Fibra de Kuraray RSC15-PVA para reforço de concreto

Kuraray RSC15-PVA Fiber for Concrete Reinforcement is a synthetic polyvinyl alcohol monofilament fibre produced for cementitious matrices where crack-width suppression, plastic-shrinkage reduction, and post-crack residual flexural response are specified. The product is classified under ASTM C1116/C1116M-23 Type III synthetic fibre-reinforced concrete and, for European conformity, falls within the scope of EN 14889-2:2006 Class II polymer fibres where a CE marking requires declaration of fibre diameter, cut length, tensile strength, elastic modulus, and alkali resistance. The RSC15 designation identifies a specific fibre geometry and surface treatment within the Kuraray PVA portfolio; exact lot values for denier, cut length, and tensile capacity must be verified against the manufacturer’s certificate of analysis, but public technical literature on high-tenacity PVA cement reinforcement reports typical fibre diameters of 0.04 mm to 0.10 mm, cut lengths from 6 mm to 12 mm, density of approximately 1.3 g/cm³, tensile strength of 0.9 GPa to 1.6 GPa, elastic modulus of 25 GPa to 41 GPa, and elongation at break of 6 % to 10 %. The intrinsic hydrophilicity of PVA, derived from pendant hydroxyl groups, gives a higher fibre–cement interfacial affinity than olefinic polypropylene surfaces and eliminates the corrosion half-cell risk associated with steel fibres. Published data for RSC15-specific performance in every application configuration is limited; therefore compliance studies should be executed using the lot certificate and project-specific aggregate packing.

In contrast to polypropylene fibre systems, which depend on fibrillated surface texture and hydrophobic pull-out friction, PVA fibre in the RSC15 family is wetted by the aqueous cement pore solution. This wetting behaviour is directly measurable by comparing contact angle on PVA film to polypropylene film; PVA surfaces exhibit a water contact angle below 60° whereas polypropylene surfaces typically exceed 90°. In a hydrating portland cement matrix with pH above 12.5, the fibre surface develops interaction with calcium hydroxide and calcium silicate hydrate, increasing the critical fibre pull-out resistance. The consequence is that a lower volume fraction of PVA fibre can meet a specified residual strength target compared with polypropylene, although the exact equivalence depends on fibre length, aspect ratio, and aggregate type. For RSC15, the manufacturer-published data sheet remains the primary source for fibre length and aspect ratio; public studies of high-tenacity PVA fibres with aspect ratios from 40 to 100 report residual flexural strength improvement, but published data for RSC15-specific configuration is limited.

How Does Hydrophilic PVA Fibre Bridging Alter Residual Flexural-Tensile Behaviour?

Unlike polypropylene fibrillated fibres that rely principally on mechanical interlock and pull-out friction, high-tenacity PVA fibres in the RSC15 family develop a strong interfacial shear resistance through hydrophilic hydration products. In a cement pore solution at pH above 12.5, the fibre surface is wetted by calcium hydroxide–saturated water, which promotes increased friction and potential low-level chemical bonding at the fibre–matrix interface. The resulting crack-bridging mechanism is characterized in flexural testing according to ASTM C1609/C1609M-19a: as the matrix cracks, fibres transfer tensile stress across the opening, and the load–deflection curve displays residual strengths at net deflections of L/150 and L/300. In comparison to polypropylene, the higher elastic modulus of PVA reduces early crack widening because fibre elongation is lower than that of olefinic fibres under equivalent stress. The post-crack residual capacity of a given dosage is measured by the residual strength indices at L/150 and L/300; published studies on PVA fibre-reinforced concrete with dosages up to 2.0 kg/m³ show residual flexural strengths in the range of 15 % to 35 % of the fibre-reinforced first-peak strength when tested under ASTM C1609. Higher-volume fractions used in strain-hardening cementitious composites, typically up to 26 kg/m³, produce multiple microcracking and tensile strain capacities above 1 %, but those formulations require high-range water reducers and viscosity-modifying admixtures to maintain fibre dispersion.

For RSC15, the distinction from lower-modulus synthetic fibres is most pronounced in early-age slab restraint testing under ASTM C1579-21, where the fibre reduces total crack area by bridging microcracks before coalescence into visible shrinkage cracks. The technical interpretation is that PVA fibre provides a higher specific bond strength than polypropylene at equal fibre volume because the fibre–matrix interface does not rely solely on surface friction; hydration products adhere to the fibre surface and create a denser interfacial transition zone over time. This mechanism is not identical to steel fibre anchorage, which depends on mechanical end hooks and a significantly higher modulus. Consequently, RSC15 can reduce crack spacing in non-structural elements but does not replicate the flexural stiffness enhancement of steel fibre at a given mass per cubic metre.

In production-scale batching, RSC15 addition requires sequencing that prevents fibre balling in twin-shaft compulsory mixers and planetary counter-current mixers. The fibres are added after coarse aggregates and a portion of batch water have been mixed for 30 s to 60 s, or through automated fibre dosing systems on ready-mixed concrete plants. The mixing time after fibre addition is extended by 2 min to 5 min compared with plain concrete to break agglomerates and distribute individual filaments. Slump measured under ASTM C143/C143M-20 typically decreases with increasing fibre dosage; the magnitude depends on aggregate surface texture, fines content, and water-reducing admixture dosage. For conventional concrete with 0.5 kg/m³ to 2.0 kg/m³ PVA fibre, no adjustment beyond standard water reducer is usually required, but dosages above 3 kg/m³ may require a high-range water-reducing admixture conforming to ASTM C494/C494M-24 Type A or Type F to restore target workability. In ready-mixed production, discharge time and drum revolutions must be monitored because extended mixing at elevated slurry temperatures can increase PVA fibre fibrillation and surface wear, though no corrosion reaction occurs. Batch-to-batch variation in fibre count and cut length can be assessed by washing fresh concrete through a 75 µm sieve and counting retained fibres; published data for RSC15-specific retention rates is limited.

