Materials and Design 66 (2015) 51–59

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Materials and Design

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Laboratory evaluation on performance of diatomite and glass fibercompound modified asphalt mixture

http://dx.doi.org/10.1016/j.matdes.2014.10.0330261-3069/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: No. 199, South Guangming Street, City of Handan,Hebei Province, China. Tel.: +86 15383202570.

E-mail addresses: hbuegql@gmail.com, guoql@hebeu.edu.cn (L. Li).

Qinglin Guo a, Lili Li b,⇑, Yongchun Cheng c, Yubo Jiao c, Chun Xu c

a School of Civil Engineering, Hebei University of Engineering, Handan, Hebei 056038, Chinab Department of Student’s Affairs, Hebei University of Engineering, Handan, Hebei 056038, Chinac College of Transportation, Jilin University, Changchun, Jilin 130025, China

a r t i c l e i n f o

Article history:Received 3 August 2014Accepted 14 October 2014Available online 23 October 2014

Keywords:DiatomiteGlass fiberStatistical regression analysisAsphalt mixture

a b s t r a c t

The purpose of this paper is to investigate the compound effects of diatomite and glass fiber on asphaltmixture. The diatomite and glass fiber compound modified asphalt mixture (DGFMAM) was prepared inlaboratory. Performances of DGFMAM were investigated by experimental method. Wheel tracking test,low temperature indirect tensile test, indirect tensile fatigue test (ITFT) and indirect tensile stiffness mod-ulus test (ITSM) were carried out. The statistical analysis of variance (ANOVA) method and statisticalregression method were used to evaluate the effects of diatomite and glass fiber on properties of asphaltmixture. Results indicate that diatomite and glass fiber improve the rutting resistance and fatigue prop-erties of control asphalt mixture. Diatomite has a significant effect on the stiffness modulus of asphaltmixture. Disadvantage of diatomite on low temperature deformation property of asphalt mixture issolved by glass fiber. DGFMAM has better travelling performances than the control mixture. It will pro-vide a reference for the design of compound modified asphalt mixture.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Asphalt pavement has been widely used in the world due to itsgood performance. It is constructed using hot asphalt mixture. Hotasphalt mixture is a typical viscoelastic material. This will result inrutting deformation at high temperature in summer and pavementcracking at low temperature in winter. And then the rutting defor-mation and cracks in pavement will affect the travelling perfor-mance of vehicles seriously [1,2]. Thereby, researchers in manycountries have been trying to modify the asphalt mixture in orderto solve these problems as much as possible.

Diatomite is a material which has light weight, high porosityand good insulation property, its reserve is huge and the cost islow. It has been used to modify asphalt mixture as a result of thesecharacteristics in recent years. And the properties of asphalt binderand mixture modified by diatomite were studied. Bao [3] and Xu[4] investigated the basic properties of diatomite modified asphaltbinder. The results suggest that the penetration and ductilitydecrease with the increase of diatomite, and the softening temper-ature of asphalt binder is increased by diatomite. Cong et al. [5]evaluated the effect of diatomite on the viscosity of asphalt, the

results indicate that the viscosity of modified binder increases withthe increase of diatomite, the diatomite modified asphalt mixtureis susceptible to low temperature cracking. Zhu et al. [6] evaluatedthe insulation property and pavement performances of diatomitemodified asphalt mixture in laboratory. The results show that diat-omite not only improves the rutting resistance significantly butalso reduces the thermal conductivity coefficient of asphalt mix-ture. And the bending stiffness modulus of diatomite modifiedasphalt binder is less than that of the control binder at low temper-ature. Tan et al. [7] studied the interaction between diatomite andasphalt, the fracture property of modified asphalt mixture at lowtemperature. The results indicate that there is no chemical reactionoccurred between diatomite and asphalt, the fracture temperatureof modified mixture is lower than that of the control mixture. Chenet al. [8] also studied the insulation performance of asphalt mix-ture modified by diatomite, the results suggest that the thermalconductivity of mixture is reduced by diatomite. Diatomite is help-ful for the surface temperature reducing of roadbed in permafrostregion. Li et al. [9] also suggested that the bending strength andbending tensile strain of diatomite modified asphalt mixture areless than that of the control mixture at low temperature. Therefore,it can be seen that the high temperature stability and thermalphysical property of asphalt mixture are improved by diatomite,but the low temperature deformation ability of diatomite modifiedasphalt mixture is declined. The pavement which is constructed

Table 2Properties of diatomite.

Property Color PH Specific gravity (g/cm3) Bulk density (g/cm3)

Value Orange 7–8 2.1–2.3 0.35–0.42

Table 3Particles size distribution of diatomite.

