g echn adation rize gra aluate g lt mixt te size est machine and laboratory method to characterize gradation segregation of large stone asphalt mixtures are developed, and a new index—D P Pi is brought forward to evaluate gra- water damage and reduced durability of the asphalt pavement, which in turn induces fatigue cracks, holes and stripping, etc.; while the part concentrated with fine aggregates is of lower poros- ity and higher asphalt content, which are prone to inducing rut, weep and other problems on the pavement [1–5]. The engineering practice demonstrates that the segregation of asphalt mixtures is one of major factors causing early-stage destruction of the asphalt judgment, sand-paving test, dynamic macro-construct measure- ment, nuclear density meter measurement, radar-dragging mea- surement, infrared thermal imaging, digital image processing method and so forth. These detection methods can be performed only after the asphalt paving is completed, but can only be used to evaluate asphalt mixtures segregation but not be used to evalu- ate segregation extent of asphalt during production and construc- tion, so it is hard to combine these methods with the current standards for controlling production and construction quality of asphalt mixtures. Accordingly, asphalt mixtures segregation ⇑ Corresponding author. Tel.: +86 13637313682; fax: +86 731 85258375. Construction and Building Materials 38 (2013) 1199–1203 Contents lists available at B ev E-mail address:
[email protected] (X. Feng). 2012 Accepted 15 October 2012 Available online 16 November 2012 Keywords: Gradation segregation Laboratory method Large stone asphalt mixtures The sum pass rate dation segregation of large stone asphalt mixtures. According to investigation results, homogeneity of large stone asphalt mixtures is the best for Bailey Method, medium for Coarse Aggregate Voids Filling Method and the worst for Superpave Method. For the same kind of design method, the homogeneity of large stone asphalt mixtures becomes worse with the increase of nominal maximum aggregate size. � 2012 Elsevier Ltd. All rights reserved. 1. Introduction Gradation segregation refers to the phenomenon that coarse and fine aggregate particles undergo segregation and concentra- tion in certain parts respectively during the process of production, transportation and paving of asphalt mixtures. In gradation segre- gation area, the part concentrated with the coarse aggregates is usually of higher porosity and lower asphalt content, resulting in pavement. In consideration of that, a great many domestic and for- eign experts as well as engineering technicians pay close attention to segregation of asphalt mixtures, and launch researches on incentive, detection method, criteria and protective measures of segregation of asphalt. Currently, the domestic and foreign research on detection method of segregation of asphalt mixtures is mainly focused on the asphalt pavement. Main detection methods include intuitive Received in revised form 30 September Received 25 August 2012 By simulating gradation s and construction, a new t h i g h l i g h t s " A new test machine to characterize gr " A new laboratory method to characte " A new index is brought forward to ev " The homogeneity of large stone aspha " Increasing maximum nominal aggrega a r t i c l e i n f o Article history: 0950-0618/$ - see front matter � 2012 Elsevier Ltd. A http://dx.doi.org/10.1016/j.conbuildmat.2012.10.003 segregation is developed. dation segregation is developed. radation segregation. ures is the best for Bailey Method. will decrease the homogeneity. a b s t r a c t egregation of large stone asphalt mixtures during production, transportation Airport Construction Corporation of CACC, Beijing 100101, China c School of Highway, Chang’an University, Xi’an 710064, China A new laboratory method to characterize asphalt mixtures Xinjun Feng a,⇑, Song Ye b, Peiwen Hao c a School of Traffic and Transportation Engineering, Changsha University of Science and T b Construction and journal homepage: www.els ll rights reserved. radation segregation of large stone ology, Changsha 410004, China SciVerse ScienceDirect uilding Materials ier .com/locate /conbui ldmat gation after being paved; mixtures in paver are fed from the center to both sides through screw feeder, while mix- diameter aggregates in the process of the production, transporta- tion and paving of large stone asphalt mixtures, which sequentially induces the respective agglomeration of the coarse and fine aggre- gates [8,9]. 