Incorporation of phosphogypsum in alkali-activated materials and their radon exhalation behavior

Abstract

From a sustainability point of view, alkali-activated materials (AAMs) are an interesting alternative for Ordinary Portland cement (OPC) in construction. Amongst other advantages, AAMs have the opportunity for the reuse of industrial by-products, in particular the ones containing silicium, aluminium, magnesium and calcium. Phosphogypsum, an industrial by-product originating from the phosphate industry, could be used for the production of AAMs. However, phosphogypsum typically contains high levels of 226-Ra (200-3000 Bq/kg), and thus its reuse requires a cautious attitude because it could increase the external gamma dose rate and any porous material containing radium forms a permanent radon source. The main goal is to produce innovative, environmental-safe AAMs, which integrate industrial by-products yet comply with necessary safety standards, such as the European Basic Safety Standards (EU-BSS). AAMs are produced based on ground granulated blast furnace slag (GGBFS) and phosphogypsum. The maximum wt% of phosphogypsum is incorporated based on the activity concentration index (ACI) defined in the EU-BSS. By varying synthesis parameters during AAM production, it is researched how they influence the radon exhalation behavior. Also, other properties, such as strength, porosity and specific surface area of produced AAMs are investigated. By varying synthesis parameters in the production of AAMs based on GGBFS and phosphogypsum, the radon exhalation was influenced. Positive correlation was found between the specific surface area of AAMs and their exhalation behavior. It is concluded that a proper selection of synthesis parameters can consolidate the radon immobilization of these particular AAMs in view of minimizing radiation exposure.