ABSTRACT
The onset of the destruction mechanism of exterior concrete walls in maritime winter climatic conditions is characterised by the following stages: the appearance of damp spots on the interior surface, peeling of the exterior surface, the appearance of cracks on the exterior surface, water saturation and finally spalling of the exterior concrete surface. Failure of the heat insulation properties begin at the stage of water saturation. The cause
of failure is the layering of the wall at the freezing depth. A network of microcracks develop in the longitudinal cross-section at the freezing depth; later these micocracks develop into a cavity. Thus, the wall thickness decreases, it’s moisture permeability increases and the heat insulation characteristics deteriorate until failure. Surplus moisture inside the exterior layer of the wall forms a cryophase volume as the exterior temperatures drop, resulting in critical expansion stresses in the concrete structure. The existence of atmospheric salts in the pore system aggravates the situation because of the appearance of osmotic pressures which increase the expansive stresses; as the exterior temperatures drop the effect increases. Destructional self-excited oscillation of the concrete matrix in the process of its saturation with atmospheric salt solutions is considered to be the prerequisite for the development of these defects. Cement paste gel allows the passage of salt ions but retains water molecules in a process of capillary infiltration. This gives rise to solutions with high and low concentrations on both sides of the semi-permeable gel membrane. The process of capillary infiltration during the balancing of the concentrations can be observed by following the penetration of chloride ions in the opposite direction. Migrational fluxes of the salt solutions through the semipermeable membrane in forward and reverse directions give rise to negative forces in the concrete matrix.
