北京明长城青砖毛细吸水性测定及其影响因素

长城是著名的世界文化遗产。近年来北京市文物局提出了长城文化带保护建设工作,且因水作为多孔材料青砖耐久性能的主要影响因素,其携带的侵蚀性介质会对青砖造成严重破坏,故需对长城主要承重材料-青砖的毛细吸水性进行研究。通过单面吸水法和卡斯特瓶法分别检测青砖的毛细吸水系数,发现卡斯特瓶法误差主要来源于水压影响和读数延迟;研究并建立了两种检测方法测试结果的关系方程或比例系数,可应用于不可取样长城青砖现场测试的毛细吸水系数转换为实际的毛细吸水系数的推算工作。此外,分析评估了环境温度、初始含水率、孔隙率和孔径4个主要因素对青砖毛细吸水性的影响,发现温度、孔隙率及孔径对毛细吸水性影响较大;且呈正相关关系,初始含水率则影响不大。

Study on Capillary Water Absorption of Grey Bricksof Ming Dynasty Great Wall in Beijing and Its Influencing Factors

The Great Wall is a famous world cultural heritage. In recent years, Beijing Municipal Bureau of Cultural Relics has proposed the protection and construction of the Great Wall Cultural Belt. As water is the main factor affecting the durability of porous materials, the corrosive media carried by water can cause serious damage to the materials. Therefor it is necessary to study on the capillary water absorption of grey bricks that are the main load-bearing materials of the Great Wall. In this paper, the capillary water absorption coefficient of grey bricks were measured by one-sided water absorption method and Custer bottle method respectively. It was found that the error of Custer bottle method came from the influence of water pressure and the reading delay. The relationship equation or proportional coefficient of the two test results were established. It can be applied to that the on-site test of capillary water absorption coefficient conversion to the actual capillary water absorption coefficient of grey bricks in the unsampled Great Wall section. In addition, the influence of four main factors, namely environmental temperature, initial moisture content, porosity and pore size on the capillary water absorption of grey bricks were also studied. It was found that temperature, porosity and pore size had a great influence on the capillary water absorption, and there was a positive correlation between them, while initial moisture content had little effect.