Macro-synthetic Fibers Research Articles

Macro synthetic fibers as reinforcement for deep beams with discontinuity regions: Experimental investigation

Macro synthetic fibers enhance the response of concrete in tension, ultimately improving its structural behavior, which leads to fully or partially replacing the conventional reinforcements in structural members. However, their applicability in shear predominant critical structural members that have complex stress fields and congested reinforcements have not been investigated. The objective of this paper is to evaluate the performance of macro synthetic fibers in critical structural applications with plausibly reduced conventional reinforcements by comparing the structural response of macro-synthetic-fiber reinforcement with that of conventional reinforcement and steel-fiber-reinforcement from available literature in order to gain perspicacity on different fiber types, fiber dosages, and congestion of reinforcements. An experimental program was conducted on three quarter-scale deep beams with discontinuity regions having reduced reinforcements. Macro-synthetic fibers were added at volume fractions (Vf) of 1% and 2%, and their performance was compared with that of the specimen without fibers. The applied load versus deflection of the beams, failure modes, cracking patterns, and strain in reinforcements were monitored during the tests until failure. The experimental results revealed that the inclusion of 2% Vf of macro synthetic fibers significantly increased the ultimate strength and post-cracking resistance of deep beams.

Precast tunnel segments for metro tunnel lining: A hybrid reinforcement solution using macro-synthetic fibers

The addition of fibers has been proven successful to simplify reinforcement in precast tunnel segments, allowing as a function of both segment typology and fiber reinforced concrete (FRC) toughness a total or partial replacement of the conventional reinforcement. Results from an experimental research aimed at comparing the structural behavior of segments made with conventional (only rebars, RC) or hybrid (rebars + fibers) reinforcement are presented. The experimental program consisted of flexural and point load tests (which reproduces the jack actions during TBM operations) carried out on four large-scale precast tunnel segments representative of a metro tunnel lining characterized by an internal diameter of 5.80 m and a thickness of 0.30 m. The main goal of the experimental program was to evaluate the possibility of using macro-synthetic polypropylene fibers (Polypropylene Fiber Reinforced Concrete, PFRC) in combination with a lower amount of conventional rebars (optimized reinforcement, RCO) for guaranteeing the required segment performance. Experimental results indicate that macro-synthetic fibers may be very effective in combination with conventional rebars to withstand the main stresses that arise in a segment both at initial and final phases, proving that the adoption of hybrid reinforcement solution using macro-synthetic fiber is possible for metro tunnel lining.

Influence of synthetic fibers’ type, length, and volume on enhancing the structural performance of rubberized concrete

This study aimed to investigate the influence of using different synthetic fibers’ (SFs) type, length, and volume on enhancing the structural performance of rubberized concrete beams. Different self-consolidating rubberized concrete (SCRC) and vibrated rubberized concrete (VRC) with different percentages of crumb rubber (CR) and SFs were tested. The main parameters were the percentage of CR (0%, 10%, 15%, 20%, and 30% by volume of sand), type of SFs (micro-synthetic fibers (MISFs) and macro-synthetic fibers (MASFs)), length of SFs (19 mm, 38 mm, 50 mm, 54 mm), and volume of SFs (0%, 0.2%, and 1%). The structural performance of the tested beams was assessed based on the characteristics of load-deflection curves, flexural stiffness, cracking behavior, displacement ductility, energy absorption, cracking moment, and bending moment capacity. The results indicated that using MISFs slightly enhanced the deformability, flexural stiffness, ductility, energy absorption, cracking moment, and bending moment capacity, while this enhancement significantly increased when MASFs were used. The results also showed that increasing the MASF length from 38 mm to 50 mm exhibited less improvement in the structural performance of rubberized beams. Meanwhile, MASF54 (MASF with 54 mm length) showed better improvement compared to MASF50 (MASF with 50 mm length) but still less than MASF38 (MASF with 38 mm length). Combining high percentage of MASF38 (1%) with high percentage of CR (30%) compensated for the reduction in the bending moment capacity (that resulted from using high percentage of CR) and helped to develop semi-lightweight concrete beams.

