Consolidation effect of composite materials on earthen sites

Based on statistics provided by UNESCO, earthen ancient and traditional sites account for about 10% of the world’s cultural heritage. Unfortunately, of the world’s endangered heritage, these earthen sites make up 57%. Generally, as earth by itself is not a resilient material, continuous exposure to recurrent decay, such as; surface stripping, fissures, gullies, and collapses, has left majority of these sites in a deplorable state. For instance, in China, the Great Wall has undergone severe decays subject to variations in humidity and temperature, hence threatening its durability and preservation. Soil has low mechanical strength hence high solubility in water. Consequently, this reduces the stability of the wall. Therefore, it is imperative to reinforce and repair soil ruins. Several consolidation techniques have over the years been proposed to rehabilitate soil failures. Recently, weather resistant consolidating materials have gained interests. Unfortunately, as there is no single consolidation product that is universally applicable for the protection of earthen sites, there is need to assess the suitability of combined consolidation products, using simple and practical methods for heritage consolidation.

In this view, a team of researchers led by Dr. Wenwu Chen from the School of Civil Engineering and Mechanics, Lanzhou University conducted thorough study in which a comparison of the effectiveness of single and composite materials was undertaken with the purpose of establishing whether composite materials were potential candidates for use in conservation. Particularly, they focused on assessing various consolidation treatments so as to determine the suitability of composite materials for future use in the consolidation of earthen sites. Their work is currently published in the research journal, Construction and Building Materials.

The authors first, considered developing a composite composed of organic and inorganic materials in different orders based on existing materials. Soils from the Great Wall of Yongchang, Gansu Province, China, were treated with five types of materials, namely, inorganic materials, organic products, composite materials composed of organic and inorganic materials in different orders, and ethanol. Changes in the color, weight, mechanical properties, water resistance, microstructures, and element composition were evaluated after treatment. Finally, synthetic evaluation was conducted using the obtained results.

The researchers observed that Better reinforcing effects were obtained by applying an organic material and then using an inorganic material. In addition, they noted that the consolidation effect of inorganic materials was much weaker than those of the composites. Compared with organic materials, organic + inorganic composites exhibited a much lesser change in color, and improved compatibility in appearance of the organic materials. Other results indicated that organic + inorganic composite materials with half the amount of organic materials and half the consumption of inorganic materials yielded obviously enhanced surface hardness, P-wave velocity, unconfined compressive strength, and water resistance.

In summary, Dr. Wenwu Chen and colleagues presented results of laboratory tests conducted on six groups of samples, in a bid to analyze the differences in the strengthening performance between composite and traditional single materials. Based on experiments conducted, the obtained results proved that the consolidation effect of certain composites was better than that of single materials. Altogether, more work considering other parameters such as wind effects, temperature and humidity is necessary as this study was exclusively done under controlled laboratory environment.