Durability of Mortar Incorporating Ferronickel Slag Aggregate and Supplementary Cementitious Materials Subjected to Wet–Dry Cycles

This paper presents the strength and durability of cement mortars using 0–100% ferronickel slag (FNS) as replacement of natural sand and 30% fly ash or ground granulated blast furnace slag (GGBFS) as cement replacement. The maximum mortar compressive strength was achieved with 50% sand replacement by FNS. Durability was evaluated by the changes in compressive strength and mass of mortar specimens after 28 cycles of alternate wetting at 23 °C and drying at 110 °C. Strength loss increased by the increase of FNS content with marginal increases in the mass loss. Though a maximum strength loss of up to 26% was observed, the values were only 3–9% for 25–100% FNS contents in the mixtures containing 30% fly ash. The XRD data showed that the pozzolanic reaction of fly ash helped to reduce the strength loss caused by wet–dry cycles. Overall, the volume of permeable voids (VPV) and performance in wet–dry cycles for 50% FNS and 30% fly ash were better than those for 100% OPC and natural sand

The problem of estimating bed-load transport: a comparison between field measures and equations for two sand-bed Italian rivers

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Le strutture a gradinata: elementi naturali di stabilizzazione dei torrenti montani

Le strutture a gradinata (“step-pool”) sono degli elementi caratteristici distintivi degli alvei montani, ma sono state riconosciute come elemento trasversale di scabrezza, con caratteristiche proprie, solo a partire dagli anni ’80 (Whittaker & Davies, 1982; Whittaker & Jaeggi, 1982; Chin, 1989). Un sostanziale contributo ad un miglioramento delle conoscenze sulla morfologia e sulla dinamica degli step-pool è arrivato negli anni ’90 grazie ai lavori di Grant (Grant et al., 1990; Grant & Mizuyama, 1991), di Billi, Lenzi e D’Agostino (Billi et al., 1998; Lenzi et al., 1997; Lenzi & D’Agostino, 1998;) e di Buffington (1995). La maggior parte di questi studi riporta ricerche di campagna con l’obbiettivo di individuare i principali parametri che descrivono le strutture a gradinata (altezza e larghezza), ed i fattori che ne condizionano l’origine e la dinamica. Attraverso alcune esperienze di laboratorio si è cercato di individuare quali sono le condizioni idrauliche necessarie per la formazione degli step-pool (vedi per es. Grant & Mizuyama, 1991; Abrahams et al., 1995), mentre molto pochi sono gli studi che hanno analizzato il trasporto solido al fondo in relazione alla formazione e le caratteristiche geometriche degli step-pool (Billi et al., 1998; Lenzi et al., 1997; Lenzi & D’Agostino, 2000). Queste strutture trasversali ripetitive, oltre a conferire ai torrenti montani una morfologia caratteristica, hanno una grande importanza in termini di stabilizzazione degli alvei stessi e nel fornire un habitat acquatico favorevole allo sviluppo di specie ittiche di pregio. Le strutture a gradinata, infatti, si trovano in una condizione di equilibrio dinamico e possono distruggersi per poi riformarsi in punti diversi in condizioni di portata elevata, con tempi di ritorno di 30-50 anni (Lenzi & D’Agostino, 2000). Anche se molti autori ritengono che i grossi clasti che costituiscono l’ossatura delle strutture a gradinata si muovano raramente, è opinione degli scriventi che queste interagiscano con i sedimenti in transito, e che questi massi siano soggetti a muoversi, anche con portate e tiranti d’acqua relativamente modesti. Per provare questa ipotesi è fondamentale effettuare delle esperienze di campo. Una serie di rilievi sono stati avviati allo scopo di identificare i rapporti tra le caratteristiche idrauliche della corrente e la formazione, il consolidamento o la rimozione delle strutture a gradinata. Preliminarmente, viene tuttavia presentato un lavori di sintesi dei dati di letteratura al fine di verificare le relazioni prodotte dai vari autori. L’obiettivo finale della ricerca finanziata con fondi INRM rimane comunque quello di comprendere la dinamica di queste strutture e di definire possibili strategie di intervento per la stabilizzazione dei torrenti montani facendo ricorso soltanto a materiali naturali presenti in alveo

Step-pool sequences of steep mountain streams. A review of their characteristics and origin

Steep mountain streams are the most numerous and ubiquitous river type in the world and represent an essential component of mountain environment and landscape. Coarse grained, steep channels typically show reaches with a staircase bed morphology, known as step-pool sequences, that may alternate with simpler streambed morphology reaches such as runs or plane beds. Though in the last decade the attention of scientists about step-pools has increased remarkably, their morphological characteristics and the processes originating them are still matter of debate. In order to contribute to the understanding of step-pools and their geomorphic significance, a large database has been set up using field and laboratory data reported on both published scientific journals and unpublished studies. The review of the existing data has been paired by some field experiment on large particle entrainment and step-pool dynamics in a mountain stream of the Northern Apennines. The literature data review has shown that very few concepts about step-pool morphology and flow hydraulics can be considered as well established. For instance, many authors report about the inverse relation between step wavelength and streambed gradient, but plot diagrams of field and laboratory data show no evidence of such a relationship. This observation implies that the hypotheses based on such an assumption need at least to be revised. The lack of correlation between step wavelength and slope seems also to be affected by the non homogeneous methods to measure the basic step-pool geometry parameters as the long tail of high values of the step wavelength to channel width ratio indicate compared to a significant clustering of data around the value of one. Many authors assume that step-pool sequences are originated only by long return interval (30-50 years) floods, in mountain streams characterised by sediment supply limited conditions. Field experiment in the northern Apennines have shown that large particles making up the steps can be entrained and steps can be completely removed or new ones formed by flood flows close to or just a bit higher than bankfull stage (2-5 years). Moreover, field observations suggest that the condition of limited sediment supply is not a prerequisite for the formation of step-pool since they were found on the bottom of ephemeral gullies or in small channels incised in very steep (35° - 40°) scree deposits of arid and semi-arid environments. All these findings have fundamental implications on the development of a general theory to explain the origin of step-pool sequences. Substantially, three main hypotheses are reported in the literature: antidunes, maximisation of flow resistance and large keystones control. These theories are analysed in the light of the field experiments carried out in our study mountain streams and compared with a further elaboration of the literature data sets. Improving our understanding of the morphology and dynamics of step-pools will result in a sounder management of steep mountain streams and in eco-compatible interventions for channel restoration in extreme floods or anthropogenic impact aftermaths

