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A State-of-the-art on Microcapsules for Asphalt Self-healing
HE Liang, HUANG Huduan, Wim Van den bergh, Tóth Csaba, GAO Jie, Karol Kowalski, Jan Valentin
Materials Reports
2020,34(15 ):15092 -15101. DOI:10.11896/cldb.19060096
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Microcapsule technology has been applied in many fields in the world, including medicine, food and chemical industry, and has broad application prospects. Introducing the microcapsule into the self-healing of the asphalt material can improve the self-healing ability of the asphalt material, self-healing in the initial stage of the crack generation and prolong the service life of the pavement. Compared with traditional crack healing methods, microcapsule self-healing technology has the advantages of energy saving and emission reduction, reducing maintenance cost and preventing micro cracks from expanding to macro cracks.
On the other hand,the self-healing microcapsule technology of asphalt is still in the preliminary exploration stage. For the application of micron-sized microcapsules in the self-healing of asphalt materials, the required compressive strength of microcapsules remains unknown, and the theory of microcapsule rupture is immature, and there is no wide consensus on the design of microcapsule preparation process parameters and the eva-luation methods of the improvement of self-healing performance of asphalt mixture containing microcapsules(AMM).Therefore, in addition to studying the influence of the preparation process, the researchers have been trying to select the appropriate preparation process to influence the parameters and the structure and performance of the microcapsules, and have achieved fruitful results. With the continuous maturity of the preparation process and the continuous optimization of the influencing parameters, the microcapsules prepared by the in-situ polymerization method have a compact structure and excellent performance.
For the self-healing of AMM, there is no wide consensus on the evaluation methods of the improvement of self-healing performance of AMM.At present, the self-healing effect of AMM is mainly manifested by different indexes, including ductility, complex modulus, tensile strength, specimen load and crack opening displacement value, and fatigue life of asphalt mixture. The road performance of the AMM was also studied.Through diffe-rent evaluation indicators, it has better self-healing effect on asphalt mixture, the incorporation of microcapsules slightly decreases the moisture stability and high temperature stability of AMM, and decreases its low temperature crack resistance greatly to barely above the requirements.
A comprehensive review on self-healing microcapsules for asphalt materials is conducted in this research. Specifically, the preparation methods of self-healing microcapsules and the main factors affecting the quality of microcapsules (core-wall ratio, reaction temperature, end point pH value, emulsifying speed and acidizing time) are compared and analyzed. In addition, the structural characterization methods of microcapsules are presented, the evaluation method and improved self-healing performance of AMM are introduced, and the mechanical performance of AMM are elaborated, the feasibility of studying the self-healing behavior of AMM via molecular dynamics is discussed. We have confidence that the microcapsules have a bright future in the development and provide reference for the application and development of micro-scale microcapsules.
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Research and Development of Relationship Between Aging Mechanism and Fatigue Properties of Asphalt
LIANG Bo, LAN Fang, ZHENG Jianlong
Materials Reports
2021,35(9 ):9083 -9096. DOI:10.11896/cldb.20010138
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The fatigue property is an important factor that affects the performance of the asphalt pavement, which is widely studied for durable pavement. With the concept of long-life asphalt pavement being put forward, the research on durability of asphalt pavement has attracted extensive attention, especially the relationship between the aging of asphalt materials and the fatigue characteristics of asphalt pavement. Environmental factors lead to the volatilization of light components and the increase of oxygen-containing functional groups, which made the asphalt materials har-den with reduction of adhesion, and more prone to fatigue cracking. The aging of asphalt affects the service life of asphalt materials and therefore affects the durability of asphalt pavement. The research on fatigue resistance of asphalt pavement involves the aging of asphalt, the selection of modifier, the testing method of self-healing property and fatigue property of asphalt, and the establishment of comprehensive model. It is a pres-sing need to comprehensively consider the multi-factors to study the fatigue resistance of the asphalt pavement to improve the durability of the asphalt pavement. According to the change of chemical composition in asphalt aging process and the self-healing property of asphalt, here the in-fluence factors of asphalt aging property, the influence of self-healing on aging and fatigue properties of asphalt, the improvement of aging properties and fatigue properties of polymer/nano-materials and composite modified asphalt, test methods for fatigue performance of asphalt and asphalt mixture and fatigue damage models of asphalt mixture are reviewed in this paper. The elaborated analysis shows that the study of anti-fatigue performance of asphalt pavement is very important to improve the durability of asphalt pavement considering multi-factor effect. It provides theoretical guidance and solving measures for prolonging the fatigue life of asphalt pavement.