Effect of Macro Synthetic Fiber on Mechanical Properties and Flexural Toughness of Nano-scale Admixture Wet-mix Shotcrete

Mechanical properties and flexural toughness are critical performance representing the supporting ability of shotcrete. Flexural toughness can also be used to evaluate the post-crack performance, which mainly depends on fiber. To further promote the supporting capacity of fiber reinforced Nano-scale admixture shotcrete, four contents of macro synthetic fiber (MSF) including 0.7%, 0.9%, 1.1% and 1.3% in volume percentages were investigated. The results indicated that the compressive strength, tensile strength and flexural strength increased firstly and then decreased as MSF content increasing from 0.7% to 1.3%, of which optimum contents were 0.9%, 0.9% and 1.1% respectively. Increasing MSF content could increase the fiber number in per unit cross-section, which could raise the cooperative bearing capacity of fiber and matrix. Therefore, the mechanical properties were improved. However, once MSF content was too high, fiber coated with cementing paste became poor. The defects and cracks were much easier to be produced because of distance between fibers and boundaries becoming smaller and smaller. Then mechanical properties deteriorated under the interaction of boundary effect and poor dispersion of fibers. Besides, flexural toughness index containing I5, I10 and I20 was raised with the increase of fiber content, which indicated the improvement of flexural toughness.

Effect of Fiber Hybridization, Strain Rate and w/c Ratio on the Impact Behavior of Hybrid FRC.

Concrete in practical applications has to inevitably suffer various impact loads. Recent research indicates that the hybrid fiber reinforced concrete (FRC) has better dynamic mechanical properties compared to the mono FRC under impact loading. Based on macro-experimentation and micro-observation, the impact behavior of the hybrid basalt-macro synthetic polypropylene FRC (BSFRC) was investigated by using ∅74 mm SHPB, SEM, and EDS. The effects of fiber hybridization, strain rate, and w/c ratio were analyzed simultaneously. The results show that the dynamic mechanical properties of BSFRC are strain-rate sensitive. Both basalt and macro synthetic polypropylene fibers (BF, SF) have a strengthening and toughening effect on concrete. Their hybridization has a similar enhancement effect but the impact toughness of concrete is further improved and the best hybrid ratio is 0.05%(BF)–0.25%(SF). BSFRC with higher w/c ratio has a higher strain rate effect while the fiber hybridization effect is weakened. Besides, the proposed constitutive model can well describe the impact behavior of BSFRC. The hydration of cement in the interface transition zones is lower with more Calcium Silicate Hydrate and less than that in the common mortar. However, the addition of BF and SF contributes to the hydration of cement and improves the performance of concrete eventually.

Experimental study on the out-of-plane strengthening of unreinforced masonry walls using cement-based fiber composites

This paper presents results from an ongoing research that is intended to study the behavior of URM walls for out-of-plane action. The effect of fiber reinforced shotcrete (FRS) as a strengthening method for the URM walls is examined. Eight URM walls were built inside a precast reinforced concrete boundary frame and strengthened with cement-based shotcrete mixes reinforced with different types of fibers. The masonry wall is 1.2x 1.2 m, and the masonry units were hollow concrete blocks (10 x 20 x 40 cm). Conventional fiber reinforced concrete (FRC) and engineered cementitious composite (ECC) were used as the strengthening layers sprayed on the surface of masonry walls. Control walls with plain shotcrete and conventional plastering mortar were also examined. Synthetic macro-fibers at dosage rate of 6 kg/m3 in FRC mix and Polyethylene micro-fibers at a dosage rate of 16 kg/m3 in ECC mix were considered in this study. The walls were placed in a carefully designed set up and tested under static central load using a hydraulic actuator with a capacity of 500 kN. The parameters recorded during testing were the applied load and out-of-plane displacement of the walls. Cracking pattern and failure modes were also monitored. The reported test results demonstrate that FRC and ECC mixes can significantly increase the out of plane strength and ductility of the URM walls.

Macro synthetic fibre reinforced concrete: Influence of the matrix mix design on interfacial bond behavior

Since the composite nature of Fibre Reinforced Concrete materials, their performance is strictly dependent on the mechanical properties of their components, matrix and fibres, but, above all, on their interaction. The collaboration of the two materials is directly responsible of the force transferring mechanism from concrete to fibres that reflects their contribute in the residual flexural strength performance. This paper aims at understanding how the concrete admixture components might affect the bond of polypropylene crimped fibres, and presents the preliminary results of an experimental campaign consisting of pull-out and compression tests. Four water cement ratios and three cement-sand ratios were considered. The experimental analysis is also supported by the calibration of a numerical model that simulates the pull-out behaviour of a single fibre.

