Preliminary study on wind slaked lime used before Qing Dynasty in China

ABSTRACT Historic lime mortars found in the masonry or architectural ruins before Qing Dynasty (1644–1912) show thicker bedding, higher strength, which may be related to the lime slaked by wind described by literature published before Qing Dynasty. The literature recorded that there existed two ways to slake lime: wind slaked and water slaked, which would have caused different properties. In order to assess the building lime properties slaked by wind, the quicklime produced by a lime manufacturer using traditional kiln techniques was collected, and then slaked by wind, mist spray and wet. The mineralogical studies show the calcium silicates like belite have been found both in quicklime and limes slaked by wind and mist. But no calcium silicates have been identified in the wet slaked lime. The lime slaked by wind has got higher strength, its compressive strength can reach 1.5 Mpa in 28 days stored in the indoor air climate, while it needs much shorter setting time. The preliminary results show that the performance of lime slaked by wind is similar to NHL2 classified by EN-459, if the quick lime is kilned from limestone with impurities. The wind slaked lime with higher strength and shorter setting time might have contributed to the magnificent constructions before Qing Dynasty in China. Both the literature and built heritage before the Qing Dynasty should be studied further. More comprehensive researches on wind slaking are needed in China in order to revitalise this traditional lime use combined with ancient wisdom for the economic conservation of built heritage in China.