article, focus on the above three sources.
Table 1 is an example calculation of the possible vertical movement that can occur at a 30.5 m (100 ft) tall masonry veneer clad concrete structure. This fictional masonry was installed at a mean temperature of 26.7 C (80 F). After one year, when the team arrives on site during a sunny day, the masonry is approximately 48.9 C (120 F). What is the net movement at the top of the building?
Thermal
100 ft ∙ 4×(10^(-6) in./in.)/(°F) ∙ 40 F=0.016 ft (0.192 in.)
30.5 m ∙ 7.2 x (10^(6) mm/mm)/(°C) ∙ 22.2 C= 0.0049 m (4.9 mm)
Moisture
100 ft ∙ 4× 10^(-4) in./in. =0.04 ft (0.48 in.)
30.5 m ∙ 4× 10^(-4) mm/mm =0.012 m (12 mm)
Concrete Shrinkage
100 ft ∙ -5× 10^(-4) in./in. =-0.05 ft (0.6 in.)
30.5 m ∙ -5× 10^(-4) mm/mm =-0.015 m (15 mm)
