Dr. Y. P. Gupta
Chairman, Yash Krishi Taknique Evam Vigyan Kendra, Allahabad.
Technical Adviser, Yamuna Bridge Information Centre, COWI – DIPL Consortium & Professor (Rtd.), Civil Engineering, MNNIT, Allahabad
Mail id [email protected]
Waste is generated from all directions. It may be from Industry, Municipality, landslides, floods, Agriculture or from any other process of human or animal activity. The waste may be in the form of solid, liquid or gas. The waste can also be divided in two categories like Biodegradable waste and Non-biodegradable waste. Not only the waste requires huge space to dump, but also pollute the environment and generate green house gases. The polluted environment is harmful to human health and for the sustainability of natural system. Thus, generation of waste must be minimized or recycled for generating resources. Generally conservation of resources revolve around three factors or “3R’s” i.e. to Reduce, Reuse or Recycle, which are integral to traditional thinking for any industry. Three major amounts of wastes are from municipality, industry and building demolition. Most of these wastes can be used in industry or human cycle after its processing. Thus industry has a big scope to start its role in waste processing and generating resources from it.
Waste: Biodegradable wastes like kitchen waste, flower waste etc can be easily degraded and used as farm soil improver. But non-biodegradable waste must be first processed and then generate resources. Wastes like demolition waste, industrial waste (like flyash) are being used or can be easily used in Construction Industry. A typical Waste Dump on Road side is shown in figure 1. When analyzed a waste dump, the typical waste product distribution for one place or time is shown in figure 2. Some techniques and places of use of waste are given here. Few wastes after processing are useful in construction industry and thus they protect the environment. However, their properties – both physical & chemical must be investigated to see the suitability and compatibility as a component of any construction material. Following Types of Relevant Waste Materials are common:
1. Demolition and Construction Waste
2. Industrial Waste
3. Natural Disaster Waste
4. Other wastes are like Agriculture Waste, hospital waste, nuclear waste etc.
Figure 5 – Typical analysis of Waste distribution from any Road Side Dump
The non Biodegradable wastes useful in Construction Industry are:
I. Demolition and Construction Waste:
- Demolition of Buildings (MALWA)
- Demolition of concrete pavement, slab etc.
- Renovation of Buildings, etc.
II. Industrial Waste:
- Fly Ash
- Thermal power plant Bottom ash.
- Slag from Steel Industry (BFS).
- Red mud from Aluminum Industry.
- Reclaimed Bitumen/Asphalt Pavement (RAP).
- Stone Dust.
- Plastic Waste etc.
III. Natural Disaster Waste:
- Landslides in Hilly areas.
- Flood carried material, etc.
Use of Non-Biodegradable Waste Materials:
Transfer of technology for use of waste should be simple and user-friendly. Thus the demolition and construction waste can be used where ever it is or at very close vicinity. Therefore, both technology and type of equipment must be relevant, simple, small and portable. The method given here is for use of Demolition waste as aggregate replacement.
Demolition Waste (MALWA) Generation:
Construction industry during rehabilitation, repairs and modernizing of buildings, produces huge waste called MALWA in common language. A typical MALWA waste dump is shown in figure 3. Out of total waste generation, construction industry accounts for about 30-40% of solid waste generation, depending upon location and time. Waste Management is generally collection, sorting and disposal at processing places like crusher plants, RMC plants etc. A typical method or steps for recycling the C&D waste is given here.
Steps in Recycling the Waste Dump:
Step 1: Collection: Recyclables differ from time to time and region to region. There can be different ways to collect it like Municipal Collectors, rag pickers etc and deposit at recycle center.
Step 2: Processing: Waste is sorted and prepared for manufacturing or processing for use as aggregate or other useful products from it.
Step 3: Manufacturing: Once separated and cleaned, the recyclables are ready to undergo for making aggregate for use as general purpose concrete for buildings, minor roads etc.
Concrete as Construction Material: Concrete is the most sustainable construction material in the World. It is a blessing that concrete is an environment-friendly product and its production generates less pollution and more facility and employment. Generally, the requirement of course aggregate in concrete is around 45%. Coarse aggregate is the fractured stone from rocks in hills or pebbles from river bed, and because of shortage/depletion of the supply of good aggregate in certain regions, the need for development of recycled aggregate technology is urgently required.
Technology for the Production of Recycled Aggregate (RA):
Technology/methodology for conversion of demolition waste to recycled aggregate (RA) has been developed by author. The Demolition waste was collected from building being renovated. The foreign matter was sorted out and rest broken into the pieces of approximately 20 & 10 mm size with the help of hammer. On large scale this should be done by light Roller Crushers. Then such material is mechanically sieved through IS sieve of 26.5 mm, 12.5 mm and 4.75 mm to remove higher & finer particles. The higher size is broken again. After sieving with 4.75 mm sieve, fines left out can be used as filler in plinth of buildings or highway embankment. A typical look and shape of this aggregate is shown in figure 4.
Use of Demolition Waste as Coarse Aggregate:
This aggregate can be used in making fresh concrete for various applications like:
1. Making general purpose concrete in the grade like M20 or similar.
2. Making bricks/blocks similar to conventional brunt clay Bricks
3. Highway Construction for Use in Dry Lean Concrete (DLC) and for use in casting curve, chute drain, median drain & side drain components.
