crumb rubber in cold recycled bituminous mixes: comparison between traditional crumb rubber and...
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Construction and Building Materials 68 (2014) 370375Contents lists available at ScienceDirect
Construction and Building Materials
journal homepage: www.elsevier .com/locate /conbui ldmatCrumb Rubber in cold recycled bituminous mixes: Comparison betweenTraditional Crumb Rubber and Cryogenic Crumb Rubberhttp://dx.doi.org/10.1016/j.conbuildmat.2014.06.0930950-0618/ 2014 Elsevier Ltd. All rights reserved.
Corresponding author.E-mail addresses: firstname.lastname@example.org (G. Dondi), piergiorg.tataranni2@unibo.
it (P. Tataranni), email@example.com (M. Pettinari), firstname.lastname@example.org(C. Sangiorgi), email@example.com (A. Simone), firstname.lastname@example.org(V. Vignali).Giulio Dondi a, Piergiorgio Tataranni a,, Matteo Pettinari b, Cesare Sangiorgi a, Andrea Simone a,Valeria Vignali a
aDICAM-Roads, Dept. of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, V.le Risorgimento 2, 40136 Bologna, ItalybGeotechnics and Geology, Dept. of Civil Engineering, Brovej 118 Building, 2800 Kgs. Lynby, Denmark
h i g h l i g h t s
Use of rubber in Cold Recycled Mixes containing 100% Reclaimed Asphalt Pavement. Comparison between Traditional and Cryogenic Crumb Rubber in Cold Recycled Mixes. The presence of Crumb Rubber influences the volumetric characteristics of mixes. The use of CCR seems to be less detrimental than TCR for mechanical characteristics. The use of TCR or CCR generates similar mechanical responses for fatigue life.a r t i c l e i n f o
Article history:Received 27 February 2014Received in revised form 30 May 2014Accepted 30 June 2014
Keywords:Cold Recycled MixesReclaimed Asphalt PavementCryogenic Crumb RubberAmbient Crumb RubberRubberized mixtureFatigue lifeWorkabilitya b s t r a c t
Today recycling is one of the most innovative and interesting techniques for the rehabilitation of des-tressed road pavements. In recent years the increased interest in this process, has led to the developmentof various alternative methods for the recovery and the reuse of road bituminous materials. Cold recy-cling is, among the recycling techniques, certainly the most studied and developed: it allows the recov-ering of bituminous material from an existing pavement without the addition of heat, whilst ensuring thecreation of high quality bound base layers. A wide range of materials have been tested together withReclaimed Asphalt Pavement (RAP) and, consequently, there is a large number of variables that can beconsidered in the mix-design process of new eco-friendly Cold Recycled Mixes. In particular, the presentresearch involves the use of Crumb Rubber within a mixture containing 100% Reclaimed Asphalt Pave-ment, cold recycled with bitumen emulsion and cement. Two different Crumb Rubbers were adopted:one from the ambient production method, and one produced with the cryogenic process. The goal of thisresearch project was to analyze and evaluate the different physical and mechanical characteristicsinduced by the shared use of two different types of Crumb Rubber in the Cold Recycled Mixes.
2014 Elsevier Ltd. All rights reserved.1. Background
For the modern road infrastructure engineer the concept of sus-tainability often requires to focus on various main design aspects:economic, environmental and architectural. In recent years thetrend is to reduce the cost of construction, maintenance and thenegative externalities (habitat fragmentation, noise and air pollu-tion, landscape alterations) caused by the new infrastructure onthe surrounding environment and the population . This leadsto the using of eco-friendly construction techniques, to reducethe use of virgin raw materials and to promote the recycling andreuse of the so-called secondary raw materials (materials which,after complete initial use, may be used repeatedly in productionas starting material). An ever increasing number of innovativeand environmentally friendly materials has been launched on themarket, and others are still under study, with the step of character-ization of the materials of crucial importance. In the field of roadengineering, the use of recycled materials has become importantbecause of the limited availability of aggregates and the difficultiesand excessive disposal costs for milled materials .
Cold Mix Asphalt (CMA) and Rubberized Asphalt Concrete(RAC), were investigated in this study. Cold Mix Asphalt has gained
Table 1Properties of the aged asphalt binder from RAP.
