GENESIS - Fibrillated Polypropylene Fiber is supplied as a slit-film, mechanically fibrillated reinforcing fiber for cementitious matrices. The fiber is produced from a high-tenacity polypropylene homopolymer feedstock extruded as a cast film, oriented in the machine direction, and fibrillated into an open three-dimensional network. This network increases specific surface area and mechanical anchorage in cement paste compared with circular monofilament polypropylene fiber. The product is classified as a Type III synthetic fiber under ASTM C1116/C1116M when used in fiber-reinforced concrete, and it does not replace primary structural reinforcement unless the project specification and structural design explicitly permit such substitution. The product is supplied in cut lengths from 6 to 24 mm, with package masses adapted to ready-mix batching. The low density of 0.90–0.91 g/cm³ (ASTM D792) yields a high fiber count per kilogram and allows distribution through the full concrete volume. The product is manufactured to a controlled cut-length distribution; batch certificates should report the retained length distribution on a 200 g sample. Fibrillation quality influences the effective fiber width distribution, and under-fibrillated film strips can reduce the mechanical anchorage that distinguishes the grade. This quality parameter is not captured by a simple cut-length sieve and should be checked by low-power microscopy against the manufacturer’s reference images.

What Distinguishes the Fibrillated Network from Monofilament, PVA, and Steel Fiber Systems?

The primary structural difference is surface architecture. Monofilament polypropylene fiber has a smooth circular or oval cross-section; load transfer in hardened cement paste relies on interfacial friction and matrix shrinkage. Fibrillated polypropylene is a film-based product that is slit and stretched to form interconnected fibrils and a branched, irregular cross-section. In fresh concrete, this network restrains plastic settlement and reduces surface evaporation stress. Under ASTM C1579, fibrillated polypropylene products at 0.9–1.8 kg/m³ are often used to reduce plastic shrinkage crack area; published data for the GENESIS grade at each intermediate dosage is limited, and comparative studies on comparable fibrillated systems report crack reduction values between 60% and 90% depending on aggregate gradation, air content, and bleeding rate. The fibrillated network can increase pumping line friction more than monofilament fiber of the same mass because the opened structure promotes mechanical interlock; this is evaluated by full-scale pump trials rather than by rotational rheometry alone.

In comparison with macro-synthetic fibers, the fibrillated polypropylene product is not designed for structural toughness indices. Macro-synthetic products have equivalent diameters from 0.3 to 0.8 mm and are tested under ASTM C1609 or ASTM C1550 for post-crack flexural performance. Fibrillated polypropylene is a microsynthetic product with equivalent diameters below 0.1 mm; its primary function is early-age crack control rather than residual strength. PVA fiber has a hydroxyl-rich surface and absorbs water, enabling strong chemical bonding in cement paste and use in strain-hardening cement composites. Polypropylene is hydrophobic and does not chemically bond; its performance relies on mechanical network and crack suppression. This absence of chemical bonding is an advantage in high-pH environments because no hydrolytic degradation mechanism is present, but it limits the post-crack tensile strength increase.

Addition order in ready-mix operations determines whether fibrillation is an asset or a defect. The fiber is introduced after aggregate and cement are charged, preferably after 50% of the mixing water has entered the mixer. In a central twin-shaft mixer with a batch size of 2.0 m³, adding 0.9 kg/m³ before cement coating of coarse aggregate produces fiber balls that are not fully opened. The mixing profile should specify 5–7 minutes at 12–15 rpm after the last bag is added; at 15–20 rpm, the dispersive energy is greater but the risk of fiber breakage increases. Slump loss of 10–20 mm relative to the plain reference mix is common at 0.9 kg/m³. The use of a high-range water-reducing admixture conforming to ASTM C494/C494M Type A or F can compensate for the increased internal friction. Field experience in truck-mixed operations shows that batching at more than 70% of drum capacity can prevent the fiber from opening fully, leaving visible fibril clusters on the initial discharge. Published data on GENESIS-specific mixing energy requirements is limited; therefore project trial batching under ASTM C192 is recommended. In laboratory rheology, the yield stress of mortar containing 0.9 kg/m³ fibrillated PP may increase by 10–20% relative to the plain reference when measured by a rotational rheometer in vane configuration at 0.5 s⁻¹. This increase is not solely a function of fiber volume; it depends on fibrillation depth and the amount of opened network. Higher fibrillation depth increases yield stress more than a marginal mass increase, which is why the dosage cannot be transferred directly between fibrillated and monofilament products of the same cut length.

