# A Non-Contact Method of Measuring Capillary Rise Based on the Hygroscopic Expansion of the Material

## TL;DR

This paper introduces a non-contact method to measure how water is absorbed by porous materials using surface deformation instead of weight changes.

## Contribution

A novel displacement-based method using digital image correlation to measure capillary rise with higher accuracy and spatial resolution.

## Key findings

- The displacement-based method accurately captures capillary rise, especially in the initial phase.
- The method outperforms gravimetric techniques by eliminating errors from surface tension effects.
- It allows testing of larger samples and enables spatially resolved moisture analysis.

## Abstract

This paper presents a novel, non-contact method for measuring capillary water uptake in porous materials based on the phenomenon of moisture-induced expansion. The proposed approach establishes a quantitative relationship between the amount of water absorbed by the material and the deformations measured on its surface. Digital Image Correlation (DIC) was used to track the displacements of reference points on gypsum specimens during capillary rise. The absorbed water mass was determined from the recorded displacements using a mechanical model that incorporates the moisture expansion coefficient. The method was validated by comparison with conventional continuous gravimetric measurements. The results demonstrate that the displacement-based approach accurately captures the capillary rise process, particularly in the initial phase, where the gravimetric method suffers from significant measurement errors due to surface tension effects. The proposed method eliminates these limitations, providing higher accuracy and temporal resolution. In addition, it enables the testing of larger samples and offers the potential for spatially resolved moisture analysis. The findings confirm that the method is suitable for studying moisture transport in porous materials and may serve as a valuable alternative to traditional gravimetric techniques.