Available online at ScienceDirect. Procedia Engineering 161 (2016 ) 42 46

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1 Available online at ScienceDirect Procedia Engineering 161 (2016 ) World Multidisciplinary Civil Engineering-Architecture-Urban Planning Symposium 2016, WMCAUS 2016 Current Methods for the Utilization of the Fresh Concrete Waste Returned to Batching Plants Aynur Kazaz a, *, Serdar Ulubeyli b a Division of Construction Management, Department of Civil Engineering, Akdeniz University, 07058, Antalya, Turkey a Division of Construction Management, Department of Civil Engineering, Bulent Ecevit University, 67100, Zonguldak, Turkey Abstract As the fresh concrete waste has a high potential to damage the environment, current methods for the utilization of the returned ready-mixed concrete were presented throughout this study. Toward this aim, an in-depth literature review was performed as a methodological approach. Thus, types of the returned concrete were first explained and the existing methods were then discussed one by one. Consequently, the current methods were determined as (i) matching with suitable customers, (ii) blending with next matches, (iii) discharging into the settling basin, (iv) discharging onto the ground, (v) producing pre-cast concrete components, (vi) recycling mechanically, (vii) using the hardened slurry cake in concrete, (viii) using the hardened slurry cake in partition wall blocks, (ix) using hydration stabilizer admixtures, and (x) using superabsorbent polymer The Authors. Published by Elsevier by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of WMCAUS Peer-review under responsibility of the organizing committee of WMCAUS 2016 Keywords: batching plant; fresh concrete waste; leftover concrete; over-ordered concrete; returned concrete; 1. Introduction Concrete waste forms the major ingredient of the construction solid waste, accounting of 50% of the total construction and demolition waste generation [1]. Although hardened concrete is not dangerous, fresh concrete can cause serious burns to human skin [2] and damage soil and water [3] as it is alkaline. Therefore, it is necessary to minimize or fully eliminate the disposal of fresh concrete waste. This can provide several benefits as follows, * Corresponding author. Tel.: ; fax: address: akazaz@akdeniz.edu.tr The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the organizing committee of WMCAUS 2016 doi: /j.proeng

2 Aynur Kazaz and Serdar Ulubeyli / Procedia Engineering 161 ( 2016 ) Reduction in the consumption of non-renewable natural resources, Reduction of areas destined for landfill, Reduction of the energy consumption, Reduction of pollution in the cement production. Given the environmental significance of the fresh concrete waste, this study aims to report current methods for the utilization of the fresh concrete waste returned to batching plants. This is because, in the related literature, these techniques have not been presented together up to date and each one of them has been investigated separately without citing the others. In this regard, the present study is the first attempt to give a full picture of utilization opportunities of these wastes. Thus, it can fill the gap in the literature. 2. Types of returned concrete The concrete returned to a batching plant can be divided into two types: (i) over-ordered concrete of which frequency depends on the accuracy of the ordering and delivery practices and (ii) leftover concrete which is always observed in a truck mixer after each delivery Over-ordered concrete As it is difficult to match specific mix types with suitable customers at short notice or to blend the returned plastic concrete with subsequent batches especially in off-peak periods, current off-site practices for a batching plant may generate a significant quantity of the fresh concrete waste through over-order from construction sites since it is easier for customers to cut corners by over-specifying than to refine the numbers by number-crunching. This is particularly prevalent in low-cost materials although it is a hidden source of revenue for large concrete suppliers Leftover concrete Aggregates can be reclaimed from the mud that results from washout and cleaning operations of truck mixer drums at the end of each working day to prevent the small amount of the fresh concrete residue from setting in the drum overnight. About 8-10 tons of the fresh concrete waste can be produced every day from a concrete batching plant with a daily output of 1000 m 3 of concrete [4], which typically corresponds to % of the total production [5]. According to Paolini and Khurana [6], there are about kg of mortar remaining or adhering to the inside of each truck mixer drum. These numerical values confirm that it represents a heavy burden for contractors, batching plants, and the environment. 3. Results and discussions Current methods of processing the returned concrete include the following opportunities and change with the type of the returned concrete as shown in Fig Direct ingredient of new batches The returned concrete can be used as a direct ingredient as partially hydrated cementitious materials (PHCMs) in the new concrete. PHCMs act as an effective setting and hardening accelerator without the need for the accelerating admixtures. Mixtures incorporating PHCMs show higher mechanical properties [7,8,9,10] Discharging into settling basin This option is applied especially by small- and medium-sized batching plants where leftover concrete material is discharged into the settling basin.

