Construction and Demolition Waste, or what we call Malba in Hindi, comprises 30 to 40% of global solid waste. This is uncontestably the largest waste stream in the world. Recycling presents an environmentally beneficial and economically feasible way to turn this 'bulky waste' into 'value'. This article simplifies this seemingly complex subject, and talks about C&D waste recycling in a way that even your grandma will understand!
If you’ve been following the Malba Project Blog, you already know what the Malba Problem is. But if you’re a new reader, let me summarise this for you.
C&D waste or Malba is largely non-biodegradable and inert [2], and globally around 35% is dumped in landfills [3]. Landfills in cities are limited in capacity and should only be used for dumping materials that have no other end-use. Malba is completely recyclable, but when it ends up in landfills, it competes for precious space with other waste streams [4]. When dumped illegally, which is the case in India, it competes for prime land space and hence is a very expensive problem. Often mixed with municipal solid waste in landfills, it releases greenhouse gases into the atmosphere and is a big contributor to global warming [1].
India currently recycles merely 1% of its C&D waste [5], and while circular economy principles and the waste hierarchy rightly stipulate reuse and reduce to be given higher priority, the value that recycling brings is creating a standardised industrial product that can be sold in bulk in the market. If we understand the Malba Problem well enough, we know that it is the “bulk” that one must solve for.
On a broad level, we at Malba Project see recycling as a simple 3-part process - Cleaning, Crushing and Sieving.
Cleaning consists of several different steps to separate impurities from the malba. It consists of the use of Magnetic Separators to separate any ferrous metallic impurities, manual or mechanical separation of plastics or other impurities that do not belong in the crusher, and mechanically washing the malba to get rid of soil. The idea is to get the input feed as close as possible to pure concrete in order to facilitate the highest replacement rate in the recycled concrete mix.
Crushing involves mechanically or manually breaking large piles into smaller pieces. Different types of crushers - jaw crushers, cone crushers - are used in this process. This is very similar to stone mining equipment and hence recycling is also a very lucrative foray from mining operators.
Sieving involves screens of different sizes as per standard industry applications. The degree of fineness of it determines its end use - whether it will be used as coarse aggregate, fine aggregate, or sand.
Once cleaned, crushed and sieved, the end product can be used in 2 ways:
We would like to emphasise here that C&D recycling plants make the process of recycling easier and standardised, but this is also a process that can be done manually, without expensive equipment. Not many Indian examples exist of buildings that have used these materials, as the uptake is still low. Some lighthouse projects that have ingeniously used C&D waste blocks are the Supreme Court Extension project in Delhi, the Chuzhi House by Wallmakers and the Block House by Collective Project, the latter two creating their own mixes to use in their projects.
Figure: 1) Chuzhi House by the Wallmakers, featuring their patented 'Shuttered Debris Wall'; 2) Block House by the Collective Project that used demolition waste from the previous building on site to create new building blocks; 3) Supreme Court Extension Block in Delhi that used recycled C&D waste blocks
“We would like to emphasise here that C&D recycling plants make the process of recycling easier and standardised, but this is also a process that can be done manually, without expensive equipment…Some lighthouse projects that have ingeniously used C&D waste blocks are the Supreme Court Extension project in Delhi, the Chuzhi House by Wallmakers and the Block House by Collective Project, the latter two creating their own mixes to use in their projects.”
There are 2 major classifications of Recycling Plants in India - by processing type and processing capacity.
C&D waste recycling plants have two processing types - wet processing and dry processing.
While dry processing broadly involves the above-mentioned steps, wet processing has an additional water-based scrubbing step in the cleaning process, that leads to a higher quality output. As per CDE Asia Limited, a pioneer in wet recycling technology, attributes such as 95% water recycling, zero liquid discharge, minimal dust pollution, and noise levels below 80dB, can be achieved through their technology. A higher quality output can replace virgin materials in concrete to a greater degree.
The second classification by processing capacity has two types of recycling plants that are prevalent in India – Stationary and Mobile recycling plants.
Figure 2: 1) Stationary C&D Waste Recycling Plant in Delhi; 2) Mobile C&D Waste Recycling Unit by Rubble Master
Stationary plants are larger in capacity and act as centralised recycling units in a city. They usually have a capacity of 100 to 350 tons/hour. They require a higher investment but are considered a more sophisticated technology than mobile plants. The stationary plants usually include sorting equipment and are suitable for areas of high density. They produce high-quality products if the input is correct [6].
Mobile plants, on the other hand, have capacities of up to 100 tons/hour. They are suitable for temporary demolition works. They are considered a more basic technology and produce lower-grade RA because they lack the cleaning technology. With the coming of new mobile technologies, we do have hope that this will not be the case for too long (see the equipment by Rubble Master). Mobile Plants in 2017 were considered economically feasible when 5000-6000 tons of waste is being processed on-site [6]. According to Engelson et al. (2017), mobile crushers can be used to produce high-quality aggregate if they deal with waste from homogenous constructions [7]. The Delhi Metro Rail Corporation, for example, has set up a centralised facility for itself in Mundka, Delhi which solely caters to the Delhi Metro projects. The input materials are large pile heads and largely pure concrete, which results in a good quality output as well, with a high replacement potential in recycled concrete. This is a model that can be adopted by other metro projects around the country as well.
The largest C&D waste recycling plant in the world is in Norway built by the CDE Group. The largest in India is in Burari, Delhi, built by CDE Asia. So technically India has state-of-the-art infrastructure for C&D waste recycling. While countries around the world struggle to create a secondary material economy for useful building materials that emerge from demolition, Indian cities have already solved that problem. The only materials left without an inherent resale value are concrete, brick debris, and soil. However, recycling technologies are slowly changing that concept altogether, turning “useless” malba into “useful” building materials, and hence paving the way towards a circular economy.
All that's left is a business model that works for India's informal sector-led secondary economy. There is a need for policies that improve the uptake of recycling and recycled materials around the country, which is potentially going to be the largest C&D waste generator globally in the near future.
