Project Portugal 2030

Summary

The research project "CO2Soil: Soil stabilization through CO2 mineralization” aims to develop an innovative, sustainable and environmentally friendly methodology to stabilise problematic soils (e.g. soft soils and loose sands), since it attempts to: (i) reduce the use of raw materials and energy consumption, due to the in-situ mixing of the soil with the stabilising solution; (ii) incorporate industrial by-products in the composition of the stabilising solution; (iii) contribute to decarbonisation of the human activity due to CO2 sequestration through the mineralisation process. The proposed methodology combines the use of mineral wastes generated by the stone extractive/processing industry with the use the carbonated solution (dissolution/fixation of CO2 in alkaline solution) to promote the precipitation of calcium carbonate (CaCO3) in the soil, inducing the development of bonds between the soil’s particles and the consequent improvement of the mechanical properties. From the mineral wastes generated in the extraction and/or the processing of stones, very rich in calcium oxide (CaO), it is possible to extract the calcium ion (Ca2+). In parallel, the CO2 previously captured from the atmosphere is dissolved and fixed in solution with the action of various fixing agents and under various conditions of pH, temperature and pressure, providing the carbonate ions (?CO?_3^(2-)) necessary to induce the precipitation of calcium carbonate, which occurs spontaneously. In order to achieve the proposed general objective, an intensive laboratory testing programme will be carried out, which is subdivided in three complementary phases, that corresponding to three secondary objectives. The first secondary objective will focus on the optimisation the process of CO2 dissolution and fixation in alkaline solution in order to have a stable carbonated solution with a high content of CO2. To achieve this objective a testing programme at the laboratory of the Chemical Engineering Department (UC) will be carried out aiming to study the effects of pressure, temperature, time and type of fixing agent on the CO2 dissolution and fixation process. The second secondary objective aims to evaluate the efficiency of the methodology proposed and to optimise the CaCO3 precipitation process through tests carried out in test tubes. The third secondary objective will be conducted at the Geotechnical Laboratory (UC) comprising a testing programme aiming to evaluate the mechanical performance of soil stabilized by CO2 mineralization using industrial waste, through the execution of monotonic and cyclic loading tests under different testing conditions. In parallel, the microstructure of the stabilised soil will also be studied through the interpretation of SEM ("Scanning Electron Microscopy") and EDS ("Energy Dispersive X-ray Spectroscopy") images. At the end of the experimental program a document with the general “Design Guidelines" will be produced, which is the final objective of research project, allowing it to be exploited in practical terms either by designers, practitioners and other researchers.