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Influence of Asphalt Grade and Content on the Properties of RAP Mixtures
ZHU Yuefeng, SI Chundi, QIAO Yaning, LI Yanwei
Materials Reports
2021,35(6 ):6086 -6092. DOI:10.11896/cldb.19100237
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In order to study the influence of new asphalt grade and content on the properties of RAP mixtures, 70
#
and 90
#
asphalt were selected to prepare the RAP mixtures with 0%, 20% and 40% RAP content. Based on the optimum asphalt content (OAC) of new binder, the OAC, OAC+0.5% and OAC-0.5% content of RAP mixtures were also fabricated. Dynamic modulus test, fatigue test and low temperature disc-shape tension test were conducted to analyze the properties of RAP mixtures. Then, for better understanding the crack resistance of RAP mixtures, the binders were extracted and recovered to study the cracking properties using G-R parameters. The mixtures results show that when using soft binder, hig-her binder content and lower RAP content, the RAP mixtures have better fatigue resistance and low temperature crack resistance. On the contrary, with harder binder and higher RAP content, the RAP mixtures have better rutting resistance. However, the low temperature results show that with 70
#
binder with OAC-0.5% and 40% RAP content, the RAP mixtures could not meet the requirement. The analysis of water stability shows that one time freeze-thaw cycle is limited to evaluate the water stability of RAP mixtures. After two time freeze-thaw cycles, the water stability of RAP mixtures is lower than that of new asphalt mixture. The G-R parameter results show that with higher RAP content and harder binder, the sextracted binders are more likely to crack.
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Research and Development Trend of Road Usage Phase Change Materials
LIU Tao, GUO Naisheng, TAN Yiqiu, YOU Zhanping, JIN Xin
Materials Reports
2020,34(23 ):23179 -23189. DOI:10.11896/cldb.19090191
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Since the phase change materials (PCMs) as building materials extensively, the diversity and function have been continuously developed, and the temperature regulation and energy saving is significant. PCMs are intelligent and spontaneous, and can effectively adjust temperature range of matrix materials, these characteristics are also applicable to the field of traffic materials, can be used for road temperature regulation to reduce temperature diseases. In addition, more road functionality adopted by using appropriate PCMs, such as snow melting, freeze-thaw resistance and reducing urban heat island effect, correspond to the sustainable development concept of intelligent transportation and green transportation in China.
However, research of PCMs of traffic materials is not mature yet, including application form of pavement and the selection of materials. Various PCMs can be divided into solid-solid and solid-liquid types according to the phase change morphology. Further, the solid-solid type has a very high phase change temperature, is difficult to meet the temperature requirements of road environment, but the solid-liquid phase with transformation of liquid morphology and volume will damage pavement structure. None of them can meet the requirements of temperature regulation effect and mechanical characteristics of phase change pavement. At present, the proposed solution is in combination with other materials.
The promising solutions include composite phase change materials (CPCMS), encapsulation, chemical bridging and microcapsule, etc. Physical adsorption can combine suitable matrix materials with solid-liquid phase change materials (SLPCMs) according to the demand. The encapsulation, such as sol-gel, form shell outside the PCMs to prevent flowability of liquid PCMs and provide enough mechanical properties. The chemical bridging reinforce relationship between matrix material and PCMs through molecular bridge. While the principle of microcapsules is similar to encapsulation, the difference of microcapsules is smaller particle size and SLPCMs as objects, microcapsules can reduce disadvantageous with road. In addition, polyurethane solid-solid phase change material (PUSSPCM) can regulate phase change characteristics by adjustment of chemical reaction,having better road applicability.
