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Shedding weight for Sustainability

One of the unmistakable trends in architecture today is the lightweight construction, where the built structure efficiently combines materials to achieve very low mass/span ratio. The lightweight building materials not only help reduce energy demand and CO2 emission during the entire life cycle of a structure but also have much less impact on the topography of the site. For instance, the lightweight timber building system has been found to be well suited to stilt construction that results in low lifecycle energy use and minimum site disruption.

For RCC construction, lightweight aggregate is the common material used in precast concrete components. These aggregates are typically expanded shale, clay or slate materials that have been fired in a rotary kiln to develop a porous structure. Diatomite, pumice, scoria and volcanic cinders are inorganic natural aggregates while, wood chips and straw mixed with a binder provide a lightweight natural aggregate. Manufactured aggregate includes bloated clay, sintered fly ash and foamed blast furnace slag. Alternatively, addition of a foaming agent in cement mortar gives a fine cement matrix which has air voids throughout its structure and introduction of a gas into cementatious slurry helps give a cellular structure after hardening. The resultant lightweight concrete reduces building’s dead load saving on structural members, reinforcement steel and volume of concrete, which lessens overall energy requirement during construction. Other advantages of lightweight concrete components are the improved thermal and sound insulation properties.

A popular alternative to heavier RCC construction is the pre-engineered building system manufactured from high strength galvanized steel members. The structural system being light in weight saves on foundations size and material and is easy to transport to site. Furthermore, its advantages like speedy erection and installation, smaller member dimensions, low maintenance, long life span and100 per cent recyclability add to the built structure sustainability features.

However, with recent advances in concrete industry, designers are now combining the advantages of lightweight concrete with structural steel to design “Composite structures”. It combines the two materials, by using structural steel columns and beams for floor construction, concrete on metal deck floors and a concrete core structure that contains elevators and emergency stairwells.

Based on the same principle is an innovative construction system from Nexcon, Canada which is a hybrid precast panel structure. It combines light-gauge-steel framing embedded in 2” to 3” concrete to produce a lightweight composite system. The combined “concrete-and-steel” panel offers the strength of a solid precast panel, while using much less concrete as compared to conventional precast. These precast panels are designed for load bearing and shear wall conditions, foundation walls, floor slab and cladding to enclose pre-engineered structures.

Similarly, there are emerging new composite materials that are combinations of two or more substances. These composite materials feature the best characteristics and properties of the constituent components and provide high strength yet lighter material. For example, fiberglass orglass-reinforced plastic (GRP) is a composite material that offers strength, lightness and flexibility as building panel systems. The latest fiberglass brick effect panels can be used in the construction of composite housing. It is weather proof, corrosion resistant and can be constructed with the appropriate insulation which reduces heat loss.

Apart from the load bearing structure, the performance of external cladding too is being optimized through lightweight systems that are designed to enhance energy efficiency. For instance, pre-engineered external wall system that has built in insulation eliminates the need for secondary insulation installation, which if not properly done may lead to higher energy consumption. Thermal Wall System (Uni-TWS) by Unitex, Australia, is one such example. It consists of expanded polystyrene foam (EPS) sheet as the walling component that provides insulation and stores heat or cold, reducing energy demands within the building.

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