Navegando por Assunto "Concreto"

Agora exibindo 1 - 20 de 30

Acesso aberto (Open Access)
Análise do comportamento mecânico de tubos de concreto com fibras de aço produzidos com materiais da região metropolitana de Belém do Pará
(Universidade Federal do Pará, 2015-09-25) OLIVEIRA, Marco Antonio Barbosa de; POMPEU NETO, Bernardo Borges; http://lattes.cnpq.br/6564259204591721; MACEDO, Alcebíades Negrão; http://lattes.cnpq.br/8313864897400179
The steel fibers in the concrete pipes have provided better mechanical performance levels. In the northern region, uniquely in Belem, no studies on the technical feasibility of this technological resource, although there is considerable deficiency of urban infrastructure. Thus become relevant conduct studies on alternative technology. This study seeks to analyze the mechanical behavior of concrete pipes with steel fibers, aiming at the technical feasibility of replacing the concrete pipe with conventional armor. The research methodology we used steel fibers in loose state and glued comb DRAMIX® 3D type 65/35 and 80/60 DRAMIX® 3D type. For each fiber type were adopted contents of 20 kg / m³ (0.25%), 30 kg / m³ (0.38%) and 40 kg / m³ (0.50%) by weight and volume fraction, respectively. The size of all concrete pipes was 600 mm diameter, wall thickness of 60 mm and effective length 1000 mm, and the cylindrical bodies of the test piece of 100x200mm and prismatic of 150x150x500mm and 150x150x550mm, which were subjected to the tests for mechanical behavior evaluation and durability. In the production of concrete with the fibers was reviewed in the fresh state with frustoconical rebate between 0 and 10 mm. The dosage of concrete with fibers was routinely employed by the company for concrete without fibers, and the strength of the fibers takes place under the rule of the mixture. The results obtained that the concrete pipe with fiber type 80/60 loose at all levels and pasted comb the levels of 0.38% and 0.50%, reached the minimum breaking load and post-cracking set by the NBR 8900 (ABNT, 2007), thus would be technically feasible as the replacement of reinforced concrete pipes conventionally, under the conditions and specifications of this study.
Acesso aberto (Open Access)
Análise estrutural de concretos produzidos com resíduos de beneficiamento de placas de mármore e granito
(Universidade Federal do Pará, 2019-05-06) BANDEIRA, Sandy Rebelo; MAGALHÃES, Edilson Marques; http://lattes.cnpq.br/1570353513360972
The present work shows the feasibility of the use of cutting residues of marble and granite slabs in concrete production. The research was carried out in a series of stages, which comprised the collection of waste in the beneficiary companies, through the process of crushing, sieving of waste and production and breaking of specimens. The chemical analysis performed by x-ray fluorescence shows that the material meets the requirements of NBR 12653: 2015 for the concentration of aluminum, silicon and iron oxides, qualifying it as pozzolanic material. The results of axial compression showed that the mixtures produced with the substitution of aggregates meet the minimum requirements of NBR 6118: 2014 for application in structural elements subjected to moderate environmental aggression, class II. The traces were dosed following the instructions of the IPT / USP dosing method. 195 samples were produced, which were ruptured at 3, 7 and 28 days. Concrete was expected to reach at least 30 MPa at 28 days. The traces produced with the substitution of the aggregates presented smaller values than the reference trait. Regarding the absorption, it was observed that the traces with substitution of aggregates presented a slight increase in water consumption, which may explain the reduction in the indices of compressive strength.
