MasterFiber F 100 is a fibrillated synthetic micro polypropylene fiber intended for secondary reinforcement of hydraulic cement concrete and mortar. The product is classified under ASTM C1116/C1116M-23 as a Type III synthetic fiber and is typically batched at 0.9 kg/m³ to 1.8 kg/m³. Within that range, its principal function is control of plastic shrinkage cracking and settlement cracking in freshly placed concrete. The material is supplied as collated, water-dispersible bundles that separate under mixer shear into a fibrillated network. Specific gravity is approximately 0.91 g/cm³ when tested in accordance with ASTM D792, and water absorption under ASTM D570 is effectively nil. The polymer melting point is approximately 160 °C, which places the material outside the thermal exposure range of normal cement hydration but within the typical melting region of polypropylene.

The fibrillated geometry differentiates MasterFiber F 100 from monofilament and multifilament synthetic microfibers. After dispersal, the fiber is present as a network of interconnected ribbon-like elements rather than as discrete cylindrical strands. The resulting surface profile increases mechanical interlock with hydrating cement paste and alters the fiber-matrix stress transfer once a crack has initiated. This does not make the product a replacement for structural steel reinforcing bars, welded wire reinforcement, or macro synthetic fibers tested under ASTM C1609/C1609M. It is a micro reinforcement for crack-width control and early-age surface integrity.

Can fibrillated geometry alter plastic shrinkage crack distribution?

Plastic shrinkage cracks develop when the evaporation rate from an unprotected concrete surface exceeds the bleed-water supply rate. Fibrillated polypropylene fibers reduce the visual severity and mean crack opening by increasing the local tensile strain capacity of fresh paste and by providing multi-directional restraint to capillary stress. Under ASTM C1579-21, a concrete panel containing 0.9 kg/m³ of MasterFiber F 100 may show lower average crack-width opening than an unreinforced control, but the measured result is a function of air temperature, wind speed, relative humidity, and finishing timing. The product is therefore specified where early-age surface quality is a contract requirement, not where a guaranteed crack-width threshold can be stated without a job-specific trial mix. Field evaporation rates above 1.0 kg/m²/h typically require supplemental fog spraying or evaporation retarders; the fiber alone does not eliminate evaporation-driven cracking in high-rate conditions.

For slabs placed in hot, low-humidity environments, the combination of fibrillated microfibers and a monomolecular curing compound reduces early-age moisture loss. The fiber network also restrains settlement cracking around reinforcing bars and slab penetrations by bridging the paste immediately after consolidation. This effect is most visible in concrete with slump below 150 mm when tested under ASTM C143/C143M-20. In higher-slump mixtures, the crack-control contribution may be less repeatable because aggregate segregation and paste volume changes alter fiber distribution.

At addition levels above 1.8 kg/m³, workability loss becomes measurable under ASTM C143/C143M-20. The magnitude depends on aggregate grading, paste volume, mixing energy, and admixture type. If a trial batch confirms acceptable slump without exceeding the approved water-cementitious materials ratio, a higher dosage may be used. Without such trial data, the dosage should remain within the published range. Any adjustment should be made with a high-range water reducer conforming to ASTM C494/C494M Type F or G, not by adding water beyond the mixture design limit.

At a ready-mix plant using a twin-shaft compulsory mixer, the fiber bundles are added after the coarse aggregate and a portion of the batch water. This sequencing promotes bundle opening without clustering. If the fiber is discharged directly onto dry cement, static charging can cause agglomeration; if it is added after the mix reaches its final plastic state, dispersion time may be insufficient. The result is a non-uniform fiber volume fraction that can be detected by wash-out testing or by visual inspection of a concrete sample. Plant-specific mixing trials remain the only reliable method for establishing the required additional mixing time.

Fiber Addition Sequencing in Forced-Action Mixers and Ready-Mix Trucks

The dispersion behavior of fibrillated polypropylene is controlled by mixer type, batch size, and addition point. In a compulsory pan mixer with high-shear blades, the bundles are typically introduced after 80% of the batch water has been added. The remaining water then assists in folding the fiber into the mortar fraction. In a ready-mix truck drum, the fiber is usually added after the coarse aggregate and water, followed by an additional mixing period at full agitation speed. The required number of revolutions should be determined by a plant trial because drum speed, blade condition, and concrete volume vary between trucks. A visual dispersion panel is typically prepared by washing a small sample through a 4.75 mm sieve; the retained fiber mass is then compared with the target dose.

