Computer Tomography as a data acquisition tool for quantifying and modeling in-pore gypsum crystallization in building materials

Syracuse, NY

In the last few decades a new type of persistent efflorescence has started appearing on ceramic brick facades in the UK, the Netherlands and in Belgium. Since the problem undermines the aesthetic appearance of masonry buildings, it results in a growing number of complaints from building owners. In the laboratory, gypsum efflorescence is typically studied via wicking tests. However, these often yield gypsum subflorescence instead, leading to significant pore clogging just below the evaporation surface. To gain further insight in that subflorescence and pore clogging, a correct quantification of the amount and the distribution of the gypsum crystalised in the pore space is necessary. Micro-CT achieves this by allowing visual inspection as well as quantitative data gathering. Because of the non-destructiveness of micro-CT, samples can be scanned before and after subflorescence/pore clogging has occurred. The suggested methodology includes visualization and characterization of the pore space. Observing the changes in pore structure, with the assumption that these are induced only by the presence of the salt crystals, it is possible to accurately quantify the volume of gypsum present, as well as the location of the affected pores in 3D. Due to the partial volume effect, the CT dataset can be used to detect objects smaller than the voxel size because the density difference between gypsum and air is large enough. The obtained results confirm the presence of a thin gypsum layer just below the evaporation surface of the sample. Other techniques such as the wicking test and MIP also confirm the observations regarding pore size change and gypsum content.

https://surface.syr.edu/ibpc/2018/BE1/1