Detecting real-time moisture uptake in spruce samples by acoustic emissions

Wood offers an environmentally friendly alternative to concrete, being sustainable and renewable. However, it also has drawbacks, such as sensitivity to environmental moisture. Moisture interaction, in particular, directly impacts the strength of timber beams and can lead to mould, making early detection of moisture uptake important. While commercial moisture metres exist, their measurements are typically local and do not represent the entire wooden component. The present study investigates the use of an acoustic emissions sensor – tested with two mounting methods – and a camera to detect moisture uptake in spruce samples. Experiments were carried out in a climate-controlled environment at 20°C/65% relative humidity. Two types of specimens were used: oven-dried samples, expected to absorb moisture, and pre-conditioned samples in norm climate to equilibrium moisture content, serving as references. To validate the results, a scale recorded weight changes at regular intervals. For the tested dry samples, a meaningful correlation was found between weight gain due to moisture uptake and changes in cross-sectional area (Rdried¯=0.96). Additionally, a strong relationship emerged between acoustic emissions and moisture uptake, marked by increased acoustic base energy due to swelling of the specimens (Rdried¯=0.88) and a plurality of crack events.