•Use of alternative materials in concrete industry is discussed (by means of LCA).•The environmental impacts of “green concretes” are significantly reduced.•LCA results are not very sensitive to the ...delivery distances of alternative materials.
A number of green concrete mixes having similar basic properties were evaluated from the environmental point of view by means of the Life Cycle Assessment method, and compared with a corresponding conventional concrete mix. The investigated green concrete mixes were prepared from three different types of industrial by-products, i.e. (1) foundry sand, and (2) steel slag, both of which were used as manufactured aggregates, and (3) fly ash, which was used as a mineral admixture. Some green concrete mixes were also prepared from a recycled aggregate, which was obtained from reinforced concrete waste. In some of the green concrete mixes the recycled aggregate was used in combination with the above-mentioned types of manufactured aggregate and fly ash. All of these materials are able, to some extent, to replace natural aggregate or Portland cement in concrete mixes, thus providing an environmental benefit from the point of view of the saving of natural resources. Taking into account consequential modelling, the credit related to the avoidance of the need to dispose of the waste materials is considered as a benefit. In case of the recycling of waste concrete into aggregate, credit is attributed to the recovery of scrap iron from the steel reinforcement. In the case of the use of steel slag, credit is attributed to the recovery of metals, which are extracted from the slag before being used as an alternative material. The disadvantage of using alternative materials and recycled aggregates can sometimes be their relatively long delivery distance. For this reason, a transport sensitivity analysis was carried out. The results indicate that the use of the discussed alternative and recycled materials is beneficial in the concrete production industry. Preference is given to the fly ash and foundry sand scenarios, and especially to those scenarios which are based on the combined use of recycled aggregate with these two alternative materials. It was found that longer delivery distances of the alternative materials do not necessarily affect the results significantly. However, variable delivery distances may have a greater effect when choosing between different alternative scenarios.
Abstract
This study introduces a novel geotechnical composite material comprising two types of fill material sourced from the paper industry—deinking paper sludge ash (DPSA) and deinking paper sludge ...(DPS). Five composites with different DPSA and DPS contents were investigated. Two composites were selected for further analyses. The technology and procedure for composite installation were implemented in field tests. The composites with 80% and 70% DPSA exhibited the elasticity required to withstand minor landslide slip deformations, in addition to achieving sufficiently high values of uniaxial compressive strength. The composites had a low maximum dry density value, which led to fewer settlements in the entire support structure. The enhanced shear characteristics can enable the construction of a thinner retaining wall. The delay between preparation and installation of the composites was further investigated. The field tests confirmed that the composites with 80% and 70% DPSA can be installed on the construction site 4 h and even 24 h after mixing. In 2018, a retaining wall structure with 70% DPSA and 30% DPS was successfully implemented near a railway line using conventional technology as followed-up research to the herein presented study. Results have been derived from work performed in the scope of the H2020 Paperchain project in which novel circular economy models centered on the valorization of the waste streams generated by the pulp and paper industry as secondary raw material for several resource-intensive sectors, including the construction sector, have been developed. Environmental benefits are savings in natural raw materials, reduction of landfill disposal as well as CO
2
emission reduction.
Zero-valent iron nanoparticles (nZVI) exhibit great potential for the removal of metal contaminants from wastewater. After their use, there is a risk that nZVI will remain dispersed in remediated ...water and represent potential nano-threats to the environment. Therefore, the behaviour of nZVI after remediation must be explored. To accomplish this, we optimised a novel method using single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) for the sizing and quantification of nZVI in wastewater matrices. H2 reaction gas was used in MS/MS mode for the sensitive and interference-free determination of low concentrations of nZVI with a low size limit of detection (36nm). This method was applied to study the influence of different iron (Fe) loads (0.1, 0.25, 0.5 and 1.0gL−1) and water matrices (Milli-Q water, synthetic and effluent wastewater) on the behaviour of nZVI, their interactions with Cd2+ and the efficiency of Cd2+ removal. The aggregation and sedimentation of nZVI increased with settling time. Sedimentation was slower in effluent wastewater than in Milli-Q water or synthetic wastewater. Consequently, Cd2+ was more efficiently (86%) removed from effluent wastewater than from synthetic wastewater (73%), while its removal from Milli-Q water was inefficient (19%). The trace amounts of Cd2+ that remained in the remediated water were either dissolved or sorbed to residual nZVI. The results of the nanoremediation of effluent wastewater with varying Fe loads showed that sedimentation was faster at higher initial concentrations of nZVI. After seven days of settling, low concentrations of Fe remained in the effluent wastewater at Fe loads of 0.5gL−1 or higher, which could indicate that the use of nZVI in nanoremediation under the described conditions may not represent an environmental nano-threat. However, further studies are needed to assess the ecotoxicological impact of Fe-related NPs used for the nanoremediation of wastewaters.
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•The use of nZVI in remediation of wastewaters can present potential nano threat.•nZVI settling and Cd removal efficiency during wastewater treatment was followed.•Use of H2 reaction gas enabled interference-free measurement of nZVI by SP-ICP-MS.•Water matrix and Fe load of nZVI play key roles in the nanoremediation process.•Cd2+ was the most efficiently removed from effluent wastewater.
