Water migration in clay-based earthen building materials containing methyl cellulose: visualization and quantification by neutron radiography during drying, remoistening, and subsequent drying

This study investigates persistent challenges in the development of sustainable clay-based building materials by analyzing the influence of moisture transport processes. Spatial and temporal evolution of moisture transport during drying and rewetting and the influence of methyl cellulose (MC) on these processes have remained insufficiently characterized in clay-based earthen materials to date. This research provides spatially resolved insights that fundamentally go beyond conventional bulk measurements. Using time-resolved neutron radiography, dehydration and water-absorption behavior are elucidated to address critical limitations of clay-based materials such as low water resistance, shrinkage, and cracking. Methyl cellulose (MC) was introduced as a functional admixture to improve water resistance and reduce shrinkage-induced cracking. Eight clay-based material formulations were systematically analyzed under controlled drying and rewetting conditions to quantify moisture transport, retention behavior, and potential crack formation. Reference samples without MC exhibited faster drying but also significantly accelerated water uptake. Depending on the mixture composition, MC-containing formulations exhibited water-absorption rates up to three times lower than those of the corresponding reference samples without MC. The neutron radiography measurements provided, for the first time, insights into the internal drying behavior of clay-based earthen materials, demonstrating that moisture transport and drying gradients strongly depend on particle size distribution and MC content. The results demonstrate that MC, as a natural and recyclable biopolymer, is particularly suitable for improving the durability of earthen construction materials without compromising recyclability. These findings provide a basis for further evaluating MC-modified earthen materials for applications exposed to moisture, particularly in settings where improved water resistance is required. Further investigations into long-term durability and repeated wetting–drying cycles are needed to assess their suitability for specific exterior applications.