This review mainly summarizes the research and development trend of phase change materials for road. The paper firstly exposes the working principle of phase change asphalt pavement, and then, the optimum application formation of phase change asphalt pavement system is determined and the technical requirements of road phase change materials are put forward. Additionally, pure phase change materials (PCMs) are screened and application prospects on road are analyzed. The composite phase change materials (CPCMs) and microcapsule technology to improve the working environment of PCMs are introduced in asphalt pavement, moreover, the adaptability and application prospects on road are evaluated. Finally, the conception of composite microcapsule with phase change and self-healing is addressed, and the diversity of intelligent pavement is enriched, as well as prospects for the future development of PCMs.
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High Temperature Stability Test for Asphalt Concrete of Pavement Materials in Highway
WU Lingling, REN Qiliang, LUO Li
Materials Reports
2020,34(22 ):22083 -22086. DOI:10.11896/cldb.20080036
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High temperature stability is one of thehighway performance of asphalt concrete. In order to better apply Supave-13, SMA-13 and AC-13C in high-grade highway pavement, and reduce the deformation of asphalt concrete pavement caused by insufficient high temperature stability, Supave-13, AC-13C and SMA-13 were subjected to dynamic stability test, uniaxial creep test, rebound modulus and compressive strength test. It was found that the dynamic stability of Supave-13 under the load of 0.7 MPa It was larger than SMA-13 and AC-13C; under the condition of 1.05 MPa load, the dynamic stability of Supave-13 was smaller than other ones; the stiffness modulus of Supave-13 mixture was significantly greater than that of the other two; rebound modulus of Supave-13 and AC-13C, were equivalent and greater than SMA-13; the compressive strength of Supave-13 was significantly greater than that of AC-13C and SMA-13; the compressive strength of both AC-13C and SMA-13 was equivalent. Comprehensive comparative analysis showed that the high temperature stability of Supave-13 was stronger than the other two asphalt mixtures.
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Effect of Cyclic Clogging-Cleaning on Water Permeability of Porous Asphalt Mixture
ZHU Xuwei, LI Bo, WEI Dingbang, WEN Weijun, ZHOU Jianing
Materials Reports
2020,34(20 ):20040 -20045. DOI:10.11896/cldb.19100083
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In order to study the anti-clogging performance of porous asphalt pavement, the porous asphalt concrete (PAC) was clogged with aeolian sand as a clogging material, and the PAC specimens after each clogging were cleaned by manual brushing, vacuum pumping and high-pressure water washing. The permeability of each specimen after clogging and cleaning was measured using falling-head permeability setup. The effect of air voids, nominal maximum aggregate size and cleaning method on the permeability of PAC under the condition of cyclic clogging-clea-ning was investigated. Based on this, the clogging sensitive particles of PAC-13 were studied. The results show that the values of permeability
k
C
after clogging and permeability after cleaning
k
R
decrease rapidly and then gradually stabilize as the number of loadings increases.The anti-clogging performance and recovery effect of permeability of PAC increases with the increase of air void and nominal maximum aggregate size.The residual rate of water permeability of PAC specimens with different air void was significantly different, and the γ value of PAC specimens with larger air void was larger under the same cycle number. The cleaning effect was ranked as high-pressure water washing > vacuum pumping> manual brushing. Particles with the size range of 0.15—2.36 mm are the key particle sizes that cause the clogging of PAC-13 specimen, the particle size of PAC-13 clogging sensitive particle gradually increases with the increase of air void
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Corrosion Assessment and Prediction of Steel Bridge Deck Based on Extreme Learning Machine
CHEN Qian, WANG Chaohui, CHEN Yuanzhao, LI Zhenxia, GUO Tengteng, CHEN Haijun
Materials Reports
2020,34(14 ):14099 -14104. DOI:10.11896/cldb.19050091
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Conductive gussasphalt mixture can melt snow and ice timely and efficiently, but it is easy to accelerate the corrosion of steel deck when it is powered on. It will affect the service performance and traffic safety of bridges. In order to solve the above problems, five kinds of conductive gussasphalt mixtures were designed and prepared. When conductive gussasphalt mixtures were powered on, the current density flowing through the steel plate was tested. The effects of types, working conditions and environmental factors of conductive gussasphalt mixtures on steel plate corrosion were studied. And the prediction model of steel plate corrosion based on the extreme learning machine neural network was established. It lays a solid foundation for the further popularization and application of snow melting technology of conductive gussasphalt mixture in the field of steel bridge deck pavement. The results show that the influence degree order of different factors on steel plate corrosion was ranked as follows: number of time on power>temperature>humidity>electrified time. The influence of number of time on power and temperature on steel plate corrosion were more significant at the level of 0.05. Compared with the traditional neural network prediction model, the extreme learning machine prediction model had better accuracy and efficiency. And its mean absolute error, mean absolute percent error and root mean squared error were 50.48%, 45.89% and 49.30% lower than the former, respectively.