Alkaline Hydrolysis, Slump Retention, and Dispersion Fault Modes in Site Batching

The long-term behaviour of PVA fibres in concrete is governed by the resistance of polyvinyl alcohol to alkaline hydrolysis. In portland cement pore solution at pH 12.5 to 13.5, PVA fibres are generally stable at ambient service temperatures, but continuous hot-water or steam-curing above 80 °C can accelerate hydrolysis and reduce fibre tensile strength. Published data for RSC15 under autoclave curing cycles is limited; therefore the fibre should not be assumed suitable for autoclaved aerated concrete without testing. Absorption of moisture by PVA fibre is higher than that of polypropylene; polyethylene storage bags must remain sealed when relative humidity exceeds 60 %. Fibres that have absorbed surface moisture may agglomerate in the mixer and produce spherical fibre balls, particularly in mixes with low water-to-cement ratios below 0.35 and high superplasticizer content. A dispersion fault mode observed on ready-mixed plants is the accumulation of fibre balls behind the stationary blade sweep of a twin-shaft mixer; correcting this requires a longer dry-mix distribution phase before water addition. Slump loss induced by fibre addition can be quantified by ASTM C143/C143M-20; when slump retention beyond 60 min is specified, mixing water and admixture sequences should be validated with a full-scale trial batch rather than extrapolated from laboratory mortar tests because the shear environment and moisture interaction differ.

Values in the table represent typical ranges for fibre classes reported in public technical literature, not lot-specific certified RSC15 data. Project qualification requires the manufacturer’s certificate of analysis and trial-batch performance data.

When RSC15 Is Compared with Hooked-End Steel Fibre in Non-Corrosive Crack-Control Applications

Selection between PVA fibre and hooked-end steel fibre involves a trade-off between modulus and durability. Steel fibre with a density of 7.85 g/cm³ and elastic modulus of 200 GPa provides higher post-crack residual capacity for a given fibre volume, but requires minimum concrete cover and is vulnerable to chloride-induced corrosion at crack mouths where passivation breaks down. PVA fibre with a density of 1.3 g/cm³ and modulus of 25 GPa to 41 GPa does not carry the same stiffness and cannot replace primary steel reinforcement in structural design; however, it eliminates the need for corrosion-control cover in non-structural crack-control slabs, tunnel linings, and repair mortars. In comparison with fibrillated polypropylene, RSC15-family PVA fibres provide higher interfacial bond strength due to surface hydroxyl groups, which increases residual strength at smaller crack openings and reduces plastic-shrinkage crack severity under ASTM C1579-21. The lower elongation at break of PVA relative to polypropylene means that PVA fibres engage load at smaller deformations but may rupture in wide cracks, whereas polypropylene fibres tend to pull out. Published direct comparisons of RSC15 with specific steel fibre grades are limited; performance equivalence must be tested under ASTM C1609/C1609M-19a for flexural residual strength and ASTM C1550-20 for round panel energy absorption.

The difference from other synthetic PVA fibre products in the same portfolio is often controlled by fibre length, surface treatment, and denier. RSC15 should be differentiated from lower-tenacity PVA products intended for textile or paper reinforcement because cementitious applications require a fibre that retains its geometry during the high-shear mixing sequence and remains distributed after placement. The model is not intended as a tensile reinforcement replacement for rebar, prestressing strand, or structural welded-wire reinforcement. Its function is crack control and toughness improvement in appropriate matrices.

Because RSC15 is a synthetic fibre, it should not be substituted for structural reinforcement without calculation under ACI 544.4R-18 or equivalent design standards. The operational boundary for the product is defined by the certified dosage range, fibre length, and aspect ratio on the lot certificate; exceeding the recommended upper dosage without a corresponding increase in fine aggregate or admixture can create fibre clumps that reduce compressive strength measured under ASTM C39/C39M-21 and compromise surface finish. In mixes with silica fume content above 8 % by mass of cement, additional water-reducing admixture should be batched before fibre addition to avoid local paste viscosity spikes that inhibit fibre distribution. No significant incompatibility with normal portland cement, slag cement, or fly ash is reported for PVA fibres, but compatibility with lithium-based admixtures and specialty cementitious systems must be confirmed by batching trials because published data for RSC15 in those matrices is limited. Storage of fibre packages below 60 % relative humidity and protection from direct solar exposure are required to maintain fibre count accuracy and prevent pre-hydration of the surface film. The product is not classified as a hazardous substance under REACH for normal handling; nonetheless, airborne fibre dust generated during cutting of palletized bulk bags should be controlled with local exhaust ventilation. Final acceptance on a project should be based on a full-scale trial mix evaluated for slump retention, plastic-shrinkage crack reduction, and residual flexural strength according to the standards referenced above.