Textile-reinforced mortars; an experimental comparative study of tensile strength improvement methods

In this article, an experimental study is conducted to compare eight improvement methods for the tensile strength of textile-reinforced mortars (TRM). 12 series of samples with different modification methods are compared to determine the most effective factors on crack initiation force and tensile strength of TRM. Eight modification methods are categorized under three main groups of mortar modification, fabric modification, and fabric-mortar interface modification. TRM's first crack force and ultimate force are considered as indices of method performance. One-way ANOVA and factorial analysis were also conducted to statically determine the most significant methods for improving TRM tensile behavior. The results showed that the modification of mortar by short fiber is the most effective method for the enhancement of TRM's first crack force. Also, the methods which led to the transfer of failure mode from mortar to fabrics were the most effective methods on TRM ultimate force improvement. The result showed that coating fabrics with epoxy affects TRM tensile strength more than all other methods. Extra enhancement of TRM ultimate force is achieved by adding silica fume to epoxy before coating the fabrics and spreading the sand and short fibers on impregnated fabrics.

Rheology, Mechanical Performance and Penetrability through Flax Nonwoven Fabrics of Lime Pastes

The use of plant fibers as a reinforcement for fragile matrices could be an option to improve the sustainability of the construction materials. These reinforcements can be in different forms as short fibers, long fibers or woven or nonwoven fabrics. The mechanical performance of the composites is significantly related to the adhesion between the matrix and the fibers. In the case of nonwoven reinforcement, to get good adhesion, the penetration of the paste is a key point. That is why this study addresses the relationship between rheology, penetration through the nonwoven fabrics and the mechanical properties of various lime pastes with different contents of water and metakaolin (MK). The effect of the binder’s grinding is also evaluated. The results indicate that MK pastes with higher w/b ratios penetrate better into nonwovens, Grinding has a negative effect on penetrability despite improving the mechanical properties of the pastes.

STUDYING THE MECHANICAL PROPERTIES OF HYBRID COMPOSITES USING NATURAL ADDITIVES WITH EPOXY

The fundamental goal of the present study is to study the effects of the natural additives with vegetable and animal sources in form (i.e. the short fibers and particle) on mechanical characteristics epoxy. (The wood dust WD, cow bones CB, date palm fiber DP, and sheep wool SW) have been chosen as natural additives with a variety of the weight ratio reinforcements for epoxy matrix, which is based upon the hybrid composites that have been produced by hand lay-up approach. Tensile, compression and flexural tests have been performed based on the American society for the testing and materials (ASTM) for the characterization of hybrid composites it has been discovered that mechanical characteristics may be increased or decreased according to the material additive type, its origins, and the utilized percentage of weight.

Effect of randomly dispersed short fibers on the flexural resistance factor of concrete beams reinforced with GFRP bars

Purpose The purpose of this paper is to investigate the potential design advantage in terms of resistance factors for normal weight concrete beams containing moderate-dose randomly dispersed short fibers and reinforced with glass fiber reinforced polymer (GFRP) bars.Design/methodology/approach An analytical model based on the current code specifications is used to calculate the moment capacity of over-reinforced sections. The vast majority of the considered beams are over-reinforced, compression-controlled. The data of the fiber-reinforced concrete (FRC) reinforced with GFRP bars are collected from three published research studies which are based on experimentally tested results. Three different types of short fibers with four volume fractions are considered. Probabilistic model is established to conduct reliability-based calibration using Monte-Carlo Simulation. Limit state function, relevant load and resistance random variables are identified, and adequate statistical parameters are selected. Target reliability index consistent with the one used to develop current design code specifications is used.Findings Reliability analysis and calibration process are carried out with the intention of estimating the flexural resistance factors for FRC beams reinforced with GFRP bars.Originality/value The predicted flexural resistance factors ranged from 0.72 to 0.95, giving the resistance factors the potential to be increased above the currently specified value of 0.65 for compression-controlled members reinforced with FRP bars.

Composites Manufactured by Stereolithography

Stereolithography (SLA) is a widely utilized rapid additive manufacturing process for prototypes and proof-of-concept models with high resolution. In order to create structurally sound components using SLA, reinforcement needs to be incorporated in the UV-based resins typically used. However, the introduction of reinforcement into vat-based SLA printers has had limited success due to a host of processing challenges including the creation of a homogeneous resin mixture and UV-inhibiting constituents. The effectiveness of using a dual curing system, consisting of a photo and thermal initiator, for the additive manufacturing of carbon fiber short-fiber composites via vat photopolymerization, was investigated. The necessary processing parameters were developed that resulted in successful printing and curing of composites at a 5% fiber volume. Manufacturing with reinforcements that have different densities from the resin creates separation issues, either suspending to the top or settling to the bottom. Following the approaches discussed in this chapter, an even distribution of short fibers was achieved throughout SLA printed samples using a modified commercial printer. Separation was overcome by inducing a continuous flow of reinforced liquid resin in the printer vat during printing. This flow field adaptation allows commercial SLA printers the ability to produce composite parts with different densities of the constituents utilized.

Experimental Investigation and Modelling of the Layered Concrete with Different Concentration of Short Fibers in the Layers

The use of steel fiber reinforced concrete (SFRC) in structures with high physical-mechanical characteristics allows engineers to reduce the weight and costs of the structures, to simplify the technology of their production, to reduce or completely eliminate the manual labor needed for reinforcement, at the same time increasing reliability and durability. Commonly accepted technology is exploiting randomly distributed in the concrete volume fibers with random each fiber orientation. In structural members subjected to bending, major loads are bearing fibers located close to outer member surfaces. The majority of fibers are slightly loaded. The aim of the present research is to create an SFRC construction with non-homogeneously distributed fibers. We prepared layered SFRC prismatic specimens. Each layer had different amount of short fibers. Specimens were tested by four point bending till the rupture. Material fracture process was modelled based on the single fiber pull-out test results. Modelling results were compared with the experimental curves for beams. Predictions generated by the model were validated by 4PBT of 100 × 100 × 400 mm prisms. Investigation had shown higher load-bearing capacity of layered concrete plates comparing with plate having homogeneously distributed the same amount of fibers. This mechanism is strongly dependent on fiber concentration. A high amount of fibers is leading to new failure mechanisms—pull-out of FRC blocks and decrease of load-bearing capacity. Fracture surface analysis was realized for broken prisms with the goal to analyze fracture process and to improve accuracy of the elaborated model. The general conclusion with regard to modelling results is that the agreement with experimental data is good, numeric modelling results successfully align with the experimental data. Modelling has indicated the existence of additional failure processes besides simple fiber pull-out, which could be expected when fiber concentration exceeds the critical value.

Geopolymers Reinforced with Natural Fibers: A Comparison among Different Sources

The performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials’ toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased.