In concrete mixture design, secondary reinforcement derived from fibrillated polypropylene is introduced to control early-age plastic shrinkage and settlement cracking without increasing steel area or adding corrosion risk. SikaFiber PPF-Multi-Length (Fibermesh 300) - Micro Fibrillated Fiber is a polypropylene-based synthetic microfiber supplied as a collated, fibrillated bundle with a multi-length gradation. The product is classified under ASTM C1116/C1116M as a Type III synthetic fiber for concrete reinforcement. In general secondary reinforcement applications, the nominal dosage is 0.9 kg/m³ (1.5 lb/yd³). The polymer has a specific gravity of approximately 0.91 and exhibits no measurable water absorption. In ready-mix production, the fiber is added after the aggregate and initial water and is dispersed by wet mixing. The principal function is plastic and early-age crack control in hydraulic cement concrete; it is not a replacement for structural load-bearing steel reinforcement, welded wire reinforcement, or post-tensioning.

The former trade name Fibermesh 300 remains in specification language for legacy projects. The product is manufactured from virgin polypropylene homopolymer, and the fibrillated network splits into discrete filaments under the shear conditions of a concrete mixer. Because the material is hydrophobic and chemically inert in the alkaline cement matrix, it does not contribute chlorides, sulfates, or reactive alkalis to the pore solution.

Which Physical Specifications Govern Batching and Compliance?

The product data sheet defines the fiber as a fibrillated polypropylene homopolymer network. The multi-length distribution after separation is typically reported as 0.25–0.75 in. (6–19 mm); however, individual filament length may vary because the fibrillated bundle is not a fixed cut monofilament. The specific gravity is 0.91, and the melting point is reported in the range of 160–170 °C. The fiber is insoluble in water and has no measurable water absorption. Tensile strength and modulus are orientation-dependent for fibrillated film fibers; when tensile properties are required for quality assurance, the supplier should furnish data tested in accordance with ASTM D2256 or an equivalent filament test method. For concrete use, the governing specification is ASTM C1116/C1116M Type III synthetic fiber. Type III materials are required to demonstrate resistance to the alkaline concrete environment and compatibility with the intended mixture. ACI 544.1R provides a review of fiber-reinforced concrete technology and should be used to distinguish micro, macro, and structural fiber functions.

The multi-length gradation is not merely a dimensional label; it influences the number of fibers per unit volume and the distribution of bridging lengths available in the plastic paste. Shorter fibrils disperse readily into paste-rich zones and provide a dense network of intersections, while longer fibrils bridge larger plastic shrinkage openings. This gradation reduces the need to specify a single cut length, which can be a source of specification conflict when comparing manufacturer data sheets. The following typical physical characteristics are used for batching and submittal review.

The hydrophobic surface of polypropylene does not absorb mixing water, but the fibrillated geometry can retain water mechanically within the bundle until dispersion occurs. This mechanical water retention is temporary and is eliminated by normal wet mixing. The product does not alter cement hydration kinetics chemically; the primary influence on fresh concrete is rheological, resulting from filament interaction and increased surface area.

When Fibermesh 300 Is Used as Secondary Reinforcement in Hydraulic Cement Mixtures

Where slab-on-ground construction is specified in accordance with ACI 302.1R, the product is incorporated to reduce plastic shrinkage cracking in large unjointed placements and in exposed interior slabs. In composite metal deck placements, the fiber is added at the same 0.9 kg/m³ dosage to control early-age cracking over deflecting deck profiles before the concrete develops flexural strength. Precast elements with thin sections and edge geometries also receive the product to reduce damage during demolding and handling. In each case, the fiber functions while the concrete is plastic to early hardened; it does not alter the structural capacity of the hardened section after cracking.

Plastic shrinkage crack control is evaluated experimentally using ASTM C1579. The method uses a restrained panel under evaporative airflow and records crack length, width, and total crack area. Fibrillated polypropylene fibers increase the strain capacity of the plastic matrix and reduce the continuity of bleed-water channels. In comparison with plain concrete, the crack-control mechanism is primarily physical: individual fibrils bridge the meniscus of shrinking paste and reduce localized crack propagation. Published data for this specific configuration is limited; therefore, project-specific testing under ASTM C1579 is warranted when crack-area limits are specified. Fiber dosage may be increased to 1.8 kg/m³ in high-evaporation environments, but elevated dosages change plastic viscosity and require trial mixing under ASTM C192/C192M.

For shotcrete and tunnel lining, fibrillated polypropylene types have been used to reduce plastic shrinkage and improve green cohesion. In dry-mix or wet-mix shotcrete, the fiber is included in the base mixture before conveyance. The low density reduces equipment wear relative to steel fiber, but hardened flexural toughness is not equivalent to steel fiber. For structural hardened-concrete toughness, macro synthetic or steel fibers tested under ASTM C1609/C1609M or EN 14651 are specified, not this micro fibrillated product.

The product does not eliminate the need for joint layout in slabs on grade. The fiber reduces plastic shrinkage cracking, but drying shrinkage after hardening remains governed by joint spacing, mix design, and curing. Project specifications should continue to require joints in accordance with ACI 360R and curing under ACI 308R.

In production-scale slab placements, a recognized practice is to dose fiber after aggregate and before the final portion of mix water. The pre-measured packaging should be added intact; manual opening of bags for partial dosing is not recommended because it introduces weighing errors and can cause fiber accumulation at the mixer charging point. Equipment with low-shear mixing, such as some dry-mix plants, may require longer mixing and visual confirmation of complete fibrillation before discharge.

