Sinopec-SVW Q-14-fibra PVA de alto módulo de alta resistência (fibra PVA HSHM) para concreto

Sinopec-SVW Q-14-High Strength High Modulus PVA Fiber (HSHM PVA Fiber) for Concrete is a polyvinyl alcohol staple fibre specified for dispersion into cementitious matrices. The Q-14 designation in vendor technical documentation is associated with a nominal monofilament diameter of 14 μm. The product is classed as high-strength high-modulus because the polymer is processed to increase chain orientation and crystallinity relative to wet-spun PVA fibre used in paper, textile sizing, or low-modulus fibre applications. Product-specific values must be taken from the lot certificate issued for each delivery; however, HSHM PVA fibres for concrete commonly fall within the following boundaries: density 1.29 g/cm³ to 1.31 g/cm³ under ISO 1183-1:2019; tensile tenacity 10 cN/dtex to 13 cN/dtex under ISO 2062:2009 or ASTM D2256/D2256M-21; initial tensile modulus 250 cN/dtex to 320 cN/dtex; and elongation at break 6% to 8%. Stress in MPa equals tenacity in cN/dtex multiplied by 100 and by density in g/cm³; at 1.30 g/cm³, the tenacity range corresponds to 1,300 MPa to 1,690 MPa and the modulus range to approximately 32 GPa to 42 GPa.

Q-14 is supplied in cut lengths including 4 mm, 6 mm, 8 mm, and 12 mm; the exact cut length and its coefficient of variation should be confirmed from the packing list or batch certificate. The fibre is not specified as a compressive-strength additive. It is used where plastic shrinkage cracking, restrained thermal cracking, impact resistance, spalling resistance, or post-crack residual flexural strength must be controlled. Application areas reported in technical literature include thin-section precast elements, sprayed concrete, repair mortars, industrial floors, and high-ductility cementitious composites, but published product-specific field data for Q-14 are limited; trial batching under the intended production equipment is required before specification lock.

What Distinguishes HSHM PVA Fibre from Polypropylene, Steel, and AR-Glass in a Cement Matrix?

At a fixed volume fraction, HSHM PVA fibre differs from polypropylene monofilament mainly in tensile strength, tensile modulus, and fibre-matrix bond behaviour. The Q-14 surface is hydrophilic and wettable by cement paste, which supports a stronger fibre-matrix interface than untreated polypropylene, but it also increases water demand and requires adequate paste volume. Hooked-end steel fibre provides higher stiffness, but its density is approximately 5.9 to 6.0 times that of the PVA fibre; at equal mass dosage, the number of steel fibres per unit volume is much lower. Steel fibre is also conductive and magnetic, and can corrode if cracks extend to the concrete surface. Alkali-resistant glass fibre has high tensile strength and modulus but lower elongation and requires adequate zirconia content for long-term cementitious exposure. The table below summarises typical published ranges for fibre classes, not Q-14-specific batch results.

At equal mass dosage, the 14 μm diameter gives Q-14 a much higher fibre count and specific surface area than larger PVA fibres. For a 12 mm cut length and density 1.30 g/cm³, the theoretical fibre count is approximately 4.2 × 10⁸ fibres/kg for the 14 μm product and 5.1 × 10⁷ fibres/kg for a 40 μm PVA fibre. The corresponding specific surface area is approximately 220 m²/kg for the 14 μm product and 77 m²/kg for the 40 μm product. Higher surface area lowers average fibre spacing at a given dosage, which can improve crack control, but it also increases paste demand and the energy required for dispersion.

The aspect ratio of the fibre is 857 for 12 mm cut length and 429 for 6 mm cut length, based on the 14 μm nominal diameter. This high aspect ratio increases pull-out resistance but also restricts fibre movement in congested aggregate packings. In concretes with coarse aggregate larger than 10 mm, the fibre may preferentially concentrate in mortar regions; the mix design should therefore include enough paste volume to coat the fibre surface and maintain workability.

Compared with commodity PVA fibre, Q-14 is directed toward structural crack bridging rather than textile sizing. The higher orientation increases tensile modulus but may reduce elongation; the product is therefore less ductile than lower-modulus PVA and requires appropriate handling in high-impact applications. Commodity PVA fibre typically exhibits tenacity below 8 cN/dtex and is not supplied with concrete-specific cut length tolerances or alkali resistance certification.

When Dosage Approaches the Upper Volume Fraction for Strain-Hardening Cementitious Response

A dosage below 1.5 kg/m³ is generally a plastic-crack-control measure. At 1.0% by volume, equivalent to 13 kg/m³ at 1.30 g/cm³, the fibre begins to modify post-crack flexural behaviour and toughness. At 2.0% by volume, equivalent to 26 kg/m³, the dosage is in the range used for engineered cementitious composites, where multiple cracking and tensile strain-hardening are required. Residual flexural strength should be measured under EN 14651:2005+A1:2007 or ASTM C1609/C1609M-19. At the upper dosage, the matrix should be designed with low fracture toughness, typically by using a water-to-binder ratio below 0.30 and fly ash or other supplementary cementitious material at 50% to 60% of binder mass. High-range water-reducing admixture is required to control rheology, and a viscosity-modifying admixture may be required to prevent segregation.

