MasterFiber MAC 360 is a structural macro synthetic fibre supplied as an embossed monofilament and introduced into concrete, shotcrete, and precast matrices where post-crack residual capacity is required. The fibre is produced from a polyolefin blend with a nominal specific gravity of 0.91 and a nominal length of 54 mm. It falls within the scope of ASTM C1116/C1116M Type III synthetic fibre-reinforced concrete and is classified for structural use under EN 14889-2. In slab-on-ground construction the fibre is used to replace welded wire mesh and light steel fabric at dosages between 1.8 kg/m³ and 7.5 kg/m³, depending on the required residual strength class. In comparison with steel fibres, the polyolefin monofilament is non-corroding, non-magnetic, and approximately 88% lower in density, which raises fibre count per kilogram but reduces stiffness and post-crack stress at wider crack openings. The product is not designed to replace primary flexural steel in continuous beams or suspended slabs; its structural contribution is the transfer of tensile stress across a cracked concrete matrix after first cracking.

Specification boundaries for MasterFiber MAC 360

Technical data used in concrete mix design should distinguish between fibre base properties and composite performance. The values below are typical published values and should be verified against the manufacturer’s certificate for the production lot. Published data for the specific pull-out bond-slip relationship of the embossed monofilament in C30/37 concrete is limited, so structural qualification programs normally rely on flexural toughness testing rather than single-fibre pull-out.

The aspect ratio is approximately 67. At this geometry, the fibre distributes with acceptable pumpability in wet-mix shotcrete up to 6 kg/m³ through a 50 mm nominal hose diameter. The stored fibre is packaged in degradable paper bags or bulk sacks, and the packaging should be kept dry. Although water absorption is below 0.1%, surface moisture can cause fibre bundles to bridge in dosing screws. The melting point of 162 °C does not represent a service temperature limit for concrete, but at temperatures above 100 °C the polymer softens and post-crack capacity should be considered ineffective in fire resistance calculations.

What performance boundaries exist in slab-on-ground replacement of welded wire mesh?

When welded wire mesh is deleted from a ground-supported slab, the concrete section still requires a defined residual flexural capacity after cracking. Preconstruction qualification for MasterFiber MAC 360 is normally performed by beam tests according to ASTM C1609/C1609M or EN 14651. In a concrete with compressive cylinder strength of 30 MPa to 35 MPa and a dosage of 3.0 kg/m³, residual flexural strengths at net deflection limits of L/600 and L/300 may be expected in the range of 1.0 MPa to 1.8 MPa, though exact values shift with aggregate angularity, paste volume, and fibre orientation. At 4.5 kg/m³, the equivalent flexural strength ratio may increase by 35% to 60% relative to 3.0 kg/m³, but slump loss of 50 mm to 80 mm is observed unless mid-range or high-range water-reducing admixtures are adjusted.

Production-scale twin-shaft compulsory mixers with 1.0 m³ batch capacity usually require 45 seconds to 60 seconds of wet mixing after fibre addition to eliminate visual fibre balls. In transit mixers, the drum should be charged at 12 rpm to 14 rpm for 4 minutes to 6 minutes after fibre dosing. Adding the full fibre dose as a single cluster into the charging hopper can produce bridging in the feed gate, especially with bulk-bag discharge systems. Sequential addition of half bags or pneumatic blowing through a dosing pipe reduces the occurrence of blade entanglement. The fibre should not be added to a dry mixer before coarse aggregate because the monofilaments can be forced into wear plate gaps and reduce seal life.

The replacement of mesh is limited to non-structural load transfer and to slab areas where the foundation provides continuous support. At free edges, construction joints, and column penetrations, conventional reinforcement or dowels remain necessary because a macro synthetic fibre does not provide the large crack-width control or load-transfer stiffness of continuous steel bars. Published data for this specific configuration is limited when fibre-only slabs are subjected to heavy rack point loads above 80 kN; a separate punching shear check is required.

Wet-mix shotcrete linings in underground construction use MasterFiber MAC 360 at 4 kg/m³ to 6 kg/m³ to achieve toughness classes for rock support. In dry-mix shotcrete the fibre is pre-blended with cement and aggregate before the nozzle; in wet-mix shotcrete it is added during batching and the mix is delivered to the pump. Pump selection influences fibre damage. Piston pumps with 50 mm to 65 mm delivery lines show less fibre fracture than screw-type pumps because the screw pump imparts continuous shear to the monofilament. At 6 kg/m³, a 50 mm hose diameter is the practical lower limit; blockages increase at smaller diameters, particularly when the coarse aggregate is larger than 8 mm. The in situ residual performance of sprayed concrete is not identical to cast beam data because spraying produces a preferential fibre orientation in the plane of the lining. The rebound stream is enriched in fibre relative to aggregate due to the low particle mass. Therefore, the actually retained fibre content should be verified by washout testing on fresh sprayed concrete or by core extraction and visual counting. Batched weight alone can overstate in-place fibre content by 10% to 25% in overhead spraying.

At the nozzle, compressed air pressure of 0.4 MPa to 0.6 MPa and a water-to-cement ratio below 0.45 are used to control rebound. The presence of the fibre does not significantly alter accelerator dosage, but mixes with fibre are stiffer after acceleration, making manual finishing more difficult. No chemical incompatibility with set accelerators has been recorded in field use, but surface embossing can trap paste and produce a more porous interfacial transition zone. Fibre balling in the nozzle is more associated with bent delivery hoses or a worn nozzle tip than with fibre geometry.