Batch-to-batch variance in bundle opening can occur if the fiber has been exposed to prolonged direct sunlight or if bagged product is torn and re-handled. Polypropylene is hydrophobic, so moisture absorption does not significantly affect dispersion. However, heated storage above 120 °C can soften the fiber and cause bundle fusion, which will reduce opening efficiency. Storage in covered, dry conditions below that temperature is therefore specified.

In a pan mixer, adding the fiber after all aggregate but before the final mixing water leads to a more uniform distribution than adding the fiber as the first ingredient. In a drum mixer, charging fiber onto aggregate in the hopper before the water addition is also acceptable. The critical operational limitation is that fibrillated bundles require mechanical shear to open. Low-shear drum mixers that have not been recharged with sufficient mixing energy may produce visible fiber balls at the discharge point. These balls are not a product defect but a dispersion failure caused by inadequate mixing time or incorrect sequencing.

For continuous mixing systems used in dry-process shotcrete, the fiber is normally pre-blended with the bagged dry mix. The feed rate must be controlled to maintain the specified dosage across each shotcrete layer. Wet-mix shotcrete containing microfibers can be pumped through standard equipment, but the nozzle operator should observe the spray pattern for evidence of blocked hoses or inconsistent fiber distribution. The fiber addition is generally limited to the lower half of the dosage range when pumping through small-diameter hoses below 50 mm.

When Fibers Are Batched Above 1.8 kg/m³ in Low-Slump Concrete

Low-slump concrete with a target slump of 20 mm to 50 mm under ASTM C143/C143M-20 has a limited paste film around coarse aggregate particles. Adding fibrillated microfibers beyond 1.8 kg/m³ increases internal friction and can produce a measurable loss in workability. This is most evident in roller-compacted concrete and dry-cast precast concrete, where the paste volume is already minimized. A dosage of 2.5 kg/m³ may require adjustment of the fine aggregate-to-total aggregate ratio or the use of a high-range water reducer to restore the specified consistency. The exact adjustment is mix-dependent and cannot be stated as a single universal value.

At higher addition levels, the fiber network also increases the apparent viscosity of the fresh matrix. This affects pumping pressure and can reduce the maximum pump distance in ready-mix operations. The pressure increase is not linear with dosage; it depends on aggregate shape, concrete temperature, and the type of pumping equipment. If a project requires a dosage above 1.8 kg/m³, a full-scale pump test using the same boom length and hose diameter is recommended. Published data for this specific configuration is limited, so the field trial should define acceptable pumping limits.

The post-crack behavior of fibrillated microfibers is evaluated under ASTM C1399/C1399M-14. The test measures the average residual strength of a fiber-reinforced concrete beam after cracking. Microfibers generally produce lower residual strength values than macro synthetic fibers, but they may improve the crack mouth opening behavior at very small crack widths. The measured values are sensitive to fiber dispersion and beam casting orientation. A beam cast with fiber balls or non-uniform distribution may show inconsistent residual strength, which is why dispersion control is critical for specification compliance.

MasterFiber F 100 differs from macro synthetic fibers in its contribution to structural design. Macro fibers are frequently tested under EN 14889-2 or ASTM C1609/C1609M to establish load-bearing residual flexural strength. MasterFiber F 100 is not intended for that service class. Its function is early-age crack control, improved surface quality, and reduced water ingress paths caused by fine cracks. In slabs-on-ground, the product may be used alongside steel reinforcing at the specified dosage, but the structural steel or macro-fiber design remains independent.

When compared with monofilament microfibers of equivalent length, the fibrillated network produces a different spatial distribution in the concrete. Monofilament fibers tend to orient more uniformly in the plane of finishing because the surface finishing operation aligns individual strands. Fibrillated fibers maintain a more three-dimensional network because the branched structure resists complete planer alignment. This does not guarantee superior crack control in every mix, but it changes the crack-arresting mechanism from single-fiber bridging to network bridging. The difference is most relevant in thin overlays and toppings where crack width is the primary concern.

For precast concrete produced in a central batch plant, the fiber can be added to the aggregate weigh hopper. In that configuration, the fiber is distributed through the aggregate before entering the mixer, reducing the likelihood of dry-fiber balling. The addition is particularly suitable for machine-cast concrete pipe, vaults, and retaining wall blocks where consistent surface quality is expected. The standard dosage remains 0.9 kg/m³ to 1.8 kg/m³, and the actual amount should be confirmed by a pre-production trial using the same aggregate moisture content and mixing cycle.

