[1]

[1] Mortar crack in brick facade

crack

[2] Expansion joint in concrete

All porous materials expand to some extent when they absorb water. This kind of deformation is generally reversible when the material dries out, except in such materials as concretes. mortars, and plasters [a]. In other words, the expansion and swelling remains in the material even after ordinary drying has completed. When a material expands, the swelling can cause cracking of both the material and it’s facade, examples of which can be seen in the figures above [1,2].

For ceramics, most expansion will occur in the first 10-12 weeks after production but can continue, at a decreasing rate, for many years [b]. The majority of volumetric changes due to moisture release or evaporation in concrete occur within the initial casting and curing phases, making precast concrete materials advantageous [a]. The small cracks that inevitably form in concrete allow moisture to penetrate into the specimens, making these specimens particularly susceptible to moisture expansion deformation [c]. This cracking allows for more moisture to enter the material, thus propagating the damage into the future.

Moisture expansion can result from any physical or chemical process which creates voids in a material. There are various preventative methods that exist to avoid the negative effects of expansion in construction materials. In brick masonry, expansion joints (unobstructed openings through the brick wythe that are filled with compressible material) can be added to allow joints to close as the brick expands [d]. Similarly, as seen in figure [3], concrete isolation joints provide relief from the tensile stresses that cause uncontrolled cracking in concrete slabs by allowing the concrete to move freely as it shrinks or expands [e].

 

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[3] Expansion joint detail

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