Novos materiais de construção com tecnologias avançadas

Este artigo pretende apenas dar um contributo, assinalando alguns exemplos em que se tem vindo a trabalhar e que refletem o uso de tecnologias avançadas na formulação e funcionalidade de materiais de construção tradicionais. Um exemplo claro é o uso de aditivos que induzem novas funções e que muitos deles pertencem ao grupo denominado como nanomateriais. A sua adição coloca quase sempre problemas de incorporação e que requerem um trabalho de ajuste das formulações e comportamentos no estado fresco ou endurecido. Este trabalho de investigação é muitas vezes essencial para a otimização das funções que se pretendem que os materiais de construção venham a demonstrar. Neste grupo de investigação, resultante da cooperação entre centros de I&D e empresas em projetos de colaboração diversos ao longo dos últimos anos, tem-se vindo a focar na introdução de novas funções em materiais de construção tradicionais, para que ganhem um papel ativo em domínios como o do conforto térmico ou da qualidade ambiental, dois pilares essenciais para uma construção mais sustentável

Unravelling the Affinity of Alkali-Activated Fly Ash Cubic Foams towards Heavy Metals Sorption

In this work, alkali-activated fly ash-derived foams were produced at room temperature by direct foaming using aluminum powder. The 1 cm3 foams (cubes) were then evaluated as adsorbents to extract heavy metals from aqueous solutions. The foams’ selectivity towards lead, cadmium, zinc, and copper ions was evaluated in single, binary, and multicomponent ionic solutions. In the single ion assays, the foams showed much higher affinity towards lead, compared to the other heavy metals; at 10 ppm, the removal efficiency reached 91.9% for lead, 83.2% for cadmium, 74.6% for copper, and 64.6% for zinc. The greater selectivity for lead was also seen in the binary tests. The results showed that the presence of zinc is detrimental to cadmium and copper sorption, while for lead it mainly affects the sorption rate, but not the ultimate removal efficiency. In the multicomponent assays, the removal efficiency for all the heavy metals was lower than the values seen in the single ion tests. However, the superior affinity for lead was preserved. This study decreases the existing knowledge gap regarding the potential of alkali-activated materials to act as heavy metals adsorbents under different scenarios

Lime mud from cellulose industry as raw material in cement mortars

This study reports the use of lime mud (LM) in cement-based-mortars. Lime mud is a waste generated in the production of cellulose by the kraft mill process. It is mainly composed of CaCO3, a small amount of magnesium carbonate and other trace minerals. Mortars were prepared by adding different amounts of LM (10, 20 and 30% by weight of cement) in dry weight. The mortar compositions were evaluated through rheology and flow table measurements, assuring that all the samples exhibited adequate conditions for testing in both equipments. The hardened state properties were also evaluated through mechanical strengths at 7, 28 and 90 days of curing. Following a waste management solution perspective, this work intend to provide a general evaluation of LM application in cement based mortars, looking at both fresh and hardened properties in order to guarantee that the final application requirements are not hindered

The California baseline ozone transport study (CABOTS)

Ozone is one of the six criteria pollutants identified by the U.S. Clean Air Act Amendment of 1970 as particularly harmful to human health. Concentrations have decreased markedly across the United States over the past 50 years in response to regulatory efforts, but continuing research on its deleterious effects have spurred further reductions in the legal threshold. The South Coast and San Joaquin Valley Air Basins of California remain the only two extreme ozone nonattainment areas in the United States. Further reductions of ozone in the West are complicated by significant background concentrations whose relative importance increases as domestic anthropogenic contributions decline and the national standards continue to be lowered. These background concentrations derive largely from uncontrollable sources including stratospheric intrusions, wildfires, and intercontinental transport. Taken together the exogenous sources complicate regulatory strategies and necessitate a much more precise understanding of the timing and magnitude of their contributions to regional air pollution. The California Baseline Ozone Transport Study was a field campaign coordinated across Northern and Central California during spring and summer 2016 aimed at observing daily variations in the ozone columns crossing the North American coastline, as well as the modification of the ozone layering downwind across the mountainous topography of California to better understand the impacts of background ozone on surface air quality in complex terrain

Intercomparison of lidar, aircraft, and surface ozone measurements in the San Joaquin Valley during the California Baseline Ozone Transport Study (CABOTS)

