Microstructure and Strength Development of Sodium Carbonate–Activated Blast Furnace Slags

Abstract

This paper presents the study of alkali activated slags where sodium carbonate acts as a primary activator. The slow activation mechanism of sodium carbonate is accelerated by sodium hydroxide and with traces of calcium hydroxide. Strength development and the progress of hydration of the mixes are studied with the phase transformation and development of microstructural features through quantitative techniques such as thermogravimetric analysis and phase-identification techniques such as Fourier transform infrared spectroscopy and X-ray diffraction. Sodium carbonate replacement with sodium hydroxide and the presence of calcium hydroxide in the binder as a replacement of the slag enhances the rate of dissolution of slag leading to a faster strength development. Calcium hydroxide is significantly increased the compressive strength even at early age. On the other hand, sodium hydroxide substitution is effective at later ages of the reaction when used at high dosages (e.g. 40%). Formation of strength giving phases such as hydrotalcite and calcium aluminum silicate hydrate are confirmed with the microstructure analysis and explains the strength development.

Utilization of sodium carbonate activator in strain-hardening ultra-high-performance geopolymer concrete (SH-UHPGC)

“…Compared to Na 2 SiO 3 , sodium carbonate (Na 2 CO 3 ) can be a promising substitution with lower environmental impact, together with wide availability and chemical stability, and success has been achieved in utilizing Na 2 CO 3 in the production of normal-strength geopolymer (Krivenko, 1994;Xu et al, 2008;Abdalqader et al, 2016;Akturk et al, 2019). It is noted that Na 2 CO 3 is exclusively manufactured by the Solvay process, where the CO 2 in the air can even be captured and reduced (Lackner, 2002;Huijgen and Comans, 2003).…”

Improving the carbonation resistance of Na2CO3-activated slag mixes via the use of reactive MgO and nucleation seeding

“…The activation of slag is initiated by the dissolution of the solid powder in the presence of an alkaline activator, followed by the formation of magnesium aluminum hydrotalcite (i.e. referred to as "hydrotalcite" throughout the manuscript) and the polycondensation of C-(A)-S-H with a low C/S ratio [2][3][4][5][6]. The alkaline activators commonly used in AAS mixes (e.g.…”

Influence of various additives on the early age compressive strength of sodium carbonate activated slag composites: An overview

“…Kovtun et al [34] also reported approximately 8 MPa and 23 MPa increase when SH was used as 20% and 50% replacement of the SC. The study by Akturk et al [28] where SH was used up to 40% replacement of SC also showed an enhancement in the early age compressive strength. The effect of various replacement levels of SC with SH on the 7 days compressive strength of SC activated slag from various studies is presented in Figure 7.…”

“…Calcium hydroxide also referred to as hydrated lime or slaked lime (LM) is one of the additives that can be incorporated into SC activated slag to reduce the carbonate ions and increase the alkalinity of the system [23]. The study by Akturk et al [28] showed that the use of LM as a 3% replacement of the slag in SC activated slag resulted in significant enhancement of the early age compressive strength as presented in Figure 2. The presence of LM in the system also increases the rate and amount of calcium aluminate silicate hydrate formation which is a reaction that contributes to the strength capacity of the composite [24].…”

“…The possible reaction of SC with calcium hydroxide similar to that of calcium oxide mentioned early might also have contributed to the enhanced 1-day compressive strength observed. Akturk et al [28] also investigated the effect of the combined use of SH and LM on the strength development of SC activated slag. The SH was used as partial replacement of SC up to 40% while the LM was used as a 3% replacement of the slag.…”