Abstract ：

This paper investigates the efficiency of acoustic emission (AE) technique for monitoring and assessing the bond slip behavior and damage characteristics of deformed rebar embedded in hybrid fiber reinforced engineered cementitious composites (ECC). A series of pull-out tests were conducted on 48 prism samples with variable rebar diameters (14 mm, 20 mm, and 25 mm), embedded length (3d, 4d and 5d), and cover thickness (2.5d, 4d, 5d and 6d). Two AE sensors, attached on ECC surface and rebar surface respectively, were utilized to critically monitor the AE activity emitted from the ECC matrix and the interface between ECC and rebar throughout the tests. The bond-slip behavior of ECC-rebar presented a more ductile performance than conventional concrete (CC)-rebar because of fiber bridging effect. The damage classification and damage characteristics were clarified by measuring AE activity. The debonding process of ECC-rebar could be divided into four main stages based on the slope changes of cumulative AE hits, and further refined into several substages based on the sudden rises of AE energy. Besides AE cumulative parameters, the Ib-values calculated from AE signals of ECC matrix and ECC-rebar interface were analyzed and compared, which behaved more effectively in identifying the development of cracks and distinguishing the maximum bond stress. Also, the AE intensity analysis was implemented to identify the micro-mechanism transformation during different bonding stages. Moreover, the AE intensity results of CC-rebar obtained from previous research and ECC-rebar in this study were compared.

Keyword ：

Engineered cementitious composites (ECC) Engineered cementitious composites (ECC) Damage characteristics Damage characteristics Damage classification Damage classification Acoustic emission (AE) Acoustic emission (AE) Pull-out test Pull-out test

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Abstract ：

The adhesion between asphalt binder and aggregate is very important to the performance and durability of asphalt pavement. In order to explore the characterisation of modified asphalt binder in microstructure during aging and rejuvenation, the virgin asphalt binder and three kinds of modified asphalt binder (styrene-butadiene-styrene block copolymer (SBS), rubber powder and high viscosity and high elasticity [HVHE] modifier) in different aging and rejuvenation condition were prepared. The micromorphology and surface adhesion were measured by atomic force microscopy. The average roughness value was used as the index to evaluate the micromorphology of asphalt binder. The surface adhesion was used as the index to evaluate the adhesion properties of asphalt binder. Results show that the "bee" structure of SBS-modified asphalt binder increased slightly after long-term aging, and the recovery effect of aromatics oil was the closest to that of the unaged one. The rubber powder-modified asphalt binder and HVHE-modified asphalt binder showed the spot structure. And no matter for short-term aging or long-term aging, aromatics oil had the best recovery effect on micro morphology. The adhesion of the three modified asphalts would decrease gradually after aging. The effects of three kinds of rejuvenator on the adhesion of SBS-modified asphalt binder and rubber powder-modified asphalt binder were different. Rejuvenator, aromatic oil and warm mix asphalt mixture (WMA) additive could rejuvenate the loss of adhesion of HVHE-modified asphalt binder to a certain extent.

Keyword ：

aging aging micromorphology micromorphology surface adhesion surface adhesion asphalt binder asphalt binder modifier modifier rejuvenation rejuvenation AFM AFM

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Abstract ：

Acoustic emission (AE) technology is widely used in structural health monitoring. Glass sand (GS) made from waste glass is a promising replacement aggregate for quartz sand (QS) in ultra-high performance concrete (UHPC). This paper addresses the effects of different factors including water-binder ratio, length of basalt fiber (BF) and ratio of GS replacing QS on the fluidity and flexural strength of UHPC notched beam under four-point flexural loads. Meanwhile, the fracture characteristics of UHPC notched beam were characterized through acoustic emission (AE) technique. The results show that water-binder ratio and replacement ratio of GS present a positive correlation with work performance of UHPC, while length of BF exhibits a negative one. The flexural strength of UHPC notched beams can be improved by the decrease of the water-binder ratio and fiber length. The effect of water-binder ratio on flexural strength is the most significant, while the addition of GS presents the minimum one. The fracture characteristics of UHPC notched beams could be favorably characterized by AE parameters. Through the analysis and comparison of the evolution of AE parameters, the differences in fracture properties of UHPC notched beams with different flexural strengths can be realized. Through this study, the fluidity and flexural performance of UHPC produced by replacing QS with GS were demonstrated, which is beneficial to the cleaner production of UHPC. Meanwhile, the AE technique presented great potential for fracture characterization of UHPC notched beam, which also provided a promising method for real-time monitoring of cracking in the diagnosis of UHPC structures.

