www.semargroups.org, www.ijsetr.com ISSN 2319-8885 Vol.02,Issue.10, September-2013, Pages:1023-1030 Effect of Flakiness Index on Bituminous Mixes SUREN MUHAMMAD SALIH 1 M.Tech, Dept of Transportation Engineering, JNTU College of Engineering, Hyderabad, A.P-INDIA, Email: surenmuhammad@yahoo.com. DR P.SRAVANA 2 Professor, Dept of Civil Engineering, JNTU College of Engineering, Hyderabad, A.P-INDIA, Abstract: Flakiness index is one of the prominent shape criteria that govern behavior and performance of aggregate in the bituminous mixes. This research has been done as a realistic study for an actual pavement construction case in Hyderabad airport in India, which a lot of pavement area cracked and failed due to existence of flaky aggregate particles. The strength and serviceability requirements of bituminous mixture such as Stability, Flow, and Voids in Total mix (VTM) and Voids Filled with Bitumen and (VFB) highly depend on the physical properties of aggregates. The change in rotation angle of coarse aggregate was found to correlate well with the internal resistance of a HMA mix. The particle shape determined how aggregate was packed into a dense configuration and also determined the internal resistance of a mix. Cubical particles were desirable for increasing aggregate internal friction and improving rutting resistance. The results which are obtained from the study showed that the strength and stability of the bituminous mixes decreases gradually by increasing flakiness index. Keywords: Bituminous concrete (B.c), Flakiness index (F.I), Flow, Hot mix asphalt (HMA), Stability, Voids Filled with Bitumen (VFB), Voids in Total mix (VTM). I. INTRODUCTION Road transport provides greater utility in transport over short and long hauls of lighter weight commodities and of lesser volumes, as also for passenger transport for short and medium hauls. Road as one of land transportation infrastructure is very important in supporting the economic for both regional and national development. The quality of material for road construction will also influence the road performance. Bituminous concrete as one of road surface material is mainly influenced by the quality of aggregates since aggregate occupies 95% by weight in total mixture. Flakiness index of an aggregate can be defined as a percentage by weight of particles whose least Dimension (Thickness) is less than 0.6 of their mean dimension. Physical shape of coarse aggregate is a very important property in performance of the bituminous mixes in the highway pavements [1]. Existence of flaky aggregates in the bituminous mixes is undesirable and a dangerous phenomenon because, of their tendency to break under wheel load either during compaction in construction stage or in service life of the pavement The flaky aggregates will also cause problem in achieving the required degree of compaction[1,2]. In flexible pavements there exists a desired property for aggregate, which is the degree of interlocking. This interlocking property is obtained by existence of angular type aggregate. Due to having more corners and angles the aggregate will produce a better interlocking and friction with the neighboring aggregates in the mix and causes more strength [1,3]. High flakiness index will produce less voids and cause bleeding [3]. This study is carried out on bituminous concrete (B.C) of grade (1) of 19 mm nominal size of aggregate. Flaky aggregates has been added gradually to the test samples from (0 to 5, 10, 15, 20, 25) %. Aggregates can either be natural or manufactured. Natural aggregates are generally extracted from larger rock formations through open excavation. Extracted rock is typically reduced to usable sizes by mechanical crushing. Manufactured aggregate is produced by other manufacturing industries such as construction and steel industries. The coarse and fine aggregate acts as the structural skeleton of pavements while bitumen functions as the glue for the mixture. If the percentage flaky aggregate that is required for each group of test samples is given in random the result will change and different properties are achieved since, in our case the feeding is given in a uniform manner. The flakiness index reduces workability [4]. II. METHODOLOGY A. Material Basically the materials that are used in this study includes aggregate and filler component of (B.C) grade (1) of 19 mm. nominal size aggregate, Base bitumen and Copyright @ 2013 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
SUREN MUHAMMAD SALIH, DR P.SRAVANA flaky aggregates. 2% filler is added to the mix. And that rate is kept constant in order observe the clear effect of flakiness index. The aggregate and the bitumen which are used in the study should pass in certain tests, for aggregate such as Los angles, abrasion test, impact value and crushing, specific gravity and water absorption see table (1). For bitumen these tests should be done like penetration, softening point, ductility, specific gravity and viscosity see table (2). The binder content for this study is chosen between 5 to 6% [5]. Fig1. Fig2. B. Aggregate Preparation for Job-Mix formula To determine the Job-mix formula, the aggregate analysis will be somewhat governed by a number of aggregate stockpiles. This can be done by separating Coarse, fine and dust into independent piles, then from each pile a mass of an amount of (5-10) kg is taken by using coning and quartering method. This phase of mix design establishes the job-mix formula that defines the actual gradation and asphalt content to be obtained in the finished construction[6]. Fig3. Figure-1, 2, and 3 Coning and Quartering.
