Carbonation rates of alkali-activated and cement based concretes

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.Materials and Environmen

Carbonation rates of alkali-activated and cement based concretes

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

Carbonation rates of alkali-activated and cement based concretes

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.Materials and Environmen

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

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.Materials and Environmen