Particle size (lm) <5 10–5 20–10 40–20 >40

Value (%) 62 27 4.4 2.1 1.4

52 Q. Guo et al. / Materials and Design 66 (2015) 51–59

using asphalt mixture modified by diatomite is more susceptible tolow temperature cracking than the common pavement. However,the asphalt pavement in seasonal frozen regions such as Jilin prov-ince of China has a severe need on low temperature property ofasphalt mixture. The asphalt pavement in these regions must havegood high temperature stability and anti-crack performance at lowtemperature simultaneously. Therefore, it is needed to improve thelow temperature deformation property of diatomite modifiedasphalt mixture.

Glass fiber is a kind of inorganic fiber with high tensile strength.In the previous studies, glass fiber has been used to modify asphaltmixture successfully in order to improve the deformation ability.Aysar et al. [10] investigated the fracture behavior of asphalt con-crete with glass fiber. It shows that the glass fiber modified mix-ture has a potential resistance to against crack initiation. Thiswill be beneficial to preventing pavement cracks at low tempera-ture. Abtahi et al. [11] thought that glass fiber improves thestrength, fatigue property and ductility of asphalt mixture. Fu[12] investigated the properties of asphalt mixture modified byglass fiber. The result suggests that glass fiber has no significantinfluence on the bending strength, but the bending failure strainincreases with the increase of glass fiber. Glass fiber improvesthe property of rutting resistance significantly. Besides, Mahrezet al. [13] indicated that the use of glass fiber in pavement mayincrease the cost of construction, but this will reduce the cost ofmaintenance. It can be found that glass fiber not only improvesthe ductility, anti-cracking property and fatigue property of asphaltmixture but also seems to be economic for the modification of mix-ture. In summary, some effects of diatomite and glass fiber onasphalt mixture are similar, and the others are different. The down-side of one modifier on the mixture can be changed by anothermodifier. Effects of diatomite and glass fiber on asphalt mixturehave been investigated in previous researches separately. The com-pound modified effects of diatomite and glass fiber are unknown. Ifdiatomite and glass fiber are used to modify asphalt mixture simul-taneously, a new kind of asphalt mixture which has good ruttingresistance and low temperature performance may be obtained.Furthermore, it will provide a technology reference for the designof mixture.

In this paper, a preparation process of diatomite and glass fibercompound modified asphalt mixture (DGFMAM) was discussed.The control asphalt was modified by diatomite. Then the modifiedasphalt and glass fiber were used to prepare DGFMAM. The speci-mens of DGFMAM for experiments were prepared in laboratory.Effects of diatomite and glass fiber on the performances of asphaltmixture were tested and evaluated.

2. Materials and preparation method

2.1. Materials

In this study, the heavy traffic asphalt AH-90 was used forexperiments. Its basic properties are listed in Table 1. Diatomiteis the calcined product, and its physical properties are presentedin Table 2. As shown in Table 3, the particle size distribution ofdiatomite was investigated according to the Standard ASTMD4464-10. Glass fiber is the short fiber from Taishan Fiberglass

Table 1Properties of the control asphalt.

Property Value Standard

Penetration (25 �C, 0.1 mm) 86 ASTM-D5Ductility (15 �C, cm) 168.5 ASTM-D113Softening point (�C) 44.5 ASTM-D36Penetration index �1.416 –

Inc., Shandong Province, China. And its properties are presentedin Table 4. Silane coupling agent was used to process the glass fiberin order to improve the bonding property of interface. The aggre-gates are limestone. As presented in Table 5, apparent specificgravities of aggregate were tested according to the StandardsASTM:C127 and ASTM:C128. The selected gradation of asphaltmixture is shown in Fig. 1.

2.2. Preparation method of DGFMAM

The control asphalt was modified by diatomite at first. The pro-cessing method has significant impact on the properties of modi-fied asphalt. A low mixing speed is difficult to ensure uniformdistribution of diatomite in asphalt. Therefore, the equipment witha speed of 600 r/min was used to blend. The specific processes ofasphalt modification are as follows.

First, diatomite and the control asphalt were weighed with therequired quality, and they were placed in the oven at 135 �C for 4 h.Second, diatomite and the control asphalt were taken out from theoven. Diatomite was added into the control asphalt. The diatomiteand asphalt were mixed by the blending equipment with a speed of600 r/min.

Based on the results of repeated test, it was found that theblending time should be set for 15 min. Besides, diatomite particleswill sink in asphalt as a result of the weight of particle when themodified asphalt is placed for a long time. So a second blendingshould be conducted when the modified asphalt was used forexperiment again.

The preparation procedures of DGFMAM are as follows.

