We assess tensile performance of Steel Reinforced Grout (SRG) and Fabric Reinforced Cementitious Matrix/Textile Reinforced Mortar, upon exposure to aggressive environments. Galvanized and ...brass-coated Ultra High Tensile Strength Steel fabrics are considered for SRG, while carbon, AR-glass, basalt and PBO fabrics are investigated for TRM, in a common cement mortar. Exposure to the aggressive environments is realized by specimen immersion for 1000 h (41.6 days) at controlled temperature in distilled water as well as alkaline, saline and acid solutions. Mechanical performance of rectangular 1-ply coupons is assessed in uni-axial traction: Ultimate strength and elongation, dissipated energy at failure and environmental conversion factors for design values are calculated and compared. It is found that significant performance difference exists in dependence of the aggressive environment under consideration. As a result, careful selection of the reinforcing fabric leads to substantial advantage in terms of durability, that should be capitalized upon at the design stage. A simple material selection matrix is presented which suggests the best reinforcing textile/aggressive environment combination for design purposes.
We investigate antiplane Stoneley waves, localized at the discontinuity surface between two perfectly bonded half-spaces. Both half-spaces are elastic linear isotropic and possess a microstructure ...that is described within the theory of couple stress materials with micro-inertia. We show that the microstructure deeply affects wave propagation, which is permitted under broad conditions. This outcome stands in marked contrast to classical elasticity, where antiplane Stoneley waves are not supported and in-plane Stoneley waves exist only under very severe conditions on the material properties of the bonded half-spaces. Besides, Stoneley waves may propagate only beyond a threshold frequency (cuton), for which an explicit expression is provided. For a given frequency above cuton, this expression lends the admissible range of material parameters that allows propagation (passband). In particular, significant contrast between the adjoining materials is possible, provided that Stoneley waves propagate at high enough frequency. Therefore, micro-inertia plays an important role in determining the features of propagation. Considerations concerning existence and uniqueness of antiplane Stoneley waves are given: it is found that evanescent and decaying/exploding modes are also admitted. Results may be especially useful when accounting for the microstructure in non-destructive testing (NDT) and seismic propagation.
The use of virgin and recycled plastic macro fibers as reinforcing elements in construction materials has recently gained increasing attention from researchers. Specifically, recycled fibers have ...become more attractive owing to their large-scale availability, negligible cost, and low environmental footprint. In this work, we investigate the benefits related to the use of fully-recycled synthetic fibers as dispersed reinforcement in Fiber Reinforced Cement Composites (FRCCs). In light of the reference performance of FRCCs including virgin polypropylene (PP) fibers only, the mechanical response of composites reinforced with polyolefin filaments treated with a sol-gel silica coating and polyethylene terephthalate (PET)/polyethylene (PE) cylindrical draw-wire fibers is here assessed through three-point bending tests. Remarkably, recycled polyolefins lead to a notable enhancement in terms of peak strength and post-crack energy dissipation capability. This improvement is ascribed to both the flattened shape of fibers and the surface coating, which turns out to be very effective at strengthening the fiber-to-matrix bond. On the other hand, PET/PE fibrous reinforcement generally leads to a lower toughness, if compared to the virgin fibers. However, no reduction in terms of peak stress is evidenced. Balancing the significance of mechanical performance and environmental sustainability in the framework of a circular economy approach, both fully-recycled fibers at hand can be regarded as promising candidates for innovative structural applications.
We discuss mechanical performance of fibre-reinforced cementitious composites under exposure to four aggressive environments, namely alkaline, saline, sulphuric acid and distilled water immersion. A ...standard commercial Portland cement based matrix is considered alongside its lightweight modification wherein quarzitic sand is partially replaced by recycled rubber crumbs. Also, virgin polypropylene fibres are contrasted to PP+PET blended fibres where the PET fraction is obtained from recycling food packaging waste. Performance is assessed in bending as well as in compression. We find that recycled based specimens perform surprisingly well and that exposure to the aggressive environments mainly affects the matrix and it is not necessarily more detrimental to the lightweight partially recycled phase. A one-way analysis of variance (ANOVA) confirms the statistical significance of the results, which fully support the idea that the adoption of a substantial recycled fraction in construction materials still allows for high performance and durability standards.
Background:
Lack of interphase compatibility between the fabric and the matrix significantly impairs the load-bearing capacity of textile reinforced mortar (TRM). In this study, we consider the ...application of two inorganic surface coatings for enhancing the interphase bond properties.
Methods:
Either of two silica-based coatings, namely nano- and micro-silica, were applied to alkali-resistant glass (ARG) and to hybrid carbon–ARG woven fabric. Mechanical performance of TRM reinforced with the uncoated and the coated fabric was compared in uniaxial tensile tests.
Results:
Mechanical testing provides evidence of a remarkable enhancement in terms of ultimate strength and deformability for the coated specimens. This effect can be ascribed to the improved hydrophilicity of the fibers’ surface and to the activation of pozzolanic reaction at the interphase. In addition, penetration of nano- and microparticles in the bundle of the textile yarns reduces the occurrence of telescopic failure.
Cement and lime currently are the most common binders in building materials. However, alternative materials and methods are needed to overcome the functional limitations and environmental footprint ...of conventional products. This Special Issue is entirely dedicated to “New frontiers in cementitious and lime-based materials and composites” and gathers selected reviews and experimental articles that showcase the most recent trends in this multidisciplinary field. Authoritative contributions from all around the world provide important insights into all areas of research related to cementitious and lime-based materials and composites, spanning from structural engineering to geotechnics, including materials science and processing technology. This topical cross-disciplinary collection is intended to foster innovation and help researchers and developers to identify new solutions for a more sustainable and functional built environment.