Self-Compacting Concrete Reinforced with Twisted-Bundle Macro-Synthetic Fiber

The use of self-compacting concrete (SCC) reinforced with fibers has great potential in the precast concrete industry as the concrete can be delivered straight into the moulds, without any vibration or compacting effort. Similarly, it has the potential to replace traditional steel reinforcement depending on the design requirements. Novel synthetic fibers have recently become available in the market, but still, limited information is available on the performance of SCC reinforced with such fibers. This paper investigates the use of twisted-bundle macro-synthetic fiber in self-compacting concrete. Three different concrete mixtures with fiber dosage of 4, 6, and 8 kg/m3 were produced in large scale batches, and their performance was compared in terms of slump-flow, compressive strength, split tensile strength, modulus of elasticity, and flexural strength. Moreover, a comprehensive evaluation of the post-cracking residual strength is presented. It was found that the mixture with 4 kg/m3 fiber content has the most satisfactory flowability, whereas 8 kg/m3 mixture achieved the highest residual flexural strength. Based on the observed post-cracking behavior, a simplified stress-crack opening constitutive law is proposed. Since the fiber dosage affects the residual flexural strength, a factor related to fiber content is recommended while determining the ultimate residual flexural strength.

Effect of basalt, polypropylene and macro-synthetic fibres on workability and mechanical properties of self-compacting concrete

In this study, the effects of different fibre types on the workability and mechanical properties of self-compacting concrete were investigated. Fresh and hardened properties of self-compacting concrete, different fibre content 0.90, 1.35 and 1.80 kg/m3 were evaluated using basalt, polypropylene and macro synthetic fibres with different fibre lengths of 24, 19 and 40 mm, respectively. The properties of fresh concrete were evaluated in terms of slump flowing, viscosity and flowability. In addition, compressive, flexural and splitting tensile strength were obtained from hardened concrete properties. To characterize mechanical properties 90 specimens were experimentally tested. The results show that the use of fibre reduces the workability of self-compacting concrete. On the other hand, tensile and flexural strength of the self-compacting fibre reinforced concrete increased with increasing fibre content, but it was determined that the fibre addition had no significant effect on the compressive strength.

Cohesive stress transfer and shear capacity enhancements in hybrid steel and macro-polypropylene fiber reinforced concrete

The link between the fracture behavior and shear capacity of fiber reinforced concrete composite is investigated. The synergy between hooked steel fibers and continuously embossed macro-synthetic fibers in providing improved fracture and post-cracking shear resistance is experimentally evaluated. The fracture responses of plain concrete, concrete with discrete hooked ended steel fibers at two volume fractions (0.5% and 0.75%) and concrete with hybrid blend of steel and macro-synthetic polypropylene fiber (0.3% steel and 0.2% macro-synthetic) are evaluated. The cohesive stress-crack separation relationships of the different composites are obtained from the fracture test responses of notched beams in flexure. There is an improvement in the early fracture response of concrete containing hybrid fiber blend when compared with steel fiber reinforcement, which is due to the higher crack closing stresses produced at small crack openings immediately after cracking. The load carrying capacity in shear obtained from the concrete composite with hybrid blend is significantly higher than the concrete with steel fiber reinforcement at identical fiber volume fraction and is identical to the response obtained from steel fiber composite with a higher volume fraction of fibers. From the full-field displacements obtained using digital image correlation (DIC), the in-situ dilatant behavior of the shear crack is established. Influence of the high early crack opening resistance seen in blends provides better crack control for the shear crack and leads to a significant improvement in the shear resistance derived from stress transfer across the rough crack faces. A mechanistic model for predicting the shear capacity of reinforced fiber composite beams, which considers the crack profile information of the shear crack obtained from DIC and the cohesive stress-crack separation relationship obtained from the fracture tests is presented. The model predicts an increase in the contact stresses on the crack faces in the fiber-reinforced composite with the inclusion of fibers, which increases the shear transfer capacity of the crack.

