Sustainability of autoclaved aerated concrete (ACC) - Essay Example

Autoclaved aerated concrete AAC though not much known in the United s, is now one of the many building products being touted as “green” or “environmentally friendly.” This paper briefly examines the advantages and disadvantages of building with AAC, paying specific attention to the aspects of the product that may lend to its designation as a sustainable building material. ACC concrete block showing the cellular pore structure (Shi and Fouad 105) AAC is not a new building material; however it is new to United States of America. It originated from Sweden in the early years of 1920 as a result of a rise in demands of timber supplies; AAC is a lightweight building stone that is manufactured (Shi and Fouad 105). AAC is used in a large number of commercial, industrial, and residential applications. This material has been used in Europe for many decades. Also leading in the use is Middle East followed by South America and Australia. Autoclaved aerated concrete is a precast product manufactured by mixing silica, cement, lime, water, and aluminum powder, and pouring it into a mold. With respect to reinforced AAC products like roof panels, lintels, steel rebar or mesh is also placed in the mold. When added to the concrete, the aluminum powder reacts with the silica, forming millions of microscopic hydrogen bubbles (Shi and Fouad 105). The hydrogen bubbles make the concrete to expand relatively five times its original volume. The hydrogen then evaporates, leaving a tightly closed-cell aerated concrete. The now aerated concrete is cut into blocks or panels which are then steam and pressure-cured in an autoclave. Unlike traditional concrete masonry units (“CMU”), AAC is a solid material system with combined insulative and structural components, and is there in a variety of products that can be used in both load and non-load-bearing applications. Complete load bearing applications, however, are only used in low-rise construction, though large panels are available to take advantage of AAC’s fire proofing, insulative and other benefits on mid and high-rise projects (Craig and Ding 102). Again, the big wall, floor, and roof panels, measuring a number of feet’s long, and feet wide, and in AAC has been used in the United States for approximately 10 years. The United States’ recent embrace of the material is likely due to, the high initial capital expenditures required in setting up domestic AAC manufacturing facilities, and the fact that, unlike many of the countries where AAC is a common product, the vast majority of residential buildings in the United States utilize timber-frame construction (Craig and Ding 102). The rest of the AAC system consists of blocks, which are stacked using thin-set mortar and not traditional cement mortar. The blocks are available in a variety of sizes and types, e.g., standard blocks, typically measuring 24 inches long, 8 inches high, and in thicknesses between 6 and 12 inches; jumbo blocks, which reduce construction time; U-blocks, which have a channel running the length of the block that once filled with concrete, provides structural support as headers and on the top course of each floor and cored blocks, which are used adjacent to corners and openings and have a centered, 4 inch vertical core at one end of the block forming running vertical core through the wall that is then filled with rebar and concrete (Craig and Ding 102). AAC lintels with integrated structural support are also manufactured and are substitutes to using the U-block system for headers. With flexibility and combined structural and insulation components, an AAC entire structure can be made using the one material. Exterior surfaces can be finished with stucco, traditional veneers or siding, while interior walls can be plastered, painted, or left unfinished, in addition to traditional sheetrock finishes. Further, AAC is easy to use and can be cut and manipulated with normal wood-working tools. AAC cut down Additional Material Use and Minimizes Waste and Pollution. The ability of a product to reduce material use, utilize recycled products, and avoid toxic emissions are what is considered in determining whether a product qualifies as “green” or can be used in a sustainable manner (Craig and Ding 103). Autoclaved aerated concrete do exemplary well in these regards. AAC use a relatively small quantity of raw material relative to the quantity of final product. Because AAC is approximately 80% air, the finished product is up to 5 times the volume of the raw material used to produce. More so, the raw materials that are used are generally many and found in most geographic regions, allowing them to be locally sourced.additionaly, much of the raw materials used in AAC production may