Abstract: A parallel-walled ventilation duct assembly with integrated low-profile subducts, and/or methods of manufacturing the assembly are provided. The assembly of embodiments includes a main shaft body defined by at least one wall surrounding an interior cavity and at least one low-profile subduct disposed within the interior cavity. The cross-sectional area of the main shaft body has a rectangular or an obround shape. The low-profile subduct includes an interior channel defined by a plurality of walls. The low-profile subduct is integrated into at least one wall of the main shaft body such that at least one wall of the plurality of walls of the low-profile subduct includes at least a portion of an interior surface of the at least one wall of the main shaft body, and the portion of the interior surface of the at least one wall includes a flat portion of the interior surface.

Abstract: A cementitious composition is created by adding sodium carbonate (also known as soda ash, natron, sodium carbonate decahydrate, sodium carbonate anhydrous, trona, etc.) and one or more rocks or minerals selected from the calcium carbonate group. A new product is claimed by combining sodium carbonate and one or more rocks or minerals selected from the calcium carbonate group. The combination of sodium carbonate and one or more rocks or minerals from the calcium carbonate group can be either layered or mixed in a dry or wet state. An exothermic reaction starts after the addition of water to the cementitious composition. The composition of the cementitious material can vary between 10% sodium carbonate and 90% of one or more rocks or minerals from the calcium carbonate group to 90% sodium carbonate and 10% of one or more rocks or minerals selected from the calcium carbonate group. Organic or inorganic additives may be added to the mixture to enhance the composition and/or the final cementitious composition.