Buildings as waste sinks

sustainability

Discarded keyboards in roof slabs and plastic bags in building foundations are  all great recycling options, write architects Chitra Vishwanath and Sharath Nayak

The garbage crisis that Bangalore went through over the last month or so prompts us to ask if buildings can be used as waste sinks. Below the building’s plinth, the land cannot sustain either biodiversity or grow food. It’s a wasted space, which can take into its fold many a kind of waste generated in the city.

Under the foundation, plinth infills and sunken floors are some of the ideal places to hold such waste. Take the under-construction house belonging to the Charis, at Singapura in Bangalore. A cleaning drive around the locality yielded 10,000 plastic bags, sachets and bottles. A layer of this waste has been placed below the foundation and within the plinth of the house. This waste stays in this place as long as the house stands.

The Charis are not the only ones to do this. The Rajagopalan residence in Vidyaranyapura, built in 2002, holds within its foundation and vaults about 50,000 plastic bags. Another interesting feature in the Rajagopalans’ house is a roof slab in-filled with discarded keyboards. This kind of RCC slab is popularly called filler slab. Filler slab is a concept where concrete below the neutral axis is replaced by a cheaper and lighter material. The added benefit is that this reduces the weight of the slab.

Materials commonly used are old Mangalore tiles, mud pots, and thermocol and coconut shells. Interesting patterns can be created in the roof when broken flooring tiles and stones are used, thereby avoiding plastering and painting of the surface. New buildings can also use debris from older buildings. Broken brick salvaged from demolitions can be used to replace aggregate of concrete in the floor base and in flagging.

Other debris can be ground and then used as replacement for sand in mortar, plinth and lintel bands. In beams and roofs, it can partially replace sand. In the present scenario, where sand is expensive and also mining of the same is creating ecological destruction, it will be worthwhile to have crushing units turning building debris to lower grade of fine aggregate to be used for non-structural purposes. By this one can hope that an economy develops around processing such waste, eventually resulting in productive use of waste.

Broken tile dado in toilets

Terrazzo floors, commonly known as mosaic, were popular till a few years back. This floor is made of waste stone chips and glass. Waste and broken ceramic tiles can also be used for dado in place of using new tiles, creating beautiful patterns. The dado is, in design terminology, a panel which forms the lower part of an interior wall, when it is done differently from the rest of the wall.

Architects, builders and house owners need to use techniques which use waste material. Manufacturers of building materials too are waking up to the possibilities of the use of waste. Roofing sheets made of discarded tetra packs, composite wood products such as hard boards, blockboards from recycled wood scrap, industrial and agricultural waste are now available in the market.

The Ministry of Environment and Forests has issued a notification dtd September 14, 1999 containing directives for greater fly ash utilisation. It specifies that within a 100-km radius from coal and thermal power plants, manufacturers of bricks use at least 25 per cent of fly ash in their products. Portland Pozzolona cement is an alternative to the commonly used Ordinary Portland cement and has fly ash as one of its constituents.

Most of us send waste water into the city sewers for treatment. It is possible to treat and reuse waste water in most cases at the building level itself, using simple natural and low-energy systems like the root zone treatment system.

In this system, one needs to build a reed bed through which water is passed and treated. While large sites can use the land available and make this system a part of the landscape, smaller sites such as the one on which the Vishwanaths’ residence in Vidyaranyapura has been built, use a part of their roof for treating the water from bath and the washing machine. 

Water from toilets or ‘black water’ too can be treated in this kind of a system by the addition of a baffle reactor. Adoption of such systems not only reduces waste generation but also contributes towards providing water security to our cities. All these possibilities show that recycling reduces the burden on natural resources. Burden is reduced on landfills and treatment plants.