Optical crack detection and assessment using cholesteric liquid crystal elastomers

As one cannot know in advance where a crack will form, currently used discrete crack monitors may miss to detect a crack if it grows outside the monitored regions. A high-resolution continuous 2D strain monitor applied to the entire surface of interest would solve this problem. Cholesteric liquid crystal elastomers (CLCEs) provide this ability, and with recent advances in chemistry, they can be applied very easily, similar to a paint coating. Here we demonstrate the detection of new cracks and monitoring of their progression using CLCE coatings applied to an extruded polystyrene insulation panel, an aerated concrete brick, and a reinforced concrete beam, respectively. Regardless of where and in which direction a crack develops, it can be easily detected thanks to a change in color. By analyzing the new color, quantitative information on the crack width can be extracted. Considering the ease of applying the CLCEs to standard building materials, the high 2D resolution strain monitoring with clear optical detection that it provides, and the low cost of the solution, we argue that CLCE coatings can have a revolutionary impact on structural health monitoring for buildings and infrastructure, to be constructed or already existing.