Investigating the reinforcement effect of geogrids in flexible pavements

Geogrids have been increasingly used to reinforce granular base course to improve the performance of flexible pavements. In this study, different interfacial behaviors of geogrid-reinforced aggregate were investigated through laboratory experiments. Influence factors affecting the reinforcement effect were analyzed, and reinforcement mechanisms were revealed.Firstly, the repeated load triaxial (RLT) test was conducted to investigate the vertical resilient deformation behavior of the reinforced aggregate. The result show that the RLT test was not effective in evaluating the reinforcement effect. To further analyze the lateral resilient deformation behavior of the reinforced aggregate, a large-scaled cyclic shear test was introduced. The result show that this method could effectively quantify the reinforcement effect of geogrids along with a term, resilient interface shear modulus.Secondly, the interfacial shear behavior of the reinforced aggregate was studied by a large direct shear test. The relative size of aggregate to geogrid aperture had a significant effect on the mechanical properties of the reinforced aggregate and interface failure modes. A guideline to optimize the combination of geogrids and aggregates was proposed based on the results.Thirdly, a modified loaded wheel tester was employed to investigate the permanent deformation behavior of the reinforced aggregate. Critical influence factors affecting the reinforcement effect were analyzed. A better reinforcement effect could be obtained by increasing the portion of effective aggregates, increasing the tensile strength of geogrids. Triaxial geogrids performed better in reinforcing aggregate than biaxial geogrids when their tensile strength were similar. The tensile strength of geogrids had much significant effects on the reinforcement compared to the aperture geometry.Last, the resilient and permanent deformation behaviors of reinforced granular base were further studied through a full-scale accelerated pavement testing to verify the laboratory results. The test program included performance testing, response testing and pavement trench. The result demonstrated that an enough permanent deformation was needed for mobilizing geogrids to constrain the lateral movement of granular particles, increase the modulus of base course, and improve the stress distribution on subgrade. For a pavement system consisting of a thin surface and base layer, a proper placement position of geogrids was at the base-subgrade interface

Laboratory Investigation on the Interface Bonding between Portland Cement Concrete Pavement and Asphalt Overlay

The interface bonding between Portland cement concrete (PCC) pavement and hot-mix asphalt (HMA) overlay plays an important role in the performance of the composite pavement. This research conducted a series of comprehensive laboratory studies to investigate the influence factors of the interface bonding strength using a self-designed direct shear test apparatus that can simultaneously apply normal stress and shear stress on a specimen. Four kinds of commonly used tack coat materials were systematically tested and compared under various combinations of normal stress and temperature. Then, coupling effects of the normal stress and temperature on the interface bonding between PCC and HMA were analyzed. The test results show that temperature has a significant impact on the adhesion of the tack coat. Emulsified asphalt was considered the optimal tack coat material because of its simple construction method. In addition, it was found that a damaged interface could still provide considerable bonding strength. Normal stress generated by traffic loads was beneficial to the interface bonding strength, especially at lower temperatures. The temperature had a significant effect on interface bonding and played a leading role in the failure mode of interface bonding

Modeling the dynamic performance of transportation infrastructure using panel data model in state-space specifications

In this study, different modeling approaches used in panel data for performance forecast of transportation infrastructure are firstly reviewed, and the panel data models (PDMs) are highlighted for longitudinal data sets. The state-space specification of PDMs are proposed as a framework to formulate dynamic performance models for transportation facilities and panel data sets are used for estimation. The models could simultaneously capture the heterogeneity and update forecast through inspections. PDMs are applied to tackle the cross-section heterogeneity of longitudinal data, and PDMs in state-space forms are used to achieve the goal of updating performance forecast with new coming data. To illustrate the methodology, three classes of dynamic PDMs are presented in four examples to compare with two classes of static PDMs for a group of composite pavement sections in an airport in east China. Estimation results obtained by ordinary least square (OLS) estimator and system generalized method of moments (SGMM) are compared for two dynamic instances. The results show that the average root mean square errors of dynamic specifications are all significantly lower than those of static counterparts as prediction continues over time. There is no significant difference of prediction accuracy between state-space model and curve shifting model over a short time. In addition, SGMM does not obtain higher prediction accuracy than OLS in this case. Finally, it is recommended to specify the inspection intervals as several constants with integer multiples

Effect of physical hardening on low temperature performance of DCLR modified asphalt

This study aims to investigate the effect of physical hardening on the low temperature performance of direct coal liquefaction residue (DCLR) modified asphalt. The extended bending beam rheometer (EBBR) method was used to evaluate the low temperature performance of DCLR modified asphalt with benzaldehyde, silane coupling agent and xylene compatibilizer. Meanwhile, the microstructure and morphology of DCLR modified asphalt before and after physical hardening were quantitatively characterized by atomic force microscope (AFM) and image processing software. In this study, the physical hardening was performed by placing the DCLR modified asphalt at low temperature conditions for a certain time. The test results show that as the conditioning temperature decreased and the conditioning period increased, both low temperature grade loss and hardening rate of asphalt increased, indicating that the low temperature performance deteriorated. Compared to the room-temperature conditions, the total number of “bee-structures” of DCLR modified asphalt under low temperature conditions were less, but the shape of a single “bee-structure” became larger and longer. The compatibilizers hindered the growth of “bee-structure”, which demonstrated that the compatibilizers could improve the low temperature performance of asphalt. The three compatibilizers had different effects on low temperature performance of DCLR modified asphalt. Among them, the silane coupling agent was the most effective, followed by benzaldehyde and xylene

