Synergistic Improvement Earthen Mortars with Tung Oil, Sticky Rice Pulp, and Aerial Lime: Application for the Conservation of Rammed Earth Structures Damaged by Exfoliation

Abstract

ABSTRACT Earthen sites are mainly made of earth and are widely located in the moist regions of south-eastern China; however, they suffer from serious damage. Sticky rice-lime mortar, one of the most important technological inventions in the ancient Chinese architectural history, are insufficient for earthen site conservation under adverse humid conditions. In this study, tung oil was used in conjunction with sticky rice pulp and aerial lime composites to evaluate the feasibility of protecting earthen sites damaged by exfoliation in moist environments. Several important experiments were conducted on a test soil as a substitute for the scarce site earth. The cohesion of the test soil with addition of tung oil (T), sticky rice pulp (R), and aerial lime (L) after 180 d was 16 times that of the untreated soil. The addition of these three materials to lean clay formed a double structure of aggregates, as determined by mercury intrusion porosimetry (MIP). The unique relationship depicting the hydraulic conductivity between TRL-treated soil and clay was uniform. Using SEM/EDS, and XRD analysis, the synergistic mechanism was primarily achieved through a TRL triangular interrelation, in which tung oil is indispensable for lean clay improvement. This study provided an effective technique for restoring deteriorated rammed earth remains made of lean clay. Two in situ pilot applications of rammed earth technology were performed on anomalous parts by multi-layer compaction to restore earth remains with potential exfoliation risk. This earth-based mortar was proved to be temporarily effective within one year of conservation.