491 research outputs found
A Novel Micromechanical - Analogical Model for Low Temperature Creep Properties of Asphalt Binder and Mixture
No full textThe ENTPE transformation is commonly used to predict the low temperature properties of asphalt binders from the corresponding mixtures experimental data and vice-versa. Nevertheless, the transformation parameter, α, associated to the ENTPE equation, cannot be directly obtained without relying on both binder and mixture testing. This paper presents a comprehensive investigation to link the ENTPE transformation to the mixture microstructure. This is accomplished by three-point bending tests on asphalt binders and mixtures, digital image processing and statistical evaluation of mixture microstructure, together with a newly proposed micromechanical-analogical model, called MCF (Moon-Cannone Falchetto), used for deriving an explicit expression of α. The values of α obtained from asphalt binder and mixture laboratory measurement are compared to the values predicted by the new formulation. The results indicate that reasonable predictions of low temperature creep stiffness of asphalt binder can be obtained when the new expression of α is used in the ENTPE transformation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Modeling of the rheological properties of asphalt binder and asphalt mortar containing recycled asphalt material
No full textThe use of recycled materials in asphalt pavements increased significantly over the years, determining well known environmental and economic benefits. Many research agencies and road authorities evaluated the impact of Recycled Asphalt Pavement (RAP) on pavement performance. Nevertheless, the mechanism governing the interaction between virgin asphalt binder and aged RAP binder is not well understood. In this paper, the effect of RAP on the rheological properties of asphalt binders and mortars is experimentally evaluated, and theoretically modeled with the objective of defining a relationship between the linear viscoelastic (LVE) properties of binders and those of the corresponding mortars.Three asphalt binder types, obtained by blending a hard and a soft binder at three different percentages, were mixed with three different contents of a Selected fraction of Recycled Asphalt Pavement, called SRAP, for preparing the asphalt mortar samples. Dynamic Shear Rheomether tests were performed on binders and mortars to determining the complex modulus over a wide range of temperatures and frequencies. The rheological properties of the compound of virgin and RAP binder were evaluated by using a new approach based on a modified version of the Nielsen model, avoiding the extraction and recovery method.The results were then modelled by using the analogical 2S2P1D model, consisting of one spring, two parabolic and one-dashpot elements combined in series and then assembled together with a second spring in parallel. Based on test results, a simple experimental relationship between the characteristic times of the binder and the percentage of RAP in the mortar was found
Microstructural and rheological investigation of asphalt mixtures containing recycled asphalt materials
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Microstructural Characterization of Asphalt Mixtures Containing Recycled Asphalt Materials
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Testing protocol to obtain failure properties of asphalt binders at low temperature using creep compliance and stress-controlled strength test
No full text[Radiotherapy in pelvic recurrences of rectal cancer].
No full textPatients with locally recurrent rectal carcinoma have an unfavourable prognosis for the high incidence of distant metastases, the infrequent feasibility of radical surgical resection, and, in these last cases, the high incidence of re-recurrences. Based on the low resectability rate of pelvic recurrences, the clear impact of tumor diameter on resectability and outcome, and the documented possibility to achieve a significant tumor downstaging and downsizing with the use of concurrent chemoradiation, it is evident that the most promising treatment several authors have considered concurrent chemoradiation followed, if feasible, by radical resection. Furthermore, based on the high local and distant failure rate after surgery, the utilization of intraoperative radiation therapy (IORT) and adjuvant chemotherapy seems justified. Some published comparisons between patients treated with and without IORT seems to suggest the possible improvement in both local control and survival in these patients. Particularly interesting issues in this field are: 1) the definition of the most effective treatment modality (both in terms of radiation dose, fractionation and techniques, and drugs to be used concurrently to radiotherapy); 2) the analysis of the prognostic impact of several factors, with the aim of designing and validating staging systems of local rectal recurrences; 3) the possibility to treat with relatively high doses also patients previously irradiated on the pelvis
Investigation on the low temperature properties of asphalt binder: Glass transition temperature and modulus shift factor
No full textThis paper investigates the effect of the glass transition temperature, T-g, and the use of modulus shift factors b(T) on the measured rheological properties of asphalt binders at low temperatures. First, temperature-frequency (T-f) sweep tests are performed with the Dynamic Shear Rheometer (DSR) on asphalt binder, and, the corresponding T-g is calculated. Next, modulus shift factors b(T) is applied to the modulus data measured at temperatures below T-g in the Cole-Cole plot. Finally, a visual comparison of master curves and the parameter assessment of 2 Spring 2 Parabolic 1 Dashpot (2S2P1D) model are used to evaluate the effect of b(T). A significant increase in dynamic shear modulus is observed when the DSR test is performed below T-g, while b(T) can take into account this phenomenon on the shape of the curves in the Cole-Cole plot. Hence, the combined use of the horizontal shift factor, a(T), and modulus shift factor, b(T), is recommended when the DSR tests are performed at temperatures lower than the corresponding asphalt binders T-g. (C) 2020 Elsevier Ltd. All rights reserved
Experimental investigation of rutting in the different phases of asphalt mixture
No full textRutting is one of the most severe failure mechanisms for asphalt pavements. This phenomenon is due to the accumulation of permanent deformation during the pavement service life. The behavior of asphalt mixture is highly affected by the properties of the asphalt binder used in the mix design. For this reason, the Multiple Stress Creep and Recovery (MSCR) test procedure was recently introduced with the objective of better evaluating the rutting resistance while replacing the conventional Superpave parameter, G*/sinδ. Good understanding of the rutting mechanism within the asphalt binder component is essential for correctly studying the mutual interactions of the asphalt mixture components: binder, fine aggregate and large particles. This paper presents the results of an experimental campaign consisting of MSCR tests performed on asphalt binder, mastic and fine aggregate matrix which compose a typical mixture for binder layer. All the tests were conducted using a Dynamic Shear Rheometer (DSR). The classical plate-plate configuration having 25 mm diameter and 1 mm gap was selected for asphalt binder and mastic tests. The cylindrical geometry was used for torsional tests on fine aggregate matrix presenting aggregate as large as 1.16mm. A single testing temperature of 60°C and three different stress levels, 100, 1600, 3200 Pa, were imposed. The results indicate that creep and recovery are function of filler concentration and stress level
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