1. Aggregates were mixed in the mixing oven at 170 �C. And thenthe diatomite modified asphalt was added, they were mixedabout 90s in order to make aggregate surface uniformly coatedby asphalt mastic, then the diatomite modified asphalt mixturewas obtained.

2. Glass fiber was added into the diatomite modified asphalt mix-ture which had been obtained in previous step. They weremixed about 90s, and then the mineral filler was added. Thediatomite and glass fiber compound modified asphalt mixturewere obtained after a second mix within 90s. Distributionstatus of glass fiber in asphalt mixture has a direct impact onproperties. So the mixing time should be increased

Table 4Physical properties of glass fiber.

Property Value Standard

Length (mm) 12 GB/T 14336 [14]Specific gravity (g/cm3) 2.5 GB/T 14335 [15]Color White –Melting temperature (�C) >1500 ASTM-D7138Tensile strength (MPa) 3100–3400 ASTM-D5035Ultimate tensile strain (%) 3.3–3.6 ASTM-D5035

Table 5Apparent specific gravities of aggregate.

Sieve size (mm) 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075

Apparent specific gravity (g/cm3) 2.817 2.704 2.821 2.655 2.689 2.645 2.652 2.710 2.682

Fig. 1. Selected gradation in experiment.

Q. Guo et al. / Materials and Design 66 (2015) 51–59 53

appropriately if the dispersion of fiber is not good. And all theprocessing time should not exceed 6 min in order to preventasphalt aging.

The diatomite and glass fiber content are percentages by thetotal weight of control asphalt mixture in this paper. From thecost-effective viewpoint of modification on mixture, three contents(0.1%, 0.2% and 0.3%) of diatomite and glass fiber were selected forexperiments. Specimens were made in laboratory. According to theStandard JTG E20-2011 [16], the Marshall specimens were double-side struck for 75 times. And then the optimum asphalt contentwas determined on the basis of Marshall results, it is 4.8% for theunmodified mixture. The physical properties of Marshall specimenwere tested according to the Standard T0706 of JTG E20-2011, andthe average values are listed in Table 6.

3. Experimental procedures

3.1. Wheel tracking test

Wheel tracking test is considered an effective method for theevaluation of high-temperature rutting resistance. It has been usedin previous studies frequently [17–19]. So this method wasemployed to evaluate the rutting resistance property of DGFMAM

Table 6Physical properties of Marshall specimen.

Modifiers content (%) Apparent specific gravity (g/cm3) Voids content (%)

(0, 0) 2.48 3.8(0.1, 0.1) 2.48 3.2(0.1, 0.2)a 2.47 3.4(0.1, 0.3) 2.46 3.1(0.2, 0.1) 2.47 3.6(0.2, 0.2) 2.46 2.9(0.2, 0.3) 2.47 4.0(0.3, 0.1) 2.45 4.1(0.3, 0.2) 2.45 4.1(0.3, 0.3) 2.46 3.7

a Note: the content (0.1, 0.2) means that the content of glass fiber is 0.1% and thecontent of diatomite is 0.2%.

in this paper. The slab specimens were compacted by rollingcompactor for 24 times, its size is 300 mm � 300 mm � 50 mm.The test was conducted at 60 �C. Stroke of test wheel is 23 cm.The wheel running speed is 42 times/min. The load is appliedon the slab through a rubber wheel 50 mm in width, its value is0.7 MPa. Specimens were placed in the oven at 60 �C for 6 h beforetest. Rutting depth was recorded during the test. Dynamic stability(DS) and permanent deformation were used to evaluate the hightemperature stability of DGFMAM. DS is calculated by the follow-ing equation.

DS ¼ ðt2 � t1Þ � Nd2 � d1

� C1 � C2 ð1Þ

where DS is Dynamic stability, times /mm; d2 is the deformation attime t2 (t2 is 60 min), mm, it is the permanent deformation gener-ally; d1 is the deformation at time t1 (t1 is 45 min), mm; C1 is thecorrection factor of equipment, it is 1.0 for this equipment; C2 isthe correction factor of specimen, it is 1.0 for the specimen in thistest; N is the running speed of test wheel, it is 42 times/min.