Effect of Flakiness Index on Bituminous Mixes C. Sieve Analysis and Blending of aggregate The test of Sieve analysis is a simple test consisting of sieving a measured quantity of material through successively smaller sieves. The weight of material retained on each sieve is weighted and expressed as a percentage of the total weight of the sample. In this study a weight of 5 kg from each portion of aggregate is taken such as Coarse, fine and dust, then passed through Bituminous concrete (B.C) of grade (1) gradation, sieves which starts from (26.5-0.075) mm as shown in table (3). After getting final results from sieve Analysis blending process is carried out by Trial and error method. In order to get the required amount by percentage of each component like coarse, fine and dust. Graph-2: Fine aggregate Sieve-Analysis. Graph-3: Dust Sieve- Analysis. Graph-1: Coarse aggregate Sieve- Analysis. Graph-4: Job-mix graphical Result
SUREN MUHAMMAD SALIH, DR P.SRAVANA D. Adjustment of Flaky aggregates Flakiness index test is Applicable on those aggregate sizes bigger than 6.3 mm. This process is carried out when the aggregate proportions such as coarse, fine and dust is identified. In order to determine the effect of flakiness index on the bituminous mix, a number of aggregate test samples have to be prepared and upon each group of samples a certain percentage of flaky aggregate is applied which start from (0 to 5, 10, 15, 20, 25) %. The test of flakiness index is carried out on each test sample which is prepared for the mix. In this manner the test sample should pass through flakiness sieves that for this study it includes (25, 20, 16, 12.5,10 and 6.3) mm. When the sieving process is over, the retained weight between any two sieves should be separated and passed through flakiness thickness gauge to identify the existing flakiness index see fig.(5). After this step in order to achieve the Required flakiness index percentage, The amount of flaky aggregates are adjusted within a sample whether by applying extra or removing the excess flaky aggregates upon each mass of flaky aggregates in a uniform and equal manner. Elongated aggregates are removed from each mass for a clear observation of change according to each percentage [7]. Fig-5. Thickness gauge E. Mix Design and Sample preparation The mix design method which is adopted in this study is Marshall Mix design method. In this method a sample of 1200g of aggregate, filler and binder mix is taken. Aggregate and filler portion is heated to a temperature between (175-190) C (Not exceeding 28 C above mixing).the compaction mould assembly and rammer are cleaned and kept pre-heated at a temperature of (95-150) C. Bitumen binder is heated to a temperature between (120-165) C. In this study the mixing temperature is 160 C because its grade is 60/70. Soon both heated bitumen and aggregate are mixed in a special pan or container either manually or by mechanical means. Then the mix is poured into the moulds and compacted at 149 C temperature with 75 blows to each side of the sample [1]. Fig-4. Test of flakiness Index. Fig-6. Sample preparation.
Effect of Flakiness Index on Bituminous Mixes A. Stability Fig-7. Marshall Samples. F. Testing When all of the samples which contain required flakiness index are prepared, then it s put in a water bath of 60 C temperature for 30-40 minutes. After this step the sample is tested by Marshall Test device to obtain stability and flow of the mix [1, 6]. It s the property of strength and bearing performance of the bituminous mixes against wheel loads and traffic intensity. From table (5) it has been observed that with increasing flakiness index stability decreased by 43%. The maximum stability is 1506 kg and sharply decreased to 858 kg at 25% flakiness index. The minimum stability is 900 Kg. See graph (5). [1] [8]. Fig-8 Marshall Test device. III. ANALYSIS OF RESULTS According to table (5) the following influences for stability, flow, void in total Mix (VTM),void filled with bitumen (VFB), density and void in mineral aggregate (VMA) can be assessed. Graph-5 Stability vs. Flakiness index. A. Flow Flow is the deformation of the bituminous mixes under a certain applied load. In this study we observe that the value of flow decreases with increasing flakiness index by 53.5%. See table (5) and graph (6). The maximum value of flow is 6.28 mm at non-flaky mix. And its 2.92 mm at 25% flakiness index. The acceptable flow limit is between 2-4 mm [1, 8].
