RECYCLING OF RECLAIMED BITUMINOUS PAVEMENT MATERIALS

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1 RECYCLING OF RECLAIMED BITUMINOUS PAVEMENT MATERIALS R.B.Ahmed 1*, A.Rahman 2, K.Islam 2, J. Amin 2, S. K. Palit 2 1 Department of Civil Engineering, Port City International University, Chittagong, Bangladesh. 2 Department of Civil Engineering, Chittagong University of Engineering &Technology, Chittagong, Bangladesh. *Corresponding Author<rayhan.tohur@gmail.com> ABSTRACT Most of the highways and roads of Bangladesh are generally constructed as flexible pavement and are generally designed with fresh aggregates and neat bitumen. During road re-construction and rehabilitation, proper handling of demolished pavement becomes a great problem. When this demolished pavement is not properly handled, it causes environmental hazards and creates disposal problems. Reusing of demolished pavement materials may become a possible alternative for pavement construction. Environmental, economic, and social benefits are the encouraging factors for pavement recycling. The global objective of sustainable development can be achieved by making use of Reclaimed Asphalt Pavement (RAP) in roadway paving new projects. The main purpose of this study is to investigate the use of RAP materials in addition of neat bitumen at various types of highway. The study describes the determination of Optimum Bitumen Content (OBC) using Marshall Mix Design method at various bitumen content. The investigation also covers the determination of bitumen content present in RAP and reclaimed aggregate gradation before Marshall Mix Design and finding out the water sensitivity of bituminous mix in terms of retained stability at OBC. The aggregates of reclaimed pavement falls within the envelope for continuously graded mix and the binder content present in RAP is 1.37%. From this design, the OBC was found as 4.92% and at OBC, the retained stability was found as 77.2%. Marshall Mix Design properties at OBC of the samples are in specified limit according to Marshall Mix Design criteria for a new pavement construction. So, it can be concluded that reclaimed pavement materials with the addition of neat bitumen can be reused as bituminous surface course successfully. Keywords: Demolished Pavement, Reclaimed Asphalt Pavement (RAP), Optimum Bitumen Content (OBC), Marshall Mix Design. INTRODUCTION Over 90 percent of Bangladesh highways & roads are constructed with flexible pavement. The design of a flexible paving mixture usually involves selecting the aggregates and bitumen to be used, testing the bitumen mixtures at different proportions of the ingredients and selecting the optimum mix design which would give the best anticipated performance in service. Flexible pavements are designed by using fine aggregates, coarse aggregates and bitumen. The materials used to build the original pavement system can be reused to make the new pavement. Flexible pavement reusing is becoming an increasingly important alternative in worldwide for pavement design, once sustainability and environmental issues have continued to receive more attention. The reference point is that of considering the use of road materials in a way, in which flexible pavement materials previously used in road construction can be reused in new road construction. (Biswas, 2013). The Mega road modernization exposes challenges of various concerns pertaining to depletion of resources like good soil and aggregates, long lead to get good quality aggregates and increase in fuel consumption etc. Furthermore, the supply of Bitumen, whose cost keeps on increasing, is dependent on foreign sources, and energy that is needed for processing new materials is becoming costlier every day. The recycling of existing bituminous mixes are the only alternatives, through the reuse of aggregates and bitumen. Use of the recycled materials in the road construction has been favored over fresh

2 materials in the light of increasing cost of bitumen, scarcity of good quality aggregates and the priority towards preservation of the environment. Considering the material and construction cost alone, it is estimated that using recycled materials, saving ranging from 14 to 34% can be achieved. It is universally recognized that an important benefit of asphalt as a pavement construction material is its ability to be recycled (Tambake et al). Concrete recycling for paving applications is now performed in many countries and has the support of the Federal Highway Administration (FHWA), which states that, The same materials used to build the original highway system can be re-used to repair, reconstruct, and maintain them. Where appropriate, recycling of aggregates and other highway construction materials makes sound economic, environmental, and engineering sense. (FHWA, 2011) FHWA further states that, The engineering feasibility of using recycled materials has been demonstrated in research, field studies, experimental projects and long-term performance testing and analysis. When appropriately used, recycled materials can effectively and safely reduce cost, save time, offer equal or, in some cases, significant improvement to performance qualities, and provide long-term environmental benefits (FHWA 2002). Reclaimed Asphalt Pavement or RAP is obtained typically from asphalt pavement surfaces that are milled off before repaving s. It also comes from asphalt that is removed during repairs of pavements or prior to replacing pavement. Most RAP materials come from removed roadways, driveways, parking lots, airports and highways as the by-product of asphalt pavement. RAP can be used for further construction of pavement and the cost can be minimized. Problems such as disposal of reclaimed asphalt materials from paving projects, high production cost of asphalt and transportation cost of virgin material are addressed by recycling of RAP. In laboratory investigation, it has been extracted the bitumen present in collected demolished pavement and determined the bitumen content & aggregate gradation of collected RAP materials. To determine stability, flow & Optimum Bitumen Content (OBC), Marshall Method of mix design has been used. Also OBC has been calculated by Equation [1] (Kadyali, 2003). To conduct the performance, retained stability test has also been conducted by Marshall Method and the retained stability has been calculated by Equation [2]. OBC = Bitumen content at (max. stability + max. density + avg. air void + 80% VFA)/4 (1) Retained Stability = (Soaked Stability / Standard Stability)*100.(2) So the following objectives have been selected for the present investigation to improve the present condition. Determination of the bitumen content in reclaimed pavement materials. Determination of the aggregate gradation in reclaimed pavement materials. Determination of OBC of reclaimed pavement with the addition of neat bitumen. To find out the water sensitiveness of the mix in terms of retained stability. METHODOLOGY Suitably designed bituminous mix will withstand heavy traffic loads under adverse climatic conditions and also fulfill the requirement of structural and pavement surface characteristics. The objective of the design of bituminous mix is to determine an economical blend through several trial mixes. The entire investigation was done according to a systematic manner to fulfil the objectives of the investigation. The total investigation is represented by work flow diagram shown in Figure 1.

