Efeito da adição de micro e nanossílica no comportamento reológico e propriedades no estado endurecido de argamassas e pastas de cimento

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência e Engenharia de Materiais.Nos últimos anos, o uso de nanopartículas tem recebido atenção especial em muitos campos de aplicação com o propósito de fabricar materiais com novas funcionalidades. As adições minerais podem ser usadas em substituição parcial ao cimento de modo a modificar as misturas nos estados fresco e endurecido e obter materiais de elevada resistência mecânica. Nesse sentido, o presente trabalho utilizou os ensaios de reologia e espalhamento na mesa de consistência para a formulação de misturas com adição de nS (nanossílica) e SF (microssílica). Essa metodologia garante que essas misturas apresentam trabalhabilidade adequada para ambos os equipamentos. Além disso, o planejamento fatorial foi usado em algumas situações para a formulação das misturas e identificação dos efeitos de nS, SF, superplastificante (SP) e relação água/aglomerante. O efeito de interação entre esses fatores sobre as propriedades no estado fresco e endurecido foi também identificado. A partir dos resultados experimentais, observou-se que o comportamento reológico das argamassas com baixa relação água/teor de sólidos totais apresenta maior dificuldade na sua caracterização, uma vez que o atrito interno entre as superfícies das partículas é intenso. A formulação de argamassas com baixa fluidez apresenta maior limitação pelo reômetro, sendo a tensão de escoamento mais afetada do que a viscosidade plástica. A presença da nS diminui o período de dormência e o tempo de pega inicial. Além disso, nS e SF geram fases similares mas com diferentes intensidades para o hidróxido de cálcio formado. A aglomeração da nS é intensa, o que prejudica o empacotamento das partículas. Em geral, o efeito combinado entre a elevada reatividade da nS com outro tipo de adição (por exemplo SF) favorece o aumento da performance do material quando comparadas com adições individuais. Nas idades iniciais, a elevada reatividade contribui para o desenvolvimento da resistência a compressão, enquanto que para as idades mais avançadas o efeito físico pode melhorar a densificação do material, tornando a matriz mais resistente. Além disso, a máxima resistência a compressão é dependente da quantidade de água adicionada, na qual é também dependente do tipo de adição empregada. Esta última variável é dependente das características físicas e química

In-depth investigation of the long-term strength and leaching behaviour of inorganic polymer mortars containing green liquor dregs

Green liquor dregs are the most challenging waste stream coming from the pulp and paper industry. Despite tremendous efforts, there are not currently any viable recycling alternatives for this massively produced waste (2 Mt/year), which inevitably ends up in landfills. Urgent actions must be undertaken to tackle this. In this work, a substantial amount of dregs was incorporated into eco-friendly, waste-based inorganic polymer (geopolymer) mortars as fine filler. Then, and for the first time, the long-term strength performance (up to 270 days) and heavy metals leaching behaviour of the dregs-containing mortars was evaluated. The effect of the mixture composition and dregs incorporation content on the fresh- and hardened-state properties of the mortars was also studied. Dregs were found to increase the initial and final setting time of the slurries, thus extending the open time before their in-situ application. The use of dregs as fine filler effectively enhances the compressive strength of the mortars, and decreases their water absorption levels. These eco-friendly building materials showed excellent long-term performance, as their strength continuously increases up to the 270th day (after mixture), and no signs of efflorescence formation were detected. Moreover, the heavy metals leaching levels of the mortars were well below the contamination limits in soil, which demonstrates the feasibility of this recycling methodology.publishe

Brown Spider (Loxosceles genus) Venom Toxins: Tools for Biological Purposes

Venomous animals use their venoms as tools for defense or predation. These venoms are complex mixtures, mainly enriched of proteic toxins or peptides with several, and different, biological activities. In general, spider venom is rich in biologically active molecules that are useful in experimental protocols for pharmacology, biochemistry, cell biology and immunology, as well as putative tools for biotechnology and industries. Spider venoms have recently garnered much attention from several research groups worldwide. Brown spider (Loxosceles genus) venom is enriched in low molecular mass proteins (5–40 kDa). Although their venom is produced in minute volumes (a few microliters), and contain only tens of micrograms of protein, the use of techniques based on molecular biology and proteomic analysis has afforded rational projects in the area and permitted the discovery and identification of a great number of novel toxins. The brown spider phospholipase-D family is undoubtedly the most investigated and characterized, although other important toxins, such as low molecular mass insecticidal peptides, metalloproteases and hyaluronidases have also been identified and featured in literature. The molecular pathways of the action of these toxins have been reported and brought new insights in the field of biotechnology. Herein, we shall see how recent reports describing discoveries in the area of brown spider venom have expanded biotechnological uses of molecules identified in these venoms, with special emphasis on the construction of a cDNA library for venom glands, transcriptome analysis, proteomic projects, recombinant expression of different proteic toxins, and finally structural descriptions based on crystallography of toxins

Innovative Recycling of Lime Slaker Grits from Paper-Pulp Industry Reused as Aggregate in Ambient Cured Biomass Fly Ash-Based Geopolymers for Sustainable Construction Material

