Properties, characterization, and decay of sticky rice–lime mortars from the Wugang Ming dynasty city wall (China)

Sticky rice–nanolime as a consolidation treatment for lime mortars

“…9c, d), as reported in the literature [4,15]. However, the morphology and size of those calcite crystals were not reduced in size, as reported in studies of both ancient and recent Chinese lime-mortars with sticky rice [4,9,10,[17][18][19]. The calcite crystals were found to be similar to the ones observed in preliminary studies with the same nanolime [24].…”

“…The presence of the sticky rice may increase biocolonization of the treated area, since it is close to the surface, and needs to be considered. In the traditional method where the sticky rice was added during the lime quenching, bacteria were eliminated by the released heat [7,10]. In the present situation, where the SR is applied directly to the object biocolonization may develop faster, especially in areas where moisture prevails.…”

“…Other researchers found that the optimal sticky rice proportion when added to the lime mortar could vary from 1 to 3% [4] to 5% of sticky rice [7]. Further studies also showed that the formation of a more compact microstructure of smaller sized calcium carbonate crystals increases the mechanical properties, as calcium carbonate crystals are covered with a layer of sticky rice thus improving their resistance to weathering processes [4,9,10,[17][18][19]. The covering of the calcite crystals by the sticky rice in the mortar was also found to reduce the penetration of water in the structure and increase its resistance to wet-dry cycles [8,18].…”

“…The sticky rice mortars were used in many historical buildings completed during the Ming (1368-1644) and the Qing (1644-1911) dynasties, such as the dyke at the Hangzhou Bay where the Quiantan river drains or the Jingzhou Historic Town Wall, one of the best preserved and largest historic town walls in Southern China that survived to date, [3,[7][8][9][10][11]. The earliest record of sticky rice-lime mortar was found in the ancient building book Tian Gong Kai Wu which was written during the Ming Dynasty (1368-1644 AD) [12].…”

“…Most of these studies differ in how the sticky lime mortars were reproduced, as they varied significantly from the traditional approach where sticky rice solution was added to the quicklime during quenching: ''Usually, lime reacts with water to generate hydrated lime with emission of a lot of heat and simultaneously create alkaline environment that can effectively suppress and kill bacteria'' [7,10] thus explaining why sticky rice did not undergo biodeterioration over time. Most studies use commercial hydrated lime [4,8,16], or slaked lime [15], while others prepared the ''lime'' solution by reacting a calcium chloride (CaCl 2 ) solution with Na(OH) [19] and in some cases using a supersaturated solution of this mixture and artificially carbonating it [3].…”