3.2. Low temperature indirect tensile test

The low temperature tensile property of asphalt mixture is animportant indicator for the evaluation of pavement anti-crackingability. There are three methods which are often used to investi-gate the low temperature performance of asphalt mixture. Theyare three-point bending method, indirect tensile method andfour-point bending method [20–22]. In general, diatomite andglass fiber distribute uniformly in mixture. For bending test, thetensile strain and fracture strength of mid-span are investigated,but there are few diatomite and glass fiber at the bottom of mid-span, the effects of modifiers on the tensile strain and fracturestrength may be little in this region. So the indirect tensile testwas employed to evaluate the anti-cracking property of DGFMAM.According to the Standard JTG E20-2011, this test was conducted at�10 �C. And a loading rate of 1 mm/min was selected. The speci-mens were compacted 75 times on each side, the size of specimenis /101.6 mm � 63.5 mm. Specimens were placed in the chamberat �10 �C for 6 h before test. The specimen was only removed fromthe chamber of �10 �C when the test began. All the test process iscompleted in a short time in order to ensure the temperature ofspecimen does not change obviously. Three parallel specimenswere used for the test of each content. The vertical deformationon the top surface of specimen and the load were recorded duringthe test. The tensile strength and tensile failure strain were calcu-lated by the following equations which are suggested by the stan-dard JTG E20-2011.

RT ¼0:006287PT

hð2Þ

eT ¼XT � ð0:0307þ 0:0936lÞ

1:35þ 5lð3Þ

XT ¼YT � ð0:135þ 0:5lÞ

1:794� 0:0314lð4Þ

where RT is the indirect tensile strength, MPa; eT is the tensile failurestrain, le; PT is the indirect tensile failure load, N; YT is the verticaldeformation, mm; XT is the horizontal deformation which is calcu-lated by YT, mm; l is the Poisson ratio; it is 0.25 in this test; h is theheight of specimen, mm.

Fig. 3. Indirect tensile fatigue test.

54 Q. Guo et al. / Materials and Design 66 (2015) 51–59

3.3. Indirect tensile fatigue test (ITFT)

Fatigue property of asphalt mixture is closely related to the ser-vice life of asphalt pavement. The better the fatigue property ofmixture is, the longer the service life of pavement is. Thereby, itis necessary to investigate the fatigue property of asphalt mixture[23]. Indirect tensile fatigue test (ITFT) is an effective methodwhich has been used in many researches [24–26]. So this methodwas used to investigate the fatigue property of DGFMAM. The spec-imens used in this experiment were the standard Marshall speci-men, its size is /101.6 mm � 63.5 mm. The specimen preparationmethod is as same as the method of low temperature indirecttensile test. Nine specimens were used for the fatigue test of eachcontent, and ninety specimens were used in this test altogether.This test was conducted at a room temperature, 16.5 �C. A stress-control mode was applied. As shown in Fig. 2, the load appliedon specimen was half-sinusoidal repeated load, its frequency is5 Hz.

In order to ensure the measurement accuracy, the minimumload is set for 0.15 KN. The maximum tensile stress at the centerof specimen was defined as the stress level, and it is calculatedby the following equation [27].

rx;max ¼2Pmax

pdhð5Þ

where rx,max is the maximum tensile stress at the center of thespecimen, MPa; Pmax is the maximum value of the load, KN; d isthe diameter of specimen, mm; h is the height of the specimen, mm.

The total number of the load is defined as the fatigue life whenthe specimen cracks completely. The test procedure was shown inFig. 3. The fatigue life of DGFMAM can be characterized by the fol-lowing equation [28].

Nf ¼ KðrÞ�n ð6Þ

where Nf is indirect tensile fatigue life; r is the stress level. K and nare constants of material.

3.4. Indirect tensile stiffness modulus test (ITSM)

The stiffness of asphalt mixture is always considered as a syn-thetic indicator of the structural properties, and it is related tothe capacity of mixture to distribute traffic loads [29,30]. There-fore, indirect tensile stiffness modulus test (ITSM) was used toinvestigate the stiffness modulus of DGFMAM in this paper. Thistest was conducted according to the Standard EN 12697-26 [31].A cooper NU-14 testing machine of asphalt material was used inthe test. In order to investigate the temperature sensitivity of mod-ulus, this test was conducted at 5 �C, 10 �C and 25 �C, respectively.Three specimens were used for the test of each content. And thesize of specimen is u101.6 mm � 63.5 mm also. They were placedin the chamber at the test temperature for 6 h before test. Theschematic diagram of the load is shown in Fig. 4. Rise time ofone impulse is 124 ms. The load duration period from the start of

Fig. 2. Schematic diagram of the load in ITFT.

the load application until the start of the next is 3.0 s. The targetdeformation in horizontal direction is 5 lm. The peak load wasadjusted according to the test value of target deformation duringthe test. Data of five waveforms were recorded after adjustment.The test procedure is shown in Fig. 5.

The stiffness modulus can be calculated by the followingequation.

