Construction and Building Materials 30 (2012) 495–499

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Construction and Building Materials

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Effects of diatomite on the properties of asphalt binder

Peiliang Cong ⇑, Shuanfa Chen, Huaxin ChenSchool of Materials Science and Engineering, Engineering Research Center of Transportation Materials of Ministry of Education, Chang’an University, Xi’an 710064, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 September 2011Received in revised form 1 November 2011Accepted 24 November 2011Available online 2 January 2012

Keywords:AsphaltDiatomiteRheological propertiesViscosity

0950-0618/$ - see front matter Crown Copyright � 2doi:10.1016/j.conbuildmat.2011.11.011

⇑ Corresponding author. Tel./fax: +86 29 82337349E-mail address: congpl@chd.edu.cn (P. Cong).

Modified asphalt binders were prepared by melt blending with different contents of diatomite. FourierTransform Infrared (FTIR) Spectroscopy was used to test the effects of diatomite on chemical propertiesof asphalt binder. The effects of diatomite on the physical properties and dynamic rheological behaviorsof the modified asphalt were investigated. The high temperature storage stability and aging properties ofthe modified asphalt binders were also studied. Experimental results indicated that there is no chemicalreaction occurred between asphalt binder and diatomite. The storage stability tests indicated that theasphalt modified with diatomite is very stable when diatomite content is less than 20%. With theenhancement of the content of diatomite to asphalt, both viscosity and complex modulus of modifiedasphalt binders increased rapidly at high temperatures. Furthermore, the diatomite modified asphaltbinders exhibited lower phase angle when temperature below to 5 �C. As a consequence, the viscoelasticproperties of the diatomite modified asphalt binders was modified, which improve its resistance to defor-mation at high temperatures and the resistance to thermal cracking at low temperature.

Crown Copyright � 2011 Published by Elsevier Ltd. All rights reserved.

1. Introduction

Asphalt is an organic mixture with various chemical composi-tions, which has been widely used as an adhesive material in manyfields, especially in pavement construction due to its good visco-elastic properties [1–3]. A little amount of asphalt (4–8% byweight) is usually suitable for acceptable pavement performance.Unfortunately, asphalt binder is a form of liquid at high tempera-ture and becomes brittle at low temperatures, which can causehigh temperature rutting, low temperature cracking, fatigue, etc.[4,5]. Furthermore, increasing traffic volume, heavy traffic loadand severe weather accelerate the asphalt pavement deterioration.So, asphalt binder should be stiffness enough to resist rutting, flex-ible enough at low temperature to avoid thermal cracking and vis-coelastic enough to show good fatigue and stripping resistances[6–9]. Base asphalt is not capable of doing so. The modificationof asphalt is an attempt to improve the performance of asphalt bin-der. Various elastomer and plastomer modifiers have been used toimprove rut resistance, fatigue resistance, cracking resistance andstripping resistance [10–14]. However, there are a relatively fewpolymers which are available as asphalt modifiers. When the poly-mer was used as asphalt modifiers, the polymers should be com-patible with asphalt in blended process with conventional mixingequipments and can maintain their main properties during pro-longed storage at high temperature [15]. Therefore, further efforts

011 Published by Elsevier Ltd. All r

.

should be made for exploring new modifiers of asphalt to obtainedbetter properties.

Diatomite is a type of mineral with low cost and abundance,which used in industry as filler, filtering agent, absorbent, clarifier,and insulator. The diatomite is a sedimentary rock, white to lightyellow in color, composed of the fossilized skeletons of diatoms,one celled algae-like plants which accumulates in marine or lacus-trine environments [16]. The skeletons are composed of amor-phous silica (silicon dioxide, SiO2), a very durable substance.Besides its amorphous silica content diatomite rocks commonlycontain carbonate and clay minerals, quartz and feldspars. Diatomsskeletons are honeycomb silica structures that give diatomite use-ful characteristics such as high absorptive capacity and surfacearea, chemical stability, and low bulk density [17]. It is also calleddiatomaceous earth or organogenetic sedimentary rock.

