Carbonation Resistance of Alkali-Activated Slag Under Natural and Accelerated Conditions

Abstract

In this paper, carbonation resistance of alkali-activated slag (AAS) pastes exposed to natural and accelerated conditions up to 1 year was investigated. Two aspects of carbonation mechanism were evaluated. The first was the potential carbonation of the main binding phases in finely powdered AAS pastes. The second was the reactivity and diffusivity of CO 2 within the bulk AAS paste. From Fourier transform infrared spectroscopy and thermogravimetric analysis coupled with mass spectroscopy time-series measurements, it was found that powdered AAS was largely carbonated within 28 days with a CO 2 uptake of 14 wt%. The main carbonation products were calcium carbonates. Nevertheless, the bulk paste samples were highly resistant to carbonation, regardless of the exposure conditions. The findings showed that the pH value (initial pH [ 12) and strength of the samples did not decrease under accelerated carbonation compared to those of the samples exposed under natural conditions. The mineralogy of the samples in these two carbonation exposures did not alter either, except for outdoor conditions. The gel pores were dominant in the pastes (pore size in range of 2-15 nm). The dense microstructure was the main barrier for CO 2 to diffuse and further react with binding phases.

Effect of curing conditions on the pore solution and carbonation resistance of alkali-activated fly ash and slag pastes

“…These are indirectly supported by the previous study of the authors where it was shown that paste S100 has a different compressive strength development in sealed and unsealed curing conditions [42].…”

Physical and Chemical Relationships in Accelerated Carbonation Conditions of Alkali-Activated Cement Based on Type of Binder and Alkali Activator

“…Figure 7 shows the decomposition temperature of hydrates and carbonates in TG/DTG [ 32 ]. Figure 8 , Figure 9 and Figure 10 show the TG/DTG results for accelerated carbonation of each specimen.…”

“…In the case of the BFS/FA blend, it is known that C–(N)–A–S–H and N–A–S–H gels are formed simultaneously; hence, it can be assumed that not only the Na + concentration but also the structure of the gel formed due to the type of binder would affect the crystallinity of the CaCO 3 produced under accelerated carbonation conditions. From the results of the F100 sample shown in Figure 10 , the difference between the decomposition amounts of 100–200 °C at high and low levels of Na + concentration is confirmed [ 32 ]; this difference is considered to depend on the degree of formation of the N–A–S–H gel. In addition, the decomposition from sodium bicarbonate or sodium carbonate is slightly increased owing to the overall carbonation level, and this increase is remarkable in specimens with high Na + concentrations.…”

Improvement in Carbonation Resistance of Portland Cement Mortar Incorporating γ-Dicalcium Silicate

“…e noncarbonated samples show weak peak at 3640 cm − 1 , which corresponds to H-O stretching vibrations of Ca(OH) 2 . e peak near 950 cm − 1 corresponds to the Q 2 vibration of the v 2 Si-O bond in the hydrate product-C-S-H [32,33]. e calcium carbonate formed by the reaction of the powdered specimen with CO 2 in air is also reflected in the FT-IR spectra.…”