Recycled C&D Waste Materials

Dr. K M Soni, Retd. Addl DG, CPWD, New Delhi


Large construction activities were taken up after Independence in India. These structures have outlived their lives now and are under demolition. From such demolitions, a considerable quantity of Construction and Demolition (C&D) waste is going to be generated. C&D waste is also being generated from repair, renovation and construction works. Hence, management of C&D waste has become a necessity.

Realising this, the Ministry of Environment, Forests and Climate Change (MoEF&CC), Government of India has notified “Construction and Demolition Waste Management Rules, 2016” in which management of C&D waste generated by an individual, organisation or authority has been covered.

Even though few C&D waste recycling plants have been installed in the country, use of recycling materials has been made in isolated projects only and as such their wide use is to be made simultaneously while ensuring their quality.

C&D Waste Management
C&D waste management pyramidFigure 1: C&D waste management pyramid
C&D waste comprises of used or rejected building materials, debris and rubble resulting from construction, repair, renovation, and demolition of structures and its waste management also includes 3Rs i.e. Reduce, Recycle and Reuse as shown in Figure 1. Reduction of the waste is made through prevention, minimisation and deconstruction. Prevention can be achieved through quality work; minimisation through demolition only after the structure has outlived its life; and deconstruction by taking out useful materials from the structure being demolished i.e. reverse way of construction. Advantage of deconstruction is that salvaged materials can be reused in works. The materials which cannot be salvaged are to be recycled and converted into useful products. In case, such management is implemented, almost all the waste can be converted into resource and very little quantity needs disposal.

C&D Waste Generation
C&D Waste Management Rules, 2016 classify C&D producing organisations into two categories as C&D waste generators and C&D waste bulk generators. The C&D waste generators are those responsible to generate any quantity of C&D waste however bulk generators are those generating C&D waste 20 tonnes or more in a day or 300 tonnes per project in a month. The bulk generators are required to segregate the waste into four categories as concrete, soil, steel-wood-plastic, and bricks and mortar.

India generates large quantity of C&D waste due to large construction, renovation, and demolition activities undertaken in the country but only few recycling facilities are available hence the waste is disposed off into dumping yards or in open. As a thumb rule, 40-60 kg per sqm C&D waste is estimated to have been generated from new construction and renovation and 300-500 kg per sqm from demolition.

C&D waste is generated from RCC, brick or stone structures. As per TIFAC (Technology Information, Forecasting and Assessment Council, 2001, C&D waste in India constituents 36% soil, sand and gravel, 31% brick and masonry, 23% concrete, 5% metal, 2% bitumen, 2% wood and 1% others. This provides an idea of C&D constituents though the percentage will vary from place to place.

Recycling of C&D Waste
Recycling is most important activity in management cycle. C&D waste is transported to the recycling plants either by the bulk generators or urban local bodies (ULBs). Some ULBs are charging tipping fees from the waste generators. Most of the ULBs are also providing land in the outskirts of the cities for recycling plants to avoid pollution in the cities.

There are three types of C&D waste recycling plants known as mobile, semi-mobile and stationary. Advantage of mobile plants is that they can be transported to the demolition sites but have limitation of processing only non-contaminated concrete or masonry waste. In the semi-mobile recycling plant, removal of contaminants is carried out manually while magnetic separation done for removal of ferrous materials. In such a plant, quality of end product is better than that of a mobile unit though such plants are not capable to process mixed demolition waste containing matters like metal, wood, plastic etc. Stationary plants are capable of carrying out all the operations. Such plants may have dry and wet processing recycling facilities. Metallic waste is first removed from C&D waste and then through screening process, aggregates of different sizes are separated. In wet processing plants, recycled materials get washed and in the last light weight materials and sludge are separated. Sludge consists of fine soil like clay and silt which is passed through press producing dried soil called filter press material.

Recycled Materials from C&D Waste
The following main materials are obtained after recycling;
  1. Sand
  2. Coarse aggregates
  3. Filter press material
Composition of coarse aggregates depends upon the C&D waste as the waste may consist of only cement concrete or a mix of soil, brick and stone masonry waste, and others. In case, C&D waste consists only cement concrete waste like from RCC members, railway sleepers and similar other concrete members, recycled materials obtained after recycling such waste will be sand and coarse aggregates. Coarse aggregates obtained from such C&D waste are called as Recycled Concrete Aggregates (RCA). When C&D waste consists of brick/stone masonry waste as well as concrete waste, coarse aggregates obtained from such waste are called as Recycled Aggregates (RA). The properties of RCA and RA are therefore different.

The properties of RCA and RA are therefore different

Recycled materials are allowed to be used in certain percentage of certain grade concrete mix as per IS 383: 2016 but not permitted in pre stressed concrete. Permitted uses of recycled sand, recycled aggregates and recycled concrete aggregates as per IS: 383 are as given in Table 1.

