Use of Aggregates From Recycled Construction and Demolition Waste in Concrete

Resources, Conservation and Recycling 50 (2007) 71–81Use of aggregates from recycled construction and demolition waste in concrete Akash Rao a , Kumar N. Jha b , Sudhir Misra a,∗ a Department of CE, IIT Kanpur, Kanpur 208016, India b Department of CE, IIT Delhi, New Delhi 110016, India Received 2 August 2005; received in revised form 23 April 2006; accepted 24 May 2006 Available online 7 July 2006 Abstract Construction and Demolition (C&D) waste constitutes a major portion of total solid waste pro- duction in the world, and most of it is used in land fills. Research by concrete engineers has clearly suggested the possibility of appropriately treating and reusing such waste as aggregate in new con- crete, especially in lower level applications. This paper discusses different aspects of the problem beginning with a brief review of the international scenario in terms of C&D waste generated, recycled aggregates (RA) produced from C&D waste and their utilization in concrete and governmental ini- tiatives towards recycling of C&D waste. Along with a brief overview of the engineering properties of recycled aggregates, the paper also gives a summary of the effect of use of recycled aggregate on the properties of fresh and hardened concrete. The paper concludes by identifying some of the major barriers in more widespread use of RA in recycled aggregate concrete (RAC), including lack of awareness, lack of government support, non-existence of specifications/codes for reusing these aggregates in new concrete. © 2006 Elsevier B.V. All rights reserved. Keywords: Construction and demolition waste; Waste management; Recycling; Recycled aggregates; Recycled aggregate concrete; Durability ∗ Corresponding author. Tel.: +91 512 2597346; fax: +91 512 2597395. E-mail addresses: akash [email protected] (A. Rao), [email protected] (K.N. Jha), [email protected] (S. Misra). 0921-3449/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2006.05.010 72 A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 1. Introduction Preservation of the environment and conservation of the rapidly diminishing natural resources should be the essence of sustainable development. Continuous industrial devel- opment poses serious problems of construction and demolition waste disposal (Topcu and Guncan, 1995). Whereas on the one hand, there is critical shortage of natural aggregates (NA) for production of new concrete, on the other the enormous amounts of demolished concrete produced from deteriorated and obsolete structures creates severe ecological and environmental problem (Chandra, 2004, 2005). One of the ways to solve this problem is to use this ‘waste’ concrete as aggregates (Khalaf et al., 2004). Such ‘recycled’ aggregate could also be a reliable alternative to using natural aggregates in concrete construction. Also there are instances of imposition of levy for disposal of such waste in landfill, (Gilpin et al., 2004). Initially, recycling of demolition waste was first carried out after the Second World War in Germany (Khalaf et al., 2004). Since then, research work carried out in several countries has demonstrated sufficient promise for developing use of construction waste as a constituent in new concrete. Construction and demolition (C&D) waste could be broken concrete, bricks from buildings, or broken pavement. Thus, Recycled Aggregate (RA) could come from the demolition of buildings, bridge supports, airport runways, and concrete roadbeds. Concrete made using such aggregates is referred to as recycled aggregate concrete (RAC). An effort has been made in this paper to present a summary of the use of recycled aggre- gates in the construction industry in different countries, and describe the salient properties of RA and RAC, especially in relation to strength and durability. The paper also briefly discusses the barriers in promoting more widespread use of RAC. 2. Construction and demolition waste management 2.1. United States of America (Gilpin et al., 2004) Of the approximately 2.7 billion metric tonnes of aggregate currently used in the USA, the pavements account for 10–15%, whereas other road construction and maintenance work consumes another 20–30%, and the bulk of about 60–70% aggregates are used in structural concrete. RA in the US is produced by natural aggregate producers, contractors and debris recycling centers, which have a share of 50%, 36% and 14%, respectively. Incentives for transportation of waste concrete and processed aggregates from production sites are given to promote use of RA, though a large part of the production is suitable only as fill or construction base. 2.2. Japan (Kawano, 2003) Although Japan has a history of more than a quarter of a century of research on the reuse of demolished concrete for concrete, yet relatively little concrete has been recycled with the primary reason being non-acceptance of concrete not complying with JIS A-5308, which lays down specifications for ready mixed concrete. In 1991, the Japanese government A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 73 established the Recycling Law, which required relevant ministries to nominate materials that they must control and to encourage the reuse and recycling of those materials under their responsibility. The former Ministry of Construction (MOC) nominated demolished concrete, soil, asphalt concrete, and wood as construction by-products. The MOCpresented the “Recycle 21 programin 1992, which specifies numerical targets for recycling of several kinds of construction by-products. Further, in April 1994, “Tentative quality specifications for reusing materials from demolished concrete for construction works” was issued by MOC. As a result of these initiatives, against a target of 90% recycling ratio, actual results improved from a mere 48% in 1990 to almost 96% in 2000, mostly as sub-base material in road construction. 