Study on the Preparation Method and Mechanical Properties of Rammed Earth from the Shanhaiguan Great Wall

Investigation of the composition range of the rammed earth from the Shanhaiguan Great Wall is of great significance for the conservation of cultural heritage. Based on the basic physical properties, shear strength parameters, and the results of XRD, FTIR, TG/DTG, and SEM/EDS analyses of the in situ rammed earth, lean clay, lime, and pregelatinized starch were used to prepare rammed earth samples. Shrinkage test, direct shear test, XRD, FTIR, TG/DTG, and SEM/EDS analyses were conducted to study the mechanical properties and the preparation method of rammed earth. The results show that the shrinkage coefficient increases with initial water content, whereas cohesion generally decreases beyond 17% and the internal friction angle exhibits comparatively smaller variations. The incorporation of lime reduces the shrinkage coefficient and increases peak shear strength, alongside an associated tendency toward brittle behavior. The incorporation of pregelatinized starch slightly increases the shrinkage coefficient, while its effect on cohesion is non-monotonic and varies with lime content. The peak shear strength exhibited a combined response to lime and pregelatinized starch contents. Based on the results of shrinkage coefficient, shear strength, thermal behavior, and microstructure, the possible formulation range under the present experimental conditions was identified as follows: an initial water content of 17–21%, a lime content of 3–4%, and a pregelatinized starch content of 1.0–1.5%.