For a 2.0% by volume dosage, the fibre surface area added to the matrix is approximately 5,720 m²/m³ of composite at a density of 1.30 g/cm³ and specific surface area of 220 m²/kg. The paste fraction must be sufficient to wet this surface; otherwise the composite becomes unworkable at low water-to-binder ratio. This is a critical processing threshold, not a trivial adjustment. Published data for Q-14 in a specific mix under this dosage is limited, and the design should be validated by trial batching.

Slump loss is not a reliable single-number specification because it is influenced by aggregate shape, paste volume, admixture type, and fibre dosage. Measured under ASTM C143/C143M-20, a high-volume PVA fibre mix may fall below the practical placement range if no high-range water reducer is used. A more informative control is spread diameter on a flow table under ASTM C230/C230M-20 or rheological yield stress measured by a vane viscometer. In production batching, workability should be adjusted by changing paste volume or admixture dosage, not by adding water beyond the specified water-to-binder ratio.

Mixing equipment selection is a process conflict at high dosage. Pan mixers and twin-shaft compulsory mixers are specified over free-fall drum mixers because the high-shear field opens fibre clumps and prevents low-energy folding at the discharge gate. The fibre should be charged after coarse aggregate and 70% to 80% of batch water to prevent balls from forming against dry cement. A mixing extension of 60 s to 90 s after fibre addition is generally sufficient; prolonged high-shear mixing beyond 300 s can damage fibre surface sizing, raise air-entraining agent demand, and increase paste temperature. Fibre dispersion should be checked by washing a fresh sample through a 5 mm sieve; retained fibre balls indicate charging sequence or mixer shear problems.

Surface finishing of concrete containing Q-14 at high dosage requires attention. Fibres may protrude at the surface after strike-off; power troweling should be delayed until the surface paste has stiffened, otherwise fibres can be pulled into visible clumps. Curing compound application under ASTM C309-19 should be checked for compatibility with the fibre surface sizing.

Batch Handling, Moisture Uptake, and Mixer-Specific Failure Modes

HSHM PVA fibre is hydrophilic and should be stored in sealed packaging below 60% relative humidity. Moisture uptake above equilibrium can reduce fibre flow from the bag and promote static clumping in pneumatic feeding systems. Drying, if required, must follow the maximum temperature and time limits stated by the vendor; uncontrolled hot-air drying above the softening region of PVA can reduce tenacity. In cold climates, sealed bags should be allowed to reach mixer house temperature before charging because static charge increases at low humidity and can cause fibre to adhere to metal hoppers and gates.

In production batching, a recurring failure mode is delayed fibre addition after all water has been charged. The fibre can float on the top of the mixture, form balls, and remain undispersed. Another failure mode is charging the fibre too early with dry cement and silica fume, which traps fibres in low-moisture agglomerates. The preferred sequence is coarse aggregate, fibre, part of the water, binder, fine aggregate, and then the remaining water and admixtures; however, the exact sequence should be set by trial batching because aggregate moisture and mixer design vary.

The chemical environment of concrete is highly alkaline, typically with a pore solution pH above 13. PVA fibre of the HSHM class is considered alkali-stable under normal hydration temperatures, but high-temperature alkali exposure can cause hydrolysis and modulus loss. Autoclave curing should not be assumed without specific vendor data. If the application requires steam curing at temperatures above 60 °C, tensile properties should be re-checked after curing to ensure that the fibre retained the specified residual strength.

PVA fibre is also used in fire-resistant concretes because the polymer begins to soften and decompose at approximately 220 °C to 250 °C, creating permeable channels that reduce pore pressure during fire. Polypropylene monofilament melts at approximately 160 °C to 170 °C. The higher softening point of PVA means that its channels form later in the heating profile; this can be beneficial or detrimental depending on the fire curve and concrete density. Published data for Q-14 under hydrocarbon fire exposure is limited, so fire-resistant concrete should be validated by furnace testing under ISO 834-1:1999 or the specified hydrocarbon curve.

Compatibility with admixtures should be confirmed for the full mix formulation. Polycarboxylate ether superplasticizers normally disperse well with PVA fibre, but formulations containing strong cationic or amine-based agents may alter fibre surface charge and dispersion. Air-entraining agents can be affected by the fibre surface area; air content should be monitored under ASTM C231/C231M-17 or EN 12350-7:2019. QC records should require the vendor to report tensile tenacity, elongation at break, initial modulus, diameter CV, cut length CV, and alkali resistance, preferably under GB/T 21120-2018 or an equivalent recognized method. The product is not a substitute for structural steel reinforcement unless the structural design explicitly accounts for fibre contribution under the governing concrete code.