2.3. EU Union (European Commission and Report, 1999; European Union Directorate General Environment, 2000; LUC Report, 1999; Winter and Hendersonb, 2003; Lauritzen, 2004) It is estimated that the annual generation of C&D waste in the EU could be as much as 450 million ton, which is the largest single waste stream, apart from farm waste. Even if the earth and some other wastes were excluded, the construction and demolition waste generated is estimated to be 180 million tons per year, and considering a population in of approximately 370 million, the per capita annual waste generation is about 480 kg. Though clear figures about recycling are not available for individual countries in EU, an EU study calculated that an average of 28% of all C&D waste was recycled in the late 1990s. Most EU member countries have established goals for recycling that range from 50% to 90% of their C&D waste production, in order to substitute natural resources such as timber, steel and quarry materials. Recycled materials are generally less expensive than natural materials, and recycling in Germany, Holland and Denmark is less costly than disposal. UKconsumed around 330 million tonnes of aggregates in 1989 of which only about 10% were recycled materials. For England only, it has been reported that in 2001, 220 million tonnes of aggregates were used of which a quarter were recycled materials. Construction and demolition waste in England and Scotland make up about two thirds and half of recycled aggregates, respectively. Realizing the importance of C&D waste, the Scottish Executive Development Depart- ment (SEDD) commissioned research to gather information on the level of use of RA. It was found that the total estimated quantity land filled by all sites was approximately 4173 kilotonnes, of which 44% was mixed construction and demolition waste, clean soil (34%), contaminated soil (13%), and contaminated construction and demolition waste and asphalt (9%). Among these, 19% of the mixed construction and demolition waste was reused/ recycled. 2.4. Bulgaria (Zaharieva Hadejeiva et al., 2003) Modernizationandconstructionof infrastructural facilities suchas roads, bridges, munic- ipal and industrial structures, since 1990s, gave rise to a large amount of construction waste, but in 2000, of the 22% of the total expenditure on environmental protection and rehabilita- 74 A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 tion, only 0.5% was spent on management of such waste. Efforts are underway by agencies including the Municipality of Sofia, and the Bulgarian Academy of Sciences, besides the Ministry of Environment and Water Resources towards better C&D utilization. Though a pilot project, called “Recycled Concrete Aggregates”, submitted in collaboration with Universities in northern France, Krupp Hazemag Group and RMN recycling company on producing of recycled aggregates fromrejected panels could not be funded under the NATO programme titled “Science for Peace”, it was highly appreciated by legislative institutions, local authorities, developers, construction companies, etc. 2.5. Hongkong and Taiwan HongKongandTaiwanhave alsoinitiatedprogrammes topromote C&Dwaste utilization in newconcrete. About 14 million tons of (C&D) is generated in Hong Kong each year. In the past, the inert portion of this material was reused in land reclamation (Fong Winston et al., 2002). However, due toincreasingoppositionmost of these projects have beeneither delayed or drastically scaled-down. In 2002, a pilot C&Dmaterials recycling facility, with a handling capacity of 2400 tonnes per day was established by the Hong Kong SAR government to produce RA for use in government projects and relevant R&D work. The facility produces material for rockfill and both coarse and fine RA. Only crushed rocks and concrete are used in this facility as part of quality control measures, which include screening out contaminants such as bricks and tiles, and a daily sampling and testing of products. The plant has already produced 240,000 tons of high quality RA. As of the end of October 2003, more than 10 projects involving reinforced pile caps, ground slabs, beams and parameter walls, external building and retaining walls, and mass concrete have consumed over 22,700 m 3 of concrete using RA. In Taiwan, a comprehensive plan for management of C&D waste was initiated only in 1999, after the severe in earthquake in Central Taiwan caused severe structural damage to about 100,000 dwellings (Huang et al., 2002). It was expected that C&D waste in excess of 30 million tons would be generated during rehabilitation of damaged structures. The plan required an immediate subsidiary program and a complete quality assurance/quality control system to support the private sectors, and establishing pilot sorting plants. These plants recycle about 80% of the material used in landfills and 30% of the material used as road base in Taiwan. 