Microstructure and shear strength evolution of a lime-treated clay for use in road construction

The results of a comprehensive experimental programme are presented for assessing the long-term microstructural modifications and evaluating the effects of microstructural rearrangement on the stress–strain behaviour of a lime-treated high-plasticity clay for road embankments. The stress–strain behaviour at different lime content and curing time was investigated by means of direct shear tests; microstructural analyses were carried out combining Scanning Electron Microscope observations and Mercury Intrusion Porosimetry tests. The results show that the stress–strain behaviour of treated clay is strongly dilatant with a high peak of strength, which increases with time and lime content. Furthermore, a hyperbolic function may be used for predicting the increase in strength at the end of the stabilisation process. Microstructural analysis shows that the treatment induces a redistribution of the porosity between macro- and micropores and an increase in matric suction, associated to a low reduction of water content and to aggregates shrinkage. This behaviour is affected by lime content and curing time since it results from the formation of the pozzolanic compounds on the surface of clay aggregates that induces both a bonding between hardened clay aggregates and an increase of their interlocking degree, with a consequent increase in the shear strength

Analisi della microstruttura di un'argilla di alta plasticità trattata con calce

Nella nota si presentano i primi risultati di una indagine sperimentale volta a studiare l’effetto del trattamento con calce sulle caratteristiche microstrutturali di un’argilla di alta plasticità, proveniente dagli scavi eseguiti nel corso dei lavori di ammodernamento di una strada di grande comunicazione in Sicilia. I provini, compattati in laboratorio a diverse percentuali di calce, sono stati sottoposti a prove porosimetriche ad intrusione di mercurio MIP ed osservazioni al microscopio elettronico SEM. L’analisi dei risultati evidenzia che l’argilla trattata con calce assume una distribuzione dei pori tipica dei materiali a doppia porosità e che gli effetti sulla microstruttura dipendono dalla quantità di calce aggiunta e dal tempo di maturazione

Criteria for Laboratory Studies on Fine Soils Treated with Lime

When selecting the appropriate materials for constructing road infrastructures, an important way for minimizing both the economical and environmental impact is to make use of lime for treating those natural soils that, involved in the earthwork for opening road fences, are not suitable, as they are in nature, to fulfill the specific requirements for being used as part of road construction, such as road embankments (including the capping layer) or the improved subgrade or, again, the sub-formation. From this point of view, the treatment of fine soils with lime (if needed, with lime and cement) can be considered as one of the main measures for preserving the natural environment since it fulfills the principles of minimizing the use of not-renewable natural resources and maximizing the reuse of those natural resources involved, in any case, in the construction of a road infrastructure. Due to the importance of the technique examined here and to its topicality, as said before the aim of the present work is to provide a specific methodology and an overall view of the performance criteria for the experimental studies that, in the design phase of the road construction, have to be carried out in laboratory in order to evaluate the suitability of soils to lime treatment, the mix design of the lime treated mixture (type of lime to be used and its content), as well as the foreseeable execution conditions in the field that have to be considered, at a technical-economical level, in the contract specification and in the assessment of the cost of the project. After that, some peculiar aspects connected with the executive operation in the construction field will be examined, attention being paid to the construction machinery, to the specific equipment and to the procedures to be followed in order to perfect the treatment process and to control the quality of the final product

Riciclaggio di leganti contenenti scarti di gomma triturata, invecchiati a lungo termine - Recycling of laboratory-prepared long-term aged binders containing crumb rubber modifier.