The California Baseline Ozone Transport Study (CABOTS) was conducted in the late spring and summer of 2016 to investigate the influence of long-range transport and stratospheric intrusions on surface ozone (O3) concentrations in California with emphasis on the San Joaquin Valley (SJV), one of two extreme ozone non-attainment areas in the US. One of the major objectives of CABOTS was to characterize the vertical distribution of O3 and aerosols above the SJV to aid in the identification of elevated transport layers and assess their surface impacts. To this end, the NOAA Earth System Research Laboratory (ESRL) deployed the Tunable Optical Profiler for Aerosol and oZone (TOPAZ) mobile lidar to the Visalia Municipal Airport (36.315∘&thinsp;N, 119.392∘&thinsp;E) in the central SJV between 27 May and 7 August 2016. Here we compare the TOPAZ ozone retrievals with co-located in situ surface measurements and nearby regulatory monitors and also with airborne in situ measurements from the University of California at Davis–Scientific Aviation (SciAv) Mooney and NASA Alpha Jet Atmospheric eXperiment (AJAX) research aircraft. Our analysis shows that the lidar and aircraft measurements agree, on average to within 5&thinsp;ppbv, the sum of their stated uncertainties of 3 and 2&thinsp;ppbv, respectively.</p

New features in the phase diagram of TbMnO3_3

The (H,T)-phase diagram of the multiferroic perovskite TbMnO$_3$ was studied by high-resolution thermal expansion $\alpha(T)$ and magnetostriction $\Delta L(H)/L$ measurements. Below $T_{N}\simeq 42$ K, TbMnO$_3$ shows antiferromagnetic order, which changes at $T_{FE}\simeq 28$ K where simultaneously a spontaneous polarization $P||c$ develops. Sufficiently high magnetic fields applied along $a$ or $b$ induce a polarization flop to $P||a$. We find that all of these transitions are strongly coupled to the lattice parameters. Thus, our data allow for a precise determination of the phase boundaries and also yield information about their uniaxial pressure dependencies. The strongly hysteretic phase boundary to the ferroelectric phase with $P||a$ is derived in detail. Contrary to previous reports, we find that even in high magnetic fields there are no direct transitions from this phase to the paraelectric phase. We also determine the various phase boundaries in the low-temperature region related to complex reordering transitions of the Tb moments.Comment: 17 pages including 9 figure

Effect of petrochemical industrial emissions of reactive alkenes and NO\u3csub\u3ex\u3c/sub\u3e on tropospheric ozone formation in Houston, Texas

Petrochemical industrial facilities can emit large amounts of highly reactive hydrocarbons and NOx to the atmosphere; in the summertime, such colocated emissions are shown to consistently result in rapid and efficient ozone (O3) formation downwind. Airborne measurements show initial hydrocarbon reactivity in petrochemical source plumes in the Houston, TX, metropolitan area is primarily due to routine emissions of the alkenes propene and ethene. Reported emissions of these highly reactive compounds are substantially lower than emissions inferred from measurements in the plumes from these sources. Net O3 formation rates and yields per NOx molecule oxidized in these petrochemical industrial source plumes are substantially higher than rates and yields observed in urban or rural power plant plumes. These observations suggest that reductions in reactive alkene emissions from petrochemical industrial sources are required to effectively address the most extreme O3 exceedences in the Houston metropolitan area

Influence of fly ash blending on hydration and physical behavior of Belite-Alite-Ye'elimite cements

A cement powder, composed of belite, alite and ye’elimite, was blended with 0, 15 and 30 wt% of fly ash and the resulting lended cements were further characterized. During hydration, the presence of fly ash caused the partial inhibition of both AFt degradation and belite reactivity, even after 180 days. The compressive strength of the corresponding mortars increased by increasing the fly ash content (68, 73 and 82 MPa for mortars with 0, 15 and 30 wt% of fly ash, respectively, at 180 curing days), mainly due to the diminishing porosity and pore size values. Although pozzolanic reaction has not been directly proved there are indirect evidences.This work is part of the Ph.D. of D. Londono-Zuluaga funded by Beca Colciencias 646—Doctorado en el exterior and Enlaza Mundos 2013 program grant. Cement and Building materials group (CEMATCO) from National University of Colombia is acknowledged for providing the calorimetric measurements. Funding from Spanish MINECO BIA2017-82391-R and I3 (IEDI-2016-0079) grants, co-funded by FEDER, are acknowledged