Interlayer Shear Failure Evolution with Different Test Equipments

AbstractThis research analyses the relationship between several configurations, failure mechanisms and states of stress imposed by testing machines, comparing the results of two devices. It focalizes on the evolution of numerous tests, performed on identical specimens, and reports the correspondent response curves obtained with two devices suitably designed to cover two kind of devices used in recent years and modified to ensure the comparison between the outcomes.The observation of a regular trend in the results suggests a strict relationship between them and the specimens’ features and also warrants the statistic reliability of the testing machines

A new proposal to assess shear fatigue resistance of asphalt pavement interfaces

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Road Materials and Pavement Design on 2021, available online at: http://www.tandfonline.com/10.1080/14680629.2021.1899966.The degree of adherence between two bituminous layers can be assessed from shear tests carried out at constant displacement speed, which allow the shear strength and stiffness of the interface to be obtained, being usual to specify a minimum strength. But stronger bonds will be more stressed, which could negatively affect their fatigue behaviour. In this work, the shear fatigue behaviour of two interfaces of different stiffness has been analysed, based on a cyclic compression test, performed at controlled stress, using the test device B described in the NLT-382 standard, included in the draft of the European pre-norm prEN 12697-48. From these tests, fatigue laws for each type of interface have been obtained. These laws, combined with a calculation method developed by the authors, have made it possible to obtain the number of cycles that each interface would withstand, under certain load hypotheses.Part of this study constitutes one of the activities carried out within the framework of the research project called SUPERBIT (Treatments for obtaining SUPERior properties and effectiveness of BITuminous coats to improve the durability of pavements) which has been included in the 2017 aid programme of the CDTI (Centre for Industrial Development and Technology), belonging to Ministry of Economy and Competitiveness of Spain. In addition, the authors would like to thank the company ARNÓ for the help received in carrying out the dynamic tests.Peer ReviewedPostprint (author's final draft

