Moisture damage of aggregate-bitumen bonds

Moisture damage of the asphalt mixture is defined as the loss of strength, stiffness and durability due to the presence of moisture (in a liquid or vapour state) leading to adhesive failure at the aggregate-bitumen interface and/or the cohesive failure within the bitumen or bitumen-filler mastic. The presence of moisture can accelerate the distress of asphalt pavement in several different modes, such as rutting, fatigue cracking, thermal cracking and the formation of potholes. In the field, the moisture damage normally happens first at the interface of two pavement layers or at the bottom of pavement layers and develops gradually upward. Once moisture has come into contact and interacted with the asphalt mixture, moisture damage could be developed by the following mechanisms: detachment, displacement, spontaneous emulsification, pore pressure, and hydraulic scour. It should be mentioned that moisture damage is not limited to only one mechanism but is the result of a combination of several mechanisms. As mentioned previously, the common modes of moisture damage of asphalt mixtures are a loss of adhesion between the aggregate and bitumen and/or a loss of cohesion in the mixture. Among these two failures, the adhesive failure is recognised as the main mode of moisture damage. Hence, the physico-chemical interactions between aggregates and bitumen in the presence of moisture are believed to partially govern the moisture sensitivity of asphalt mixtures, which can also affect the serviceability, performance and durability of the asphalt pavement. This thesis describes the work that was carried out with regard to the moisture damage evaluation of aggregate-bitumen bonds through different procedures. The fundamental properties of the individual material such as the chemical composition and rheological properties of bitumen, moisture absorption, surface morphology and mineralogical composition of aggregates were first characterised. Two types of equipment, namely the dynamic contact angle (DCA) analyser and dynamic vapour sorption (DVS) system were used for determining the surface energy of the bitumen and aggregates, respectively. The obtained surface energy results were then combined thermodynamically to determine the work of adhesion between aggregate and bitumen, and the reduction in the adhesive properties if water is introduced into the system. Three established mechanical tests consisting of the standard peel test, Pneumatic Adhesion Tensile Testing Instrument (PATTI) test and a pull off test were developed and redesigned to make sure that these tests are practical, reliable and feasible to measure the bonding strength of aggregate-bitumen combined specimens. The composite substrate peel test (CSPT) was developed to prepare composite substrates using crushed coarse aggregates as a more practical replacement for the aggregate substrates prepared from aggregate boulders. Finally, the moisture damage results from mechanical tests and thermodynamic results were compared and correlated with the basic physico-chemical properties of the original materials. The results showed that in the dry condition, all techniques used in this research, including the mechanical tests and the surface energy tests led to similar results, with bitumen rather than aggregates dominating the bonding properties of aggregate-bitumen systems. After moisture conditioning, the four mechanical tests, including standard peel test, CSPT, PATTI test and pull-off test showed similar moisture sensitivity ranking and failure surface results demonstrating the good correlation between these four tests. In addition, based on the comparison conducted, the four mechanical tests are all considered to be reliable to evaluate the moisture sensitivity of different aggregate-bitumen systems. However, based on the aggregates considered in this research, the moisture sensitivity parameters obtained from the surface energy tests are suggested unreliable to evaluate the moisture sensitivity of aggregate-bitumen systems

Laboratory evaluation of Rediset modified bitumen based on rheology and adhesion properties

Warm mix asphalt (WMA) could significantly reduce the production temperature of asphalt mixtures. Lower production temperature meaning reduced fossil fuel consumption and greenhouse gas emission which in turn avoid environmental pollution in the road construction process. This study aims to characterise the properties of bitumen with the addition of a type of WMA additive – Rediset. The influence of Rediset on bitumen surface energy was evaluated by using the Dynamic Contact Angle (DCA) test. Complex modulus and phase angle of bitumen were evaluated through frequency sweep test using Dynamic Shear Rheometer (DSR). The high-temperature viscosity of bitumen was measured using a corn and plate system which installed in the DSR equipment. Finally, the Pneumatic Adhesion Tensile Testing Instrument (PATTI) test was performed to measure the tensile strength and moisture susceptibility of aggregate-bitumen combinations. The results show that the Rediset reduces the surface energy of bitumen. Moreover, as seen in the DSR test, the complex modulus increased while the phase angle decreased at the low frequency range due to the addition of Rediset. The decreased bitumen viscosity because of the addition of Rediset demonstrating reduced mixing and compaction temperature of asphalt mixture. In addition, the addition of Rediset could improve the bonding strength of aggregate-bitumen combinations at medium and high service temperatures but has no influence at low temperature. Furthermore, the Rediset is able to increase the retained tensile strength which in turn reduces the moisture susceptibility of asphalt mixture