Acesso aberto (Open Access)
Análise experimental da eficiência de bielas de concreto simples e armado em modelos locais e globais
(Universidade Federal do Pará, 2019-03-21) FREIRE, Marília Caires; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485; https://orcid.org/0000-0001-8905-9479
Reinforced concrete beams are usually designed by sectional analysis methods, where Bernoulli hypothesis is taken into account, assuming that strains are linearly distributed along the cross-sectional area of the element. However, many practical situations require distinct calculation alternatives, made by both fundamentally empirical code expressions and numerical or analytical solutions from the Strut-and-Tie Method. This is the case of deep beams, where a bottle-shaped strut is formed and the influence of its reinforcement ratio is generally discounted by the current design codes. Therefore, an experimental study was performed to assess the efficiency of plain and reinforced concrete struts, by local and global models, respectively represented by diamond-shape panels loaded in small bearing areas and deep beams, since in both the resistant mechanism seems to be directly related to the flow of stresses in the concrete strut. The results showed similar behaviors among the models regarding strains in concrete and reinforcement, as well as equivalent failure modes resulting from a splitting crack of the strut. With the increase of transverse reinforcement ratio, gains of ultimate strength, ductility and cracking control were observed, mainly for specimens with mesh reinforcement, as well as higher and safe results for the analysis by the strut efficiency factors. On the other hand, the assessment of shear strength by the design codes showed unconservative predictions with increasing transverse reinforcement. This way, it is confirmed that solutions by strut-and-tie models are more suitable methods for the efficient and safe design of structures with regions of disturbance in the stress-strain distribution.
Acesso aberto (Open Access)
Análise não linear de vigas de concreto armado com fibras de aço
(Universidade Federal do Pará, 2019-08-20) FIGUEIRA, Fábio Rogério Mendonça; OLIVEIRA, Dênio Ramam Carvalho de; http://lattes.cnpq.br/1324105476558186
In the present work, a proposal is presented for the calculation of the ultimate strength, MR, of reinforced concrete beams with steel fibers (CRFA), considering the non-linear behavior of this material. For this purpose, the proposals of five normative recommendations, ACI 544.4R-88 (1988), RILEM TC 162-TDF (2002), CECS 38 (2004), CEB-FIP (2010) and DAfStb (2010). To evaluate the proposal, a database with 42 beams was used, which broke the bending. The performance of the proposal is judged as a function of the parameter ⅄ = Mexp / Mteo, which defines the ratio between the experimental (BD) and theoretical resistances. It should be noted that the parameter ⅄ is evaluated in terms of accuracy, dispersion, safety and classified according to an adaptation of Demerit Points Classification - DPC. Finally, we present the nonlinear simulation of the moment-curvature relationship with the help of the SAP 2000 software, applying the equations proposed by RILEM TC 162- TDF (200) and the equations developed by Moraes Neto (2013) for the residual resistance of this material.
Acesso aberto (Open Access)
Aplicando concreto de elevada resistência reforçado com fibras de aço na supressão do reforço convencional de vigas em concreto armado de resistência normal
(Universidade Federal do Pará, 2020-01-14) SOUSA, Elielson Oliveira de; MORAES NETO, Bernardo Nunes de; http://lattes.cnpq.br/5790058515094077
High strength steel fiber reinforced concrete (HS-SFRC) used as suppression of conventional reinforcement normal strength reinforced concrete beams (NS-RC) has been in the current experimental research. Five 150x300x2700 mm³ size beams were prepared and submitted to four point bending test until failure. The beam reference have been produced without steel fibers (fc = 30.0 MPa), with longitudinal reinforcement ratio (ρl,t = 0.91%), and transverse reinforcement (ρw = 0.11%), representative of practice applications. Four other HS-SFRC beams were produced with fc = 60.0 MPa, ρl,t = 0.39% (≈ 60.0% suppression relative to reference beam), ρw = 0.0 % (100.0% suppression) and fiber consume (Cf) alternating in 45,0,60,0, 75,0 and 90,0 kg/m³. The behavior beams was analyzed from load-displacement and moment-curvature relations. The viability to design HS-SFRC beams with suppression conventional reinforcements was verified based on these results and material characterization tests, exposing equivalent mechanical behavior and some cases higher that of NS-RC beams.