Recently, most mineral materials have been widely used for themodification of polymers. The layered silicates have been success-fully used to improve the thermal, mechanical and barrier proper-ties of polymers [18–20]. SBS/KC compounds have beensuccessfully used to improve the high temperature storage stabil-ity of SBS modified asphalt [21,22]. Diatomite was often used asthe filler of polymer due to its lightweight, high void content,low density and strong sorption performance. However, there havebeen a few reports about the preparation of the diatomite modifiedasphalt.

In this paper, modified asphalts were prepared by melt blendingwith diatomite powder. The chemical property of asphalt binder,diatomite and diatomite modified asphalt binder was analyzedseparately by Fourier Transform Infrared (FTIR) Spectroscopy. The

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496 P. Cong et al. / Construction and Building Materials 30 (2012) 495–499

effects of diatomite on the physical properties and dynamic rheo-logical behaviors of the modified asphalt were investigated. Thehigh temperature storage stability and aging properties of themodified asphalts were also studied.

2. Experimental

2.1. Raw materials

The asphalt type of AH-70 was obtained from Panjin Petrochemical Industry,Liaoning Province of China, with penetration of 73 (0.1 mm at 25 �C, 100 g and5 s), softening point of 45.6 �C, ductility of at least 150 cm (at 15 �C) and viscosityof 0.44 Pa s (at 135 �C).

Diatomite was obtained from Shenzhen Jitong diatomaceous Earth Co. Ltd., withbulk density 0.29 g cm�3, maximum particle size 19 lm, PH 7.2.

2.2. Methods

The diatomite modified asphalt binders were prepared using FLUKO FM300mixer. Asphalt binder was heated until it has become sufficiently fluid at around150 �C in the mixer. After that, diatomite was added into asphalts and, the mixtureswere blended at 3000 rpm rotation speed about 30 min to ensure the diatomite uni-formly dispersing in the asphalt binders.

Fourier Transform Infrared (FTIR) Spectroscopy (NEXUS, Thermo Nicolet, USA)was used to obtain the IR spectra of asphalt binder. Sample was prepared by castingfilm onto a potassium bromide (KBr) thin plate, and the spectra were obtained by4 cm�1 resolution.

Brookfield viscometer (Model DV-II+, Brookfield Engineering Inc., USA) was em-ployed to measure the rolling viscosity of modified asphalt binders in according toASTM D4402. Approximately 30 g of asphalt are heated in an oven so that it is suf-ficiently fluid to pour into the sample chamber. The amounts of asphalt used varywith the different sizes of the spindles. The sample chamber containing the asphaltsample is then placed in the thermo container. After the desired temperature is sta-bilized for about 30 min, the spindle is lowered into the chamber to test theviscosity.

The storage stability of diatomite modified asphalt binders was tested as fol-lowing procedure: before the sample was poured into a glass tube, the inner wallof the glass tube was coated a thin layer of isolated agent made by glycerin andFrench chalk powders at the weight ratio 2:1. The tube was sealed by soft tampion,and stored vertically and immovably in an oven at 163 ± 5 �C for 48 h. Then theglass tube containing the diatomite modified asphalt was took out of the ovenand put into an icebox for 4 h ± 5 min to solidify the sample. All glass tubes werebroke into pieces with a hammer carefully to remain unbroken cylindrical asphaltsamples. The cylindrical asphalt sample was cut horizontally into three equal sec-tions. The sections from the top and bottom were placed in separate dishes in anoven at 163 �C until asphalt binder has well fluid to pour into softening point rings.The difference in softening points (DS) between top and bottom sections as well asthe change compared with the original asphalt was used to evaluate the storage sta-bility, that is, the segregation of the diatomite in the asphalt.

Dynamic shear properties were measured with Physical MCR 101 dynamicshear rheometer (DSR, Anton Paar Inc., Austria) in a parallel plate with 1 mm gapand 25 mm diameter at temperature range 30–90 �C, and a 8 mm diameter parallelplate with 2 mm gap at temperature range �20 to 40 �C. A DSR temperature sweeptest was performed under the strain controlled mode at a constant frequency of10 rad s�1. All tests were performed within the linear viscoelastic range. Complexmodulus and phase angle at different temperatures were recorded automaticallyduring the test.