Sm ¼F � ðlþ 0:27Þ

h� Zð7Þ

where Sm is the indirect tensile stiffness modulus, MPa; F is the peakload, N; l is the Poisson ratio; it is 0.25, 0.30, 0.40 at 5 �C,15 �C,25 �C respectively; Z is the deformation in horizontal direction,mm; h is the height of specimen, mm.

4. Results and discussion

4.1. Rutting resistance of DGFMAM

Rutting resistance results were obtained by wheel tracking test,and the average values of DS and permanent deformation werelisted in Table 7.

As shown in Table 7, Dynamic stability (DS) of DGFMAMincreases with the increase of diatomite and glass fiber, and thepermanent deformation decreases with the increase of diatomiteand glass fiber. The maximum dynamic stability (DS) of DGFMAMis 2.1 times of the corresponding value of the neat mixture. And theminimum permanent deformation of DGFMAM is reduced to about40% of the control mixture. A higher dynamic stability (DS) repre-sents a better rutting resistance [32]. Therefore, it means that rut-ting resistance of asphalt mixture is improved by diatomite andglass fiber. This results agree with the studies of Bao and Zhuet al. [3,6]. But the relationship between modifiers and high tem-perature performance of mixture is not indicated due to the lackof the enough results in their studies, the quantitative relationshipshould be determined in order to make further design of DGFMAM.And this will be discussed in the next section.

Fig. 4. Schematic diagram of the load in ITSM.

Fig. 5. Indirect tensile stiffness modulus test.

Table 7Results of wheel tracking test.

Modifiers content (%) DS (times/mm) Permanent deformation (mm)

(0, 0) 696 6.93(0.1, 0.1) 868 6.42(0.1, 0.2) 1050 5.76(0.1, 0.3) 1400 4.47(0.2, 0.1) 919 5.90(0.2, 0.2) 1088 4.83(0.2, 0.3) 1260 4.28(0.3, 0.1) 1068 5.66(0.3, 0.2) 1235 4.72(0.3, 0.3) 1465 4.19

Fig. 6. Indirect tensile strength.

Fig. 7. Indirect tensile failure strain.

Q. Guo et al. / Materials and Design 66 (2015) 51–59 55

4.2. Low temperature performance of DGFMAM

Indirect tensile tests were conducted at �10 �C in order to eval-uate the effects of diatomite and glass fiber on low temperatureperformance of asphalt mixture. The tensile strength and tensilefailure strain were calculated based on the test data. The averagevalues of them were shown in Figs. 6 and 7, respectively.

As shown in Fig. 6, the changing of indirect tensile strength hasan unclear trend. This trend may be caused by the random errors ofspecimen manufactured process and the random distribution ofaggregates. So the indirect tensile strength of DGFMAM is notchanged obviously. It shows that a small amount of diatomiteand glass fiber (60.3%) has no effects on the indirect tensile

strength of mixture. But when the diatomite amount increasesand more than 10%, the indirect tensile strength will decrease obvi-ously [9]. It can be seen from Fig. 7 that the tensile failure straingradually increases with the increase of modifiers. And accordingto the results of Li et al. [9], it is known that the failure straindeclines with the increase of diatomite. Therefore, the increase oftensile failure strain is caused by the glass fiber which distributesuniformly in asphalt mixture. According to the opinions of Fu[13], the tensile stress of asphalt mortar can be dispersed by glassfiber, and the micro-cracks in asphalt mortar can be prevented by

Fig. 8. Indirect tensile fatigue lives of specimen.

Table 9Results of ITSM.

Modifiers content (%) Sm (MPa)

5 �C 15 �C 25 �C

(0, 0) 12,031 5776 2365(0.1, 0.1) 12,589 6762 2628(0.1, 0.2) 13,379 6869 3116(0.1, 0.3) 13,736 7045 3257(0.2, 0.1) 12,933 6388 2850(0.2, 0.2) 13,528 6977 3331(0.2, 0.3) 13,603 7153 3229(0.3, 0.1) 12,802 6212 2695(0.3, 0.2) 12,208 6356 2799(0.3, 0.3) 13,088 6860 3079

56 Q. Guo et al. / Materials and Design 66 (2015) 51–59

glass fiber, so the deformation property of the control asphalt mix-ture is enhanced by glass fiber. In a word, diatomite and glass fiberhas no effects on the tensile strength, but the deformation ability ofasphalt mixture is improved by glass fiber. It suggests that glassfiber is beneficial for the reduction of low temperature crackingand fatigue cracking in pavement.

4.3. Fatigue performance of DGFMAM

Indirect tensile fatigue tests were carried out in order to inves-tigate the effects of diatomite and glass fiber on the fatigue prop-erty of mixture. The test values of fatigue life were listed inTable 8. The stress level r is the peak value of half-sinusoidal load.