Carbon steel slag is quite commonly used in road construction to replace natural aggregate. Since it is important to evaluate such a replacement from the environmental point of view, a Life Cycle ...Assessment was carried out in order to compare the environmental impacts of the construction of asphalt wearing courses with the use of siliceous aggregates (the “conventional scenario”), and the use of alternative, steel slag aggregates (the “alternative scenario”). The main advantage of the alternative scenario is that a reduction can be achieved in the consumption of natural aggregate, as well as in the quantity of slag deposited on landfill sites. On the other hand larger amount of bitumen is needed as a binder. However, the results of the Life Cycle Assessment (based on consequential modelling) revealed that the alternative scenario is to be significantly preferred if the following impact categories are taken into account: Acidification, Eutrophication, Photochemical Ozone Creation and Human Toxicity. In the case of the discussed indicators, the impacts are reduced to a level equal to about 80% of the conventional scenario impacts. This benefit was additionally evaluated by means of a transport sensitivity analysis, which provided results which could be useful for road managers working on case studies using similar construction materials. The alternative scenario is more sustainable than the conventional scenario with regard to the discussed impact categories even when taking into account long delivery distances of the steel slag aggregate (∼100 km) and minimal delivery distances of the siliceous aggregate. Considering similar delivery distances in both scenarios, the alternative scenario was found to be beneficial also with regard to the Global Warming, but only when the delivery distance of the steel slag aggregates did not exceed 160 km.
•Use of natural and artificial aggregates were compared by means of LCA.•The research findings can be interesting for road construction managers.•Use of EAF C slag aggregates is beneficial from environmental point of view.
Anion-exchange high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was used for simultaneous speciation of chromate, molybdate and arsenate. The ...repeatability of measurement tested for multielemental standard solution of chromate, molybdate and arsenate (50 ng mL
of Cr, Mo and As, pH 12) was ± 0.9%, ± 4.9% and ± 4.1%, respectively. Limits of quantification (LOQs) were low (0.53 ng mL
for chromate and arsenate and 1.03 ng mL
for molybdate, expressed as elemental concentrations). A wide linear concentration range (from LOQs to 500 ng mL
) was obtained. The performances of this method enabled simultaneous speciation analysis in samples of water from lysimeters, in which three geotechnical composites, made of recycled waste, were installed in parallel in compacted and uncompacted, 20 times less dense form. The release of toxic chemical species of elements into lysimetric waters from each composite was studied. The results revealed that the degree of compaction and the composition of composites both have a significant influence on leaching of chromate, molybdate and arsenate. The study proved that multielemental speciation analysis is fast and cost-effective method for investigations of environmental impacts of materials, made from recycled waste, and can be used in other similar applications.
This paper presents an experimental investigation of the compressive behavior of high-strength self-compacting concrete exposed to temperatures up to 600 °C. Ten different concrete compositions were ...tested, in which part of the cement (by weight) was replaced by three different mineral additives (5-15% metakaolin, 20-40% fly ash and 5-15% limestone). The stress-strain curves, compressive strength, modulus of elasticity and strain at peak stress were evaluated from uniaxial compression tests. Scanning electron microscope micrographs were also taken to evaluate the damage caused by the high temperatures. A sharp decrease in mechanical properties and an increase in peak strain were observed already after 200 °C for all mixes tested. The different mineral additives used in this study affected the variations of residual compressive strength by 24% and peak strain by 38%, while the variations of residual modulus elasticity were 14%. Comparing the obtained results with the recommendations for compressive strength given in regulatory code EN 1992-1-2 for high strength concrete, it can be concluded that the strength loss observed in EN 1992-1-2 at temperatures up to 400 °C is too conservative. The Popovics model for the relationship between stress and strain provided a good approximation for the experimentally determined stress-strain curves at different temperatures.
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•Different types of nZVI were used for the remediation of effluent water from SBWTP.•Remediation depends on the reactivity of nZVI, iron load, mixing and settling times.•In-house nZVI ...effectively disinfected effluent water, but contaminated it with B.•Ammonium N was formed from organic N and by the reduction of nitrates and nitrites.•Nanofer25 slurry the most effective removal of elements and inactivated pathogens.
Nanoremediation procedures are usually designed so that only one contaminant or similar class of contaminants is being considered. In the present work, a holistic approach was applied towards processes which simultaneously occur after the treatment of real effluent water from a small biological wastewater treatment plant (SBWTP) with different nanoscale zero-valent iron (nZVI) particles. Three different types of nZVI particles were tested: in-house nZVI, commercially available Nanofer STAR and Nanofer25 slurry, which differ in reactivity and their methods of synthesis. In order to optimise the conditions for the efficient removal of selected elements, nitrogen species, and pathogenic bacteria (Coliform bacteria, Escherichia coli, Intestinal Enterococci and Clostridium perfringens), effluent water samples were treated with different iron loads from each of the investigated nZVI at various mixing and settling times.
