| Salt scaling is superficial damage caused by freezing a saline solution on the surface of a cementitious body. The damage consists of the removal of small chips or flakes of binder. The discovery of this phenomenon in the early 1950's prompted hundreds of experimental studies, which clearly elucidated the characteristics of this damage. In particular it was shown that a pessimum salt concentration exists, where a moderate salt concentration (∼3%) results in the most damage. Despite the numerous studies, the mechanism responsible for salt scaling has not been identified. In this work it is shown that salt scaling is a result of the large thermal expansion mismatch between ice and the cementitious body, and that the mechanism responsible for damage is analogous to glue-spalling. When ice forms on a cementitious body a bi-material composite is formed. The thermal expansion coefficient of the ice is ∼5 times that of the underlying body, so when the temperature of the composite is lowered below the melting point, the ice goes into tension. Once this stress exceeds the strength of the ice, cracks initiate in the ice and propagate into the surface of the cementitious body, removing a flake of material. The glue-spall mechanism accounts for all of the characteristics of salt scaling. In particular, a theoretical analysis is presented which shows that the pessimum concentration is a consequence of the effect of brine pockets on the mechanical properties of ice, and that the damage morphology is accounted for by fracture mechanics. Finally, empirical evidence is presented that proves that the glue-small mechanism is the primary cause of salt scaling.; The primary experimental tool used in this study is a novel warping experiment, where a pool of liquid is formed on top of a thin (∼3 mm) plate of cement paste. Stresses in the plate, including thermal expansion mismatch, result in warping of the plate, which is easily detected. This technique revealed the existence of stresses from several other sources, including thermal expansion mismatch between the pore water and the solid cement, and wedging of cracks by newly formed ice.; To analyze the experimental data from the warping experiment, it was necessary to measure several material properties. Results from these measurements were used to substantiate a recent analysis of the beam bending experiment, which is a technique for measuring permeability. In addition, these results indicated that thermopermeametry, another technique for measuring permeability, was applicable to rigid materials. Comparison of the permeability measured by these two techniques indicated that the pore fluid in cement paste exhibits anomalous thermal expansion. Finally, the cause of swelling when cement paste is exposed to salts was investigated. |