SUREN MUHAMMAD SALIH, DR P.SRAVANA Graph-6 Flow vs. Flakiness index. B. Void in total mix (VTM) From the table (5) and graph (7) it has been observed that VTM is decreasing with increasing of flakiness index by 34.19 %. It s decreased from 2.31 % at 0% flakiness index to 1.52 % at 25% flakiness index, while its limit is between 3-6 % [1, 8]. Graph-8 VFB vs. Flakiness index. D. Void in mineral aggregate (VMA) In table (5) and graph (9) it s observed that the value of VMA is decreasing with increasing of flakiness index by 4.4%.VMA value is 15.71 % at 0% flakiness index and 15.02 at 25 % flakiness index. The VMA limit is between 12-14% for nominal maximum size of aggregate 19 mm [1, 8]. Graph-7 VTM vs. Flakiness index C. Void filled with bitumen (VFB) According to the obtained results from table (5) and graph (8), it s observed that the value of VFB is increased by 4.85% from 85.49 % at 0% flakiness index to 89.85 % at 25% flakiness index. The standard limit for VFB is between 65-75% [1, 8]. Graph-9 VMA vs. Flakiness index E. Density According to table (5) and graph (10) we observe that the value of density is increasing with increasing of flakiness index by 0.84%. At 0% the value of density is 2.36 g/cc, but in 25 % flakiness index is 2.38 %.
Effect of Flakiness Index on Bituminous Mixes the Mix decreases the more voids are filled by bitumen. So they are inversely proportional. Graph-10 Density vs. Flakiness index IV. CONCLUSIONS Though VMA is an attribute which is related with filler ratio and viscosity of the bitumen but, also it can be influenced by flakiness index as well. Since we can see that VMA is related with VTM, which decreases with increase of flakiness index and both of them are influenced by particle shape and geometry. It can be observed that density is also related with VTM and flakiness index. When the void in the mix decreases it implies that the mix is getting denser. Density increases with increase of flakiness index. V. REFERENCES From the results that are obtained from this study it has been concluded that flakiness index should be kept below 25 % for a better strength and durability. Increase of flakiness index highly decreases the stability due to negative performance of flaky aggregates in the mix, since it s evident that flaky aggregates are weak and thin and don t have a good interlocking ability and strength to form a good bond with surrounding aggregates. Flow is decreasing with increase of flakiness index in the mix, because due to lack of degree of interlocking, the sample disintegrates earlier. So low flow value will be obtained. Flow is a characteristic that varies by property and quantity of the bitumen depending on the elastic and viscous property of the bitumen. [1] S.K khanna and C.E.G. Justo -A.Veeraragavan, Highway materials and pavement testing,2009 pp: 60,88,155-156 and160. [2] Principle and Practice of Highway engineering By Dr. L.R.Kadyali and Dr.N.B Lal. 2008, pp: 447. [3] Hot mix Asphalt Materials, mixtures,design and construction by Freddy L. Roberts, Prithvi S.kandhal, E. Ray Brown, Dah-Yinn Lee and Thomas W. Kennedy.1991 pp: 105-107, pp: 178. [4] Bambang Ismanto SISWOSOEBROTHO, Kariantoni GINTING and Titi Liliani SOEDIRDJO Workability and Resilient Modulus of Asphalt Concrete Mixtures containing flaky aggregates shape Journal of the Eastern Asia Society for Transportation Studies, Vol. 6, pp. 1302-1312, 2005. Void in total mix. (VTM) is decreased with increasing of flakiness index because, in case of flat and thin aggregates which lack an angular and cubical form, the aggregate particles will be drawn nearer to each other by compaction and form a denser configuration. Then voids between aggregate particles are reduced and filled more and more by bitumen and filler particles. This is a negative phenomenon, because presence of voids in the mix within acceptable range is very mandatory. In high temperature condition the bitumen inside the mix flows into those voids, so nonexistence of those voids will cause bleeding and cracking in the pavement. But in case of angular and cubical aggregates the required percentage of voids can be obtained properly. Void filled with bitumen (VFB) is a property that is highly related to VTM. The more void percentage in [5] Indian standard IS:2386 part 2,4 and 7 and IS:6241.1997. [6] Mix design method for Asphalt concrete and other hotmix types. By Asphalt institute 1995. pp: 24-25, 61. [7] D. Sakthibalan Influence of Aggregate Flakiness on Dense Bituminous Macadam & Semi Dense Bituminous Concrete Mixes STUDENTS PAPER COMPETITION 2009. [8] MORTH specification section 500. pp: 183-187. Acknowledgement I express my Respect and gratitude for Dr.S.Amarendra Kumar, Manager at R&D EPC Division, GMR Infrastructure Ltd, Hyderabad, India, for his kind help during accomplishment of this thesis.
SUREN MUHAMMAD SALIH, DR P.SRAVANA Author s Profile: Suren Muhammad Salih, Received his Bachelor, Degree in Civil Engineering from University Salahaddin,Arbil, IRAQ. Presently he finished his Master of Technology in Jawaharlal Nehru Technological College of Engineering, Department of Civil Engineering, specialization in Transportation Engineering, Hyderabad, INDIA.