Effect of using calcined clays, silica fume and limestone powder on the compressive strength and chloride binding capacity of cementitious pastes

Document Type : Research Article

Authors

1 Department of civil and environmental engineering, Amirkabir university of technology, Tehran, Iran.

2 Department of civil and environmental engineering, Amirkabir university of technology, Tehran, Iran

Abstract

Chloride ions ingress is one of the major reasons for the deterioration of reinforced concrete structures, particularly those exposed to marine environments. The use of supplementary cementitious materials (SCM) has been introduced by many researchers as a practical approach to reducing corrosion of embedded steel caused by chloride ions penetration. In addition to the effects of SCM on transfer properties of cement-based materials, their influence on the binders' chloride binding capacity should be studied to evaluate the durability of mixtures against chloride attack. In this investigation, the chloride binding capacity of pastes containing silica fume (SF), limestone powder (LS), and three samples of calcined clays (CC) as SCMs, have been compared with Portland cement (PC) paste. The chloride binding capacity has been measured by the equilibrium method for samples submerged in different concentrations of NaCl solution (0.1, 0.3, 0.5, 1 and 2 molar) for 42 days. Furthermore, compressive strength tests after 7, 28 and 90 days of curing, X-ray diffraction (XRD) analysis, and Friedel’s salt (FS) quantification by thermogravimetric analysis have been carried out. Results indicated that by increasing the kaolinite contents of raw clays, the chloride binding capacity and FS amounts of samples submerged in 2 M NaCl solution have been increased up to 242.5% and 169.5%, respectively. While, samples with LS and SF had generally lower chloride binding capacity than PC paste. The 10% replacement of PC by SF and LS led to 37.5% and 9.8% lower formation of FS in samples submerged in 2 M NaCl solution.

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