THE MICRO ICE LENS PUMP - A NEW SIGHT OF FROST ATTACKAND FROST TESTING

摘要

Frost damage is primarily caused by the expansion of ice and the resulting hydraulic pressures. However, damage can only occur if at least locally a critical degree of saturation is reached. In most concrete building components this condition is not reached even after a long period of isothermal capillary suction. Freeze-thaw cycles lead to an additional saturation. In this contribution the micro ice lens model is described and based on it the micro ice lens pump. Using an improved thermodynamic description the conditions are defined, under which the triple phase equilibrium of pore water, pore ice and vapor is stable in a region between 0°C and -60°C. For this primarily a negative pressure in the unfrozen gel pore water must be generated which increases with every Kelvin below freezing point by 1.22 MPa. During cooling water migrates from gel pores to ice and the gel shrinks. During heating the gel expands again and sucks water from external sources since the bulk ice is still frozen. The micro ice lens pump leads to an additional saturation. Frost attack and freeze thaw testing are therefore, primarily processes of saturation. Destruction sets in only after a critical value is reached. The internal damage is primarily due to these physical processes. In scaling chemical and physical effects are superimposed. Both are quantified by CDF-/CIF-test with high precision and reproducibility. Consequences are shown.