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Surface Texture of Cement Concrete Pavement: a Review
CONG Zhuohong, CHEN Hengda, ZHENG Nanxiang, ZHOU Wanjun
Materials Reports
2020,34(9 ):9110 -9116. DOI:10.11896/cldb.19010079
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China is the country with the longest miles of Portland cement concrete (PCC) pavement in the world. PCC pavement is widely applied in rural areas and tunnels of high-grade highway. The surface textures of PCC pavement in long tunnel are easy to be worn to be a mirror. So its surface friction declines rapidly to cause more traffic accidents. Surface textures of PCC pavement are the main parts to provide anti-skidding performance and make noise.
The surface textures of PCC pavement are mainly made up of macrotexture and microtexture. Macrotexture is formed by construction, which allows water to escape beneath a vehicle’s tires to prevent hydroplaning. Microtexture is the fine-scale roughness contributed by the fine aggregate in the concrete mortar to provide surface friction on sunny days. According to the construction time, the textures of PCC pavement can be classified as fresh and harden concrete. Textures for fresh concrete are done between the placement and curing of concrete. The forms include burlap dragging, transverse brooming, transverse or longitudinal tining. Transverse tining is the most common texturing technique used by state highway agencies. Textures for harden concrete are done after the formation of its strength. The forms include diamond grinding, diamond grooving and next generation concrete surface (NGCS). They are also available for restoring surface friction or lowering tire-pavement noise on existing PCC pavement. Because of aggregate and concrete strength, diamond grinding has some defects on land area. The next generation concrete surface is the most recent new concrete texture introduced in the past 20 years. It synthesizes diamond grinding and grooving techniques to make a diffe-rent texture which are more consistent and durable.
The main problems of PCC concrete are tire-pavement noise and wearing of textures. On-Board Sound Intensity (OBSI) is applied to evaluate the noise of textures. Transverse tining makes the loudest noise of all of the textures. NGCS and conventional diamond grinding (CDG) seem to be the quietest pavements. Exposed aggregate makes louder noise itself, but with combination of NGCS or CDG, it can be quiet a lot. The ASTM E274 locked-wheel skid method is used to measure friction. The loss of friction is attributed to the wearing of textures. NGCS has stable friction because of wider land area.
Transverse grooving is widely used in China. There are less researches about PCC textures on mainland. Most of them are focused on the construction parameters of transverse grooving. There are less applications for other forms of textures. For the exposed aggregate, there are more researches than applications. Diamond grinding is still confined to the research stage. It is the first time for the NGCS that is introduced to China.
This review offers the research progress of PCC textures. The types, construction parameters, application and problem were emphasized. Textures have great impact on tire-pavement noise and friction. New textures introduced by this paper could provide reference for the future application of PCC with lower noise and stable friction.
