Sustainable Built Environment (cid:150) A Structural Engineer(cid:146)s Point Of View

Human activities have disrupted the balance of nature's ecosystems and resources, leading to unsustainable levels of consumption, population growth, and urbanization. The built environment, which has the greatest material flows, contributes significantly to embodied energy. To address these issues, there is an urgent need to reduce the human footprint, live within nature's means, and promote sustainability in the built environment. Various sustainable building materials and practices are discussed, including wood wool boards, Tec Eco cement, ferrocement, and the use of recycled materials. Organic fiber materials and fillers can also be used to create carbon sinks in cementitious building materials.


Introduction
For the last several Billion years nature has nurtured the planet evolving complex eco-systems that recycle and conserve energy and materials. Sun is the source of energy . Waste from one natural metabolism is the input of another. Plants and animals live together in mutually inter-dependant ways.
Mechanisms for regulation exist which prevent overgrowth or dominance. Due to occasional climate change such as fire, earthquake, wind etc. species get wiped out and new species take over. Nature comes back to a balance position after such disasters and it takes thousands or millions of years. Meanwhile along came human beings. We are responsible for many changes affecting geosphere-biosphere such as salinity, deforestation, pollution, global climate change etc.
Consensus exists that we are responsible for climate change and a rising frequency and severity of storms, draughts, floods etc. Our presence in nature, with our present day lifestyle , is non stable and non sustainable. Driven by our intelligence, greed and arguably cheap fossil fuel energy and behavior like a new predator before which no living thing can stand, we are taking over.
Starting from a steam engine followed by oil, abundant energy and thousands of innovations later we hold a tiger called technology by its tail. It is bigger than we are and in its name five to six hundred billion tonnes of matter are moved about the planet to create twenty or thirty billon tonnes that we actually use. Resources are limited. Needs change and things we make and use get worn out and thrown out as waste. Vital earth systems are unable to cope and are rapidly going out of balance. Efficiencies and costing of Processes and products made do not account for value of natural capital consumed. (for example true cost of energy, water, sand, cement, steel etc.) There is an urgent need to reduce footprint of human beings.

Global Population Growth
In October 2004 a WWF report, The Living Plant Report 2004, says humanity is already consuming 20% more natural resources than the earth can produce. The Challenge of 21st century is learning to live within the means provided to us by the nature. There is ample evidence that increase in consumption per person and population growth have compounded to unsustainable levels.
Urban settlements in developing countries are growing five times faster than those in developed countries. Cities in developing countries are already facing enormous backlogs of shelter, infrastructure and services resulting in overcrowded transportation, poor sanitation and pollution.
Opportunity for change is greatest in the built environment which has the greatest material flows on the planet with the largest take and waste impacts. Architects, Engineers, Specifiers are uniquely positioned to take advantages of the changes that are occurring and take the rest of the supply chain into delivering sustainability.

Building Materials and Embodied Energy
Cement is a major source of CO 2 emissions. As seen in the GLOBAL POPULATION GROWTH figure it has low embodied energy and relatively high thermal capacity compared to other building materials such as glass and steel (as seen in the graph). But it is the most widely used material on earth and hence the environmental impact is immense. (Gaga Joules per Ton is the unit of measurement.) SUSTAINABLE BUILT ENVIRONMENT However, the graph on the next page shows the true picture. It shows the contribution of major construction materials in the embodied energy of a building.
As can be seen, the contribution to the total embodied energy of a building of three construction materials, namely, Concrete, Masonry and Steel, is very high. They constitute about 50% of the embodied energy in the construction stage of a building. These three materials are also responsible for the structure on which the  1926 1931 1936 1941 1946 1951 1956 1961 1966 1971 1976 year Million metric tonnes Embodied energy in a typical building building stands. Essentially this means that optimisation/ finding alternative means of structural systems and design approaches could lead to substantial reduction in embodied energy and in making the structure sustainable.

TheProcess of Change
Our present day lifestyle use of resources can be summarized in the sketch below.
Linkages that affect earth system flows Materials are in the utility zone between the take and waste. They add value to our lives but the molecules used and wasted affect Earth Systems This should essentially involve Reducing, re-using, recycling, recovering Use more renewable resources and less non-renewable resources. Re-engineering the materials we use. Changing molecular flows using non fossil. Realizing that Sustainablity is good business sense.
Sustainable Material for Built Environment 1. One of the first things to be done is to use lighter materials.
This reduces the weight and hence the structural requirements of support systems and foundations. Lighter material also reduce energy requirement of lifting in place to upper floors. Enclosure elements such as walls can be made lighter -e.g. saw dust bricks in cement binder. Use of wood wool (made from shavings of small dia timber) can also be done in walling. There is a considerable saving in lifetime energies (as against embodied energies as construction stage) on account of high insulation values. Wood wool sheet houses with infill core provide a structural system as well as excellent thermal insulation of roofs and side walls. Wood wool boards are made from long wood fibrous strands and inorganic binders such as Magnesite bonded boards. Be-cause of their versatile nature, the boards find large scale applications in low-cost housing, shuttering, sandwich type boards for insulation, false-ceilings, etc., A typical composition for making wood wool boards is as follows : Wood wool = 3 kg, portland cement = 6 kg, and water = 3 kg. For a board of 2.5 cm thickness the weight per square meter is 10 to 11 kg. This means it is 5 times lighter than brick masonry. Cost-wise, wood wool boards are much cheaper than solid wood or other panels bonded with synthetic and natural adhesives. They are superior in physical properties such as thermal conductivity, sound absorption. Greater Sustainability of years. Carbonates formed in sea water is an example. With capture of CO 2 , use of organic fiber materials and fillers for strength and insulation, cementitous building material can eventually become a carbon sink. Organic fibers include wood fibers, saw dust, sugarcane bagasse, hemp, coir etc. 3. FERROCEMENT as an alternative to conventional reinforced concrete has been used for construction of dwelling units. Ferrocement uses much lower quantities of high energy content materials such as Cement and Steel. 4. Use of recycled materials such as Fly ash and blast furnace slag is on the rise. Geopolymers is another promising area.

