Numatsmail
Numatsmail
Autor(a/res): Dimas Alan Strauss Rambo, Flávio de Andrade Silva, Romildo Dias Toledo Filho e Otávio da Fonseca Martins Gomes.
Resumo: The work in hand presents the results of an experimental investigation on the thermo-mechanical properties of a textile refractory composite reinforced with polymer coated basalt fibers under tensile loading. The composites were produced as a laminate material using basalt bi-directional fabric layers as reinforcement. A high alumina cement matrix was used in the matrix composition which was designed using the compressible packing method. A series of uniaxial tensile tests was performed under temperatures ranging from 25 to 1000 °C. The cracking mechanisms were discussed and compared to that obtained at room temperature. Thermogravimetry and X-ray diffraction analysis were used to study the deterioration/phase changes as a function of the studied temperatures. Scanning electron microscopy (SEM) was used to study the damage processes in the fiber–matrix interfaces after exposure to high temperatures. The obtained results indicated that the presence and the type of coating can become a deterministic factor in the tensile response of the composite submitted to elevated temperatures. A sudden drop in the serviceability limit state of the composite was observed above 400 °C, caused by the degradation of the polymer used as a fiber surface coating, the degradation of the basalt fiber and by the dehydration process of the refractory matrix.
Acesse AQUI e confira o artigo.
Autor(a/res); Saulo Rocha Ferreira, Flávio de Andrade Silva, Paulo Roberto Lopes Lima e Romildo Dias Toledo Filho.
Resumo: This experimental research investigation aims to explain the influence of several treatments on the sisal fiber properties and bonding strength with a cement based matrix free of calcium hydroxide. Four different treatments were studied: hornification, alkali treatment with calcium hydroxide, polymer impregnation with styrene butadiene and a combination of hornification and polymer impregnation. Modifications in the sisal fiber structure were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). Water absorption and direct tensile tests were performed on the fibers to determine the influence of the treatments on their physical and mechanical properties. In order to study the sisal fiber–matrix bond, pullout tests were performed in fiber embedment lengths of 5, 10, 25 and 50 mm. All applied treatments resulted in a reduction of the water absorption capacity and increase in tensile strength and stiffness. Significant improvements in the fiber–matrix interface were verified through the pullout test for the several used treatments. The hornification treatment increased the elastic and frictional bond, whereas the polymer and hybrid treatments resulted in a fiber slip-hardening behavior.
Acesse AQUI e confira o artigo.
Autor(a/res): Mònica Ardanuy, Josep Claramunt eRomildo Dias Toledo Filho.
Resumo: In the last few years, an increase in interest has been given to the use of cellulose fibers as alternatives for conventional reinforcements in composites. The development of commercially viable environmentally friendly and healthy materials based on natural resources is on the rise. In this sense, cellulosic fibers as reinforcements for cement mortar composites constitute a very interesting option for the construction industry. This paper presents a review of the research done during the last years in the area of the cement-based composites reinforced with cellulose fibers. The fibers used, processing methods, mechanical behavior and durability are presented. The main achievements found have been the development of durable cement composites with optimized fiber–matrix adhesion. Moreover, the recently developed textile composites will allow obtaining high performance materials reinforced with vegetable fibers.
Acesse AQUI e confira o artigo.
Autor(a/res): Eduardo M. R., Marcos M. Silvoso, Fernando L. B. Ribeiro e Romildo D. Toledo-Filho.
Resumo: This paper presents a method to find the adiabatic temperature rise of concrete by retro-analysing temperatures measured in the field. The construction phase is simulated with a 3D finite-element model that considers the coupling between thermal and chemical phenomena due to cement hydration. A genetic algorithm is used to find the main parameters that characterise the adiabatic temperature curve and that better fit the temperatures measured in the field for a given structure. This method was applied to the construction of the spillway gate pier of a hydroelectric power plant. The good agreement between numerical results and temperature measurements points to the feasibility of the proposed method.
Acesse AQUI e confira o artigo.
Autor(a/res): Gideon P. A. G. van Zijl, Volker Slowik, Romildo D. Toledo Filho, Folker H. Wittmann e Hirozo Mihashi.
Resumo: Two of the main activities of RILEM Technical Committee 208-HFC Subcommittee 2 were the preparation and publication of the state-of-the-art report on durability of strain hardening cement-based composites (SHCC), and the performance of comparative laboratory testing on SHCC. In this paper the comparative mechanical tests are reported, as performed in laboratories of five participating institutions. The purpose was to investigate and compare the crack patterns in terms of crack widths and spacing, and subsequently to make recommendations for a suitable test setup and procedure towards characterizing cracking in this class of materials. Such standardized procedures are required for future systematic and objective research towards durability of these materials in their in-service conditions, i.e. their resistance to deterioration processes in the cracked state. Standardized test procedures are also required for durability testing and guidelines for structural design with SHCC, which is the focus of follow-up committee activity in TC 240-FDS.
Acesse AQUI e confira o artigo.