Acesso aberto (Open Access)
Aproveitamento dos resíduos cauliníticos das indústrias de beneficiamento de caulim da região amazônica como matéria-prima para fabricação de um material de construção (pozolanas)
(Universidade Federal do Pará, 2007-12-18) BARATA, Márcio Santos; ANGÉLICA, Rômulo Simões; http://lattes.cnpq.br/7501959623721607; https://orcid.org/0000-0002-3026-5523
The Capim and Jarí regions are the most important kaolin district in the Amazon region, with the largest Brazilian reserves of high whiteness kaolin for paper coating products. Kaolin is obtained from three companies (IRCC, PPSA and CADAM) which produce annually around 1,000 M ton kaolinite-rich wastes derived mainly from the centrifugation phase of the process. The sludge is disposed on artificial sedimentary lakes covering large areas. Another type of kaolin waste is related to a non-processed iron-rich hard or flint kaolin, that overlays the so-called soft kaolin horizon (the main ore). These wastes exhibit appropriate characteristics for the production of high-reactivity metakaolin because they are extremely fine and composed of mainly by kaolinite. The main purpose of this work is to evaluate the feasibility of using these wastes as raw materials to produce mineral admixtures for OPC concretes. The wastes were firstly characterized for x-rays diffraction, thermal analysis, infrared spectroscopy, x-rays fluorescence and SEM. Three heating temperatures were evaluated: 750ºC, 850ºC and 900ºC, followed by pozzolanic activity tests based on traditional mechanical assays using Portland cement and hydrated lime mortars, and “Chapelle” test. The results showed that the more reactive pozzolans are those produced at temperatures that gave rise to higher LOI. The optimum burning temperature to produce metakaolinite from the hard kaolin was obtained at 750ºC while those from the Rio Jari and Rio Capim wastes were at 850ºC and 900ºC. The main reason is related to differences in the amounts of defects from three different wastes. The flint kaolin and Rio Jari waste are mainly composed by a “high-defect” kaolinite while the kaolinite from Rio Capim waste is a “lowdefect” kaolinite. In concrete test using different pozzolans those with metakaolin from wastes improved the mechanical and durability properties in comparasion to silica fume, a industrially manufactured metakaolin and reference concretes.
Acesso aberto (Open Access)
Avaliação da durabilidade de concretos produzidos com agregado miúdo reciclado de cerâmica vermelha
(Universidade Federal do Pará, 2016-02-05) MORAES, Ruan Fabrício Gonçalves; SOUZA, Paulo Sérgio Lima; http://lattes.cnpq.br/4933212993218783
The generation of waste from civil construction (WCC) in Brazil and in the world are of great proportions. However, its reuse does not occur in the same proportions that are generated by construction, is added to this, the need to find solutions for the landfilling of these wastes, unsustainable consumption of natural resources, where deposits already present signals aggregate shortage. Therefore, the use of red ceramic as recycled aggregate, reduces costs for the production of concrete, brings awareness of environmental cooperation and sustainability. In this scenario, the literature is still scarce in relation to the concrete durability properties for this kind of aggregate. Thus, this study aimed to improve and disseminate knowledge about these waste in construction. To this end, mixtures were made with water / cement ratio of 0.45; 0.55 and 0.65, where the aggregate has been replaced by natural fine ceramic aggregate in 0%, 12.5% and 25%, each percentage was subjected to pre-wetting rate of 40%, 60% and 80%. Subsequently, the durability of concrete produced with fine ceramic aggregate (FCA) was evaluated through capillary absorption, carbonation, electrical resistivity and chloride ion penetration. With the results obtained it can be concluded that the slump test was satisfactory in most mixtures, with respect to durability, in general, all mixtures with ceramic recycled aggregate had higher durability than the reference, especially in mixtures with 25% AMC. Pre-wetting rates were effective in most mixtures, showing satisfactory influence on the final results in all tests. So it managed to show great feasibility of using this waste in concrete, improving their performance.
