Optimization of Asphalt Mix Improved by the Addition of Scrap Tires

The design of improved asphalt mix is achieved by the use of three major variables , weight of s crap tires replaced by coars e base aggregate , particles size of scrap tires finally the weight of binder used (bitumen). The i mproved asphalt mi x (IAM) requires a balance between rut resistance and durability to resist cracking and moisture damage (stripping) .Accordingly several fa ctors that influence rut resistance and durability are considered during the design process:

A blend of reclaimed ground tire rubber reacted with asphalt cement at elevated temperature has been used as a binder in various types of bituminous construction.Rehabilitation and maintains this blend is called "asphalt-rubber".Acceptance of asphalt-rubber systems has been primarily regional, depending some what on the favorable experience gained during experimental stages of use.The information on performance of these systems has been fragmented and difficult to asses, not only has field data presented interpretation problems but evaluation of the asphalt -rubber material in the laboratory has also been fraught with difficulty [7] .
The use of recycled tire did not develop as a solution environmental solid waste tire disposal problem [8,9], but as a promising modifier for the improvement of asphalt concrete.Recycle tires (RT) can be used in hot mixes in either of two primary categories: As a replacement of aggregate, where it is mixed with aggregate and then coated with asphalt cement binder (dry process), or as a modifier of asphalt cement binder itself, where such a modified binder is used to coat aggregate particles (wet process).There is extensive excellent literature available on both processes and technologies [8][9][10][11][12][13][14][15], but a brief description is given on wet process as it was the only one used in British Columbia.
Such modified asphalts mix can increase a high temperature stiffness, which boosts resistance to rutting, bleeding, and flushing.They reduce low temperature stiffness, which fights thermal cracking, improves fatigue resistance, also fights raveling and stripping.
The most commonly added group modifiers are the styrene/butadiene polymers (scrap tires) followed by natural rubber and crumb rubbers both virgin and recycled.The lessused plastomeric modifiers include the familiar polypropylene and polyethylene, as well as ethyl-vinylacetate and PVC.
The styrene/butadiene group increases stiffness, crack resistance (including low temperature thermal cracking), that improves the adhesion properties of binder.The generally addition of this component improves mixtures especially at a rate (3-6% wt) of binder depending on the PG grade of asphalt [16][17][18][19].
In the super pave mixture design system binder grade is selected based on climatic data traffic loading and traffic speed, which is soft enough at low temperatures to resist thermal cracking and stiff enough at high temperature to resist rutting [20].Also, there are some performance characteristics of asphalt concrete mixtures for which the properties of asphalt cement binder play an important role, such as durability.
Additionally they may be situations, where the properties of the aggregate portion of a particular mix can not be changed because of local conditions, economics, or frictional characteristics.In these cases an improvement in the characteristics of the mix will need to be obtained through change or improvement of asphalt binder cement or the replacement of aggregate by portion PDF created with pdfFactory Pro trial version www.pdffactory.com of waste tires at (10-50 %wt.) [21][22][23][24] ,the fatigue life for dry mix (cold process) is three times as long as that wet mix (hot process) , also the type of scrap tire used to make this improvement is not effect wheel tracking very much , but has a significant effect on fatigue resistance [24,25,26].

The aim of present work:
The purpose of this study is to identify and verify using all available state-of-the art sources ,how the coarse tire rubber can be utilized in asphalt concrete mixture for construction meeting standard quality performance related specifications such as more crack resistance ,lesser degree of rutting ,longer life ,decreased life cycle costs ,reduction of traffic noise ,improved resistance to permanent deformation at high temperatures , decreased pollution and ,increased environmental quality, due to improvement of thermomechanical properties performance.
Then a main approach is to study the effect of different operating variables (concentration of scrap tires wt.%, concentration of binder wt.%, and particle size of scrap tires) on the final operating mechanical, chemical and thermal properties of improved asphalt concrete mixtures by applying the central composite rotatable design (Box-Wilson design) to reach the optimum operating variables, with the use of both techniques hot (wet) and cold (dry) in preparation these mixes.
Also to determine the optimum coarse rubber particle size substituting aggregate in hot and cold mix ,the concentration of this coarse aggregate substitute ,and finally the optimum concentration of binder used to gave excellent performance and durability in characteristic and application properties.

