In 2008, the Comptroller and Auditor General of India stated that no estimates or guesstimates existed for the amount of construction and demolition (C&D) waste being generated in the country. Even though, built-up area has significantly increased in the last decade, the figures for C&D waste have remained at 10-12 million tons.
New construction generates waste 40-60kg/sqm of built-up area while, repair and renovation of existing buildings generates waste 40-50kg/sqm of built-up area and demolition of buildings generates waste 300-500kg/sqm of built-up area. However, the actual figures could be close to 530 million tons. Recycling of this construction and demolition (C&D) waste annually has an untapped potential of creating recycled products that can help to:
• Reduce the stress on natural resources and carbon footprint of the construction industry • Foster innovation in young minds to create products out of waste
• Generate employment for several people
• Facilitate community participation
• Encourage artists to use waste and divert materials from the landfill
• Divert C&D waste to low cost housing, small scale urban or rural construction work, landscaping, small scale rural infrastructure such as embankments, street furniture, and interior works
The Construction Development Laboratory (CDL) of Lafarge cement, concrete and aggregates tested demolition waste to identify its reuse in the construction industry. Two samples were tested. The first one consisted of demolished concrete and the second one consisted of demolished mortar and brick. The specific gravity, water absorption and sieve analysis tests were conducted on this debris. The material collected from site varied in size from 150mm to < 0.150mm. The aggregate was segregated as >25mm and <=25mm. Aggregates <=25mm were used to carry out the tests. Only 35.8% of Sample 1 and 42.0% of Sample 2 was <=25mm and was appropriate for actual testing. Tests results on <=25mm were as follows:
• Specific Gravity – The specific gravity of Sample 1 is 2.37 and of Sample 2 is 2.1. The specific gravity of coarse aggregates used for the purpose of structural concrete ranges from 2.5-3.0. Hence specific gravity of Sample 1 is 17.5%-22.5% and sample 2 is 25% to 30% lower compared to materials which are currently used in the market.
• Water Absorption – The water absorption % in Sample 1 is 6.38% and Sample 2 is 12.36%. Water absorption % of coarse aggregates that are used for the purpose of structural concrete ranges from 0.5-4%. Hence, water absorption in Sample 1 is 2-3 times and Sample 2 is 5-6 times higher water absorption compared to virgin aggregates.
• Sieve Analysis – Sample 1 & 2, both do not comply with IS Standards Specification. Aggregates form the skeleton of concrete which includes cement and water as well. The proportioning of aggregates of different shape and size determines the fresh and hardened properties of concrete. Single sized aggregate of 10mm and 20mm have been identified by Indian Standard Code as appropriate for the manufacture of structural concrete.
The significantly high water absorption percentage in both the samples was above the current market standards and is a challenge. The brick and mortar sample showed even higher absorption rate than concrete. As lesser water absorption means better durability of the structure, this makes reuse of the recycled concrete aggregates a concern in both the cases.
Furthermore, the demolition waste consisted of iron particles, thermocol and glass as well. In order to develop a commercially viable product, segregation of these materials is very important. Also, to obtain single sized aggregates of 10mm and 20mm which are in compliance with the standards, a specialized crusher is required. Thus, concrete and brick waste may not be suitable for structural concrete but can be a good proposition for lean mix concrete. The age of the building can also be determined from the sample.
Research on reuse of construction and demolition waste started in 2012 at I.I.T Bombay. In fact, IIT Bombay sponsored a pilot project to explore the possibility of reusing the demolition waste generated within the campus during the demolition and repair works of buildings. The space allotted for this purpose is approximately 1500-2000 sq. ft.