A bending beams rheometer (BBR), Cannon Instrument Company. was used toconduct low temperature creep tests. The asphalt binder beams (125 � 12.5 �6.25 mm) were prepared in an aluminum mold. In preparation, the asphalt binderwas heated to a fluid condition, poured into the mold and allowed to cool downat room temperature for approximately 90 min. The sample was then cooled toapproximately �5 �C for 1 min and demolded. Plastic strips were used to releasethe beam from the mold. Sets of the sample beams were submerged in a methanolbath with a constant temperature of �10 or �18 �C. After storage for differentlengths of time 60 min, the rectangular beam was placed on two stainless steel sup-ports (102 mm apart) and loaded with 100 g. The deflection of the center point wasmeasured continuously with a linear variable differential transformer (LVDT). Thecreep stiffness (S) and creep rate (m) of the binders were determined at loadingtimes 60 s.

The thin film over test (TFOT) was employed to simulate the short-term oxida-tion that occurs during the hot mix process in accordance to ASTM D1754. The per-cent retained penetration, aging index and increment of softening point all wereused to evaluate relative resistance of diatomite modified to oxidative aging overan extended period of in-service pavement use. The related equations were ex-pressed as follows:

Percent Retained Penetration : PRP ¼ P2

P1� 100% ð1Þ

Increment of softening point : DT ¼ T2 � T1 ð2Þ

Aging Index : AI ¼ lg½lgðV2 � 103Þ� � lg½lgðV1 � 103Þ� ð3Þ

where P (0.01 mm), T (�C) and V (Pa s) denote penetration, softening point and vis-cosity, respectively. The subscripts 1 and 2 present original and aged diatomite mod-ified asphalt binders.

3. Results and discussion

3.1. Diatomite properties

The key factors for diatomite quality exists by many oxides areshowed in Table 1 by ICP (Inductively coupled plasma, Atom Scan2000) analysis, such as SiO2, Al2O3, Fe2O3, MgO and CaO. But thekey factor to diatomite quality is the content of amorphous silica.In diatomite making procedure, using different resources leads tothe change of content of SiO2. The content of SiO2 is the mostimportant component for the utilization of diatomite. The honey-comb silica structure can give diatomite useful characteristics suchas high absorptive capacity, chemical stability and low bulkdensity.

The Brunauer–Emmett–Teller (BET) test was conducted todetermine textural parameters of diatomite, such as BET surfacearea, pore volume, pore area, and average pore diameter using sur-face area apparatus (Model F-Sorb 2400, Beijing App-one Technol-ogy Co., Ltd.). Results are tabulated in Table 2. As shown in Table 2,the BET surface area of diatomite is 22.13 m2 g�1. The surface areaof the macropore, mesopore and micropore regions of diatomitewas 0.76, 20.04 and 1.33 m2 g�1, respectively. The total surfacearea increased, primarily due to increases in the mesopore andmicropore regions. The increase of the mesopore area is due tothe partial blockage of macropores (exceed 50 nm) and larger mes-opores (exceed 7 nm) by colloidal-size (2–5 nm) ferrihydrite parti-cles. Similarly, the increase of micropore area can be attributed tothe pore blockage by colloidal-size ferrihydrite as well as addi-tional micropores provided by microporous ferrihydrite.

3.2. FT-IR test

Fig. 1 gives Fourier Transform Infrared (FTIR) Spectroscopyanalysis curves of original asphalt binder, diatomite and diatomitemodified asphalt binder with 15% diatomite at 25 �C. The resultsindicated that the strong peaks of 2924 cm�1 and 2853 cm�1 arethe stretching vibration absorption bands of the alkyl (CAH) of as-phalt binder. The CAH asymmetric deforming in CH2 and CH3, andCAH symmetric deforming in CH3 vibrations are observed at1461 cm�1 and 1376 cm�1. The characteristic absorption peakaround 1545–1640 cm�1 is attributed to C@C stretching vibrationsin aromatics. The positions of absorption bands in the curves ofsamples containing diatomite are nearly the same when diatomitewas added into asphalt. The only difference is the stretching vibra-tion absorption band of SiAO appears at 1032 cm�1, which is closeto the SiAO stretching vibration absorption band position of diato-mite according to diatomite’s infrared absorption spectrum asFig. 1 showed. Besides this, no other new peak is appeared in theinfrared absorption spectrum of modified asphalt binder contain-ing diatomite. Therefore, it can be confirmed from the analysis ofthe infrared absorption spectrum that no chemical reaction is oc-curred between asphalt and diatomite, the diatomite merely blendphysically with asphalt binders.

