Fibers, Volume 9, Issue 4 (April 2021) – 6 articles

Reconstruction of buildings and structures is becoming one of the main directions in the field of construction, and the design and production of works during reconstruction are significantly different from the ones of new buildings and structures. After carrying out a number of studies on the inspection of the technical condition of buildings in order to determine the effect of defects on the bearing capacity, the criteria for assessing the state of floor slab structures were identified. Conclusions on the state and further work of elements of reinforced concrete structures are considered. The authors achieve the aim of reinforcing flexural elements of reinforced concrete structures with fiber-reinforced mortar, which is especially important for floor elements with increased operational requirements. A technique for constructing a reinforcement layer using fiber-reinforced mortar from coarse basalt fiber has been developed. The parameters of basalt fiber in the reinforcement layer are substantiated. A method for solving problems of the operation of multilayer coatings under the influence of operational loads is used, in which the model prerequisites for describing the operation of layers are simplified, where the bearing layers are represented by classical Kirchhoff-Love plates. When solving problems, the maximum possible number of design features of flexural members is taken into account, in combination with appropriate experimental studies, the method allows us to consider all the variety of structures for reinforcing coatings and meet the needs of their practical application. Full article

Cellulose microfibrils (CMFs) and micronized rubber powder (MRP) can be derived from low or negative-cost agricultural/industrial waste streams and offer environment-friendly and cost-effective pathways to develop engineering products. This study investigated the efficacy of adding these micromodifiers on the performance characteristics of asphalt binders. In this work, samples were produced using a mixture of slow-setting anionic asphalt emulsion with various combinations of MRP (at 0, 2 and 10 wt %) and four types of CMFs (hydrophobic and hydrophilic with crystalline ratios of 86% and 95%) at 0, 2 and 5 wt %. The performance of modified asphalt samples was assessed by penetration depth (PD), softening point (SP), and penetration index (PI). Linear regression analysis showed that adding CMFs and/or MRP reduced PD and increased SP values. The type of CMFs significantly affected the performance, which becomes more distinct with the increased weight content of CMFs. While hydrophilic CMFs caused increases in SP and PI values, no clear trend was seen to determine the effect of CMF crystallinity. It was also discovered that the combined addition of CMF and MRP achieved similar PI values at lower total weight content compared to using MRP alone. Full article

Plant fibres and especially flax can be distinguished from most synthetic fibres by their intricate shape and intrinsic porosity called lumen, which is usually assumed to be tubular. However, the real shape appears more complex and thus might induce stress concentrations influencing the fibre performance. This study proposes a novel representation of flax fibre lumen and its variations along the fibre, an interpretation of its origin and effect on flax fibre tensile properties. This investigation was conducted at the crossroads of complementary characterization techniques: optical and scanning electron microscopy (SEM), high-resolution X-ray microtomography (µCT) and mechanical tests at the cell-wall and fibre scale by atomic force microscopy (AFM) in Peak-Force Quantitative Nano-Mechanical property mapping (PF-QNM) mode and micromechanical tensile testing. Converging results highlight the difficulty of drawing a single geometric reference for the lumen. AFM and optical microscopy depict central cavities of different sizes and shapes. Porosity contents, varying from 0.4 to 7.2%, are estimated by high-resolution µCT. Furthermore, variations of lumen size are reported along the fibres. This intricate lumen shape might originate from the cell wall thickening and cell death but particular attention should also be paid to the effects of post mortem processes such as drying, retting and mechanical extraction of the fibre as well as sample preparation. Finally, SEM observation following tensile testing demonstrates the combined effect of geometrical inhomogeneities such as defects and intricate lumen porosity to drive the failure of the fibre. Full article

Fiber-reinforced geopolymer composites (FRGCs) were considered in terms of application in various areas, and a review is presented in this article. FRGCs are emerging as environmentally friendly materials, replacing cement in the construction industry. An alternative inorganic binder such as a geopolymer matrix promotes environmental awareness on releasing less CO₂. The inorganic matrix geopolymer is considered a greener cement for FRGCs. Various types of fiber reinforcements and their role toward the improvement of tensile, flexural, impact strength, fracture toughness, and energy absorption in overall mechanical performance in FRGCs were discussed. FRGCs and their properties in mechanical response, with correlation toward microstructure evolution at room and elevated temperatures, were also discussed. Simultaneously, the durability and impact strength of FRGCs and damage area as a function of the energy absorption were presented with 3D reconstruction images. Moreover, 3D images will cover the internal volume of the FRGCs with internal porosity and fiber orientation. Hybrid fiber reinforcement adds an extra step for the application of geopolymer composites for structural applications. Full article

The present paper proposes a useful closed-form solution for a wide class of mechanical problems, among which one of the most relevant and debated is the deboning process of Fiber-Reinforced Polymer (FRP) strips glued to generic materials and possibly intended as a mode-II fracture process. Specifically, after outlining well-known equations, a novel piecewise analytical formulation based on a cascading solution process is proposed with the aim of keeping the mathematical expressions of the relevant mechanical quantities as simple as possible. Although other analytical solutions and numerical procedures are already available in the literature, the present one is capable of handling the softening or snap-back response deriving from the full-range simulation of the depending process with no need for complex numerical techniques. This is obtained by considering the slip at the free end of the strip as the main displacement control parameter. After some comparisons between the proposed closed-form solution and experimental results available in the literature, some mechanical considerations are highlighted by elaborating on the results of a parametric study considering the variation of the main geometric and mechanical quantities. The numerical code implemented as part of the present study is available to readers in Open Access. Full article

We show numerically that ultra-short pulses can be generated in the mid-infrared when a gas filled hollow-core fiber is pumped by a fundamental pulse and its second harmonic. The generation process originates from a cascaded nonlinear phenomenon starting from a spectral broadening of the two pulses followed by an induced phase-matched four wave-mixing lying in the mid-infrared combined with a dispersive wave. By selecting this mid-infrared band with a spectral filter, we demonstrate the generation of ultra-short 60 fs pulses at a 3–4 µm band and a pulse duration of 20 fs can be reached with an additional phase compensator. Full article