Laboratory Investigation of Properties of Asphalt-Rubber Concrete Mixtures

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TRANSPORTATION RESEARCH RECORD 1417 93 Laboratory Investigation of Properties of Asphalt-Rubber Conrete Mixtures TAISIR S. l<hedaywi, ABDEL RAHMAN TAMIMI, HASHEM R.

1 TRANSPORTATION RESEARCH RECORD Laboratory Investigation of Properties of Asphalt-Rubber Conrete Mixtures TAISIR S. l<hedaywi, ABDEL RAHMAN TAMIMI, HASHEM R. AL-MASAEID, AND KHALED KHAMAISEH A study was undertaken to investigate (a) the effet of rubber onentration and rubber partile size on properties of asphalt ement, (b) the effet of rubber onentration and rubber partile size on properties of asphalti onrete mixtures, and ( ) the effet of rubber on water sensitivity of asphalti onrete mixtures. Three types of materials were used: one type of rubber obtained by hopping the tread peel from srap truk tires, one type of asphalt ement with a penetration grade of 8 to 1, and one type of rushed limestone aggregate. Four onentrations of rubber (5, 1, 15, and 2 perent by total weight of asphalt-rubber mixes) and three rubber partile sizes (Nos. 16-2, Nos. 2-5, and Nos. 5-2) were also used. Results indiated that penetration, dutility, flash point, and speifi gravity were inversely related to the inrease of rubber onentration in the binder, whereas the softening point was diretly related to the inrease of rubber onentration in the binder. Results show that asphaltrubber onrete mixtures have lower stability and higher flow than do asphalti onrete mixtures without rubber. The experiments also indiated that retained stability of all asphalti onrete mixtures was aeptable, exept for the retained stability of the mixture with rubber partile sizes of No. 5-2 at a 2 perent rubber onentration. As the use of tires has inreased, the growing pile of srap tires has been eyed as a heap soure of rubber for preparing rubberized asphalt. Early experiments showed that these tires ould be ground and mixed with hot asphalt in large perentages to produe a material that had properties superior to those of the base asphalt (J). MDonald (2) alled for the use of 33 perent (by weight) devulanized rubber with the remaining proportion omposed of 85 to 1 penetration-grade asphalt ement. The asphalt was heated to 42 F when rubber was added and mixed until a jell onsisteny was aquired. This omposition was applied to the pavement in amounts of 1 galyd 2 ; then about 45 lbyd 2 of aggregate hips were applied to omplete the membrane. Morris and MDonald (3) introdued the use of digestions of srap rubber in asphalt that ontained up to 25 perent by mass of omminuted tire-tread rubber; this material has been widely used in the United States. To prevent raks in the substane from being refleted through overlays, this preparation normally is applied as a hip-seal surfae treatment with approximately 2 perent rubber added to the asphalt - ement. Shnormeier ( 4) studied the onditions of a pavement in Phoenix, Arizona, omposed of asphalt rubber that was laid between 1969 and Asphalt rubber used in the Phoenix Civil Engineering Department, University of Siene and Tehnology, lrbid, Jordan. pavement was produed by two methods: the MDonald proess, in whih hot asphalt is mixed with 25 perent ground tire rubber to establish a reation and diluted with kerosene; and the Arizona refinery proess, in whih hot asphalt is mixed with 18 to 22 perent ground rubber to establish a reation, then diluted with an extended oil. Shnormeier onludes that asphalt rubber has superior engineering properties, suh as a remarkable retention of visosity, redution in the volume hanges in the subgrade as a result of moisture hanges, and a redution in maintenane that ours when asphalt is used, as observed in the survey of streets and roads; he reommends the use of asphalt rubber in rak filling and joint sealing. Lalwani et al. (5) made a study on asphalt-rubber using rubber partiles that had a gradation of two parts No. 5 (3 µm) to one part No. 3 (6 µm). The study indiated that_ an inrease in rubber onentrations redues the temperature sensitivity of the binder while it inreases the toughness at 25 C. Roberts and Lytton (6) developed a mixture design method to use asphalt-rubber binders in onrete for flexible airport pavements. Rubber from ground srap tires was used beause it is widely available. Two types of asphalt rubber were used in the study. Type A ontained 25 perent rubber by weight and Type B ontained 18 perent rubber. These two types were used in preparing Marshall speimens. A suessful mixture design, obtained with asphalt-rubber binders, exhibited higher stabilities than do similar mixtures made with asphalt ement. In studying the appliation of asphalt rubber as an asphalti onrete rak sealant, Chehovits and Manning (7) found that asphalt-rubber sealants have improved temperature suseptibility harateristis and higher elastiity than the unmodified asphalt sealants. They speified that for a material to perform adequately as an asphalti onrete rak sealant, it must have suffiient flexibility throughout the range of temperatures enountered in servie to remain bonded to the rak faes. OBJECTIVES The objetives of this researh are as follows: To study the effet of rubber onentration and rubber partile size on properties of asphalt ement, To study the effet of rubber onentration and rubber partile size on properties of asphalti onrete mixtures, and