Experimental Exploration of Influence of Recycled Polymer Components on Rutting Resistance and Fatigue Behavior of Asphalt Mixtures

Rutting and fatigue of asphalt pavements, as two important distresses, are significantly influenced by the properties of binders. This study aimed to improve the resistance of asphalt mixtures to permanent deformation and fatigue using two recycled waste-polymer components in recycled crumb rubber (CR) and polyethylene (PE). The assessed pavement properties of the modified asphalt mixtures were characterized by wheel tracking, uniaxial penetration, and four-point bending (4PB) tests. The wheel tracking test indicated that the integrated modification technique, by functionally incorporating PE and CR, enhanced the dynamic stability of the asphalt mixtures and that PE dosage was a key variable. From the uniaxial penetration test, it was revealed that the shear strength of the asphalt mixtures at high temperature could be improved by the integrated modification method, indicating the method’s potential to reduce the flow rutting of asphalt pavements. Meanwhile, both the CR and PE were shown to increase the cohesive behavior of the asphalt mixtures, with the friction angle value sensitive to PE dosage. The addition of PE reduced the fatigue life of the asphalt mixtures; the CR improved the PE-modified mixtures’ fatigue resistance. The findings from this study will be beneficial in developing sustainable and durable asphalt pavements, tailoring the reuse of different types of polymer wastes in asphalt pavements, and minimizing waste disposal at landfills

Tomato Chlorosis Virus Infection Facilitates \u3cem\u3eBemisia tabaci\u3c/em\u3e MED Reproduction by Elevating \u3cem\u3eVitellogenin\u3c/em\u3e Expression

Transmission of plant pathogenic viruses mostly relies on insect vectors. Plant virus could enhance its transmission by modulating the vector. Previously, we showed that feeding on virus infected plants can promote the reproduction of the sweet potato whitefly, Bemisia tabaci MED (Q biotype). In this study, using a whitefly-Tomato chlorosis virus (ToCV)-tomato system, we investigated how ToCV modulates B. tabaci MED reproduction to facilitate its spread. Here, we hypothesized that ToCV-infected tomato plants would increase B. tabaci MED fecundity via elevated vitellogenin (Vg) gene expression. As a result, fecundity and the relative expression of B. tabaci MED Vg was measured on ToCV-infected and uninfected tomato plants on days 4, 8, 12, 16, 20 and 24. The role of Vg on B. tabaci MED reproduction was examined in the presence and absence of ToCV using dietary RNAi. ToCV infection significantly increased B. tabaci MED fecundity on days 12, 16 and 20, and elevated Vg expression on days 8, 12 and 16. Both ovarian development and fecundity of B. tabaci MED were suppressed when Vg was silenced with or without ToCV infection. These combined results suggest that ToCV infection increases B. tabaci MED fecundity via elevated Vg expression

Effect of different viscous rejuvenators on chemical and mechanical behavior of aged and recovered bitumen from RAP

