The effect of curing conditions (sealed and unsealed) on the pore solution composition and carbonation resistance of different binary alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes is investigated in this study. The studied mixtures were with FA/GBFS ratios of 100:0, 70:30; 50:50, 30:70, 0:100. Ordinary Portland cement (OPC) and Cement III/B (70 wt% of GBFS and 30 wt% OPC) pastes with the same precursor content were also studied to provide a baseline for comparison. Accelerated carbonation conditions (1% (v/v) CO2, 60% RH for 500 days) were considered for evaluating the carbonation resistance of the pastes. The results show a substantial lower [Na+] in the pore solution of the unsealed cured samples compared to the sealed cured samples. It is also found that unsealed curing of the samples leads to a faster carbonation rate. Additionally, it is observed that the carbonation rate decreases with increasing GBFS content independent of the curing conditions. The potential risks with respect to carbonation of the pore solution are also identified and discussed.@en

Carbonation of alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes has been investigated after one year of exposure to 0.038 % (v/v) CO2 at 20°C, 55% RH. In particular, the aim was to study the gel deterioration in the samples and changes of the compositions and proportions of the individual chemical domains after carbonation. For that purpose, a new method called PhAse Recognition and Characterization (PARC) [1] based on SEM-EDS elemental mapping was used. The paste bulk chemical composition was evaluated with PARC and XRF. The crystalline products of carbonation were determined and quantified with X-ray diffraction (XRD). Local microanalysis shows that carbonation of the pastes was occurring predominantly around GBFS particles (carbonation of Ca-(Na-)Al-Si-H+Mg gel) and throughout the gel (carbonation of Ca-(Na-)Al-Si-H and Ca-(Na-)Si-H). @en

Quantification of the CO2 binding capacity of reinforced concrete is of high importance for predicting the carbonation potential and service life of these structures. Such information is still not available for alkali activated materials that have received extensive attention as a sustainable substitute for ordinary Portland cement (OPC)-based concrete. To address this gap, this paper evaluates the CO2 binding capacity of ground powders of alkali activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes under accelerated carbonation conditions (1 % v/v CO2, 60% RH, 20°C) for up to 180 days. The CO2 binding capacity, the gel phase changes, and the carbonate phases are investigated with complementary TG-DTG-MS, FT-IR and QXRD techniques.@en

In this paper, PARC software was used to determine the spatial distribution of the dominant reaction products, their chemical composition and area/volume percentage in alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) pastes. The pastes reacted at different rates and dominant compositional domains were Mg rich gel around GBFS particles, i.e. Ca-(Na-)Al-Si+Mg, while the domains further form the GBFS and FA particles consisted mainly of Ca-(Na-)Al-Si. The reaction degree of GBFS and FA was calculated. Alkali-activated GBFS reacted faster in the studied alkaline conditions, reaching 66 % reaction at 28 days as GBFS contains 99 vol.-% of highly-reactive calcium and magnesium-rich aluminosilicates. The reaction degree in alkali-activated FA and GBFS paste was lower, as FA contains 31 vol.-% of nonreactive phases (quartz, mullite, hematite). The results obtained from PARC were compared with independent bulk analytical techniques X-ray fluorescence (XRF) and X-ray diffraction (XRD).@en