Lime slaker grits and biomass fly ash are solid wastes produced by the Kraft paper-pulp industry that are commonly disposed of in landfill. However, recent studies and European regulations discourage such disposal practices. This work investigates an alternative and innovative way to recycle and reuse these wastes in the production of green geopolymeric mortars intended for application in the construction industry. Here, biomass fly ash was used as the main source of alumino-silicate in the binder precursor (70 wt.% substitution to metakaolin), and grits (ranging from 1-12.5 mm, as provided by the industry) were reused as aggregate. Aggregate granulometry was also completed by using a commercial natural siliceous sand (<1 mm). Mortars using sand only were prepared for comparative reasons. The implemented mix was designed to investigate the influence of the grits on the mortar's properties such as its binder/aggregate ratio, workability, bulk density, water sorptivity, and compressive strength. At the same time, waste reuse was analysed in light of its limitations and potentialities. Moreover, in the pursuit of sustainability, the manufacturing process that was followed was highly cost-effective in ambient curing conditions (20 degrees C, 65% RH), which avoided the use of any external source of energy as commonly used in geopolymers processing. The achieved results proved that the combined use of these wastes, which to date has hardly been explored, along with ambient manufacturing conditions increases the material sustainability. The produced mortars are suitable for innovative applications in various fields, with a particular focus on construction and contribute to the circular economy

Bi-Layered Porous/Cork-Containing Waste-Based Inorganic Polymer Composites: Innovative Material towards Green Buildings

Reduction of the energy consumption and CO2 emissions by the building sector might be a huge driver to mitigate climate change. One promising approach to mitigate energy consumption is the use of lightweight and low thermal-conductivity materials that could reduce the energy losses inside buildings and at the same time the use of heating and cooling devices that generate associated CO2 emissions. In this study, different strategies to produce lightweight and low thermal conductivity inorganic polymers were evaluated and compared, including the first ever production of bi-layered porous/cork-containing waste-based inorganic polymer composites. The bi-layered composites showed the lowest density (461 kg/m3) and thermal conductivity (94.9 mW/m K) values and reasonable compressive strength (0.93 MPa) demonstrating their interesting potential for enhancing the energy efficiency of buildings. Moreover, these composites were produced at room temperature, using an industrial waste (biomass fly ash) as precursor and a highly sustainable and renewable resource as light aggregate (cork), preventing the depletion of natural resources and the use of fossil-fuel derivates, respectively

The Role of an Industrial Alkaline Wastewater in the Alkali Activation of Biomass Fly Ash

Alkali-activated materials are generally considered a more sustainable alternative to Portland cement binders. This derives not only from the use of solid wastes as precursors, but also from the low temperatures required for their synthesis. However, to increase the environmental advantages of these materials, alternative activators should be explored, as the common route involves the use of commercial activators such as sodium silicate or sodium hydroxide solutions. In this work, the possibility of using an alkaline industrial wastewater, coming from a Portuguese paper and pulp industry, as a partial replacement of the commercial sodium hydroxide solution was studied. The results show that the use of the industrial wastewater decreased the workability of the pastes and their setting times, higher incorporations inducing a stronger reduction. Despite this, the results demonstrate the feasibility of replacing up to 25 vol.% of the sodium hydroxide solution with the industrial wastewater without compromising the mechanical performance of the binder. The compressive strength of this composition reached 22.7 MPa, this being slightly higher than the value seen in the reference (20.0 MPa). The use of a waste-containing activator, as reported here, might be a key driver to foster the wider use of this technology

Sustainable and efficient cork - inorganic polymer composites: an innovative and eco-friendly approach to produce ultra-lightweight and low thermal conductivity materials

In this investigation cork was used as a low density aggregate in the production of ultra-lightweight and low thermal conductivity inorganic polymer (geopolymer) composites. This novel and highly sustainable material, synthesised at room temperature (23 °C), may decrease the energy losses inside buildings, thus contributing to the United Nations development goals regarding energy and climate change. The ultra-low density (260 kg/m3) and low thermal conductivity (72 mW/m K) shown by the cork-composites are the second lowest ever reported for inorganic polymer composites, only being surpassed by that of polystyrene-inorganic polymer composites. However, cork is a fully renewable and sustainable resource, while polystyrene is manufactured from non-renewable fossil fuels, and for that reason our strategy has an additional sustainability advantage. Moreover, the cork-inorganic polymer composites do not release any toxic fume when under fire conditions, which is a major advantage over polymeric-based foams.R. M. Novais wishes to thank FCT project H2CORK (PTDC/CTMENE/6762/2014), and R. C. Pullar wishes to thank FCT (Portuguese Fundation for Science and Technology) grant IF/00681/2015, for supporting this work. This work was developed in the scope of the project CICECO - Aveiro Institute of Materials UID/CTM/50011/2013 (Compete Reference: POCI-01-0145-FEDER-007679), Associated Laboratory of University of Aveiro, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.publishe

Novel Inorganic Products Based on Industrial Wastes

This contribution reports the use of industrial wastes, red mud and tionite, obtained upon refining and extraction of bauxite and titania ores, respectively. For red mud, two applications were explored: geopolymers and clinker/cement. According to this study, only after 14 days the effects of addition of red mud are translated into technological properties of geopolymers. Moreover, in small proportions the mechanical strength was improved at 28 days curing, certainly due to the high alkaline nature of the waste. Belitic clinkers with balanced amounts of cementitious phases were produced at 1,350 degrees C. Mortars cured for 10 days produced from those clinkers/cements show mechanical strength that tends to increase when high amounts of C3S are formed. The relative content of C2S is also important in the hardening process. With the addition of red mud, the technological properties of the mortars were enhanced due to the pozzolanic reactivity of this sludge. The tionite was selected to be recycled as ceramic pigment. The colorimetric parameters of tionite pigment calcined at 1,200 degrees C and its application in transparent glaze show a light brownish colour, due to the strong brightness (L*). This colour should be exalted by the intercalation of metal ions present in the sludge that could form a metal bearing rutile phase. In the glaze, the yellow component (+b*) doubled and responds for the final beige coloration

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