Ermüdungs- und Heilungseigenschaften von Asphalt

This thesis, consisting of 7 peer-reviewed international journal publications is devoted to the investigation of fatigue and recovery properties of asphalt materials. Concerning the cracking mechanisms, the effects of both cracking in asphalt mixture and cracking at layers’ interface were considered. Since several test types are available for determination of asphalt mixture fatigue resistance, there is no consensus between researchers about the appropriate fatigue test. Considering the stress controlled test mode, it was found that uniaxial tension-compression test is the most reliable for evaluation of the asphalt mixture fatigue resistance. Furthermore, a new fatigue procedure was introduced, able to overcome the shortcomings if only a single test temperature is considered for the fatigue evaluation process (cp. EN 12697-24). This procedure allows a plausible evaluation of the asphalt mixture fatigue performance considering wide temperature range, with a marginally increased laboratory effort. Recovery potential of asphalt mixtures was addressed based on the concept of dissipated energy. The influence of several internal and external factors (bitumen polymer modification, ageing condition, binder content, degree of compaction and rest period duration) on recovery properties of asphalt mixtures was investigated. In order to overcome large scattering of the experimental results and consequently an erroneous evaluation of asphalt mixture recovery potential, a new recovery index was introduced. Moreover, the recovery potential of a specific asphalt mixture was investigated in detail, taking into consideration biasing effects such as nonlinearity and self-heating, observed during cyclic loading. Considering various asphalt mixtures and tack coats, the influence of test temperature and compressive normal stress on layers’ interface fatigue behaviour was determined. Based on this preliminary work, optimal test parameters were proposed, allowing a successful fatigue evaluation of the layers’ interfaces. Additionally, the comparison between results from the proposed cyclic shear fatigue procedure and results from monotonic shear test was performed. It was found that the resulting shear strength from monotonic shear test can be used only as a rough indicator for long term interface bonding performance, because not all research and field experience could be reflected in the test results.Diese Dissertation, bestehend aus 7 internationalen Peer-Review Publikationen, widmet sich der Untersuchung der Ermüdungs- und Heilungseigenschaften von Asphalt. Hinsichtlich der Rissmechanismen wurden die Effekte der Rissbildung, sowohl im Asphalt, selbst als auch an der Grenzfläche zwischen den Asphaltschichten untersucht. Mit Hilfe der Auswertung, der während eines Ermüdungsversuchs dissipierten Energie, erfolgte der Vergleich der gängigen spannungsgeregelten Ermüdungstestmethoden. Es wurde festgestellt, dass sich der einaxiale Zug-Druck-Wechselversuch sehr gut für die Beurteilung des Ermüdungswiderstandes von Asphalt eignet. Weiterhin wurde das Problem der normgemäßen Analyse des Ermüdungsverhaltens (vgl. EN 12697-24) bei einer einzigen Prüftemperatur beleuchtet. Ein neues Ermüdungskonzept wurde entwickelt, das eine plausible Bewertung des Ermüdungswiderstandes von Asphalt über den gesamten Gebrauchstemperaturbereich mit einem geringfügig erhöhten Laboraufwand ermöglicht. Die Bestimmung der Heilungseigenschaften von Asphalt erfolgte auf der Grundlage des Konzepts der dissipierten Energie. Die Einflussgrößen unterschiedlicher Prüfvariablen (Bindemittelgehalt, Verdichtungsgrad, Lastpausendauer, Alterungszustand, Bindemittelsorte) auf die Heilungseigenschaften wurden analysiert. Weiterhin wurde ein neuer Index zur vergleichenden Bewertung des Heilungsvermögens entwickelt, der eine Reduzierung der materialbedingten Streuung im Prüfergebnis ermöglicht. Schließlich erfolgte eine detaillierte Untersuchung des Heilungspotentials, wobei die bei der zyklischen Belastung beobachteten Nebeneffekte Nichtlinearität und Selbsterwärmung von der eigentlichen Materialheilung isoliert wurden. Unter Berücksichtigung verschiedener materialspezifischen Parametern wurde der Einfluss der Prüftemperatur und Normalspannung auf den Ermüdungswiderstand der Grenzfläche zwischen den Asphaltschichten bestimmt. Es wurden die optimalen Prüfparameter vorgeschlagen, mit denen eine bestmögliche Ermüdungsbewertung des Schichtenverbundes erfolgen kann. Anschließend konnte mit Hilfe des Vergleichs der Ergebnisse aus zyklischen und monotonen Scherversuchen festgestellt werden, dass die Scherkraft aus dem monotonen Scherversuch nur als grober Indikator für die Bestimmung der Lebensdauer des Schichtenverbundes herangezogen werden kann

Green Concrete for a Better Sustainable Environment

This book, Green Concrete for a Better Sustainable Environment, aims to cover recent advances in the development of green concrete solutions and discuss the best ways to leverage opportunities in this domain. Concrete can be described as green concrete if it has one of the following features; it uses waste material as at least one of its components, its production process does not lead to environmental destruction, or it has high performance and life cycle sustainability. At present, natural resources are running out. Cement and concrete made from industrial and construction waste can be regarded as valuable resources for civil infrastructure construction. Green concrete will not only contribute to a circular economy, but can also help to reduce the amount of embodied energy and CO2 emissions associated with cement manufacturing and aggregate quarrying. Using green concrete can also mitigate the environmental threats associated with industrial waste materials. This book covers the theoretical, experimental, applied and modelling research studies on the materials, products and structures related to sustainable cement-based composites

Material effects on strawbale wall seismic capacity

Strawbale construction is a sustainable, viable alternative to conventional building practices. As a newly introduced appendix to the International Residential Code (IRC), the strawbale construction requirements may benefit from further evaluation and possible refinement. Such evaluation and refinement may lead towards code change proposals that will improve the provisions and make strawbale construction safer and more accessible to the general public. This seismic test series addressed the effect of mesh wire type on ductility and the validity of the existing wall slenderness limits. The tests focused on slender walls dominated by flexural deformations. Welded wire mesh wall performed better than the woven wire mesh wall of the same detailing, yet fell short of expected values. Slenderness must continue to be analyzed as the results of a wall using 14” bales were impacted by bale irregularity. The additional tests done as part of this thesis, including vertical load tests and materials testing, added to the understanding of strawbale construction performance and expanded the corpus of strawbale wall test data. All tested walls performed satisfactorily under vertical loading in post-seismic conditions. The purpose of this test series was to validate and potentially suggest improvements to the building code provisions to enhance the prevalence and safety of strawbale construction

