Factors That Influence the Strength Developing during Carbonation of Mineral Waste Compacts

The carbstone process enables valorisation of non-hydraulic slags and ashes into high quality construction materials. The process makes use of accelerated carbonation by treating various kinds of slags with CO2 at elevated pressure (5-20 bar) and temperature (up to 140°C) without addition of binders. The carbonates that are produced in-situ during the carbonation reaction act as a binder cementing the slag particles together. The carbonated materials can compete with concrete products (C35/C45) and have excellent environmental and technical properties. The materials have the additional advantage of sequestering 180-200 g CO2/kg slag. In this process the mineral waste is stabilized and CO2 is permanently sequestered in the form of carbonates. However, in order to enhance the sequestration potential and further improve the quality of the building materials, it is essential to understand the factors that influence the development of strength during carbonation.

In a 4 year study the influence of several parameters (composition of raw materials, grain size distribution, moisture content, shaping of materials using different compaction pressures, temperature and pCO₂ during carbonation) on the carbonation rate and strength development of carbonated materials was investigated. In this paper two of these parameters, i.e. moisture content and pCO₂ pressure, that have a profound effect on the carbonation rate and strength development of the carbonated product will be discussed.