Sinopec-SVW CD-I-fibra PVA de alto módulo de alta resistência (fibra PVA HSHM) para concreto

Sinopec-SVW CD-I High Strength High Modulus PVA Fiber (HSHM PVA Fiber) for Concrete is a polyvinyl alcohol monofilament supplied in cut lengths for direct addition to portland-cement-based matrices. The CD-I designation identifies a concrete-specific grade produced by wet spinning, hot drawing, and acetalization, which raises tensile stiffness and limits the water sensitivity of unmodified polyvinyl alcohol. Manufacturer-published quality data for this concrete grade typically list a monofilament diameter of approximately 0.04 mm, cut lengths of 6 mm, 8 mm, and 12 mm, a density of 1.30 g/cm³, tensile strength of at least 1400 MPa, and tensile modulus of at least 35 GPa. Elongation at break is reported in the 6–9% range. The resulting aspect ratio ranges from 150 for the 6 mm fiber to 300 for the 12 mm fiber at the stated diameter.

The values in Table 1 are representative manufacturer-reported data. They do not replace incoming-fiber verification, because filament diameter, length distribution, and surface oiling can vary between production campaigns.

Moisture content is specified because polyvinyl alcohol is hygroscopic and surface wetness changes flowability through dosing equipment.

What Distinguishes CD-I from Standard PVA and Low-Modulus Synthetic Fibers in Crack Bridging?

The functional difference is primarily the combination of high tensile modulus and controlled elongation. Standard textile-grade PVA fibers generally have lower molecular orientation and therefore lower tensile strength and modulus. CD-I fiber is drawn to higher orientation, yielding a tensile modulus above 35 GPa, which is higher than standard PVA and far higher than fibrillated polypropylene, whose tensile modulus is typically between 3.5 GPa and 5.0 GPa. In a cracked cementitious matrix, this higher modulus permits greater stress transfer across a crack at the same opening. Polypropylene fibers are therefore used mainly for controlling plastic shrinkage cracking, whereas CD-I grade is used in hardened-state crack-bridging and strain-hardening applications when dosed at 1.5–2.0 vol%.

Compared with hooked-end steel fibers, CD-I has lower tensile modulus than steel at 200 GPa, but its density of 1.30 g/cm³ is much lower than that of steel at 7.85 g/cm³. At a dosage of 1 vol%, the CD-I fiber mass is approximately 13 kg/m³, whereas the same volume fraction of steel fiber requires approximately 78.5 kg/m³. The PVA fiber surface is also hydrophilic and develops chemical adhesion to cement paste, while steel fibers rely mainly on mechanical anchorage and friction. Steel fibers introduce corrosion concerns in cracked and chloride-exposed concrete; PVA fiber is non-corroding. However, the lower modulus of PVA relative to steel means that the post-crack residual strength at equal volume fraction is generally lower unless the fiber volume is optimized for the specific matrix.

AR-glass strands have tensile modulus near 72 GPa and tensile strength above 1.0 GPa, but their elongation at break is typically 2–4%. The lower elongation limits energy absorption under impact. CD-I PVA has lower modulus than AR-glass but higher elongation and a non-brittle failure response, while avoiding corrosion and the high density of steel. Published data for the specific surface treatment and single-filament pullout energy of this commercial grade in a given mix design is limited, so comparative values should be confirmed by project-specific bond testing.

At addition rates between 1.5 vol% and 2.0 vol%, the CD-I fiber mass in a concrete or mortar mixture is 19.5 kg/m³ to 26.0 kg/m³ based on a fiber density of 1.30 g/cm³. The workability response is not linear with dosage because the monofilament surface area increases paste-phase viscosity. In twin-shaft compulsory mixers, a dosing sequence that places the fiber after dry blending of aggregates and cementitious materials but before the complete water addition is used to limit agglomeration. A typical sequence involves adding 60–70% of the mixing water containing polycarboxylate-ether high-range water reducer after fiber introduction, mixing for 120–180 s, then adding the remaining water while visually inspecting for fiber balls. Dosage rates above 2.5 vol% in conventional ready-mix equipment frequently produce non-uniform distribution unless matrix viscosity is optimized and fiber addition is controlled to prevent localized wetting.

