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Travel surveys provide valuable inputs to a variety of models. While they are well-established, and reliable, they are also associated with large expenses (both in terms of time and actual cost). With the emergence of social media and alternative data sources, researchers and practitioners often wonder if such data sources can supplement (or obviate the need for) conventional data collection efforts. In this research, we empirically examine of the use of different social media data for such applications. Data from three popular Social Media is examined and compared with data from conventional travel-diary surveys for the city of Thessaloniki, Greece. Both spatial and temporal aspects of the activities' representation are considered. The findings of this research contribute towards the identification of methodologies that can support the inference of meaningful travel information from Social Media, which could in turn improve ITS applications.

Leisure activities travel demand plays an important role in transportation, as it accounts for a significant amount of trips performed. Due to data limitations the examination of this trip purpose has received moderate attention so far. The evolution of pervasive systems in conjunction to the increased use of Social Media provide a large amount of data that can be used for the development of leisure activities travel demand models. This study provides an initial investigation of the data collected from Social Media and the potential of using it for leisure activities demand modelling. A data analysis framework is provided that distinguish user classes of residents and tourists and investigates the temporal and spatial patterns as well as the probability of deriving activity locations.

The aim of the present study is to test diatomite rocks as alternative pozzolanic materials that could be used for the manufacturing of pozzolanic cements in Greece. The diatomite rocks used occur in Samos Island and in the Elassona, Greece. The Samos diatomites were mainly consisted of calcite and opal-A, whereas the Elassona diatomite consisted of opal-A, clay minerals, feldspars and quartz. As a result, the Samos samples were rich in CaO and SiO2, while the Elassona ones were rich in SiO2, Al 2O3 and Fe2O3. The specific surface of the laboratory-produced cements was high, with the grindability of the Elassona diatomites being lower than that of Samos. The water demand of all blended cements was higher than that of the laboratory produced OPC. The late compressive strength of most diatomite cements studied was improved with respect to the lab OPC. © 2004 Elsevier Ltd. All rights reserved.

A clayey diatomite rock originating from Greece, mainly composed of opal-A, smectite and vermiculite was tested for the production of lightweight aggregates (LWAs) by mixing the raw material with 2-5% sawdust. The mixtures were pelletized, dried at 100 °C and burnt to 1100 °C. The laboratory LWA had strength and density similar to commercial LWAs originating from Germany and Denmark. The porosity of their mantle was lower than that of the inner part. Pores were abundant, ranging from irregular to spherical and from 2 to 500 μm in size, resulting in low apparent density values. The texture of the Greek and German LWA was clearly amorphous, whereas subhedral crystal assemblages were detected in the interior of the Danish LWAs. LWA produced by the Greek clayey diatomite rocks can be utilized for the production of LWA on an industrial scale. © 2004 Elsevier Inc. All rights reserved.

Tuffaceous rocks and lavas of the Pliocene age exist on Kimolos Island, Aegean Sea, Greece. These tuffaceous rocks have been locally transformed to clinoptilolite and mordenite tuffs. The former are porous and relatively soft, whereas the latter are massive and hard. The diagenetic transformation of volcanic glass to clinoptilolite and mordenite took place in an open hydrological system by circulation of alkaline ground waters. The fluids responsible for mordenite formation had probably higher temperature than that of clinoptilolite due to high heat flow rates originating from the emplacement of lavas in their vicinity. Even though clinoptilolite and mordenite tuffs have similar chemical analyses, the composition of mordenite exhibits lower variability than that of clinoptilolite. Regarding cement properties, those cements containing mordenite tuff have a slightly higher strength than that of cements with either Milos pozzolana or clinoptilolite tuff. The higher strength of mordenite cement is probably due to the higher zeolite content of the mordenite tuff and also its higher reactive silica content. In addition, when compared to Milos pozzolana, the zeolite tuffs demand more water to produce paste of the same consistency. This means that when zeolitic cement is used for concrete production, it is likely that a superplasticizer needs to be added in the mixture. In conclusion, the use of zeolitic tuffs as an additive in cement is promising. However, the full evaluation of these materials demands a thorough examination in areas related to their specialised properties and also extended testing on concrete produced with these materials. © 1997 Elsevier Science Ltd.