3 Figure 1: Work Flow Diagram RECLAIMED PAVEMENT MATERIALS COLLECTION & PULVERIZING Reclaimed pavement materials were collected about a required amount and brought into the transportation laboratory of civil engineering department. Firstly, the collected pavement are cleaned. Mud, grass and other foreign materials are removed manually from the upper surface of reclaimed pavement. Secondly, after cleaning, they are dried properly in order to remove water, if present. And finally it was pulverized to separate from each other. Then the pulverized materials were used to determine the existing bitumen content in it, to determine aggregate gradation, flakiness & elongation index, to perform Marshall Mix design and finally water sensitivity test in terms of retained stability. The reclaimed pavement materials collected, were plant bituminous mix.the collected pavement materials & pulverized materials has been represented in Figure 2. Figure 2: Collected Pavement materials after Pulverizing LABORATORY INVESTIGATION To investigate the properties of reclaimed bituminous pavement, several tests were conducted in the Transportation Laboratory of Department of Civil Engineering, Chittagong University of Engineering & Technology. It includes determination of bitumen content & aggregate gradation, blending of Reclaimed Bituminous Materials with Neat Bitumen, Marshall mix design and performance tests. Determination of Bitumen Content Bitumen was extracted from reclaimed pavement materials by using AASHTO T 164. Bitumen content has been calculated using Equation [3]. Bitumen Content= [{W (W 1+W 2)}*100] / W (3) Where, W, W 1& W 2 are Total Weight of sample taken, Weight of sample after washing with kerosene & Weight of filler material stored on filter paper after filtering respectively.

4 Determination of Aggregate Gradation Screening tests are typically conducted through sieve analysis according to AASHTO Standards T-27 and T-11. Some highway agencies and DOTs utilize their own screening test methods, such as Florida DOT FM1 T-027. It has been used ASTM codes for aggregate gradation in the present investigation Blending of Reclaimed Bituminous Materials with Neat Bitumen Pulverized demolished bituminous pavement materials have been mixed with neat bitumen with varying content so as to fulfil the requirements of the relevant standards. The required quantity of the mix is taken so as to produce compacted bituminous mix specimens of thickness 63.5 mm approximately. 1100gm of demolished pavement materials are required to produce the desired thickness. The aggregates are heated to a temperature of 170 to 180 C the compaction mould assembly and rammer are cleaned and kept pre-heated to a temperature of 120 C to 145 C. The bitumen is heated to a temperature of 140 C to 150 C and the required amount of first trial of bitumen is added to the heated aggregate and thoroughly mixed. The mix is placed in a mould and compacted with number of 75 blows for each face of the specimen. EXPERIMENTAL RESULTS & DISCUSSION Reclaimed bituminous pavement collected from the site is generally a mixture of aggregates, bitumen and foreign materials. At the initial stage of investigation, the foreign materials have been removed from demolished pavement and turned the larger size into workable required size for the design. Bitumen Content in Reclaimed Pavement Materials After bitumen extraction, the bitumen content present in reclaimed pavement materials is found from Equation [3] and the content is 1.37%. The partial process of bitumen extraction is shown in Figure 3. Aggregate Gradation of Reclaimed Materials After extraction of bitumen from pulverized pavement materials, reclaimed aggregates are found, which are further graded according to standard. The aggregate gradation curve is shown in Figure 4. Figure 3: Bitumen extraction Figure 4: Aggregate gradation curve From the Figure 4, it is seen that the curve is S-shaped. So, the aggregates of the collected pavement sample seem to be a well-graded sample. Properties of Neat Bitumen For this study, 80/100 grade bitumen has been used because of its availability and also to reduce the cost of pavement construction. The properties of neat bitumen have been represented in Table 1.

