偶联剂改性沥青的性能研究

偶联剂改性沥青的性能研究

王浩

摘要:文章使用蒸馏水作为试验用水，研究经过偶联剂DB－570处理的沥青的浸润能力，通过使用ADSA软件和LB－ADSA方法测量了不同含量硅烷偶联剂的沥青的接触角，并且计算了改性沥青的表面能，文章通过扫描式电子显微镜分析了沥青膜。结果表明，随着硅烷偶联剂含量的增加，沥青表面的蒸馏水的静态接触也随之增大，沥青与集料之间黏附性也随之提高，沥青能够更好地包裹在集料表面。

The Effect and Characterization of Modified Asphalt by Coupling Agent

Introduction

Asphalt pavement as one kind of senior pavement is widely used，but the early damage phenomenon of asphalt pavement is very serious．Water damage is one of the major phenomenonsin early damage to the asphalt pavement，appearing in the asphalt pavement widespread．Studies have shown that the adhesion between asphalt and aggregate in asphalt concrete pavement largely affect the ability to resist water da mage．How to enhance the adhesion between asphalt and aggregate is the key to improve the water damage resist ability of asphalt pavement．Coupling agent known as"molecular bridge"，adding coupling agent in organicmaterial or treating inorganic fillers with coupling agent，can make two relative inert materials cross－linking by means of winding up covalent bond or molecule chains，thereby improve the performance of composites．The study adopts the method by adding modifier to asphalt directly，chooses silane coupling agent DB－570as interface modifier，measures static contact angle on asphalt surface with difference adding amount by sessile drop method，and alculate the surface tension of modified asphalt，and then evaluates the modification effects by SEM test，analyses the microcosmic morphology of whetstone interface by using SEM．

Background

Adhesion Theory．Water damage mechanism，analyzing mainly based on adhesion theory．Adhesion refers to physical and chemical effect when bonding an object with another object．Factors influenced adhesion between asphalt and aggregate include the interfacial tension on thesurface of the asphalt and aggregate，the chemical composition of asphalt and aggregate，theviscosity of asphalt and the surface structure of aggregates，the porosity of aggregate，cleanliness ofaggregate，etc．The traditional theory of adhesion includes mechanics theory，chemical reaction theory，the theory of surface tension，surface structure theory，molecular orientation theory，electrostatic theory，etc．These types of theories have their own strong points，and explain the studyof asphalt aggregate system adhesion mechanism from different perspectives．Some literatureconsiders that only wetting can not establish a firm adhesion，wetting is an important qualification for good adhesion，but not the only qualification．However，the current theory develops rapidly，such as the latest research of Texas A＆M Dr．Lytton et al from the United States shows that the surface free energy can be better characterized the adhesion properties of the mixture．And it is feasible to forecast the spallation of asphalt according to the theory．This research analyzes thesurface tension of modified asphalt based on surface energy theory．

Surface Tension．Surface energy theory considers that the adhesion betweenasphalt and aggregate is mainly derived from energetic effect principle，which is formed by wetting asphalt and aggregate．The wetting ability of the asphalt is the close contact capacity of the surface between asphalt and aggregate．Asphalt wetting ability，like other liquids，relate to cohesive force of its own．

When asphalt spreading and wetting the surface of aggregate，it will produce energy exchange．The energy exchange is a surface phenomenon;it depends on close contact and mutual attraction of asphalt and aggregate．As the great adhesion between water and aggregate，the water can be immersed in asphalt－aggregate interface and formed of water－asphalt－aggregate surface contact．The internal tension between asphalt and aggregate relates to the type of aggregates and asphalt．

Currently，surface tension component method is usually used to calculate the surface tension of all kinds of polymers，it is a method to decompose the surface tension into various components by interaction force between molecules，and then to sum up components by geometric mean method orharmonic mean method．The surface tension component method includes Fowkes method，geometric mean method，harmonic mean method，LW－AB method，Young equation method，etc．Based on the study of Young，Zhu Dingyi derives a new method to calculate solid surface tensionγ_sgand solid－liquid surface tensionγ_slon infinite solid phase plane，through the establishment of a new wetting system of limited liquid－solid interface．The expressions of surface tension on infinite solid phase plane and liquid－solid interfacial tension are as follows．

In the formula，γ_lgis surface tension of distilled water，its numerical value is72．88mJ．m－2．θ₁is contact angle．Above formula only provides theoretical so-lution，does not add any assumptions，it takes solid surface tension and liquid－solid interfacial tension as the function of liquid surface tension and contact angle．Liquid surface tension and contact angle can be gained through experiment，so only getting contact angle experimental data;the formula can calculate liquid－solid interfacial tension and solid surface tension．This study measures the static contact angle of the

modified asphalt surface based on this research by sessile drop method to calculate the surface tension of modified asphalt．

Sessile Drop Method．Sessile drop method is a method to measure contact angle by optical method;the method can be used to measure local contact angle of solid surface，and then get their wettability．Sessile drop test can directly measure the angle of the liquid/solid tangents on liquid/solid/gas three－phase contact point．This method has two basic assumptions are as follows．

(1)The liquid droplet is vertical symmetrical along the axle wire，so that no matter from which perspective the results are the same．

(2)Only the interfacial tension and the gravity of liquid droplet will make a difference to the shape of liquid droplet．

Experimental Results and Analysis

Test Materials．The asphalt used in the tests are 90#heavy traffic asphalt produced by the Panjin Northern Asphalt Co．，Ltd．The key indication of the asphalt are as follows:25℃Penetration 65mm，5℃ductility 39cm，softening point 63．9℃Coupling agent used in the test is DB－570 which Chemical name forγ(methacryloyloxy)propyl trimethoxysilane formula:CH₂=C(CH₃)COOCH₂CH₂CH₂

