Kelly Cristiane Gomes

Iron Distribution in Geopolymer with Ferromagnetic Rich Precursor

Geompolymers and their engineering applications have attracted significant attention of the scientific community. This is due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. The iron content is significant, reaching around 10% in metakaolinite, for instance. The role of iron in geopolymers still lacks systematic investigation. This can be attributed to the limitations presenting nuclear magnetic resonance (NMR) spectroscopy, which is a widely used technique to study geopolymers structure. Ferromagnetic elements such as iron, which is often present in some precursors, affect the magnetic response of the material, compromising the proper analysis of its structure by NMR results. Iron content in some industrial residues may be several times higher as it is often found in metakaolinite. This work presents x-ray diffraction, infrared and Mössbauer spectroscopy studies on the distribution of iron species in iron oxide/hydroxide-rich precursor, which was used to synthesized geopolymers.

Adhesion of Geopolymer Bonded Joints Considering Surface Treatments

In this study the adhesion properties of a geopolymer-based adhesive on metallic substrates are investigated, considering different surface conditions. Mechanical treatments (grit-blasting and sand-blasting) and chemical treatments (nitro-phosphoric acid and silanization) were performed on steel and aluminium plates. Single lap joint specimens were tested in order to access the influence of these pretreatments on the shear bond strength. The surfaces were scanned and the average surface roughness parameters were used in order to assess their effect on bond strength. The results indicated that the effect of individual surface roughness parameters alone is not statistically significant when correlated with bond strength. In general, chemical treatments were usually less effective than mechanical treatments alone for both steel and aluminium joints with geopolymers as adhesives.

Adhesion of Ceramic Plates with Geopolymer

The detachment of ceramic tiles from buildings is a problem that still persists in several modern constructions. Although there are several specific techniques for the prevention of tiles from detaching this issue still requires in-depth research in order to be fully solved. These detachments happen commonly in facades that are submitted to the incidence of solar rays on the surfaces. In this work, the adhesion of porcelanate-adhesive-substrate was investigated through direct detachment tests according to Brazilian standards. Two types of adhesives were used: a commercial adhesive, classified by Brazilian standard as being of high adhesion (ACIII-E) and a geopolymer, developed through alkaline activation of metakaolin with sodium silicate. The bonded systems were submitted to two temperature exposure regimes. In general, geopolymeric adhesives had better adhesion than the systems bonded with ACIII-E adhesive mortar, especially with temperature increase.

Geopolymeric Adhesives for Aluminium Joints

Bonded joints have been used in substitution of more traditional techniques as screws, rivets and mainly welding. However, the applications in which the work temperatures are relatively high remain as an obstacle to the use of more common polymeric adhesives. In this sense, the study of adhesive properties of thermally stable materials as the geopolymers becomes a need. This work deals with the adhesion of aluminium sandwich beams using geopolymeric adhesives. Metakaolin-based geopolymers were used as adhesives, activated with sodium and potassium silicates. Shear mode adhesion tests were accomplished and the results indicate the possibility for use of these new adhesives.

Mechanical Performance of Natural Fibers Reinforced Geopolymer Composites

The use of geopolymers as matrix in composites with syntactical fibers have been studied and proposed in the literature. Nonetheless, for the best know of the authors, there are no researches about the use of geopolymers as matrix in composites with natural fibers. The use of natural fibers is increasing in the automotive industries. One of the problems to expand the use of natural fibers in composite materials is the low fire resistance of the classical type of polymers. In this sense, geopolymeric matrices open up horizons for this type of application. This paper studies composites with geopolymeric matrices reinforced with two types of natural fibers: sisal (Agave Sisalana) and pineapple leaf fiber (PALF-Ananas Comosus). The mechanical properties of these new composites are investigated by mechanical tests. The results confirm the increasing in the mechanical performance whenever the fibers are under traction stress.

Alkaline Activation of Aluminum and Iron Rich Precursors

The alkaline activation of aluminosilicates materials has been motivated by their enhanced thermomechanical properties. Despite the majority of studies comprise the evaluation industrial byproduct of precursors (fly ash and slag), metakaolin (Al2O3.2SiO2) is acknowledged to have structure and chemical composition characteristics that make it very reactive as far as alkaline activation is concerned. In tropical regions of the earth, as is the case in northeastern Brazil, there are some waste (kaolin waste, red brick waste and weathered tropical soils) whose alkaline activation potential have not yet been fully studied. These sources are known to have other metals such as iron in its structure, which might affect the alkaline activation. This paper aims to evaluate the potential of alkaline activation of these wastes. Chemical and structural characterization were performed by means of x-ray fluorescence, x-ray diffraction, infrared spectroscopy and compressive strength. The results indicate that all studied waste presented significant potential as precursor material for alkaline activation.

