Fibra Kuraray RECD15-PVA para reforço de concreto

Kuraray RECD15-PVA Fiber for Concrete Reinforcement is a high-modulus polyvinyl alcohol monofilament produced by hydrolysis of polyvinyl acetate and supplied as chopped strands for dry-mix, wet-mix, and sprayed concrete. The designation identifies a fibre within the concrete-reinforcement portfolio rather than a textile, papermaking, or chopped-strand mat grade. The polymer surface carries pendant hydroxyl groups that promote wetting and adhesion to hydrating cement paste; this distinguishes the product from hydrophobic polypropylene fibres with equivalent chopped geometry. The material is classified under ASTM C1116/C1116M-23 as a Type III synthetic fibre and, where European conformity is required, can be supplied under EN 14889-2:2006 factory production control. Because manufacturer lot certificates can vary by cut length, finish, and dispersibility package, the values that follow are representative published data for high-modulus Kuraray PVA concrete fibres and shall be confirmed against the lot-specific technical data sheet before production batching.

What are the published physical and mechanical specifications for RECD15?

The specification set is dominated by monofilament diameter, cut length, tensile strength, and elastic modulus because these variables control fibre count, crack-bridging potential, and post-crack flexural response. Representative values for the high-modulus REC series are summarised in Table 1. Single-fibre tensile properties are determined under ASTM D3822-20, not on a fibre bundle, because bundle average values would conceal the fibre-to-fibre ultimate strength distribution. Density is tested on the dry polymer under ISO 1183-1:2019. The cut length is grade-specific and shall be selected according to maximum aggregate size and placement method; published data for this specific RECD15 configuration is limited and shall be verified with the certificate of analysis.

At the stated geometry, a single fibre has a volume of approximately 1.51 × 10⁻⁵ cm³ and a mass of approximately 1.96 × 10⁻⁵ g. One kilogram therefore contains on the order of 51,000,000 individual filaments. At a dosage of 1.0% by volume, the fibre mass is 13 kg/m³, which delivers more than 650,000,000 discrete crack-bridging elements per cubic metre. This fibre count is the principal reason a low-mass addition can influence plastic shrinkage crack width and early-age microcrack distribution under restraint; the effect on hardened flexural residual strength is governed by dosage, bonding, and matrix strength rather than fibre count alone.

Evaluating Post-Crack Residual Strength with ASTM C1609 and C1399

Post-crack performance is evaluated in a closed-loop servo-controlled testing machine under ASTM C1609/C1609M, which records load-deflection response and derives flexural performance parameters such as f₆₀₀^D and f₁₅₀^D at net deflections of L/600 and L/150. The test requires beam dimensions of 150 × 150 × 500 mm when aggregate size permits and a minimum of three specimens from a given batch to capture fibre distribution variability. ASTM C1399/C1399M is used when deflection-controlled equipment is not available; it measures average residual strength after a cracked beam is reloaded under a steel plate. PVA fibre-reinforced concrete tested under these methods typically exhibits a distributed post-crack residual load response rather than a single dominant crack opening; the exact f₆₀₀^D and f₁₅₀^D values cannot be transferred from other fibre types and shall be established by trial batching at the project dosage. For shotcrete, the panel test of ASTM C1550-20 and the energy absorption requirements of EFNARC are more appropriate than beam tests because sprayed concrete receives fibre orientation from high-velocity placement. Published data for this specific RECD15 configuration is limited in public literature; therefore, project qualification testing under the governing standard is mandatory.

Dosage selection is governed by the performance objective. For plastic shrinkage control in flatwork, additions of 0.6 kg/m³ to 1.8 kg/m³ are commonly evaluated; at 0.9 kg/m³ the calculated fibre population is approximately 45,900,000 filaments per cubic metre. For post-crack flexural strengthening and slab replacement of light-gauge steel mesh, volume fractions from 0.5% to 1.0% are more typical, corresponding to 6.5 kg/m³ to 13 kg/m³ for a 1.30 g/cm³ polymer density. The addition of the fibre does not alter the validity of the water-cementitious materials ratio required for durability compliance under ACI 318-19 exposure categories; any water added solely to restore slump after fibre addition shall be offset by additional cementitious material or high-range water reducer to maintain the specified ratio.

