Effect of Ca(OH)2 Addition on the Engineering Properties of Sodium Sulfate Activated Slag

Abstract

Alkali-activated slag is considered as a sustainable construction material due to its environmentally friendly nature. To further promote the sustainable nature of alkali-activated slag, a sodium sulfate activator is suggested to be used since it can be obtained naturally and generates lower greenhouse gas emissions. However, the mixtures activated by sodium sulfate exhibit low early strength and very long setting times. This study investigates the effects of calcium hydroxide (Ca(OH)2) addition on some engineering properties such as rheology, setting time, mechanical properties, porosity, and microstructure of sodium sulfate activated ground granulated blast furnace slag (GGBFS). Furthermore, the changes of chemical groups in reaction products and phase identification have been evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Test results showed that Ca(OH)2 addition can substantially increase the reaction rate and the compressive strength at early ages. In addition, the very long setting times of the sodium sulfate-activated mixtures were shortened by the addition of Ca(OH)2. SEM analysis confirmed that the incorporation of excessive amounts of Ca(OH)2 could lead to a less well-packed microstructure although the reaction degree of GGBFS remained the same at later ages as compared to the sodium sulfate mixture. It was also revealed that in case of the Ca(OH)2 addition into sodium sulfate activator, the main reaction products are chain-structured C-A-S-H gels and ettringite.

Effect of sodium sulfate activation on the early age behaviour and microstructure development of hybrid cementitious systems containing Portland cement, and blast furnace slag

“…Some authors pointed out that the availability of SCMs is not sufficient to fully supply the future demand of cement [10]. In addition, some drawbacks have been reported for its application, with the main focus on operative issues like long setting times, poor early strength development and high (accelerated) carbonation rate due to the low content of carbonatable phases of these systems (when compared to PC concrete mixes) [11]- [14]. None of these problems are an issue when using sodium silicate / hydroxide as activator.…”

Using Fumed Silica to Develop Thermal Insulation Cement for Medium–Low Temperature Geothermal Wells

“…The CS of FS10V50 was increased to 5.85 MPa by adding 10% SR-RA but decreased by adding 10% Ca(OH) 2 . The addition of CH shortened the setting times but decreased the CS, resulting from that excessive CH addition can increase the early reaction rate but is not effective in improving the reaction rate at the later ages [ 90 , 91 ]. Furthermore, it is believed that excessive calcium hydroxide reduces cement strength, as excessive alkali adsorption on the surface of cement particles prevents hydration [ 92 , 93 ].…”

Phase Evolution of Hybrid Alkali Sulfate-Activated Ground-Granulated Blast Furnace Slag Cements

“…This mechanism also explains why the addition of portlandite powder in minor quantities enhances the early age dissolution of GGBFS, but the further dosage increase has almost no effect in the reaction kinetics. 28 These are interesting results because the sole analysis that mixing sodium sulfate and PC reduces the portlandite formation could lead to a misleading prediction of a lower DoR of the GGBFS. In reality, the sole increase in the pH in the pore solution will have a more beneficial effect in terms of GGBFS dissolution.…”