4. Making benches for park and pedestrian paths etc.
A typical application one of above items is given below:
Manufacturing Bricks / Blocks with Concrete using Recycled Aggregate and for General purpose Construction:
A concrete mix with 50% Conventional aggregate and 50% recycled aggregate was designed in the grade of M15 with cement content like 200 Kg/cum. All the materials were taken for a smaller batch and weighed as per design requirement. Materials were mixed in mixture and tested for workability/reology. The slump of such concrete is quite normal and showed a behavior similar to conventional concrete. With this concrete, bricks of size 230x115x70 mm and interlocking blocks were cast which were similar to conventional burnt clay bricks. Some concrete cubes were also cast with such concrete to find its strength. They were cured in open with water sprayed a few times in the day. Shape of such bricks is shown in figure 5. For the comparison of their efficiency, such bricks and few burnt clay bricks in Ist quality were tested for Compressive Strength, Density etc.
Compressive strength and density for both types of bricks is given in Table 1. It is seen that strength and density of such bricks with recycled aggregate is more than conventional bricks. Similarly such bricks gave higher density than conventional bricks. This is advantageous in many cases like laying on road sides or in foundations etc.
||Av. Strength (MPa)
Performance and use of such bricks:
These bricks were / can be easily used in conventional wall construction of buildings as shown in figure 6. They are also good for Road side soling and foundations etc.
Recycled Concrete Material (RCM):
Waste Concrete Material, is another material obtained from demolition of concrete slabs, pavement, foundation etc. This is similar to demolition waste. This material can be crushed by mechanical means into manageable fragments of 20 & 10 mm nominal size by crusher as in demolition waste case. Thus obtain Recycled Concrete Material (RCM). RCM is comprised of highly angular conglomerates of crushed quality aggregate and hardened cement. RCM is rougher and more water absorbent than its virgin constituents. RCM aggregate can also be used as aggregate in making concrete after proper mix design similar to as given for demolition waste and for making blocks/Bricks etc.
Use of Waste as Fine aggregate (Sand):
Following waste materials can be used as replacement of sand:
- Fly ash
- Stone Dust from stone crusher plants
- Blast furnace slag
a) Fly ash as Sand replacement:
Fly ash is a by-product produced during the operation of coal-fired power plants. Fly ash particles are very smooth and quite spherical in shape. These particles range from 1 to 150 µm in diameter, depending on the type of collection system. A typical shape of fly ash particles is seen in figure 7.
Fly ash particles finer than 10 microns get adsorbed on cement particles giving a negative charge causing dispersion of cement particle flocks, thereby releasing the water trapped within the cement particle flocks and improves workability. Thus it can be used as partial replacement of cement as pozzolanic material, However, particles over 45 microns do not work as pozzolanic material, so it can be used as fine sand or sand replacement. Even the bottom ash collected from power plants can be used for sand replacement. However their properties must be in the inert category.
b) Stone Dust from stone crusher plants:
While crushing the boulders by crusher plant for getting coarse aggregate, some fines are also generated. These fines are normally in the size of 4.75 or similar of this. Their property is quiet similar to crushed coarse aggregate and shape is also similar. They are very good as fine aggregate (Sand).
Advantages of Using Wastes in Construction:
The technologies and methods used for development of resources should complement the use of local resources and waste management. Some advantages of using Demolition Waste in Construction are:
- Disposal of Demolition waste becomes easier.
- By making use of locally available demolition waste as aggregates, there would be sufficient reduction in aggregate requirement at construction site.
- By producing recycled aggregate bricks, top soil of earth will be saved which is otherwise used in making burnt clay bricks and thus environmentally viable & more agriculture produce at top soil.
- It can generate work for unemployed people similar to collecting plastic waste by Rag pickers etc, and deposit it at Concrete batching plants.
- The processing waste will also make the system Sustainable and can also conserve energy.
- The finer material passing through 4.75 mm sieve can go back to river bed in the same trucks which bring sand from there.
Medium Scale / Small Scale Industry set up for generating Resource from Demolition Waste:
Since the waste is being generated all over the places and it will differ in its properties from place to place and time to time. Therefore, the demolition waste and/or waste concrete material should be managed locally or recycled at nearby place as far as possible (recycling unit should be light, portable and tailor made to that area). As far as possible such aggregate produced should be used in that area itself. Following Machinery/Equipment are generally needed for processing the demolition waste.
Medium Scale / Small Scale Industry set up for generating Resource from Demolition Waste:
1. Crusher Plant (light)
2. Sieve of required size
3. Small RMC plant or Weigh batcher
4. Small testing kit for basic properties and mix design. etc
Since the waste is being generated all over the country, so as far as possible, its management efforts should be focused at decentralized locations through small scale or medium scale Industries or units. Using these wastes, an industry can easily set up near each of the cities.
Poverty Alleviation through Waste Recycling Concept:
The poverty alleviation in the developing Countries can be effectively achieved by creation of employment opportunities. If processing of Waste is taken up at a large scale in each city and town of the Country, then huge manpower will be required to collect it, transport it, sort it, process it and market it in proper shape. It can also reduce the total cost of concrete to poor people as they also need it for their use (as seen during rigid pavement construction and shown in figure 8)