Pullout modelling of viscoelastic synthetic fibres for cementitious composites

The problem of the pullout of a viscoelastic synthetic fibre embedded in a cementitious matrix and subjected to an external time-dependent axial load is considered in the present work. A 1D phenomenological model able to simulate the contribution of viscoelastic relaxation as well as the hardening behavior due to abrasion phenomena during slippage is developed. The cement matrix compliance is neglected with respect to the fibre elongation. The interfacial shear stress between the fibre and the surrounding matrix is assumed to depend on the slippage distance through a second degree polynomial law, thus involving three constitutive parameters. Two distinct phases are recognized: An earlier debonding stage followed by the effective fibre pullout process. Two different creep functions have been assumed for modelling the viscous response of polymeric fibres: A function based on the fraction-exponential Rabotnov operator and a classical exponential model. Identification of the governing constitutive parameters allows obtaining the relation between the external strain and the axial displacement, which has been compared with experimental results provided by pullout tests both on plain and treated fibres, finding a good agreement. It is shown that the proposed approach can predict the whole pullout process of discrete synthetic macrofibres.

Influence of fire on temperature gradient and physical-mechanical properties of macro-synthetic fiber reinforced concrete for tunnel linings

Abstract This study aims to evaluate the effect of fire on the physical, mechanical, and microstructural properties of macro-synthetic fiber reinforced concrete. Results demonstrated that internal heating rate is constant through time and is a function of the distance from the fire. Temperature gradient values are nonlinear, reduce at greater distances from the heated surface and with the duration of the fire. Microstructural analysis shows the severe dehydration of hydrated products, which negatively influences the mechanical properties of the composite. Above 205 °C the formation of nesosilicates is verified. Residual flexural strength values reduce by over 85% after the fire exposure due to deterioration of the reinforcing mechanism. Compressive strength and elastic modulus drastically reduce with temperature increase. The present study contributes to the absent literature on the post-fire mechanical behavior of MSFRC, suggests an alternative approach to the post-fire evaluation of tunnel structures, and aids in the definition of post-fire safety parameters.

Evaluation of post-cracking behavior of fiber reinforced concrete using indirect tension test

This paper presents an experimental investigation on the applicability of the novel double-edge wedge splitting (DEWS) testing technique to evaluate the mechanical properties of fiber reinforced concretes (FRCs) with low fiber content. This study aims to validate the DEWS test for the structural evaluation of FRCs with softening behavior, which is also considered by the design codes for structural applications. In this case, the occurrence of post-peak instability is critical. This instability could compromise the residual strength evaluation, especially for the serviceability limit state (SLS). The experimental studies focused on three main aspects affecting the DEWS test response: effect of test displacement rate, effect of fiber content, and orthotropy of FRCs. Two different groups of FRCs (reinforced with steel and macrosynthetic fibers) were mechanically evaluated, both at the SLS and ultimate limit state. The variation of the test displacement rate had no significant impact on the FRC post-cracking pattern. The DEWS test could detect behavioral variations induced by altering the fiber content and fiber orientation on both composites. This variation was more evident for higher crack opening levels because the post-peak instability may compromise the DEWS results in the SLS.

Research on the impact response and model of hybrid basalt-macro synthetic polypropylene fiber reinforced concrete

This paper experimentally studied the impact behavior of hybrid basalt-macro synthetic polypropylene fiber reinforced concrete under impact loads (101–102 /s) with a split Hopkinson pressure bar (SHPB) device. The fiber content of basalt fiber (BF) was 0.05%, 0.075% and 0.1% and that of macro synthetic polypropylene fiber (SF) was 0.15%, 0.25%, 0.35% and 0.5%. Both static and impact tests were conducted to investigate the effect of strain rate and fiber hybrid ratio on the dynamic performance of the hybrid FRC, i.e. impact strength, dynamic increase factor (DIF), impact strain and toughness. The test results indicate that the hybrid FRC is strain-rate sensitive and a proper fiber hybrid ratio can improve the impact performance of concrete. DIF and lgε̇ are linearly related, whereas the impact strain, toughness and strain rate present quadratic polynomial relationship. Both BF and SF can enhance the impact strength of concrete. However, BF has a better enhancement effect than SF in terms of improving impact strength but not as good as SF in improving impact toughness. Also, appropriate BF and SF hybrid ratio can enhance the impact strength and toughness of concrete but excess fiber content has a weakening effect. In this study, the optimal fiber hybrid ratio was 0.075%–0.35% (BF-SF) which had the best impact resistance. Finally, a damage dynamic constitutive model suitable for the hybrid FRC was proposed to fit the test curves from SHPB test based on Zhu-Wang-Tang (ZWT) constitutive model.

