This paper presents the experimental results of recycled coarse aggregate concrete and results are compared with the natural crushed aggregate concrete. The fine aggregate used in the concrete, i.e. recycled and conventional is 100 percent natural. The recycled aggregate are collected from four sources all demolished structures. For both types of concrete i.e. M-20 and M-25, w/c ratio, maximum size of aggregate and mix proportion are kept constant.
The development of compressive strength of recycled aggregate concrete at the age of 1,3,7,14,28, 56, and 90 days; the development of tensile & flexural strength at the age of 1,3,7,14 and static modulus of elasticity at the age of 28 days are investigated. The results shows the compressive, tensile and flexural strengths of recycled aggregate are on average 85% to 95% of the natural aggregate concrete. The durability parameters are also investigated for recycled aggregate concrete and are found to be in good agreement with BIS specifications.
IntroductionAny construction activity requires several materials such as concrete, steel, brick, stone, glass, clay, mud, wood, and so on. However, the cement concrete remains the main construction material used in construction industries. For its suitability and adaptability with respect to the changing environment, the concrete must be such that it can conserve resources, protect the environment, economize and lead to proper utilization of energy. To achieve this, major emphasis must be laid on the use of wastes and byproducts in cement and concrete used for new constructions. The utilization of recycled aggregate is particularly very promising as 75 per cent of concrete is made of aggregates. In that case, the aggregates considered are slag, power plant wastes, recycled concrete, mining and quarrying wastes, waste glass, incinerator residue, red mud, burnt clay, sawdust, combustor ash and foundry sand. The enormous quantities of demolished concrete are available at various construction sites, which are now posing a serious problem of disposal in urban areas. This can easily be recycled as aggregate and used in concrete. Research & Development activities have been taken up all over the world for proving its feasibility, economic viability and cost effectiveness.
The main reasons for increase of volume of demolition concrete / masonry waste are as follows:-
- Many old buildings, concrete pavements, bridges and other structures have overcome their age and limit of use due to structural deterioration beyond repairs and need to be demolished;
- The structures, even adequate to use are under demolition because they are not serving the needs in present scenario;
- New construction for better economic growth;
- Structures are turned into debris resulting from natural disasters like earthquake, cyclone and floods etc.
- Creation of building waste resulting from manmade disaster/war.
In many densely populated countries of Europe, where disposal of debris problem is becoming more and more difficult, the recycling of demolition waste has already been started. As per the survey conducted by European Demolition Association (EDA) in 1992, the several recycling plants were operational in European countries such as 60 in Belgium, 50 in France, 70 in the Netherlands, 120 in United Kingdom, 220 in Germany, 20 in Denmark and 43 in Italy. The recycling of construction & demolition waste becomes easy & economical, wherever combined project involving demolition and new construction are taken up simultaneously. The possible uses of construction and demolition wastes are given in Table 1.
Recycling and Reuse of Construction & Demolition Wastes in Concrete
It has been estimated that approximately 180 million tones of construction & demolition waste are produced each year in European Union. In general, in EU, 500 Kg of construction rubble and demolition waste correspond annually to each citizen. Indicatively 10% of used aggregates in UK are RCA, whereas 78,000 tons of RCA were used in Holland in 1994. The Netherland produces about 14million tons of buildings and demolition wastes per annum in which about 8 million tons are recycled mainly for unbound road base courses.
USA is utilizing approximately 2.7 billion tons of aggregate annually out of which 30-40% are used in road works and balance in structural concrete work. A recent report of Federal Highways Administration, USA refers to the relative experience from European data on the subject of concrete and asphalt pavement recycling as given in Table 3.The rapid development in research on the use of RCA for the production of new concrete has also led to the production of concrete of high strength/performance.
Indian StatusThere is severe shortage of infrastructural facilities like houses, hospitals, roads etc. in India and large quantities of construction materials for creating these facilities are needed. The planning Commission allocated approximately 50% of capital outlay for infrastructure development in successive 10th & 11th five year plans. Rapid infrastructural development such highways, airports etc. and growing demand for housing has led to scarcity & rise in cost of construction materials. Most of waste materials produced by demolished structures disposed off by dumping them as land fill. Dumping of wastes on land is causing shortage of dumping place in urban areas. Therefore, it is necessary to start recycling and re-use of demolition concrete waste to save environment, cost and energy.
