Research on the Modification of Two Traditional Building Materials in Ancient China

Article excerpt

Authors: Li Zuixiong [1,3]; Zhao Linyi (corresponding author) [1,3]; Li Li [2]; Wang Jinua [2]

Introduction

In the late 1970s, a group of residential remains of the Yangshao Period were discovered at the Dadiwan site in Qin?an County, Gansu Province, China [1]. One of these discoveries is named as ?original palace? (number F-901) in the archaeological world, and is the largest and top leveled residential site in prehistoric times. This site belongs to the middle Yangshao Period and was used for convocation, worshiping and religious ceremonies by tribes or tribe allies over 5000 years ago. When it was discovered, the site had a bright and clean house floor that was of exquisite workmanship. Preliminary research [2] indicates that the housing floor of the site was made by lightweight calcined Kunkur as aggregate and the powder of calcined ginger nut mixed with a small amount of laterite as bonding materials. After more than five thousand years, the compressive resistance of the floor is close to that of cement mortar No.100. Moreover, the remains of kilns for burning light weight concrete and ginger nut were discovered nearby the site. The research shows that the calcinated temperature of ginger nut could reach up to 900[degrees]C [3]. Ginger nut is a type of ginger stone (locally called as ginger nut) in quaternary loess and is composed of 60-80% calcium carbonate and 10-20% clay mineral. When ginger nut is calcinated at a temperature of 900[degrees]C, it will produce 25.8% [beta]-CaSiO[sub.3], 17.6% Ca[sub.2]Al[sub.2]SiO[sub.7] and 33.9% CaO. [beta]-CaSiO[sub.3] and Ca[sub.2]Al[sub.2]SiO[sub.7] are hydraulic binding materials, and CaO is a non-hydraulic binding material [4]. Therefore, the building materials of F-901 floor in which manmade hydraulic binding materials had been used can be called as the earliest ?concrete? in the world, which is a miracle in the history of architecture [3].

Aga soil is another kind of silicate building material widely used in Tibet, and it is the siliceous limestone [5] that contains 70?~?93% CaCO[sub.3] and 7?~?30% SiO[sub.2]. When Aga soil is used as building material for floor and house (roof), the unburned Aga soil with 40% in a diameter of 5.6 mm, 30% in a diameter of 2.6 mm and 30% 0.15 mm diameter will be made to pulp at the ratio of 0.32 water and then is rammed by a special stone pester. Until the grout completely becomes solid, it will be sanded first and then repeatedly polished with sheepskin and butter. This technique is called ?ramming Aga? [6], and for centuries, this traditional material and building technology have been used to construct floors and roofs of temples in Tibet.

In Tibet, there are over one thousand temples that are very valuable cultural relics, such as the well-known Potala Palace, Norbulingka Summer Palace and Sakya Monastery. The Chinese government attaches great importance to the conservation of Tibetan cultural relics. In the last two decades, two large projects for the conservation and restoration of key relics including the Potala Palace and Sakya Monastery have been carried out [5, 7]. The restoration work focuses on ancient buildings and murals, and the main kinds of deterioration are associated with Aga soil used in the roofs. In Tibetan, traditional materials for the roofs of the temple are unburned Aga soil that was crushed into the powder of 0.15 mm in diameters as ?gelation? and it was mixed with proper amount of natural gum [6] to make mortar. But unburned Aga soil has low strength and poor weathering resistance but the property of chemical gelatinization. Influenced by the freezing and thawing cycles and the fluctuating temperature and humidity, the natural gum will quickly deteriorate and break. When the rain infiltrated through the cracks, wooden components will decay, fall apart or become leaning, causing subsequent deterioration, such as detachment, large-area loss, disruption and flaking, and thus terribly damaging the murals [7]. …