Elastic and Transport Properties of Steam-Cured Pozzolanic-Lime Rock Composites Upon CO2 Injection

Abstract:

Understanding the relationship between pozzolanic ash-lime reactions and the rock physics properties of the resulting rock microstructure is important for monitoring unrest conditions in volcanic-hydrothermal systems as well as devising concrete with enhanced performance.

The recent discovery in the depths of the Campi Flegrei volcanic-hydrothermal systems of a natural process forming a fiber-reinforced, concrete-like rock with enhanced elastic and strength properties calls for further research to investigate the physico-chemical conditions contributing to undermine or enhance the properties of the subsurface rocks of volcanic-hydrothermal systems and, in turn, build upon those processes that the ancient Romans unwittingly exploited to create their famous concrete.

To study this, we prepared 8 samples by mixing the pozzolana volcanic ash, slaked lime, aggregates of Neapolitan Yellow tuff, and seawater from Campi Flegrei in the same ratios as the ancient Romans. Each sample contained a lime-to-pozzolana ratio of 1:2 by weight and a water-to-binder (pozzolana plus lime) ratio of 0.4 by weight. Neapolitan Yellow tuff made up 20% of the weight of the mixture. To mimic the conditions of the caldera, we used mineral seawater from a well in the Campi Flegrei region rich in sulfate, bicarbonate, calcium, potassium, and magnesium ions. The samples were cured under steam conditions as well. We measured baseline properties of porosity, permeability, and the acoustic velocity through the samples in order to calculate the bulk, shear, and Young’s modulus. Subsequently, half of the samples were injected with CO₂- rich aqueous solution and the changes in their microstructure and physical properties measured.

Our findings show how a steam- and sulfur-alkaline- rich environment affects both transport and elastic properties of the samples and how they may change in response to microstructural changes due to potential chemical instabilities such as possible new flux of CO₂ into a volcanic-hydrothermal system.