3 44 Aynur Kazaz and Serdar Ulubeyli / Procedia Engineering 161 ( 2016 ) Fig. 1. Methods for benefiting from the returned concrete. A series of interconnected washout pits can be used to allow the progressive settlement of cement solids and other fines. By doing so, the sufficiently drained solid sludge is either used as a fill material or disposed in landfills Discharging onto ground As the most used method, excess concrete material is discharged onto the ground at a particular location in the plant until hardened although this does not seem to be an environmentally friendly method. Hardened concrete is then dumped to a landfill or crushed to produce aggregates Pre-cast components Pre-cast concrete elements (e.g., blocks for breakwaters or retaining walls, pads, and bulkheads) are produced by the over-ordered concrete at the batching plant. However, this possibility can be very limited by local market conditions and opportunities Mechanical recyclers This option used for over-ordered and leftover concrete especially by large-sized batching plants includes mechanical reclamation systems. The coarser sand and aggregates can be reused as a replacement of natural fine aggregates for new construction works in where they can be as competitive as virgin aggregate. About 42% can be recycled as coarse aggregate from concrete waste [1]. Concrete that contains 15-30% recycled fresh concrete waste aggregates is optimum for producing normal strength concrete [11,12]. Although the reluctance of most concrete producers, especially some of the smaller ones, in reclaiming aggregate from the concrete waste seems to be due to the relatively high operating cost and initial capital investment, the costs of dumping the over-ordered concrete waste to landfill areas are double that of the aggregate recycling plan [1].

4 Aynur Kazaz and Serdar Ulubeyli / Procedia Engineering 161 ( 2016 ) Hardened slurry cake in concrete To replace natural aggregates, hardened slurry cake remained after coarse and fine aggregates in residual fresh concrete is recycled and taken. In case of the use of this waste in the new fresh concrete, some important physical properties are adversely affected. However, it is possible to match the designed compressive strength of concrete containing no more than 30% hardened slurry cake aggregate with that of the corresponding natural aggregate concrete. Therefore, hardened slurry cake can be used for non-structural concrete production [4] Hardened slurry cake in partition wall blocks The hardened slurry cake can also be used in the production of partition wall blocks. In this case, blocks produced with waste aggregates of 50% show the highest compressive strength. Overall, it is feasible to utilize it in non-loadbearing concrete products [13] Hydration stabilizer admixtures For the over-ordered concrete, recycling can be made by chemical systems based on the addition of extended setcontrol or hydration stabilizer admixtures (i.e., super-plasticizers). These were originally developed for the overnight and weekend stabilization of the returned plastic concrete and for the long-haul stabilization of concrete that has to be placed at long distances from the batching plant [3]. The concrete mix can be maintained in a deactivated state for maximum 3 days. It is established that no more than 1 or 2 m 3 per mix can be activated, and the newly batched concrete is mixed with it. Set-retarding admixtures do not adversely affect important mechanical parameters of concrete. Also, the longer the setting time of the blended batch, the higher the strength [6,7,14,15]. Hence, it is feasible to use these admixtures Superabsorbent polymer (SAP) For the over-ordered concrete, recycling efforts can be realized by chemical systems based on the addition of a non-toxic additive called SAP into the truck mixer drum without the need of any specific equipment. After its addition, a mixing process of 6-7 minutes takes place, followed by discharging and curing procedures. Thus, 1 m 3 returned concrete can be transformed into 2.4 tons of new aggregates. Concrete with 100% of new aggregates has been developed and marketed in Japan. It is possible to use new aggregates for the non-structural concrete production without adverse effects on the mechanical characteristic of concrete [16]. 4. Conclusions In this study, methods for benefiting from returned concrete in batching plants were determined and discussed. In conclusion, these methods can be listed as (i) matching with suitable customers, (ii) blending with next matches, (iii) discharging into settling basin, (iv) discharging onto the ground, (v) producing pre-cast concrete components, (vi) recycling mechanically, (vii) using the hardened slurry cake in concrete, and (viii) using the hardened slurry cake in partition wall blocks, (ix) using hydration stabilizer admixtures, and (x) using superabsorbent polymer. As a research implication, this study may help researchers who will investigate the returned concrete from the economic, technical, and managerial point of view. In terms of the practical implication, it may attract attention of industrial practitioners to benefit from such wastes. As a social implication, the selection of suitable methods of processing the returned concrete can save and enhance the sustainability of the overall environment and affect society positively.

