Effects of Deicing Salts on the Scaling Resistance of Concrete

Abstract

The scaling resistance of concrete with strength grades of 30 MPa (C30) and 50 MPa (C50) subjected to different types (A and B) and concentrations (3, 5, and 20%) of deicing salt solution were studied using an accelerated freezing-thawing test. Deicing Salt A was composed of about 80% sodium chloride and 20% calcium chloride, B was composed of 70% sodium chloride, 25% magnesium chloride and 5% calcium chloride. The changes in strength, mass loss and relative dynamic modulus of elasticity of concrete were examined during the testing. The results showed that the salt scaling resistance of C50 was better than that of C30. The former could pass 160 freezing-thawing cycles while the latter could pass only 95 cycles. Specimens showed the largest deterioration when subjected to 5% solution, and the smallest deterioration when subjected to 20% solution after 200 cycles. Deicing salts with a higher percentage of NaCl and CaCl2 demonstrated a more obvious deterioration effect on concrete. The incorporation of 5% silica fume (by the mass of binder) or 1% high-efficiency air entraining agent significantly improved the salt scaling resistance of the concrete, even no visible deterioration was observed after 200 cycles. The main scaling deterioration features of concrete include surface spalling and cracking. Microstructural examinations indicated that formation of Friedel’s salt resulting from chemical reaction between NaCl or CaCl2 and calcium aluminate hydrates could lead to the deterioration of concrete during salt scaling testing.