SikaFiber Novomesh B&BMA Macro is supplied as a dry engineered blend of macro and micro synthetic reinforcing fibres for placement in ready-mixed concrete, precast concrete, and wet-mix sprayed concrete. The macro component is a continuously embossed polyolefin monofilament with a nominal length of 40 mm to 54 mm and an equivalent diameter of 0.3 mm to 0.8 mm; the micro component is a monofilament or fibrillated polyolefin fibre with a nominal length of 6 mm to 12 mm. The blend is classified as a polymer fibre for structural use under EN 14889-2:2006 and falls within the Type III synthetic fibre definition of ASTM C1116/C1116M-10a. The macro fraction mobilises after matrix cracking to provide residual flexural strength and energy absorption; the micro fraction reduces plastic shrinkage cracking, plastic settlement, and bleed-water channelling during the initial 24 h after placement.

Published data for this specific branded configuration is limited; when current manufacturer technical data sheet values are unavailable, class-level ranges for synthetic macro and micro fibre systems are used for proportioning and performance verification. The B&BMA Macro designation identifies the macro fraction as the primary post-crack reinforcement, while the micro fraction is present for early-age crack control rather than structural load transfer.

In twin-shaft compulsory mixers with nominal batch capacities between 1.5 m³ and 4.5 m³, the blend is charged after the aggregates and before the mixing water. A post-fibre mixing interval of 30–60 s is generally sufficient for visual homogeneity at batch temperatures below 30 °C. Fibre-ball formation has been observed on production lines when free moisture on coarse aggregate exceeds 3% and the fibres are dosed before the aggregate stream has fully covered the mixer flights. The monofilament micro fraction in this blend reduces static-charge clustering compared with fibrillated-only micro fibre, but vibratory feeder discharge rates above 12 kg/min can still create transient concentration gradients in the aggregate transfer belt.

For truck-mixer addition, the blend is introduced at a minimum mixing speed of 12 rpm to 18 rpm for at least 5 min after the last bag is added. Worn mixing blades and hardened concrete build-up on drum walls can increase fibre accumulation; routine washout inspection is recommended in continuous production. No pre-drying of the polyolefin fibre is required at relative humidity up to 80% and storage temperature below 50 °C. The polyolefin is hydrophobic and does not initiate corrosion, but oil contamination from conveyor belts can reduce fibre-matrix bond and should be excluded from the batching path.

In pumped concrete, the macro fibres align preferentially with the concrete flow direction through 125 mm to 150 mm internal diameter hoses. Obstruction is generally absent at dosages up to 5.0 kg/m³ when the mortar phase is cohesive and the coarse aggregate content is reduced by 2–5% by volume. Fibre addition increases apparent yield stress; maintaining a target slump of 150±30 mm commonly requires an additional 0.5–1.5% high-range water reducer by mass of cementitious material over the control mix.

What limits dosage selection for slabs and sprayed concrete?

Dosage is governed by the required post-crack residual flexural strength, the plastic shrinkage crack-control objective, and the fresh concrete placement method. Manufacturer-published guidance for this blended system generally places total dosage between 2.5 kg/m³ and 5.0 kg/m³ for ground-supported slabs and between 3.5 kg/m³ and 6.0 kg/m³ for wet-mix sprayed concrete. Dosages below 2.5 kg/m³ can still reduce early-age cracking through the micro component but often do not produce repeatable post-crack performance under EN 14651 beam testing. In concretes with cementitious content below 350 kg/m³, dosages above 6.0 kg/m³ have been associated in field reports with pump pressure increases of 20–35% and a slump-flow reduction from 600 mm to 450 mm in self-consolidating mixtures.

The lower dosage boundary is also limited by the surface area of the micro component required to intercept bleed-water channels. In slab batches with low fines content, micro fibre addition below 0.9 kg/m³ may not provide measurable plastic shrinkage crack reduction under ASTM C1579-21; the blend formulation should therefore be selected so that the micro fraction reaches at least this threshold before the macro dosage is optimised for hardened-state performance.

For sprayed concrete, dosage confirmation is performed through plate-type energy absorption testing under EFNARC 1999 or ASTM C1550. A specified plate energy absorption of 700 J at 25 mm central deflection is frequently achieved with synthetic macro fibre dosages between 3.0 kg/m³ and 6.0 kg/m³; class-level results depend on aggregate gradation, accelerator chemistry, and nozzle air-flow energy. The use of an equivalent steel fibre dosage without beam or plate validation is not acceptable.

