Sinopec-SVW Q-13-fibra PVA de alto módulo de alta resistência (fibra PVA HSHM) para concreto

Sinopec-SVW Q-13-High Strength High Modulus PVA Fiber（HSHM PVA Fiber） for Concrete is a chopped high-tenacity polyvinyl alcohol microfibre engineered for dispersion in hydraulic cementitious matrices. The product is specified where early-age plastic shrinkage cracking, microcrack propagation, and low-crack-width toughness require a fibre with higher elastic modulus than conventional polypropylene microfibre. The Q-13 model designation identifies the high-strength high-modulus variant rather than commodity textile or low-modulus PVA fibre. In concrete practice Q-13 is typically supplied as cut monofilament with nominal cut lengths of 6 mm, 8 mm, or 12 mm; the equivalent filament diameter is distributed in the 0.020–0.030 mm range. The base polyvinyl alcohol molecule presents pendant hydroxyl groups, so the filament surface is hydrophilic and participates in a stronger polar interaction with pore solution and cement hydration products than olefinic fibres such as polypropylene. This surface characteristic influences both fibre dispersion and fresh-concrete water demand. The density of PVA is approximately 1.28–1.30 g/cm³, which permits dosage by mass to produce a high fibre count per unit volume. For a nominal filament diameter of 0.025 mm, a cut length of 8 mm, and a density of 1.29 g/cm³, the calculated filament count is approximately 2 × 10⁸ filaments per kilogram; the corresponding aspect ratio is approximately 320. This high count density matters because crack control in concrete is governed by fibre spacing and the number of fibres crossing a developing crack plane. A higher filament count at a given mass dosage reduces centre-to-centre fibre spacing and increases the probability that a microcrack intersects a fibre. Q-13 is intended for incorporation into ready-mixed concrete, precast elements, repair mortars, and wet-mix shotcrete, where it functions as a non-corroding microfibre. Procurement documents frequently reference ASTM C1116/C1116M-10a Type III synthetic fibre-reinforced concrete and EN 14889-2:2006 polymer fibres; Q-13 belongs to the microfibre class under EN 14889-2:2006 Class I because the equivalent diameter is below 0.3 mm.

The fibre is not described as a direct volumetric substitute for structural steel reinforcement. Published data for the specific flexural response of Q-13 in large-scale structural sections is limited; specification should therefore be based on approved performance testing of the target concrete mixture rather than interpolation from other PVA grades. In cementitious systems the crack-bridging mechanism is governed by fibre modulus, fibre aspect ratio, interfacial bond strength, and the number of fibres crossing a crack plane. High-modulus PVA fibre can restrain sub-millimetre cracks more effectively than polypropylene microfibre at equivalent fibre volumes, but its post-crack capacity at larger crack widths remains below that of steel macrofibre.

What Limits the Replacement of Steel Fibre with HSHM PVA in Structural Sections?

In structural concrete, steel macrofibre is normally specified where post-crack residual flexural strength at crack widths above 0.5 mm is required. Q-13 differs in both mechanical behaviour and application boundary. The PVA filament has a tensile strength at or above 1,100 MPa, which is comparable to some steel fibres, but its elastic modulus is approximately 25 GPa to 30 GPa, roughly one-seventh to one-eighth that of steel at approximately 200 GPa. The lower fibre modulus means that for a given strain and crack width, the PVA fibre carries less stress than a steel fibre of similar aspect ratio. Q-13 is therefore used primarily for microcrack control and plastic shrinkage, and as a secondary reinforcement to improve toughness, impact resistance, and crack distribution. In load-bearing structural applications it is not a replacement for deformed steel macrofibre or conventional reinforcement without explicit design verification.

The substitution boundary is also controlled by fibre density and dosage. Steel macrofibre at 20–40 kg/m³ provides macro-crack bridging and post-peak flexural capacity, while Q-13 is commonly dosed at 0.6–2.5 kg/m³ for microcrack control and at higher dosages up to 4.0 kg/m³ in specialty cementitious composites. Because PVA density is approximately six times lower than steel, a given mass dosage produces a much higher filament count. However, the fibre’s high surface area and hydrophilic surface raise the water demand and reduce slump at higher addition levels. Unless mixture water content is held constant and a high-range water reducer is used, increased dosage can produce fibre balling and non-uniform fibre distribution. This workability penalty is one of the principal practical limits on replacement of steel fibre with Q-13.

A direct comparison of Q-13 against steel and polypropylene alternatives is given in the following matrix. The values are representative industrial ranges and should be confirmed against the supplying mill’s certificate of analysis for the specific batch.

Specification Matrix and Lot-Level Certificate Parameters

Specification compliance for Q-13 is evaluated through a combination of fibre physical-property tests and concrete performance tests. Fibre tensile properties are determined on single filaments with a gauge length of 20 mm and a constant rate of extension according to ASTM D3822/D3822M-14 or equivalent producer methods. Linear density is reported in decitex under ISO 1973:2021. Density is measured by pycnometry or immersion according to ISO 1183-1:2019. The nominal certificate-of-analysis values shown below are representative high-strength high-modulus PVA fibre ranges; lot-specific certificates should be requested where concrete performance testing is not duplicated.