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Preparation and Performance of Cement Pavement Temperature-adjusting Phase Change Materials Under Low Temperature
ZHU Hongzhou, CHEN Ruipu, GOU Shan, WANG Daqian, HU Lanxin
Materials Reports
2021,35(14 ):14198 -14203. DOI:10.11896/cldb.20050159
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To prepare and select temperature-adjusting phase change materials for cement pavement under low temperature, expanded graphite was used as the carrier for phase change materials, the phase change properties of octanoic acid-decanoic acid and tetradecane were studied. In this study, the optimum eutectic mass ratio of octanoic acid-decanoic acid was determined by step-cooling curve experiments and the lowest eutectic mixture phase change temperature theory. The phase change process and chemical property of the two phase change materials were investigated by differential scanning calorimetric (DSC)analysis experiments, fourier transform infrared spectrometer(FT-IR)experiments and thermogravimetric analysis (TGA)experiments. The results show that: The low temperature phase change range of octanoic acid-decanoic acid and tetradecane is about -1.8—2.5 ℃, and their phase change performance is less affected by heat release from cement hydration.Octanoic acid-decanoic acid and tetradecane meet the requirements of low temperature phase change materials. However, tetradecane has a higher enthalpy of phase change, so it is recommended as a phase change material to regulate temperature for cement pavements at low temperatures; after multiple phase change cycles, there is no chemical change in octanoic acid-decanoic acid and tetradecane, their phase change properties are stable. The adsorption of expanded graphite to tetradecane is better, and it is a physical adsorption. After encapsulation,there is little change in phase change performance of tetradecane.
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Domestic and Foreign Research Progress of Air-entraining Agents for Low-slump of Plastic Concrete and No-slump of Dry-hard Concrete Used in Highway Concrete
BAI Yafei,WANG Dongmin
Materials Reports
2020,34(7 ):7099 -7106. DOI:10.11896/cldb.19030152
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Air entraining agent, as an admixture capable of introducing a large number of evenly distributed, closed and stable microbubbles in the mixing process of concrete mixture, has been highly concerned by researchers and peers at home and abroad since its discovery. Because on the one hand, it can effectively improve the workability, water retention and cohesiveness of concrete mixture, and improve the fluidity of concrete; on the other hand, it can greatly improve the frost resistance, salt resistance, impermeability, sulfate corrosion and alkali-resistant aggregate reaction performance of concrete, effectively reduce the thermal diffusion and conductivity of concrete, and can improve the volume stability of concrete, enhance the weather resistance of field structures, thereby prolonging the service life of highway concrete and improving durability of highway concrete. The air entraining agent is mainly used for structures with high frost resistance requirements, such as concrete dams, pavements, bridge decks, airport road surfaces and other large areas that are susceptible to freezing, and has a very broad research and application prospect.
However, today’s air entraining agents, for highway concrete, especially low-slump of plastic concrete and non-slump of dry-hard concrete, have always had difficulty in ventilating, poor foaming of introduced bubbles, poor foam stability, and air bubbles. The problems of large diameter and uneven distribution of bubbles lead to serious problems such as poor workability, frost resistance and durability of highway concrete. In recent years, the focus of research has been based on how to effectively solve the problem of air entrainment dynamometer, poor foaming of introduced bubbles, poor bubble stability, large bubble diameter, and uneven bubble distribution.
At present, research has been carried out on raw materials such as rosin resins, alkyl and alkyl arene sulfonic acids, fatty alcohol sulfonates, sapiens, etc., and in recent years, researchers at home and abroad have based on the above raw materials, from the perspective of structural design, through the effective modification of molecules and the introduction of a certain amount of special functional groups, which have made some exploration and progress on the problems of air entraining agents in highway concrete.
This paper discusses the definitions and types of air-entraining agents about low-slump of plastic concrete and no-slump of dry-hard concrete used in highway concrete and its evaluation methods from a new perspective, focusing on the domestic and foreign research progress of air-entraining agents about low-slump of plastic concrete and non-slump of dry-hard concrete used in highway concrete. And the latest research progress of air-entraining agents in highway concrete is analyzed from the new perspectives of molecular type, synthesis, design, model and so on, and a comprehensive review of the research status of low-slump of plastic concrete and non-slump of dry-hard concrete for highway concrete in terms of workability, frost resistance and durability, and two “ideal” air entraining agent molecular structure models are proposed based on our research results. It is helpful to understand the effect of air entraining agent for highway concrete on low-slump plastic and no-slump of dry-hard concrete, and better designs directly and develops a new air entraining agent used in low-slump of plastic concrete and no-slump of dry-hard concrete in highway concrete.