Si(OCH₃)_3．

Aggregate:the aggregates used in test are from the first quarry of Dun Hua

Preparation of Modified Asphalt．The preparation method of modified asphalt sample:heat the base asphalt on the oven to 160℃，slowly pour the cou-pling agent that has weighed until the asphalt completely melted，stir them 5 min in speed of 450 rpm，and put asphalt into the refrigerator immediately after stirring to make the asphalt cooled rapidly，that is the method of preparation for required asphalt．The percentage of coupling agent occupies the quality of modified asphalt are 0．1%，0．2%，0．3%，0．4%，0．5%，0．6%，0．7%，0．8%，0．9%，1．0%．

Measurement for Static Contact Angle of Modified Asphalt by Sessile Drop Method．First，use glass plate with side length of 7．5 cm as a substrate，place glass plate in oven 160℃to preheat，make the modified asphalt completely melted in the oven 160℃．，and then drop a small amount of asphalt on glass plate，use scraper(doctor－blade，Paul N．Gardner Company，USA)to smear asphalt on the surface of glass plate by means of“draw－down”to make asphalt become a smooth surface and completely cooled at room temperature．And then take a view of the sample by using

wetting angle measuring apparatus JJC－I produced by Changchun Optical Instrument Factory to get wetting angle of the sample’s surface．The surface tension of pure liquid water is stronger than most other high polymers and more stable，so the study chooses distilled water as test liquid droplet．In order to try to avoid hysteresis effect of contact angle causing by vibration of liquid droplet，the experiment uses(1－2)mm close－filling method．The liquid droplet size is about 3μL，and the diameter should be controlled in the range of 2 mm，and the measurement time is controlled by 10s or less to prevent changing of contact angle by evaporation of liquid during the test procedure．The test repeated 5 times with samples of same adding amount and takes the average value of the 5 set contact angle data．Test temperature is 25℃，relative humidity is 60%－70%．The static contact angles of distilled water on the surface of modified asphalt are as below．

Fig．1 The image of contact angle between water and asphalt

Average Value of Contact Angle

Fig．2 The average value of contact angle

It can be seen from figure 2，the contact angle of distilled water on the asphalt surface increasedafter adding modifier，and with the adding amount of modifier increase the contact angle showed anincreasing trend．When the adding amount of modifier between 0．1%－0．3%，the contact angle did not change significantly;when the adding amount of modifier up to 0．4%，the contact angle increases more significantly;when the adding amount of modifier between 0．4%－0．8%，the contact angle increased with the increasing of modifier adding amount;when the adding amount of modifier up to 0．8%，the contact angle increases smoothly．

Calculation of Surface Tension of Modified Asphalt．Eq．1，Eq．2 andthe Young equation are essentially the same;they are all based on wetting balance foundation on non－reactive liquid－solid interface．Distilled water and asphalt does not produce chemical reaction on the interface，in line with the above conditions．So this study calculates the surface tension of modified asphalt by adding different amount modifier according to the Eq．1．

Fig．3The surface tension of asphalt

It can be seen from the figure，the surface tension of asphalt reduces after adding modifier．When the adding amount of the modifier between 0．3%－0．8%，the reductive trend of modified asphalt surface tension obviously;when the adding amount up to 0．8%，the reductive trend of modified asphalt surface tension gently．Thus，when the adding amount of modifier is 0．8%，the modified effect is optimum．

SEM Analysis．Since the result of static water－boiling test can not reflect the bonding condition between modified asphalt and aggregate interface clearly，the present study uses SEM to observe microcosmic morphology．The making method of the sample:wash aggregate surface by distilled water，dry it in oven at 150℃，place the dried aggregate in 150℃asphalt 10S，put it out and then cool in the air，at last，cut the aggregate particles that parceled by asphalt．The electron micrographs of the hetstone interface are shown in the following figure．

Fig．4The bonding interface between base asphalt and granite

Fig．5The bonding interface between base asphalt and basalt

The SEM images of whetstone interface of granite and basalt are shown in the above picture．It can be seen from the picture，the interface between asphalt and stone is very clear，and you can see a small amount of pores and defects，the bonding interface is non－continuous，it indicates that asphalt does not fully wet the interface of aggregate particles．Under the role of load and other external condition，these pores and defects are the potential reason for damage of asphalt pavement．

Fig．6The bonding interface between modified asphalt and granite

Fig．7The bonding interface between modified asphalt and basalt

The SEM images of whetstone interface of granite and basalt are shown in figure6 and figure 7．The interface between asphalt and stone is very fuzzy，and its three－dimensional transition zone is continuous;the interface between asphalt and aggregate is fully bonding，without flaws and air gaps．It indicates that the interface bonding of granite and basalt are good．

Conclusion

With the adding amount of the modifier increases，the contact angle of modified asphalt is gradually increased，indicating the hydrophobicity of asphalt enhanced．The surface tension of modified asphalt decreases，surface activity increased．

Observing the adhesive surface between asphalt and aggregate by SEM，theimages show that the interface of basic asphalt with granite and basic asphalt with basalt are very clear and with small amount defections on asphalt membrane．But the interface of modified asphalt with granite and modified asphalt with basalt are fuzzy and with more complete asphalt membrane．The Electron microscopy results showed that the surface activity of modified asphalt increased，the contact angle of modified asphalt increased gradually，the adhesion between modified asphalt and aggregate better than adhesion between base asphalt and aggregate．

(此文发表在2012年第105－107卷《Applied Mechanics and Materials》杂志上)