Table 1: Permitted use of recycled sand, RCA and RA as per IS 383: 2016
Sl. No. Type of Aggregates Maximum utilisation
Plain cement concrete (%) Reinforced concrete (%) Lean concrete (Less than M15 grade) (%)
1 RCA 25 20(Only upto M25 grade) 100
2 RA Nil Nil 100
3 Fine aggregates (RCA) 25 20(Only upto M25 grade) 100

In IS 383, recycled fine and coarse aggregates are grouped under manufactured aggregates. Manufactured aggregates are those manufactured from other than the natural sources like processing materials, using thermal or other processes such as processing, washing, crushing and scrubbing. Fine aggregates are those, most of which passes 4.75mm sieve as per the grading given in the code. Thus sand is classified as fine sand.

Recycled Concrete Aggregates (RCA) contain not only original aggregates but also hydrated cement paste adhering to its surface resulting into reduction of specific gravity and increasing porosity leading to higher water absorption compared to natural virgin aggregates. Recycled Aggregates (RA) have further higher absorption and lower specific gravity compared to virgin aggregates and RCA.

From Table 1, it may be seen that use of recycled sand and RCA is allowed in plain cement concrete and RCC of M25 Grade or below as partial replacement while RA, recycled sand and RCA in lean concrete (upto M15 Grade). Thus, RA has very limited applications.

Manufactured Products from Recycled C&D Waste
Cement concrete products like pavement blocks, kerb stones, and tiles (Fig. 6) are being manufactured from recycled materials using sand and RCA. RMC of grade allowed in IS: 383 is also produced from such materials.

Products from plant of ILFS Environmental Infrastructure & Services LtdFigure 6: Products from plant of ILFS Environmental Infrastructure & Services Ltd

Cement concrete blocks are also being manufactured by the companies from recycled materials. Some companies produce such blocks only from RCA (Fig. 7) generally resulting into adequate compressive strength, uniformity and consistency. A company has also manufactured cement concrete blocks from RA however as source of RA cannot be same, the percentage constituents, uniformity and consistency in properties cannot be ensured easily and thus quality has to be monitored closely.

Makkar (2018) has reported use of concrete blocks manufactured from Recycled Aggregates (RA) in Supreme Court additional office complex, New Delhi by CPWD, produced from Burari plant, Delhi (Fig. 8). These blocks were used in external walls, toilet walls and lift well walls (non load bearing structures) after required tests when the company was able to produce them of desired compressive strength of 10 MPa. Pull out strength for the fasteners used in the project was also found satisfactory. The size of the blocks used was 400x200x100 mm and in total 17.50 lakh blocks were used. Issue of handling of such blocks is also to be resolved by way of manufacturing small size of blocks. CPWD has included block masonry from recycled materials in its Delhi Schedule of Rates.

Solid and hollow blocks from RCA

Thus, RCA has wide applications but there is very little application of RA at present. As such, use of RA has to be found out in other applications as the quantity of RA produced is more than RCA due to large masonry structures being demolished. Probable use of RA includes in sub bases of roads and under floors in buildings. Initially, even partial replacement of RA can be attempted in granular sub base (GSB), and full use can be stipulated for filling under floors, plinth protections, footpaths, sunken floors etc, and even in CC road/footpath and drain constructions. Similarly use of filter press material has to be found out. Its applications in manufacturing clay bricks, filling in embankments and horticultural operations appear to be feasible. After the efficacy of RA and filter press material is established in various applications, specifications are to be framed and provisions included in IS/IRC codes so that C&D waste can be converted into a resource with confidence.

Concluding Remarks
Recycling of C&D waste has become essential as per “Construction and Demolition Waste Management Rules, 2016”, and also from environmental considerations. Recycled materials from C&D waste can be directly used as construction materials or concrete products can be manufactured from them.

Specifications, tests and quality assurance methods are to be developed for recycled materials so that they can be used with confidence by architects and engineers. Awareness and capacity building has also to be generated among administrators, engineers, and public for such products through articles, seminars and conferences.

References
Construction and Demolition Waste Management Rules, 2016, Ministry of Environment, Forest and Climate Change.

file:///C:/Users/Owner/Desktop/cpwdwz1/Burari-CD-Facility-2015.pdf

https://www.godrejconstruction.com/Construction/hollow-concrete.aspx?id=8&menuid=4121

Soni, K M (2014), Avoidance of Waste Generation for Construction and Demolition Waste Management. Preliminary publications, Indian Buildings Congress, Vol. XXI (2), 14-19.

Makkar, B B (2018). Supreme Court Additional Office Complex, N. Delhi – Innovative technologies Intervention. Emerging & Innovative Technologies for Sustainable Development, CPWD, New Delhi.

NBM&CW February 2021

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