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Environmental Adaptability of Epoxy Grouting Materials for Micro Cracks in Cast-in-place Cement Concrete for Bridge Deck
LU Youfu, WANG Chaohui, WANG Xuecheng, FAN Zhentong, XIAO Xudang
Materials Reports
2022,36(1 ):20090252 -7. DOI:10.11896/cldb.20090252
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In order to determine the performance change of epoxy grouting materials for concrete micro cracks under extreme environmental conditions,four kinds of epoxy grouting materials (EP, EP/AD-Ⅰ, EP/AD-Ⅱ and EP/AD-Ⅲ) were prepared by using epoxy resin E-54, polyether amine D230 curing agent and three active diluents (AD-Ⅰ, AD-Ⅱ and AD-Ⅲ). The impact strength was used as the evaluation index to compare and analyze the flexibility of four kinds of epoxy grouting materials at room temperature and low temperature. Based on the tensile properties and interfacial bond strength of epoxy grouting materials, the evolution law of mechanical properties of different grouting materials under high temperature impact, temperature change and freeze-thaw cycles was explored. The results show that compared with pure epoxy grouting material, the reactive diluent weakens the low temperature flexibility, high temperature impact resistance, temperature denaturation resistance and frost resistance of epoxy grouting materials. Among them, AD-Ⅲ active diluent has the best effect on improving the toughness of epoxy grouting material at room temperature, but its impact toughness at -10 ℃ is 31.4% lower than that of pure epoxy grouting material. After high temperature impact, tempe-rature change treatment and freeze-thaw cycle, the tensile properties and bond strength of four kinds of epoxy grouting materials have different degrees of decline. Under high temperature impact, the bond strength of the four kinds of epoxy grouting materials lost greatly, with a decrease of 14.67%, but the bond strength was still higher than 2.5 MPa. During temperature change conditions, the bond strength of epoxy grouting materials decreases by 3.5%. The tensile properties of epoxy grouting materials are significantly affected by freeze-thaw cycles, but the tensile strength is still greater than 40 MPa, and the elongation at break is still higher than 4.0%.
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Research Progress and Prospect of Molecular Dynamics of Asphalt Systems
HE Liang, LI Guannan, ZHENG Yufeng, Alessio Alexiadis, Jan Valentin, Karol J Kowalski
Materials Reports
2020,34(19 ):19083 -19093. DOI:10.11896/cldb.19070106
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With the rapid development of China road engineering, asphalt concrete has been widely used in road engineering. In recent years, the research on asphalt materials is not limited to macroscopic performance experiments, but also extended to mesoscopic and microscopic scale to develop multiscale research. The molecular dynamics is a kind of microscopic research methods which is carry out the integral algorithm under different conditions to track molecular trajectories of research objects. Molecular dynamics was widely used in bitumen material design and microscopic mechanism research in molecular scale. The advantage is deeply explained the phenomenon and properties of asphalt system from the aspect of molecular motion. Therefore, many scholars study bitumen system by combining macroscopic test and molecular dynamics simulation, which will promote the development of asphalt materials.
In this paper, molecular dynamics of bitumen system was comprehensively analyzed, general equilibrium steps of bitumen molecular dynamics model were constructed. The effectiveness of bitumen molecular dynamics model was verified by density, glass transition temperature, viscosity and solubility parameters. The nano-aggregation, self-repair, modification, aging, interfacial adhesion mechanisms of bitumen researchs based on molecular dynamics were comprehensively analyzed. The results show that the molecular dynamics method of bitumen materials was in early exploration stage, but the development potential is significant. Research on the dynamic behavior of bitumen components molecules by molecular dynamics method can reveal time-dependent molecular motion law that the normal test cannot be observed, predict bitumen macroscopic properties, target on bitumen molecular structures to put forward the improve measurement of bitumen road performance, promote the development of asphalt pavement multi-scale experimental simulation and lay the foundation for asphalt materials genome research.