A direct substitution of steel fibre with an equivalent mass of synthetic macro fibre is not valid. Steel fibre and synthetic macro fibre operate through different tensile modulus, aspect ratio, and bond mechanisms and therefore require separate dosage and design verification. The following table summarises representative published property ranges for fibre classes rather than product-specific acceptance values.

Against a micro-only fibre product, the macro fraction in this blend supplies residual flexural strengths that are typically reported between 1.0 MPa and 3.5 MPa at CMOD 0.5 mm under EN 14651 at dosages of 3.0–5.0 kg/m³. Micro-only fibres generally do not provide measurable residual flexural strength above 0.5 MPa at the same crack opening in concrete with matrix strength 30–40 MPa. Against a straight macro synthetic product, the presence of the micro component reduces early-age crack width under restrained shrinkage testing, but it does not increase the post-crack toughness beyond the macro fibre dosage contribution.

Compared with welded wire mesh, the synthetic fibre blend is distributed in three dimensions rather than a single plane, but it is not a substitute for conventional longitudinal reinforcement in primary flexural members unless explicitly designed using residual strength models. The blend is applicable to ground-supported slabs, overlays, and sprayed concrete linings where crack-width control, post-crack ductility, and corrosion resistance are the governing requirements.

During power trowelling of ground-supported slabs, surface protrusion of macro fibres can occur when bleed water is closed too early. The operational boundary is to delay trowelling until the bleed water sheen has disappeared and to avoid rapid surface drying. Protruding fibres can be removed by mechanical saw cutting or are enclosed by subsequent floor coverings; they do not present a corrosion staining issue.

In precast concrete, the blend is used in secondary elements where demoulding and handling stresses require crack-width control and improved impact resistance. The fibre does not affect early-age heat of hydration or set time, but it can reduce visible surface void area when used with an appropriate external vibration regime of 50–80 Hz for 20–40 s per form section. Impact resistance in slab-on-grade applications is typically evaluated under ACI 544.2R-17 repeated impact testing; synthetic macro fibre blends increase the number of blows to first crack and failure over plain concrete.

When wet-mix sprayed concrete is specified without welded wire mesh

Wet-mix sprayed concrete producers have used synthetic macro fibre blends to replace welded wire mesh in temporary and permanent linings where corrosion protection and rebound reduction govern. In wet-mix equipment with accelerator injection at the nozzle, the fibre blend is introduced at the weigh batcher or truck mixer, not through the nozzle. The maximum aggregate size is generally 40 mm; the macro fibre length and aggregate size are selected so that fibre length does not exceed 0.4 times the pump hose internal diameter. For a 50 mm internal diameter nozzle hose, fibre length is therefore limited to approximately 30–40 mm. Longer macro fibres at higher dosages can induce nozzle pulsation and blockages when accelerator dosage exceeds 6% by mass of binder.

The lower density of synthetic fibre reduces rebound compared with steel fibre, but rebound mass depends on air flow, accelerator dose, and nozzle angle. Field reports from sprayed concrete operations indicate that steel fibre rebound can exceed 25% under adverse conditions, while synthetic macro fibre rebound commonly remains between 10% and 20%; published data for this specific blended configuration is limited. The micro fraction improves cohesion and reduces mix drainage, which is particularly relevant in overhead spraying. The polyolefin blend is inert in the alkaline sprayed concrete environment and does not interfere with alkali-free or sodium silicate accelerated systems.

Quality assurance under EN 14889-2 and related test standards

The product is acceptable for structural use only when the batch certificate lists the actual fibre length distribution, the melt-flow index of the base polyolefin component, and the declared dosage for the specified toughness class. The melt-flow index is controlled under ISO 1133-1:2022; values outside the manufacturer’s declared interval can alter fibre deformation behaviour during extrusion and change concrete workability. No volatile organic solvent or amine-based surface treatment is known to be present in this blend. Compatibility with air-entraining admixtures should be tested because hydrophobic synthetic fibres can temporarily adsorb air-entraining surfactants and reduce the air void spacing factor under ASTM C457.

For production acceptance, beam specimens 150 mm × 150 mm × 550 mm are cast under external vibration at 50 Hz, with a notch depth of 25 mm for EN 14651. A closed-loop servo-hydraulic testing frame with crack mouth opening displacement control at 0.05 mm/min for the first 0.1 mm and 0.2 mm/min thereafter is used. The first batch of each mix design is tested at the target fibre dosage, the lower-bound dosage, and the upper-bound dosage to define the operational tolerance window before production runs begin.

The polyolefin fibre is inert under REACH registration obligations and is not classified as hazardous under CLP. No RoHS restricted substance is present in the synthetic fibre concentrate above the maximum concentration values. These statements apply to the polymer fibre component and do not extend to the concrete admixture system.