Accelerated Carbonation of Vibro-Compacted Porous Concrete for Eco-Friendly Precast Elements.

This research studied the effect of accelerated carbonation in the physical, mechanical and chemical properties of a non-structural vibro-compacted porous concrete made with natural aggregates and two types of recycled aggregates from construction and demolition waste (CDW). Natural aggregates were replaced by recycled aggregates using a volumetric substitution method and the CO2 capture capacity was also calculated. Two hardening environments were used: a carbonation chamber with 5% CO2 and a normal climatic chamber with atmospheric CO2 concentration. The effect of curing times of 1, 3, 7, 14 and 28 days on concrete properties was also analysed. The accelerated carbonation increased the dry bulk density, decreased the accessible porosity water, improved the compressive strength and decreased the setting time to reach a higher mechanical strength. The maximum CO2 capture ratio was achieved with the use of recycled concrete aggregate (52.52 kg/t). Accelerate carbonation conditions led to an increase in carbon capture of 525% compared to curing under atmospheric conditions. Accelerated carbonation of cement-based products containing recycled aggregates from construction and demolition waste is a promising technology for CO2 capture and utilisation and a way to mitigate the effects of climate change, as well as promote the new circular economy paradigm.

Carbon Emission Evaluation of CO2 Curing in Vibro-Compacted Precast Concrete Made with Recycled Aggregates.

The objective of the present study was to explore three types of vibro-compacted precast concrete mixtures replacing fine and coarse gravel with a recycled/mixed concrete aggregate (RCA or MCA). The portlandite phase found in RCA and MCA by XRD is a "potential" CO2 sink. CO2 curing improved the compressive strength in all the mixtures studied. One tonne of the mixtures studied could be decarbonised after only 7 days of curing 13,604, 36,077 and 24,635 m3 of air using natural aggregates, RCA or MCA, respectively. The compressive strength obtained, XRD, TGA/DTA and carbon emission evaluation showed that curing longer than 7 days in CO2 was pointless. The total CO2 emissions by a mixture using CO2 curing at 7 days were 221.26, 204.38 and 210.05 kg CO2 eq/m3 air using natural aggregates, RCA or MCA, respectively. The findings of this study provide a valuable contribution to carbon emission evaluation of CO2 curing in vibro-compacted precast concrete with recycled/mixed concrete aggregates (RCA or MCA). The technology proposed in this research facilitates carbon capture and use and guarantees enhanced compressive strength of the concrete samples.

The Effect of Acanthocardia tuberculata Shell Powder as Filler on the Performance of Self-Compacting Mortar.

In this research, the feasibility of using Acanthocardia tuberculata shell waste from the canning industry in the manufacturing of self-compacting mortar (SCM) was tested. The seashells were finely ground to be used as filler instead of the limestone filler normally used in this type of SCM. First, a physicochemical and microstructural characterisation of all raw materials was carried out, including the particle size distribution of both fillers. Subsequently, the self-compactability properties in the fresh state of SCM were evaluated using a total substitution by volume of limestone filler for seashell powder, using different self-compactiblity parameters. The mineralogical phases of all the SCM tested were identified once hardened by means of X-ray diffraction technique, thermogravimetric and differential thermal analysis. In addition, the mechanical properties, water absorption capacity, dry bulk density and accessible porosity of water of hardened mortars at 28 days of curing were analysed. The effect of replacing limestone filler by Acanthocardia tuberculata filler resulted in a decrease in compressive strength of 29.43, 16.84 and 2.29%, respectively. The results indicate that it is possible to completely replace natural limestone filler with Acanthocardia tuberculata shell filler without significantly affecting the mechanical properties of SCM.

Performance of Sustainable Mortars Made with Filler from Different Construction By-Products.