Axial stress-strain behavior of macro-synthetic fiber reinforced recycled aggregate concrete

This study aims to investigate the axial stress-strain behavior of macro-synthetic fiber reinforced recycled aggregate concrete. Concrete cylinders reinforced with macro-synthetic fibers were tested under axial compression, with the variation of three different replacement ratios of recycled aggregates (i.e., 0, 50 and 100%) and three different dosages of macro polypropylene fibers (i.e., 0, 0.5 and 1% of volume of recycled aggregate concrete). A comparative study of the existing stress-strain models for steel fiber reinforced normal and recycled aggregate concrete with the test results indicates that the stress-strain behavior of steel fiber reinforced normal and recycled aggregate concrete can be well predicted by these existing models. No stress-strain model for macro-synthetic fiber reinforced normal and recycled aggregate concrete has been developed. Based on the test results, a stress-strain model is developed in this work by modifying the parameters of best performing stress-strain model for steel fiber reinforced normal aggregate concrete. The proposed model can effectively predict the stress-strain behavior of both steel and macro-synthetic fiber reinforced normal and recycled aggregate concrete. Test results show that the peak stress, peak strain and ultimate strain of concrete specimens increase with the increase in fiber dosage and the addition of fibers has a better effect on recycled aggregate concrete and as compared to normal aggregate concrete.

Mechanical and Durability Characteristics of Latex‐Modified Fiber‐Reinforced Segment Concrete as a Function of Microsilica Content

This study evaluated the performance of latex‐modified fiber‐reinforced concrete (RC) segments as a function of the substitution level of microsilica and type of reinforced fiber, to address the problem of corrosion of steel segments and steel‐reinforced fiber segments, which are commonly used to shield tunnel‐boring machine (TBM) tunnels in urban spaces. Our study compared macro synthetic, steel, and hybrid (macro synthetic fiber + polypropylene fiber) reinforcing fibers. The substitution levels of microsilica used were 0, 2, 4, and 6%. The target strengths were set at 40 and 60 MPa to test compressive strength, flexural strength, chloride ion penetration resistance, and impact resistance. Testing of latex‐modified and fiber‐reinforced segment concrete showed that the compressive strength, flexural strength, and chloride ion penetration resistance increased with an increasing substitution level of microsilica. These improvements were attributed to the densification of the concrete due to filling micropores with microsilica. Micro synthetic fiber was more effective in terms of improved compressive strength, flexural strength, and chloride ion penetration resistance than steel fiber. These results were due to the higher number of micro synthetic fibers per unit volume compared with steel fiber, which reduced the void volume and suppressed the development of internal cracks. The optimal microsilica content and fiber volume fraction of micro synthetic fiber were 6% and 1%, respectively. To evaluate the effects of the selected mixtures and hybrid fibers simultaneously, other mixing variables were fixed and a hybrid fiber mixture (combination of macro synthetic fibers and polypropylene fibers) was used. The hybrid fiber mixture produced better compressive strength, flexural strength, chloride ion penetration resistance, and impact resistance than the micro synthetic fibers.

Glass macrofiber self‐compacting concrete: Fiber distribution and mechanical properties in thin walls and slabs

Alkali‐resistant glass macrofibers for concrete reinforcement are recently available; reductions in thermal or drying shrinkage cracks and the replacement of conventional welded mesh in some structural elements appear as the main applications. When considering thin elements, it has been recognized that the flow and wall effects have strong influence on the residual properties of steel fiber‐reinforced self‐compacting concrete (FR‐SCC); some effects were also observed in the case of polymer fibers but there are no references about glass macrofibers. This paper studies the variation of the mechanical properties in thin walls and slabs cast with SCC incorporating glass macrofibers; the results are compared with those obtained on similar elements molded with steel and synthetic macrofibers SCC. The wall effect and the flow rate affect fiber distribution in glass FR‐SCC, and lead to significant differences in the residual mechanical properties along thin elements, and also in the first crack strength.