Central Pollution Control Board has estimated current quantum of solid waste generation in India to the tune of 48 million tons per annum out of which, waste from construction industry only accounts for more than 25%. Management of such high quantum of waste puts enormous pressure on solid waste management system.
In view of significant role of recycled construction material and technology in the development of urban infrastructure, TIFAC has conducted a techno-market survey on 'Utilization of Waste from Construction Industry' targeting housing /building and road segment. The total quantum of waste from construction industry is estimated to be 12 to 14.7 million tons per annum out of which 7-8 million tons are concrete and brick waste. According to findings of survey, 70% of the respondent have given the reason for not adopting recycling of waste from Construction Industry is "Not aware of the recycling techniques" while remaining 30% have indicated that they are not even aware of recycling possibilities. Further, the user agencies/ industries pointed out that presently, the BIS and other codal provisions do not provide the specifications for use of recycled product in the construction activities.
In view of above, there is urgent need to take following measures:-
- Sensitization/ dissemination/ capacity building towards utilization of construction & demolition waste.
- Preparation and implementation of techno-legal regime including legislations, guidance, penalties etc. for disposal of building & construction waste.
- Delineation of dumping areas for pre-selection, treatment, transport of RCA.
- National level support on research studies on RCA.
- Preparation of techno-financial regime, financial support for introducing RCA in construction including assistance in transportation, establishing recycling plant etc.
- Preparation of data base on utilization of RCA.
- Formulation of guidelines, specifications and codal provisions.
- Preparation of list of experts available in this field who can provide knowhow and technology on totality basis.
- Incentives on using recycled aggregate concrete-subsidy or tax exemptions.
The properties of RAC has been established and demonstrated through several experimental and field projects successfully. It has been concluded that RCA can be readily used in construction of low rise buildings, concrete paving blocks & tiles, flooring, retaining walls, approach lanes, sewerage structures, subbase course of pavement, drainage layer in highways, dry lean concrete(DLC) etc. in Indian scenario. Use of RCA will further ensure the sustainable development of society with savings in natural resources, materials and energy.
Experimental InvestigationsIn the present paper, an endeavor is made so as to compare some of the mechanical properties of recycled aggregate concrete (RAC) with the natural aggregate concrete (NAC). Since the enormous quantity of concrete is available for recycling from demolished concrete structures, field demolished concrete is used in the present study to produce the recycled aggregates. The concrete debris were collected from different (four) sources with the age ranging from 2 to 40 years old and broken into the pieces of approximately 80 mm size with the help of hammer & drilling machine. The foreign matters were sorted out from the pieces. Further, those pieces were crushed in a lab jaw crusher and mechanically sieved through sieve of 4.75 mm to remove the finer particles. The recycled coarse aggregates were washed to remove dirt, dust etc. and collected for use in concrete mix. The fine aggregate were separated out, and used for masonry mortar & lean concrete mixes, which is not part this reported study. But these were found to suit for normal brick masonary mortar and had normal setting and enough strength for masonary work.
Concrete MixesThe two different mix proportions of characteristic strength of 20 N/ mm2 (M 20) and 25 N/mm2 (M 25) commonly used in construction of low rise buildings are obtained as per IS 10262 – 1982 or both recycled aggregate concrete and natural aggregate concrete. Due to the higher water absorption capacity of RCA as compared to natural aggregate, both the aggregates are maintained at saturated surface dry (SSD) conditions before mixing operations. The proportions of the ingredients constituting the concrete mixes are 1:1.5:2.9 and 1:1.2:2.4 with water cement ratio 0.50 & 0.45 respectively for M-20 & M-25 grade concrete. The ordinary Portland cement of 43 grade and natural fine aggregates (Haldwani sand) are used throughout the casting work. The maximum size of coarse aggregate used was 20 mm in both recycled and natural aggregate concrete.
