Effective Utilisation of Construction and Demolition Waste (Cdw) As Recycled Aggregate in Concrete Construction – A Critical Review

Solid wastes are the inevitable production of the operations of various industries like construction Industry, Machines Manufacturing Units, Textile industry etc. In India the construction industry generates large amounts of waste, which can be composed of different origin materials, most of them classified as non-hazardous. Construction and Demolition waste (CDW) constitutes a major portion of total solid waste production in the world and most of it is used in landfills. Dumping of these construction and demolition waste in landfill causes contamination of soil, water and air from toxic substances. Research by structural concrete engineers has clearly suggested the possibility of appropriately treating and reusing such waste as aggregates in new concrete. The aim of this paper is to explore the separation process of CDW and further use of recycled aggregates from construction and demolition waste (CDW) in concrete mixes. A review of most recent research and legislation applied in India is developed regarding the production of concrete by using these recycled aggregates.


INTRODUCTION
Rapid industrial development causes serious problems all over the world such as the depletion of natural aggregates and creates an enormous amount of waste material from construction and demolition activities. One way to reduce this problem is to utilize recycled concrete aggregates in the production of concrete. Recycled aggregates are the main component of old concrete and recycling operations have the added benefit of reducing landfill disposal.
Construction and Demolition (C&D) waste constitutes a major portion of total solid waste production in the world, and most of it is used in landfills. Research by concrete engineers has clearly suggested the possibility of appropriately treating and reusing such waste as aggregates in new concrete, especially for lower level applications. This study discusses recycled aggregates (RA) produced from C&D waste and their use in concrete construction. Along with a brief overview of the engineering properties of recycled aggregates, the study also gives a summary of the effect of recycled aggregate son the properties of fresh and hardened concrete. Recycled aggregates are treated with epoxy resin to reduce the water absorption. This research, however, shows that the recycled aggregates that are obtained from site-tested concrete specimen make good quality concrete. The influence of aggregates of varying sizes on the compressive strength, split tensile and water absorption of concrete is presented in this paper.

OBJECTIVES
• The main objectives of this study are to reduce, reuse and recycle C & D wastes.
• C & D wastes can be used as an aggregate replacement in concrete.
• Recycled aggregates can also be used in structural concrete by applying special mixture, curing and casting methods. • Construction waste is highly attractive compared to non -renewable natural resource.

LITERATURE REVIEW
• Khatib (2005) concretes made with 25% and 100 % of RFA present reduction of 15% and 30% in the compression strength.
• 2007 conclude use of 30% of RFA will not affect the compression strength.  (3,10), Decrease specific gravity (3), Increase abrasion loss (3,11,12) , In which first concrete has 100% of river sand , second concrete has 50% of river coarse aggregate., Third concrete has 100% of recycled aggregate. Water absorption of concrete R0, R50, and R100 was tested on 15 cm cube in hardened concrete testing. Necessary to use quality recycled concrete coarse aggregate and to follow the specific rules for design and production of this new concrete type. • The effect of fully replacing natural aggregate with several sources of recycled concrete aggregates.
• Compressive strength and slump are 40 and 60MPa and slump between 75 and 125mm.
• The RCA concrete had modulus of elasticity values up to 19% lower than NA concrete.
• As evaluated and was proportional to the modulus of elasticity of concrete incorporating the RCA as coarse aggregate.
• Fracture energy of RCA concrete was measured using single edge notched doublecantilevered beam specimen.
• Fracture energy of RCA concrete was found to increase with an increase in aggregate strength.

CONCLUSIONS
According to these test results, the performance of recycled aggregate concrete, even with the total replacement of coarse natural with coarse recycled aggregate, is mainly satisfactory, not only in terms of the mechanical properties, but also the other requirements related to mixture proportion design and production of this concrete type. The only two properties those are lower than for the natural aggregate concrete properties are the modulus of elasticity and shrinkage deformation. Because of that, it is not recommended to apply this type of concrete for structural elements for which large deformations can be expected. Also, this type of concrete shouldn't be used for structures exposed to aggressive environment conditions without appropriate previous testing, as there are opposing conclusions about durability-related properties of RAC in existing literature