Partners and International Organizations
(English)
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EAWAG, Dübendorf (CH), Università Ca'Foscari di Venezia (I), DVGW Technologiezentrum Wasser, Karlsruhe (D), University of Crete, Heraclion (GR)
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Abstract
(English)
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Motivation and goals
Through construction activities, large quantities of concrete admixtures are potentially introduced into the environment. The majority of these chemicals are sulfonated compounds, such as sulfonated naphthalene- and melamine-formaldehyde-condensates (SNFC and SMFC, respectively) used as superplasticisers, as well as plasticisers, such as lignosulfonates (LS). Today, these chemicals are employed in about 30 % of all new structures and are essential for a number of special applications. Although large amounts of SNFC, SMFC and LS are used and distributed widely, little is known about their life-cycles and environmental behaviour. Within the ANACAD project, BMG focused on building a mass-flow model to allow (i) a comparative analysis of all inputs, sinks and emissions within the complete life-cycle of a superplasticiser, and (ii) a risk assessment of the most relevant emissions. Supplementary experimental investigations of leaching and biodegradation behaviour were carried out together with our partners, who were also responsible for the development and application of required new analytical procedures. The goal was to develop an understanding of the overall movement and fate of a ubiquitously used chemical product group.
Leaching behaviour and biodegradation
The release of SNFC, SMFC and LS from concrete was investigated and quantified through controlled laboratory experiments. Sequential leaching experiments with finely crushed concrete specimen showed that the leachable fraction of these admixtures corresponds to ca. 20 % of the original input in the case of SNFC and LS, and ca. 60 % in case of SMFC. For SNFC it could be shown that only monomeric compounds (impurities or abiotic degradation products) can be leached, but not the actual active ingredient.
Biodegradation experiments focused (i) on tests that European regulatory agencies recommend or regard as compulsory, and (ii) on concrete leachates to supplement data for the actual products. Under OECD 301 biodegradation test conditions, only SNFC-derived leachates were readily biodegradable based on CO2 evolution. However, all leachates showed almost complete elimination based on DOC removal, showing that uptake by sludge is an important mechanism for removing SNFC-, SMFC- and LS-derived compounds from wastewater.
Mass-flow analysis
A mass-flow model considering all inputs, sinks and emissions within the complete life-cycle of a superplasticiser has been established for the application of SNFC in Switzerland (due to analytical limitations, no model could be developed for SMFC and LS). This model takes into account inputs of water, cement, aggregates and SNFC for the production of pre-cast, ready-mix and on-site concrete, using Switzerland as model system. The model distinguishes between active ingredient and different degradation products/impurities and keeps track of the masses of all entities during production of SNFC, the construction, use and decommissioning of concrete structures, as well as storage and different uses of waste concrete in order to calculate all emissions into treatment plants and receiving waters. Calculations for different scenarios show that (i) mainly monomeric, biodegradable SNFC constituents are emitted into the environment, and (ii) emissions from waste concrete (e. g. during storage or use in road foundations) are by far the most relevant. In comparison, the various wastewater streams from construction activities are not very important. Based on calculated annual mass-flows and emissions of SNFC-derived compounds, and on the expected environmental behaviour of the different emitted compounds, no detrimental effects on the environment or human health are expected. The mass-flow model developed within this project can be adapted to different countries/regions and products.
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