Unit RAP 10-10+ RAP 5-10 RAP 0-5
% Binder (on mass of RAP) % 3.10 3.27 6.13Penetration @ 25 C dmm 9 7 7Soft. point C 73.8 75.5 78.8Dynamic Visc. @ 60 C Pas 52,625 58,015 95,305Heptane insolubles % 42.4 41.2 39.6
G. Dondi et al. / Construction and Building Materials 68 (2014) 370375 371increasing popularity in the last ten years for its versatile proper-ties. The benefits of using this eco-friendly material are above allthe reduction in energy consumption and emissions duringproduction and laying. Hence, compared to the traditional hottechnique it is possible to design high-performance paving withoutthe addition of heat . There are many other advantages of usingcold technique, for example Cold Mix Asphalt mixtures can be pro-duced in concrete plants. Since the laying is carried out at ambienttemperature materials can be handled with more flexibility intime. CMA mixtures can be used in many fields: from the rehabil-itation of more or less deep layers to the functional upgrading ofhigh traffic roads, and minor maintenance activities.
Highway engineers around the world have tried to incorporatescrap tire rubber in asphalt pavements since the 1950s . Thetask was difficult and early applications of rubber in Hot MixAsphalt concretes provided little or no benefit. It was not untilthe 1960s that a formulation was discovered that brought clearprofits. After a long period of research the so-called Asphalt Rubberwas introduced in the United States market in the mid 1980s andtoday is considered an environmentally friendly alternative toconventional asphalt pavements . Though few authors and stud-ies highlighted some environmental issues regarding hazardousfumes and emissions . According to the ASTM definition, AsphaltRubber is a blend of asphalt cement, reclaimed tire rubber, andcertain additives in which the rubber component is at least 15 percentby weight of the total blend and has reacted in the hot asphalt cementsufficiently to cause swelling of the rubber particles.
Crumb Rubber markets encourage the development of newtechnologies that use the material, and nowadays there is a largenumber of different solutions . For each application the mate-rial characterization is a basic step to understand the fundamentalproperties of the materials used.
Generally there are two different techniques to incorporate rub-ber either hot or cold in the bituminous mixture. The first one isthe wet process, in which rubber is inserted in the asphalt cementof the mix . In the dry process, instead, rubber is incorporateddirectly in the mixture blend . The rubber particles in the firstcase act as bitumen modifier pairing the effects of traditionalmodifiers (SBS, EVA, etc.)  and in the second case they becomepart of the mixture mastic and contribute to the layer enduranceduring its service life. Asphalt Rubber is not the solution to thewaste tires problem, but when utilized by agencies preferring itsbeneficial engineering characteristics such as durability, flexibility,strength, road noise attenuation and resistance to cracking, itcontributes significantly to the reduction of the amount of wastetires .
The present research starts from the idea that Crumb Rubbercan be advantageously used in a Cold Recycled Mixture containing100% aggregates from Reclaimed Asphalt Pavements . The aimis to evaluate the different properties associated to the bituminousmixture by using either Traditional or Cryogenic Crumb Rubber.The former is produced at ambient temperature and here it wasnamed Traditional Crumb Rubber, but it appears as AmbientCrumb Rubber (ACR) in several scientific publications. The researchfocuses also on the influence of particle size of the two differenttypes of Crumb Rubber on the mechanical behavior of mixtures.The rubber particles are incorporated directly into the mixturesblends and become part of their mastics.
The lack of specific technical requirements and procedures test-ing and controlling Cold Recycled Mixtures with Crumb Rubberdemands for a careful preliminary research step. Variables thatplay a significant role include: percentages, type and particle sizeof rubber, type and gradation of RAP, percentage of bituminousemulsion, temperature and aging time. The study has firstlyfocused on the mix-design with particular attention to the materi-als compactability and workability . Gyratory compaction wasthe application of choice for the laboratory densification process.Mechanical tests either static and dynamic were selected for themechanical characterization of the specimens. Eventually the useof Indirect Tensile Fatigue tests has been introduced to assess thefatigue strength of each mixture .3. Materials and experimental program
The materials used in the experimentation are: Reclaimed Asphalt Pavement(RAP), Traditional Crumb Rubber (TCR), Cryogenic Crumb Rubber (CCR), Cement(C) an