Functional Elements to Serve as Structural Components
There are several other functional elements in a building that can serve the structural purpose of load-bearing other than enclosing elements such as walls. One such example is a window frame in Ferrocement. This eliminates structural element such as lintel (a small beam over window to support brickwork above it), and other functional elements such as window jams and window sills. Ferrocement staircases and tanks are other examples. Much of the dead weight from conventional staircases can be removed and the functional elements such as steps of staircase become the structural members. In water tanks made with Ferrocement the weight of the tank is about 10% of the water stored as against 50 to 75% in case of RCC and Masonry tanks. Here the functional element of enclosing water serves the structural purpose also.
A geodesic dome constructed using Ferrocement provides the same comforts as a conventional room but at a much lower embodied energy per unit. A complete Ferrocement roof, wall, kitchen platform dwelling (having appearance like a normal house) can be constructed in Ferrocement after using much less embodied energy. These are do it yourself technologies and have the advantages of using local materials and virtually no machinery and electricity for construction.

Change in Design Approach
Most constructions 100 years ago were load bearing structure types. Some structures particularly wooden frame and brick masonry structures (such as wadas and houses) were constructed as composite constructions. The wooden frames were used for spanning rooms while the walls were with brick/masonry/ clay or stone masonry stiffened with wooden members. Stilt floor was not required at all. Today the aspect of time has been playing a major role in deciding the construction system. An RCC structure is constructed first and later bricks are added as walls. These walls are only functional and do not serve any structural purpose. This allows the flexibility of knocking down walls and rearranging the living space inside. It, however, leads to walling elements not serving any structural purpose. Other than the use of low embodied energy' materials to make construction more sustainable, functional features should also serve, partially or fully, a structual purpose.

Limitations
The concept of using materials with low embodied energy is applicable primarily to low rise buildings. The energy economics completely gives way in case of high rise structures on several accounts. First of all the design parameters such as earthquake and wind, against which the structure is to stand, start governing the design, as against gravity for low rise buildings. This necessitates use of steel and concrete leading to higher embodied energy. Generally load bearing structures cannot be constructed beyond 3 stories. Materials such as stabilized clay blocks, Ferrocement, Wood wool sheet wall panels (with in-filled cores) have limitations on heights. There is a limitation of using such sustainable materials in todays cities where ground coverage is required to be minimized.
On this background, it can be concluded that sustainable building materials and construction techniques can best be used to improve quality of construction in rural and semi urban areas.

Glossary
Embodied Energy : Total Energy used in material production, transportation and assembling into a building at construction stage.
Thermal capacity : Heat required to change temperature of a material by a given amount. This is low for steel and high for cement and concrete.
GJ : Giga Joules (Joules is a measuring unit for energy) Masonry : Brickwork, Stone work, Blockwork construction in a building Structural System : Arrangement of building components to transfer loads from self weight of materials of buildings, furniture, human beings, stored materials etc to ground.
Re-Engineering : Redesign of a product, by a consumer or user. to make them last for longer time with proper maintenance and repair.
Built Environment : Buildings, structures etc. along with the utilities within them.
Lifetime Energy : Energy used at construction stage as well as during lifetime (this includes embodied energy at construction stage as well as energy used for cooling, heating, lighting, maintenance etc during stage of use during lifetime of a building) Infill Core : Typically a core filled with strong material to take loads enclosed by thermal insulating outer skin. Shuttering : Material used for making an enclosure in which material like concrete is poured.
Thermal Conductivity : Ability of a material to transfer heat by conduction within its body. This is high for steel and low for wood and wood wool sheets. Low thermal conductivity gives better comfort in case of extreme climates.
Carbonation : Chemical process in which CO2 is absorbed and Carbonates (typically CaCO3) are formed Calcining : This is process opposite of Carbonation. It is carried out in the process of making cement where Carbonates are converted to cement and CO2 is released.
Ferrocement : A construction technique in with several steel wire meshes are clamped together to get desired shape and then cement and sand mix is squeezed into the layers of meshes to get a strong building component.
Fly Ash : Ash remaining after burning of wood or coal Blast Furnace Slag : A by product in the process of making steel. It has properties like cement.
Geopolymers : These are chains or networks of mineral molecules. Cements made from Geopolymers emit 80 to 90 % less CO2 Geodesic Dome : Spherical shape constructed using series of triangles connected to each other (like a football) a concept popularised by Buckminster Fueller.
Stilt : Typically a floor with no walls (only columns) such as parking floor in an apartment building B. V. Bhedasgaonkar