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Research Progress on Digital Image Evaluation Method of Homogeneity of Asphalt Mixture
ZHAO Yi, YANG Xuan, HAO Zengheng, LIANG Naixing, TIAN Yufeng
Materials Reports
2020,34(23 ):23088 -23099. DOI:10.11896/cldb.19070174
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Digital image processing technology is a forward-looking, intelligent technology, which has been widely used in industry, transportation, medicine and other fields. The homogeneity of asphalt mixture is directly related to the road performance and service life of asphalt pavement, which is one of the main factors leading to the early damage of asphalt pavement. The homogeneity evaluation method of asphalt mixture based on digital image processing technology has the characteristics of high detection frequency, low cost, convenient operation, strong objectivity, real-time continuous and so on, which has been concerned by many engineering researchers and builders.
When using digital image processing technology to evaluate the homogeneity of asphalt mixture, digital image processing and homogeneity algorithm are the key to determine the evaluation results. At present, researchers at home and abroad focus on image denoising technology, image threshold segmentation method, homogeneity evaluation method and other aspects have made rich research findings, For example,the influencing factors of image acquisition, the adaptability of image enhancement method, the segmentation principle of adhesive particles and the para-meters of aggregate recognition have been studied,and the aggregate distribution of asphalt mixture is analyzed by two-dimensional image technology or three-dimensional CT scanning technology, and the homogeneity algorithm, evaluation index and standard are emphatically analyzed to evaluate quantitatively the homogeneity of asphalt mixture. However, the digital image evaluation method and standard of homogeneity of asphalt mixture have not formed a unified standard at home and abroad. There are few reports on the rapid, real-time and continuous digital image eva-luation technology of the paving homogeneity and compaction homogeneity in the asphalt mixture construction process. Therefore, the digital image evaluation technology of homogeneity of asphalt mixture in image acquisition, digital image processing, homogeneity algorithm, real-time early warning feedback, program development and other aspects still need further exploration and research.
In this paper, the research progress and development direction of the digital image evaluation method of homogeneity of asphalt mixture are discussed for the digital image processing technology of asphalt mixture. Firstly, this paper summarizes the digital image processing technology of asphalt mixture at home and abroad. Then,the two-dimensional homogeneity evaluation methods of asphalt mixture paving surface and compacted asphalt mixture surface aggregate and the three-dimensional homogeneity evaluation method of compacted asphalt mixture structure aggregate are summarized. Finally,the problems and prospects in the study of the digital image processing technology of homogeneity of asphalt mixture are proposed, so as to to provide reference for the engineering application of asphalt mixture homogeneity digital image detection and evaluation technology.
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Quantitative Analysis of Structural Changes of Asphalt Mastic with Curve-fitted of FTIR Spectrum in Salty High Temperature and High Humidity
ZHANG Qinling, HUANG Zhiyi
Materials Reports
2020,34(8 ):8083 -8089. DOI:10.11896/cldb.19040057
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In order to study the effects of high temperature and high humidity on the chemical composition of asphalt mastic in the coastal salt environment in south of China, the fourier transform infrared spectra (FTIR) of base- and SBS modified asphalt mastics at different salt concentrations(0%,5% and 10% by weight of water, respectively) were analyzed. In order to deeply analyze the absorption peak overlapping zone of 1 780—900 cm
-1
wavenumbers in the asphalt mastics spectrum, the numbers and position of the overlapping sub-peaks were determined based on the second derivative, and the curve fitting analysis was performed on the superimposed band by Origin 2017 software. The effect of salt high temperature and high humidity environment on the chemical components of asphalt mastics were indirectly characterized by the area ratio of the sub-peak and the overlapping zone. The curve fitting results showed that the infrared index of base- and SBS asphalt mastics showed a consistent change with the increase of numbers of dry-wet cycles in different salt concentration, the values of sulfoxide indexes and aromatic indexes increased, and the aliphatic branch indexes, aliphatic index and butadiene indexes decreased. Because of the “salting out” effect of inorganic salts, the salt aggravate the ageing of asphalt mastics in water under the effect of dry-wet cycles. The SBS asphalt mastics shows better anti-agei-ng performance with a lower increase in sulfoxide index after ageing. The research results showed that FTIR technique combined with the curve fitting analysis method could reflect changes in internal chemical composition of asphalt mastics under the coupling effect of salt solution and dry-wet cycles, which also provided an effective method for evaluating the aging of asphalt materials in salt high temperature and humidity environment.
