Effect of Chloride Concentration on the Freeze-Thaw Resistance of Concrete

Performance test methods intend to provide a fast, accurate and precise determination of a particular building material property and thus determine the associated material performance. In concrete, various performance tests are used to classify existing or to approve new materials, to compare concrete compositions or to determine causes of damage in existing structures. The challenge of such test methods is to accelerate natural (very slow) mechanisms to determine the material performance precisely within a short time. However, the attack on the material must not be unrealistically intensive, but must represent reality, just in fast motion. The performance tests used to demonstrate the freeze-thaw resistance of concrete employ a 3% NaCl solution, with literature data ranging from 1% to 10% showing that low concentrations can result in higher surface scaling. In this paper, mortar and concrete specimens are tested at 0, 1, 3, 6, and 9% NaCl solution following the CDF procedure (DIN CEN/TS 12390-9:2017-05). The results are discussed against the background of the existing literature and show that the damage is critically dependent on the pore system and thus also on the effect of the micro-ice lens pump. With increasing freeze-thaw exposition, the pessimum in the external damage shifts towards a de-icing salt concentration of 6%. Furthermore, a novel test methodology based on 3D-laserscanning is presented to determine scaling accurately by eliminating side effects that are typically present in current standards.