Central and transit mixer protocols require the fiber to be added before concrete is discharged. The dry fibrillated bundle should be charged into the mixer with the aggregates or after initial water addition, and wet mixing should continue for a minimum of 4–5 minutes after the fiber is added to separate the fibrillated network. Pre-measured degradable packaging is intended to break down in the mixing water; torn or wet packages should not be handled if degradation has begun. Because the product has a specific gravity of 0.91, it does not settle in normal-weight concrete in the same manner as steel fiber; however, non-uniform distribution can occur if mixing energy is low or if concrete is discharged too quickly. In low-shear mixers, the fiber may require additional mixing time. In high-shear twin-shaft compulsory mixers, dispersion is generally faster, but the final uniformity must be verified by visual inspection of a fresh concrete sample under ASTM C94/C94M uniformity guidance.

Slump and air content should be rechecked after fiber addition. The fibrillated bundle can reduce slump through increased particle interaction; the magnitude depends on aggregate grading and water content. No specific water demand correction is used without trial mixing. Batch-to-batch variance in fiber distribution is minimized by consistent addition timing and mixing time. A recognized failure mode is fiber balling when the bundle is added to a low-slump mix without sufficient shear. If balling is observed, the batch should be mixed longer, and the dosage sequence should be revised.

Comparative Behaviour Against Monofilament Polypropylene and Steel Fiber Systems

Fibrillated multi-length polypropylene fiber differs from monofilament polypropylene in geometry, dispersion mechanism, and surface area. Monofilament fibers are extruded as discrete round or shaped strands with a fixed cut length; fibrillated fibers are produced as a film that splits into an irregular network under mixer shear. At equal addition mass, the fibrillated product generally produces a higher filament count per kilogram because the separated fibrils are thinner than standard monofilaments. This geometry increases the number of crack-bridging filaments in the plastic paste. Steel fiber has a density of approximately 7.85 g/cm³ and provides hardened flexural toughness through mechanical anchorage; it is used at project-specific dosages that are typically higher than synthetic microfiber dosage. The polypropylene product is non-corroding and does not create galvanic contact, but its elastic modulus is lower than steel and it is not a substitute for structural reinforcement.

The distinction between microfiber and macrofiber is specification-critical. The product is a micro fibrillated fiber intended for plastic crack control. Hardened-concrete flexural performance is assessed using ASTM C1609/C1609M or EN 14651, and macro synthetic or steel fibers are required when a specified residual flexural strength must be demonstrated. Specifiers should not substitute this product for macro synthetic fiber or steel fiber in those applications.

When ambient storage conditions are humid or wet, the pre-measured packaging may degrade before batching, and the product should be stored in dry covered conditions. The fiber itself does not absorb water and is resistant to moisture; the package is the moisture-sensitive component. The product should not be exposed to sustained temperatures exceeding approximately 160 °C before or after concrete placement, because polymer softening may occur. The material does not contribute chlorides, sulfates, or other corrosive ions to the concrete pore solution.

The product is not intended for primary structural reinforcement. It does not replace welded wire reinforcement for flexural crack-width control after the concrete has cracked in the hardened state. In structural slabs where post-cracking load transfer is required, steel or macro synthetic fiber systems tested under ASTM C1609/C1609M or EN 14651 should be specified. The microfiber may be used in conjunction with conventional reinforcement and with other fibers only if trial batches confirm uniform dispersion and air-void stability.

Polypropylene is hydrophobic and chemically inert in the alkaline environment of portland cement paste. The fiber does not participate in hydration reactions and does not alter setting-time chemistry; physical surface area may slightly change water demand and air-void spacing. The product is compatible with conventional air-entraining and water-reducing admixtures, but the fiber surface can retain air bubbles, producing small changes in measured air content that must be compensated in the admixture dosage. No chloride, sulfate, or alkali contribution is expected from the polymer.

Three Standardised Criteria Govern Specification Submittals and Quality Control

For construction submittals, the product data sheet should demonstrate classification under ASTM C1116/C1116M Type III synthetic fiber and state the polymer type, specific gravity, and recommended dosage. The delivered material should be in intact pre-measured packages. Batch certificates should confirm the fiber grade and reject material that is contaminated with oil, grease, or other bond-breaking films. Field quality control includes visual inspection for fiber distribution in fresh concrete and standard fresh property tests under ASTM C143/C143M for slump, ASTM C231 for air content, and ASTM C172/C172M for sampling.

Trial batches are required when the product is combined with air-entraining admixtures, high-range water reducers, or supplementary cementitious materials. Polypropylene fibrillated fibers are not known to react with normal air-entraining agents, but the increased fiber surface can alter air-void formation and slump; therefore, trial mixing under ASTM C192/C192M is necessary. The fiber should be added at the same time sequence intended for full production. In prestressed and post-tensioned concrete, the product is generally not used as primary prestressing reinforcement and should be accepted only when the project specification permits secondary synthetic microfiber use. For shotcrete, the product may be used as secondary crack control in accordance with ACI 506R if the mixture and fiber addition rate are confirmed in field panel tests.

No end-use statement should imply structural equivalence to steel reinforcement. The product acts as micro-scale crack control in the plastic and early-hardened state; hardened-section capacity remains under the governing structural code and reinforcing steel design.