Destructive and non-destructive mechanical characterisation of chocolate with different levels of porosity under various modes of deformation

Chocolate exhibits a complex material response under the varying mechanical loads present during oral processing. Mechanical properties such as Young’s modulus and fracture stress are linked to sensorial attributes such as hardness. Apart from this link with hardness perception, these mechanical properties are important input parameters towards developing a computational model to simulate the first bite. This study aims to determine the mechanical properties of chocolate with different levels of micro-aeration, 0–15%, under varying modes of deformation. Therefore, destructive mechanical experiments under tension, compression, and flexure loading are conducted to calculate the Young’s modulus, yield, and fracture stress of chocolate. The values of Young’s modulus are also confirmed by independent ultrasonic mechanical experiments. The results showed that differences up to 35% were observed amongst the Young’s modulus of chocolate for different mechanical experiments. This maximum difference was found to drop with increasing porosity and a negligible difference in the Young’s modulus measurements amongst the different mechanical experiments is observed for the 15% micro-aerated chocolate. This phenomenon is caused by micro-pores obstructing the microscopic inelastic movement occurring from the early stages of the material’s deformation. This work provides a deeper understanding of the mechanical behaviour of chocolate under different loading scenarios, which are relevant to the multiaxial loading during mastication, and the role of micro-aeration on the mechanical response of chocolate. This will further assist the food industry’s understanding of the design of chocolate products with controlled and/or improved sensory perception

Seismic load-resisting capacity of plastered straw bale walls

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 57-58).Straw bales have been incorporated into buildings for centuries, but only recently have they been explored in academic settings for their structural potential. Straw bale building is encountering a growing audience due to its social and economic benefits. Plastered and reinforced straw bale wall assemblies have been found comparable to wood frame construction in resisting vertical and lateral loads. A number of straw bale residences have been constructed in the highly seismic state of California, while recent efforts have expanded its presence to quake-prone areas in developing countries like Pakistan and China. As this is a burgeoning arena of research, only empirical tests have been conducted. This thesis introduces a computer simulation of a wall assembly under lateral loading, using two techniques: a multi-layer shell element and an equivalent compression strut frame in SAP2000. The models assume homogeneity, and based on the results, areas for improvement and further research are suggested.by Jennifer S. Hsiaw.M.Eng

Static behavior of cob: Experimental testing and finite element modeling

The aim of this paper is to implement a numerical model to reproduce the nonlinear behavior of cob walls under shear loading. Axial compression, pull-off, and diagonal compression tests were carried out to derive the mechanical parameters. In addition, the stress-strain relationships, the nonlinear behavior, and the failure modes were defined. The experimental results were then used to calibrate a finite-element model. The material behavior was simulated through a macromodeling approach adopting the total strain rotating crack model. A sensitivity analysis was conducted to assess the effects of varying the parameters with higher uncertainty on the structural behavior. The numerical model achieved good correspondence with the experimental results in terms of simulation of the shear stress-shear strain relationship and of damage pattern. (c) 2019 American Society of Civil Engineers.- The authors wish to express their gratitude to Mr. Andre Gardei for his important support in the experimental program and to Mr. Andreas Barner and Ms. Manuela Peuschel for their support with photogrammetric analyses. This study was funded by the European Commission within the framework of the project NIKER (Grant No. 244123) dealing with improving immovable Cultural Heritage assets against the risk of earthquakes. The study was partly financed by FEDER funds through the Competitivity Factors Operational Programme (project POCI-01-0145-FEDER-007633) and by national funds through the Portuguese Foundation for Science and Technology (project PTDC/ECM-EST/2777/2014 and Grant No. SFRH/BPD/97082/2013)