It can be seen from Fig. 8 that the fatigue lives of DGFMAM areall greater than the control mixture significantly, especially at lowstress levels. The fatigue curves of DGFMAM move to the right side.It means that the fatigue life of DGFMAM is larger than the life ofthe control mixture for a specified stress level. So, the fatigue resis-tance property of asphalt mixture is improved by modifiers. Butthe improved mechanism of diatomite and glass fiber on the fati-gue property can not be determined by fatigue lives directly. So afatigue model which was shown in Eq. (6) was used to analyzethe fatigue property of the modified and the control asphalt mix-ture. Fatigue parameters were obtained by the nonlinear regres-sion method. The results were given in Table 8.

As shown in Table 8, the correlation coefficients of all mixturesare greater than 0.90, it means that the selected fatigue model canbe used to characterize the fatigue properties of DGFMAM and thecontrol asphalt mixture, all these regressions are successful.According to the Eq. (7), it can be found that the greater K and nare, the longer fatigue life is. The fatigue parameters (K and n)are changed by diatomite and glass fiber, Most of K and n of DGF-MAM are greater than that of the control mixture. This is the rea-son for the enhancement of fatigue lives. In addition, theparameters (K and n) of DGFMAM increase with the increase ofdiatomite. The parameter K of the control mixture is increased byglass fiber, but it decreases slightly when fiber content is greaterthan 0.2%. The parameter n of DGFMAM has a minimum valuewhen the content of glass fiber is 0.2%. Thereby, the changingtrends of K and n with the modifiers are different, the improvedmechanism of diatomite and glass fiber on fatigue property arecomplex, a further analysis should be conducted using othermethod.

4.4. Stiffness modulus of DGFMAM

Indirect tensile stiffness modulus tests (ITSM) were carried outaccording to the Standard EN 12697-26. Stiffness modulus of DGF-MAM and the control mixture at 5 �C, 15 �C and 25 �C were inves-tigated, and the average values were given in Table 9.

As shown in Table 9, the stiffness modulus of DGFMAM ishigher than that of the control mixture at every temperature. Thestiffness modulus of DGFMAM and the control asphalt mixture

Table 8Fatigue parameters of asphalt mixture.

Modifiers content (%) K n R2

(0, 0) 294.9 3.095 0.96(0.1, 0.1) 339.2 3.524 0.96(0.1, 0.2) 381.2 3.604 0.92(0.1, 0.3) 389.7 3.744 0.97(0.2, 0.1) 352.5 3.060 0.95(0.2, 0.2) 434.2 3.395 0.98(0.2, 0.3) 449.6 3.464 0.93(0.3, 0.1) 378.3 3.432 0.91(0.3, 0.2) 408.9 3.571 0.95(0.3, 0.3) 415.2 3.617 0.96

decrease with the increase of temperature. It can be seen fromthe data in Table 9, the stiffness modulus at different temperaturesare very different in values, the comparative analysis can not bemade directly using the stiffness modulus. The modulus ratio hasbeen widely used to evaluate the modification effect of modifiersin the area of composite material [33]. Therefore, the stiffnessmodulus ratio was defined as the stiffness modulus of DGFMAMto the modulus of control mixture in this paper. And then the ratiosat different temperatures are shown in Fig. 9.

As shown in Fig. 9, the stiffness modulus ratio is changed line-arly with temperature, this trend agrees with the result obtainedby Moreno et al. [34]. The maximum stiffness modulus of DGF-MAM are 1.14 times (5 �C), 1.24 times (15 �C), 1.41 times (25 �C)the corresponding values of control mixture. The minimum stiff-ness modulus are 1.05 times (5 �C), 1.08 times (15 �C), 1.11 times

Fig. 9. Stiffness modulus ratio at different temperatures.

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(25 �C) the values of control mixture. It indicates that the stiffnessmodulus of control asphalt mixture is increased by modifiers, andthis effect is more significant at high temperature than the effect atlow temperature. According to the regression results, it can beinferred that the stiffness modulus ratio is less than 1.0 when thetemperature is lower than �10 �C. In other words, the stiffnessmodulus of DGFMAM is less than the modulus of control mixture.So the modifiers result the decrease of stiffness modulus at lowtemperature. It can be explained using the results of Tan et al.[7]. The addition of diatomite may be the main reason for decreaseof stiffness modulus. Diatomite is a lightweight and elastic mate-rial, asphalt is a viscoelastic material, the modulus of asphalt istemperature dependent. Modulus of diatomite is less than themodulus of asphalt at low temperature. So the diatomite particlesin asphalt are flexible inclusions, and these flexible inclusionscause the decrease of modulus of diatomite modified asphalt bin-der. It leads to the decline in stiffness modulus of modified asphaltmixture eventually.