Concrete-level performance is typically evaluated through plastic shrinkage cracking under ASTM C1579/C1579M-21 or flexural toughness under ASTM C1399/C1399M-10(2015). Published data for the exact Q-13 grade under these tests is limited; mixture qualification should therefore include laboratory verification with the intended cement, aggregate, and admixture combination. The fibre’s contribution is strongly influenced by matrix strength, aggregate packing, and curing. A high-modulus PVA microfibre in a low-water-cement-ratio high-strength matrix with a dense interfacial transition zone exhibits a more pronounced crack-arrest effect than the same dosage in a high-water-cement-ratio porous matrix.

Production-scale batching experience indicates that Q-13 should be introduced into the mixer before water or after the coarse aggregate has formed a dry interlock, not as a late addition to high-slump paste. In twin-shaft compulsory mixers with batch volumes between 1.0 m³ and 2.0 m³, gradual addition through a vibrating screen or fibre dispenser over 30–60 s prevents the formation of fibre agglomerates at the charge point. A dry-mix interval of 60–120 s after fibre addition disperses the filaments across the aggregate surfaces; water and admixtures are then introduced, followed by a wet-mix interval of 90–180 s. Adding Q-13 directly into the water stream or into a paste-rich central zone can produce fibre balls that remain after normal mixing. Fibre balls observed on production lines are usually traceable to rapid addition, inadequate dry preblending, or excess batch water. Once formed, these agglomerates are not readily re-dispersed by extended mixing and may appear in hardened concrete as low-strength inclusions.

At dosages above approximately 0.9 kg/m³, slump loss is commonly observed in ordinary concrete mixtures. The loss arises from the large surface area of the hydrophilic fibre network; compensation with additional water is inappropriate because it raises the water-cement ratio and reduces strength. Polycarboxylate ether superplasticizer is the preferred correction, added as part of the total liquid demand. In truck-mixed concrete, Q-13 is best added before final slump adjustment, and the drum should rotate at mixing speed for at least 5 min after fibre addition. Published data for exact slump reduction values in field Q-13 mixtures is limited; therefore batching trials with the actual aggregate moisture condition are required before full production.

When Q-13 Is Used in Wet-Mix Shotcrete and Precast Repair Mortars

In wet-mix shotcrete, Q-13 is often dosed at 0.6–1.5 kg/m³ to improve cohesion, reduce rebound, and control plastic shrinkage. The fibre’s low density and high filament count assist in maintaining homogeneous suspension during pumping. Published data for the specific Q-13 grade in shotcrete rebound reduction is limited; however, high-modulus PVA microfibres generally reduce rebound compared with plain concrete by increasing the tensile capacity of the fresh matrix. The dosage should be confirmed through spray trials under the project’s specific pump type, hose length, and accelerator regime. Because some alkali-free shotcrete accelerators influence the ionic strength of the pore solution, compatibility testing between Q-13, accelerator, and high-range water reducer is required. For typical hose diameters of 50–65 mm and air volumetric flows of 8–12 m³/min, Q-13 at the stated dosage remains suspended; higher dosages may increase shear viscosity and require additional superplasticizer. Spray trials under ACI 506R are recommended for field validation.

In precast repair mortars, Q-13 at 1.0–2.5 kg/m³ is used to reduce early-age cracking in restrained repairs. The fibre is dispersed into the dry mortar blend before wetting. High-shear mixing is not required for fibre dispersion, but the mixer must generate sufficient aggregate movement to avoid stagnant paste pockets. The main operational boundary is the thickness of the repair layer; fibre length should not exceed approximately half the minimum section thickness to prevent fibre alignment restrictions at the substrate interface. For a 20 mm repair layer, the 6 mm fibre is usually preferred over the 12 mm fibre.

Dispersion Behaviour, Storage Boundaries, and Incompatibilities

The fibre disperses best when its surface moisture content is low. Packaging should be stored in dry conditions below 60 % relative humidity and protected from direct water contact. Moisture absorption can increase fibre-to-fibre adhesion and reduce free flow through dosing equipment. If the fibre has visible clumping, it should not be force-fed into the mixer in its agglomerated state; pre-separation by a mechanical carding or air-separation unit is preferred. Exposure to continuous hot water above approximately 90 °C is an operational boundary because PVA begins to soften and dissolve; Q-13 is not intended for concrete elements that remain saturated at elevated temperature for extended periods. Strong oxidizing acids and certain organic solvents are incompatible with PVA and should be avoided in contact with the packaged fibre. There is no corrosion mechanism in chloride-bearing concrete, which is a principal advantage over steel fibre in marine or de-icing salt exposure.

The fibre’s alkali resistance in ambient-temperature saturated calcium hydroxide solution is generally high; PVA fibres retain their integrity in the alkaline pore solution of ordinary Portland cement concrete. Published data for Q-13 retention after specific alkali immersion is limited. For concretes with high cement alkali equivalent or calcium sulfoaluminate binder systems, compatibility testing is advisable. The fibre does not undergo the same oxidation or rust expansion as steel, but it should not be specified where high-temperature fire insulation is exclusively required, because organic fibre will degrade at temperatures above approximately 220 °C; the resulting microchannels may be relevant for some fire-spalling control but should not be treated as fire-resistance reinforcement without full-scale furnace testing.