5 Table 1: Properties of neat bitumen Bituminous Properties Value Specific Gravity (gm./cc) 1.01 Flash Point (ºC) 302 Fire Point (ºC) 315 Penetration Value (0.1 mm) 98.0 Solubility (%) 95.6 Softening Point (ºC) 47 Loss of Heating (%) Elongation (cm) Performance Test To determine stability, flow & OBC of the bituminous mixes Marshall Method has been used. Selected additional bitumen content were 2.63%, 3.13%, 3.5%, 4%, 4.5%, 5% for the preparation of trial Marshall Specimen, when the existing bitumen content in reclaimed pavement was 1.37%. The experimental results have been presented in Table 2 and the Marshall Properties have been plotted against bitumen content in Figure 5. The OBC has been calculated from Figure 5 using Equation [1]. Table 2: Marshall Mix Design properties Bitumen Content (Existing+ Additional)% 4.0 ( ) 4.50 ( ) 4.87 ( ) 5.37 ( ) 5.87 ( ) 6.37 ( ) Density, Gb (gm/cm 3 ) Theoretical Specific Gravity Gt, (gm/cm 3 ) Air Void Vv, % VMA,% VFB, % Flow mm Stability kn

6 Figure 5: Properties of Marshall Parameters From Table 2, Marshall Properties has been plotted in Figure 5 and OBC has been calculated using Equation [1]. From Figure 5, it has been found that, Bitumen content at maximum stability = 4.72%, Bitumen content at maximum density = 5.00% Bitumen content at average air void = 4.70% & Bitumen content at 80% VFB = 5.25% OBC = Bitumen content at (max. stability + max. density + avg. air void + 80% VFA)/4 = ( )/4 = 4.92% So, the OBC value is 4.92%. Therefore this OBC has been used for Retained Stability test as per STP The retained stability has been calculated using equation 2 and found as 77.2% which is shown in Table 3. Table 3: Results of Retained stability test Type Stability kn Retained stability, % Soaked 7.46 Standard Hence, it has been found that the Marshall stability of this blended mix is 9.98 kn at OBC 4.92% & retained stability is 77.2%, which has marginally satisfied the Marshall Criteria CONCLUSIONS The road network in Bangladesh is in a deplorable state due to long neglect as a result of lack of funds for maintenance and rehabilitation. Reclaimed bituminous mix is being used extensively both in developed and developing countries in new road structure and they are continuously developing this technology in order to get more strength of pavement using reclaimed pavement materials. But in our country, reclaimed material is not used in new road construction yet. So RAP materials can be considered in new road construction for the following reasons.

7 1. Reusing of reclaimed asphalt pavement in new road construction has been considered from two main environmental aspects point of view: (a) Solving the increasing waste disposal crisis and (b) Save the depletion of natural resources. 2. Recycling of Asphalt pavement in new road construction cost will be reduced as some percentage of bitumen content exists in RAP as well as aggregate cost is almost absent. 3. Use of recycled pavement materials along with neat bitumen marginally satisfies the Marshall criteria for heavy tire pressure road. So it can be used for any type of road construction. 4. As the retained stability in our investigation is above the minimum requirement, the road construction with reclaimed materials will be stable during wet season and will last for longer period. REFERENCES S. K. Khanna and C. E. G. Justo, HIGHWAY ENGINEERING, 7 th edition, India. Kadyali, L.R & Lal, N.B.; Principles And Practices of Highway Engineering ;4 th Edition.2003, India. Tutul Biswas, DESIGN OF FLEXIBLE PAVEMENT USING RECYCLED FLEXIBLE PAVEMENT MATERIALS, Department of Civil Engineering, Chittagong University of Engineering & Technology. (September, 2013) Spurti O. Tambake, Dheeraj. N. Kumar and Manjunath. K. R., LABORATORY INVESTIGATION ON HOT MIX ASPHALT USING RECLAIMED ASPHALT PAVEMENT (RAP) FOR BITUMINOUS CONCRETE MIX, IJRET: International Journal of Research in Engineering and Technology. Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice, PUBLICATION NO. FHWA-HRT , APRIL Imad L. Al-Qadi, Mostafa Elseif and Samuel H. Carpenter, RECLAIMED ASPHALT PAVEMENT A LITERATURE REVIEW, Research Report FHWA-ICT , Illinois Center for Transportation, March Arshad Hussain and Qiu Yanjun, Effect of Reclaimed Asphalt Pavement on the Binder Rheological Properties, International Journal of Current Research, (6), June 2012, Saskatchewan Highways and Transportation, Standard Test Procedure Manual, Retained Marshall Stability STP