3.3. Rotational viscosity

The effect of viscosity on asphalt binder’s workability is veryimportant in selecting proper mixing and compacting tempera-tures. The effects of the concentration of diatomite on rotational

Table 1Chemical composition of the diatomite.

Compositions SiO2 Al2O3 Fe2O3 CaO TiO2 MgO K2O Na2O Ignition loss

Content (%) 78.89 8.63 2.47 0.96 0.74 0.62 1.27 0.81 4.26

Table 2Summary of BET data for diatomite.

Textural parameters Results

BET surface area (m2 g�1) 22.13Macropore region (m2 g�1) 0.76Mesopore region (m2 g�1) 20.04Micropore region (m2 g�1) 1.33Total pore volume (cm3 g�1) 0.058Macropore volume (cm3 g�1) 0.02Mesopore volume (cm3 g�1) 0.038Micropore volume (cm3 g�1) 0.000449Average pore diameter (nm) 9.35

Fig. 1. FTIR spectra of: (1) original asphalt binder, (2) diatomite modified asphaltbinder and (3) diatomite.

P. Cong et al. / Construction and Building Materials 30 (2012) 495–499 497

viscosity at 135 �C are showed in Fig. 2. The viscosity increasesquickly when the diatomite content is lower than 20%. But the vis-cosity increasing trend decrease when the diatomite content isabove 20%. The viscosity of original asphalt binder is 0.44 Pa s, itis 1.24 Pa s for modified asphalt binder with 15% diatomite. Itmaybe attributing to the Einstein particle affects which is causingthe increase in viscosity. From the consideration of practical appli-cation, the optimum viscosity range for asphalt is not too high forcompacting asphalt mixture. If viscosity of modified asphalt binderis too high, the mixture becomes too hard to compact the pave-ment and it is difficult to form an eligible pavement surface. There-fore, the diatomite contents should strictly control to meet the

Fig. 2. Viscosities of diatomite modified asphalts versus diatomite contents at135 �C.

requirement of viscosity. The rotational viscosity results indicatedthat the diatomite can improve the high temperature performance.But the higher the percentage of diatomite would increase the con-structing difficulty.

3.4. Storage stability

The storage stability problem of modified asphalt binder is thekey technical problem in the use of many asphalt/modifier blendsas an actual alternative to original asphalt. The diatomite modifiedasphalt binders are considered multiphase systems in which thediatomite are dispersed into the asphalt binder phase, the differ-ence in the solubility parameter and density between diatomiteand asphalt, phase separation would take place during storage athigher temperatures due to Brownian motion followed by gravita-tion. Granules of diatomite dispersed in asphalt are usually accu-mulated and subside to the bottom of the asphalt, which maycause changes in properties of asphalt binders between the topand the bottom sections in the tube. The high temperature storagestability of the diatomite modified asphalts is measured and the re-sults are showed in Fig. 3. The differences between softening pointsof the top and the bottom for diatomite modified asphalt bindersare 0.3 �C when the diatomite content are 5%, and it is 0.5, 0.9and 1.4 �C for modified asphalt binder with 10%, 15% and 20%,respectively. This indicated that storage stability of asphalt bindermodified with diatomite is very stable when the diatomite contentis less than 20%. However, the differences of softening point in thetop and the bottom increase with the increasing of diatomite con-tent. This is maybe attributed to the granules of diatomite areaccumulated and subsided to the bottom of the asphalt/diatomiteblending at a high temperature since the gravity effect. Accordingto the rule of the difference of softening point measurement is notmore than 2.2 �C, the diatomite modified asphalt binder can beused in pavement after storing at high temperature for long time,which is very convenient for user.