2.2. Structure of gradation segregation test machine of large stone asphalt mixtures On the basis of the above analysis, a new gradation segregation test machine of large stone asphalt mixtures (as shown Fig. 1) is developed to evaluate the extent of segregation during the produc- tion and construction of large stone asphalt mixtures by simulating the actual situation of gradation segregation in the process of the production, transportation and paving of large stone asphalt mix- tures with reference to domestic and international research [10,11]. 2.3. Method to test gradation segregation of large stone asphalt mixtures (1) Mix 6–8 kg large stone asphalt mixtures according to the mix proportion, then add them into the pre-heated metal ilding Materials 38 (2013) 1199–1203 tures in the central part fall down through gravity force, which readily leads to strip segregation in the central part; paved mixtures might also present segregation in the joint part of the lengthened screw feeder originated from a rough ridge due to inappropriate adjustment. (5) Screw conveyor of the paver stretches too long upon too broad paving width so that large stone asphalt mixtures have to be conveyed in a long distance, which results in aggregate segregation. Based on the afore-mentioned analysis on gradation segrega- tion of large stone asphalt mixtures, the following mechanisms of gradation segregation can be concluded: As known to all, diameter and movement amount of aggregates in mixtures are different cannot be reduced and prevented. In view of this, it is in urgent need to study the issue for developing an effective method to eval- uate gradation segregation of asphalt mixtures in line with China’s actual engineering situation and turn it into an effective means to control the production and construction quality of asphalt mixtures. Large stone asphalt mixtures is easier to get segregated in com- parison with traditional asphalt mixtures due to the equaling to or more than 26.5 mm nominal maximum, higher content of the coarse aggregates, lower content of the asphalt and smaller particle adhesive force. Therefore, this paper carries out the study on a new laboratory method to characterize gradation segregation of large stone asphalt mixtures based on the analysis of the causes of large stone asphalt mixtures segregation. 2. Development of laboratory method of gradation segregation of large stone asphalt mixtures 2.1. Analysis on the causes of gradation segregation of large stone asphalt mixtures In review of the domestic and international research [1–7], causes of gradation segregation of large stone asphalt mixtures can be summarized from the following five aspects: (1) Local rupture emerges on riddler of large stone asphalt mix- tures mixing machine, which brings about over-large size aggregate to mineral mixture. Besides, too short mixing time as well as severe wear-off and break-off of mixing blade can also lead to uneven mixing of large stone asphalt mixture. (2) When unloading mixtures from the storage barrel of mixing machine to the dump truck or from the dump truck to the paver hopper, the large diameter aggregates are easy to spread around and roll down in the surrounding of the trans- port truck carriage or paver accepting hopper, causing gra- dation segregation of the mixture. (3) Due to poor condition of road on the construction site, over- steep cone slope of the mixture stockpile as well as the sharp start and brake of the transport truck, large size aggregates can be scattered everywhere severely, resulting in aggre- gates segregation. (4) In the process of mixture paving, both side boards will be erected in the case of little residual mixture in the accepting hopper, leading to that large diameter aggregates mixtures are concentrated on the scrapers and transported to mix- ture-dividing room. These aggregates will form flake segre- 1200 X. Feng et al. / Construction and Bu from that of the common mixture, when