Tensile performance of textile reinforced inorganic matrix composites strongly depends on the matrix-to-fabric bond strength, that is the weak chain in the system. In this work, we investigate the ...role of multi-walled carbon nanotubes (MWCNT) dispersion in an amorphous silica nano-coating for AR-glass and carbon fabric Textile Reinforced Mortar (TRM) composites. Two lime mortars are considered at 56-day curing. Comparative mechanical testing in uni-axial tension show remarkable enhancements in terms of mean ductility, strength and energy dissipation capabilities. Besides, coating successfully hinders telescopic failure and delamination, which significantly narrows data scattering and benefits design limits. Crack pattern analysis reveals that coating promotes diffuse cracking in the specimen, with gradual and progressive damage buildup. Indeed, mean crack width and mean crack spacing are consistently reduced. BET, optical and E-SEM microscopy supports the action mechanism of the coating, that promotes wettability, surface roughening and imparts a remarkable increase in the specific surface area of the reinforcement.
We describe a novel class of interface-functionalised textile-reinforced mortar (TRM) composite materials reinforced with basalt and alkali-resistant glass multifilament textiles embedded in a ...commercially available hybrid lime-cement mortar, usually applied for masonry retrofitting. Spotlight is set on improving the mechanical (tensile) performance of the system through a scalable and easy-to-apply surface treatment for the dry textiles. The treatment consists in soaking the textiles in highly-diluted epoxy resin, to which rice husk ash (RHA) is later added, acting as pozzolanic filler. The resulting functionalised textiles exhibit remarkable adhesion with the matrix owing to the presence of RHA having high specific surface area and rich amorphous content. Three different RHA powders are assessed and their performance is compared to that of plain silica fume. The role of RHA milling is also discussed. The RHA/epoxy coating significantly improves the ultimate tensile strength and energy dissipation capability of the TRMs. In particular, for basalt-textile reinforced composites, the mean tensile strength is three times as large as that of uncoated specimens, whereas the dissipated energy at failure is nearly four times as much. Furthermore, the surface treatment qualitatively changes the cracking pattern of the TRMs, for many diffused small cracks appear during tensile testing, and this provides evidence of effective stress distribution in the matrix as a result of superior interface adhesion.
•A novel surface coating for textile-reinforced mortar composite system is proposed.•The coating is epoxy-based and uses rice husk ash (RHA) particles as active filler.•Three RHA powders are considered differing by rice variety and combustion process.•Uniaxial tensile tests on basalt- and glass-TRM prismatic coupons are conducted.•The coating leads to enhanced strength, toughness and crack pattern in TRM samples.
Strain-hardening cement-based composites (SHCC) represent a new frontier for improving the resistance of concrete structures against highly dynamic loading regimes, e.g., in the case of impact. A ...novel testing device was designed to characterize the shear behavior of such pseudo-ductile cementitious composites, whose dynamic response is extremely complex. The newly developed shear testing device was adapted to investigate the performance of fiber-reinforced, cementitious composites under both quasi-static and impact regimes. In the framework of setup validation and standardization, this article focuses on the investigation of the shear behavior of SHCC specimens and spotlights the influence of two main experimental shear parameters: shear span and notch depth. The purpose-specific shear device was integrated into a hydraulic testing machine and a gravity Split-Hopkinson tension bar (SHTB) for quasi-static and impact shear experiments, respectively. Shear spans of 2 mm and 5 mm were introduced by modifying the test setup. Furthermore, the specimens were shaped through sawn U-notches with varying depths of 3 mm, 5 mm, and 7 mm. The shear response of the SHCC specimens was monitored by means of Digital Image Correlation (DIC), which enabled the accurate derivation of strain fields, cracking behavior, and fracture modes on the specimen surface. The results showed that both shear span length and notch depth regulate the shear/tension fracture propagation. With an appropriate shear specimen shape, the desired dominant shear fracture could be obtained.
•A novel silica coating of PP fibres for Fibre Reinforced Concrete is investigated.•Coating strengthens the interphase bond and increases peak strength and dissipation.•To discriminate between matrix ...and fibre-bond enhancement, curing time is considered.•Curing affects energy dissipation in coated specimens, reducing also data scattering.•Failure mechanism moves from fibre slippage to matrix failure in the interphase zone.
This work investigates the effect of a fast, acid-catalysed sol-gel silica nano-coating on the mechanical performance of draw-wire Polypropylene (PP) fibres used as dispersed reinforcement in Fibre Reinforced Concrete (FRC). The failure mechanism is investigated. To this aim, the role of curing time is also considered. Mechanical performance is assessed in pull-out and three-point bending tests of un-notched beams. Coating deeply affects the post-cracking behaviour of FRC, which shifts from brittle (plain concrete), to softening (uncoated) and finally to plastic-softening (coated fibres). Remarkably, 28-day curing improves over 8-day curing in terms of energy dissipation capability for coated fibres only. This suggests that fibre-to-matrix bond enhancement moves the failure mechanism from delamination at the interface to failure in the interphase zone. In the former case, failure is inconsistent and occurs independently from the curing time while in the latter failure depends on the matrix quality.
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