Fibra Kuraray RECS100L-PVA para reforço de concreto

Kuraray RECS100L-PVA Fiber is a monofilament polyvinyl alcohol reinforcement fiber produced for cementitious matrices that require distributed microcrack control and secondary flexural toughness without metallic corrosion. The fiber is identified by a nominal linear density of 100 dtex, a cut length of 12 mm, and an effective diameter of approximately 0.10 mm, yielding an aspect ratio of 120:1. The PVA polymer is semicrystalline, with a density of 1.30 g/cm³ and a melting point near 225 °C. Unlike polypropylene macrofibers, the hydroxyl-bearing surface of PVA is hydrophilic, which reduces the film of mixing water that can otherwise act as a slip plane at the fiber-matrix interface. Product conformity is assessed under EN 14889-2:2006 for polymer fibres for concrete and ASTM C1116/C1116M for fibre-reinforced concrete.

In conventional concrete, the typical dosage is 0.6 kg/m³ to 1.5 kg/m³, equivalent to 0.05 vol% to 0.12 vol% and approximately 5 million to 12.5 million fibers per cubic metre using the nominal 100 dtex linear density. At these addition levels, the fiber functions primarily as early-age crack control and damage-resistance reinforcement, not as a replacement for primary structural bars. Field records from twin-shaft compulsory mixers show that the product disperses more uniformly when added after the coarse aggregate and a portion of the batch water; dry addition to aggregate before moisture creates fibrous masses that persist at the mixer discharge.

What Mechanical Properties Govern RECS100L Performance in Hardened Concrete?

The tensile strength of 1,200 MPa and Young’s modulus of 36 GPa place the product above polypropylene macrofibers and below steel fiber in stiffness and strength. The elongation at break of 7.5% permits crack bridging at small crack openings but is lower than many polypropylene macrofibers, meaning that once a crack localizes, fiber rupture can occur before complete pullout if the embedment length is short. The hydrophilic character of PVA creates a chemical bond to the cement matrix that is higher than that of polyolefin fibers. In single-fiber pullout, the interfacial bond is often high enough to produce fiber rupture rather than pullout at embedment lengths above 0.5 mm; the exact transition depends on matrix strength and fiber diameter. This rupture-dominated response contributes to early-age crack control but can limit post-crack ductility in high-strength matrices because the fiber may snap before frictional sliding fully develops. The melting point of 225 °C creates an operational upper boundary; continuous curing above 180 °C is not recommended without specific trial validation because published data for RECS100L in autoclaved systems are limited.

Dispersion behaviour and mix design boundaries

At 0.6 kg/m³ to 1.5 kg/m³, the fibers are distributed as discrete monofilaments rather than fibrillated networks. In a twin-shaft compulsory mixer with a batch volume of 3 m³, the recommended sequence is to introduce the fiber after 70–80% of the mixing water and the coarse aggregate have been charged. A post-fiber mixing period of 3–5 min at 12–18 rpm is generally sufficient. For ready-mixed concrete in truck drums, 5 min at 10–12 rpm after fiber addition is common. The product should not be added to dry aggregate before water; field reports from central mixing plants describe fiber balling at the discharge gate when this sequence is used, particularly in mixes with coarse sand and low water-to-cement ratio.

Slump reduction is dosage-dependent. At 0.6 kg/m³, the fall is commonly 10–20 mm; at 1.5 kg/m³, it may reach 25–40 mm depending on aggregate gradation and paste volume. Increasing water content to compensate is not acceptable because it raises the water-to-cement ratio and reduces compressive strength. A polycarboxylate ether superplasticizer conforming to ASTM C494/C494M Type A or Type F can restore workability without adding water. Air content should be verified with ASTM C231/C231M, because the fiber surface can alter air-void coalescence during placement and vibration.

Overdosing beyond 2.0 kg/m³ introduces a processing cliff-edge in low-workability mixes: the fresh concrete may transition from pumpable to non-pumpable over a 0.2 kg/m³ increment when the paste volume is below 280 L/m³. The exact threshold varies with mixer geometry, aggregate shape, and superplasticizer dosage; therefore, trial batching is required when the target dosage exceeds 1.5 kg/m³. In high-shear counter-current mixers, mixing beyond 10 min after fiber addition has been observed to increase fiber entanglement and decrease finishability, but published data for this specific configuration are limited.

Shotcrete and precast placement impose different constraints. In wet-process shotcrete, the fiber is added at the batch plant; the nozzle operator verifies homogeneous fiber distribution before accelerator injection because alkali-free accelerators can create local stiffening around fiber clumps. In dry-process units, the fiber is combined with aggregate and cement at the batching line and passes through the pneumatic feed; the density of 1.30 g/cm³ limits the segregation that occurs with steel fiber. In precast tunnel segments, dosage levels of 0.6–0.9 kg/m³ have been used to reduce demolding edge damage, but project-specific flexural testing under ASTM C1609/C1609M is needed to verify residual strength.

When RECS100L Is Substituted for Steel Fiber or Polypropylene Macrofiber

The substitution decision depends on the required post-crack strength and the exposure environment. Steel fiber at 20–40 kg/m³ yields higher residual flexural strength because steel has a Young’s modulus of approximately 200 GPa, compared with 36 GPa for RECS100L. A one-for-one volumetric substitution of PVA for steel is not appropriate where structural load redistribution depends on high post-crack strength. In corrosion-sensitive slabs, however, RECS100L eliminates the rust bleeding and surface spalling associated with near-surface steel fiber; its density of 1.30 g/cm³ is also lower than steel at 7.85 g/cm³.

Relative to polypropylene macrofiber, RECS100L has higher tensile strength and modulus, a more hydrophilic fiber-matrix interface, and a lower dosage required for equivalent plastic shrinkage crack control in restrained slab tests evaluated under ASTM C1579-21. Polypropylene macrofibers often require higher addition rates to compensate for weaker frictional pullout resistance, and their low modulus limits crack-width restraint once cement paste separates. Against alkali-resistant glass fiber, PVA provides lower modulus but greater apparent ductility because it elongates approximately 7.5% before rupture, whereas AR glass fails at roughly 2–3% elongation. The PVA surface also does not release the sharp respirable splinters associated with brittle glass fiber breakage during mixing and finishing.

Specification compliance requires beam-level flexural validation, not compressive cylinder substitution

Because compressive strength tests cannot capture residual flexural capacity, fiber-reinforced concrete containing RECS100L is specified using ASTM C1609/C1609M-19a beam tests for flexural residual strength and ASTM C1579-21 for restrained plastic shrinkage cracking. General material requirements fall under ASTM C1116/C1116M; European specification is EN 14889-2:2006. The manufacturer’s batch certificate typically reports cut length, linear density, tensile strength, and density. A quality management system certified to ISO 9001:2015 covers production; however, conformity to the product standard does not guarantee the concrete mixture design, which remains the responsibility of the concrete producer.

Internal vibration can orient fibers perpendicular to the vibrating head if the poker is inserted vertically and withdrawn slowly; orientation affects flexural residual strength measured by ASTM C1609/C1609M. In production, external form vibrators for precast elements may create layered fiber orientation, with higher fiber concentration near form faces. This spatial anisotropy means that cube or cylinder compressive specimens are unsuitable for verifying fiber distribution; sawed beams from full-depth cores or test panels are required.

Storage conditions are 5–35 °C and <65% RH in closed packaging; PVA is hygroscopic, and moisture regain above 2% can affect auger feeding in automatic dosing systems. The fiber should not be used as primary reinforcement or in structural applications where yield-line calculations rely on steel area. In air-entrained concrete, trial batching is required because the fiber surface can shift the air-void spacing factor measured under ASTM C457/C457M. Extended mixing beyond 10 min after fiber addition is not recommended; the operational limit is mixer-specific, but excessive shear can damage the monofilament and lower its crack-bridging efficiency.

For slab-on-grade applications, finishing should be timed before fiber fuzzing becomes pronounced. Power troweling with worn blades can expose surface fibers, producing a hairy finish that requires subsequent burnishing or pan finishing. A dosage of 0.6–0.9 kg/m³ is typical for machine-troweled warehouses, while 1.0–1.5 kg/m³ is reserved for slabs with higher early-age restraint or exposed exterior weathering. The concrete should be cured with a liquid membrane compound conforming to ASTM C309 or equivalent, because evaporation before final set can leave surface fibers partially debonded from the paste.