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Recycled Technology of Urban Road Construction Waste and
Miscellaneous Fill Used as Subgrade Fillings
Bingkang Liu a
Jinso...
contractibility are both positive properties of materials which could be viewed as ideal subgrade
fillings. To achieve the...
Modification Experiment
Based on the property tests of specimens shown above, the soil specimen A can not satisfy the
cons...
Unconfined Compressive Strength Test
Unconfined compressive strength test can be used to detect the subgrade fillings stre...
Various sorts of soil stabilizers have different modification mechanisms. Taking lime as
Calcium-Based Stabilizer for exam...
Advanced Building Materials
10.4028/www.scientific.net/AMR.250-253
Recycled Technology of Urban Road Construction Waste an...
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Recycled Technology of Urban Road Construction Waste and Miscellaneous Fill Used as Subgrade Fillsings

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Recycled Technology of Urban Road Construction Waste and Miscellaneous Fill Used as Subgrade Fillsings

  1. 1. Recycled Technology of Urban Road Construction Waste and Miscellaneous Fill Used as Subgrade Fillings Bingkang Liu a Jinsong Fan b Huimin Hu Lihui Fu School of Civil Engineering, Hefei University of Technology, Hefei, China, 230009 a liubingkang@hfut.edu.cn, b fanjinsong163@163.com Key words: miscellaneous fill, subgrade fillings, CBR, cold recycling technology, soil modification Abstract: Continuously increasing municipal renovation and roadbed excavation produced a considerable quantity of solid waste each year such us miscellaneous fill mixed with broken pavement fragments and brickbats, which resulted in a series of urban environment and soil resource issues. Comprehensive recycling technology for soil modification to attain the strength requirements of subgrade fillings from the related road construction codes is necessary and even urgent, since the usual soil replacement is not the economic and environment-friendly method. The field investigation and laboratorial tests hereby had been completed to confirm the application potentials of typical soil specimens selected from different locations. The experimental results indicate some of specimens can be reused as subgrade fillings in road construction immediately and others should be treated by soil amelioration. To further certify the practicality of this recycled technology and broaden its range of application, three typical reutilization and treatment techniques, cold recycling, soil solidification and dynamic consolidation are introduced into engineering projects. Introduction Urban road excavation and pavement renovation always produced a large amount of construction waste each year, which constituted a high proportion of the gross municipal solid waste (MSW) [1-2]. This kind of construction waste caused by road construction is usually composed of subgrade fillings as major components with a handful of cement or concrete fragments and a little domestic garbage. It is typical miscellaneous fill that is usually vaguely defined in the engineering as soil mixed by solid wastes with different grain sizes and various natures. Its heterogeneous composition and uncontrolled engineering performance determine its application difficulty in real construction. Recently, the most common treatment method is soil replacement by discarding previous miscellaneous fill and then instead bringing into qualified soil body used as subgrade fillings. Unfortunately, it will create more problems in succession such us taking up more space, using more transport vehicles, consuming more soil resource and inevitably contaminating urban environment or increasing construction cost. With the noticeable increasing construction waste in urban area, correlative issues concerning environmental pollution and resource-wasting should not be ignored. In recent two decades, researchers and engineers at home and abroad completed a series of experiments and practices to investigate the natures of this kind of miscellaneous fill mixed with MSW, confirm its composition, and improve its road performance for reaching related construction standards by means of proper treatment methods. Besides soil as principal part, systematic experiments and tests by different research groups indicated that selected soil specimens usually contained all kinds of MSW originated from those disused construction materials such us cracked asphalt concrete or concrete blocks, brickbats, rubbles, metals, etc. and a small quantity of life solid waste such us saw dust, plastic, or even paper scrap, glass and so on [3-4]. Meanwhile, its chemical composition is more or less referring to silicate, oxidate, hydride, carbonate, sulphate and sulfide, etc [5]. Despite the internal composition and ingredients proportion are so multifarious, most of them have some common characteristics: thickness misproportion in soil layers, considerable deformation, low strength, compressibility and collapsibility [6]. Based on the test, it also has several beneficial natures making it entirely possible to be applied in the road renovation. Proper permeability, low frost heaving rate, unconspicuous plasticity and minor Advanced Materials Research Online: 2011-05-17 ISSN: 1662-8985, Vols. 250-253, pp 3460-3464 doi:10.4028/www.scientific.net/AMR.250-253.3460 © 2011 Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 140.254.77.133, Ohio State University Library, Columbus, USA-08/02/16,19:42:21)
