Page 482 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.27

FIGURE 13.21 Rotated shelf angles cause cracked masonry.

Pavement Delamination. Concrete base slabs and mortar setting beds shrink at different
rates. Contraction of a concrete base and cementitious setting bed combines with expansion
of clay brick paving units to induce a shear stress between the two materials. The level of
that stress typically equals the shear strength. Thus, cracking and delamination are the nat-
ural and virtually certain results. Attempts to bond masonry pavements to base slabs with
conventional or latex mortars have often been unsuccessful, providing annual failure rates
of 2.4 percent. Masonry paving units should be set on a sand bed. 27