Acesso aberto (Open Access)
Avaliação da durabilidade de concretos produzidos com agregados graúdos reciclados provenientes de cerâmicas vermelhas com diferentes taxas de pré-saturação
(Universidade Federal do Pará, 2013-09-05) REIS, Felipe José Losada; SOUZA, Paulo Sérgio Lima; http://lattes.cnpq.br/4933212993218783
The amount of waste generated by the construction industry has been calling attention lately due to the size with which acts as the environmental impact of using non-renewable natural sources materials and increasing the amounts of waste produced by the urban environment. In Brazil, this estimate is around 90,000 tons generated per day. The proposed use of aggregate from CW ( construction waste ) as part of structural concrete becomes even more interesting from the moment we are seeking a reduction in costs for the production of concrete , carrying environmentalist mentality when sparing use of natural resources which some are already starting to run out. Banks of sand and pebble sources begin to fade due to the wide use of these aggregates in the concrete produced in Belém and inland cities in the state of Pará. The need for new sources of aggregates makes us seek in construction waste likely sources of aggregates responding in a similar fashion to natural. Considering this proposal, this dissertation evaluated the durability of concrete produced with the addition of ceramic CW through trials of water absorption by capillarity, carbonation, chloride ion penetration and electrical resistivity. To that end, we replaced the natural coarse aggregate by ceramic coarse aggregate by 50%, where this percentage of recycled aggregate was subjected to the rates of pre - saturation of 60 %, 80 % and 100 %. According to the results it can be seen that the presence of RCCA (recycled ceramic coarse aggregate), regardless of the degree of pre- saturation was significant in all the results, the fact that the concrete while leaving more susceptible to loss of durability, it showed a pattern of behavior in relation to the reference mixtures. The closest matches conventional concrete mixtures were made by containing pre- saturated with water at a rate of 80 % ceramic aggregates.
Acesso aberto (Open Access)
Captura de carbono em placas de concreto permeável
(Universidade Federal do Pará, 2020-06-12) SANTOS, Caio José Bastos Marques; CORDEIRO, Luciana de Nazaré Pinheiro; http://lattes.cnpq.br/9126233381230999; https://orcid.org/0000-0001-7931-4042
The production of cement has an impact on the environment from the release of co2 where carbon dioxide acts directly on the phenomenon of "greenhouse effect". Although cement production generates high rates of carbon dioxide, cement hydration products have the ability to reabsorb carbon dioxide from a physical-chemical phenomenon called carbonation. This research related this physical-chemical phenomenon to a material considered sustainable, such as permeable concrete. This type of concrete can be used on non-reinforced floors. The research focuses on analyzing the ability to capture co2in permeable concrete slabs. As for carbonation, mixtures produced with two granulometric bands of pebble and CP II F agglomerate with a/c ratios of 0.33 and 0.37 were analyzed in protected and unprotected environments, and in an accelerated environment in a co2 chamber. A chemical phenolphthalein indicator was used to assess the occurrence of carbonation in five ages of reading and image analysis software to study the carbonated surfaces. The material showed satisfactory results in terms of mechanical, water and carbonation depth parameters, having reabsorbed the atmosphere gas from the cement paste that surrounds the aggregate grains of the material's granular skeleton.
Acesso aberto (Open Access)
Comportamento de argamassas de revestimento quanto à retração, fissuração e mecanismo de descolamento em substratos de concreto
(Universidade Federal do Pará, 2013-10-22) LIRA, Mariana Domingues von Paumgartten; MACEDO, Alcebíades Negrão; http://lattes.cnpq.br/8313864897400179
This research aims to evaluate the retraction, by the mortar superficial movement, occurrence of cracking and detachment of the mortar. Were choosed two types of substrate, one with a 30 Mpa resistance and other with 40 MPa resistance, also were used two types of mortar, one with additive and other lime based, two thicknesses of coating layer, from 15 mm and 30 mm, and was simulated the exposure condition that the region has.For this, tests were performed to characterize the mortar in the fresh state (consistency, water retention, air entrainment and mass density) and in the hardened state (compressive strength, tensile strength in bending, specific gravity, water absorption, voids and density). After preparation of the samples for evaluation, were taken the measures of superficial movement of the mortar for 28 days and the occurrence of cracks and detachment, as well as the verification of the bond strength of the coating and also the loss of water by evaporation of mortars. As a result of this research, it was observed that the variation of the resistance of the substrate analysis not showed a significant difference in the shrinkage, as well as the thickness of the layer to some series. It was also found that the type of mortar, or the material composition, has a direct influence on retraction. With regard to water loss by evaporation from the mortar, it can be seen that the additive achieved greater success in water retention materials. In the test of bond strength, was found that the most significant influence was in relation to the composition of the mortars and that they had values above the minimum allowed by regulatory norm.
