Sustainable insulating foams based on recycled polyurethanes from construction and demolition wastes

Background: Polyurethane (PU) foams contained in construction and demolition wastes (CDW) represent a great environmental impact, since they usually end in landfill or incineration processes. The goal of this work is to develop a way to formulate PU foams, maintaining (or ever improving) their performance, by the re-use of those industrial wastes. This procedure will allow minimize both the volume of disposal to be treated by other ways and the amount of pristine raw material needed to produce new PU foams. Methods: In this work, new rigid and soft polyurethane (PU) foams have been formulated with addition of recycled PU foams coming from demolition of buildings. Density, Fourier transform infrared analysis, compression properties and thermal conductivity were measured to characterize the resulting foams. Results: The work showed that addition of filler coming from recycled PU foams should be limited to low percentages, in order to allow good foam evolution from the reactants. Thermal conductivity values of modified rigid foams are worse than those of pristine foam, which is undesirable for thermal insulation purposes; however, in the case of soft foams, this parameter improved to some extent with low levels of recycled PU foam addition. Conclusions: The studied procedure could contribute to reduce the thermal conductivity of pristine soft PU foam, which would be of interest for applications where thermal insulation matters.

Alkali-Activated Hybrid Cements Based on Fly Ash and Construction and Demolition Wastes Using Sodium Sulfate and Sodium Carbonate

This article demonstrates the possibility of producing alkali-activated hybrid cements based on fly ash (FA), and construction and demolition wastes (concrete waste, COW; ceramic waste, CEW; and masonry waste, MAW) using sodium sulfate (Na2SO4) (2–6%) and sodium carbonate (Na2CO3) (5–10%) as activators. From a mixture of COW, CEW, and MAW in equal proportions (33.33%), a new precursor called CDW was generated. The precursors were mixed with ordinary Portland cement (OPC) (10–30%). Curing of the materials was performed at room temperature (25 °C). The hybrid cements activated with Na2SO4 reached compressive strengths of up to 31 MPa at 28 days of curing, and the hybrid cements activated with Na2CO3 yielded compressive strengths of up to 22 MPa. Based on their mechanical performance, the optimal mixtures were selected: FA/30OPC-4%Na2SO4, CDW/30OPC-4%Na2SO4, FA/30OPC-10%Na2CO3, and CDW/30OPC-10%Na2CO3. At prolonged ages (180 days), these mixtures reached compressive strength values similar to those reported for pastes based on 100% OPC. A notable advantage is the reduction of the heat of the reaction, which can be reduced by up to 10 times relative to that reported for the hydration of Portland cement. These results show the feasibility of manufacturing alkaline-activated hybrid cements using alternative activators with a lower environmental impact.

Sustainable Solutions with Geosynthetics and Alternative Construction Materials—A Review

Geosynthetics have proven to provide sustainable solutions for geotechnical and geoenvironmental problems when used with natural materials. Therefore, the expected benefits to the environment when geosynthetics are associated with unconventional or alternative construction materials will be even greater. This paper addresses the use of geosynthetics with wasted materials in different applications. The potential uses of alternative materials such as wasted tires, construction and demolition wastes, and plastic bottles are presented and discussed considering results from laboratory and field tests. Combinations of geosynthetics and alternative construction materials applied to reinforced soil structures, drainage systems for landfills, barriers, and stabilisation of embankments on soft grounds are discussed. The results show the feasibility of such combinations, and that they are beneficial to the environment and in line with the increasing trend towards a circular economy and sustainable development.

Mortars with CDW Recycled Aggregates Submitted to High Levels of CO2

Construction and demolition wastes (CDW) are generated at a large scale and have a diversified potential in the construction sector. The replacement of natural aggregates (NA) with CDW recycled aggregates (RA) in construction materials, such as mortars, has several environmental benefits, such as the reduction in the natural resources used in these products and simultaneous prevention of waste landfill. Complementarily, CDW have the potential to capture CO2 since some of their components may carbonate, which also contributes to a decrease in global warming potential. The main objective of this research is to evaluate the influence of the exposure of CDW RA to CO2 produced in cement factories and its effect on mortars. Several mortars were developed with a volumetric ratio of 1:4 (cement: aggregate), with NA (reference mortar), CDW RA and CDW RA exposed to high levels of CO2 (CRA). The two types of waste aggregate were incorporated, replacing NA at 50% and 100% (in volume). The mortars with NA and non-carbonated RA and CRA from CDW were analysed, accounting for their performance in the fresh and hardened states in terms of workability, mechanical behaviour and water absorption by capillarity. It was concluded that mortars with CDW (both CRA and non-carbonated RA) generally present a good performance for non-structural purposes, although they suffer a moderate decrease in mechanical performance when NA is replaced with RA. Additionally, small improvements were found in the performance of the aggregates and mortars with CRA subjected to a CO2 curing for a short period (5 h), while a long carbonation period (5 d) led to a decrease in performance, contrary to the results obtained in the literature that indicate a significant increase in such characteristics. This difference could be because the literature focused on made-in-laboratory CDW aggregates, while, in this research, the wastes came from real demolition activities, and were thus older and more heterogeneous.

