Influence of sodium hydroxide on the performance and hydration of lime-based low carbon cementitious materials

Abstract To increase the recycling of industrial solid waste in cement-based materials, lime-based low carbon cementitious materials (LCM) as green binder materials have shown bright prospects. To further improve the properties of LCM, different dosages of sodium hydroxide as alkali activators were mixed with LCM in the test, and this study focused on the influence of sodium hydroxide on the performance and hydration of LCM. The strength, workability, hydration and microstructure of LCM in the presence of sodium hydroxide were investigated in detail and compared to those of the original LCM. The test results indicated that the minor amounts of sodium hydroxide remarkably improved the mechanical properties of LCM at early ages (3 and 7 days). Additionally, the further hydration of mineral admixtures was affected by the presence of sodium hydroxide, which resulted in a slight improvement of the mechanical properties of LCM at the later stage. The formation of ettringite in the hydrates of LCM was suppressed by the addition of sodium hydroxide. Moreover, the Ca/Si ratio of the C-(A)-S-H gel formed in the sodium hydroxide activated LCM was lower than that in the plain LCM, and a minor amount of C-(N)-A-S-H gel formed in the hydrated paste due to the Na uptake in the C-A-S-H gel. Therefore, sodium hydroxide modified the composition of hydrates in the LCM to a certain extent during the hydration process.