Autor(a/res): Oscar A. Mendoza Reales, Caterin Ocampo, Yhan Paul Arias Jaramillo, Juan Carlos Ochoa Botero, Jorge Hernán Quintero, Emílio C. C. M. Silva, Romildo Dias Toledo Filho

Resumo: Decoupling the individual effects of multiwalled carbon nanotubes (MWCNTs) and surfactants when used as reinforcement materials in cement-based composites is aimed in this study. Powder MWCNTs were dispersed in deionized water using different types of surfactants as chemical dispersing agents and an ultrasonic tip processor. Cement pastes with carbon nanotubes additions of 0.15% by mass of cement were produced in two steps: first, the MWCNT/surfactant dispersions were combined with the mixing water, and then, cement was added and mixed until a homogeneous paste was obtained. Mechanical properties of the pastes cured at 7 days were measured, and their fracture behavior was characterized using the linear elastic finite element analysis. It was found that the reinforcing effect of MWCNT was masked by the negative effect of surfactants in the cement matrix; nevertheless, nanotubes were capable of increasing both stress and strain capacity of the composite by controlling the crack propagation process at the tip of the crack.

Acesse AQUI e confira o artigo.

Autor(a/res): Marco Pepe, Thiago Melo Grabois, Marco Antonio Silva

Resumo: In this study the application of the single-particle compression test is discussed as an alternative method for the mechanical characterisation of coarse aggregates generally employed in concrete manufacturing. This leads to an estimation of the tensile strength and fracture energy of the aggregate particles. A wide range of aggregate types is considered. In particular, the mechanical responses of crushed limestone and river gravel are compared with expanded clay, recycled concrete and clay brick aggregates. In addition, physical properties are assessed experimentally and correlated to the aggregates' mechanical performance. Despite the high data scatter presented, the results demonstrate the ability of the proposed approach to accurately determine fracture energy and strength histories using single-particle compression. Overall, the porosity governs the mechanical behaviour of particles. Moreover, direct relationships between mechanical and physical properties yield consistent and expected results that validate the methodology.

Acesse AQUI e confira o artigo.

Autor(a/res): Johny C. Silva, Geisa E. Oliveira, Romildo D. Toledo Filho, Fernando G. Souza Jr.

Resumo: Aiming to reduce the anthropogenic environmental impact some wastes can be used as raw material in other process. Considering that, coffee grounds powder before and after acetylation process were used as a filler in a new composite material that is able to clean up spilled oil from the surface of water. The polymeric matrix was a polyurethane and maghemite nanoparticles was used as filler to provide magnetic properties to the material. In this study, four different materials were prepared: the first was the resin matrix; the second was the composite containing only 5% w/w of magnetizable nanoparticles; the third was the composite containing 5% w/w of the magnetizable nanoparticles and 10% w/w of coffee grounds; and the last was similar the former but containing acetylated coffee grounds powder. All of the obtained materials were characterized by FTIR, XRD, TGA, magnetic force and susceptibility, density, water absorption amount and oil removal capability. The results showed that each gram of composite material containing 10% of coffee grounds powder was able to sorb (9.6 ± 0.5) grams of crude oil, while the composite containing the same amount of acetylated coffee grounds was able to remove (9.4 ± 0.6) grams of crude oil. The significant advantage of the acetylation process is the lower absorption of water in comparison to the non-acetylated analogous material. The results demonstrated that the hydrophilic tendency decreases significantly. The water/oil ratio absorbed by the materials decreased from 1.07 when using composite containing coffee grounds, to 0.41 when composite containing acetylated coffee grounds was used.

Acesse AQUI e confira o artigo.

Autor(a/res): Cordeiro, G. C., Paiva, O. A., Toledo Filho, R. D., Fairbairn, E. M. R., Tavares, L. M.

Resumo: This paper reports an investigation of a very-long-term compressive-behavior evaluation of concretes containing sugarcane bagasse ash (SCBA). Initially, two different SCBA samples collected in two sugarcane plants located 1,800 km apart and 8 years apart in sampling interval were compared. From these ashes, two series of conventional and high-strength concretes were mix-designed within the Compressible Packing Model aiming for 28-day compressive strengths of 25 and 60 MPa, respectively. In the first series, a SCBA (SCBA-1) was used as a cement replacement with 10 %, 15 %, and 20 % by mass content. The different concretes were evaluated by compressive strength at 7, 28, 90, 180 days, and 1 and 10 years, and by modulus of elasticity at 28 days and 10 years. The second series of concretes was examined with similar procedures performed on the first series and another SCBA (SCBA-2, 15 % cement replacement). Compressive strength in 7, 28, 90, and 180 days, and modulus of elasticity at 28 days were evaluated. The results showed that both SCBA-1 and SCBA-2 presented similar characteristics to be considered pozzolanic materials. The effect of these ashes on the compressive strength was positive considering the cement-replacement levels used, especially for later testing ages. The results also demonstrated that all first-series concretes presented gain in compressive strength and modulus of elasticity up to 10 years of hydration. At this age, no significant differences were found in compressive strength for conventional and high-strength mixes containing SCBA compared to their respective reference mixes.

Acesse AQUI e confira o artigo.