mixtures are under the influence of external force, the velocity of the large diameter aggre- gates particles will definitely get larger than that of small large plate and evenly spread the mixtures with a shovel. (2) Paste wax paper on the tilted baffle to prevent the falling large stone asphalt mixtures from adhering to it. (3) Add large stone asphalt mixtures into feeding hopper for spreading after the temperature drops to 130–140 �C, then open valve below the feeding hopper to let the mixtures fall down. (4) After large stone asphalt mixtures completely fall into the two storage hoppers underneath baffle, fill the mixtures from front and rear storage hopper into corresponding con- tainers and perform extraction test to measure the gradation of mixtures in the front and rear storage hoppers. (5) Calculate the sum of passing rate difference (D P Pi) of the mixtures in sieves with different size in the front and rear storage hoppers, and use D P Pi to evaluate the extent of gra- dation segregation of large stone asphalt mixtures. Fig. 1. Gradation segregation test machine of large stone asphalt mixtures. 3. Large stone asphalt mixtures design 3.1. Technical characteristics of raw materials (1) Asphalt used in the research is ESSO A-70# asphalt, main technical characteristics test is performed according to stan- dard test methods of asphalt. The main technical character- istics are shown in Table 1, which meets the technical requirements of the construction specification. (2) Limestone from Luquan city of Hebei province is used as mineral aggregate of the test. Main technical characteristics tests are performed according to standard test methods of aggregate. All test results have met the requirements of specified specification. 3.2. Gradation design of large stone asphalt mixtures Firstly, two kinds of large stone asphalt mixtures with the gra- dation of TJ-30 and SP-30 were designed respectively with Coarse Aggregate Voids Filling Method and Superpave Method. Then, three kinds of large stone asphalt mixtures with gradation of BL- 25, BL-30 and BL-40 were designed with Bailey Method [12]. Curve for the gradation of the five kinds of designed large stone asphalt mixtures is shown in Fig. 2. 3.3. Determine optimal oil-stone rate of large stone asphalt mixtures Five kinds of oil-stone rate of large stone asphalt mixture are determined by means of Marshall Methods. The physical and mechanical properties under optimal oil-stone rate are shown in Table 2. It can be concluded from Table 2 that the rest indexes of the five large stone asphalt mixtures meet the requirements of specified specification except that voids filled with asphalt of SP- 30 mixtures exceeds the scope. 4. Gradation segregation tests on large stone asphalt mixtures In order to compare gradation segregation extent between large stone asphalt mixtures and conventional asphalt concrete mix- tures, gradation segregation tests on the five large stone asphalt mixtures and AC-13 asphalt mixtures with identical raw materials were performed and the results are shown in Table 3. Five conclusions can be drawn from Table 3: (1) The front hopper passing rates of five large stone asphalt mixtures and AC-13 asphalt mixtures are higher than that of the rear hopper. Although a passing rate difference exists between the front and rear hopper, the sum of the passing rate difference between front and rear hopper for large stone asphalt mixtures is much higher than that for AC-13 asphalt mixtures. This result demonstrates that both large stone Table 1 Main technical characteristics of asphalt. Technical index Units Test value Technical requirements Penetration (25 �C, 100 g, 5 s) 0.1 mm 67 60–80 Ductility (15 �C, 5 cm/min) cm >100 >100 Softening point �C 48.2 >46 Wax content % 2.1 62.2 Thin-film oven test Quality change % 0.05 �0.8 to +0.8 Penetration ratio % 77.6 P61 tion rate in m gate X. Feng et al. / Construction and Building Materials 38 (2013) 1199–1203 1201 Fig. 2. Curve design of the grada Table 2 Physical mechanics indexes of large stone asphalt mixtures under optimum oil-stone Gradation types Oil-stone rate (%) Bulk density (g/ cm3) Volume of air voids (%) Voids aggre TJ-30 3.7 2.452 4.2 12.62 SP-30 4.0 2.487 3.0 11.94 BL-25 3.9 2.451 