SikaFiber Novocord - Micro Fibrillated Fiber is a polypropylene-based, collated-fibril additive supplied as a free-flowing fibrous mass for secondary reinforcement of cementitious systems. Its intended function is reduction of plastic-state crack propagation in concrete and mortar, with supplementary micro-crack control after hardening. The fibrillated morphology is generated by longitudinal slitting and stretching of an extruded polyolefin film, producing a high specific surface area that anchors in the cement paste matrix. In accordance with ASTM C1116/C1116M-23, the product falls within the Type III synthetic fiber-reinforced concrete category when added at the manufacturer-specified dosage. Published technical data indicate a typical dosage band of 0.6 kg/m³ to 1.8 kg/m³ for general concrete, with the upper value reserved for elements exposed to rapid surface water loss or restrained sections during early-age loading from shrinkage.

Values are lot-specific and shall be confirmed through project trial batching where the fiber is specified for fracture-sensitive work. Product-specific published data for fiber length distribution after high-shear pin-mixer dispersion are limited; batching trials are required when mixer tip speed exceeds 12 m/s.

Material Constitution and Fibre Geometry

The polymeric base is a virgin polypropylene homopolymer with a nominal density of 0.91 g/cm³ when tested under ISO 1183-1:2019. The product is hydrophobic, with water absorption below 0.1% under ISO 62:2008, and it does not participate in alkali-silica reaction. Differential scanning calorimetry under ISO 11357-3:2018 places the melting endotherm between 160 °C and 170 °C, which is below the temperature reached during high-pressure steam curing cycles. Therefore, the fiber remains dimensionally stable under standard atmospheric concrete curing but is not suitable as the sole reinforcement in post-fire structural elements. The fibrillated network opens into interconnected micro-filaments after mechanical action in a compulsory mixer, producing a specific surface area substantially higher than a monofilament fiber of equal denier. This geometry provides multiple contact points for cement paste adhesion but also increases sensitivity to dry-feed addition rate.

The product is resistant to alkali hydrolysis, chloride attack, and ultraviolet degradation when embedded in a cementitious matrix. Because the fiber is encapsulated, solar exposure during aggregate storage does not affect its properties; however, loose fiber bags should be stored below 50 °C and away from direct sunlight to prevent heat-induced film shrinkage. In high-pH environments above 13, the polymer backbone is stable over the service life of normal concrete; long-term testing under saturated Ca(OH)₂ at 40 °C for 12 months shows no loss of tensile response beyond initial orientation effects. The hydrophobic surface has practical consequences for water-cement ratio control: water demand increases as dosage increases, and this increase must be measured during trial batching rather than taken from published product literature.

On concrete grade C32/40 interior slab placements with a 150 mm thickness and 20 mm maximum aggregate size, the fiber is typically batched at 0.9 kg/m³ in ready-mixed concrete with a 100 mm target slump. The addition sequence on a 1.0 m³ twin-shaft compulsory mixer is to charge the aggregates, cement, and pozzolanic binder, then introduce the fiber over 45 s to 60 s while the mixer operates at full speed. After the fiber is visibly dispersed, the first 70% of batch water is added, followed by admixtures and the remaining water. This sequence avoids the formation of dry fibril agglomerates that can appear when the fiber is added simultaneously with the first water. For floor slabs without structural joints, the fiber is combined with 5.5% ± 1.0% total air and a polycarboxylate ether superplasticizer dosage adjusted to offset the 10–20 mm slump demand of the fiber network. Slabs produced under this regime show plastic shrinkage crack width reduction in ASTM C1579-21 restrained panels of more than 40% relative to control, measured 6 h after casting at an evaporation rate of 1.0 kg/m²/h.

Mortar and render applications use the fiber at 0.6 kg/m³ to 0.9 kg/m³ in dry-mix and wet-mix formulations. In thin-section repair mortars applied at 10 mm to 25 mm thickness, restrained ring testing under ASTM C1581/C1581M-18a shows delayed crack initiation. The product is not intended for structural repair because the low elastic modulus of polypropylene does not transfer tensile stress across a cracked section. When used in exterior plasters, the fiber is compatible with silicate-based pigments and air lime mortars; however, high-speed pin mixers with tip speeds above 12 m/s may over-fibrillate the bundles and reduce the effective fiber length, so paddle mixers are preferred.

Why Is Addition Rate Critical in Central Mix Plant Operations?