2 94 To investigate the effet of rubber on water sensitivity of asphalti onrete mixtures. LABORATORY WORK The experimental work was divided into two stages: investigation of properties of asphalt-rubber binders and determination of properties of asphalt-rubber onrete mixtures. To evaluate the effet of rubber additives on the behavior of asphalt ement, the following variables were investigated: Rubber ontents of 5, 1, 15, and 2 perent by total weight of asphalt-rubber mix; Rubber partile size passing and retained on the following sieves: No. 16-2, No. 2-5, and No. 5-2; and Mixing temperature of at least 16 C based on the range of 16 C to 23 C, whih is found in the literature (8). Materials Used The following materials were used in this study: Asphalt ement-one penetration-grade asphalt ement (8-1) was used in this study. This asphalt was obtained from Jordan Petroleum Refinery. This type of asphalt was hosen beause it is widely used in pavement onstrution. Table 1 gives a summary of the results of some tests performed on the asphalt. Rubber-The rubber used in the study was obtained by hopping a tread peel of srap truk tires at ambient temperature using a speial mahine. The tires were produed by Dunlop Company-Japan and were manufatured with natural rubber (9). The speifi gravity of the rubber obtained is.985. Tread is an external rubber layer proteting the arass from wear and damage aused by the road surfae. It is the part that omes in diret ontat with the road and generates the fritional resistane that transmits a vehile's driving, braking, and ornering fores to the road. The rubber gradation inluded partile sizes between the No. 16 and No. 2 sieves. Three parts of rubber between these two sieves were used in this testing. The samples were sieved on the following sieves: No. 16-2, No. 2-5, and No Aggregate-One type of limestone aggregate was used in this study. This aggregate is the most ommonly used in pavement onstrution in Jordan. The gradation used in this study onformed to the wearing layer speifiations of the TRANSPORTATION RESEARCH RECORD 1417 Jordanian Ministry of Publi Works. This gradation is given in Table 2. Table 3 gives a summary of the properties of the aggregate. Preparation of Asphalt-Rubber Binders The suggested proedure for preparing asphalt-rubber binders was based largely on the experiene of researhers ( 6) and inluded the following steps: 1. Asphalt ement was heated in an oven at a temperature of at least 16 C. 2. The stainless steel beaker used for mixing was leaned and kept in the oven at a temperature of at least 16 C. 3. The required amount of asphalt was weighed into the beaker; then the amount of rubber required to yield the desired rubber-to-asphalt ratio was weighed. 4. The beaker was plaed on a hot plate to maintain a mixing temperature of at least 16 C. The laboratory mixer used was then plaed so that the propeller was about 1.5 m above the bottom of the beaker. 5. The mixer was started, and the prepared amount of rubber was added gradually to the beaker while stirring. The speed of the mixer was inreased up to 5 rpm. The mixing was ontinued for at least 3 min and until the homogeneous asphalt-rubber binder was obtained. 6. At the end of the mixing operation, the asphalt-rubber binder was used to prepare speimens for the penetration, softening point, flash point, dutility, and speifi gravity or to mix with the heated aggregate to prepare asphalt-rubber onrete speimens. Measurement of Properties of Asphalt-Rubber Binders Properties of eah asphalt-rubber binder were determined using ASTM standard tests. The following tests were run on eah binder: Penetration of three speimens for eah binder was determined using ASTM D5. Softening point of three speimens for eah binder was determined using ASTM D36. Flash point of three speimens for eah binder was done using ASTM D92. Three measurements of dutility for eah binder were made using ASTM Dl 13. TABLE 1 Properties of Asphalt Cement Used in Study Property ASTM Test Designation Test Result,.Penetration (.1mm) at 25 C, 1gm, 5 Se Dutility (m) at 25 C Speifi gravity Softening point ( C), ring and ball Flash point ( C) Note:- 1mm =.394 in. D 5 D 113 D 7 D 36 D