Uptake of potentially toxic elements by edible plants in experimental mining Technosols: preliminary assessment

A study was carried out to evaluate the absorption of potentially toxic elements from mining Technosols by three types of vegetable plants (broccoli (Brassica oleracea var. italica), lettuce (Lactuca sativa) and onion (Allium cepa)), the different parts of which are intended for human and farm animal consumption (leaves, roots, edible parts). The preliminary results obtained highlight the importance of the design of the mining Technosols used for agricultural purposes, obtained from soils and sediments of mining origin and amended with residues of high calcium carbonate concentrations (limestone filler and construction and demolition wastes). The experiment was carried out in a greenhouse, and the total metal(loid)s concentration (As, Pb, Cd, Cu, Fe, Mn and Zn) of the soil, rhizosphere, aqueous leachates and plant samples was monitored, the translocation and bioconcentration factors (TF and BCF, respectively) being calculated. The characterization of the soils included a mobilization study in media simulating different environmental conditions that can affect these soils and predicting the differences in behavior of each Technosol. The results obtained showed that the levels of potentially toxic elements present in the cultivated species are within the range of values mentioned in the literature when they were cultivated in soils with calcareous amendments. However, when the plants were grown in contaminated soils, the potentially toxic elements levels varied greatly according to the species, being higher in onions than in lettuce. Experiments with the use of lime filler or construction and demolition wastes for soil remediation result in crops that, in principle, do not present health risks and are similar in development to those grown on non-contaminated soil.

Durability and Abrasion Resistance of Innovative Recycled Pervious Concrete with Recycled Coarse Aggregate of Different Quality under Sulfate Attack

Construction and demolition wastes (C&DWs) have raised a large number of ecological and environmental problems. Recycling C&DWs into arecycled concrete aggregate (RCA) will help save natural resources effectively and reduce the negative impact of C&DW on the environment. Innovative pervious concrete (IPC) can mitigate extreme weather disasters, such as rainstorms, and overcome the low strength and poor durability of traditional pervious concrete. In this study, innovative recycled pervious concrete (IRPC) is prepared by combining RCA with IPC, which has broad application prospects and ecological friendliness. This study investigates the effect of RCA quality grades and replacement rates on the mechanical property, permeability, sulfate resistance and abrasion resistance of IRPC. IRPC mixtures were prepared with three different quality grades (high, medium and low qualities) of aggregates named as NA, RCA1 and RCA2. Moreover, the replacement rate of RCA for NA varied as 0%, 25%, 50%, 75% and 100%. The IRPC specimens were tested for compressive strength, mass loss and abrasion resistance after different sulfate wetting-drying cycles of 0, 30 and 60. The results exhibited that the initial compressive strength of all types of IRPC was more than 40 MPa. The compressive strength and mass of most IRPC increased first and then decreased slightly with the passage of a number of sulfate wetting-drying cycles, indicating IRPC has good resistance to sulfate attack. Sulfate attack and the addition of RCA will reduce the abrasion resistance of IRPC. However, when the replacement rate is lower than 50%, and the RCA quality is better (attached mortar content < 25%), the abrasion resistance of IRPC will be improved under sulfate attack. The experimental results might be useful as a reference and design methodology for employing IRPC in pavement applications in the future.

Monitoring and Assessment of Groundwater Quality at Landfill Sites: Selected Case Studies of Poland and the Czech Republic

In order to protect the components of natural environment, each landfill must be properly secured and the monitoring program should be adopted. This study aims to present a comparative analysis of groundwater quality at selected landfill sites in Poland and the Czech Republic, with a special attention given to the levels and temporal changes of heavy metals (HMs) concentrations measured in collected groundwater samples. A secondary objective was to detect possible leakages of pollutants from the landfill body, into the groundwater, and further into the environment. The assessment of groundwater quality was based on a comparison of HMs concentrations with standards provided by the European environmental laws. On the basis of the long-term monitoring period, it was revealed, for the Polish landfill site, that the groundwater quality is improving over time, especially due to remedial works applied. For the Czech landfill, it was observed that the quality of groundwater is not negatively affected by the operation of the landfill, but in the immediate vicinity of the landfill, the groundwater quality is significantly affected by the agricultural use of neighbouring lands, as well as by the storage of construction and demolition wastes. The results showed that the leachate did not leak outside the landfills, especially due to minimal concentrations of HMs, measured in groundwater samples, taken from the piezometers located in the outflow direction from the landfills.