Acesso aberto (Open Access)
Comportamento mecânico dos efeitos da substituição parcial do cimento por sílica ativa em eco concretos
(Universidade Federal do Pará, 2016-05-27) PIRES, Gabriela de Oliveira; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357
The exploitation of natural resources for construction purposes generates millions of tons of waste, thus being developed several studies to recycle this waste and the use of construction waste (CW) in the produced concrete. The pig silicon-iron production industry also produces tons of waste, silica fume, which can also be used in concretes and mortars in replacement / addition relative to cement. The main focus of this research is the study of the interaction of concrete produced with natural aggregates and aggregate coarse recycled concrete (CRCA) with partial replacement of silica fume relative to cement. The main objective of this dissertation is to analyze the influence of different levels of silica fume on the mechanical behavior of concrete produced with natural and concrete aggregates produced with different levels of ACRC. The experimental program was divided into three stages, it was first made the characterization of the material and processing of ACRC. The second phase consisted of the elaboration of the traits for different types of concrete by IPT/EPUSP method, and the same divided into three groups with 0%, 25% and 50% use of AGRC in partial replacement of coarse aggregate, each subdivided group levels with 0%, 5% and 10% replacement of cement with the silica fume. After curing the concrete were tested at the ages of 28 and 91 days with the following assays: compressive strength, splitting tensile strength and static modulus of elasticity. With the results can be concluded that mechanical performance of concrete with recycled concrete aggregates increased significantly in relation to the concrete reference (without silica) with respect to compressive strength and tensile and modulus of elasticity.
Acesso aberto (Open Access)
Concretes with red mud coarse aggregates
(2012-06) OLIVEIRA, Dênio Ramam Carvalho de; ROSSI, Carlos Rodrigo Costa
Red mud (RM) is a mineral waste, residue of the Bayer process used to obtain alumina from bauxite. While the exploration of rolled pebble damages the environment and is much more controlled by the government, the huge RM disposal areas do not stop increasing and polluting soil, rivers and groundwater sources in Amazon. In this work, the material mixtures used to produce coarse aggregates presented up to 80% of RM, 30% of metakaolin and 30% of active silica as recycled waste. Several tests were carried out to determine the aggregates physical properties and to evaluate the mechanical performance of the concretes with the new aggregates, including hydraulic abrasion strength, and the results were compared to the reference ones, i.e. rolled pebble concretes. Additionally, the sintering process neutralizes any toxic substance as occur in some RM products like tiles and bricks, and these results have encouraged an industrial or semi-industrial production of RM aggregates for concretes.
Acesso aberto (Open Access)
Concreto auto adensável com agregado miúdo reciclado de concreto
(Universidade Federal do Pará, 2019-03-29) BERNARDO, Karen Suely Martins; CORDEIRO, Luciana de Nazaré Pinheiro; http://lattes.cnpq.br/9126233381230999; https://orcid.org/0000-0001-7931-4042
A more sustainable approach in the production of self-compacting concrete (SCC) aims to replace the natural aggregates by recycled concrete aggregates, however this substitution affects the properties of the concrete produced. This research propose evaluate the effect of the fine recycled aggregate on the properties in the fresh and hardened state of self-compacting concrete using a methodology of dosage focused on the rheology of materials. The dosage study was performed through an adaptation of the Gomes method, and four levels of FNA substitution by FRCA were determined (10%, 20% and 30%). Were analyzed the fresh state properties according to the parameters established according to the specifications on the subject and by the normative prescription of reference, and the properties in the hardened state. In this study, was observed a decrease in apparent viscosity, passing ability and segregation resistance, proportional to the increase in FNA substitution. However, all mix designs have attend the required of self-compacting, with minimum adjustments. All concretes obtained axial compressive strength at which fit in the structural concrete class. Therefore, through the responses founded during the dosing study, it was possible to produce self-compacting concretes with 30% of FRCA that met the requirements established.
