Soil compaction and soil bulk density are key soil properties affecting soil health and soil ecosystem services like crop production, water retention and purification and carbon sequestration. The standard method for soil bulk density measurements using Kopecky rings is very labour intensive, time consuming and leaves notable damage to the field. Accurate data on bulk density are therefore scarce. To enable large-scale data collection, we tested a new portable gamma ray sensor (RhoC) for in situ field and dry bulk density measurements up to 1 m depth. In this first validation study, measurements with the RhoC-sensor were compared with classic ring sampling. Measurements were made in two agricultural fields in the Netherlands (a sandy clay loam and a sandy soil), with large variation in subsoil compaction. At 10 locations within each field, three soil density profiles were made. Each profile comprised six depth measurements (every 10 cm from 10 to 60 cm depth) using the RhoC-sensor and Kopecky rings, resulting in 30 pairwise profiles and 180 measurements in total per field. At an average soil density of 1.5 g/cm3, the relative uncertainty was 9% for the Kopecky rings and 15% for the RhoC-sensor. Because the RhoC-sensor is easy and quick to use, the higher relative uncertainty can easily be compensated for by making additional measurements per location. In conclusion, the RhoC-sensor allows a reliable quantitative in situ assessment of both field and dry bulk density. This provides the much-needed possibility for rapid and accurate assessment of soil compaction. The acquisition of this data supports the calculation of soil organic carbon stocks and is indispensable for (national) soil monitoring, to assess soil health and to inform sustainable land management practices for sustained or improved soil health and provision of soil ecosystem services, such as requested in the proposed EU Directive on Soil Monitoring and Resilience.

The risk of frost damage to building materials is strongly dependent on the water content, particularly when the water content is high. Therefore, to understand the moisture behavior of materials with high water content is essential to predict the frost damage risks of buildings. While little liquid water transfer takes place over the capillary saturation under unfrozen conditions, the pressure drop of the unfrozen water contained in the frozen domain (cryosuction) may be a strong driving force for water transfer during the freezing processes. Therefore, in this study, we investigated water transfer in a building material over capillary saturation during freezing through a one-dimensional freezing experiment using the gamma-ray attenuation method and hygrothermal simulations. In the experiment, an aerated concrete specimen, with a water content greater than the capillary saturation, was subjected to a temperature gradient by cooling the specimen bottom to the freezing temperature. The results show that significant water transfer occurred even in the capillary-saturated material during freezing and thawing. Water moved to the cold side in the material and the most significant water accumulation was observed at a position where the temperature was close to 0 degrees C. The hygrothermal simulation, including the freezing processes, confirmed that cryosuction was a dominant driving force of water movement and accumulation in the material compared with other driving forces, such as gravity and temperature gradient. Moreover, mechanism of the water accumulation at a position where the temperature was close to 0 degrees C was discussed from the perspective of water chemical potential distribution and water conductivity of the material. The findings of this study will help develop a more reliable model for evaluating moisture damage risks by considering the hygrothermal behaviors of building envelopes.