4.5. ANOVA on properties of DGFMAM

It can be found that the rutting resistance, low temperature fail-ure strain, fatigue life and stiffness modulus of control mixture areall improved by diatomite and glass fiber based on the aboveresults. But the significant factor which affects these properties isunknown. However, this study aimed to determine the effect ofdiatomite and glass fiber on pavement properties of asphalt mix-ture, for this purpose and provide a better understanding, the sta-tistical analysis of variance (ANOVA) method was applied toinvestigate the significance of modified effects of diatomite andglass fiber. The analysis of variance (ANOVA) method is often usedto evaluate the percent contribution of each factor on theresponses [35,36]. In this paper, a two-factor analysis of variancewithout replication was used to evaluate the significance of theeffects of diatomite and glass fiber on the properties of asphaltmixture. The significance level (a) employed in this investigationwas 0.05. The F-tests were performed according to a confidencelevel 95%. The analysis results were listed in Table 10.

As shown in Table 10, P-values of DS and permanent deformationare all less than the significance level a, the values of F of DS andpermanent deformation are greater than the critical value (F-crit).It means that glass fiber and diatomite have significant effects onrutting resistance. There are two reasons for these improvements

Table 10Two- factor ANOVA without replication on the properties of asphalt mixture (a = 0.05).

Item Source of variance Fa

DS Diatomite 45.44Glass fiber 8.47

Permanent deformation Diatomite 43.54Glass fiber 8.18

RT Diatomite 0.02Glass fiber 0.75

eT Diatomite 0.33Glass fiber 7.19

K Diatomite 11.26Glass fiber 4.91

n Diatomite 10.04Glass fiber 14.32

Sm (5 �C) Diatomite 9.19Glass fiber 1.70

Sm (15 �C) Diatomite 8.41Glass fiber 5.40

Sm (25 �C) Diatomite 10.03Glass fiber 3.30

a Note: F, the F value; P-value, the probability of F value; F-crit, the critical value. a, th

probably. On the one hand, diatomite particles prevent the flowingof asphalt molecules, so the anti-shearing capacity of asphalt masticis increased. On the other hand, a lot of stress transfer networks ofglass fiber are formed in the local positions of asphalt mixture.Thereby, the shearing strain of asphalt mastic is reduced, and thepermanent deformation was reduced finally.

In addition, P-values of RT are both greater than a. It shows thatdiatomite and glass fiber have no significant effects on the indirecttensile strength of asphalt concrete at low temperature. Accordingto the results of eT, it can be seen that diatomite has no significanteffect on the indirect tensile failure strain (eT). But glass fiber affectthe indirect tensile failure strain (eT) significantly. It means that thelow temperature deformation ability of asphalt mixture areimproved by glass fiber. Deformation ability of DGFMAM is betterthan that of the diatomite modified mixture.

According to the results of K and n, it can be found that K and nare both improved by diatomite significantly. And the effect ofglass fiber on fatigue property is on the parameter n only, whichis related to the stress levels. It means that the fatigue propertyof asphalt mixture is improved by diatomite and glass fiber.

P-values of diatomite on stiffness modulus are all less than a.Therefore, diatomite has a significant influence on the stiffnessmodulus of mixture. And P-values of glass fiber on stiffness modu-lus are all greater than a. It suggests that glass fiber has no signif-icant effect on stiffness modulus of asphalt mixture when itsamount is less than 0.3%.

4.6. Regression analysis on properties of DGFMAM

The change laws of properties of DGFMAM are important for themixture design. So the statistical regression analysis was used toanalyze the property changing laws of DGFMAM. In this study, amultivariable linear regression model was selected for the analysis.The aim is to model the variation of a quantitative response vari-able y in terms of the variation of two explanatory variables. Theexpression of this model is shown in Eq. (8).

Yi ¼ b0 þ b1X1i þ b2X2i þ li ð8Þ

where b0, b1, b2 are the partial regression coefficients, li is stochas-tic error. (Yi, X1i, X2i) is the observation of sample, Yi is the responsevariable, X1i and X2i are two factors. In this paper, Yi represents thetest results of property, X1i is the content of glass fiber, X2i is thecontent of diatomite.

P-value F-crit Significant

0.002 6.499 Yes0.037 6.499 Yes0.002 6.499 Yes0.039 6.499 Yes

0.982 6.499 No0.528 6.499 No0.737 6.499 No0.047 6.499 Yes

0.023 6.499 Yes0.084 6.499 No0.028 6.499 Yes0.015 6.499 Yes

0.032 6.499 Yes0.292 6.499 No0.037 6.499 Yes0.073 6.499 No0.028 6.499 Yes0.142 6.499 No

e significance level.

