Changes in the Microstructure during Weathering and by Using Different Additives

Before the Second World War, building details made from rammed concrete with precise shape and surface like sandstone had been widely used in large regions. They were used as basic decorative materials in the buildings of style Art Nouveau from Scandinavia to the Black Sea. A production technique to manufacture architectural details from rammed concrete was traditional in northern countries, although, forgotten nowadays. This production method was renewed by “Pamats” Ltd in 1991. The rammed concrete details are invaluable material for restoration works and architecture, particularly in the regions of style Art Nouveau (Figure 1,2). Such material with high surface quality is being used for restoration, in modern interiors, in garden architecture, etc. Deterioration and corrosion of rammed concrete surface are influenced by water migration during exposition in the atmosphere. Manual work and low quality of raw materials are reasons for creating cracks, discrepancies of the structure and surface, appearance of light patches of crystalline salts on the surface, and other defects. Investigations of microstructure, chemical microanalysis, pore size distribution and physical properties of standard samples, natural and artificial weathered samples were carried out. The porosity and major pore sizes of weathered concrete are larger than ones of standard sample. Light patches of crystalline salts in the structure and on the surface of weathered concrete were observed. According to the chemical analysis, light crystalline is water-soluble compound containing Ca ions. Ions of these compounds shift from structure to surface of concrete together with water. The commercial additives and fly ash were used to increase the durability and surface quality of rammed concrete details. According to the data of investigation, commercial additive of Microsilica was defined as the most perspective additive for limiting corrosion and migration of Ca ions to concrete surface