Evaluation of the matrix of plaster with incorporation of rubber of tires for use in construction

[EN] The use of gypsum in the Brazilian construction industry has been growing steadily in recent years, when the drywall system started to be used in the internal seals of all types of buildings. The new use this should be added the traditional use of gypsum as coating material applied directly on walls and ceilings and as casting material. Given the above, this paper studies some physical characteristics of gypsum composites produced with the addition of tire rubber residues. The experimental program included the completion of the following tests: mass density in plastic and hardened state, tensile strength in bending, compressive strength, tensile strength in bending, ultrasound and scanning electron microscopy (SEM). The incorporation of crumb rubber content was 5% and 10% relative to the mass of gypsum. Two different tire rubber particle sizes were used: a thin called (#0.075 mm) and thick (# 2.38 mm). The results provide a reduction in the bulk density value. It was found that the adhesion of the rubber particles in the gypsum matrix does not present satisfactory results in coarse. This adhesion deficiency, found in SEM testing, was responsible for the lower flexural strength, tensile strength in bending and compression in plaster composites with coarse when compared to the results of composites with fine grain. With respect to ultrasound testing, it was found that the rubber delays sound propagation time. Lastly, the technical feasibility of the study was tested by means of test specimens, which proved to be efficient.[PT] O uso do gesso na construção civil brasileira vem crescendo continuamente nos últimos anos, quando o sistema drywall passou a ser utilizado nas vedações internas de todos os tipos de edificações. A essa utilização nova somam-se os usos tradicionais do gesso como material de revestimento e como material de fundição. Diante do exposto, este trabalho estuda algumas características físicas de compósitos de gesso produzidos com a incorporação de resíduos de borracha de pneus. No programa experimental foram realizados os seguintes ensaios: densidade de massa no estado plástico e endurecido, resistência à ruptura na flexão, resistência à compressão, resistência à tração na flexão, ultrassom e microscopia eletrônica de varredura (MEV). O teor de incorporação da borracha de pneus foi de 5% e 10% em relação à massa de gesso. Duas diferentes granulometrias de borracha foram utilizadas: a denominada fina (#0,075 mm) e a grossa (#2,38 mm). Os resultados proporcionaram uma redução no valor da densidade de massa. Identificou-se que a aderência das partículas de borracha na matriz de gesso não apresenta resultados satisfatórios na granulometria grossa. Esta deficiência de aderência, constatada na MEV, foi responsável pela menor resistência à flexão, à tração na flexão e à compressão nos compósitos com a granulometria grossa, quando comparados aos resultados dos compósitos com a granulometria fina. Com relação aos ensaios de ultrassom, constatou-se que a borracha retarda o tempo de propagação do som. Por fim, a viabilidade técnica do estudo foi testada por meio de corpos de prova, onde se mostrou ser eficiente.À agência de fomento FAPESP – Fundação de Amparo à Pesquisa do Estado de São Paulo, pelo auxílio financeiro.Pinto, N.; Fioriti, C.; Paya Bernabeu, JJ.; Akasaki, JL. (2016). Avaliação de matriz de gesso com incorporação de borracha de pneus para utilização na construção civil. Revista Tecnológica. 25(1):103-117. https://doi.org/10.4025/revtecnol.v25i1.29894S10311725

Rice straw ash: A potential pozzolanic supplementary material for cementing systems

[EN] Biomass waste from rice straw has many management problems, including field firing causing severe air pollution and natural organic decomposition resulting in methane emission. The conversion of this waste to ashes may offer the possibility of reusing them in cementing systems. For the first time ashes from different parts of the rice plant (Oryza sativa) were characterised from the chemical composition point of view: rice leaf ash (RLA), rice leaf sheath ash (RlsA) and rice stem ash (RsA). Microscopic studies on ashes revealed heterogeneity in the distribution of chemical elements in the remaining cellular structure (spodograms). The highest concentration of SiO2 was found in dumbbell-shaped phytoliths (%SiO2 > 78%). In the global chemical composition of ashes, SiO2 was also the main oxide present. According to Vassilev¿s classification of chemical composition, RLA belongs to the K-MA zone (medium acid), RlsA to the K-zone (low acid) and RsA to the S-zone (high acid). Calcination temperatures ¿550 ¿C completely removed organic matter from the straw and ashes underwent significant sinterisation by calcining at 650 ¿C due to the presence of potassium chloride. Here, ashes from global straw (rice straw ash, RSA) are characterised (via X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetry) and tested from a reactivity point of view (reaction towards calcium hydroxide) in order to assess the possibility for its reuse in cementing systems. Results from pastes made by mixing RSA and calcium hydroxide showed that the pozzolanic reactivity of the ashes is important (hydrated lime fixation of 82% for 7 days and 87% for 28 days in RSA:hydrated lime paste) and cementing C S H gel is formed after 7 and 28 days at room temperature. Compressive strength development of Portland cement mortars with 10% and 25% replacements by RSA yielded 107% and 98% of the strength of control mortar after 28 days of curing. Frattini test confirmed the pozzolanicity of the RSA blended cements. These reactivity results are very promising in terms of the potential reuse of ashes in cementing systems.The authors acknowledge the financial support of the Ministerio de Economia y Competitividad MINECO, Spain, and FEDER funding [Project: B1A2015-70107-R] The authors thank the Electron Microscopy Service of the Universitat Politecnica de Valencia (Spain).Rosello Caselles, J.; Soriano Martínez, L.; Santamarina Siurana, MP.; Akasaki, JL.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2017). Rice straw ash: A potential pozzolanic supplementary material for cementing systems. Industrial Crops and Products. 103:39-50. https://doi.org/10.1016/j.indcrop.2017.03.030S395010