For structural engineered cementitious composites, the product is used at 2.0 vol% in combination with low water-to-cementitious-material ratios, supplementary cementitious materials, and fine aggregates without coarse aggregate in some formulations. The exact mixture design varies with matrix fracture toughness, because the transition from strain-softening to multiple cracking requires fiber bridging stress to exceed matrix first-cracking stress. Flexural toughness is commonly measured under ASTM C1609/C1609M four-point bending, while compressive strength testing follows ASTM C39/C39M or EN 12390-3. The use of CD-I fiber does not replace primary steel reinforcement in load-bearing members; contribution to structural capacity must be validated through large-scale testing and design codes such as ACI 544 or conformity under EN 14889-2:2006.

In slab-on-grade applications, CD-I is often specified at 0.5–1.0 vol% for crack-width control and impact resistance. At these lower dosages, the fiber does not require major mix redesign, but the water reducer demand can still increase because the hydrophilic surface adsorbs water and dispersant molecules. Comparative trial batches with an equal-slump reference mix are necessary to isolate the fiber’s effect on fresh-state workability from the effect of the adjusted high-range water reducer.

Because the CD-I grade has an aspect ratio up to 300, it is classified as a micro-fiber in ASTM C1116/C1116M-23. The high aspect ratio improves crack spacing but also increases the minimum paste volume needed to coat the fiber surfaces; therefore the product is not a direct mass substitute for steel fiber. A matrix with paste volume below approximately 0.35 m³/m³ may not adequately coat the additional fiber surface at dosages above 1.5 vol%, producing fiber agglomeration and reduced post-crack flexural toughness.

When High-Temperature or High-RH Conditions Apply to Handling and Curing

Humidity control is a defined operational boundary because polyvinyl alcohol is hygroscopic. Storage in sealed packaging is required when ambient relative humidity exceeds 65%. If packaging is exposed and fiber moisture content rises above 0.5%, flow through dosing equipment is impaired and the fiber may clump during addition. Manufacturer handling guidance commonly recommends pre-drying at 60°C for 4 h before use under such conditions. Drying above 80°C is not recommended for ordinary concrete-grade PVA fiber because it may alter the surface finish and affect fiber–matrix interfacial bond.

In service, the fiber is cold-water-insoluble, but prolonged hydrothermal exposure above 120°C can reduce tensile retention depending on acetalization degree and matrix alkalinity. Published data for this specific configuration is limited for high-pressure steam curing above that threshold; therefore autoclave cycles for high-strength precast elements should be qualified by residual flexural or tensile testing on fiber-reinforced specimens. In normal moist curing and ambient service below 80°C, the acetalized high-modulus PVA fiber is considered resistant to portland cement pore solution; however, strong oxidizing or strong acid environments fall outside the intended use envelope.

Fiber–Matrix Interface and Specification Compliance

The fiber–matrix interface governs whether the CD-I grade ruptures or pulls out during crack opening. Because the fiber surface is hydrophilic, it bonds strongly to calcium-silicate-hydrate phases. A controlled surface oiling content is applied by the manufacturer to limit chemical adhesion and promote slip. If the surface oiling content is too low, fibers may fracture before developing full pullout resistance; if it is too high, interfacial friction may be insufficient. This parameter is therefore part of incoming-fiber quality control in precast production. Acceptance testing should include cut-length distribution by sieve analysis, single-filament tensile response under ASTM D3822 or ISO 5079:2020, and concrete performance testing under ASTM C1116/C1116M-23 Type III synthetic fiber requirements. In the European regulatory framework, batch conformity is assessed under EN 14889-2:2006 for polymer fibers used in concrete.

Differences from other synthetic fibers also appear in volumetric efficiency. Because PVA has a density near that of cement paste and a high surface energy, it does not float to the surface during vibration as some polypropylene fibers do. This reduces production rejects in slip-formed and extruded concrete elements. However, the same hydrophilic behavior increases water demand and may require a higher polycarboxylate-ether dispersant dose than a polypropylene-fiber mix of equal workability. Comparative tests in the same mix design without accommodating this property will penalize the PVA fiber unfairly; the comparison must be made at equal fresh-state workability after adjusting the high-range water reducer.