Sandro Marden Torres

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.

Compósitos à base de gesso com resíduos de EVA e vermiculita

Gypsum is one of the oldest known building materials. Some of its properties confer advantages such as fire resistance, thermal and acoustic insulation. This work aims to study the physical and mechanical properties of gypsum-based composite with the incorporation of residues from the footwear industry ethylene vinyl acetate (EVA) and vermiculite. The aim to develop these composites is to produce components for thermal protection of masonry. To determine the influence of different residue levels of EVA and vermiculite, and the water/plaster ratio on the bulk density, flexural and compressive strength, five different percentages of these materials were incorporated combined with three water/plaster ratios. The results were analyzed by multivariate statistics and indicated that the density of both composites and the flexural strength of the composite with vermiculite had a greater influence of the water/plaster ratio, while the percentage of aggregate shows greater influence on the flexural strength of the composite with EVA and compressive strength of both composites.

Impregnation of Bambusa Vulgaris with Polymeric Resins

There are more than one thousand of bamboo species around the world, but in some areas the most common is the Bambusa vulgaris. Comparing with other species used in construction, it is more susceptible to insect attack and its strength is slower. This work shows some studies made using culms of this bamboo with the aim to improve its durability and mechanical properties by impregnation of polymeric resins into their vases. Some information about Bambusa vulgaris microstructure is done. The percentage of vases, fibers and parenchyma was measured using an optical microscope. The absorption of this species in liquids with different viscosities was determined. Using an equipment to force the liquid into the vases, time of penetration of fluids with different viscosity was measured. Results show that the fluids penetrate most easily in the internal vases, where the diameter is greater than that close to external face of the culms and confirm that it is possible to fill the bamboo vases with viscous fluid as oil or polymeric resins. The attack of insect was eliminated when a impregnation with a resin made by 80 % de styrene + 20 % de metilmetacriyate was applied to Bambusa vulgaris culms.

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.

Structural Integrity Assessment of Precast Concrete Slabs Employing Conventional and Recycled Coarse Aggregates via Vibration Tests

Precast slabs were tested, consisting of ceramic blocks supported by concrete ribs and with a concrete topping a few centimeters thick. These structures are very common in Brazil, being employed for the construction of houses and small buildings. In one of the tested slabs, recycled coarse aggregate was employed while conventional aggregate (granite gravels and quartz sand) was employed in the other tested slab. This study is part of a broader experimental programme which was designed to assess the applicability of concrete containing recycled aggregates as conventional aggregate replacement. In order to get insight into the structural behavior of slabs with recycled aggregates, the main focus of this paper is to assess the effect of structural load level on vibration parameters (Resonance Frequency, Damping Ratio and Transit Time). Full scale slab structural integrity was assessed by following changes in these parameters via a vibration (modal) test employing impact excitation. The structures were tested for several static load ratios (load to ultimate loading ratios (55%, 82% and 98%)). Visual inspection of induced cracking was also performed. The results obtained indicate a reduction of stiffness in both slabs up to 50% of the stiffness of the respective uncracked structure, which followed a similar trend despite the aggregate types. As for the damping ratios, the recycled aggregate containing slab showed lower values in comparison to the control slab with conventional aggregate. Whereas the former results might indicate similar load capacity, the latter, in principle, may have implications for the vibration serviceability limit state of structures. However, although structures with lower damping ratio can potentially present vibration problems, these studied elements are not often subjected to excessive vibration in its service life.

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.