The total two mixes were cast using natural aggregate and eight mixes were cast using four type of recycled aggregate concrete for M-20 & M-25. The development of compressive strength is monitored by testing the 150-mm cubes at 1, 3, 7, 14, 28, 56 and 90 days. In one set 39 cubes were cast for each mix. The cylinder strength and corresponding strain & modulus of elasticity were measured in standard cylinder of 150x300 mm size at the age of 28 days. The prism of size 150x150x700 mm and cylinder of size 150x300mm were cast from the same batches to measure Flexural strength and splitting tensile strength respectively. This paper reports the results of experimental investigations on recycled aggregate concrete.
Properties of Recycled Concrete Aggregate
Particle Size DistributionThe result of sieve analysis carried out as per IS 2386 for different types of crushed recycled concrete aggregate and natural aggregates. It is found that recycled coarse aggregate are reduced to various sizes during the process of crushing and sieving (by a sieve of 4.75mm), which gives best particle size distribution. The amount of fine particles (<4.75mm) after recycling of demolished were in the order of 5-20% depending upon the original grade of demolished concrete. The best quality natural aggregate can obtained by primary, secondary & tertiary crushing whereas the same can be obtained after primary & secondary crushing incase of recycled aggregate. The single crushing process is also effective in the case of recycled aggregate.
The particle shape analysis of recycled aggregate indicates similar particle shape of natural aggregate obtained from crushed rock. The recycled aggregate generally meets all the standard requirements of aggregate used in concrete.
Specific Gravity and Water AbsorptionThe specific gravity (saturated surface dry condition) of recycled concrete aggregate was found from 2.35 to 2.58 which are lower as compared to natural aggregates. Since the RCA from demolished concrete consist of crushed stone aggregate with old mortar adhering to it, the water absorption ranges from 3.05% to 7.40%, which is relatively higher than that of the natural aggregates. The Table 4 gives the details of properties of RCA & natural aggregates. In general, as the water absorption characteristics of recycled aggregates are higher, it is advisable to maintain saturated surface dry (SSD) conditions of aggregate before start of the mixing operations.
Bulk DensityThe rodded & loose bulk density of recycled aggregate is lower than that of natural aggregate except recycled aggregate-RCA4, which is obtained from demolished newly constructed culvert. Recycled aggregate had passed through the sieve of 4.75mm due to which voids increased in rodded condition. The lower value of loose bulk density of recycled aggregate may be attributed to its higher porosity than that of natural aggregate.
Crushing and Impact ValuesThe recycled aggregate is relatively weaker than the natural aggregate against mechanical actions. As per IS 2386, the crushing and impact values for concrete wearing surfaces should not exceed 45% and 50% respectively. The crushing & impact values of recycled aggregate satisfy the BIS specifications except RCA2 type of recycled aggregate for impact value as originally it is low grade rubbles.
Compressive StrengthThe average compressive strengths cubes cast are determined as per IS 516 using RCA and natural aggregate at the age 1, 3, 7, 14, 28, 56 and 90 days and reported in Table 5. The table 4 shows that the target cube strength was achieved at 28 days for all types of concrete. As expected, the compressive strength of RAC is lower than the conventional concrete made from similar mix proportions. The reduction in strength of RAC as compare to NAC is in order of 2- 14% and 7.5 to 16% for M-20 & M-25 concretes respectively. The amount of reduction in strength depends on parameters such as grade of demolished concrete, replacement ratio, w/c ratio, processing of recycled aggregate etc.
Splitting Tensile & Flexural StrengthThe average splitting tensile and flexural of recycled aggregate are determined at the age 1, 3, 7, 14, & 28 days varies from 0.30 -3.1 MPa and 0.95- 7.2 MPa respectively. The reduction in splitting and flexural strength of RAC as compared to NAC is in order of 5-12% and 4 -15% respectively.