4.5 12.83 BL-30 3.8 2.460 3.9 12.57 BL-40 3.8 2.441 4.2 13.37 Technical requirements – 3–6 P11.5 asphalt mixtures and AC-13 asphalt mixtures have undergone gradation segregation under gravity force, and of large stone asphalt mixtures. . ineral (%) Voids filled with asphalt (%) Marshall stability (kN) Flow value (mm) 67.13 18.13 7.84 78.03 19.65 6.61 68.74 19.67 7.40 69.83 18.29 7.30 65.27 15.05 8.97 55–70 P15 Measured value Ta bl e 3 G ra da ti on se gr eg at io n te st re su lt s of la rg e st on e as ph al t m ix tu re s. Si ev e si ze s (m m ) Pa ss in g ra te (% ) TJ -3 0 SP -3 0 B L- 25 B L- 30 B L- 40 A C -1 3 Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs Th e fr on t st or ag e h op pe rs Th e re ar st or ag e h op pe rs D if fe re n ce in th e fr on t an d re ar st or ag e h op pe rs 53 10 0. 0 10 0. 0 0 37 .5 10 0. 0 10 0. 0 0 10 0. 0 10 0. 0 0 10 0. 0 10 0. 0 0 83 .8 10 0. 0 16 .2 31 .5 87 .1 10 0. 0 12 .9 86 .6 10 0. 0 13 .4 10 0. 0 10 0. 0 0 88 .2 97 .7 9. 5 26 .5 57 .5 92 .7 35 .2 72 .0 99 .2 27 .2 86 .4 99 .3 12 .9 74 .3 93 .8 19 .5 55 .1 95 .4 40 .3 19 49 .4 91 .1 41 .7 60 .1 94 .4 34 .3 65 .9 90 .2 24 .3 57 .9 86 .6 28 .7 44 .4 84 .5 40 .1 16 43 .3 82 .0 38 .7 52 .5 90 .2 37 .7 57 .8 84 .6 26 .8 47 .4 79 .3 31 .9 39 .3 76 .8 37 .5 10 0. 0 10 0. 0 0 13 .2 35 .9 73 .6 37 .7 38 .1 79 .6 41 .5 44 .4 74 .9 30 .5 36 .1 71 .0 34 .9 28 .5 63 .5 35 88 .2 98 .0 9. 8 9. 5 27 .9 59 .2 31 .3 27 .8 66 .3 38 .5 31 .1 63 .7 32 .6 24 .9 56 .0 31 .1 19 .7 46 .5 26 .8 62 .1 85 .8 23 .7 4. 75 20 .2 36 .3 16 .1 23 .0 51 .5 28 .5 23 .1 38 .1 15 20 .2 37 .5 17 .3 16 .9 34 .5 17 .6 35 .3 60 .6 25 .3 2. 36 13 .9 19 .9 6. 0 18 .0 34 .0 16 17 .2 24 .8 7. 6 15 .4 22 .3 6. 9 12 .4 20 .1 7. 7 23 .6 38 .3 14 .7 1. 18 10 .8 14 .8 4. 0 14 .2 23 .5 9. 3 13 .0 17 .0 4 11 .7 15 .5 3. 8 9. 1 14 .2 5. 1 19 .7 27 .5 7. 8 0. 6 8. 4 11 .2 2. 8 10 .7 17 .1 6. 4 9. 1 11 .7 2. 6 8. 0 11 .0 3 6. 6 10 .7 4. 1 18 .5 25 .1 6. 6 0. 3 6. 6 8. 5 1. 9 7. 7 11 .9 4. 2 6. 1 7. 9 1. 8 5. 6 8. 0 2. 4 4. 9 8. 2 3. 3 13 .6 17 .1 3. 5 0. 15 5. 3 6. 4 1. 1 5. 0 7. 8 2. 8 4. 7 6. 2 1. 5 4. 0 6. 0 2 3. 1 5. 8 2. 7 8. 0 10 .6 2. 6 P 46 6. 1 69 5. 5 22 9. 4 51 5. 6 77 5. 5 25 9. 9 45 8. 8 61 8. 4 15 9. 7 49 3. 8 68 4. 6 19 0. 8 42 3. 8 66 0. 1 23 6. 3 36 9. 1 46 3. 1 94 .0 1202 X. Feng et al. / Construction and Buildin gradation segregation rate of the former is higher than that of the latter. (2) With the decrease of sieve size, passing rate difference between the front and rear hopper of sieves with different size for five kinds of large stone asphalt mixtures varies like a parabola. The difference reaches a peak (32.6–41.7%) when the sieve size ranges from 9.5 mm to 26.5 mm. Moreover, a larger nominal size of large stone asphalt mixtures corre- sponds to an earlier peak. With the decreasing sieve size, passing rate difference between the front and rear hopper of sieves with different size for AC-13 asphalt mixtures also varies along a parabola. When the sieve size is 4.75 mm, a peak is presented. However, the peak value, which is 25.3%, is much smaller than that of large stone asphalt mixtures. (3) In the five kinds of large stone asphalt mixtures, coarse aggregates with the size from 4.75 mm to 26.5 mm have the highest passing rate difference between the front and rear copper. The difference accounts for 85.1–93.1% of that for the large stone asphalt mixtures. As for AC-13 asphalt mixtures, higher passing rate difference between the front and rear hopper mainly appears to coarse aggregates with the size from 2.36 mm to 13.2 mm. The difference accounts for 78.2% of that for AC-13 mixtures. It can be concluded from data as above that the coarse aggregates with the size from 4.75 mm to 26.5 mm of large stone asphalt mixtures have a more serious segregation than other size aggregates, while coarse aggregates with the size from 2.36 mm to 13.2 mm of AC-13 asphalt mixtures presents a more serious segregation than other size aggregates. (4) In order to distinguish segregation level of large stone asphalt mixtures, sum of passing rate difference between the front hopper and rear hopper (D P Pi) is taken as index to evaluate gradation segregation of mixtures in the study. Accordingly, gradation segregation of asphalt mixtures is