Fibrillated micro-polypropylene products have a lower bulk density than cement and a high electrostatic charge potential when handled in dry conditions below 30% relative humidity. Field observations from continuous batching plants indicate that dumping a 0.9 kg pre-bagged unit into an empty mixer or onto a static powder surface can lead to localized fiber balls that survive the full mixing cycle. The recommended practice is to meter the fiber under a moving aggregate stream at a rate no greater than 1.0 kg/min per 1.0 m³ of batch capacity in pan and planetary mixers. For twin-shaft mixers of 2.0 m³ to 3.0 m³ batch size, the same mass can be added over 60 s to 90 s with the mixer blades in high-speed mode. In truck-mixed concrete, the fiber should be introduced through the loading hopper after the first 50% of aggregate and water are in the drum, then mixed at 12 rpm to 18 rpm for at least 5 min after the fiber is loaded. If the fiber is not fully dispersed after this interval, the batching sequence shall be recorded and a sample of fresh concrete inspected under 100× magnification to check for undispersed fibril bundles. The plant operator should not compensate with additional water without a corresponding adjustment to the water-cement ratio and shall record any water addition on the delivery ticket as required by ASTM C94/C94M-23.

When Addition Rate Exceeds 1.0 kg/min in a 1 m³ Pan Mixer

Forced-action pan mixers of 1.0 m³ batch volume produce a characteristic dry-feed failure when the micro fibrillated fiber is introduced too rapidly. The charge builds at the mixer wall as a low-density mat, and the blades pass beneath it without cutting the bundle. If mixing continues for more than 2 min, the mat absorbs water only at its exterior, forming a moist shell over a dry core. These pseudoparticles remain visible on the hardened surface of a 150 mm slab as white fibrous clusters 5–10 mm in diameter. Such clusters create local zones of high porosity and reduce abrasion resistance under ASTM C779/C779M-12 procedures. Production controls therefore limit the feed rate to 0.5 kg/min to 0.75 kg/min in pan mixers, with the fiber added to the moving aggregate before water or after 20% of the water is added. The lower rate applies when the environment has a relative humidity below 30% and the aggregate moisture content is below 0.5% because electrostatic clumping is more pronounced. If the operation cannot provide a controlled feed, the fiber shall be pre-mixed by hand into the sand fraction for 60 s before charging the full aggregate batch. This boundary condition is not generally required for monofilament microfibers of equivalent dosage, which have a lower surface area and disperse more readily at feed rates up to 1.5 kg/min per 1.0 m³.

Comparative Behaviour Against Monofilament and Steel Fibre Classes

The primary difference between Novocord and a monofilament microfibre is the fibrillated network geometry. A monofilament of circular cross-section develops plastic-state crack control by capillary disruption at a dosage of 0.6 kg/m³ to 0.9 kg/m³, but its crack-count reduction may be lower in restrained slabs when compared with an equal mass of opened fibrillated material. The fibrillated product splits into multiple micro-filaments under mixer shear, increasing the linear length of distributed fiber per unit volume. This is beneficial for plastic shrinkage crack width suppression but can increase the water demand by 2% to 5% at 1.2 kg/m³, as observed in paste rheology measurements using a rheometer with a vane rotor at a shear rate of 1 s⁻¹. By contrast, a monofilament fiber of equivalent dosage typically shows a water demand increase below 2%. The choice between these two classes is therefore governed by the crack-control objective and the available slump reserve.

Relative to steel fibers, the micro fibrillated product does not provide structural post-crack flexural toughness. Steel fibers of 35 mm length and 0.55 mm diameter are specified under ASTM C1609/C1609M-19 for residual flexural strength at net deflections of L/600 and L/150. The micro polypropylene fiber has a modulus of elasticity approximately 3–4 GPa, compared with 200 GPa for steel, and therefore cannot substitute for reinforcing bars or steel fibers in load-bearing sections. It shall be specified only as secondary reinforcement in accordance with ASTM C1116/C1116M-23 and EN 14889-2:2006 Class I micro-synthetic fibre. In chloride exposure, the non-metallic fiber does not participate in galvanic macrocell current, whereas steel fibers require attention to crack width and concrete cover.

Regulatory and Quality-Control Compliance Matrix

In precast tunnel segment casting, the microfibrillated fiber is frequently used at a dosage of 0.9 kg/m³ in self-consolidating concrete with a spread diameter of 650 mm to 750 mm under ASTM C1611/C1611M-21. The fiber is introduced in the central batch mixer after the high-range water reducer is added to avoid dry electrostatic adherence to the mixer lid. Workability retention on a 0.75 m³ batch has been controlled by a V-funnel flow time of 5 s to 9 s; values above 12 s indicate insufficient dispersion or excessive fines loss. The product does not replace structural reinforcement in high-eccentricity segments or spandrel beams; such elements require additional reinforcing bars detailed in accordance with Eurocode 2 or ACI 318-19. For exposed aggregate surfaces, the fibrillated fibers may become visible after the surface retarder is removed; this condition is controlled by burnishing or by using a lower dosage of 0.6 kg/m³ in panels where surface appearance is the controlling acceptance criterion.