Acesso aberto (Open Access)
Concreto reforçado com fibras de bambu (Dendrocalamus Giganteus)
(Universidade Federal do Pará, 2019-11-14) FERNANDES, Robson da Silva; PICANÇO, Marcelo de Souza; http://lattes.cnpq.br/4535052395600357; https://orcid.org/0000-0001-7313-1229
Vegetable fibers appear as an alternative to manufacture structural elements in relation to metal and synthetic fibers that have high costs, also causing pollution to the environment due to their manufacturing process. This study analyzes the results of mechanical tests of a fiber reinforced concrete of bamboo bark (Dendrocalamus Giganteus), for use in cementitious plates, obtained experimentally in cylindrical and prismatic specimens according to ABNT standards and international recommendations. Composite traces were determined by means of a pilot study, 1: 2.12: 2.88: 0.58 using the CP-IV pozzolanic cement. The experimental program consisted of a 25 MPa Fck reference concrete and three dosages corresponding to 0.5%, 1.0% and 1.5% by volume of bamboo fiber to the concrete mass, forming four dosages in total. After curing, according to NBR 5738 (2003), prismatic specimens were tested for flexural tensile strength according to NBR 12142 (2010) / JSCE-SF4 (1984) and cylindrical specimens to evaluate the strength. from CRB to axial compression, according to NBR 5739 (2018), to diametric compression tensile, according to NBR 7222 (2011) and static modulus of elasticity, according to NBR 8522 (2008). In the axial compression test the presence of bamboo did not provide an increase of resistance in relation to the reference concrete. However for the tensile and flexural strength, the mixing with the addition of bamboo fiber generated a strength gain of 7% and 9%, respectively, compared to the concrete without addition. It can be concluded that insertion of fiber from bamboo bark increases the tensile strength of the composite.
Acesso aberto (Open Access)
Efeitos do tipo, tamanho e teor de agregado graudo na resistencia e energia de fratura do concreto
(Universidade Estadual de Campinas, 2004-09-28) POMPEU NETO, Bernardo Borges; DUCATTI, Vitor Antonio; http://lattes.cnpq.br/4679656185466685; FERREIRA, Itamar; http://lattes.cnpq.br/9135346053526486
This thesis presents the results of the experimental study carried out for considering the effects of the type, size and amount of coarse aggregate on the behavior of normal and high strength concretes, and on relationship among the fracture energy and typical mechanical strength of concrete. The experimental concrete mixtures were made with basalt and granite coarse aggregates having maximum size particle 9.5 mm e 19 mm and volumetrically fraction in the mixture ranging from 0.65 to 0.75. The water to cementation materiais ratio ranged from 0.35 to 0.50. The high strength concrete mixtures contained a fixed amount of 10 percent of silica fume in relation to the weight Portland cement used and a proper addition of superplasticizing agent. Sixteen (16) concrete batching, and one hundred and ninety two tests were carried out to measure the mechanical resistance of concrete (compressive strength, flexure strength, spittling tensile strength, modulus of elasticity) and fracture energy. The fracture properties measured in agreement of the RILEM test methods. The concrete compressive strength ranged from 40 to 60 MPa, and from 70 to 110 MPa, for moderate and high strength concretes, respectively, depending on the type of coarse aggregate utilized. The results showed that the concrete resistance (compressive, flexure, spittling tensile) and fracture energy, at given water to binder ratio, depend on type, particle dimension and content of coarse aggregate. The characteristic length of Hülerborg^ fictitions cracks model increases with the variation in the particle dimension of coarse aggregate.
