Steel fiber bond strength to estimate fRi parameters

This paper presents the results of the safety assessment of the β coefficient that correlates the residual flexural tensile strength parameters f (i = 1, 2, 3, and 4) in steel fiber reinforced concrete (SFRC), collected through experimental notched beam flexural tests in three points, according to the fib Model Code 2010 (fib, 2013), with the bond strength (f) of the hook-end type steel fiber in the concrete mix. The SFRC beams were chosen, which presents the load-opening ratio curve of the crack, F-CMOD (Crack Mouth Opening Displacement) in softening behavior, the compressive strength of the concrete, 25 MPa < f < 80 MPa, the fiber volume content, 0.25 % < V < 0.80 % and the fiber aspect ratio, 60 < l/d < 95. The results in 46 prisms notched of the database formed by 13 studies, showed a considerable influence of the f x f ratio with lower variability of around 10%. Thus, through statistical resources, empirical proposals were established to estimate the residual flexural tensile strengths, as a viable and economical alternative to the design project.

Steel fiber bond strength to estimate fRi parameters

This paper presents the results of the safety assessment of the β_1 coefficient that correlates the residual flexural tensile strength parameters fRi (i = 1, 2, 3, and 4) in steel fiber reinforced concrete (SFRC), collected through experimental notched beam flexural tests in three points, according to the fib Model Code 2010 (fib, 2013), with the bond strength (fu,f) of the hook-end type steel fiber in the concrete mix. The SFRC beams were chosen, which presents the load-opening ratio curve of the crack, F-CMOD (Crack Mouth Opening Displacement) in softening behavior, the compressive strength of the concrete, 25 MPa < fc < 80 MPa, the fiber volume content, 0.25 % < Vf < 0.80 % and the fiber aspect ratio, 60 < lf/df < 95. The results in 46 prisms notched of the database formed by 13 studies, showed a considerable influence of the fRi x fu,f ratio with lower variability of around 10%. Thus, through statistical resources, empirical proposals were established to estimate the residual flexural tensile strengths, as a viable and economical alternative to the design project.

A novel algorithm for significantly increasing the fiber volume fraction in the reconstruction model with large fiber aspect ratio

Geometric reconstruction is an important precondition for the computational micromechanics analysis of chopped fiber reinforced composites. When fiber aspect ratio increases, the maximum fiber volume fraction in reconstruction model reduces rapidly because of jamming limit, which greatly limits the application of reconstruction methods. A novel algorithm is proposed to significantly increase the fiber volume fraction in the reconstruction model of the chopped fiber reinforced composites with large fiber aspect ratio. The algorithm is made up of two stages. At the first stage, fibers are packed into the sublayers of initial filling space to preliminarily design fiber orientation distribution. The unidirectional arrangement of fibers is adopted to achieve high fiber volume fraction. At the second stage, a new multi-step fiber shaking strategy is used to introduce randomness into reconstruction model. The high fiber volume fraction over 30% is achieved within the wide range of fiber aspect ratio from 50 to 200 while the results of the existing methods are not more than 10%, showing the remarkable increase of the fiber volume fraction under large fiber aspect ratio. The proposed algorithm is verified by the statistical results of the four representative microstructural characteristics from reconstruction model and realistic material.

Innovative Insulating Materials from Coriander (Coriandrum sativum L.) Straw for Building Applications

Straw represents 60-80% of the aerial part of the coriander plant. Because of the increasing demand for vegetable oil from fruits for food, cosmetics or the chemical industry, the availability of straw will grow strongly in the future. Its high lignocellulose content (62%) makes this crop by-product an interesting raw material for producing bio-based building materials. Bulk materials can be obtained by refining the straw through twin-screw extrusion in the presence of water. The fiber aspect ratio of refined straw can be varied (22.9-26.5) by applying different liquid/solid ratios (0.4-1.0), leading to a variation in the tapped density of the resulting bulk material (110-61 kg/m3). For the lowest density, thermal conductivity is 47.3 mW/(m.K). Twin-screw refining can also be conducted from an aqueous borax solution. Refined straw thus becomes fire-proofed, making it usable as loose fill in housing. Insulation blocks of medium density, associating straw and a starch-based binder, can also be produced through compression molding. With a density of 155 kg/m3 and a thermal conductivity of 55.6 mW/(m.K), the optimal cohesive blocks (7.5 mm milled straw and 15% binder), cold-pressed at 87 kPa for 30 s, are promising alternatives for the thermal insulation of buildings (e.g., filling of walls, interior partitions, etc.).

Optimization of process parameters for preparing straw fiber from corn stalk rind

To study the influence of process parameter changes on the properties of raw material obtained from corn rind, a central composite design (CCD) methodology with four factors and five levels was applied to statistically optimize the parameters. The stalk size, soaking time, working temperature, and processing speed were selected as influencing factors. The available fiber ratio, initial beating degree, and fiber aspect ratio were chosen as indicators. Response surface analysis methodology was employed for optimization. The results showed that the optimal range of parameters were as follows: 8 to 13 cm for the stalk size, 18 h for the soaking time, 60 °C for the working temperature, and 98 to 112 r·min-1 for the processing speed. In this optimal condition, the available fiber ratio was higher than 95%, initial beating degree was greater than 11 °SR, and fiber aspect ratio was greater than 50. The results could be applied to design and optimize the D200 type stalk fiber preparation machine and the process of making raw material.

Effect of Steel Fiber Aspect Ratio on the Properties of High Strength Self Compacting Concrete

The High strength concrete defined as per IS 456 as the concrete having characteristic compressive strength more than 65 MPa. The self-compacting concrete has lot of advantages including concreting at congested reinforcement locations, better finish, good compaction etc. The inclusion of fibers in the concrete mix decreases the brittle nature of concrete thereby the ductility increases. Different types of fibers are available for inclusion in concrete like steel, glass, polypropylene, basalt, etc. In the present investigation, high strength concrete having characteristic strength of 90 MPa was developed and hooked ended steel fibers are used and the hardened properties are determined. Steel fibers having diameter of 1 mm and lengths of 25 and 50 mm were added to concrete in 0.125%, 0.25% and 0.5% by volume of concrete. Three hardened properties compressive strength, split tensile Strength and flexural strength were determined. Out of the two lengths of fiber i.e with two aspect ratios, the fiber with 50 mm length yielded better results.

Theoretical and Experimental Analysis of Tensile Characters of Prosopis Juliflora Fiber-Reinforced Phenol Formaldehyde Composites

The experimentally perceived tensile characters (tensile strength and tensile modulus) of Prosopis juliflora fiber reinforced phenol formaldehyde composites with different fiber aspect ratios (FAR) and fiber loadings (FL) have been fabricated and compared with the prevailing reinforcement theories. This analysis illustrates that the most favorable fiber aspect ratio and fiber loading of Prosopis Juliflora Fiber reinforced PF composites. FAR136 and 20 weight% of fiber loading were found as good combination to attain better bonding with superior mechanical characteristics in the Phenol Formaldehyde polymer matrix. In this study, an evaluation is made between theoretical models and experimental data. Theoretical models like parallel and series, Halpin-Tsai and modified Halpin-Tsai have been trying to fit the experimental data.