Dosing Limits and Processing Boundaries in Slab, Precast, and Shotcrete Systems

In flatwork, the effective dosage window is bounded on the lower end by inadequate fiber count per unit volume and on the upper end by finishability loss. At 0.6 kg/m³, the number of fibrillated fibers per cubic metre may be insufficient to create a continuous network in a 100–150 mm thick slab after coarse aggregate settlement; at 1.2 kg/m³ and above, power trowel operations may pull fibrils to the surface when the bleed water film is absent. The product should therefore be specified at 0.6–0.9 kg/m³ for interior slabs, unless the specification requires higher dosages for severe evaporation conditions. In dry-mix shotcrete, static charge accumulation at relative humidity below 30% causes the fiber to adhere to hopper walls and feed augers; anti-static packaging or pre-wetting the fiber reduces this condition. In wet-mix shotcrete, dosage rates of 1.0–2.0 kg/m³ are used to improve cohesion and reduce sag in overhead applications; line velocities should be maintained above 20 m/s to avoid lateral segregation of the low-density fiber. Rebound reductions compared with plain shotcrete are reported in ACI 506.1R, but the magnitude is highly nozzle-operator dependent.

In extruded or slipformed precast elements, the fibrillation network has a tendency to orient parallel to the flow direction. This anisotropic orientation can produce greater shrinkage restraint along the machine direction than across the width, visible as directional crack-width differences in exposed panels. Published data for GENESIS in high-shear extrusion is limited; process trials should include free-shrinkage measurement in both directions under ASTM C1579 or a project-specific restrained shrinkage method.

Polypropylene’s saturated hydrocarbon backbone is stable in the alkaline pore solution of Portland cement. In immersion testing at pH 12.5–13.5, the fiber retains more than 90% of its tensile strength after 28 days. Chloride content is typically below 0.01% by mass of fiber, so the product does not add a significant chloride burden to reinforced concrete governed by ACI 318 or EN 206. The fiber is non-corrosive and does not require minimum cover. However, polypropylene is combustible, with a melting peak near 165 °C; storage areas should be kept below 50 °C and away from ignition sources. Continuous service temperature in the hardened matrix should not exceed 80–90 °C because polymer relaxation reduces load transfer and the fiber modulus decreases markedly near the melting point. Strong oxidizing acids and hot aromatic solvents are incompatible; typical concrete admixtures, including calcium chloride and sulfate-bearing cements, do not degrade the fiber but may influence matrix fiber bond.

When the Product Is Evaluated as a Replacement for Welded Wire Mesh

Welded wire mesh is passive at the time plastic shrinkage cracking occurs because it is placed below the surface and only engages after the surrounding concrete hardens and cracks. The fibrillated polypropylene product is distributed through the full thickness and engages immediately after placement. At dosages below 0.5% by volume, however, it does not provide measurable flexural strength increase; therefore it cannot replace welded wire mesh for structural load transfer, crack-width control under service loads, or restraint after hardening. In slab-on-ground applications where wire mesh is specified only for shrinkage and temperature reinforcement, some project specifications permit a reduction or elimination of mesh when the synthetic fiber is used at the specified dosage and the slab is designed as a non-structural element. This decision requires the licensed design professional to verify that the expected tensile strain demand does not exceed the post-crack contribution of the fiber network. Under ASTM C1399, the post-crack flexural performance of fibrillated polypropylene microsynthetic fiber at typical dosages is low; the product should not be confused with macro-synthetic polymer fiber that is engineered to produce residual flexural strength at specified deflections.

GENESIS is supplied in water-soluble or degradable bags. In ready-mix use, the whole bag is introduced without opening; the packaging must be stored below 60% relative humidity to prevent premature dissolution. Bags are often pre-weighed at 0.5 kg or 1.0 kg, with one 0.9 kg bag matched to 1 m³ at the standard dosage. Batch-size calibration should not assume volumetric water-soluble bag strength if the bag is damaged. If the product is evaluated for non-cementitious polymer compounding, the processing temperature window is narrow. In a twin-screw extruder with L/D 40:1, barrel temperatures above 170 °C collapse the fibrillated structure, while temperatures below 155 °C yield incomplete wetting. The acceptable setpoint window of 155–165 °C is therefore a ≤ ±5 °C threshold around 160 °C. Published data for GENESIS in this specific configuration is limited; resin processors should not extrapolate from cementitious dispersion results to melt compounding without controlled rheological trials.

Regulatory documentation should be checked per project. Polypropylene polymers are exempt from registration as polymers under REACH Article 2(9), but the propylene monomer and any processing aides must meet applicable registration and restriction requirements. The product is generally not expected to contain cadmium, lead, mercury, hexavalent chromium, PBB, or PBDE above the maximum concentration values of RoHS Directive 2011/65/EU; a material-specific certificate is required for formal compliance. For food-contact applications, unpigmented polypropylene may comply with FDA 21 CFR 177.1520 if appropriate antioxidants and processing conditions are used, but this status does not transfer automatically to fibrillated concrete fiber unless the manufacturer confirms the exact formulation. Project specifications should require a batch certificate showing cut-length distribution, tensile strength, and packaging mass; published data for the GENESIS fiber across all global standard annexes is limited.