Acesso aberto (Open Access)
Efeitos do tipo, tamanho e teor de agregado graúdo no módulo de deformação do concreto de alta resistência
(2011) POMPEU NETO, Bernardo Borges; OLIVEIRA, Dênio Ramam Carvalho de; RAMOS, Danielle
Concrete, material with heterogeneous and complex composition, is the main structural material applied in the construction industry. From the structural point of view its main property is the mechanical strength. The behavior of concrete based on conceptual studies of granular resistance can lead to a safer structural design and better use of the material. This paper presents the results of a study conducted to evaluate the effects of type, size and content of coarse aggregates on the modulus of deformation of high strength concretes. The concrete mixture studied contains basalt or granite aggregates with maximum dimensions of 9.5 mm and 19.0 mm and water/cement ratio of 0.35. The deformation modulus of the material was determined using the linear length of Load-CMOD curve (displacement of the crack mouth opening) from three point bending tests performed using a middle span cracked beam, following the propositions made by the RILEM 89-FMT technical committee.
Acesso aberto (Open Access)
Eficácia das fibras de aço no reforço ao cisalhamento de vigas de concreto armado sem estribos: investigação experimental
(Universidade Federal do Pará, 2019-11-27) MAUÉS, Kássio Anderson Castro; MORAES NETO, Bernardo Nunes de; http://lattes.cnpq.br/5790058515094077
Several research papers have been dedicated to the investigation of the behaviour of steel fibre reinforced concrete (SFRC) under several types of forces. Due to its mechanical property to transfer forces through cracks, it has been observed that SFRC presents substantial contribution to shear resistence. The present paper investigates the effects of steel fibres on the shear reinforcement of concrete beams without stirrups under four-point bending tests. For that purpose, five beams were cast and tested. The dimensions of the beams were 150 mm×300 mm×2700 mm, with 1.54% and 0.16% of tension and compression longitudinal reinforcement ratios, respectively. Two of the beams were manufactured as references, that is, without fibres, with one of them having conventional transversal reinforcement with stirrups and the other with no reinforcement to shear. The other three beams were reinforced with steel fibres only in the shear span in the proportions of 45 kg/m³, 60 kg/m³ and 75 kg/m³ of the concrete volume, which represent 0.6%, 0.8% and 1.0%, respectively. Concrete strength of 30 MPa was used for all the specimens. In addition to the typical characterization of concrete and steel used in this research, flexural test was performed on SFRC in order to obtain the residual stress response of the material, whic h is paramount for the evaluation of the strength of the beam. From the experimental results, it could be concluded that steel fibres exhibited satisfatory performance under shear forces in the cases of higher fibre content, for which a change in failure mode was observed: from shear failure to flexural failure. Furthermore, for the three fibre contents used, the possibility for partial or total replacement of the transversal reinforcement was confirmed. Additionally, it was demonstrated that the use of steel fibres in the content of 60 kg/m³ and 75 kg/m³ allows for the reduction of the longitudinal tension reinforcement to attain flexural strength similar to that of the reference beam with stirrups
Acesso aberto (Open Access)
Estudo da colmatação em concretos permeáveis para tráfego leve e de pedestres
(Universidade Federal do Pará, 2020-05-28) TEIXEIRA, Mísley da Cruz; CORDEIRO, Luciana de Nazaré Pinheiro; http://lattes.cnpq.br/9126233381230999; https://orcid.org/0000-0001-7931-4042
Permeable concrete is a material mostly used as paving coating to reduce the effects of surface sealing. The material’s susceptibility to clogging is considered as a disadvantage, and it became an object of study in research about this material, as this one which evaluated the effect of clogging on permeable concretes used as pavement coating to light traffic. To this end, an experimental program was elaborated to characterize the material, designed with different percentages of fine aggregate, and to evaluate the evolution of clogging in permeable. The specimens were submitted to characterization and permeability tests after deposition cycles of different types of sediments (sand and clay) and cleaning by aspiration. The results of fresh material characterization corroborated the common assertion in the academic community that the insertion of fine aggregate in mix compositions increases the unit mass and the mechanical strengths and reduces the void percentage and the permeability of the concretes. The clogging tests proved that larger particle size sediments (sand) caused a loss of permeability due to sealing of the upper layer of the specimen, with loss ratios up to 21,13% at the end of the 20th sedimentation cycle, while the smaller particle size sediments (clay) induce to a deeper clogging, with a permeability reduction varying of 8,45% to 16,46%. The maintenance efficiency was proven by total recovery of clogging by sand, and a recovery percentage of 96,85% to clogging by clay. These results make it possible to declare that any particle size can clog the material, but also it is easy to recover its permeability by maintaining/cleaning of the pavement, which confirms that the pavement lifespan and raining capacity are directly associated to its periodic cleaning.