  2. 2. contractibility are both positive properties of materials which could be viewed as ideal subgrade fillings. To achieve the recycling application, some other disadvantages and restrictions on further application such us its uneven composition and non-uniformity of characteristics have to be overcome by making detailed origin analysis, instituting rational classification systems with proper indicators. For this purpose, this paper firstly completed a series of field investigation and experimental tests on selected soil specimens, then acquired effective data to evaluate their roadbed performance, and finally chose the appropriate construction equipments, procedures and construction technology, which will be introduced as below. Specimen Property Test The field survey illustrated that miscellaneous fill mixed with MSW with complex composition from one site to another generally originated by excavating old roadbeds. To acquire the rational soil natures, four soil specimens (marked with A, B, C and D) were selected in separated areas of Hefei, China. Fig. 1 shown below illustrates soil specimen in the original location. To effectively evaluate the application potentials of selected soil specimens in real recycle projects, raw specimens should be separated firstly with different particle diameters. The precise statistic result is listed in Table 1 to tell the proportion of solid waste which has particle diameter over 6mm in gross weight of each soil specimen. Table 1 and Fig.2 show us some detailed materials natures of soil specimens A-D (main soil body with particle diameters less than 6mm) on the basis of the Test Methods of Soils for Highway Engineering (JTG E40-2007) which provides specific experiment items and testing procedures. Table 1 Materials properties testing results Specimens A B C D Proportion of Solid Waste(in gross weight)* % 20.3 2.3 53.5 4.4 Natural Moisture Ratios % 17.1 18.2 18.7 14.5 Free Swelling Ratio % 44 23 39 48 Plastic Limits 20.3 19.8 22.6 20.1 Plasticity Index 24.2 15.1 19.8 32.2 Optimum Moisture Content % 13.0 13.2 14.5 15.0 Maximum Dry Density g/cm3 1.80 1.94 1.80 1.85 CBR % 4.28 15.5 9.61 7.76 *Define 6mm (Diameter) as the limit between solid waste blocks and soil Fig.1 Soil specimen in original position Fig. 2 Soil specimen size distribution curves A three-level classification system of miscellaneous fill mixed with MSW is proposed carefully for the purpose of analyzing materials origin, confirming proportion of ingredients and evaluating application potentials. These three classes with related indicators and specifications are illustrated in Table 2. Advanced Materials Research Vols. 250-253 3461
  3. 3. Modification Experiment Based on the property tests of specimens shown above, the soil specimen A can not satisfy the construction codes and therefore the proper soil modification seems necessary. The first-level lime (CaO&MgO≥60% of gross weight) had been chosen as inorganic binder to improve specimen A’s road performance. Compaction test and unconfined compressive strength test were selected to evaluate the modification effects. Table 2 Evaluation of soil specimens based on the three-level classification system Third Class(soil properties ) Symbol Classification indicators Symbol Classification indicators Classification descriptions A J SK weak swelling soil(Free Swelling Ratio<65%); low liquid limit clay (δef <50) ;CBR<5% Not qualified for road embankment or roadbed fillings B J SK weak swelling soil(Free Swelling Ratio<65%) ;low liquid limit clay (δef <50) ;CBR>8% Qualified for road embankment and roadbed fillings C J SK weak swelling soil(Free Swelling Ratio<65%) ;low liquid limit clay (δef <50) ;CBR>8% Qualified for road embankment and roadbed fillings D J TT weak swelling soil(Free Swelling Ratio<65%);high liquid limits clay (δef >50) ;CBR 5%-8% Qualified for road embankment J-construction waste S-life waste G-industrial waste H-mixed waste SK- massive rocks content≥50% of gross weight TT- massive rocks content < 50% of gross weight Massive rocks are defined as soil particles with size diameter over 6 mm. Road performace evaluation* Specimens First Class(origins) Second Class(proportion of solid waste) * According to Specifications for Design of Highway Subgrades (JTG D30-2004) Compaction Test The first-level lime had been added into specimen A by different sets with proportions of 5%, 7% and 8%. Fig.3 describes the optimum moisture content slightly raises and the maximum dry density slowly reduces with increasing lime contents, which manifests the maximum dry density becomes insensitive to the change of moisture contents. This new trend of diminished maximum dry density by increasing lime proportion also demonstrates this modification method effectively broaden the applicable scope of soil materials for qualified strength. It means that feed with same amount of water, soil specimens become more compact after soil modification with lime than before. Fig.3 Optimum moisture content & maximum dry density changes 3462 Advanced Building Materials
  4. 4. Unconfined Compressive Strength Test Unconfined compressive strength test can be used to detect the subgrade fillings strength. It made three groups of 7 cylinder specimens with different sets of lime admixture (5%, 7%and 8%) to determine their 7 days strength. According to Technical Specifications for Construction of Highway Roadbases (JTJ 034-2000), experiment results and evaluation are summarized in Table 3. Table 3 Experimental results and evaluation on specimen A mixed with lime Highways&First Class Roads Other Roads Highways&First Class Roads Other Roads 5% 0.79 0.125 × √ 7% 0.95 0.089 √ √ 8% 0.82 0.101 √ √ Evaluation ≥0.8 0.5-0.7 Lime Content Average Intensity Value (Mpa) Deviation Coefficient of 7 cylinder specimens Cv Required Minimum Intensity(Mpa) Experiment results and evaluation indicate lime as additive in specimen A can effectively improve its road performance. They also recommend that 7% seems to be the