Properties of Self-Compacting Mortars with Different Contents of Synthetic Macro Fiber

This study is devoted to investigating engineering properties of Self-Compacting Mortar (SCMs) produced with synthetic macro fiber. For this purpose, five different mix designs were prepared with a constant w/c ratio of 0.55 to sustain self-compatibility. Fiber content in these mixtures were changed from 0% to 5%. Engineering properties were investigated in terms of workability, mechanical properties and abrasion resistance. Compressive strength and flexural strength tests were conducted on the specimens exposed to three different water curing age 7 days, 28 days and 56 days respectively. In this study, also optimum synthetic fiber amount was determined to sustain self-compatibility of mortar. It was revealed that 2 and 3 kg/m3 synthetic macro fiber ratio are the key proportions to improve workability and flexural strength properties of hardened mortar. Moreover, adding fiber to mortar decreased abrasion resistance at 28 days age. In reverse, fiber addition increased abrasion resistance at 56 days age.

Flexural Performance Evaluation of Fiber-Reinforced Concrete Incorporating Multiple Macro-Synthetic Fibers

Fiber-reinforced concrete (FRC) is a promising construction material mainly because of the crack-controlling mechanisms that discrete fibers can impart to inherently brittle concrete. Macrofibers, in particular, have been proven effective for providing post-crack ductility and toughness, while synthetic fibers are a promising solution to avoid corrosion-related durability issues. To assess the performance enhancement provided by macro-synthetic concrete fibers, this study performs flexural tests on FRC beams containing three different types of macro-synthetic fibers. The selected fibers include polypropylene (PP), polyvinyl alcohol (PVA), and alkali-resistant glass (ARG) macrofibers mixed at volume fractions of 0.5%, 1.0%, and 1.5%. Static and dynamic fresh properties are monitored using the vibrating Kelly ball (VKelly) test. Beam specimens are then placed under a third point bending configuration, as per ASTM C1609 Standard, to measure load versus mid-span deflection. Strength and toughness parameters are derived from the load–deflection data to assess the flexural performance of the FRC composite systems under consideration. The parameters of interest include first peak strength (pre-crack flexural strength) and post-crack residual strength and toughness provided by fiber addition. Of the mixtures tested, ARG fiber mixtures show the highest residual strength and toughness values, followed by PP and PVA fiber mixtures. ARG fibers produce the most workable mixtures at all fiber volumes, while PVA fibers show a tendency to encounter dispersion issues at higher volume doses. The outcome of this study is expected to facilitate the selection of fibers by giving insight into their relative contribution to fresh and hardened flexural properties of FRC.

Image Processing and Machine Learning to investigate fibre distribution on fibre-reinforced shotcrete Round Determinate Panels

Fibres in fibre reinforced concrete (FRC) and fibre reinforced shotcrete (FRS) are known to increase the toughness of the composite material thanks to their ability to transfer tensile stresses even after cracks have opened. However, fibres are deemed responsible for uncertainty in mechanical performance of FRC and FRS. This uncertainty is ascribed to how the fibres are physically located with respect to the crack. In this study a novel approach is presented to measure the distribution of fibres from digital images. A computer code that features Image Processing and Machine Learning algorithms has been developed to extract: i) the 2D location, ii) the mode of failure, iii) the orientation, iv) the pull-out length for each single fibre and v) the total number of fibres bridging the crack. The Machine Learning Algorithm is trained with a database that is attached to this article. This methodology, apart from giving an understanding of how fibres are distributed over the crack, provides the main input of several numerical models that simulate the behaviour of FRC/FRS taking into account the position and orientation of each single fibre. The main advantage of this approach over existing methods is that the hardware required to carry out the analysis consists of a simple smartphone camera while an output with errors within a few thousands parts of the actual measures.The algorithm is employed to analyse the fibres’ distribution for 9 Round Determinate Panels (RDP) made of wet-mix shotcrete. The spatial 2D-location of fibres in the crack is tested for randomness with a Monte Carlo procedure and the fibres’ distribution is found to follow an Independent Random Process. For fibres that pulled-out from one side of the crack, a further 3D investigation has been carried out. The analysis on the fibres’ orientation confirmed the conclusion found by other authors that fibres tend to align perpendicular to the direction of spraying. Furthermore, it is unlikely to find fibres perpendicular to the crack surface. This last conclusion, however, is specific of the properties of fibres tested in this study, and in general, of macro synthetic fibres that tend to snap when their orientation is closer to the direction of the main stress. Finally, in the attempt of examining the representativeness of smaller version round determinate panels, the fibres’ distribution of 3 Mini RDP has been assessed and is found to be comparable to that of full size RDP. This suggests that a similar fibre’s distribution can be achieved even in a panel that is half the weight of the full size RDP.