Mixing, Dispersion, and Batch-to-Batch Processing Requirements

Fibre addition at the aggregate charging point of a pan mixer or twin-shaft high-shear mixer provides more uniform distribution than dumping the full bag onto the head water in a free-fall drum mixer. The hydrophilic fibre surface can adsorb mix water and increase apparent cohesiveness; the resulting slump loss is batch-specific and can be compensated with an ASTM C494/C494M Type F or Type G high-range water reducer in trial batching. A target mixing interval of 5 min at high shear after the last fibre is added is a starting point; truck drum speed in ready-mix production should be held at 12 rpm to 15 rpm for 5 min after fibre dosage. Free-fall drum mixing above 0.75% by volume is not recommended because the calculated fibre surface area at 1.0% by volume is approximately 1,000 m²/m³, which increases the probability of agglomeration and balling. Air content shall be checked according to ASTM C231/C231M because polyvinyl alcohol fibres can stabilise entrained air bubbles and change the spacing factor measured under ASTM C457/C457M. Batch-to-batch charge weights should be recorded to the nearest 0.1 kg/m³; ready-mix batching accuracy follows ASTM C94/C94M.

When PVA Fibre Substitutes Steel Macro-Fibres in Slab and Shotcrete Reinforcement

The substitution is not mass-equivalent because steel and PVA have different densities, fibre counts, and elastic moduli. PVA at 1.30 g/cm³ has roughly one-sixth the density of steel at 7.85 g/cm³, and its elastic modulus of 41 GPa is about 0.21 times the 200 GPa modulus of carbon-steel fibre. Under ASTM C1609/C1609M, this lower modulus produces a more gradual post-crack load rise at small crack openings, whereas hooked-end steel fibres mobilise anchorage earlier in the crack-opening range. The PVA fibre compensates through higher fibre count and matrix bonding: at 1.0% by volume, the product distributes more than 650,000,000 filaments per cubic metre, while a typical 25 kg/m³ dose of 0.75 mm × 60 mm hooked-end steel fibre supplies roughly 120,000 fibres per cubic metre. In wet-shotcrete tunnel linings and pool shells, PVA eliminates corrosion staining and magnetic interference; steel fibre is excluded from some installations where ACI 506R-16 requires non-metallic reinforcement or where chloride exposure class C2 under ACI 318-19 would demand additional cover. The product should not be considered a direct structural substitute for conventional flexural steel reinforcing bars in members governed by ACI 318-19 Chapter 9; it functions as distributed crack control and post-crack residual strength enhancement, not as primary bar reinforcement unless project-specific design provisions and testing permit alternative use.

Plastic Shrinkage Crack Control and Curing Boundary Conditions

Plastic shrinkage cracking occurs when the evaporation rate from the fresh concrete surface exceeds the bleeding rate, as described in ACI 305R-20. PVA fibre addition changes the plastic-state crack pattern by bridging the developing capillary-stress field, but it does not replace early curing. ASTM C1579-21 provides a restrained panel test for comparing plastic shrinkage crack area of control and fibre-reinforced concrete mixtures under calibrated evaporation; ASTM C1581/C1581M-18a quantifies restrained shrinkage cracking over time in rings. In production concrete, a PVA fibre addition of 0.6 kg/m³ to 1.8 kg/m³ is evaluated for flatwork and topping placements. When the evaporation rate exceeds 1.0 kg/m²/h, fogging, evaporation retarders, wind breaks, or wet burlap shall be used; the fibre additive cannot compensate for the loss of surface bleed water at high temperature and low relative humidity. For slabs-on-ground finished with a steel trowel, the finish operation should begin only after surface bleed water has disappeared; premature finishing can drag fibre into a surface mat and produce a fuzzy texture. Saw cutting should follow the timing guidelines of ACI 302.1R-15 and is not delayed solely by fibre presence.

Storage conditions affect dispersibility. The product is supplied in moisture-resistant bags and should be stored sealed at 20 °C to 40 °C and below 60% relative humidity. Opened bags should be consumed within the same working shift if the plant ambient relative humidity exceeds 60%, because polyvinyl alcohol fibre can adsorb atmospheric moisture and develop clumps that reduce uniform dispersion. The fibre is not recommended for use in concrete containing high air contents above 8% unless a trial batch confirms uniform fibre distribution and stable air-void spacing under ASTM C457/C457M. It shall not be used as a substitute for curing; it does not prevent thermal cracking caused by high internal temperature gradients above 30 °C difference between core and surface in mass placements. For aggressive chemical environments, the cementitious matrix, not the PVA fibre, governs long-term durability; the fibre itself is resistant to alkali, but compatibility with acidic environments below pH 4 or strong oxidisers shall be confirmed with the manufacturer before use.