Testing Earthen Building Materials
Adobe is a building material obtained by adding straw or marsh plants to clayey and appropriate soil, remolding it with water, and then forming via molding and drying it in atmospheric conditions.
It is used as load-bearing, filling, and coating elements in the buildings. Since the raw material of adobe is soil and water, it has been preferred since ancient times. Adobe was widely used until the 19th century but has lost its prominence by the invention and development of industrial products such as brick, reinforced concrete, and steel. It is stated that 30% of the world population still live in adobe buildings nowadays. Proximity to raw materials, being easy workability, low costs and being environmental-friendly are the main reasons behind this preference.
Anatolia, along with neighboring Mesopotamia, Iran and Mediterranean civilization, is a region where the early examples of adobe findings, buildings and settlements were located and preserved as possible. Çatalhöyük (Konya), Aşıklı Höyük (Aksaray), Alacahöyük (Çorum), Hattusa (Çorum), Sargon’s Palace (Malatya), and Conical Dome Houses of Harran (Şanlıurfa) in our Turkey can be can be given as examples of structures built with adobe. Çatalhöyük and Hattusa are also included in UNESCO's World Heritage List as cultural heritage. There are many settlements with earthen architecture on the list throughout the world. For instance, Bam (Iran), Djenne and Timbuktu (Mali), and Shibam ve Sana’a (Yemen) is a city drawing interest with their unique earthen architecture.
Mudbrick structures have different construction techniques according to the geography where they are located. Adobe brick constructions are observed in central and eastern parts of Anatolia with arid and low rates of forestation; In the northern, western, and southern parts, which have a temperate or rainy climate and especially forested areas, there is a mudbrick filling between the timber structural frame. This construction system has been frequently used for dwelling in both urban and rural areas since the late Middle Ages. It has also formed the civil architecture of many areas in Anatolia and the Balkans since the 17th century. There are many examples of traditional houses with timber and adobe construction system in Turkey.
Adobe is affected by environmental and climatic conditions as it is a natural material. It is exposed to the corrosive effects of atmospheric conditions such as wind and rain weathering of atmospheric conditions such as wind and rain. Different methods have been developed to increase the strength of soil material. The oldest and most common among them is adding straw, reeds, fine aggregates of stone or ceramic pieces and other organic materials to the mud prepared to be dried in the sun.
Consolidation methods of adobe have varied in time due to technological development and the use of different raw materials. These can be classified as mechanical, physical, and chemical. Mechanical consolidation includes the selection of soils and interventions in block manufacturing and physical and chemical consolidation includes the additives to be added to the mortar. Improving particle size distribution of the soil and applying press and vibration during molding is a mechanical method and using both traditional and innovative materials such as organic fiber plant, cement, lime, gypsum, gypsum, and lime (Alker), pozzolan (pumice, silica fume, tuff, blast furnace slag, fly ash, etc.), wool, bitumen, industrial waste (resins, electrolytes and cellulose), glass fiber, air-entraining and inorganic fiber as additives are physical and chemical methods. In addition, using these methods jointly or separately affects the properties of adobe and increases its resistance especially against external factors.
Physical, chemical and mechanical tests are performed in the laboratory in order to characterize adobe material and and determine its durability properties. The investigations are divided into two as the selection of the soil to be used in mud-brick construction and the determination of the properties of the produced mudbrick. Samples can be created in the laboratory or on-site environment or can be obtained from historical buildings. According to TS 2514 ‘Kerpiç Bloklar Yapım ve Kullanma’, consistency test, tensile strength test, shrinkage test, sludging test, and compressive strength test are performed for determination of adobe soil, and compressive strength test and water dispersion test are performed for analysis of adobe. Although the standard has been repealed, it continues to be used in research. In addition, granulometric (sieve analysis) and hydrometry (precipitation analysis) analyses are preferred to determine the grain size distribution of the soil to be used and the silt and clay ratios in it. Various experiments are carried out on adobe samples in line with the data and technical possibilities that are desired to be obtained. Specific weight, composite ratio, moisture ratio, shrinkage test, capillary absorption, thermal conductivity coefficient and erosion resistance are determined for physical properties. Soluble salt, protein and oil tests, ignition loss, acid loss and sieve analyses are carried out for chemical and petrographic properties and images of aggregates and sections of the adobe are examined by stereo and polarized microscope. Compressive strength, flexural strength, modulus of elasticity and diagonal shear strength are conducted for mechanical properties.
In addition to researches performed in a laboratory environment, advanced techniques have also been used for the material characterization of adobe. The advanced analysis methods such as XRD (X-Ray Diffraction) used for mineralogical analysis, SEM-EDS (Scanning Electron Microscopy-Energy Dispersive Spectroscopy) used for microstructural and chemical analysis and MIP (Mercury Intrusion Porosimetry) used for the determination of pore size distribution.
