Frequency-dependent response of snow in uniaxial compression and comparison with numerical simulation

La determinazione del modulo di Young è fondamentale nello studio della propagazione di fratture prima del rilascio di una valanga e per lo sviluppo di affidabili modelli di stabilità della neve. Il confronto tra simulazioni numeriche del modulo di Young e i valori sperimentali mostra che questi ultimi sono tre ordini di grandezza inferiori a quelli simulati (Reuter et al. 2013)⁠. Lo scopo di questo lavoro è stimare il modulo di elasticità studiando la dipendenza dalla frequenza della risposta di diversi tipi di neve a bassa densità, 140-280 kg m-3. Ciò è stato fatto applicando una compressione dinamica uniassiale a -15°C nel range 1-250 Hz utilizzando il Young's modulus device (YMD), prototipo di cycling loading device progettato all'Istituto per lo studio della neve e delle valanghe (SLF). Una risposta viscoelastica della neve è stata identificata a tutte le frequenze considerate, la teoria della viscoelasticità è stata applicata assumendo valida l'ipotesi di risposta lineare della neve. Il valore dello storage modulus, E', a 100 Hz è stato identificato come ragionevolmente rappresentativo del modulo di Young di ciascun campione neve. Il comportamento viscoso è stato valutato considerando la loss tangent e la viscosità ricavata dai modelli di Voigt e Maxwell. Il passaggio da un comportamento più viscoso ad uno più elastico è stato trovato a 40 Hz (~1.1•10-2 s-1). Il maggior contributo alla dissipazione è nel range 1-10 Hz. Infine, le simulazioni numeriche del modulo di Young sono state ottenute nello stesso modo di Reuter et al.. La differenza tra le simulazioni ed i valori sperimentali di E' sono, al massimo, di un fattore 5; invece, in Reuter et al.⁠, era di 3 ordini di grandezza. Pertanto, i nostri valori sperimentali e numerici corrispondono meglio, indicando che il metodo qui utilizzato ha portato ad un miglioramento significativo.

Rheology of bituminous mastics and mortars containing crumb rubber from tyres: a novel dry-hybrid technology

This report studied the effect of crumb rubber in the asphalt mixture. The mixtures were also having limestone filler as a modifier. Mastic and mortar (mastic-fine aggregate system) mixture having different quantities of crumb rubber and limestone filler modifiers have been tested in order to find the best rutting resistance combination with an acceptable stiffness. The rheological tests on bituminous mastics and mortars have done in the laboratories in Nottingham Transport Engineering Centre (NTEC) and University of Bologna (DICAM). In the second chapter, an extensive literature review about the binders, additives, asphalt mixtures, various modelling and testing methods have been reviewed. In the third chapter, the physical and rheological properties of the binders have been investigated using both traditional devices and DSRs. The forth chapter is dedicated to finding the behaviour of the modified mastics (Binder-modifier system) with different combinations. Five different combinations of crumb rubber and limestone filler mastic tested with various methods using Dynamic Shear Rheometers. In the fifth chapter, in order to find the effect of the modifiers in the rheological properties of the complete asphalt mixture, the fine aggregates added to the same mastic combinations. In this phase, the behaviour of the system so-called mortar; binder, rubber, filler and fine aggregates) has been studied using the DSR device and the traditional tests. The results show that using fine crumb rubber reduces the thermo sensibility of the mastic (Binder Bitumen System) and improves its elasticity. Limestone filler in the other hand increases the mixture stiffness at high Frequencies. Another important outcome of this research was that the rheological properties of the mortars were following the same trend of the mastics, therefore study the rheological properties of the mastic gives an upright estimation of the mortar.

Development and Characterization of Biopolymers

Development and characterization of biopolymers was done in AIJU’s laboratories. AIJU, Technological Institute for children’s products and leisure is based in Spain. The work has the aim to study qualities and characteristics of bioplastics’ blends, in order to design where improvements can be executed. Biopolymers represent a sector with great development possibilities because they combine high technical potential and eco-sustainability. Nowadays, plastic pollution has becoming increasingly concerning, particularly in terms of management of waste. Bioplastics provide an alternative for the disposal of products, reducing the volume of waste and enhancing the end of life recovery. Despite the growing interest in biopolymers there is some gaps that need be filled. The main objective on this work, is the optimization of bioplastics mechanical properties, to find suitable substitutes, as similar as possible to conventional plastics. Firstly, investigations on processability of biomaterials has been deepen since the project deals with toy manufacturing’s sector. Thus, starting from laboratory scale the work aspires to expand industrially. By working with traditional machines, it was notable that, with some limited modifications, the equipment can perform the same functions. Therefore, operational processes do not emerge as an obstacle to the production chain. Secondly, after processing bio-blends, they are characterized by thermal tests (melt flow index, differential scanning calorimetry-DSC, thermogravimetry-TGA) and mechanical tests (traction and flexural tests, Charpy impact, SHORE D hardness and density). While the compatibility does not show relevant results, mechanical improvements has been visualized with addition of more ductile materials. The study was developed by inclusion of sustainable additive VINNEX® to blends. The thesis has highlighted that integration of more flexible materials provides elasticity without compromising bioplastics’ properties.