Comparing ion diffusion in alternative cementitious materials in real time by using non-destructive X-ray imaging

Abstract

Alternative cementitious materials (ACMs) are receiving increasing attention worldwide but there is a lack of knowledge around the resistance of these materials against harmful ion intrusion. In addition, current accelerated test methods that measure ionic diffusion under an electric field are not reliable when comparing binders with vastly different pore solution chemistry. This paper overcomes these issues by using laboratory transmission X-ray microscopy (TXM) and micro X-ray fluorescence (μXRF) imaging to make real-time measurements of ion diffusion in paste and mortar samples for five commercially available ACMs and an ordinary portland cement.The results compare the apparent ion diffusion rate, quantify the change in the ion diffusion rate over time, and give insights into ion binding. The results show that after 42 d of ion exposure that the samples made with calcium aluminate cement had the lowest rate of ion penetration while the samples with alkali activated and calcium sulfoaluminate cement had the greatest rate of ion penetration. The portland cement had an ion penetration level that was between these two. Also, both the alkali-activated and calcium sulfoaluminate samples showed a decrease in the rate of penetration over time. These measurements are important to quantify the sustainability of ACMs, better justify their uses where durability are a concern, and guide future durability testing for these promising materials.