3.5. Dynamic rheological properties

The most important effects of modifier on asphalt binder are thechanging of viscoelasticity because there is strong correlation be-tween rutting resistance and elastic modulus at high temperature.Dynamic shear test can be used to determine the complex modulus(G⁄) and the phase angle (d). The complex modulus can be related

Fig. 3. Effect of diatomite content on the storage stability of the modified asphalt.

Fig. 4. Relation of temperature and complex modulus and phase angle at 10 rad/s.Fig. 6. Relation of temperature and G⁄/sind at 10 rad/s.

Table 3Effect of diatomite on high performance gradeof asphalt binder.

Diatomite content(%)

TSHRP (G⁄/sind = 1 kPa)

0 70.85 72.210 75.915 78.3

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to the material strength and the phase angle provides informationabout the ratio between elastic and viscous response during theshearing process. The curves of G⁄ and d versus temperature forthe diatomite modified asphalt binders in a range of temperature�20 to 40 �C is showed in Fig. 4. It can be seen that diatomite re-sults in reduction of complex modulus and phase angle when tem-perature lower than 5 �C. But diatomite increases the complexmodulus and decrease phase angle at high temperature. It is indi-cated that the diatomite modified asphalt binders have better flex-ibility than original asphalt binder at low temperature. The phaseangle is more sensitive to the chemical and physical structure ofmodified asphalt binder. Phase angle is defined as the phase differ-ence between stress and strain in an oscillatory test and it is zeroand 90� for elastic and viscous materials. The phase angle of diat-omite modified asphalt binder is less than that of original asphaltbinder at the same temperature. The decreasing extent of phaseangle becomes greater with the content of diatomite increases attest temperature. This trend revealed that the elastic response ofasphalt binder was improved when diatomite was added into as-phalt binders. Fig. 5 showed that the curves of G⁄ and d versus tem-perature for the diatomite modified asphalt binder in a range oftemperature 30–90 �C. The drastic increase in the complex modu-lus exhibited a more viscoelastic behavior of the modified asphaltsthan that of original asphalt binder at high temperature. Moreover,it can be seen that with increasing diatomite contents, the complexmodulus of the modified asphalt binders increases significantly.Compared with original asphalt binder, the phase angles of diato-mite modified asphalt decreased at the same temperature. Thistrend indicates the increase in elastic properties of the diatomitemodified asphalt binder at high temperature.

The Strategic Highway Research Program (SHRP) teststake advantage of the rheological measurements to analyze the

Fig. 5. Relation of temperature and complex modulus and phase angle at 10 rad/s.

properties of asphalt binders used in road pavements, whichadopted the temperature of the asphalts when G⁄/sind is equal to1 kPa as a criterion for the asphalt binder at high temperature.The rheological parameter G⁄/sind is defined as rutting parameterto demonstrate resistance of asphalt to the permanent deformationunder repeated loads. Plots of rutting parameter versus tempera-ture are displayed in Fig. 6 for original and diatomite modified as-phalt binder. The rutting parameter of modified asphalt binder isincreased with diatomic contents increasing. As shown in Table3, when G⁄/sind was equal to 1 kPa the temperature of asphaltbinders was 70.8 �C for original asphalt binder, and it is 72.2 �C,75.9 and 78.3 for diatomite modified asphalt binders with the con-tents of 5 wt%, 10 wt% and 15 wt%, respectively. It is indicated thatthe diatomite is more helpful for the improvement of ruttingresistance.

3.6. Low temperature creep properties

The bending beam rheometer (BBR) is used to accurately evalu-ate asphalt binder properties at low temperatures at which asphaltbinders were too stiff to reliably measure rheological propertiesusing the parallel plate geometry of the DSR equipment [23,24].The BBR test measured creep stiffness (S) and m-value (m) of as-phalt binders. Stiffness indicated the susceptibility to low temper-ature cracking as designated by SHRP. The Superpave technologyspecified that the creep stiffness must not exceed 300 MPa to pre-vent low temperature cracking. The low-temperature cracking ofpavement would be occurred only after a period of using, thus thisspecification addresses these properties using aged asphalt binder.The rate of change of asphalt binder stiffness with loading timewas represented by the m-value. A high m-value was desired. Aminimum m-value of 0.3 after 60 s was required by the SuperpavePG binder specification.