Preparations of improvement asphalt mix samples:
A flow chart of experimental mix system is shown in figures (1&2).Weigh in to separate pans the amount of each size fraction required to prepare a batch standard design asphalt mix (aggregate(fine & coarse) , cement(filler) ,and asphalt cement( binder)) at the classification of each component shown in table (2).The pan of a batch mix was put on a hot plate (0-250˚C) with continuous mechanical mixing (950 cycle/min) until the temperature of standard aggregate asphalt mixture reaching 168˚C (hot wet process step).The second step is to form a crater in the hot mix asphalt concrete mixture in order to replace percent of scrap tire particles about (10-30) %wt and (1-5) cm diameter of particles size due to Central Composite Rotatable Design experimental program [27] (CCRD) with the aggregate ( dry & cold process) ,then mold these prepared mix in to a clean ,hot and crease molder assembly then face the compaction hammer (Germany comp. in asphalt lab ,ring No. 11142) after place appear toweling cut to size in the bottom of mold then place the mold assembly on the compaction pedestal in to mold holder apply 52 blows with compaction hammer prepaid circularly to the base of mold , remove the base plate and collar then reverse and reassemble the mold with the application of same no.blows , after compaction remove the base plate and leaving specimen in atmosphere field for 24 hrs.Before any test applied, then applied the final characteristic tests mechanical, chemical, and thermal properties in order to reach the optimum improvement mix conditions for PDF created with pdfFactory Pro trial version www.pdffactory.comconcentration of scrap tires and concentration of binder [20,21].
Different particle size of scrap tires of 50 mm and smaller than it was collected manually from the local street of Baghdad.And the designed of experiments were carried out according to the Central Composite Rotatable Design CCRD [27] for three variables in fifteen experiments for preparing improved asphalt mix as follow: X 1 = concentration of scrap tires replacement in asphalt mix (coarse aggregate) = (10-30%wt).X 2 = particle size of scrap tires replacement in asphalt mix= (1-5) cm (thickness).X 3 = concentration of binder used in asphalt mix = (3-6.5)%wt The response of experiments conducted according to Box-Wilson method was fitted to a second order poly-nominal (mathematical model from which the optimum response was calculated as shown in table (3).

Material in experimental programme:
Different particle size of scrap tires of 50 mm and smaller than it was collected manually from the local street of Baghdad.
The asphalt binder is brought from the middle spot of Iraq in Al-Durra refinery factory.Where this type of binder is tested (at the asphalt lab / university of technology) and then gave passing properties to use it as a binder in the improvement of asphalt mix as shown table (4).

Testing of standard and improvement asphalt mix: Physical properties: -Bulk unit weight (γ):
This type of design factor is determined for both standard and improvement samples by clamping and weigh samples in both air and water, then recorded the weight in both cases, this factor is calculated by the use of equation below: γ = W A /V = W A /W A -W W Where: W A = weight of sample in air (gm).V= volume of sample = volume of displacement water (cm 3 ).W w = weight of sample in water (gm).

-Theoretical unit weight (ψ):
This type of test is determined by the use of stable prepared sample to calculate the percent of air void depending on weight of samples and weight of all component used ( aggregate ,filler , binder , scrap tires ) , and use the equation below : and specific gravity of binder (gm/cm 3 ) W c , G c = volume (cm 3 ), weight (gm) and specific gravity of coarse aggregate (gm/cm 3 ) W f , G f = volume (cm 3 ), weight (gm) and specific gravity of filler (gm/cm 3 ) W mf , G mf = volume (cm 3 ), weight (gm) and specific gravity of mineral filler (gm/cm 3 ).

-Wet and dry density:
This type of test is determined by the exposure of prepared sample to air (dry) and water (wet) then applied the general density equation.

