Optimisation of mortar with Mg-Al-Hydrotalcite as sustainable management strategy lead waste

This study analyses how a Mg-Al-Hydrotalcite with carbonate in the interlayer influences the hydration of mortar allowing the management of lead waste (solid or liquid) in a cement-based material. First, the compatibility of hydrotalcite with the cementitious matrix was studied through heat of hydration, workability, consistency, compressive strength and mineralogical phase formation. The changes produced by the incorporation of hydrotalcite were not drastic and the compatibility with the cement was verified. Lead was added in oxide and nitrate form to mortar with or without hydrotalcite and the same properties were evaluated, including a leaching test. The incorporation of lead delayed the hydration, this effect being increased by the hydrotalcite, which happened in the first instants of hydration. The addition of hydrotalcite counteracted the negative effect of lead in compressive strength values. The interaction between the hydrotalcite and the lead waste was favoured by the formation of plumbites under the pH conditions of cement hydration. Consequently, this interaction would seem to be superficial. The lead leaching decreased to values included in the “Non-Hazardous” limit of the environmental classification, very close to “Inert”. All mortars were produced by two mixing procedures to establish differences. When hydrotalcite was included, the compressive strength was higher in the second procedure and lead leaching showed better behaviour in the first procedure. This research expands the possibilities of the management of solid and liquid waste contaminated with lead by using a Mg-Al-Hydrotalcite in cement-based matrices

The Effect of TiO2 Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements

Mortars with two different binders (Portland cement (PC) and high alumina cement (HAC)) were modified upon the bulk incorporation of nano-structured photocatalytic additives (bare TiO2, and TiO2 doped with either iron (Fe-TiO2) or vanadium (V-TiO2)). Plastic and hardened state properties of these mortars were assessed in order to study the influence of these nano-additives. Water demand was increased, slightly by bare TiO2 and Fe-TiO2, and strongly by V-TiO2, in agreement with the reduction of the particle size and the tendency to agglomerate. Isothermal calorimetry showed that hydration of the cementitious matrices was accelerated due to additional nucleation sites offered by the nano-additives. TiO2 and doped TiO2 did not show pozzolanic reactivity in the binding systems. Changes in the pore size distribution, mainly the filler effect of the nano-additives, accounted for the increase in compressive strengths measured for HAC mortars. A complex microstructure was seen in calcium aluminate cement mortars, strongly dependent on the curing conditions. Fe-TiO2 was found to be homogeneously distributed whereas the tendency of V-TiO2 to agglomerate was evidenced by elemental distribution maps. Water absorption capacity was not affected by the nano-additive incorporation in HAC mortars, which is a favourable feature for the application of these mortars

Influence of Two Polymer-Based Superplasticizers (Poly-naphthalene Sulfonate, PNS, and Lignosulfonate, LS) on Compressive and Flexural Strength, Freeze-Thaw, and Sulphate Attack Resistance of Lime-Metakaolin Grouts

A new range of grouts prepared by air lime and metakaolin (MK) as a pozzolanic admixture has been obtained by using as dispersing agents two polymers, namely poly-naphthalene sulfonate (PNS) and lignosulfonate (LS), with the aim of improving the fluidity of the fresh grouts. Fluidity and setting times of the grouts were assessed. Differences in the molecular architecture and in the anionic charge density explained the different adsorption of the polymers and the different performance. The higher anionic charge of PNS and its linear shape explained its better adsorption and effectiveness. The pozzolanic reaction was favoured in grouts with PNS, achieving the highest values of compressive strength (4.8 MPa after 182 curing days). The addition of PNS on lime grouts slightly decreased the frost resistance of the grouts (from 24 freeze-thaw cycles for the polymer-free samples to 19 or 20 cycles with 0.5 or 1 wt % of PNS). After the magnesium sulphate attack, grouts were altered by decalcification of hydrated phases and by formation of hexahydrite and gypsum. A protective role of portlandite against magnesium sulphate attack was clearly identified. Accordingly, the polymer LS, which preserves a significant amount of Ca(OH)2, could be an alternative for the obtaining of grouts requiring high sulphate attack resistance

Development of Photocatalytic Coatings for Building Materials with Bi₂O₃-ZnO Nanoparticles

The aim of this study was to develop versatile coatings that can protect the stone surfaces of Architectural Heritage. Two different 3D media, namely superhydrophobic (SPHB) and hydro-oleophobic (OHB), were utilized as host matrices for nanostructured photocatalysts (Bi2O3-ZnO 8/92). These photocatalysts were sensitive to visible light to enhance their efficiency when exposed to sunlight. To prevent the nanophotocatalyst from clumping together in the 3D media, non-ionic dispersant additives (Tween20, TritonX-100, and Brij35) were incorporated. The optimized suspensions were then applied to various substrates such as sandstone, limestone, and granite. The effectiveness of the coatings was assessed by evaluating the hydrophobicity, oleophobicity, and photocatalytic activity of the coated substrates. The Bi2O3-ZnO photocatalyst exhibited higher activity in the SPHB medium compared to the OHB medium. To simulate real-life conditions, the coated substrates were subjected to accelerated weathering tests to predict their durability. Despite a significant reduction in their thickness, the coatings demonstrated sustained hydrophobic efficiency and self-cleaning capability after the accelerated ageing tests

Maculopapular eruptions associated to COVID-19: A subanalysis of the COVID-Piel study.

A previous study has defined the maculopapular subtype of manifestations of COVID-19. The objective of our study was to describe and classify maculopapular eruptions associated with COVI-19. We carried out a subanalysis of the maculopapular cases found in the previous cross-sectional study. Using a consensus, we defined seven clinical patterns. We described patient demographics, the therapy received by the patient and the characteristics of each pattern. Consensus lead to the description of seven major maculopapular patterns: morbilliform (45.5%), other maculopapular (20.0%), purpuric (14.2%), erythema multiforme-like (9.7%), pytiriasis rosea-like (5.7%), erythema elevatum diutinum-like (2.3%), and perifollicular (2.3%). In most cases, maculopapular eruptions were coincident (61.9%) or subsequent (34.1%) to the onset of other COVID-19 manifestations. The most frequent were cough (76%), dyspnea (72%), fever (88%), and astenia (62%). Hospital admission due to pneumonia was frequent (61%). Drug intake was frequent (78%). Laboratory alterations associated with maculo-papular eruptions were high C-reactive protein, high D-Dimer, lymphopenia, high ferritin, high LDH, and high IL-6. The main limitation of our study was the impossibility to define the cause-effect relationship of each pattern. In conclusion, we provide a description of the cutaneous maculopapular manifestations associated with COVID-19. The cutaneous manifestations of COVID-19 are wide-ranging and can mimic other dermatoses