Effects of sodium chloride on the mechanical properties of slag composite matrix geopolymer

In this paper, neutral salt sodium chloride (NaCl) was used as an activator for geopolymer, a slag composite matrix. Compressive tests, scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analytical tests were carried out to measure the unconfined compressive strength, observe the microstructure and analyse the composition of hydration products of the sodium chloride-added geopolymer. The results showed that its strength, for most mixes, met the standards for 32·5 grade slag Portland cement. The mechanism of the strength increase of the slag composite matrix geopolymer by adding sodium chloride was a result of sodium ions and chloride ions being engaged separately in hydration reactions with the slag composite matrix geopolymer, which generated new strengthening hydration products such as tabular-, needle- and rod-shaped crystals (3CaO·Al₂O₃·(xCaCl₂·yCaSO₄)·12H₂O), and zeolite ores (0·8CaO·0·2Na₂O·Al₂O₃).