Chemical properties:
This type of test is determined by the preparation of different concentration of chemical solutions (100% H2O , 5% H2SO4 (acidic sol.), and 5% NaOH (alkali sol.)),PDF created with pdfFactory Pro trial version www.pdffactory.comthen all prepared standard ( table 2 ) and improvement samples as conditions in ( table 3 ) is soaked for 7 days at 50°c after ward recorded the change in weight every 24 hrs to check which of samples is more chemically stable than others (optimum one).

Mechanical properties:
This type of test is determined by the use of Marshall Machine tester in asphalt lab / of building eng.Depart.) due to ( ASTM D155982 -Marshall apparatus ) stability and dynamically measurement , where put the prepared sample horizontally in the center of this tester then exposure it to sever load until failure occurs and this factor is called flow and record the failure of stable sample only after load stable occur then called stable value .

Results and Discussion
The statistical analysis system (SAS) soft ware is used for estimating mathematical model representing the second order response surface fitted to the design points and responses (table 5 The evaluation of the optimum operating conditions for improvement asphalt mix was performed by using a computer program namely (optimization techniques.The results of optimization are: X1= concentration of scrap tires (wt %) = 20 gm.X2= particle size of scrap tires (cm) = 3.0.X3= concentration of binder asphalt (wt %) 6.482.
PDF created with pdfFactory Pro trial version www.pdffactory.com The effect of operating conditions on the characteristic properties of final improved asphalt mix: Effect of scrap tire concentration on the properties of asphalt mix.Physical properties: Figs.
(3,4) shows the effect of set concentrations of scrap tires on the physical properties of improved asphalt mix ( bulk unit weight, theoretical unit weight, wet and dry density ,V.T.M ) under optimum particle size (3 cm).
It appears that both bulk unit weight and theoretical unit weight of improved mix are increased with increasing the concentration of scrap tires with preference of optimum mix (No.11, 20 % wt S.T, 6.482 % of B, and 3 cm P.Z) of 1.865 gm/cm 3 and 2.47 for theoretical one.These values of density are decreasing with increasing concentration of scrap tire then become constant at optimum mix.Conditions (No.11, 20%wtS.T , 6.482% wt B, 3 cm P.Z) due to the properties of scrap tires [7,8] 7) Shows the effect of set concentration of scrap tires on the V.T.M ( void of total mix) at optimum particle size (3 cm), which is decreased for increasing the concentration of scrap tires due to the randomly shape of scrap tire particles with preference of optimum one (No.11) of (8.2) V.T.M ,which agreement with standard one of ( 8 ) only .

Chemical properties
Figs. (8, 9, and 10) show the effect of different chemical solutions

Mechanical properties
Figs. (11,12) show effect of set concentrations of scrap tires on the mechanical properties of final improved mix (stability (KN), flow modulus of elasticity (mm)).
It appears that all stability values of improved mix are decreased with increasing concentrations of scrap tires with preference for optimum one No.11 of 7.99 KN than standard of 7.8 KN.Also this improved mix give high modulus of elasticity and less distortion with increasing concentration of scrap tires for optimum mix No.11 at 7.8 mm flow than other standard one distorted at (8 mm) due to the characteristic properties of tires [7,8].

Effect of concentrations for binder (asphalt) on the final improved asphalt mix. Physical properties
Figs. (13, 14, 15, 16, and 17) show the effect of set concentrations of binder on the physical properties of final asphalt mix (bulk unit weight, theoretical unit weight, V.T.M, dry and wet density at optimum particle size (3cm).
It appears that the weight of bulk unit is increased at increasing weight of binder with preference for optimum one (No.11) of (1.866 PDF created with pdfFactory Pro trial version www.pdffactory.comgm/cm 3 ) than standard one of (1.86 gm/cm 3 ), also the theoretical unit weight is increased with increasing concentration of binder with preference of optimum one at (2.47) ratio than other standard at (2.46) ratio.
And Fig. ( 15) Shows the decreasing concentration of binder to reach (8) V.T.M like standard mix applied due to the characteristic properties of tires [7,8] And figs.(23,24) shows the effect of particle size of waste tires on the density of final improved mix where, values of dry density are decreased with increasing particle size due to characteristic properties of scrap tires with preference for optimum mix of (2.20 gm/cm 3 ) than standard one of (2.24 gm/cm 3 ) .The values of wet density are increased with increasing particle size until reach (1.23 gm/cm 3 ) for optimum mix No.11 like standard one due to the characteristic properties of aggregate.