3 Khedaywi et al. TABLE 2 Aggregate Gradation Sieve Size Perentage Passing 1 in in in. 68 No No No No. 2 6 Note:- 1 in m "' Jordanian Speifiation Limits Speifiation"' Speifi gravity of three speimens for eah binder was performed using ASTM D7. Measurement of Properties of Asphalt-Rubber Conrete Mixes The variables involved for this part of the investigation are as follows. Rubber ontent:, 5, 1, 15, and 2 perent by total weight of binders; Rubber size: No. 16-2, No. 2-5, and No. 5-2; and Binder ontent: 4, 5, 6, 7, and 8 perent by total weight of mix. To determine the properties of the asphalt-rubber onrete, the Marshall test method proedure was used as part of this study. A total of 12 speimens were prepared for this part of the study. All of these speimens were tested for Marshall stability, flow, air voids, voids in mineral aggregate, and unit weight. The tests were onduted aording to MS-2 (JO) and ASTM D1559. Water Sensitivity of Asphalt-Rubber Conrete Mixes The Marshall immersion test was used to evaluate the influene of rubber on moisture resistane of asphalt-rubber onrete mixes (11). In this test, Marshall stability is measured for _wet and dry speimens at 4 perent air voids. A total of 48 speimens were prepared. The speimens were divided into two groups. One group was ured in air at room temperature for 24 hr (unonditioned) and then put in a water bath at 6 C for 3 min. The other group was immersed in a water bath at 6 C for 24 hr (onditioned). Both groups were tested in dupliate using the Marshall apparatus. Moisture damage is evaluated on the basis of Marshall stability for onditioned and unonditioned speimens. TEST RESULTS AND DISCUSSION Effet of Rubber Conentration and Rubber Partile Size on Properties of Asphalt Cements Penetration Figure 1 presents the relationship between penetration of the binders and rubber ontent for the three sizes of rubber partiles being used. This figure shows that the penetration dereases with the inrease of the perentages o_f rubber in the binders. Binder with No. 2-5 rubber partile size shows higher values of penetration, whereas binder with No rubber partile shows lowest values of penetration. Softening Point Figure 2 shows that the softening points of the binders are diretly proportional to the inrease of rubber onentrations in the binders. Flash Point Figure 3 shows that flash points of the binders are inversely related to the inrease of rubber onentrations in the binder. Asphalt-rubber binder with No. 2-5 rubber partiles shows higher values of flash point, whereas binder with No rubber partiles shows the lowest values of flash point. Dutility Figure 4 shows that dutility of binders dereases and then inreases with inreasing rubber ontent in the binder. Asphalt-rubber binders with finer rubber partiles (No. 5-2) show slightly higher dutility, whereas binder with No rubber partiles shows lower dutility. 95 TABLE 3 Properties of Aggregate Type of ASTM Test Bulk Apparent water Aggregate Designation Speifi Speifi Absorption Gravity Gravity (%) Limestone oarse aggregate Limestone fine aggregate Limestone mineral filler