The effect of diatomite on stiffness and m-value of asphalt bin-der at �10 and �18 �C is showed in Table 4. The results revealedthat the stiffness of all asphalt binder satisfies the SHRP Superpavespecifications at �10 �C, and all asphalt binders show higher thanthe required minimum m-value. The high stiffness value was

Table 4Effect of diatomite on low temperature performance asphalt binder.

Diatomite content (%) �10 �C �18 �C

S (MPa) m S (MPa) m

0 89.5 0.438 312.3 0.3025 94.9 0.447 337.3 0.29310 118.5 0.456 378.6 0.29815 129.3 0.451 461.2 0.284

Table 5Effect of short-term aging on related properties of diatomite modified asphalt binders.

Diatomite content (%) Mass loss (%) PRP (%) DT (�C) AI

0 0.138 78.3 4.7 0.01855 0.117 81.1 4.6 0.0179

10 0.108 82.9 4.4 0.011615 0.096 86.7 4.1 0.0097

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obtained when diatomite was added into asphalt binder. Thoseindicate that the asphalt concrete using diatomite modified asphaltbinders maybe susceptible to low temperature cracking, especiallyin cold areas and/or weather. Nonetheless, the stiffness and m-va-lue of the diatomite modified asphalt binders meets the SHRPSuperpave specifications at �10 �C. And the m-value of asphaltbinders increases when diatomite was added into. But original as-phalt binder does not satisfy the SHRP Superpave specifications at�18 �C. The stiffness value increase and m-value decrease whendiatomite is added into asphalt when temperature is �18 �C.Therefore, the diatomite does not improve availably the low tem-perature properties of asphalt.

3.7. Aging properties

Table 5 lists the variation in related properties of modified as-phalt binders with different content of diatomite after short-termaging. The results show that the mass loss, softening point incre-ment (DT) and aging index (AI) of modified asphalt binder de-creases, and the percent retained penetration (PRP) increaseswith diatomite content increasing after aging. Generally, the con-tent of fractions with large molecules in asphalt increases andthe content of the small molecules decreased during the aging. Itleads to increase of the softening point and viscosity. But, diato-mite restricts the oxidation of asphalt, which decreased the hard-ening process of the asphalt. Thus, the results indicated that thediatomite cannot affect remarkably the thermo-oxidative agingresistance of asphalt.

4. Conclusions

Modified asphalt binders were prepared by melt blending withthe different contents of diatomite. The relative performance ofdiatomite and modified asphalt binder were investigation. Thediatomite analysis results showed that the SiO2 is the key factorto diatomite quality and the total surface area of diatomite in-creased due to increase in the mesopore and micropore regions.There is no chemical reaction occurred between asphalt and diato-mite, the adding of diatomite merely lead to the physical blendingof asphalt and diatomite powers. The storage stability of the mod-ified asphalts decreased with the increasing of diatomite content.However, the difference of softening point in the top and the bot-tom of the diatomite modified asphalt was not more than 1.5 �Cwhen the content of diatomite is lower than 20%. In addition, thediatomite can increases the viscosity and cannot affect the

thermo-oxidative aging resistance of asphalt binder remarkably.The DSR test results indicated that modified asphalt binders exhib-ited higher complex modulus and lower phase angle when temper-ature more than 5 �C. But the complex modulus of diatomitemodified asphalt binder was lower than that of original asphaltwhen temperature lowers than 5 �C. Whereas the BBR test resultsindicated that the stiffness increase when diatomite was addedinto asphalt and the m-value show different changes at �10 �Cand �18 �C.

Acknowledgment

Supported by the Special Fund for Basic Scientific Research ofCentral Colleges, Chang’an University (Number: CHD 2012JC058).

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