Shotcrete applications introduce a different set of constraints. In wet-mix shotcrete, the fiber is batched at the ready-mix plant and pumped to the nozzle. The addition should not exceed the point at which pump pressure becomes unstable. In dry-mix shotcrete, the fiber is blended with the dry cement and aggregate before the water is added at the nozzle. The dry-mix addition must be uniform, because the fiber cannot redistribute after the material is sprayed onto the receiving surface. The specified dosage for shotcrete is often at the lower end of the general range, unless the project specification requires higher early-age crack control.

Because polypropylene is electrically non-conductive and chemically inert in alkaline concrete, MasterFiber F 100 does not contribute to corrosion. It does not form a galvanic cell with embedded steel, and it is not affected by chloride exposure. The material is also resistant to alkali hydrolysis under normal concrete pore solution conditions. These properties support its use in marine, wastewater, and chemical-exposure environments where corrosion resistance of secondary reinforcement is specified.

The term “Enhanced Fibrillated” in the product name refers to the controlled fibril spacing and the bundle-opening profile of the fiber. The enhancement is intended to improve dispersion in modern forced-action mixers and to increase the number of individual filaments per kilogram after mixing. That number is not fixed because it depends on mixing shear, batch time, and aggregate abrasion. A wash-out test on a fresh concrete sample can be used to verify that the fiber has opened. The test does not replace hardened property testing but provides a rapid field control method for dispersion quality.

MasterFiber F 100 should not be combined with hydrophobic admixtures in a manner that causes fiber floatation. If the admixture alters the surface tension of the mix water before the fiber bundles are fully wetted, the fiber may migrate toward the surface during placement. This can create a visible surface concentration after finishing. The effect is more pronounced in high-slump concrete with excess paste. Where such admixtures are necessary, the fiber addition point should be moved earlier in the mixing sequence, or a pre-dispersion trial should be conducted to verify that fiber distribution remains uniform.

For specifications requiring compliance with European test methods, the synthetic fiber may be evaluated under EN 14889-2 for polymer fibers. The resulting classification relates to the fiber’s effect on concrete properties and its influence on durability. MasterFiber F 100 is generally specified under ASTM C1116/C1116M-23 in North American projects, while European projects may require additional documentation under EN 14889-2. The project specification must be checked because the two systems are not interchangeable.

In low-water-cementitious-materials concrete containing silica fume or metakaolin, the paste fraction is denser and more cohesive. Fibrillated microfibers can still disperse if the mixer provides sufficient shear. The presence of silica fume increases paste demand and may exacerbate workability loss at the upper dosage limit. A trial batch should therefore include the same supplementary cementitious materials and the same mixing time intended for production. If the trial is conducted without silica fume and then silica fume is added in production, the dispersion behavior may not be representative.

The fiber is packaged in controlled-weight bags that are added directly to the mixer. The bag material is designed to degrade and disperse under mixing, but in dry-cast and very low-slump mixes, remnants of the bag can occasionally appear at the surface if mixing time is too short. This is an operational issue rather than a material failure. The bag addition method is convenient for fast-track placements because it reduces handling and allows the batching operator to add a known mass without weighing individual fibers.

At the upper dosage of 1.8 kg/m³, the number of fiber elements per cubic meter is high enough to influence the finishability of hardened surfaces. Power troweling can embed surface fibers into the paste or expose them if finishing begins too late. The finishing operation should be timed to the concrete setting behavior, not to a fixed clock time. A hard trowel finish may produce a smooth surface if the concrete is finished at the correct stage. If surface texture is critical, a test slab should be finished using the same tools and crew expected in production.

MasterFiber F 100 is not a viscosity-modifying admixture and does not act as a thixotrope in self-compacting concrete. Its effect on passing ability and slump flow should be evaluated by ASTM C1611/C1611M-21 if self-compacting concrete is specified. The dosage in self-compacting concrete is generally lower than in conventional concrete because the high paste volume changes fiber suspension and flow behavior. A filtration or sieve-stability test may also be used to verify that the fiber does not separate from the suspension during long-distance pumping.

No conclusion or summary is appended. The requirements for each application must be derived from the project specification, the concrete mixture design, and trial batch data generated with the same materials and equipment intended for production.