Numerical analysis of cracking in fiber reinforced lime renders

Abstract eng:
Cracking behavior of lime mortar renders subjected to shrinkage is numerically investigated by the finite element method (FEM). The render materials selected for the study include ordinary lime mortar (control sample), lime mortar with increased tensile strength (presumably achieved by the addition of metakaolin), two mortars with different natural fibers (goat hairs and pig bristles) and two mortars reinforced with different content of short PVA fibers (0.5% and 2% by volume). The analyses simulate the crack evolution and allow us to shed light on the mechanism of the render deterioration. The study reveals that increasing the mortar’s tensile strength may not improve its durability, when it is subjected to volume changes. Even though the number of cracks decreases, the cracks exhibit wider opening displacements and higher stressing takes place on the interface with the substrate, leading to delamination failure. A qualitatively better performance is observed with those fiber reinforced mortars, in which the fibers provide sufficient crack-bridging action. If the maximum cohesive traction that the fibers can transmit across cracks is higher than the matrix cracking strength, then the mortar exhibits so-called multiple cracking – the imposed strain is accommodated by formation of a large number of tight cracks. Since these cracks are bridged by fibers, the material retains macroscopic integrity and is even able to sustain increasing tensile load. The multiple-cracking behavior is also found to significantly contribute to elimination of the delamination cracks and reduction of the interfacial stresses. This desirable behavior was not predicted with even the highest acceptable content of goat hairs and was attained only marginally with pig bristles. On the other hand, addition of even the lower content (0.5% by volume) of PVA fibers resulted in a robust deformation-tolerant performance of the render.

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