Influence of fly ash and decreasing water-powder ratio on performance of recycled aggregate concrete Investigation results of the combined effect of partial cement replacement with fly ash, and the use of recycled concrete aggregate to improve the sustainability of concrete, are presented in this paper. The compressive strength, capillary water absorption, water permeability, and chloride ion penetration, are analysed by testing nine concrete mixtures, in which the fly ash content and water to powder ratio were varied. The results show that compressive strength slightly decreases as the fly ash content increases, but that this can be compensated by reducing the water to powder ratio. Utjecaj letećeg pepela i smanjenja vodovezivnog omjera na svojstva betona s recikliranim agregatom U radu su prikazani rezultati ispitivanja zajedničkog učinka djelomične zamjene cementa s letećim pepelom i upotrebe recikliranog agregata s ciljem poboljšanja održivosti betona. Ispitivano je devet betonskih mješavina, u kojima su varirani količina letećeg pepela i vodovezivni omjer, analizirani su: tlačna čvrstoća, kapilarno upijanje, vodopropusnost i otpornost na prodor klorida. Dobiveno je da se povećanjem količine letećeg pepela neznatno smanjuje tlačna čvrstoća, ali da se smanjenjem vodovezivnog omjera to može nadomjestiti.

This paper presents results regarding the phase composition, microstructure and textural properties of two types of aggregates, which were prepared via crushing or pelletization of alkali-activated Class F fly ash and cured under different conditions. The alkali activator was the same for aggregate products, containing an alkaline solution consisting of 8 M NaOH and Na-silicate (8 M NaOH/Na-silicate = 1:2.5 mass ratio). The aforementioned properties were influenced by two different preparation procedures combined with varying curing regimes (under normal conditions at 20 °C, RH 40–60% for 28 and 120 days and under an accelerated regime, at 65 °C for 5 days). Aggregates were characterized using X-ray diffraction (XRD), Fourier-transform transmission infrared spectroscopy (FTIR), back scattered electron microscopy with energy dispersive spectrometer (BSE-EDS) analyses and mercury intrusion porosimetry (MIP). The results showed noteworthy structural and textural diversities between the two types of aggregate. The method of preparation and curing regime affected the formation of the N-A-S-H structure and the texture of the alkali-activated fly ash product, with the crushing method giving an advantage.

Fire statistics database and analysis represent the basis for the fire risk identification, analysis and assessment. Temporal analyses of timber structural fire incidents occurring from 2010 to 2014 in rural settlements in Serbia (Žabalj, Žitište) and in Novi Sad urban area from 2011 to 2013 are carried out. The aim of the study is to gather and analyse data on various causes of fires in order to determine the extent to which existing data can be used in fire risk assessment. This research illustrates how the patterns of timber structural fire incidents vary in urban and rural areas, with the time of the day, the day of the week, and the month of the year. It is shown that significant differences exist with respect to fire causation over time and the types of buildings and settlements.

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