Carbonation of concrete with construction and demolition waste based recycled aggregates and cement with recycled content

Durability is a major concern in concrete (particularly recycled concrete) structures exposed to carbonation-induced corrosion, given the social, economic, environmental and safety implications involved. This article explores carbonation performance in concrete with 25% or 50% mixed recycled construction and demolition waste aggregate, alone or in conjunction with cement containing 25% fired clay construction and demolition waste. Irrespective of cement type, the mean carbonation depth was slightly greater in materials with 25% or 50% recycled aggregate than in concretes with 100% natural aggregate, although the difference was not statistically significant for the 25% replacement ratio. In all the concretes studied, the carbonation coefficient was below the 4 mm/yr0.5 indicative of good quality. Based on the prediction model proposed in Spain’s concrete code, reinforcement passivity was guaranteed in all these types of concrete when exposed to class XC1 to XC4 carbonation environments for substantially longer than their 100 year design service life.This study was funded under research projects BIA 2013-48876-C3-1-R, BIA2013-48876-C3-2-R and BIA2016-76643-C3-1-R awarded by the Ministry of Science and Innovation and grant GR 18122 awarded to the MATERIA Research Group by the Regional Government of Extremadura and the European Regional Development Fund, ERDF. In 2016 University of Extremadura teaching and research personnel benefitted from a mobility grant (MOV15A029) awarded by the Regional Government of Extremadura and in 2018 from a José Castillejo (CAS17/00313) scholarship granted by the Spanish Ministry of Education, Culture and Sport. Philip Van den Heede is since October 2017 a postdoctoral fellow of the Research Foundation—Flanders (FWO) (project number 3E013917) and acknowledges its support.Peer reviewe

Addressing potential sources of variation in several non-destructive techniques for measuring firmness in apples

Measurements of firmness have traditionally been carried out according to the Magness Taylor (MT) procedure; using a texture analyser or penetrometer in reference texture tests. Non-destructive tests like the acoustic impulse response of acoustic firmness sensors (AFSs), a low-mass impact firmness sensor Sinclair International (SIQ-FT) and impact test (Lateral Impact – UPM) have also been used to measure texture and firmness. The objectives of this study were to evaluate the influence of different sources of variation in these three non-destructive tests and to evaluate their respective capabilities of discriminating between fruit maturity at two different harvest dates, turgidity before and after dehydration treatment and ripening after different storage periods. According to our results, fruit studied an unexpected AFS trend with turgidity. Contact measurements (Lateral Impact – UPM and SIQ-FT) appeared highly sensitive to changes in turgidity, but were less able to follow changes in ripening caused by storage period. Contact measurements were suitable for detecting differences between fruits from different harvest dates and showed higher correlation coefficients with reference texture tests than acoustic measurements. The Lateral Impact – UPM test proved better at separating fruits according to turgidity than the SIQ-FT instrumen

Microbial interactions with mineral building materials

An overview is presented of research on the interactions between micro-organisms and mineral building materials (concrete and natural stone), performed at the Magnel laboratory for concrete research of Ghent University, in collaboration with other research groups. A first research topic is the deterioration process taking place in concrete sewer systems and manure storage facilities, called biogenic sulphuric acid (BSA) corrosion. This process can be mimicked by pure chemical or microbial degradation tests. The problem of chemical tests with sulfuric acid is that they do not take into account a possible biocidal activity of the concrete. Nevertheless, microbial tests confirmed that it is preferable to use a material with a high neutralisation capacity to limit bioteterioration. Therefore, a model for biogenic sulfuric acid attack should include the concrete alkalinity as a parameter, next to other durability related parameters such as porosity. A second topic is the application of bacteria for bioconsolidation and self-healing. Bacterially induced carbonate precipitation was investigated as a surface treatment for cementitious materials and limestone. The biodeposition treatment resulted in an increased resistance of concrete towards water absorption, carbonation, chloride penetration and freezing and thawing. In porous limestone, consolidation by biodeposition could be achieved at depths up to 30 mm and more. The overall strength increase in this zone amounted to more than 300%. With regard to microbial selfhealing, bacteria were immobilized on diatomaceous earth or inside microcapsules, before introduction into the concrete mixture. Incorporation of diatomaceous earth with Bacillus sphaericus in mortar specimens allowed selfhealing of 0.15 mm - 0.17 mm cracks by calcium carbonate precipitation, 40 days after crack formation. Introduction of bacterial microcapsules enabled self-healing of cracks having a width of almost 1 mm in three weeks time. Another application of micro-organisms on concrete is for the creation of green concrete walls. For these walls the concrete is purposefully designed to obtain a specific microstructure and bioreceptivity as substrate for biological growth. Concrete with magnesium phosphate cement and carbonated Portland cement concrete were applied to obtain sufficiently low pH values. Other important factors that determine bioreceptivity such as concrete porosity and surface roughness were also optimized for biological growth

Nitrate reducing CaCO3 precipitating bacteria survive in mortar and inhibit steel corrosion

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Waste fibrecement: An interesting alternative raw material for a sustainable Portland clinker production

This paper aims to examine the use of fibrecement waste as an alternative raw material for Portland clinker kilns with enumeration of possible limitations. Numerical simulations were carried out to maximise the use of fibrecement waste in clinker kilns taking into account the compositional variation of the waste, its behaviour within a clinker kiln, the impact on the energy consumption and finally the influence on the carbon footprint calculated from the decarbonation. Furthermore, experimental clinkers were produced corresponding with waste dosages that were esteemed as realistic by the numerical simulations. These clinkers were fully analysed and evaluated according to the above described evaluation concept. © 2012 Elsevier Ltd