Key Engineering Materials Vol. 634

Abstract: The dimensional instability of vegetable fibers due to hygroscopicity results in a gradual loss of adherence in cement based composites which, when in service, are submitted to a natural variation of humidity. Such an effect reduces the contribution of the fiber as a reinforcement and can cause the early rupture of the material. In this work, a treatment of the sisal fibers is performed with the applying of wetting-drying cycles in order to alter their crystalline structure and improve the dimensional stability of the fiber to withstand the variation of humidity: 6, 10, 20, 30 and 34 cycles were applied in order to evaluate the effect on the properties of fiber; a tensile test, the morphological characterization (MEV) and the evaluation of the chemical structure of fiber were carried out. The effect of the treatment on fiber-matrix behavior was evaluated using the pull-out test. Embedded lengths of 16, 20, 30, 40 and 44 mm were defined through a factorial design and used in the test. It is verified that the use of 10 wetting-drying cycles causes less damage to the tensile strength and the elastic modulus of the fiber and contributes to a better adherence with the matrix, with an increase of up to 23 % compared with the untreated fiber. The statistical analysis of the interaction effect between the studied factors, using 2^K factorial design with central composite design, indicates that the number of cycles can be decreased when using a longer length of the embedded fiber.Keywords: wetting-drying cycles, pull out test, tensile strength..

Abstract: The aim of this research is the development and mechanical characterization of self-compacting soil cement composites with the incorporation of fly ash, metakaolin and sisal fibers. The mentioned composites, based on natural raw materials (raw earth and vegetable fibers), which are abundant in nature and have low cost and low environmental impact could be used as a more sustainable alternative than conventional industrialized materials for applications that don ́t require high structural performance (minimum strength equals to 2 MPa). A residual soil, constituted by 35% of fines and 65% of granular material was selected and the matrix was designed using a computational routine, based on the compressible packing model (CPM). The rheology of the matrix was adjusted by the slump flow test having as a target the spreading value of 600 mm. The matrix presented uniaxial compression strength of about 3.3 MPa after 28 days of curing. After 240 days of curing it was noticed an increase in the compressive strength to 7.5 MPa. This can be traced back to the pozzolanic reactions that takes place in the system. The soil cement composites were produced with three different sisal fiber contents: 0.5, 1.0 and 1.5% (in relation to the weight of dry soil) and a fiber length (L_e) of 20 mm. Under compression, the incorporation of fibers has significantly influenced the post-peak behavior, increasing the toughness and the strain capacity. Under four point bending loading, the presence of fibers have contributed to increase the peak strength and the residual strength with expressive gains of toughness. The composites presented strength values as high as 1.8 MPa (1.0% of fibers) when they were subjected to bending loads. The use of sisal fibers as reinforcement modified the fracture mechanisms of the composites, changing it from a brittle to a ductile behavior.

Abstract: This paper presents some considerations on the impacts of industrialized construction materials to Planet Earth. It comments about sustainability and show that large part of the present generation has not met their basic needs, starting with the house. So, in this context, with the actual economic model, it becomes difficult to ensure that future generations are able to meet their own needs. Some considerations about possibilities of building with reduced environmental impact is presented. Comments about raw earth as building material are made. New possibilities to give stability to this material against water action is discussed. Finally, it shows some contemporary constructions made with earth in Brazil.

Abstract: Fibrous structures based on natural fibers have gained a key space when it is required to perform functions like separation, drainage, filtration, protection and soil reinforcement. The use of natural fibers turns engineering work more sustainable, since they are renewable, biodegradable, energy efficient and non-toxic raw materials. In this work, the influence of degradation caused by UV rays, heat and moisture on the mechanical behavior of vegetal natural fibers used in geotextiles, including sisal, coir and banana fibers, was studied. Natural fibers have been subjected to accelerate aging agents using QUV equipment and to real conditions, in contact with soil over a 3 months period. Samples were removed every 15 days and their mechanical behaviour evaluated under tensile. Moreover, the morphological modifications in the fibers structure have been also analyzed using SEM. The results show a significant degradation over the first 15 days for all types of fibers used. Sisal and banana fibers subjected to degradation in soil, present higher tensile strength loss over time than fibers subjected to accelerate aging tests in QUV. For geotextiles design, important remarks from the results can be obtained including: banana fibers are quite degraded by aging and soil conditions making them difficult to be applied in geotechnical engineering; sisal and coir fibers present high potential to perform various functions in contact with soil.