3. Properties of aggregate made from C&D waste Recycled concrete aggregate could be produced from (a) recycled precast elements and cubes after testing, and (b) demolished concrete buildings. Whereas in the former case, the aggregate could be relatively clean, with only the cement paste adhering to it, in the latter case the aggregate could be contaminated with salts, bricks and tiles, sand and dust, timber, plastics, cardboard and paper, and metals. It has been shown that contaminated aggregate after separation from other waste, and sieving, can be used as a substitute for natural coarse aggregates in concrete (Nagataki et al., 2004). As with natural aggregate, the quality of recycled aggregates, in terms of size distribution, absorption, abrasion, etc. also needs to A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 75 be assessed before using the aggregate. Some of the important properties of such recycled aggregate are discussed in the following paragraphs. 3.1. Size distribution It has been now generally accepted that, recycled aggregates, either fine or coarse, can be obtained by primary and secondary crushing and subsequent removal of impurities. Generally, a series of successive crushers are used, with oversize particles being returned to the respective crusher to achieve desirable grading. The best particle distribution shape is usually achieved by primary crushing and then secondary crushing, but from an economic point of view, a single crushing process is usually most effective. Primary crushing usually reduces the C&D concrete rubble to about 50 mm pieces and on the way to the second crusher, electromagnets are used to remove any metal impurities in the material (Corinaldesi et al., 2002). The second crusher is then used to reduce the material further to a particle size of about 14–20 mm. Care should be taken when crushing brick material because more fines are produced during the crushing process than during the crushing of concrete or primary aggregates. 3.2. Absorption The water absorption in RA ranges from 3 to 12% for the coarse and the fine fractions (Jose, 2002; Katz, 2003; Rao, 2005) with the actual value depending upon the type of concrete used for producing the aggregate. It may be noted that this value is much higher than that of the natural aggregates whose absorption is about 0.5–1%. The high porosity of the recycled aggregates can mainly be attributed to the residue of mortar adhering to the original aggregate. This, in fact, also affects the workability and other properties of the new concrete mix as discussed separately. 3.3. Abrasion resistance Very limited literature is available on the abrasion resistance of RA. However, studies on the use of such aggregates as sub-base in flexible pavements show promising results. These recycled aggregates have also been used in generating concrete that is further used in rigid pavements. As discussed earlier in the paper, they are extensively used in USA, UK and other countries as new material for rigid pavements (Gilpin et al., 2004; Khalaf et al., 2004). 4. Properties of concrete made with recycled aggregate Concrete mixes using RA can be designed in much the same way as those using NA, provided the extra absorption in the former is appropriately accounted for when determining the unit water content. The salient features of the recommendations of the RILEMcommittee 76 A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 (RILEM, 1994) for proportioning of RAC are given below: • When designing a concrete mix using recycled aggregate of variable quality, a higher standard deviation should be employed in order to determine a target mean strength based on a required characteristic strength. • When coarse recycled aggregate is used with natural sand, it may be assumed at the design stage, that the free w/c ratio required for a certain compressive strength will be the same for RAC as for conventional concrete. • For a recycled aggregate mix to achieve the same slump, the free water content will be approximately 5% more than for conventional concrete. • The sand-to-aggregate ratio for RAC is the same as when using NA. • Trial mixes are mandatory and appropriate adjustments depending upon the source and properties of the RA should be made to obtain the required workability, suitable w/c ratio, and required strength, of RAC. 4.1. Properties of fresh recycled aggregate concrete (RAC) The workability of RACfor the same water content in the concrete is lower as reported by many researchers, especially when the replacement levels exceed 50% (Topc¸u and Sengel, 2004). In order to improve the workability, certain measures in the direction of changing the moisture condition of the RA, have been suggested (Oliveira et al., 1996; Poon et al., 2002, 2004). In another study several concrete mixes were prepared with varying methods of recycled coarse aggregate preparation, in terms of saturation. It was found that, extra water corresponding to absorption of the aggregate mixed during concrete preparation produced the most consistent results as far as workability is concerned (Rao, 2005). The air content of the RAC is slightly higher (∼4% to ∼5.5%) than concrete made with NA (Katz, 2003) at 100% replacement. This increased air content could be attributed to the higher porosity of the RA. The bulk density of fresh concrete made with natural aggregates is in the range of ∼2400 kg/m 3 , whereas the concrete made with recycled aggregates is significantly lighter, ∼2150 kg/m 3 , regardless of the type of cement (Topcu and Guncan, 1995; Katz, 2003). The lower density is the result of the specific gravity of the aggregates, which is related to the type of concrete used for producing the aggregate. In addition, increased air content in the recycled concrete, leads to an additional reduction in the density of the fresh concrete. 