The reduction of pH from ~12.5 to ~9 by carbonation of the pore solution of reinforced cementbased concrete structures results in the reinforcement corrosion. The rate of carbonation is an important input for design of the concrete cover depth and the service life prediction of reinforced concrete structures because the initiation of reinforcement corrosion is usually considered as the end of service life of concrete infrastructure. The information from the field carbonation of alkali activated concrete is in most cases limited and related to exposure shorter than 40 years. In this paper, a comparative study regarding accelerated and natural carbonation of alkali-activated concretes and cement-based concretes has been carried out. The pH and carbonation depths are periodically measured. The results show that, despite the low porosity of alkali-activated concrete with 50 wt. % slag, these concretes must have an appropriate curing in order to be used in exposure classes where carbonation is an issue, due to their lower carbonation resistance compared to cement-based concrete. Regardless the exposure conditions, the pH of carbonated alkali-activated concrete was maintained above 9. Finally, recommendations for alkali activated concrete applications and their improved carbonation resistance are given.@en

The aim of RILEM TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories.@en

The use of alkali-activated slag (AAS) has been recognised for a long time as an alternative solution to Ordinary Portland cement-based binders. However, the durability of AAS-based binders is still unknown1, which limits their application in engineering practice. Carbonation is of the great interest for AAS since it induces both chemical and physical changes. The change of the pore structure after carbonation and CO2 uptake for AAS are rarely reported. This paper investigates the carbonation of AAS pastes in natural (laboratory and outdoors (unsheltered)) and accelerated conditions. The effect of the different exposure conditions on AAS pastes was studied in terms of the gel pore structure, chemical and mechanical properties.@en

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 CO2 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 CO2 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 CO2 to diffuse and further react with binding phases.@en

Carbonation of the pore solution in alkali-activated materials (AAMs) produces alkali and/or alkali-earth carbonates. When the carbonate solubility in the water is very high (case of the most alkali carbonates), it is very hard to determine the carbonation depth in AAMs with the phenolphthalein indicator frequently used in Ordinary Portland Cement (OPC)-based materials. Carbonation gradually decreases the alkalinity of the pore solution, while the color after spraying phenolphthalein changes from colorless to pink when pH< 13 and changes back to colorless when pH< 8.2. The color change with phenolphthalein indicator may still exist in the less alkaline areas where carbonation may have already occurred. Therefore, using the indicator test is likely to underestimate the depth to which carbonation reaction has occurred in AAMs and more complete assessment is required. This study investigates the carbonation front in alkali-activated fly ash (FA) and blast furnace slag (BFS) pastes in natural laboratory conditions. Monitoring carbonation front in the samples after one year of exposure has been carried out under polarized light microscope (PLM), and environmental scanning electron microscope (ESEM). The carbonation products were sharply distinguished from the other constituents of the paste, by their crystallographic and optical characteristics under PLM, and characterized by X-Ray diffraction (XRD). @en