Concrete can be degraded due to various environmental factors such as rain, extremes of temperature, and exposure to corrosive substances. In particular, hydrogen sulfide—a gas that exists in the environment—transforms into sulfuric acid, which is a corrosive substance, upon combining with rainwater.
In a new research reported in EPJ B, Matthew Lasich from Mangosuthu University of Technology, Durban, South Africa, explores the detrimental outcomes of the adsorption of natural gas constituents that occur in the environment, as well as mixtures of a number of such gases, into one of the materials that form concrete—cement hydrate. Lasich discovered that a pre-treatment that targets the adsorption sites in cement hydrate, at which the majority of hydrogen sulfide molecules are attached, would be required to preserve concrete infrastructure from the corrosive effects. Yet, this method could turn out to be challenging due to their wide distribution.
It is the porous nature of concrete that makes it vulnerable to natural gas adsorption. Its structure is formed of a cement matrix that combines together aggregates of sand particles. As part of this research, the researchers carried out a nanoscale analysis based on Monte Carlo simulation to simulate the migration of gas molecules into the cement hydrate structure.
Firstly, they recorded the adsorption level over a range of temperatures for methane, ethane, ethene, and ethyne to ascertain the ingestion of each gas species into cement hydrate. This enabled them to analyze the effect of molecular size and shape on the sorption of gases in cement hydrate. As a next step, they conducted a similar study for natural gas constituents, such as carbon dioxide, nitrogen, and, most importantly, hydrogen sulfide.
Their simulations indicate that a particular combination of molecular size and surface area is needed for higher uptake into cement hydrate. Compared to all gases studied in this research, hydrogen sulfide adsorbed most readily, and ethyne adsorbed more readily compared to methane in spite of being a “heavier” molecule since its molecular shape better helped in this regard.