divided into three levels: (1) No gradation segregation or slight gradation segregation occurs when D P Pi is in the range of 0–100%; (2) Moderate gradation segregation occurs when D P Pi is in the range of 100–200%; and (3) Severe gra- dation segregation occurs when D P Pi is larger than 200% [13]. The following conclusion can be drawn that the value of D P Pi for the five large stone asphalt mixtures exceeds 100%, such kind of segregation is deemed as moderate or severe gradation segregation. The value of D P Pi for AC-13 asphalt mixtures is less than 100%. Its segregation is regarded as slight gradation segregation. The above data demonstrate that larger stone asphalt mixture is easier to get segregated than conventional concrete asphalt mixtures. This conclusion is identical to that of common study. (5) The rank of gradation segregation extent for the three large stone asphalt mixtures with nominal maximum aggregate size of 31.5 mm is BL-30 < TJ-30 < SP-30, which demon- strates that mixing homogeneity of large stone mixture is the best for Bailey Method, medium for Coarse Aggregate Voids Filling Method, and the worst for Superpave Method. The rank of gradation segregation extent for the three large stone asphalt mixtures with different nominal maximum aggregate sizes designed by Bailey Method is BL-25 < BL- 30 < BL-40, which shows that the mixing homogeneity for the same design method becomes worse with the increase of nominal maximum aggregate size. 5. Conclusions g Materials 38 (2013) 1199–1203 Important results obtained from this study are summarized below: (1) A new test machine and laboratory method for characteriz- ing gradation segregation of large stone asphalt mixtures are developed. Moreover, the sum of mixture degradation pass- ing rate difference between the front and rear hopper (D P Pi) are put forward as index to evaluate degradation segregation of asphalt mixtures. (2) The homogeneity of large stone asphalt mixtures is the best for Bailey Method, medium for Coarse Aggregate Voids Fill- ing Method and the worst for Superpave Method. (3) For the same kind of design method, the homogeneity of large stone asphalt mixtures becomes worse with the increase of maximum nominal aggregate size. Acknowledgements This study was supported by National Natural Science Founda- tion of China. Project No. 51078046, Hunan Provincial Natural Sci- ence Foundation of China. Project No. 12JJ3050 and Open Fund of Key Laboratory of Special Environment Road Engineering of Hunan Province (Changsha University of Science & Technology). Project No. kfj110402. References [1] Zheng Xiao-guang, Xu Jian, Cong Lin, et al. Influence of segregation on asphalt mixture performance. J Highway Transp Res Dev 2008;25(11):16–9. [2] Peng Yu-hua. Research on characteristic distinguishing and controlling means of the segregation in asphalt mixture. Xi’an: Chang’an University; 2006. [3] Li-han LI, Xu-rong MA. Influence research of gradation segregation on performance of asphalt mixture. J Tongji Univ: Nat Sci Ed 2007;35(12):1622–6. [4] Flintsch GW, de Leon, McGhee, Al-adi IL. Pavement surface macrotexture measurement and application. Transportation Research Record. Washington (DC): Springer; 2003. [5] Schorsch M, Chang C-M, Baladi GY. Effect of Segregation and Propagation of Top-Down Cracks. Transportation Research Record. Washington (DC): Springer; 2004. 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Feng et al. / Construction and Building Materials 38 (2013) 1199–1203 1203 A new laboratory method to characterize gradation segregation of large stone asphalt mixtures 1 Introduction 2 Development of laboratory method of gradation segregation of large stone asphalt mixtures 2.1 Analysis on the causes of gradation segregation of large stone asphalt mixtures 2.2 Structure of gradation segregation test machine of large stone asphalt mixtures 2.3 Method to test gradation segregation of large stone asphalt mixtures 3 Large stone asphalt mixtures design 3.1 Technical characteristics of raw materials 3.2 Gradation design of large stone asphalt mixtures 3.3 Determine optimal oil-stone rate of large stone asphalt mixtures 4 Gradation segregation tests on large stone asphalt mixtures 5 Conclusions Acknowledgements References