Mechanical properties
Figs . (25 and 26) show the effect of set particles size on the mechanical properties (stability, flow) of final improved asphalt mix at optimum concentration of scrap tires 20%wt.It appears that values of stability are decreased with increasing particle size with preference of optimum mix of (7.89 KN) due to the characteristic properties of tires [7,8].

Thermo-Mechanical properties
The thermo-mechanical properties (stability, and flow) were studied at sever conditions (60˚ C and PDF created with pdfFactory Pro trial version www.pdffactory.com4˚C) for both optimum improved asphalt mix (No.11, 20 %wt S.T, 6.482 wt %B, 3cm P.Z) and standard asphalt mix.It appears that the stability of optimum asphalt mix is higher than standard one with less distortion ,also give excellent performance properties ( more crack resistance, lesser degree of rutting, longer life,decreassed life cycle costs, and improve the resistance to permanent deformation at high temperature) [7,8] as shown in table (6).

Thermo-Physical properties
The thermo-physical properties (unit bulk weight, theoretical unit weight, V.T.M, dry and wet density) were studied at severs conditions (60˚C, 4˚C) for both optimum improved mixes (20% wt.S.T, 6.482wt% B, 3cm P.Z).It appears that both bulk and theoretical unit weight have excellent results than standard one ,also both wet and dry density for optimum mix is less than standard one with preference of optimum one which is reduction all traffic noise (see table 7) [7,8].

Conclusions:
Based on the present work the following conclusions can be drawn regarding the improvement of asphalt mixture that will be used in the local street paving by the use of scrap tires waste: 1. [21]-Yusuf M., P.E Kauser , J.P.E Jim , L.L.M Devi P. ,Alicia L.L. " Evaluation the effect of coarse and fine rubber particle on laboratory rutting performance of asphalt concrete mixture " , email:mehta@rowan.edvNJ 08028 , pp.1-17 .

Table (1) shows the details data for scrap tires in
, see Fig. (5), but shows an increasing for wet density with increasing of S.T concentration reached higher wet density for optimum mix (No.11) of 1.23 gm/cm 3 due to the characteristic properties of aggregate a shown in Fig. (6).Fig. (

(
100% H 2 O, 5% H 2 SO 4 , 5% NaOH) on final improved asphalt mixtures, where the change in weight is increased with increasing time of aging until reach constant values.All improved samples have excellent chemical resistance than standard asphalt mix with constant and preference stability in weight( due to the change in weight observations) for optimum mix (No. 11) due to the chemical resistance of scrap tires[7,8].
This details supplied by both general traffic office and amanat Baghdad /solid waste office for small and large cars.PDF created with pdfFactory Pro trial version www.pdffactory.com

Figure ( 5 )
Figure (5) shows the effect of scrap tires on density of mix.

Figure
Figure (11) shows the effect of scrap tires on stability of final mixes.

Figure ( 16 )
Figure (16) shows the effect of binder (%wt.) on the dry density of final mixes.

Figure ( 23 )
Figure (23) shows the effect of particle size of S.T on the dry density of final mixes.
Figure (26) shows the effect of particle size of S.T on the flow of final mixes.

Table ( 2) show the classification of standard improved asphalt mix *
design of base component (B.C) supplied from the general building laboratory center / properties of building materials ( asphalt , cement , coarse , sand ) for standard base asphalt mix .

Table ( 3) results of experiments planned according to CCRD real variables.
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Figure (19) shows the effect of binder (% wt.) on the flow of final mixes.
T Figure (18) shows the effect of binder (% wt.) on the stability of final mixes.

) shows the effect of particle size of S.T on the unit weight of final mixes.
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) shows the effect of particle size of S.T on the theoretical unit weight of final mixes.
Figure (22) shows the effect of particle size of S.T on the V.T.M value for final mixes.