The microstructure and sulfate resistance mechanism of high-performance concrete containing CNI

Abstract

It is found from previous studies that the incorporation of calcium nitrite inhibitor (CNI) together with mineral admixtures could weaken the resistance of mixtures to sulfate attack. To better understand the mechanism of this phenomenon, the influence of CNI on the microstructure of cement-based materials is studied by means of quantitative X-ray diffraction, mercury intrusion porosimetry, and scanning electronic microscopy technique. The test results demonstrate that the incorporation of CNI accelerates the formation of calcium hydroxide and ettringite crystals, and weakens the pore refinement effect caused by the secondary hydration reaction of fly ash and microsilica. At the age up to one year, the relative crystal quantity in mixture containing CNI is always higher than that in control mixture without CNI. The reasons for the degradation in sulfate resistance of mixtures may be attributed to the increase of the calcium hydroxide and ettringite crystals formed, the increase of micropore size and the degradation of secondary hydration reaction. Based on the experimental results, conclusion can be drawn that NCI should be used cautiously in practical engineering when high resistance to sulfate attack is required.