Structural damage evaluation of industrial masonry chimneys

Abstract

This document presents a systematic analysis of the damage causes of industrial masonry chimneys, i.e. cracking patterns, materials’ degradation and structural displacements. The methodology includes an adequate geometric evaluation with identification of each observed lesion, their situation and their environmental conditions. The industrial process temperatures have been documented, hence maximum temperatures and gradients during chimney’s service life were evaluated, and any possible crack pattern because thermal loads was analyzed. In addition, chemical composition (SEM, EDS and DRX) and mechanical properties (compressive and bending strengths) were assessed. Microstructural analyses were useful to detect certain elements and compounds related to corrosion or degradation processes of mortar and steel. Analytical and FE models were made to evaluate the influence of each possible damage source, i.e. temperature gradients, corrosion and chemical reactions producing expansion in the mortar. The effect of internal pressures (because corroded steel) were successfully modelled as spring elements in vertical and horizontal cracks, which matched experimental data obtained in real structures. These results have demonstrated the relation between horizontal displacements of the crown and the position of the internal stairs (made in steel bars embedded in the masonry). Once cracked, either by corrosion or by temperature, the water entrance through the cracks produces chemical reactions with the combustion sulphurs, present in the mortar because of combustion gasses. These reactions generate an expansion inside the masonry located only in one façade. Hence, differential displacements generate the curvature and the consequent drift.