Page 34 - Demo

SCIENCE & INNOVATION34 SCIENCE & INNOVATION AAC WORLDWIDE %u2022 2.2025tion reaction of hydrogen peroxide (H%u2082O%u2082) activated by organic catalase. Catalase is an enzyme synthesised by most cells of living organisms to control the harmful effects of oxidation of biomolecules due to aerobic metabolism of cells or accidental exposure to oxidising chemical species of exogenous origin. In nature, there are various forms of catalase, differing in structure, sequence, and composition of the catalytic centre, all of which, however, have in common that they can catalyse the oxidation-reduction dismutation reaction of H%u2082O%u2082.The reactions are as follows:2H%u2082O%u2082 %u2192 O%u2082+2H%u2082Oreduction: H%u2082O%u2082 %u2192 [O]+H%u2082Ooxidation: H%u2082O%u2082+[O] %u2192 O%u2082+H%u2082OThe enzymatic activity of catalases is thus capable of breaking down millions of molecules of H%u2082O%u2082 per second into water and molecular oxygen with an optimum pH range of 4 to 11, depending on the species [4]. The hydrogen peroxide dismutation reaction is characterised by a strongly exothermic decomposition enthalpy even at room temperature (approx. 25%u00b0C), so no additional heat supply is required.This ability of catalase is exploited in BAAC. As the reaction takes place within the cement slurry, the oxygen released will form porosities that increase the volume of the mass and consequently reduce the final density of the composite.Among the various biological organisms capable of supplying the catalase enzyme to the system, ENEA researchers have identified yeast cells and in particular the Saccharomyces cerevisiae strain, the common brewer%u2019s yeast, widely used in activities that require leavening and fermentation, particularly in the production of wine, bread, and beer.The first experimental tests on the feasibility of the idea determined the reactive capacity and quantity of gas produced by first mixing just the yeast, dissolved in water at a concentration of 10 g/l, with hydrogen peroxide (titrated to a 35% concentration in water) (Fig. 1) and then adding just the commercial cement, without the addition of aggregates and lime (Fig. 2).The result highlighted another important characteristic of bio-aeration, namely that of its functioning in complete independence from the materials used in the cementitious mix composition. This circumstance made certain components of conventional AAC mix design superfluous, in particular calcium hydroxide, which has the predominant task to react with the aluminium powder, forming hydrogen gas molecules.The experimentation for the validation of BAAC then continued with the fine-tuning of the components of the mix design, consisting mainly of cement, sand, yeast, water and hydrogen peroxide. The modulation of the quantities of aerating agent (yeast and H%u2082O%u2082) corresponded to different values of the final density. The increase was assessed in percentage terms in relation to the height of the specimen made without the aerating agent using a formwork with dimensions of 10x10 cm.Fig. 2: Section of the consolidated specimen, consisting of cement, yeast cells and H%u2082O%u2082.Fig. 1: Development of the aeration process in the system consisting of yeast cells and H%u2082O%u2082.