Fibra Nycon RECS100-PVA para reforço de concreto (20 denier)

Nycon RECS100-PVA Fiber for Concrete Reinforcement (20 denier) is a polyvinyl alcohol monofilament synthetic fiber supplied as a Type III synthetic fiber-reinforced concrete component under ASTM C1116/C1116M. The 20-denier designation is a linear mass density of 20 g per 9,000 m; it is not a direct diameter specification. For a circular monofilament with a typical high-tenacity PVA density of 1.29 g/cm³, the equivalent diameter is approximately 0.047 mm. Because cut length is batch-specific, the number of filaments per kilogram is calculated as N = 9×10⁹/(D×L), where D is denier and L is cut length in millimetres. An 8 mm cut length therefore yields approximately 5.6×10⁷ filaments per kilogram under ideal monofilament conditions. The product should be accompanied by EN 14889-2:2006 documentation when used under the Construction Products Regulation 305/2011 and by a manufacturer batch certificate that states cut length tolerance, tensile properties tested under ASTM D2256/D2256M, and alkali resistance data for cementitious service. Published property data for this specific product are limited; typical high-tenacity PVA fiber class ranges should not replace project-specific incoming inspection.

How does 20-denier monofilament geometry alter early-age crack bridging in concrete?

Early-age plastic shrinkage cracking occurs when capillary tension in the pore water exceeds the tensile capacity of fresh or just-set concrete. A 20-denier PVA monofilament with an assumed diameter of 0.047 mm and cut length of 8 mm has an aspect ratio of approximately 170:1. At a dosage of 0.9 kg/m³, the fiber volume fraction is 0.0698% and the calculated average cubic fiber spacing is approximately 2.7 mm if the filaments were uniformly distributed and randomly oriented; at 1.8 kg/m³, the volume fraction is 0.1395% and the spacing decreases to approximately 2.1 mm. The corresponding reinforcement index V_f×l/d is 0.119 at 0.9 kg/m³ and 0.238 at 1.8 kg/m³. These values are within the range commonly specified for plastic shrinkage crack control, but they do not by themselves indicate strain-hardening tensile response. The fine diameter increases filament surface area and the total length of available crack intercepts. PVA is hydrophilic and forms a chemical bond with cement hydration products, particularly calcium-silicate-hydrate and portlandite surfaces, which raises pull-out resistance compared with hydrophobic polypropylene fibers at a similar aspect ratio. The fiber does not eliminate evaporation-driven shrinkage; it redistributes crack opening into multiple finer cracks after crack initiation. Restrained-shrinkage testing should be carried out according to ASTM C1581/C1581M or ASTM C157/C157M with project-specific curing, because plastic settlement and drying rate control remain primary strategies.

Mixer compatibility, slump retention, and batching sequence for RECS100-PVA-reinforced concrete

In ready-mix concrete, fiber introduction is governed by ASTM C94/C94M and ACI 544.3R. The high fiber count and hydrophilic surface of 20-denier PVA can increase water demand and mixer torque compared with an unreinforced reference batch. In twin-shaft compulsory mixers and central mixers, field experience indicates that adding fiber to the aggregates before water injection reduces fiber balling and floating, whereas adding dry fiber directly onto wet paste in a stationary mixer can produce clumps that do not redisperse at low drum speed. A dry-mix interval of 30–60 seconds before water addition is used in some central mixers, but the exact interval is equipment-dependent and should be tuned to blade speed and batch volume. Transit-mixer after-loading should be conducted at full mixing speed for a duration sufficient to achieve uniform single-fiber dispersion; ACI 544.3R describes common after-loading practices and suggests verification by wash-out sampling. Slump testing under ASTM C143/C143M and density/air testing under ASTM C138/C138M and ASTM C231/C231M should be performed before and after fiber addition to quantify the rheological effect. If the target slump is between 100 mm and 150 mm, a Type F or mid-range water-reducing admixture conforming to ASTM C494/C494M may be required to offset water demand. At high dosage, the fine filaments can increase paste viscosity and reduce measured slump; the magnitude should be established by trial batch because aggregate grading and admixture package dominate the response. Dosage levels above 1.8 kg/m³ should not be specified solely from fiber-class data; published data for this specific product are limited.

Where the product is handled by pneumatic fiber-dosing equipment, the 20-denier filaments present a low bulk density and can bridge at rotary-valve inlets, transfer hoppers, and flexible lance outlets if moisture is present. Field observations from central mix plants indicate that batches stored above relative humidity of 60% may form fiber nests that survive batching and appear as clumps at mixer discharge. In such operations, moisture-exposed fiber should not be forced through the dosing line; it should be dried or separated by mechanical fluffing before use. The dosing equipment should be calibrated for the specific cut length and fiber count, because the mass flow behavior of a 20-denier product differs from that of coarser macro-synthetic fibers and steel fibers. Loss-in-weight feeders and vibratory tray feeders with air slides are commonly used to maintain consistent addition; feed rate must be calibrated against actual fiber bulk density and moisture content rather than assumed from manufacturer nominal values.