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Estimation of Air Void Content of Dense Graded Water-covering Asphalt Layer Based on GPR
CUI Lilong, LING Tianqing, ZENG Fangui, LIANG Lijuan, LI Rukai
Materials Reports
2021,35(4 ):4092 -4098. DOI:10.11896/cldb.19120099
Abstract
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In order to solve the problem that ground penetrating radar (GPR) can not predict the air void content of water-covering asphalt layer with metal plate reflection method, three kinds of FDTD numerical models of pavement structure with different incident angles of pulse are established to study the influence of the dispersion of pulse on the reflection coefficient of monochromatic wavelet. Under the assumption of dry-wet layers system, a nonlinear calculation algorithm is proposed based on the theory of full waveform inversion with the considering of the incident angle of pulse. The dielectric constant and air void content of dry asphalt layer can be obtained through the nonlinear calculation algorithm utilizing GPR when the surface of layer is covered water. The reliability of the algorithm is validated by employing FDTD numerical models of dry-wet layers system with seven different moisture contents as well as the laboratory test. The results show that in the range of incidence angle of three numerical models, the variation of reflection coefficient of monochromatic wavelet is very small, which can be regarded as a constant, meaning the excitation value of incident wavelet corresponding to each frequency is the same. The synthetic pulse reconstructed by nonlinear calculation algorithm match the real wave well. The error of dielectric constant estimated by metal plate reflection method and nonlinear calculation algorithm increases with the rising of moisture content of wet asphalt layer, while the error growth of nonlinear calculation algorithm is much smaller than that of metal plate reflection method. Compared with the metal plate reflection method, the relative error of the dielectric constant, the bulk specific density of asphalt mixture and the air void content obtained by the nonlinear calculation algorithm are reduced from 10.9% to 1.6%, from 4.6% to 1.1%, and from 24.9% to 7.2%, which proves the nonlinear calculation algorithm can effectively eliminate the influence of water covering on the asphalt layer to calculate the dielectric constant and air void content of dry asphalt layer accurately, providing an accurate and effective way for the real-time monitoring of asphalt layer compaction quality and intelligent compaction technology.
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Study on Adhesion Properties of Broken Pebble and Asphalt Based on Surface Energy Theory
GENG Jiuguang, LAN Qian, LIU Guangjun, ZHOU Hengyu, LIU Runxi
Materials Reports
2020,34(20 ):20034 -20039. DOI:10.11896/cldb.19070258
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Aiming at the problem that the composition of broken pebbles is complex and its composition varies with particle size, based on the surface energy theory, the adhesion properties of asphalt and broken pebbles with different particle sizes were studied. The surface energy of asphalt and broken pebble was tested by sessile drop method and capillary rise method, and the adhesion work and peeling work of asphalt and broken pebble system were calculated. The comprehensive energy ratio (
CER
) was used to evaluate the adhesion properties of broken pebbles and asphalt in the four asphalt mixtures. The results show that the addition of anti-stripping agent will reduce the surface energy of the asphalt, increase the polar component, and reduce the dispersion component. Due to the different chemical composition, mineral composition and surface charge of broken pebble with different particle sizes, the surface energy of broken pebble with different particle sizes is different and the order from large to small is 5—10 mm, 10—15 mm, 3-5 mm, 0—3 mm. The adhesion work of 0—3 mm and 3—5 mm broken pebbles to SK90 asphalt, SBS modified asphalt,SK90 asphalt and SBS modified asphalt with anti stripping agent are better than that of 5—10 mm and 10—15 mm broken pebbles, and the peeling work of 0—3 mm and 5—10 mm broken pebbles to these four kinds of asphalt are less than that of 3—5 mm and 10—15 mm broken pebbles, which shows that the compatibility of different particle size broken pebbles and asphalt is different in adhesion perfor-mance. The results of water stability test of the mixture show that it is reasonable to evaluate the adhesion performance of broken pebble and asphalt with CER, and the size of CER can be used as the basis for selecting the material combination of asphalt aggregate system (especially the aggregate with complex composition),which provides theoretical and technical support for the application of broken pebbles in actual engineering.
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