optimum adding proportion of lime. It also reveals the application potential for similar inorganic binder materials. Utilization and Treatment Technology Cold Recycling Technology. Cold recycling technology is a typical technique for pavements and roadbeds reconstruction. It usually crushes the discarded road construction waste into pieces within limited particle sizes, adds some new or fine aggregate or inorganic binder as supplements, and then completes a set of technical process such us milling, crushing, mixing, paving and compacting into forms. It has some more obvious advantages than traditional technics. Saving construction material by recycling waste, simplifying the construction process by accomplishing each process continuously, protecting environment by simplifying transportation sections are several significant strong points. ALLU Screener Crusher made by ALLU Finland Ltd. can be fixed on the common excavators for solid waste separation, crush, grind, aeration, mixing, feeding and loading (shown in Fig.4). Material crushing Material blending Fig. 4 ALLU Screener Crusher Soil Solidification. Soil stabilizers are usually divided into Calcium-Based Stabilizer (CBS) and Non-Calcium-Based Stabilizer (NCBS), which can stimulate soil activity, ameliorate soil microstructure and improve soil strength. CBS contains lime, cement, fly ash and slag as well as NCBS refers to ionic soil stabilizer (ISS, Condor SS, Roadpacker, etc.), enzyme(CMC2, Perma-Zyme, etc.), polymer(Road Oyl, Consoild 444,etc.) and so on. Advanced Materials Research Vols. 250-253 3463
  5. 5. Various sorts of soil stabilizers have different modification mechanisms. Taking lime as Calcium-Based Stabilizer for example, the procedures of ion-exchange, carbonation, crystallization occur in succession and interact simultaneously. Lime stabilized soil is the common product of lime solidification based on the main chemical reaction presented as Equation.1. xCa(OH)2+SiO2+(n-x)H2O→xCaO·SiO2·H2O (1) The main product of this chemical reaction is CSH (calcium silicate hydrate) which generates cementation to bond minor particles with soil particles. The colloidal particles of CSH can also fill up interspaces between soil particles for enhancing compactness and strength of soil body dramatically. The working mechanism of polymer stabilizer is physical but not chemical. It commonly does not change the inner structure of soil microstructure, but does concentrate and solidify the soil particles to yield strong adherence by enclosing single soil particle. Heavy-tamping Method. Heavy-tamping method initially invented by Mena Technology Company in France with another name dynamic consolidation method usually hoists the heavy punch up to 8-25m and then makes it in free fall to press the top-soil repeatedly. It can transform kinetic energy from heavy punch into shock wave and dynamic stress in the deep soil body, force the soil particles to realign and become compact. Simple construction process, low cost and ideal effect make it previous in engineering projects. It also can improve the bearing capacity, compression modulus, increase dry density, reduce the void ratio, and eliminate the collapsibility, expansibility or liquefaction. Heavy-tamping method has been certified with broaden applications for different soils. For miscellaneous fill used as subgrade and ground fillings, the compressibility of roadbed and building foundation can reduce by 20~100% and strength can rise by 200~500%. It is not easy to conclude the mechanisms in one single theory. Nowadays, dynamic consolidation theory, vibration wave compaction theory and solid micromechanics are both recommended as acceptable theories. Conclusion In order to explore the application potentials of miscellaneous fill with solid waste caused by road excavation and renovation, specimens A, B, C and D are selected to be tested to acquire their material properties. The comprehensive evaluation shows us it is entirely possible to reutilize most of them as subgrade fillings directly or just ameliorate them by some methods at the guidance of related road construction codes and regulations. In engineering projects, cold recycling technology, soil modification with additives and heavy-tamping method are recommended as several effective ways to implement recycling and utilization technology. Acknowledgement The authors are grateful for support received from the Hefei Administration of Key Construction Projects and Hefei University of Technology (research item: “Comprehensive Utilization and Technical Research on Urban Road Construction Waste and Miscellaneous Fill”, 2008-2009). References [1] Tapan Narayana: Waste Management, Vol.29(2009), p.1163–1166 [2] Zhenying Zhang, Shiming Wu, Yunmin Chen:Chinese Journal of Geotechnical Engineering, Vol.22, No.1 (2000), p.35-39 [3] Huiwen Wan, Shuyan Yang, Chisun Poon: Science and Technology of Overseas Building Materials, Vol.28, (2007), p. 47-50 [4] D.T.C. Yao, Y. Y. Tsai: Advanced in Earth Structures: Research to Practice (GSP151), 2006, p.157-164 [5] Z. Salem, K. Hamouri, R. Djemaa, K. Allia: Desalination, Vol.220(2008), p.108–114 [6] Dingguo Yang, Ruiqian Wu, Qiuping Wang: Journal of Shaoxing University, Vol.25(2005), p. 69-71 3464 Advanced Building Materials
  6. 6. Advanced Building Materials 10.4028/www.scientific.net/AMR.250-253 Recycled Technology of Urban Road Construction Waste and Miscellaneous Fill Used as Subgrade Fillings 10.4028/www.scientific.net/AMR.250-253.3460 DOI References [1] Tapan Narayana: Waste Management, Vol. 29(2009), p.1163–1166. 10.1016/j.wasman.2008.06.038 [5] Z. Salem, K. Hamouri, R. Djemaa, K. Allia: Desalination, Vol. 220(2008), p.108–114. 10.1016/j.desal.2007.01.026

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