One way to contribute to sustainability in the construction sector is through the incorporation of construction by-products from their own activities. This work intends to extend the possibilities for enhancement of these by-products through the incorporation of four different ones, as fillers, in mortar production. The influence of these incorporations in mortar production was compared with a reference mortar with siliceous filler in its fresh state; workability, entrained air content and fresh density, and in its hardened state; capillary water absorption, water vapour permeability and shrinkage (up to 91 days); and adhesive, compressive, and flexural strength; the last two were studied over time (up to 180 days). Despite the reduction in compressive strength, both in the short and long term, there was a gain in adhesive strength when the construction by-products were incorporated. Regarding the physical properties and durability studied, no relevant differences were found with respect to the reference mortar. According to the European Specifications, these mortars could be used as regular or coloured rendering and plastering mortars, and masonry mortars, and these findings promote the circular economy in the construction sector.

Arthropod biodiversity patterns point to the Mesovoid Shallow Substratum (MSS) as a climate refugium.

The determinants of biodiversity patterns in the subterranean habitat called Mesovoid Shallow Substratum (MSS) are not well-understood. In this study, thirty-three scree slopes at high altitudes were selected across the Sierra de Guadarrama National Park in central Spain to investigate the effect of ten environmental variables on the abundance and species diversity of the spider and springtail assemblages from the colluvial MSS. In each locality, a multiperforated PVC tube with a pitfall trap inside was buried up to 1 m deep, and generalized linear models and Mantel tests were used to analyze the effect of mainly climate- and habitat-related variables on the diversity patterns of both taxa. A total of 1143 individual spiders belonging to 54 species and 40 811 springtail individuals belonging to 62 species were collected. The analyses indicated that cold temperatures and the presence of forest cover on the surface significantly enhance richness and abundance in the two taxa. Environmental similarity also had a small positive effect on faunistic similarity. However, the effects of temperature and habitat detected on spider richness and abundance were stronger than on springtails, whereas the reverse was found regarding faunistic similarity. These results indicate that subterranean dwellers respond differently to the same environmental factors, which in turn, points to a different degree of affinity for the MSS. The MSS plays an important role in the survival of high mountain arthropod species, acting as a climate refuge, so the protection of this habitat should be prioritized.

The study of hidden habitats sheds light on poorly known taxa: spiders of the Mesovoid Shallow Substratum.

The scarce and biased knowledge about the diversity and distribution of Araneae species in the Iberian Peninsula is accentuated in poorly known habitats such as the Mesovoid Shallow Substratum (MSS). The aim of this study was to characterize the spiders inventory of the colluvial MSS of the Sierra de Guadarrama National Park, and to assess the importance of this habitat for the conservation of the taxon. Thirty-three localities were selected across the high peaks of the Guadarrama mountain range and they were sampled for a year using subterranean traps specially designed to capture arthropods in the MSS. Species accumulation curves were built both for the observed species richness and for the non-parametric richness estimators. The literature was reviewed in order to update the distributional maps of the rarest species. Forty-two species were collected, of which four were species new to science. More than half were represented by one or two individuals which caused the accumulation curves to rise slowly and to end without reaching an asymptote. Almost half of the species showed significant increases in their Iberian distribution ranges. Two species were recorded for the first time in the Iberian Peninsula and 32 species were new additions to the spider checklist of the Sierra de Guadarrama National Park.

A Double Barrier Technique with Hydrotalcites for Pb Immobilisation from Electric Arc Furnace Dust.

A new line of mortars incorporating hydrotalcites was developed. This research article shows the results of a study of a double barrier technique (DBT) for Pb immobilisation from electric arc furnace dust (EAFD) in mortars with the addition of three different hydrotalcites (H1, H2, and H3). Electric arc furnace dust (EAFD) is a hazardous waste due to its heavy metal leachability. The aim was to obtain a mortar in which, due to its chemical composition, heavy metal leaching satisfied environmental criteria. Previously, a physical and chemical characterisation of mortar material components was carried out. The leaching behaviour of Pb from EAFD in double barrier (DB) mortars with different hydrotalcites was analysed for compressive strength to determine treatment effectiveness. DB mortars could be considered monoliths because their compressive strengths were higher than 1 MPa but exhibited a decrease due to hydrotalcite incorporation. The mortar EAFD25_H2 (with ethylenediaminetetraacetate (EDTA) in the interlayer of the hydrotalcite) showed one minor reduction in compressive strength with respect to the reference mortar because formation of Portlandite was observed, which is a characteristic of cement hydration. The conventional immobilisation mortar (EAFD25) did not achieve Pb immobilisation. However, DB mortars with dimercaptosuccinate (DMSA) in the interlayer of the hydrotalcite reduced Pb release by ~50%, from 20.29 mg kg-1 (EAFD25) to 9.88 mg kg-1 (EAFD25_H3). In addition, EAFD25_H3 included the lowest hydrotalcite content, thereby improving the immobilisation ratio. The results of this study contribute to better Pb immobilisation, thus satisfying environmental criteria.