4.2. Properties of hardened RAC 4.2.1. Compressive strength Though researchers have reported a reduction in strength in RAC, it should be noted that the extent of reduction is related to the parameters such as the type of concrete used for making the RA (high, medium or low strength), replacement ratio, water/cement ratio and the moisture condition of the recycled aggregate (Crentsil et al., 2001; Ajdukiewicz and Kliszczewicz, 2002). For example, Katz found that at a high w/c ratio (between 0.6 and 0.75), the strength of RACis comparable to that of reference concrete even at a replacement level of 75% (Katz, 2003). Rao found the strength of RAC and reference concrete to be A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 77 comparable even at 100% replacement, provided that the water–cement ratio was higher than 0.55 (Rao, 2005). However, as the water–cement ratio is reduced to 0.40, the strength of RAC was only about 75% of the reference mix (Rao, 2005). Apart from the water–cement ratio, the moisture condition of the RA also appears to affect the compressive strength. Limited work has been reported attempting to relate the strength to the condition of the aggregates (oven dried, air dried, saturated surface dry, etc.), though the findings are inconclusive (Rao, 2005; Poon et al., 2004). 4.2.2. Flexural and tensile strength The ratio of the flexural and the splitting strengths to the compressive strength is in the range of 16–23% and 9–13%, respectively (Katz, 2003). These values are about 10–15% lower compared to the recommendations of ACI 363R. A study by Rao, shows a reduction in strength of 15–20%compared to reference concrete at 100%replacement (Rao, 2005). In another study, where the direct tensile strength of concrete was determined, it was found that difference in the tensile strength of RACand reference concrete at 28 days was less than 10% (Ajdukiewicz and Kliszczewicz, 2002). Studies have also shown that use of supplementary cementitious admixtures, such as silica fume, etc. helps improve the properties of RAC (Ajdukiewicz and Kliszczewicz, 2002). 4.2.3. Bond strength Very limited work on bond strength of RAC has been done. Nevertheless, it has been reported that, the effect of use of RA on the bond stress at failure is quite small compared to factors such as the type of bars used (plain rounds or ribbed bars). Areduction of upto 10%in the bond strength of the RAC has been reported at 100% replacement by RA (Ajdukiewicz and Kliszczewicz, 2002). 4.2.4. Modulus of elasticity The modulus of elasticity for RAC has been reported to be in the range of 50–70% the normal concrete (Oliveira et al., 1996; Ajdukiewicz and Kliszczewicz, 2002; Rao, 2005) depending on the water–cement ratio and the replacement level of RA. However, more experimental data is required in this area, before conclusive results can be drawn especially in applications of RAC where the modulus of elasticity or the stress-strain behavior, is a critical parameter. 4.2.5. Creep and shrinkage The use of RA in concrete induces a large shrinkage due to the high absorption of these aggregates. Some studies by show that in RAC at the age of 90 days, the shrinkage could be about 0.55–0.8 mm/m, whereas the comparable value for NAC is only about 0.30 mm/m (Katz, 2003). However, the test results for creep in normal laboratory conditions are not so clear, though some studies have shown the tendency to be reversed, i.e. the creep after 1 year is about 20% lower than concrete with NA (Ajdukiewicz and Kliszczewicz, 2002). Though more work is needed in the area, it appears that the overall behavior of RAC and NAC may be comparable when viewing the combined effect of shrinkage and creep. 78 A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 4.3. Durability of hardened RAC Durability studies have been done to better understand the effect of using different qualities of RA on the properties of the RAC. Though, some studies have shown that RAC is significantly more permeable than NAconcretes, it should also be noted that the durability properties can be improved by using flyash, condensed silica fume, etc. Some of the results available in literature are discussed in the following paragraphs. 