Keyword ：

fracture characterization fracture characterization notched beam notched beam UHPC UHPC material factor influence material factor influence AE AE

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Abstract ：

In order to study the reversibility between aging and rejuvenation of modified asphalt binder, a kind of virgin asphalt was selected, and then three kinds of modified asphalt were prepared based on this virgin asphalt. The short-term and long-term aging tests were carried out for the four asphalts. Then three kinds of rejuvenation tests were carried out for the aged asphalt, including commercial rejuvenator, aromatic oil and warm mix rejuvenator. Dynamic shear rheometer (DSR) was used to carry out frequency scanning tests at different temperatures. According to the principle of time temperature equivalence, the master curves of different modified asphalts were constructed, and the rheological properties of asphalt during aging and rejuvenation were studied. By comparing the parameters including complex modulus and hardening index, the rejuvenation effects of viscoelastic properties of modified asphalt were evaluated. Based on the complex modulus of virgin asphalt and modified asphalt, the aging rejuvenation reversible index RM of modified asphalt is proposed to evaluate the recovery of rheological properties of asphalt by different rejuvenators. The results show that the modulus of three kinds of modified asphalt will increase with the deepening of aging. Warm mix rejuvenator can reduce the complex modulus of virgin asphalt, SBS modified asphalt and rubber powder modified asphalt most significantly, followed by the rejuvenator, and the aromatics oil reduced least obviously. This applied to both short-term aging and long-term aging. This research provides a better understanding on the effectiveness and limitation of current rejuvenation techniques and rejuvenators on common asphalts, which is good for the further improvement on production and techniques. (C) 2021 Elsevier Ltd. All rights reserved.

Keyword ：

Modifier Modifier Aging Aging Asphalt binder Asphalt binder Hardening index Hardening index Rheology Rheology Rejuvenation Rejuvenation Complex modulus Complex modulus

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Abstract ：

Different aggregate gradations of asphalt concrete possess dissimilar skeleton structures, leading to diverse macroscopic and mechanical characteristics. Acoustic emission (AE) technology can realize real-time monitoring of the whole damage evolution process of materials. The objective of the present investigation was to demonstrate the fracture characteristics of asphalt concrete with three types of aggregate gradations, including dense-graded asphalt concrete (AC), stone mastic asphalt (SMA), and open-graded friction course (OGFC) under indirect tensile load on account of the acoustic emission (AE) technique. The Marshall compaction method was used to prepare specimens, and the indirect tensile test (IDT) and AE monitoring were conducted simultaneously at different temperatures. The corresponding AE parameters containing energy, cumulative energy, count, and cumulative count were adopted to characterize the fracture process of asphalt concrete with different aggregate gradations. The impact of temperature on the damage characteristics of asphalt concrete was also assessed. Test results indicated that the AE parameters could effectively classify the damage stages of asphalt concrete, and specimens with different aggregate gradations exhibited different AE characteristics during failure processes. The combination of AE parameters and cumulative AE parameters can accurately characterize the damage characteristics of asphalt concrete. SMA specimens possessed the best overall performance among these three types of asphalt concrete in terms of the variations in energy and cumulative energy at different temperatures. The findings obtained in this study can provide a practical AE-based evaluation approach for demonstrating the fracture mechanism of asphalt concrete with different aggregate gradations.

Keyword ：

fracture behavior fracture behavior temperature effect temperature effect acoustic emission acoustic emission aggregate gradation aggregate gradation asphalt concrete asphalt concrete

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Abstract ：

Asphalt pavement is inevitably affected by the rainfall in service stage. The interaction between vehicle and rainfall would cause the hydrodynamic pressure. What's more, pavement temperature also is changing with time. Temperature history and hydrodynamic pressure would influence the moisture diffusion in the pavement. Thereby, moisture uptake of stone, asphalt mortar and mixture at different temperatures and pressures were obtained by weighing. A pressured device was developed to evaluate impact of pressure on the moisture uptake. Diffusion coefficients of those materials were determined based on Fick's second law. And then, 2D micro mechanical FE model of asphalt mixture was developed with the help of digital image processing technology. Effects of temperature and pressure on moisture diffusion depth were analyzed using FEM. Results showed that the rise in temperature and pressure caused the increment of diffusion coefficient. This also resulted in the ascending of moisture diffusing depth. Influence of mortar characteristic on moisture diffusion was more significant than that of aggregate. Under the actions of wet-dry cycles, the moisture concentration in the deep part of mixture risen monotonously, while it varied periodically in the shallow part. The longer the drying period was, the lower the moisture concentration. Moisture concentration of asphalt pavement may be largest at 0.2-0.5 times the layer thickness after intermittent rainfalls. Although pressure can accelerate the diffusion, influence of hydrodynamic pressure on the diffusing depth was not outstanding since the actuation duration of the tire on pavement was too short. (C) 2020 Elsevier Ltd. All rights reserved.