Abstract: This paper deals with the characterization of acoustic insulation behaviour of hybridsandwich composite panels for application in modular house construction. These sandwich panelsare a sustainable, light-weight and durable solution, since are based on natural fibers structureimpregnated with a thermosetting polymer. In this way, three different types of hybrid compositepanels containing polyurethane core and laminated composite skins were produced and analyzed,varying the composition of laminates. The composite laminates of the prototypes were producedusing a vacuum infusion technique and were composed of glass and jute fibers, impregnated with apolyester resin. The solutions developed were compared with a standard, composed of plasterboardshaving different thicknesses and used for thermal and acoustic insulation. Acoustic insulationcharacterization was performed on specimens with 220x220 mm size in a sound proof acousticchamber. The tested sandwich panels showed promising results; however, their overall performancewas lower as compared to the performance of standard solutions used for comparison. Nevertheless,the specific acoustic insulation performance, i.e. sound reduction per unit mass of material for thedeveloped sandwich panels was significantly higher as compared to the standard materials,indicating better suitability of this innovative solution for light-weight construction and modularhousing.

Abstract: After submitted to early age carbonation curing, mechanical and physical properties of high initial strength sulfate resistant Portland cement (HS SR PC) pastes were investigated, which were compared to those of non-carbonated reference pastes. Carbonation was performed for 1 and 24 hours, at the best conditions of CO₂ capturing, previously determined by the authors. Despite the compressive strength and elastic modulus of the 1h carbonated pastes were slightly higher than those of the reference pastes, their absorbed water content and porosity was slightly higher than that of the reference. In the case of 24h carbonation, its compressive strength decreases significantly because of its much higher porosity, although the new solid carbonated calcium silicate phase presents a much higher specific mass than those of the solid phases of the 1 hour and non-carbonated pastes.

Abstract: Heat treatment of wood is a promising alternative in improving its dimensional stability. The action of heat ensures the good quality of the treated wood product, with better performance in environments with high humidity. To prove the positive effect of this treatment, a test in which the specimens are weathered for a certain period of time termed as natural aging was performed. The aim of this study was to evaluate the effect of aging on heat-treated medium-density fiberboard (MDF) panels. Commercial MDF panels produced with pinewood adhesive and urea-formaldehyde were used. The experiment included seven test treatments [at 200, 225, and 250°C heat temperatures for 5 and 10 min] and a control treatment (without heat treatment). The products subjected to these treatments were weathered for 40 days, and climatological data were monitored daily. The results suggested that: 1) There is a decreasing trend in density with increasing time and temperature; 2) the treatment time and temperature had no effect on the ownership of the static bending for modulus of elasticity (MOE); 3) the time period is correlated with the treatment temperature for modulus of rupture (MOR) property; and 4) the thermal treatment of MDF panels did not allow the maintenance of the properties of MOR and MOE static bending strength after natural aging.

Abstract: The need to insert the durability factor on dimensioning concrete structures has been stimulating the development of new models to predict the service life of those structures. Among those new models, the use of data from Non-Destructive Testing (NDT) is recommended. It is known that electrical resistivity is a parameter related with permeability and, in consequence, with the resistance of the concrete against the intrusion of aggressive agents. Electrical resistivity may be monitored with time by a NDT method, by a low cost and easy execution technique. However, some parameters of this essay need to be further discussed in the literature aiming to standardize this technique. Thus, this study had the goal to verify the influence of test specimen’s shape in measurements of electrical resistivity. In order to that, cylindrical and prismatic test specimens have been molded from a same type of concrete and electrical resistivity was monitored during a period of 120 days. Results show significant differences between the values obtained. Test specimens in cylindrical shape had the higher results. A good correlation between factors was found with R² higher than 0.94.

Abstract: This study includes the identification of parameters for the characterization of the structural behavior of thin plates composed of geopolymer mortars structured with bi-directional carbon fiber mesh. Initially, facade projects, designed by offices in São Paulo using the concepts of sustainable architecture, promoting the use of geopolymeric materials are presented. Then shows the composition of the geopolymer mortar used in this study and the characterization of their mechanical properties. As part of the experimental program, this study evaluates the plate bending behavior and the effect of pull-out test and push-off test of the metallic inserts. It has used the advanced features of ATENA computational mechanics program, which correspond to the state of the art in Finite Element Modeling of reinforced concrete structures, which allow the calibration of the mathematical model based on information from the experimental program. The numerical results showed satisfactory adhesion with the experimental results. It also has emphasized the importance of validation of these results on the determination of loads collapse of structural elements, as is reflected positively in the field of Structural Engineering in the face of increasing advancement of surface modeling programs and technological innovations in according to sustainability criteria for constructions materials.

Abstract: A kinetic based comparison between expansion tests for alkali-aggregate reactivity was carried out deriving critical rates from test criteria, in an earlier paper. The present paper checks the assumptions and models of that earlier comparison against results with real aggregates varying in alkali reactivity. Using the same approach, for each aggregate, expansion rates for three expansion tests were estimated, corrected for alkalinity and depicted as an Arrhenius plot. The relationship used data from NF P18-590, ASTM C 1260 and ASTM C 227 expansion test-methods and shows linear Arrhenius plots for several aggregates, aligned almost parallel to the line obtained for test criteria. Aspects related to the different experimental conditions on test-methods and their effects are discussed. The proposed conclusion is that both standards and aggregate results, in the given conditions, are not inconsistent from the kinetic point of view. Some suggestions are made for improving the accuracy of the relationship obtained.