4.3.1. Carbonation On the basis of carbonation test done after 6 months of curing, the carbonation depth of the recycled concrete has been found to be 1.3–2.5 times greater than that of the reference concrete (Crentsil et al., 2001; Levy Salomon and Paulo, 2004). It is seen that for the same water-binder ratio, the carbonation depths of RAC are slightly higher than that of NAC (Otsuki et al., 2003). This increase in the carbonation depth could be attributed to increased permeability of the RAC on account of the presence old mortar adhering to the original aggregate, and the old interfacial transition zone (ITZ) between them. 4.3.2. Freezing and thawing resistance There is no common opinion in the literature as far as the frost resistance of RAC is concerned. In a study where the effect of mortar content adhering to the aggregate on the freezing and thawing resistance of RAC was studied, it was found that provided the quality of the concrete rubble is good, the adhering mortar may not adversely affect the performance of RAC (Gokce et al., 2004). In another study it was found that the freezing and thawing resistance of RAC using RA made from non-air-entrained concrete was quite poor, though the RAC met the requirements of air entrainment. On the other hand, the concretes made with the recycled coarse aggregates originated from air-entrained concretes were highly frost resistant (Salem and Burdette, 1998; Zaharieva et al., 2004). The likely shortcomings in the performance of RACto freezing and thawing can be attributed to the pore structure of the previously hardened cement paste that adheres to the surface of the recycled aggregate. This porous matrix absorbs water during mixing, increasing the water-cement ratio of the paste. 5. Barriers in promoting use of RA and RAC Acceptability of recycled material is hampered due to a poor image associated with recycling activity, and lack of confidence in a finished product made from recycled mate- rial. Cost of disposal of waste from construction industry to landfill has a direct bearing on recycling operations. Low dumping costs in developing countries also acts as a bar- rier to recycling activities. Imposition of charge on sanitary landfill can induce builders and owners to divert the waste for recycling. Some of these issues act as barriers in promoting more widespread use of recycled aggregate and concrete made with recycled aggregate. A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 79 5.1. Lack of appropriately located recycling facilities Construction and demolition waste is generated in small quantities at locations which could be widely separated. Therefore, portable equipment is needed, which can be used and set up close to a demolition site. Transporting waste over large distances makes the proposition of using C&D waste uneconomical. Lack of such plants is a major barrier for ‘Newcomers’ in the field of C&D waste management. Commissioning of appropriately located recycling crusher units in a pilot plant can help in lowering barriers against recycling of construction & demolition waste. 5.2. Absence of appropriate technology There are very few commercially viable technologies for recycling construction and demolition wastes, and methods that can be used to crush C&D waste on a commercial scale are urgently required. In fact, when the technology is established, other issues such as quality control of raw material and finished product, etc. can be taken up. 5.3. Lack of awareness Lack of awareness towards recycling possibilities and environmental implications of using only fresh mined aggregates are the main barriers due to which C&Dwaste is disposed only in landfills. Creating awareness and dissemination of information relating to the above barriers andthe properties of concrete made withrecycledaggregate are essential tomobilize public opinion and instill confidence in favor of the recycling option. There is a need to create a market for recycled products by involving the construction industry and encouraging them to use recycled materials in projects. 5.4. Lack of government support Alack of government support and commitment towards development of recycling indus- try is often seen. Developing appropriate policy supported by proper regulatory framework can provide necessary impetus. It will also help in data compilation, documentation and control over disposal of waste material. 5.5. Lack of proper standards Apart from the specifications of RILEM (RILEM, 1994), JIS and those used in Hong Kong, only very limited codal specifications/standards regarding use of recycled aggregates are available. In fact, use of concrete with 100% recycled coarse aggregate for lower grade applications is allowed in Hong Kong, though for higher grade applications (above M35 concrete), only 20% replacement is allowed, and the concrete can be used for general applications, except in water retaining structures. In Japan, JIS has drafted a Technical Report, TRA 0006 “Recycled Concrete Using Recycled Aggregate” to promote the use of concrete made with recycled aggregate. Development of relevant standards for recycled materials would provide producers with targets and users an assurance of quality of material. 80 A. Rao et al. / Resources, Conservation and Recycling 50 (2007) 71–81 Standards formulated in the above mentioned countries can be a guideline for development of specifications. 6. Concluding remarks Use of recycled aggregates in concrete provides a promising solution to the problem of C&D waste management. Based on a survey of production and utilization of RA in RAC, and the properties of RA and RAC discussed in this paper, it is clear that RAC can be used in lower end applications of concrete. With tailor made pilot studies, RA can be used for making normal structural concrete with the addition of flyash, condensed silica fume, etc. Greater efforts are needed in the direction of creating awareness, and relevant specifications to clearly demarcate areas where RAC can be safely used. References Ajdukiewicz A, Kliszczewicz Alina. Influence of recycled aggregates on mechanical properties of HS/HPC. Cement Concrete Composites 2002;24:269–79. 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