4 96 TRANSPORTATION RESEARCH RECORD No No. 2 D No. 2 - No. 5 o No. 5 - No. 2 1 t:> No No. 2 o No. 2 - No. SO o No. SO - No E 8 E C) :i a a - - -o-._ o 7 6 so 4 =t :::J FIGURE 1 Effet of rubber ontent on penetration of asphalt-rubber binders. FIGURE 4 Effet of rubber ontent on dutility of asphaltrubber binders :> No No. 2 D No. 2 - No. 5 o No. 5 - No. 2 t> No No. 2 D No. 2 - No.so No. SO-No. 2 6 _ a.. ri.5 Vl > 1::1.., 1.1S 45, '' ' ' 1 1S 2 FIGURE 2 Effet of rubber ontent on softening point of asphalt-rubber binders. 1.1 ' ' ' '' L----_J 5 1 1S 2 FIGURE 5 Effet of rubber ontent on speifi gravity of asphalt-rubber binders ; Q Ill nl u: 3 6 No No. 2 D No. 2 - No. 5 o No. SO - No ' '----.,, FIGURE 3 Effet of rubber ontent on flash point of asphaltrubber binders. Speifi Gravity Figure 5 shows the relationship between the speifi gravity of the binders and rubber ontent for various sizes of rubber partiles. Speifi gravity is inversely related to the inrease in the rubber ontent. The data olleted for the speifi gravity of various binders indiqted that asphalt-rubber binder made up of No. 5-2 rubber partiles shows higher values of speifi gravity, whereas rubber-asphalt made up of No rubber partiles shows lower values. Effet of Rubber Content and Rubber Partile Size on Properties of Asphalt-Rubber Conrete Table 4 and Figures 6 to 9 summarize the measured properties of asphalt-rubber onrete mixtures. The effet of rubber ontent and the size of the rubber partile on properties of asphaltrubber onrete mixtures are disussed next.

5 Khedaywi et al. 97 TABLE 4 Perent of Rubber Properties of Asphalt-Rubber Conrete Mixture at 4 perent Air Voids Binder Content (%) Marshall Stability (Kgf) Flow (.25mm) VMA (%) Unit Weight (Mgm 3 ) Ret. Stab. (%) Asphalt-Rubber Binder Made up of No.16-No.2 Rubber Partiles Asphalt-Rubber Binder Made up of No.2-No.5 Rubber Partiles Asphalt-Rubber Binder Made up of No.5-No.2 Rubber Partiles Note:- 1kgf = 2.2 1bf, 1mm.394 in. I Mgm bft 3 Marshall Stability Figure 6 presents the relationship between Marshall stability and rubber ontent in the binder at 4 perent air voids for various rubber partile sizes. This figure shows that Marshall stability dereases with inreasing rubber ontent in the binder. Flow Figure 7 shows that flow inreases with an inrease in rubber ontent in the binder. Bituminous onrete mixtures with No rubber partiles show lower flow values, whereas bituminous mixtures with No. 2-5 rubber partiles show higher flow values. Voids in Mineral Aggregate Figure 8 presents the relationship between voids in mineral aggregate (VMA) and rubber ontent in the binder at 4 perent air voids for various sizes of rubber partiles. This figure shows that VMA inrease with inreasing rubber ontent in the binder. Retained Stability Evaluation of water sensitivity of asphalt onrete mixtures is mainly based on the retained stability (RS), whih is the ratio between wet and dry stabilities. Most researhers indiate that this ratio should not be less than 75 perent. There en :a 13 Ill 125 'iii &. 12 ::E: :i. No No. 2 o No. 2-No. 5 o No. 5-No. 2 o------b=- -==::_ o.,_..., """--:;--o.,,o 2 25 E E Ln N )I 13 u:: t:i. No No. 2 o No. 2 - No. 5 o No. 5 - No FIGURE 6 Relationship between rubber ontnt and Marshall stability at 4 perent air voids. FIGURE 7 Relationship between flow and rubber ontent at 4 perent air voids.

