Page 35 - Demo

AAC WORLDWIDE %u2022 2.2025 SCIENCE & INNOVATION 35The results are summarised in Fig. 3, in which each point (blue values obtained on the side of the test specimens, orange values obtained in the centre) represents the arithmetic mean of three individual measurements.The results obtained in this experimental phase together with their repeatability made it possible to establish certain fundamental aspects:%u00a01. The rising process takes place at differentspeeds depending on the amount of hydrogenperoxide added to the dough.2. The growth process ends within 15 - 20 minutesafter the addition of H%u2082O%u2082 and the consequentstart of the dismutation reaction, at the end ofwhich the setting process begins.3. The trend of the change in height of the specimen can be approximated to a linear function ofthe quantity of hydrogen peroxide added to themixture. The aeration reaction is independentfrom the presence of other chemical componentsin the mixture and only associated with thepresence of hydrogen peroxide and yeast. It istherefore possible to identify other sources ofhydrogen peroxide, e.g. sodium percarbonate,a product of sodium carbonate and hydrogenperoxide that releases H%u2082O%u2082 in water, making itavailable for bio-aeration. The solid nature ofsodium percarbonate allows the preparationof premixes where all the components of theBAAC mix design are present in dry form, wherebio-aeration can be activated with just the addition of water, thus simplifying the productionprocess.Constituent materials and mix designFor all the reasons described above, the basic mix design of BAAC is considerably simplified compared to that of traditional AAC. The essential components are therefore cement (Portland CEM II A-LL 42.5R), sand (Silverbond SA600), water (at room temperature) and the aerating system consisting of peroxide (in liquid or solid form) and yeast. In the production phase, the last ingredient to be added to the mixture is peroxide.The final density can be scaled up mainly by varying the amount of H%u2082O%u2082 added to the mixture.The following table summarises the average weight percentages of the BAAC components for a density of 500 kg/m%u00b3.The laboratory mixing phase of the components has a duration of approximately 10 minutes and is concluded by the addition of the peroxide followed by an additional final mixing. Once the setting phase of the cement is completed, the specimen assumes a consistency that enables its removal from the formwork, following which it is processed and placed in an autoclave where it is heated to 190%u00b0C under saturated steam conditions for a total of 12 hours.Table 1: BAAC mix designComponent%u00a0 %%u00a0Silica sand%u00a0%u00a0 35%u00a0Portland cement%u00a0 23%u00a0Water%u00a0 40%u00a0Yeast%u00a0 0,5%u00a0H%u2082O%u2082/yeast ratio%u00a0 2,3Fig. 3: Graphical representation of the BAAC specimen growth as a function of different percentages of H%u2082O%u2082.