When RECS100-PVA is specified for wet-mix shotcrete or precast extrusion, equipment parameters require preconstruction validation

For wet-mix shotcrete, the 20-denier PVA product can improve green-structure cohesion and reduce rebound, but it also increases pump-line viscosity and may require adjustment of accelerator type and dose. ACI 506R and ASTM C1436/C1436M provide placement guidance and test methods for fiber-reinforced shotcrete. The delivery hose diameter and nozzle tip must be selected relative to cut fiber length; a common industry practice is to maintain a hose diameter at least three times the cut length, but published data for this specific fiber in shotcrete are limited and spray-panel testing is required prior to production. Flexural toughness of shotcrete panels can be evaluated under ASTM C1550/C1550M; preconstruction panels should be cored and tested at the project’s specified energy absorption levels. The fine denier may produce surface fibers after erosion or finishing, and trowelling behavior should be evaluated separately.

In precast extrusion and slip-formed products, the high fiber count can increase extruder power draw and produce anisotropic alignment parallel to the auger flow. This alignment may enhance longitudinal post-crack response but does not provide equivalent transverse crack control. Low water/cementitious pastes below 0.30 may have insufficient liquid volume to wet the increased fiber surface; a polycarboxylate ether plasticizer is typically required to maintain workability. The auger gap, die opening, and forming speed must be adjusted to prevent fiber segregation near forming surfaces. A full-scale trial extrusion is the only reliable method to confirm surface quality, fiber distribution, and green strength; laboratory-scale mortar tests do not capture the shear and orientation conditions of production equipment.

Comparative fiber chemistry and property-based functionality in cementitious matrices

The selection of a synthetic fiber in concrete depends on density, tensile strength, elastic modulus, elongation at break, surface chemistry, and alkali resistance. RECS100-PVA belongs to the high-tenacity PVA fiber class, which is distinguished from polypropylene microfibers by higher tensile strength and elastic modulus and by a hydrophilic surface that participates in cement hydration chemistry. This chemical bond reduces fiber pull-out at small crack openings, but it also produces a stiffer paste response and may demand greater water-reducer dosage than a hydrophobic polypropylene fiber at the same mass loading. Unlike steel fibers, PVA does not corrode and does not create surface staining; however, its elastic modulus is roughly 25–35 GPa versus 200 GPa for steel, so it is not a direct volumetric substitute for steel in primary moment-resisting applications. Unlike alkali-resistant glass fibers, PVA is not brittle and does not require zirconia content above 16% for cementitious durability, although continuous exposure to hot water or strongly acidic conditions may reduce performance. Table 1 presents typical published property ranges for fiber classes; values for the specific 20-denier product must be taken from supplier batch documentation.

Values in Table 1 are representative of commercial fiber classes and are not lot-specific acceptance limits for Nycon RECS100-PVA. Synthetic fiber tensile properties are tested under ASTM D2256/D2256M; steel fiber tensile properties are commonly reported under ASTM A370/A370M or supplier specification. The PVA dosage range reflects common practice for plastic shrinkage control and non-structural secondary reinforcement; higher dosages may be used in engineered cementitious composites only after direct tensile validation.

At equal cut length, the 20-denier designation yields a higher filament count per kilogram than coarser denier products. A 20-denier fiber at 8 mm cut length yields approximately 5.6×10⁷ filaments/kg, whereas a 60-denier fiber at the same length yields approximately 1.9×10⁷ filaments/kg. This difference explains why fine PVA fiber is specified where early-age microcrack interception is critical, while higher-denier or macro-synthetic fibers may be selected where post-crack residual load at larger crack widths is required. The distinction is not inherently superior; it is a selection based on service crack width target and placement constraints.

Within the project specification, operational boundaries for RECS100-PVA should be defined by the specifying engineer. The product is not a replacement for conventional steel reinforcing bars, welded-wire reinforcement, or structural steel fibers unless a direct design calculation using measured post-crack residual strength from ASTM C1609/C1609M demonstrates equivalence. For structural slab-on-ground applications where flexural toughness is specified, the specification should state mid-span residual loads at L/600 and L/150 deflections and require third-party testing before construction. The fine fiber may increase paste viscosity, reduce slump, and alter air-void structure; total air content should be measured under ASTM C231/C231M to distinguish entrained air from fiber-induced viscosity changes. Storage should be in sealed containers below 40 °C and below 60% relative humidity; fiber exposed to moisture or high humidity may form clumps that compromise dispersion. Because PVA has a finite swelling response in hot water, continuous service in saturated water above 60 °C or in strong acids should be evaluated by immersion testing; published data for this specific configuration are limited. Acceptance criteria should be tied to EN 14889-2:2006 or ASTM C1116/C1116M batch documentation, not to generic fiber-class property comparisons.