Study of Sticky Rice−Lime Mortar Technology for the Restoration of Historical Masonry Construction

Abstract

Replacing or repairing masonry mortar is usually necessary in the restoration of historical constructions, but the selection of a proper mortar is often problematic. An inappropriate choice can lead to failure of the restoration work, and perhaps even further damage. Thus, a thorough understanding of the original mortar technology and the fabrication of appropriate replacement materials are important research goals. Many kinds of materials have been used over the years in masonry mortars, and the technology has gradually evolved from the single-component mortar of ancient times to hybrid versions containing several ingredients. Beginning in 2450 BCE, lime was used as masonry mortar in Europe. In the Roman era, ground volcanic ash, brick powder, and ceramic chip were added to lime mortar, greatly improving performance. Because of its superior properties, the use of this hydraulic (that is, capable of setting underwater) mortar spread, and it was adopted throughout Europe and western Asia. Perhaps because of the absence of natural materials such as volcanic ash, hydraulic mortar technology was not developed in ancient China. However, a special inorganic-organic composite building material, sticky rice-lime mortar, was developed. This technology was extensively used in important buildings, such as tombs, in urban constructions, and even in water conservancy facilities. It may be the first widespread inorganic-organic composite mortar technology in China, or even in the world. In this Account, we discuss the origins, analysis, performance, and utility in historic preservation of sticky rice-lime mortar. Mortar samples from ancient constructions were analyzed by both chemical methods (including the iodine starch test and the acid attack experiment) and instrumental methods (including thermogravimetric differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, and scanning electron microscopy). These analytical results show that the ancient masonry mortar is a special organic-inorganic composite material. The inorganic component is calcium carbonate, and the organic component is amylopectin, which is presumably derived from the sticky rice soup added to the mortar. A systematic study of sticky rice-lime mortar technology was conducted to help determine the proper courses of action in restoring ancient buildings. Lime mortars with varying sticky rice content were prepared and tested. The physical properties, mechanical strength, and compatibility of lime mortar were found to be significantly improved by the introduction of sticky rice, suggesting that sticky rice-lime mortar is a suitable material for repairing mortar in ancient masonry. Moreover, the amylopectin in the lime mortar was found to act as an inhibitor; the growth of the calcium carbonate crystals is controlled by its presence, and a compact structure results, which may explain the enhanced performance of this organic-inorganic composite compared to single-component lime mortar.

Introduction of Microbial Biopolymers in Soil Treatment for Future Environmentally-Friendly and Sustainable Geotechnical Engineering

“…In ancient Egypt, earth engineering methods were developed to create river embankments to control the annual flooding of the Nile river [2]. Engineers in ancient China used a sticky rice mortar that contained amylopectin as a construction binder for the Great Wall [3].…”

Materials Science Challenges in Radiocarbon Dating: The Case of Archaeological Plasters

“…12 In China, reports suggest that rice was used to change the grain size, and ultimately the mechanical properties, of historical plasters. 14 The curing reactions described in Eqs. 1 and 2 can change depending on the composition of its components.…”

“…15,16 From that time period forward, plaster has been observed in archaeological contexts throughout the world, including the Far East, the Levant, Africa, Europe, Scandinavia, and the Americas. 6,9,10,14,[17][18][19][20] Plaster can serve a structural function or an aesthetic purpose in buildings, 14 and it has also been used in cultic contexts as funerial coverings. 17 The types of aggregates found within a plaster specimen can provide information about what materials were available to people, how they reused materials, and how advanced their knowledge of the plaster production process was.…”

“…In fact, a handful of existing studies has demonstrated that plaster dating is quite problematic. One of the major impediments is that unburnt limestone, added either intentionally to increase bulk or unintentionally due to inhomogeneous heating during preparation, causes a dilution of the 14 C, which corresponds to artificially old dates. Furthermore, diagenesis of the plaster can change the 14 C levels, either higher or lower, by dissolution and contact with water that has a different isotopic composition than the plaster itself.…”

“…One of the major impediments is that unburnt limestone, added either intentionally to increase bulk or unintentionally due to inhomogeneous heating during preparation, causes a dilution of the 14 C, which corresponds to artificially old dates. Furthermore, diagenesis of the plaster can change the 14 C levels, either higher or lower, by dissolution and contact with water that has a different isotopic composition than the plaster itself. So far, the most accurate method to date a plaster with radiocarbon is to extract short-lived charred botanical remains, like seeds, and to date those inclusions.…”