CD40 Ligation Releases Immature Dendritic Cells from the Control of Regulatory CD4+CD25+ T Cells

AbstractWe report that disruption of CD154 in nonobese diabetic (NOD) mice abrogates the helper function of CD4+CD25− T cells without impairing the regulatory activity of CD4+CD25+ T cells. Whereas CD4+ T cells from NOD mice enhanced a diabetogenic CD8+ T cell response in monoclonal TCR-transgenic NOD mice, CD4+ T cells from NOD.CD154−/− mice actively suppressed it. Suppression was mediated by regulatory CD4+CD25+ T cells capable of inhibiting CD8+ T cell responses induced by peptide-pulsed dendritic cells (DCs), but not peptide/MHC monomers. It involved inhibition of DC maturation, did not occur in the presence of CD154+ T-helper cells, and could be inhibited by activation of DCs with LPS, CpG DNA, or an agonistic anti-CD40 mAb. Thus, in at least some genetic backgrounds, CD154-CD40 interactions and innate stimuli release immature DCs from suppression by CD4+CD25+ T cells

Molecular characterization and functional analysis of adrenergic like receptor during larval metamorphosis in Crassostrea angulata

National Basic Research Program of China [2010CB126403]; NSFC [41176113]; Program for Changjiang Scholars and Innovative Research Team in University [IRT0941]; Earmarked Fund for Modern Agro-industry Technology Research System [nycytx-47]Numerous reports have associated the catecholamines with larval settlement and metamorphosis in bivalve mollusks. However, little information about the receptors during larval development is available. In this study, for the first time we clone and characterize the cDNAs designated as adrenergic-like receptor (AR(cga)) from Crassostrea angulata. The deduced protein AR(cga) has high similarity with alpha(2)-adrenergic receptor (alpha(2)-AR) from Ixodes scapularis, and includes three major domains composed of a transmembrane domain with seven transmembrane motifs, a relatively long third cytoplasmic loop and a short fourth inner terminal domain. Using a real-time PCR approach, expression profiles of the AR(cga) were analyzed in adult tissues and during larval development. In adult oyster, the AR(cga) was expressed ubiquitously, although transcript levels varied between organs; the highest mRNA level was detected in labium followed by mantle and gonad. AR(cga) expression increased during larval development and reached the highest level at eyespot larvae, and then the expressions were maintained in a high level during metamorphosis. The temporal and spatial expression profile of mRNA was examined from trochophore to eyespot larva stages by whole mount in situ hybridization. In the four stages, AR(cga) mRNA was mainly detected in the cerebral ganglion and or the apical organ, the pedal ganglion and around the heart. The ganglion differentiation was found in the early umbo-veliger larva. To evaluate the possible regulation of AR(cga) by adrenaline in the oyster metamorphosis, competent larvae were exposed to the neurotransmitter adrenaline. AR(cga) expression increased for the first 12 h after treatment and then AR(cga) mRNA level decreases gradually to the same level of untreated control group. Overall, these results suggest that AR(cga) might play a considerable role in signal transduction during the larval metamorphosis of C. angulata (C) 2012 Elsevier B.V. All rights reserved

Molecular characterization and functional analysis of adrenergic like receptor during larval metamorphosis in Crassostrea angulata

National Basic Research Program of China [2010CB126403]; NSFC [41176113]; Program for Changjiang Scholars and Innovative Research Team in University [IRT0941]; Earmarked Fund for Modern Agro-industry Technology Research System [nycytx-47]Numerous reports have associated the catecholamines with larval settlement and metamorphosis in bivalve mollusks. However, little information about the receptors during larval development is available. In this study, for the first time we clone and characterize the cDNAs designated as adrenergic-like receptor (AR(cga)) from Crassostrea angulata. The deduced protein AR(cga) has high similarity with alpha(2)-adrenergic receptor (alpha(2)-AR) from Ixodes scapularis, and includes three major domains composed of a transmembrane domain with seven transmembrane motifs, a relatively long third cytoplasmic loop and a short fourth inner terminal domain. Using a real-time PCR approach, expression profiles of the AR(cga) were analyzed in adult tissues and during larval development. In adult oyster, the AR(cga) was expressed ubiquitously, although transcript levels varied between organs; the highest mRNA level was detected in labium followed by mantle and gonad. AR(cga) expression increased during larval development and reached the highest level at eyespot larvae, and then the expressions were maintained in a high level during metamorphosis. The temporal and spatial expression profile of mRNA was examined from trochophore to eyespot larva stages by whole mount in situ hybridization. In the four stages, AR(cga) mRNA was mainly detected in the cerebral ganglion and or the apical organ, the pedal ganglion and around the heart. The ganglion differentiation was found in the early umbo-veliger larva. To evaluate the possible regulation of AR(cga) by adrenaline in the oyster metamorphosis, competent larvae were exposed to the neurotransmitter adrenaline. AR(cga) expression increased for the first 12 h after treatment and then AR(cga) mRNA level decreases gradually to the same level of untreated control group. Overall, these results suggest that AR(cga) might play a considerable role in signal transduction during the larval metamorphosis of C. angulata (C) 2012 Elsevier B.V. All rights reserved