Table 11Results of regression analysis on properties.

Item Coefficient R2 F P-value

b0 b1 b2

DS 647.30 587.70 1954.40 0.93 44.77 0.0001Permanent deformation 7.17 �2.68 �7.61 0.95 64.70 0.0000RT 3.38 0.76 �0.34 0.13 0.50 0.6262eT 2898.59 3093.64 �573.03 0.72 9.20 0.0110K 297.82 163.58 317.24 0.82 16.15 0.0024n 3.18 �0.13 1.63 0.55 4.29 0.0608Sm (5 �C) 12308.09 �86.36 4428.64 0.76 10.94 0.0070Sm (15 �C) 6107.50 �974.80 3931.80 0.75 10.55 0.0077Sm (25 �C) 2492.59 �288.03 2745.30 0.75 10.34 0.0081

58 Q. Guo et al. / Materials and Design 66 (2015) 51–59

The partial regression coefficients (b0, b1 and b2) can beobtained by the least square method [37]. The F-tests were per-formed according to a confidence level 95% in order to verifiedthe applicability of this regression model. The results of regressionanalysis are presented in Table 11.

As shown in Table 11, the correlation coefficients (R2) of regres-sion analysis on RT and n are small, and the corresponding P-valuesof them are higher than the significance level (a = 0.05). Therefore,there are no linear relationships between these properties and themodifiers. The correlation coefficients (R2) of other regressions areall greater than 0.7, the results of F-test for other properties showthat there are good linear relationships between these propertiesand the modifiers. Besides, b1 and b2 of DS are positive constants,b1 and b2 of permanent deformation are negative constants. Thismeans that diatomite and glass fiber have positive effects on rut-ting resistance of mixture. And the influence of diatomite on rut-ting resistance is more effective than that of glass fiber becauseb2 of diatomite is greater than b1 of glass fiber. Diatomite has anadverse influence on the tensile failure strain (eT) as a result of anegative partial regression coefficient. b1 of eT is positive, so glassfiber increases the tensile failure strain. The adverse effect of diat-omite on eT is compensated by glass fiber. These results suggestthat the low temperature deformation ability of asphalt concreteis improved by glass fiber. For the regression results of fatigueproperty, b2 of diatomite is greater than b1 of glass fiber. It suggeststhat the influence of diatomite on fatigue property is more effec-tive than that of glass fiber. The changing law of the parameter Kwith the modifiers is linear. According to the regression resultsof stiffness modulus, it shows that the stiffness modulus isincreased by diatomite, and glass fiber has a minus influence onstiffness modulus of asphalt mixture. The stiffness modulus isreduced by glass fiber. It is similar to the results of asphalt mixturemodified by other fibers [28]. In addition, the optimum amounts ofdiatomite and glass fiber can be determined based on the regres-sion results which are obtained in laboratory and the requirementsof pavement.

5. Conclusions

In this paper, the performances of diatomite and glass fibercompound modified asphalt mixture were investigated. The fol-lowing conclusions can be drawn based on the above study.

� Diatomite and glass fiber improve rutting resistance of asphaltmixture significantly, and the relationship between ruttingresistance property and modifiers is linear while the amountsof modifier are little. The influence of diatomite on rutting resis-tance property is more significant than glass fiber.� Diatomite and glass fiber have no significant effects on tensile

strength of asphalt mixture at low temperature when their con-tents are little. Diatomite causes the decrease of tensile failure

strain, but glass fiber can increase tensile failure strain signifi-cantly. Disadvantage of diatomite on low temperature propertyof asphalt mixture is overcame by glass fiber.� Diatomite and glass fiber improve the fatigue property of

asphalt mixture, DGFMAM has a better fatigue performancethan the control mixture. The pavement which is constructedwith DGFMAM will have a longer service life than that withthe control mixture.� The stiffness modulus of DGFMAM is greater than that of the

control mixture. And it is less than the modulus of the controlmixture when the temperature below �10 �C. Diatomite is asignificant factor for the change of stiffness modulus. Glass fiberdecreases the stiffness modulus.

In summary, the pavement constructed with DGFMAM willhave a better travelling performance than the pavement con-structed with the control mixture. A trial section of DGFMAMshould be constructed in the future in order to determine its appli-cability for different regions.

Acknowledgement

The authors express their appreciation for the financial supportof National Natural Science Foundation of China under Grant Nos.51378236, 51278222, 51408258; China Postdoctoral Science Foun-dation funded project (2014M560237) and Science & TechnologyDevelopment Program of Jilin Province (20140203002SF).

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