© 2019 Elsevier Ltd Due to scarcity of virgin natural materials, the use of reclaimed asphalt pavement (RAP) has been promoted and encouraged in pavement engineering. However, note that the bituminous binder in RAP has been seriously aged due to long-term service exposure to the atmosphere. It is thus paramount to effectively restore properties of the RAP by adding proper rejuvenators. In this study, five rejuvenators were designed with different viscosities and applied to rejuvenate the aged binder. The changes in chemical compositions of bitumen caused by ageing and rejuvenating were evaluated by a SARA (Saturate, Aromatic, Resin and Asphaltene) analysis method. Brookfield viscosity, Dynamic Shear Rheometer (DSR) and Direct Tension (DT) were further conducted to evaluate the physical and mechanical properties of bituminous binders. Surface Free Energy test was applied to characterize the adhesion and moisture damage behavior of aged and rejuvenated binders. The experimental results showed that the ageing process increased resins and asphaltenes, which in turn improved the colloidal stability of the aged binder. The five rejuvenators designed in this research had a similar effect in restoring the rheological properties and stiffness of the aged bitumen to a similar level as that of the virgin binder. However, the viscosity level of rejuvenator has different impacts on tensile elongation at break, brittle fracture stress, adhesion property and moisture resistance of rejuvenated binders, in which the rejuvenator with an optimal viscosity may obtain the best rejuvenating performance

Polyoxometalate-supported Pd nanoparticles as efficient catalysts for the direct synthesis of hydrogen peroxide in the absence of acid or halide promoters

A Keggin-type polyoxometalate (Cs1.5H1.5PW12O40)-supported Pd catalyst is efficient for the direct synthesis of H2O2 from H-2 and O-2 in the absence of any acid or halide additives under atmospheric pressure.NSFC [20625310, 20773099, 20873110]; National Basic Research Program of China [2005CB221408]; Program for New Century Excellent Talents in Fujian Provinc

Sustainable utilization of bauxite residue (Red Mud) as a road material in pavements: A critical review

Sustainable utilization of the bauxite residue (red mud) generated from the alumina refining has recently increased due to increased environmental concerns because of its high alkalinity and problematic pollutants when placed in landfills. This paper attempts to review recent research findings of utilizing red mud as a road material in pavement structures in literature, including road bases and asphalt mixtures. Previous laboratory investigations indicated that red mud is feasible to be used as a raw material in road bases with satisfactory unconfined compressive strength (UCS), frost resistance and durability performance, but their durability during the service life of the pavement is still unclear. The incorporation of red mud in asphalt mastics was found to be able to improve its stiffness, such as softening point, complex modulus, and viscosity. In terms of asphalt mixtures, replacing limestone filler in mixtures by red mud resulted in some positive effects on mechanical behaviors, high bulk density and good rutting resistance. However, the moisture susceptibility and raveling resistance of asphalt mixtures became relatively worse because of the addition of red mud. Referring to this overview, it is necessary to qualify the long-term service performance of road base materials prepared with red mud by using laboratory accelerating evaluation or road trials. For asphalt mixtures prepared with red mud, how to improve durability, in particular moisture resistance, will be a future research focus. In addition, the influence of red mud on cracking resistance at low temperature, fatigue properties and long-term durability of asphalt mixtures is still needed to be further explored

Defect-induced helicity-dependent terahertz emission in Dirac semimetal PtTe2 thin films

Nonlinear transport enabled by symmetry breaking in quantum materials has aroused considerable interest in condensed matter physics and interdisciplinary electronics. However, the nonlinear optical response in centrosymmetric Dirac semimetals via the defect engineering has remained highly challenging. Here, we observe the helicity-dependent terahertz (THz) emission in Dirac semimetal PtTe2 thin films via circular photogalvanic effect (CPGE) under normal incidence. This is activated by artificially controllable out-of-plane Te-vacancy defect gradient, which is unambiguously evidenced by the electron ptychography. The defect gradient lowers the symmetry, which not only induces the band spin splitting, but also generates the giant Berry curvature dipole (BCD) responsible for the CPGE. Such BCD-induced helicity-dependent THz emission can be manipulated by the Te-vacancy defect concentration. Furthermore, temperature evolution of the THz emission features the minimum of the THz amplitude due to the carrier compensation. Our work provides a universal strategy for symmetry breaking in centrosymmetric Dirac materials for efficient nonlinear transport and facilitates the promising device applications in integrated optoelectronics and spintronics.Comment: 27 pages, 5 figure