A new genus and species of Haplobainosomatidae (Diplopoda: Chordeumatida) from the MSS of the Sierra de Guadarrama National Park, central Spain.

The chordeumatidan fauna of the Iberian Peninsula is far from being well known, but recent efforts are improving that knowledge. Samplings carried out in the Milieu Souterrain Superficiel (also known as the Mesovoid Shallow Substratum) on several screes of the Sierra de Guadarrama National Park (central Spain) have led to the discovery of a new species of chordeumatidan millipede. This new species belongs to the family Haplobainosomatidae, which is mainly known from the northern Iberian Peninsula, and thus this is the first record of the family in central Spain. However, the extremely simple gonopods of this species are so different from all other known species of the family that it must be placed in a new genus. In this work, a complete description of the species, named as Guadarramasoma ramosae gen. & sp. nov., with a detailed iconography based on scanning electron microscopy images is provided together with a distribution map and a brief discussion of the implications of this new finding.

Distinctive Collembola communities in the Mesovoid Shallow Substratum: First data for the Sierra de Guadarrama National Park (Central Spain) and a description of two new species of Orchesella (Entomobryidae).

Two new species of the genus Orchesella Templeton, 1836 have been identified following intensive sampling in the Colluvial Milieu Souterrain Superficiel (Mesovoid Shallow Substratum, or MSS) of the Sierra de Guadarrama using Subterranean Sampling Devices (SSD). The data were obtained from the first extraction of the traps between May and October of 2015. During a study of the Collembola taxon, 32 different genera (61 species) were identified. The highest representative genus presence in almost all traps was Orchesella, with two new species. One of the two species described had been misidentified until this study was carried out, indicating that their preferential habitat had not been sampled; the second species had never been identified. The community of the Orchesella species in the Colluvial MSS was investigated, leading to the conclusion that this environment has its own assemblage of characteristic species. The opportunity to study specimens that belong to five species of the genus Orchesella, including three previously recollected, has allowed for obtaining reliable information regarding their macrochaetotaxy. A part of this chaetotaxy is proposed as a useful diagnostic tool for the species of the genus. In conclusion, it can be affirmed that this study has demonstrated that the Colluvial Mesovoid Shallow Substratum (Colluvial MSS) has its own fauna, and it supports the hypothesis that it constitutes a new biotope, at least for Collembola.

Combined Effects of Non-Conforming Fly Ash and Recycled Masonry Aggregates on Mortar Properties.

This work evaluates the effects of using non-conforming fly ash (Nc-FA) generated in a thermoelectric power plant as filler material for mortars made with natural sand (NA) and recycled sand from masonry waste (FRMA). The incorporation of powdered recycled masonry filler (R-MF) is also tested as an alternative to siliceous filler (Si-F). Three families of mortars were designed to study: the effect of replacing Si-F with Nc-FA on mortars made with NA; the effect of replacing Si-F with Nc-FA on mortars made with 50% of NA and 50% of FRMA; and the effect of replacing Si-F with R-MF on mortars made with NA and FRMA. Replacing Si-F with Nc-FA is a viable alternative that increases the mechanical strength, the workability and durability properties and decreases the shrinkage. The use of FRMA and Nc-FA improved the mechanical strength of mortars, and it slightly increased the shrinkage. The replacement of Si-F with R-MF on mortars made with FRMA is not a good alternative, because it has a negative impact on all of the properties tested. This work can help both to reduce cement and natural resources' consumption and to increase the recycling rate of Nc-FA and FRMA.