The wall clay, which is a component of Tsuchikabe, is mixed with straw to prevent cracking caused by drying shrinkage and to improve workability during construction by plasterers. However, it is known that mixing straw improves workability but also reduces the uniaxial compressive strength of the wall clay. In recent years, due to changes in rice cultivation processes, it has become difficult to obtain straw as a material for Tsuchikabe, leading to the search for alternative fiber materials. In this study, we manufactured three types of micro-fibrillated cellulose (MFC) with different pulping processes from native herbaceous plants and evaluated their effectiveness as reinforcing materials for wall clay. Additionally, as a comparison, we added mechanically fibrillated cellulose nanofibers (CNF) derived from purified cellulose fibers to the wall clay and conducted evaluations. Adding MFC or CNF to the wall clay reduced its flowability. The cracking ratio of the dried wall clay test specimens was significantly lower in the specimens containing MFC or CNF, which contain almost no lignin, than in the specimens without fibers, indicating that uniform drying shrinkage occurred. Compression test results showed increased uniaxial compressive strength and toughness in specimens containing MFC or CNF. Particularly, specimens containing MFC, which has almost no lignin and high hemicellulose content, exhibited the highest uniaxial compressive strength and elastic modulus. The compressive strain was increased as the fiber diameter decreased, suggesting that the fibers formed a network structure between the soil particles. These results indicate that MFC and CNF, which contain almost no lignin, act as reinforcing agents that simultaneously prevent cracking in wall soil and enhance compressive strength. Since MFC and CNF can be produced from all higher plants, they are expected to be utilized as new reinforcing materials to replace traditional straw.