6 98 TRANSPORTATION RESEARCH RECORD S 1:> No No. 2 o No. 2 - No. SO o No. SO-No. 2 D No No. 2 No. 2 - No. SO No..SO - No so :.a 2 VI 7 "C GI ::! GI :: 6 11'--l.L-'I, -'----' s 1 1S 2 so 1 1S 2 FIGURE 8 Relationship between rubber ontent and VMA at 4 perent air voids. FIGURE 9 Retained stability versus rubber ontent at 4 perent air voids. fore 75 perent RS was used as the aeptane-rejetion riterion (11). Figure 9 shows the relationship between RS and rubber ontent for the three sizes of rubber partiles used in asphalt-rubber binders. RS was inversely related to the inrease in rubber ontent in the binder for the three asphaltrubber onrete mixtures. The RS of all mixtures was aeptable, exept for the RS of the mixture with No. 5-2 rubber partile sizes at 2 perent rubber ontent, whih was not aeptable. CONCLUSIONS On the basis of the results of this study, the following onlusions are made: The addition of rubber to the asphalt ement hanges the properties of binders. Penetration, dutility, flash point, and speifi gravity of the asphalt-rubber binder are inversely related to the inrease in rubber onentration in the binder. However, the softening point is diretly related to the inrease in the rubber onentration. The dutility and speifi gravity of the asphalt-rubber binder derease as the size of the rubber inreases. Mixtures prepared with asphalt-rubber binders exhibit lower stabilities than do similar mixtures made up of asphalt ement binder. In ontrat, inorporating rubber into asphalti onrete mixtures inreases the flow of these mixtures. For mixtures made up of asphalt-rubber binders, VMA slightly inreases with an inrease in the rubber ontent in the binder. The retained Marshall stability of all mixtures was found aeptable, exept the RS of mixtures with No. 5-2 rubber partile size at 2 perent rubber ontent. Crumb Rubber. In Transportation Researh Reord 821, TRB, National Researh Counil, Washington, D.C., 1981, pp MDonald, C. H., A New Pathing Material for Pavement Failures. In Highway Researh Reord 146, HRB, National Researh Counil, Washington, D.C., 1966, pp Morris, G. R., and C. H. MDonald. Asphalt-Rubber Stress Absorbing Membranes Field Performane and State-of-the-Art. In Transportation Researh Reord595, TRB, National Researh Counil, Washington, D.C., 1976, pp Shnormeier, R. H. Fifteen-Year Pavement Condition History of Asphalt Rubber Membranes in Phoenix, Arizona. In Transportation Researh Reord 196, TRB, National Researh Counil, Washington, D.C., 1986, pp Lalwani, S., A. Abushihada, and A. Halsa. Relaimed Rubber Asphalt Blends Measurement of Rheologial Properties to Aess Toughness Resilieny, Consisteny and Temperature Sensitivity. Pro, Assoiation of Asphalt Paving Tehnologists, Vol. 51, 1982, pp Roberts, F. L., and R. L. Lytton. FAA Mixture Design Proedures for Asphalt-Rubber Conrete. In Transportation Researh Reord 1115, TRB, National Researh Counil, Washington, D.C., 1987, pp Chehovits, J., and M. Manning. Materials and Methods for Sealing Craks in Asphalt Conrete Pavements. In Transportation Researh Reord 99, TRB, National Researh Counil, Washington, D.C., 1983, pp Oliver, J. W., Modifiation of Paving Asphalt by Digestion with Srap Rubber. In Transportation Researh Reord 821, TRB, National Researh Counil, Washington, D.C., 1981, pp Dunlop Servie Manual. Car and Truk Tires. Dunlop Company, Japan, Mix Design Methods for Asphalt Conrete and Other Hot-Mix Types. Manual Series 2. Asphalt Institute, College Park, Md., Tunniliff, D. G., and R. E. Root. Antistripping Additives in Asphalt Conrete-State-of-the-Art. Pro., Assoiation of Asphalt Paving Tehnologists, Vol. 51, 1982, pp REFERENCES 1. Huff, B. J., and B. A. Vallerga. Charateristis and Performane of Asphalt-Rubber Material Containing a Blend of Relaim and Publiation of this paper sponsored by Committee on Charateristis of Nonbituminous Components of Bituminous Paving Mixtures.

Degradation of Dense Aggregate Gradings

TRANSPORTATION RESEARCH RECORD 1228 73 Degradation of Dense Aggregate Gradings BALA SuBRAMANYAM AND Mowu P. PRATAPA As the degradation of aggregates affets the properties of bituminous onrete, various