Keyword ：

Moisture diffusion Moisture diffusion Hydrodynamic pressure Hydrodynamic pressure Dense asphalt mixture Dense asphalt mixture Wet-dry cycles Wet-dry cycles Temperature history Temperature history

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Abstract ：

The application of rubber particles made of scrap tires to asphalt mixtures has good economic and social values. Considering the practical performance of asphalt mixtures applied in pavements, this research studied the high temperature stability, low-temperature crack resistance and water stability of a rubber-modified asphalt mixture. Rubber-modified asphalt binder was firstly prepared based on wet process. The corresponding asphalt mixture specimen was then fabricated using Marshall method. Finally, rutting test, low-temperature bending test, Marshall immersion test and freeze-thaw splitting test were carried out, respectively. The experimental results showed that the addition of rubber particles significantly improved the high-temperature stability of the asphalt mixture with dynamic stability enhancing by 102%. The low-temperature crack resistance and water stability performance of the rubber-modified asphalt mixture were better than that of the matrix asphalt mixture, which increased by 49% and 5% for low temperature flexural strength and freeze-thaw splitting tensile strength, respectively. Due to the addition of rubber particles, the pavement performance of the rubber-modified asphalt mixture improved.

Keyword ：

environmentally benign processing environmentally benign processing property property polymeric materials polymeric materials

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Abstract ：

Fibers have been commonly used to enhance the cracking resistance of asphalt mixtures. However, the reinforcing actions of different fibers have presented diverse effects. Therefore, three kinds of fibers, including glass fibers, basalt fibers and steel fibers, were selected to investigate their influences on the low temperature properties and cracking resistance of asphalt mixtures in this paper. Indirect tensile testing (IDT) was conducted to obtain basic properties such as the Poisson's ratio and moduli. The digital image correlation (DIC) technique was employed to measure the deformation and strain. The crack inhibition action was evaluated by the failure time. The results showed that the fiber type has no influence on the Poisson's ratio of the mixture. However, the addition of fibers remarkably affects the mixture modulus. The modulus and ultimate tensile strength of the reinforced mixture decline after the addition of fibers. The gaps between the compressive and tensile moduli are also increased by the addition of fibers. Moreover, the addition of fibers not only substantially improves the mixture ductility but also delays the fracture process. The fiber reinforced asphalt concrete (FRAC) presents a higher fracture energy (FE) and dissipated creep strain energy (DCSE) than that of the control concrete. Among the selected fibers, basalt fibers exhibit optimal crack resistance performance, while steel fibers are not recommended due to their smooth appearance.

Keyword ：

Indirect tensile testing Indirect tensile testing Fiber characteristics Fiber characteristics Low temperature properties Low temperature properties Digital image correlation Digital image correlation Asphalt mixture Asphalt mixture

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Abstract ：

Recycling of waste glass is an efficient way to protect the environment and save resources. This study evaluated the effective utilizations of glass sand (GS) to replace the quartz sand (QS) in typical ultra-high performance concrete (UHPC) and river sand (RS) in ultra-high performance river sand concrete (UHPRC). Ultra-high performance glass concretes (UHPGC) with different substitution ratios were prepared. The working performances and mechanical properties were evaluated, respectively. Meanwhile, the fracture characteristics of typical UHPC, UHPRC and UHPGC were characterized by acoustic emission (AE) parameters. Results show that the fluidities of typical UHPC and UHPRC are significantly enhanced by the addition of GS. The replacements of QS and RS by GS improve the compressive strengths of UHPC and UHPRC. When the replacement ratio of GS is 75%, the compressive strengths of typical UHPC and UHPRC both reach the maximum. The addition of GS presents no significant effects on flexural and splitting tensile strengths. Moreover, the fracture processes of UHPC, UHPRC and UHPGC under different loading conditions can be favorably characterized by AE amplitude and energy. The scanning electron microscope (SEM) tests of concrete mixes reveal the change trends of mechanical and fracture properties from the microcosmic point of view. The cleaner production of UHPGC realized the recycling of waste glass from landfill, which presents great potential for the future sustainable development of UHPC in bridge structures. (c) 2020 Elsevier Ltd. All rights reserved.

Keyword ：

Mechanical properties Mechanical properties Aggregate replacement Aggregate replacement Acoustic emission Acoustic emission UHPC UHPC Glass sand Glass sand

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Abstract ：

Phase change materials (PCMs) can adjust the external temperature by changing their phase states. In order to understand the application of PCMs in asphalt pavements, this paper mainly studied the classification, mechanism, thermoregulation effects of PCMs and the preparation method of composite phase change materials (CPCMs). In addition, the effects of directly incorporated PCMs and composite ones on the properties of asphalt binder and asphalt mixture were described. Results show that directly incorporated PCMs play a role in thermoregulation. However, there is high temperature leakage phenomenon, which has a significant adverse effect on the road performance of asphalt binder and asphalt mixture. CPCMs effectively prevented leakage, reduced the adverse impact on the physical properties of asphalt binder. It is an ideal way to add CPCMs as an alternative component to asphalt mixture. CPCMs improved the heat storage and release capacity of asphalt mixture and the road performance of asphalt mixture, such as high-temperature stability, low-temperature anti-cracking had been improved. (C) 2020 Elsevier Ltd. All rights reserved.

Keyword ：

Road performance Road performance Composite phase change materials Composite phase change materials Thermoregulation Thermoregulation Phase change materials Phase change materials

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