consist of recycled materials. Again, with regard to embodied energy, AAC consumes approximately 50% and 20% less energy than that needed to produce concrete and CMUs, respectively (Craig and Ding 103). Though AAC’s light weight helps cuts down shipping costs, AAC construction becomes less cost effective if the construction site is far from the manufacturing facility. Even in regions where the cost of building with AAC may be higher now than conventional building methods, this initial cost must be balanced against savings due to lower operating and maintenance costs, the structure’s greater lifespan, cuts initial outlays for needed heating and cooling systems, and lower insurance costs (David 178). Autoclaved aerated concrete is additionally seen as sustainable building product because of its good insulating qualities that leads to increased energy efficiency. AAC’s thermal efficiency results from three factors. First, AAC structures lead to solid wall construction with integrated insulation. The all wall coverage prevents the thermal bridging linked with conventional stud-framed walls, which essentially leave cold gaps around every stud and header. AAC is inorganic, noncombustible, and virtually fireproof. it has a high melting point. As a result, the use of AAC eliminates the need for additional fireproofing materials. Moreover, because AAC is completely inert, it does not emit toxic gases even when exposed to fire (David 178). Another quality contributing to the sustainability of a building product is its ability to reduce and absorb noise or to improve or maintain indoor air quality. Due to its many independent air cells, which dampen sound transmission, AAC has good sound insulation and absorption qualities. Because of this benefit, many of the first applications of AAC in the United States have been the construction of hotels and freeway sound walls (David 178). There are few disadvantages to building with autoclaved aerated concrete. First, there are currently only five AAC manufacturing facilities in the United States. As a result, projects far from manufacturing facilities will suffer from higher initial costs. Both the costs and availability of AAC are expected to improve as AAC manufacturers invest in additional plants. Second, building with AAC has a learning curve both with respect to the construction community as well as with local governments (David 178). Few contractors are a currently familiar with the product, and trained masons must adjust to using thin-set mortar, which requires less precision in its application. Conclusion Due to its relatively low consumption of readily available raw materials, excellent durability, energy efficiency, relative cost effectiveness, and ability to be recycled, AAC Is well deserving of its “green” designation and is therefore sustainable in the long run. AAC is sustainable because of its environmental friendliness. It also cuts on the material needed for its production and there are no emissions which are not environmentally friendly being released from its production. AAC also make use of recycled products and that make it more environmentally friendly and that is what it guarantees safety. Autoclaved aerated concrete is a versatile lightweight construction material and usually used as blocks. Compared with normal (ie: “dense” concrete) aircrete has a low density and excellent insulation properties. Autoclaved aerated concrete block with a sawn surface to show the cellular pore structure (Picture courtesy H+H UK Ltd.) Detailed view of cellular pore structure in an aircrete block. The formation of air voids to produce a cellular structure is what gives it low density. These structures are 1mm - 5mm across and are what gives material the appearance. Blocks have strengths ranging from 3-9 Nmm-2. Densities range from about 460 to 750 kg m-3. AAC blocks are best for insulations. It is possible to construct almost an entire house from this blocks, including walls, floors - using reinforced aircrete beams, ceilings and the roof. Autoclaved aerated concrete is easily cut to any required shape. . Works cited Shi, Caijun, and Fouad H. Fouad. Autoclaved Aerated Concrete: Properties and Structural Design. Farmington Hills, Mich: American Concrete Institute, 2005. Print. 5th International Conference on Autoclaved Aerated Concrete: Bydgoszcz, Poland September 14-17, 2011: "securing a Sustainable Future" to Be Held at Bydgoszcz to Celebrate 60 Years of Aac Experience in Poland. Krako?w: Fundacja Cement, Wapno, Beton, 2011. Print. Ballast, David K. Architect's Handbook of Construction Detailing. Englewood Cliffs, N.J: Prentice Hall, 1990. Print. Langston, Craig A, and Grace K. C. Ding. Sustainable Practices in the Built Environment. Oxford: Butterworth-Heinemann, 2001. Print. Read More