novel geopolymeric material cured at room temperature

[EN] Alkali activated binders are a new class of binding material with comparable or enhanced performance to Portland cement. These binding materials are obtained by a chemical reaction between an aluminosilicate material and a highly alkaline solution. In most cases, the setting hardening process of this binder is performed at high curing temperatures. In this paper, alkali activated mortars based on vitreous calcium aluminosilicate (VCAS) cured at room temperature are evaluated. Mechanical strength development and microstructural analysis (scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and mercury intrusion porosimetry) of these materials are performed. Mortars yielded compressive strength ¡-89 MPa after 360 days. This is the first time that VCAS is used as aluminosilicate source material in the production of alkali activated mortars cured at room temperature.The authors acknowledge the Ministerio de Ciencia e Innovacio´ n of the Spanish Government (projecto. BIA2011-26947) and the Vitrominerals company for supplying VCAS samples.Mitsuuchi Tashima, M.; Soriano Martínez, L.; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2013). novel geopolymeric material cured at room temperature. Advances in Applied Ceramics. 112:179-183. https://doi.org/10.1179/1743676112Y.0000000056S17918311

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

The effect of microencapsulated phase‐change materials (MPCM) on the rheological properties of pre‐set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s−1. New empirical equations were developed to quantify the time‐dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D‐geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear‐induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.publishedVersio

Effect of oxidant concentration, exposure time, and seed particles on secondary organic aerosol chemical composition and yield

We performed a systematic intercomparison study of the chemistry and yields of secondary organic aerosol (SOA) generated from OH oxidation of a common set of gas-phase precursors in a Potential Aerosol Mass (PAM) continuous flow reactor and several environmental chambers. In the flow reactor, SOA precursors were oxidized using OH concentrations ranging from 2.0 × 10[superscript 8] to 2.2 × 10[superscript 10] molec cm[superscript −3] over exposure times of 100 s. In the environmental chambers, precursors were oxidized using OH concentrations ranging from 2 × 10[superscript 6] to 2 × 10[superscript 7] molec cm[superscript −3] over exposure times of several hours. The OH concentration in the chamber experiments is close to that found in the atmosphere, but the integrated OH exposure in the flow reactor can simulate atmospheric exposure times of multiple days compared to chamber exposure times of only a day or so. In most cases, for a specific SOA type the most-oxidized chamber SOA and the least-oxidized flow reactor SOA have similar mass spectra, oxygen-to-carbon and hydrogen-to-carbon ratios, and carbon oxidation states at integrated OH exposures between approximately 1 × 10[superscript 11] and 2 × 10[superscript 11] molec cm[superscript −3] s, or about 1–2 days of equivalent atmospheric oxidation. This observation suggests that in the range of available OH exposure overlap for the flow reactor and chambers, SOA elemental composition as measured by an aerosol mass spectrometer is similar whether the precursor is exposed to low OH concentrations over long exposure times or high OH concentrations over short exposure times. This similarity in turn suggests that both in the flow reactor and in chambers, SOA chemical composition at low OH exposure is governed primarily by gas-phase OH oxidation of the precursors rather than heterogeneous oxidation of the condensed particles. In general, SOA yields measured in the flow reactor are lower than measured in chambers for the range of equivalent OH exposures that can be measured in both the flow reactor and chambers. The influence of sulfate seed particles on isoprene SOA yield measurements was examined in the flow reactor. The studies show that seed particles increase the yield of SOA produced in flow reactors by a factor of 3 to 5 and may also account in part for higher SOA yields obtained in the chambers, where seed particles are routinely used.National Science Foundation (U.S.). Atmospheric Chemistry Program (Grant AGS-1056225)National Science Foundation (U.S.). Atmospheric Chemistry Program (Grant AGS-1245011

Ion-exchanged geopolymer for photocatalytic degradation of a volatile organic compound

In thepresentworkitisshownhowgeopolymerscanbeusedtocontrolindoorandoutdoorair pollution byphotolysisof2-ButanoneasaVolatileOrganicCompound(VOC).Anionexchange procedurewasfollowedtoincorporateTiO2 into ageopolymer(IEG),anddifferent2-Butanone concentrations wereusedinabatchreactorunderdryandhumidconditions.Variationon 2-Butanone concentrationwasfollowedbygaschromatography.ALangmuir Hinshelwood modelwas used todeterminethedisappearancerateofreactantattheinitialstageofthereaction.Gasca-Tirado, J.; Manzano-Ramirez, A.; Vazquez-Landaverde, PA.; Herrera-Diaz, EI.; Rodriguez-Ugarte, ME.; Rubio-Avalos, JC.; Amigó Borrás, V.... (2014). Ion-exchanged geopolymer for photocatalytic degradation of a volatile organic compound. Materials Letters. 134:222-224. doi:10.1016/j.matlet.2014.07.090S22222413