Effect of sugar cane straw ash (SCSA) as solid precursor and the alkaline activator composition on alkali-activated binders based on blast furnace slag (BFS)

[EN] Alkali-activated materials (AAM) comprise one of the solutions to diminish the use of Portland cement in building construction and, consequently, a reduction in the environmental problems related to CO2 emissions and energy consumption may be achieved. These kinds of binders are obtained when a mineral precursor (calcium silicate or aluminosilicate material) is mixed with an alkaline solution. In this study, the blast furnace slag (BFS) combined with a new waste from the sugar cane industry, sugar cane straw ash (SCSA), is utilised. This new residue was studied replacing partially the blast furnace slag in BFS/SCSA proportions of 100/0, 85/15, 75/25, 67/33 and 50/50. The alkaline solution concentration plays an important role in obtaining AAM with good mechanical properties. Therefore, this paper intends to assess the influence of the activating solution (composed of sodium hydroxide and sodium silicate) through different H2O/Na2O (called g) and SiO2/Na2O (called e) molar ratios. For BFS/SCSA proportions of 100/0 and 75/25, the g values assessed were 22, 28 and 37, whereas the e values selected were 0 and 0.75. In order to study the effects of SCSA in the mixture, other BFS/SCSA proportions (0¿50% replacement) were assessed by only g and e ratios of 28 and 0¿0.75, respectively. To reach these objectives, mortars and pastes were manufactured in order to study their behaviour in the following tests: compressive strength (3, 7, 28 and 90 days of curing at 25 C), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and field emission scanning electron microscopy (FESEM). The results showed that the alkaline solution influenced the compressive strength development, and specimens reached more than 60 MPa after 90 days of curingThe authors would like to thanks to CNPq processo no 401724/2013-1 and the "Ministerio de Educacion, Cultura y Deporte" of Spain ("Cooperacion Interuniversitaria" program with Brazil PHB-2011-0016-PC). Thanks are also given to the Electron Microscopy Service of the Universitat Politecnica de Valencia.Moraes, J.; Mitsuuchi Tashima, M.; Akasaki, JL.; J.L.P.Melges; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Soriano Martínez, L.... (2017). Effect of sugar cane straw ash (SCSA) as solid precursor and the alkaline activator composition on alkali-activated binders based on blast furnace slag (BFS). Construction and Building Materials. 144:214-224. https://doi.org/10.1016/j.conbuildmat.2017.03.166S21422414

Calculation of t8/5 by response surface methodology for electric arc welding applications

[EN] One of the greatest difficulties traditionally found in stainless steel constructions has been the execution of welding parts in them. At the present time, the available technology allows us to use arc welding processes for that application without any disadvantage. Response surface methodology is used to optimise a process in which the variables that take part in it are not related to each other by a mathematical law. Therefore, an empiric model must be formulated. With this methodology the optimisation of one selected variable may be done. In this work, the cooling time that takes place from 800 to 500ºC, t8/5, after TIG welding operation, is modelled by the response surface method. The arc power, the welding velocity and the thermal efficiency factor are considered as the variables that have influence on the t8/5 value. Different cooling times,t8/5, for different combinations of values for the variables are previously determined by a numerical method. The input values for the variables have been experimentally established. The results indicate that response surface methodology may be considered as a valid technique for these purposes.Valcuende Payá, MO. (2014). Calculation of t8/5 by response surface methodology for electric arc welding applications. Thermal Science. 18(1):149-158. doi:10.2298/TSCI130418162VS14915818

Evaluation of the Pozzolanic Activity of Uncontrolled-Combusted Sewage Sludge Ash

[EN] Waste management is a crucial issue facing modern society. The generation of sewage sludge is increasing annually due to the urbanization and improvement of sanitation systems of cities. The construction sector has emerged as a solution for the elimination of waste due to the enormous volume of materials that this sector can absorb. This paper evaluates the pozzolanic activity of sewage sludge ash (USSA) obtained following an uncontrolled-combustion process, a simple and economic procedure. Compressive strength of Portland cement/USSA mortars with 5%¿25% by weight USSA were evaluated. Calcium hydroxide/USSA and Portland cement/USSA pastes were chemically and physically characterized through thermogravimetric/differential-thermogravimetric (TG/DTG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The increase in the replacement of Portland cement by USSA is associated with an increase in the compressive strength of mortars. These values for USSA containing mortars cured for 90 days were in the range of 49.6¿55.4 MPa, higher than the one reached by the reference mortar. According to the microstructural analysis, the increment on the compressive strength can be attributed to the formation of hydrated products (C¿S¿H, C¿A¿S¿H, and C¿A¿H) by the pozzolanic reaction of USSA.This research was financed in part by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (Capes)Finance Code 001, and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) (Processo Nos. 309015/2015-4 and 478057/2013-0). Thanks go to the Scanning Electron Microscopy Service of FEIS/UNESP, Servico Municipal Autonomo de Agua e Esgoto (SEMAE) from the Sao Jose do Rio Preto city (Sao Paulo, Brazil).Istuque, DB.; Reig, L.; Soriano Martinez, L.; Borrachero Rosado, MV.; Pinheiro Melges, JL.; Akasaki, JL.; Paya Bernabeu, JJ.... (2021). Evaluation of the Pozzolanic Activity of Uncontrolled-Combusted Sewage Sludge Ash. Journal of Materials in Civil Engineering. 33(6):1-12. https://doi.org/10.1061/(ASCE)MT.1943-5533.000376511233