Acesso aberto (Open Access)
Estudo da potencialidade da cinza da casca do murumuru, um resíduo agro industrial amazônico como filler ao concreto estrutural
(Universidade Federal do Pará, 2022-11-17) SOUZA, Milleno Ramos de; CORDEIRO, Luciana de Nazaré Pinheiro; http://lattes.cnpq.br/9126233381230999; https://orcid.org/0000-0001-7931-4042; TEIXEIRA, Marcelo Rassy; http://lattes.cnpq.br/8912916360456192
The use of agro-industrial waste in the partial replacement of cement in concrete has been the subject of research that analyzes the possible improvements in mechanical and physical properties and durability of the concrete, in addition to providing the use of mineral additions of natural origin or partial replacement in relation to the constituent materials of the composite, waste that would have inappropriate disposal, such as open-air landfills and burning. With this scenario, the study aims to research the use of murumuru husk ash (MHA), an agro-industrial waste generated specifically in the Amazon region as partial replacement of cement in structural concrete and evaluate the physical, chemical and mineralogical characteristics of the ash to act as filler in concrete, and its properties in the fresh and hardened state in concrete. With this purpose, the MHA underwent the physical-mechanical characterization tests such as specific mass, pozzolanic activity with Portland cement, pozzolanic activity with lime and BET test, also performing the mineralogical and chemical analysis of the ash. For concreting, a mix 1:1.6:2.4 (by mass) with water/cement ratio of 0.43 was considered, with replacement levels of 0%, 6%, 9% and 13% of the cement mass by MHA. After the dosage, the tests were performed on the concrete in its fresh and hardened state: slump test, specific mass, compressive strength (28 days), tensile strength in diametrical compression, water absorption by capillarities, specific mass in the hardened state, modulus of elasticity and morphological evaluation, through the Scanning Electron Microscope (SEM). Checking first the properties of concrete in the fresh state, it is evaluated that the insertion of the waste decreased the consistency and decreases the specific mass, except the concrete for the content of 6% that there was a 10% increase in the specific mass in relation to the concrete reference. Regarding the properties in the hardened state, the replacement by CCM showed an increase specifically in compressive and tensile strength in the 6% content at 28 days around 1% and 9% respectively, occurring a decrease in the contents of 9% and 13%. The results showed that there is a technical feasibility with partial replacement of 6% of MHA in cement, using plasticizer additive to improve workability
Acesso aberto (Open Access)
Estudo e avaliação do uso de resíduos do processo Bayer como matéria-prima na produção de agregados sintéticos para a construção civil
(Universidade Federal do Pará, 2010-03) SOUZA, José Antônio da Silva; QUARESMA, João Nazareno Nonato; http://lattes.cnpq.br/7826389991864785
The large amount of solid waste coming from mines and metallurgical industries became a serious social-environmental problem. The physical and chemical features of this material can raise a great interest in other industries. The ceramic industry might be a great costumer for most of this material, since it can supply the current lack of raw material. The red mud, main industrial residue of the alumina manufacturing, has been a very interesting input for several kinds of aggregates manufacturing used for the concrete production in civil engineering. In this context, this paper deals with studies concerning the red mud recycling to be applied as raw material for the synthetic light aggregate production to be used as an alternative material in the civil construction industry. This is because of its physical-chemical features and the large amount annually produced (around 10 million tons within two factories in the North of Brazil). The studies completed in this work show the feasibility of aggregates manufacturing, with different properties and possibilities. These properties depend on the parameters control such as content of free silica and clay, and the sintering temperature. Such variables allow to perfectly controlling the glassy phase formation which is responsible for the aggregate properties such as: porosity, mechanical resistance and density. This material can be used for conventional or special concretes to supply the civil engineering needs.