Modulus of ElasticityThe static modulus of elasticity of RAC has been reported in Table 4 and found lower than the AC. The reduction is up to 15% .The reason for the lower static modulus of elasticity of RCA is higher proportion of hardened cement paste. It is well establish that Ec depends on Ec value of coarse aggregate, w/c ratio & cement paste etc. The modulus of elasticity is critical parameter for designing the structures, hence more studies are needed.
DurabilityThe following parameters were studied to assess the influence of recycled aggregates on durability of concrete:
Freeze-Thaw ResistanceIn the freeze-thaw resistance test (cube method), loss of mass of the concrete made with recycled aggregate was found sometimes above and below than that of concrete made with natural aggregate. The results were so close that no difference in freeze thaw resistance (after 100 cycles) could be found. The literature also found that the effect of cement mortar adhering to the original aggregate in RAC may not adversely affect the properties of RAC.
Obstacles in Use of RCA & RACThe acceptability of recycled aggregate is impeded for structural applications due to the technical problems associated with it such as weak interfacial transition zones between cement paste and aggregate, porosity and transverse cracks within demolished concrete, high level of sulphate and chloride contents, impurity, cement remains, poor grading, and large variation in quality.
Although, it is environmentally & economically beneficial to use RCA in construction, however the current legislation and experience are not adequate to support and encourage recycling of construction & demolished waste in India. Lack of awareness, guidelines, specifications, standards, data base of utilization of RCA in concrete and lack of confidence in engineers, researchers and user agencies is major cause for poor utilization of RCA in construction. If the Govt wishes these obstacles can easily be removed.
Recycled aggregate posses relatively lower bulk density, crushing and impact values and higher water absorption as compared to natural aggregate. The compressive strength of recycled aggregate concrete is relatively lower up to 15% than natural aggregate concrete. The variation also depends on the original concrete from which the aggregates have been obtained. The durability parameters studied at SERC(G) confirms suitability of RCA & RAC in making durable concrete structures of selected types.
There are several reliable applications for using recycled coarse aggregate in construction. However, more research and initiation of pilot project for application of RCA is needed for modifying our design codes, specifications and procedure for use of recycled aggregate concrete. The subject of use of RCA in construction works in India should be given impetus, because of big infrastructural projects are being commissioned including Common Wealth Games in 2010.
- Hansen, T.C. (1992), "Recycling of Demolished Concrete Masonry, Rilem Report No. 6, E&FN Spon, London, Great Britain, pp. 316.
- Oikonomou,N.D.(2005)"Recycled Concrete Aggregates," Cement & Concrete Composites, Vol. 27, pp315-318.
- Thielen,G.(2004)"Concrete Technology Reports 2001- 2003,"German Cement Works Association.
- US Deptt. of Transportation (2000) "Recycled Materials in European Highways Environment-Uses, Technologies and Policies," Int. Technology Exchange Programme.
- Biojen,J. (1996) "Waste Materials and Alternative Products "Pro's and Con's" Concrete for Environmental enhanced and Protection, E & FN Spon, pp. 587-598.
- Buchner, S. and Scholten, L.J. (1992). "Demolition and Construction Debris Recycling in Europe," European Demolition Association (EDA).
- Ferguson, J.; Kermode, O.N.; Nash, C.L.; Sketch, W.A.J. and Huxford, R.P. (1995), "Managing and Minimising Construction Waste," Institution of Civil Engineers, Thomas, Telford Publications, U.K., pp. 1-60.
- Gottfredsen, F.R. and Thogerson,F. (1994), "Recycling of Concrete in Aggressive Environment," Demolition and Reuse of Concrete and Masonry; Rilem Proceeding 23, E & FN Spon, pp. 309-317.
- Hansen, T.C. (1986) "Recycled Aggregate and Recycled Aggregate Concrete, Seocnd state of Art Report, Development 1945–1985," Rilem TC-DRC, Material & Structure, Vol. 19, No. III. pp. 201- 248.
- Hendricks, Ch.F. (1996), "Recycling and Reuse as a Basis of Sustainable Development in Construction Industry," Concrete for Environment, Enhancement and Protection, E&FN Spon, pp. 43-54.