5 46 Aynur Kazaz and Serdar Ulubeyli / Procedia Engineering 161 ( 2016 ) Acknowledgements The authors acknowledge the financial supports provided by Committees on Research Grants of Akdeniz University and Bulent Ecevit University. This study is based on a research project supported financially by TUBITAK under the grant number MAG-113M428. References [1] V.W.Y. Tam, C.M. Tam, Economic comparison of recycling over-ordered fresh concrete: a case study approach, Res. Cons. Rec. 52 (2007) [2] W. Peters, Alkali burns from wet cement, Can. Med. Assoc. J. 130 (1984) [3] J.A.F. Papi, Recycling of fresh concrete exceeding and wash water in concrete mixing plants, Mater. Const. 64 (2014) 1-9. [4] S. Kou, B. Zhan, C. Poon, Feasibility study of using recycled fresh concrete waste as coarse aggregates in concrete, Const. Build. Mater. 28 (2012) [5] CSI (Cement Sustainability Initiative), Recycling Concrete, World Business Council for Sustainable Development, Switzerland, [6] M. Paolini, R. Khurana, Admixtures for recycling of waste concrete, Cem. Conc. Comp. 20 (1998) [7] C. Lobo, W.F. Guthrie, R. Kacker, A study on the reuse of plastic concrete using extended set-retarding admixtures, J. Res. Nat. Inst. Stand. Tech. 100 (1995) [8] A.M. Soliman, M.L. Nehdi, Self-accelerated reactive powder concrete using partially hydrated cementitious materials, ACI Mater. J. 108 (2011) [9] A.M. Soliman, M.L. Nehdi, Effect of partially hydrated cementitious materials and superabsorbent polymer on early-age shrinkage of UHPC, Const. Build. Mater. 41 (2013a) [10]A.M. Soliman, M.L. Nehdi, Effect of partially hydrated cementitious materials on early-age shrinkage of ultra-high-performance concrete, Mag. Conc. Res. 65 (2013b) [11]S.L. Correia, F.L. Souza, G. Dienstmann, A.M. Segadaes, Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments, Waste Manag. 29 (2009) [12]G.K. Arunvivek, G. Maheswaran, S.S. Kumar, M. Senthilkumar, T. Bragadeeswaran, Experimental study on influence of recycled fresh concrete waste coarse aggregate on properties of concrete, Int. J. App. Eng. Res. 10 (2015) [13]S. Kou, B. Zhan, C. Poon, Properties of partition wall blocks prepared with fresh concrete wastes, Const. Build. Mater. 36 (2012b) [14]Y. Okawa, H. Yamamiya, S. Nishibayashi, Study on the reuse of returned concrete, Mag. Conc. Res. 52 (2000) [15]A. Haddad, B.R. Cortes, A.J. Evangelista, Use of cement hydration stabilizer admixture at ready mix concrete to avoid material waste, Adv. Mater. Res. 818 (2013) [16]G. Ferrari, M. Miyamoto, A. Ferrari, New sustainable technology for recycling returned concrete, Const. Build. Mater. 67 (2014)