Considerato che l'uso di gomma triturata (CRM) nella tecnica stradale negli USA risale ad oltre 40 anni fa, il riciclaggio di conglomerati contenenti CRM costituisce oggi un'area di ricerca di indubbio interess

Sviluppo di un mezzo di prova in laboratorio per la valutazione della resistenza meccanica degli strati superficiali

Gli Autori presentano i risultati di uno studiomirato alla messa a punto di un nuovo metodo di prova per la valutazione in laboratorio della resistenza agli sforzi tangenziali dei conglomerati bituminosi destinati a costituire strati d’usura. Alla base di un tale sviluppo prototipale, vi è la considerazione dellameccanica del contatto pneumatico-pavimentazione, al fine di riprodurre nel modo più realistico possibile l’effetto della sollecitazione tangenziale generata in corrispondenza di punti singolari, dato che proprio per questi punti è più difficile riprodurre in laboratorio la degradazione superficiale cui sono soggetti

Morfologia ed analisi delle immagini applicate allo studio dei bitumi modificati con polimeri

Vengono presentati i risultati di uno studio di laboratorio condotto su campioni di bitume modificato con diversi tipi di polimeri e precisamente Stirene-butadienestirene (SBS), Etilen-vinilacetato (EVA) ed etilen-butilacrilato (EBA), le cui proprietà fisico-chimiche vengono riportate nell’articolo

Influence of the Hourly variation of Temperature on the Estimation of Fatigue Damage and Rutting in Flexible Pavement Design

The work presented in this paper offers a contribution to understand to what extent different discretization modes for describing a whole day can affect the estimation of in-service durability of a flexible pavement, in relation with concomitant traffic flow fluctuations. Calculation of the stress–strain state was carried out with an elastic multi-layer model, and performance laws were implemented for verification of the major distress mechanisms that are able to affect the prediction of a flexible pavement’s service life. Results from the prediction of the fatigue life allow one to conclude that no big mistakes are made when evaluating the total damage by describing climatic conditions via daily average temperatures to be assigned to seasonal periods, as in routine design practice. The situation is completely different with regard to the estimation of damage for cumulated permanent deformation in bituminous layers: there is evidence for underestimation of the total rut depth, when calculated assuming a simple daily variation,as happens in the ordinary pavement design practice. A correct estimation of rut depth produced by accumulation of permanent deformation in bituminous mixtures cannot, in fact, leave out of consideration an accurate analysis and an equally correct superposition of the hourly variation in temperature and traffic

PG dei bitumi stradali per il territorio italiano

L’ARTICOLO SINTETIZZA IL LAVORO DI RICERCA SVOLTO DALL’UNIVERSITÀ DI PALERMO PER DEFINIRE - SU BASE TERRITORIALE NAZIONALE - LE TEMPERATURE CARATTERISTICHE DETERMINANTI PER LA QUALIFICAZIONE DEI BITUMI, CONFORMEMENTE ALLE SPECIFICHE SUPERPAVE. NE SONO DERIVATE CARTE TEMATICHE DELLE TEMPERATURE MASSIME E MINIME DI PROGETTO DELLE PAVIMENTAZIONI STRADALI CHE I TECNICI POTRANNO UTILIZZARE PER LA SELEZIONE DEI LEGANTI BITUMINOSI

Production of innovative, recycled and high-performance asphalt for road pavements

The paper deals with a specific laboratory study aiming at perfectioning recycled asphalt with high mechanical performance, for surface and structural layers of flexible pavements. The aim of the research was to combine in the samematerial themaximum possible quantity of recycled asphalt (RA), coming from degraded asphalt layers, together with high structural performance of the recycled mixtures obtained (mainly stability, load spreading properties, rutting and fatigue resistance) that should not be lower, or possibly better than those offered by traditional asphalt mixture, made with virgin binder and aggregate. For this purpose, innovative recycled mixtures, close-graded and with high mechanical performance, characterized by high content of recycled asphalt (up to 50%) and designed for surface, binder and base layers were investigated in a laboratory study. The results of physical and mechanical characterization tests show that, by controlling the homogeneity of recycled material and by using new bitumen with adequate rheological properties, it is possible to obtain paving mixtures with high content of recycled materials that, in relation to their intended use (surface, binder or base layer), can be considered as “high-performance mixtures