La misura del trasporto solido nel Fiume Reno.

Questo lavoro nasce da una Convenzione di Ricerca, ancora in corso con l’Autorità di Bacino del Fiume Reno, dal titolo “Misura delle portate solide, in sospensione e al fondo, del fiume. Reno ed inquadramento geomorfologico e sedimentologico. La quantificazione del trasporto solido fluviale e lo studio dei processi attraverso cui esso avviene costituiscono aspetti di grande importanza, perché rappresentano il punto d’unione tra i fenomeni d’erosione nella parte montana dei bacini idrografici e quelli di deposito che si verificano nelle piane alluvionali e alla foce dei corsi d’acqua. Il trasporto solido influenza direttamente anche la dinamica morfologica dell’alveo attraverso i processi di scavo, sedimentazione ed erosione di sponda; il suo studio diventa pertanto basilare, non solo nella pianificazione della gestione delle coste, per le quali la conoscenza della quantità di sedimenti apportati a mare rappresenta un parametro nodale spesso non noto, ma anche per la scelta degli interventi di sistemazione, riqualificazione o rinaturalizzazione delle aste fluviali. Nelle pagine seguenti verranno proposti i risultati delle misure effettuate in situ, nel periodo 2004/2006. Durante gli eventi di piena sono state effettuate misure della portata liquida e solida, con particolare attenzione al trasporto solido di fondo, mentre in condizioni di magra è stato effettuato un campionamento del materiale del letto

Land use changes, torrent control works and sediment mining: effects on channel morphology and sediment flux, case study of the Reno River (Northern Italy)

As with most Italian rivers, the Reno River has a long history of human modification, related also to morphological changes of the lower Po River since Roman times, but in the last decades, significant land use changes in the headwaters, dam construction, torrent control works and extensive bed material mining have caused important channel morphology and sediment budget changes. In this paper, two main types of channel adjustment, riverbed incision and channel narrowing, are analysed. Riverbed degradation is discussed by comparing four different longitudinal profiles surveyed in 1928, 1951, 1970 and 1998 in the 120 km long reach upstream of the outlet. The analysis of channel narrowing is carried out by comparing a number of cross-sections surveyed in different years across the same downstream reach. Field sediment transport measurements of seven major floods that occurred between 2003 and 2006 are compared with the bedload transport rates predicted by the most renowned equations. The current low bedload yield is discussed in terms of sediment supply limited conditions due to land use changes, erosion-control works and extensive and out of control bed material mining that have affected the Reno during the last decades

Channel morphology evolution and bedload transport of the Reno River in northern Italy

In the last century decades many Italian rivers have been remarkably affected by human interventions; 3 main types of channel changes: streambed degradation, channel narrowing, channelization streambed degradation, ; Aim of this study: analyse Reno River adjustments during the last century and relate channel geometry response to the main disturbance factors

Channel morphology evolution and bedload transport of the Reno river in northern Italy

The Reno R., as many other Italian rivers, has been significantly affected by man activity since Romans time, but in the last decades significant land use changes in the headwater, extensive bed material mining, dams construction, torrent-control works and large fluids extraction from the underground caused important channel morphology and sediment fluxes changes. To better understand such morphological changes and their causes, the hydraulic geometry data of several cross sections and the longitudinal profile data of the Reno river, surveyed at different times, were analysed emphasizing a dramatic streambed incision that took place between 1950s and 1980s, with a volume of sediment lost of about 18 x106 m3. At the same time a field campaign was started in 2003 collecting representative bed material samples and sediment transport measurements with Helley-Smith bedload sampler to assess the present river dynamics and evolution. Bedload transport rate resulted very low also during floods larger than bankfull stage and even those equations renown in the literature to underpredict bedload transport overestimate the sediment transport of the Reno R. Among the equations used those predicting transport rates closer to the actual surveyed values are modified Meyer-Peter & Muller equation The river transport capacity always resulted by far larger than sediment supply and no significant relation was found between flow parameters and the bedload transport rates measured. The occurrence of cyclic peaks and lows of bedload rate and a clear seasonality were as well. Sediment deficit of the Reno river system results from many factors including an increase in forest cover, presence of dams for agricultural and hydroelectric purposes, engineering works on the watershed and on the river channel, large bed material exploitation and likely a decrease in flood frequency