The results demonstrated that in-house nZVI, which is the most reactive of the nanoparticles tested, most effectively removed metals and inactivated pathogenic bacteria. However, the application of in-house nZVI is restricted, as it contaminates the remediated water with B, which originated from the reagents used in its synthesis. To a certain extent, all of the investigated types of nZVI reduced nitrates and nitrites to ammonium cations. The additional formation of ammonium nitrogen was the result of the interactions of the nZVI with the organic nitrogen present in the effluent water. At an optimised iron load, mixing time, and settling time, the most efficient removal of elements and disinfection of pathogens was achieved when Nanofer25 slurry was applied.
Based on a road reconstruction case study, the advantages and disadvantages of two alternative road pavement rehabilitation techniques, a hypothetically defined comparable traditional approach and an ...actually used cold-in-place-recycling approach, both of which enable a comparable extension of road service life of about 20 years, were investigated by means of Life Cycle Assessment. The results showed that the considered environmental impacts of the traditional approach exceeded those of the cold-in-place-recycling approach: by only 1% with regard to Global Warming, by 18% with regard to Acidification, by 15% with regard to the Abiotic Depletion of Fossil Fuels, and by 16% with regard to primary energy consumption. In the case of the traditional approach, the use of larger amounts of natural aggregate and the transportation of materials significantly contributed to emissions and the consumption of fossil fuels and energy, whereas the cold-in-place-recycling approach was sensitive to the use of cement, whose production results in relatively high emissions, especially of greenhouse gasses. In the case of the traditional approach, sensitivity analyses were carried out with regard to the use of aggregate from a quarry instead of a gravel pit, and to the delivery distance of material hauled away from the distressed road during rehabilitation works (extending the one-way delivery distances from 20 to 100 km). It was found that, if aggregate from a quarry is used instead of from a gravel pit, then the various environmental impacts of the traditional approach would exceed those of the cold-in-place-recycling approach by factors which range between 1.3 and 1.7. Increasing the transportation distance of hauled-away materials from 20 km to 100 km, the impacts of the traditional approach would exceed the impacts of the cold-in-place-recycling approach by a factor of 1.4 (Global Warming) and 1.6 (Acidification and Abiotic Depletion of Fossil Fuels). A further sensitivity analysis was carried out in the case of the cold-in-place-recycling approach, with regard to the use of Portland cements containing different amounts of clinker. It was found that the use of cements with a higher clinker content results in an increase in the Global Warming impact to a level significantly higher than that of the traditional approach.
•Environmental benefit of recycling versus conventional scenario was confirmed.•However, carbon footprints of two compared scenarios are similar.•Recycling scenario is very sensitive to the type of Portland cement.
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•Variations in chemical composition have an effect on the slag mineralogy.•The leaching of ladle slag is governed by surface phenomena.•Variations in cooling treatment and steel type ...have a small effect on leachability.•The solubility-controlling minerals were predicted by geochemical modelling.•Mineralogical identification of the solubility-controlling minerals (Ca(OH)2, CSH).
In this study, the leachability of freshly produced ladle slag derived from both austenitic and ferritic stainless steel production, and from electrical and structural steel production, was investigated, in order to determine whether variations in the chemical and mineralogical composition of these slags affect their leaching behaviour. The effect of the method used for slag cooling was also studied. The results obtained by using the single batch test were combined with those obtained by means of more sophisticated characterisation leaching tests, which, in combination with geochemical speciation modelling, helped to better identify the release mechanisms and phases that control the release of individual elements. It was found that, although variations in the chemical composition of the slag can affect the slag's minerology, neither such variations, nor the choice of the slag cooling treatment, have a significant effect on the leachability of individual elements, since the leaching is governed by surface phenomena. In fact, the mineral transformations on the slag surface, rather than the bulk mineral composition, dictate the release of these elements from the ladle slag. The solubility-controlling phases were predicted by multi-element modelling, and verified to the extent made possible by the performed mineralogical investigations.
•Cement pastes containing α-Al2O3 submicron particles and a PCE superplasticizer.•Microstructure of the fresh pastes is controlled by the Specific Surface Area.•Widening particle size distribution ...has a minor role on packing and porosity.•Progressive initial hydration retardation on increasing α-Al2O3 particle content.•Slightly enhanced microstructure of hardened pastes at replacement levels of 2 and 4wt%.
The aim of this study was to clarify the micro-scale processes which control the fresh and hardened properties of hydrating cement pastes containing up to 10wt% of α-Al2O3 submicron particles and a polycarboxylate-type superplasticizer. The main factor controlling the changes in the microstructure and properties of the fresh pastes with increasing α-Al2O3 cement replacement levels was found to be the increase in the total specific surface area, whereas particle packing played only a minor role. However, in the case of the hardened pastes much more complex and somewhat counteracting effects were observed. Depending on the cement replacement level of the pastes, the sum of these effects was either a hardly noticeable improvement in their mechanical properties, compared to those of the reference paste, or even a reduction in them. These differences decreased with increasing curing time.
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