Fracture properties of GGBFS-blended fly ash geopolymer concrete cured in ambient temperature

Fracture characteristics are important part of concrete design against brittle failure. Recently, fly ash geopolymer binder is gaining significant interest as a greener alternative to traditional ordinary Portland cement (OPC). Hence it is important to understand the failure behaviour of fly ash based geopolymers for safe design of structures built with such materials. This paper presents the fracture properties of ambient-cured geopolymer concrete (GPC). Notched beam specimens of GPC mixtures based mainly on fly ash and a small percentage of ground granulated blast furnace slag were subjected to three-point bending test to evaluate fracture behaviour. The effect of mixture proportions on the fracture properties were compared with control as well as OPC concrete. The results show that fracture properties are influenced by the mixture compositions. Presence of additional water affected fracture properties adversely. Fracture energy is generally governed by tensile strength which correlates with compressive strength. Critical stress intensity factor varies with the variation of flexural strength. Geopolymer concrete specimens showed similar load–deflection behaviour as OPC concrete specimens. The ambient cured GPC showed relatively more ductility than the previously reported heat cured GPC, which is comparable to the OPC specimens. Fly ash based GPC achieved relatively higher fracture energy and similar values of KIC as compared to those of OPC concrete of similar compressive strength. Thus, fly ash based GPC designed for curing in ambient condition can achieve fracture properties comparable to those of normal OPC concrete

Microphysical explanation of the RH-dependent water affinity of biogenic organic aerosol and its importance for climate

This is the final version of the article. Available from American Geophysical Union via the DOI in this record.A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single-parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources.The data presented in the paper will be available through the Bolin Centre database (http://bolin.su.se/data/). The EC H2020 European Research Council ERC (ERC-StGATMOGAIN-278277 and ERC-StG-QAPPA-335478) and integrated project 641816 CRESCENDO Svenska Forskningsrådet Formas (Swedish Research Council Formas) (2015-749), Knut och Alice Wallenbergs Stiftelse (Knut and Alice Wallenberg Foundation Wallenberg Fellowship AtmoRemove), Academy of Finland (grants 272041 and 259005), Natural Environment Research Council (NERC grants NE/M003531/1 and NE/J02175X/1), Norwegian Research Council (EVA grant 229771), Natural Sciences and Engineering Research Council of Canada (NSERC, grant RGPIN/04315-2014), National Science Foundation (NSF, grants ATM-1242258, AGS-1242932, and AGS-1360834), U.S. Environmental Protection Agency (EPA, STAR grant R835410), National Oceanic and Atmospheric Administration (NOAA, CPO award 538NA10OAR4310102), Electric Power Research Institute (EPRI, grant 10004734), U.S. Department of Energy (DOE, grants BER/ASR DE-SC0016559 and DE-SC0012792), Georgia Institute of Technology, and NordForsk (Nordic Centre of Excellence eSTICC) are gratefully acknowledged for funding. The climate model simulations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputing Centre. Benjamin Murphy is acknowledged for useful discussions

Microphysical explanation of the RH-dependent water affinity of biogenic organic aerosol and its importance for climate

A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single-parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources. Plain Language Summary The interaction of airborne particulate matter ("aerosols") with water is of critical importance for processes governing climate, precipitation, and public health. It also modulates the delivery and bioavailability of nutrients to terrestrial and oceanic ecosystems. We present a microphysical explanation to the humidity-dependent water uptake behavior of organic aerosol, which challenges the highly simplified theoretical descriptions used in, e.g., present climate models. With the comprehensive analysis of laboratory data using molecular models, we explain the microphysical behavior of the aerosol over the range of humidity observed in the atmosphere, in a way that has never been done before. We also demonstrate the presence of these phenomena in the ambient atmosphere from data collected in the field. We further show, using two state-of-the-art climate models, that misrepresenting the water affinity of atmospheric organic aerosol can lead to significant biases in the estimates of the anthropogenic influence on climate.Peer reviewe

Characterisation of mechanical and thermal properties in flax fabric reinforced geopolymer composites

This paper presents the mechanical and thermal properties of flax fabric reinforced fly ash based geopolymer composites. Geopolymer composites reinforced with 2.4, 3.0 and 4.1 wt% woven flax fabric in various layers were fabricated using a hand lay-up technique and tested for mechanical properties such as flexural strength, flexural modulus, compressive strength, hardness, and fracture toughness. All mechanical properties were improved by increasing the flax fibre contents, and showed superior mechanical properties over a pure geopolymer matrix. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were carried out to evaluate the composition and fracture surfaces of geopolymer and geopolymer/flax composites. The thermal behaviour of composites was studied by thermogravimetric analysis (TGA) and the results showed significant degradation of flax fibres at 300 °C