- Kikuchi, M. and Yasunaga, A. (1994), "The Total Evaluation of Recycled Aggregate and Recycled Concrete" Demolition and Reuse of Concrete and Masonry, Rilem Proceedings 23, E&FN Spon, pp. 367-377.
- Lauritzen, E.K. (1994), "Introduction," Disaster Planning, Structural Assessment, Demolition and Recycling, Rilem Report No. 9, E&FN Spon pp.1 –10.
- Mc Laughliu, J. (1993), "A Review of the Prospect for Greater Use of Recycled and Secondary Aggregate in Concrete," Concrete, The Concrete Society Journal, Vol. 27, NO. 6,pp. 16-18.
- Merlet, J.D. and Pimienta, P. (1994), "Mechanical and Physico- Chemical Properties of Concrete Produced with Coarse and Fine Recycled Concrete Aggregates," Demolition and Reuse of Concrete and Masonry, Rilem Proceeding 23, E&FN Spon, pp. 343-353.
- Nikon, P.J. (1986), "Recycled Concrete an Aggregate for Concrete–a Review," Rilem TC-37, DRC, Materials Structures, Vol. 19, No. 111.
- Pauw, C.D. (1994), "Reuse of Building Materials and Disposal of Structural Waste Material," Disaster Planning, Structural Assessment, Demolition and Recycling, Rilem Report 9, E&FN Spon, pp. 133-159.
- RILEM TC 121 DRG Recommendation (1994), "Specification for Concrete with Recycled Aggregates," Materials and Structure, Vo. 27, No. 173, pp. 557- 559.
- Singh, S.K., Sharma, P.C., and Nagraj, N. (1997), "State-of-Art Report on Recycled Aggregate Concrete," SERC Report, Ghaziabad.
- Sharma, P.C., Singh, S.K. and Nagraj, N. (1998), "Future of Recycled Aggregate Concrete in India," National Seminar on New Materials and Technology in Building Industry, July 24-25, Vigyan Bhawan,New Delhi, pp. IV-197-IV- 205.
- Singh, S. K. and P. C. Sharma (1998)"Recycling and Reuse of Building Waste in Constructions- A Review," All India Seminar on Concrete for Infrastructural Development, Roorkee, pp 317-329.
- Tavakoli, M. and Soroushian, P. (1996), "Strength of Recycled Aggregate Concrete made using Field Demolished Concrete as Aggregate," ACI Materials Journal, Vol. 93, No.2, pp.182-190.
- Tavakoli, M. and Soroushian, P.(1996), "Drying Shrinkage Behavior of Recycled Aggregate Concrete," Concrete International, Vol. 18, No. 11, pp. 58-61.
- Vyncke, J. Rousseau, E. (1994), "Recycling and Construction and Demolition Waste in Belgium : Actual Situation and Future Evaluation," Demolition and Reuse of Concrete & Masonry, Rilem Proceeding 23, E&FN Spon, pp. 57- 69.
- Yogishita, F. et al. (1994), "Behavior of Reinforced Concrete Beams containing Recycled Coarse Aggregate" Demolition and Reuse of Concrete & Masonry Rilem Proceeding 23, E&FN Spon, pp. 331-342.
- Yangani, K., Hisaka, M. and Kasai, Y. (1994), "Physical Properties of Recycled Concrete using Recycled Coarse Aggregate made of Construction with Finishing Mater4ials," Demolition and Reuse of Concrete & Masonry, Rilem Proceeding 23, E&FN Spon, pp. 379-390.
- Sharma, P.C., Nagraj, N.(1999), "Recycled Aggregate Concrete and Its Importance in Indian Conditions"– All India Seminar on Indian Cement Industries : Challenges and Prospects of Cement" Chandrapur (Maharashtra)
- Ramammurthy, K. & Gumaste, K.S.(1998), "Properties of Recycled Aggregate Concrete," Indian Concrete Journal, pp. 49-53.
- Rahal, K. (2007) "Mechnical Properties of Concrete with Recycled Coarse Aggregate," Building & Environment,Vol. 42, pp 407-415.