Application of Geopolymeric Adhesives in Ceramic Systems Subjected to Cyclic Temperature Environments

The Brazilian experience with the use of ceramic tiles in facades dates back to the 17th century. Many modern buildings still use such an architectural option, which leads to an increasing industry of cementious adhesives. Despite several recommendations in standards, there is still a huge problem with ceramic detachments. This paper discusses observations in some field case scenarios as well as assesses the potential use of a new type of adhesive, characterized by having low CO2 emissions in its productions chain. In this study, the adhesive properties were determined in a porcelain tiles-adhesive-substrate system through the pullout test. The roughness of the tiles was also determined. Three types of adhesives were used: a high-performance commercial adhesive, classified by the Brazilian standard as high adherence (ACIII-E), and two alkaline type adhesives [alkaline-activated metakaolinite (MK) and alkaline-activated weathered soils (SI)]. These geopolymeric adhesives were activated with alkaline metals using sodium and potassium silicates. The bonded systems were subjected to room temperature, 55°C, and cyclic regimen. In field cases, it has been observed that detachments most often occur in facades subjected to a greater incidence of sunlight on their surfaces. The experimental study points out that the alkaline activation of aluminum silicates improved adhesive and thermo mechanical properties in comparison with commercial adhesives. In general, the geopolymeric adhesives had better adhesion than those which were adhered with the commercial adhesive ACIII-E, especially under increased temperature.

Viability of Sugarcane Bagasse Ash as Precursor Material to Solar Absorbers Films

The availability of fossil resources decreases over the years, constituting a problem that needs to be properly treated. In this context, it is necessary the exploration of alternative and renewable sources of energy, particularly the use of solar energy incident on the planet. The aim of this work is to examine the feasibility of the application of sugarcane bagasse ash as a precursor material for obtaining an inorganic polymer that will form the absorber film for use in solar collectors for medium and high temperature. Through mechanical particle size separation of ash and its physicochemical characterization, it was possible to prove that the chemical and mineralogical composition of the raw material is favorable for use in alkaline synthesis Furthermore, the ash particle size large achieved the best results of properties optical and microstructural, favoring its application to obtain films to be applied to selective surface. It was also observed that the metallic copper substrate had the best interaction with the film providing the best results in absorption of ultraviolet visible region.

Supercritical carbonation of lightweight aggregate containing mortar: Thermal behavior

Lightweight concrete shows good insulation properties, depending on several parameters such as mix design and aggregate type. Perlite aggregate is one of the most effective aggregates for such a purpose, mainly because of its low thermal conductivity (0.04 W/m.°C), but is not available globally. This paper explores the potential use of another source of thermal efficient aggregate, vermiculite (0.058 W/m.°C) which is available in Brazil and other countries where perlite is absent. Cylindrical samples were cast by using two lightweight aggregates, perlite and vermiculite, and treated with supercritical carbon dioxide. Supercritical carbonation (SCC) of concrete can improve mechanical, thermal and durability features. In this paper, the effect of SCC on the thermal behavior of lightweight mortars was investigated with regards to physical and microstructure features and thermal behavior due to cooling.

Behavior of Sisal Fiber Mat Reinforced Alkaline Activated Metakaolin Matrix under Direct Flame

Biodegradable containing composites are increasingly present in several industries, mainly because they are renewable but also for their engineering properties. Despite environmentally friendliness has become an issue of paramount importance, the use of natural fibers has some limitations, especially when high temperature exposure is concerned. Geopolymers are known to withstand temperatures as high as 1000°C, preserving significant mechanical properties. This paper aims to explore the potential use of sisal fiber reinforced alkaline activated in high temperature environment. The composites were exposed to direct flame and visual changes and temperature profile were assessed up to 35 minutes. The results shows that material behavior works as an insulation barrier with a c.a. 80% temperature reduction between the direct flame exposed surface to the opposite side. Also, samples with thickness above 5mm maintained their integrity without developing smoke or spreading flame throughout the study time.