In precast segment production, MasterFiber MAC 360 is added at 2.5 kg/m³ to 4.5 kg/m³ to reduce edge chipping and handling damage. External vibrators compact the mix. Thin sections below 50 mm tend to orient fibres with the flow, and trial castings are required to set the maximum dosage for a given mould. A maximum coarse aggregate size of 10 mm may be specified above 4 kg/m³ to prevent fibre accumulation around blockouts.

If alkali-free accelerators are used in wet-mix shotcrete

Alkali-free accelerators based on aluminium sulfate are commonly used with macro synthetic fibre shotcrete for tunnel and mine applications. The accelerator dose is typically 6% to 10% by mass of cement. At these doses, the open time after nozzle discharge is reduced to 2 minutes to 5 minutes, and the mix hardens with a fine-grained ettringite-rich matrix. MasterFiber MAC 360 does not react chemically with the accelerator and remains stable in the alkaline pore solution. However, the rapid viscosity increase can immobilize fibre clusters before full dispersion if the fibre is added too late in the mixing sequence. The recommended addition point is at the batch plant, not in the truck at the shaft, because late addition may result in a reduction in measured residual strength of 20% to 30%. This is a mixing-order limitation, not a chemical incompatibility. In underground lining jobs, batching records should record fibre addition time and drum revolutions before pump discharge to control this variation.

The compatibility with chlorinated water and sulfate-bearing groundwater is governed by the concrete matrix and not by the polyolefin fibre. The fibre does not participate in chloride-induced corrosion, and no passivation or cathodic protection interaction is required. This distinguishes the product from steel fibres in marine or chloride-laden service. However, in high-temperature fire endurance, the polymer will melt and leave channels in the concrete. If the section is required to maintain post-crack capacity after fire, a hybrid system with steel fibres or conventional reinforcement should be considered.

Verifying fibre distribution without destructive core sampling

Fresh concrete fibre content can be checked by the washout procedure referenced in EN 14889-2. A representative sample of 20 kg to 30 kg of fresh fibre-reinforced concrete is washed over a 5 mm sieve; the retained fibres are dried and weighed. The result is compared with the intended dosage in kg/m³ using the known fresh density of the concrete. A deviation greater than ±10% from the target may indicate a batching calibration error or fibre loss in the charging system. For hardened concrete, saw-cut surfaces can be photographed and fibres counted per unit area, but this method is orientation-dependent and may underestimate fibres aligned perpendicular to the cut plane. The relationship between surface fibre count and three-dimensional dosage should be established for each mix design.

In floor slabs, bull-floating and power-trowelling orient a proportion of fibres into the horizontal plane. This changes the relationship between ASTM C1399/C1399M beam specimens and actual floor performance. Beams prepared by consolidation with a vibrator may show a more vertical orientation than trowelled floors. For performance verification, specimen preparation should follow the same placing and finishing method as the production slab. The use of round panel tests per ASTM C1550 or square panel tests per EN 14488-5 is recommended for sprayed concrete because the panel geometry better represents fibre orientation in a sprayed lining.

Compared with cold-drawn steel fibres, MasterFiber MAC 360 has a lower elastic modulus of 9.5 GPa versus approximately 210 GPa for steel. At the same volume fraction, steel fibres mobilize higher residual stress at crack widths above 0.5 mm, while macro synthetic fibres are more compliant and may require a higher dosage to achieve equivalent crack-width control. The density difference, 0.91 versus 7.85 g/cm³, produces a much higher number of individual fibres per kilogram. This closer fibre spacing contributes to early crack control but does not change the elastic modulus of the uncracked concrete. Steel fibres can corrode at exposed surfaces and can interfere with magnetic induction reading of concrete cover. Macro synthetic fibres are non-magnetic and do not produce surface staining.

Compared with micro polypropylene fibres, which are typically 6 mm to 19 mm long and dosed at 0.6 kg/m³ to 1.2 kg/m³, MasterFiber MAC 360 is not intended solely for plastic shrinkage control. Micro fibres reduce surface bleed and early plastic settlement cracking; they have limited influence on hardened concrete toughness because their short length cannot bridge wider structural cracks. Macro synthetic fibres are not a substitute for air-entraining admixtures in freeze-thaw durability, nor a substitute for proper curing. The combined use of micro and macro synthetic fibres is permissible and sometimes specified for separate crack-control stages, but the total synthetic volume should be considered in mix design to avoid excessive slump loss.

The distinction from welded wire mesh and steel rebar is primarily placement reliability. Mesh is positioned at a specified depth and can be displaced during concrete placement, lowering its structural value. Fibre reinforcement is distributed throughout the concrete matrix at the time of mixing, but its orientation is affected by placement and finishing. This creates a different failure mechanism: distributed fibre bridging rather than discrete bar yield. In slab design, the two systems are not interchangeable in all load cases. The fibre option becomes viable where the load is distributed, the substrate is uniform, and crack widths are limited to serviceability thresholds. At concentrated loads, joints, or structural connections, bar reinforcement remains mandatory.

Within the macro synthetic fibre category, products differ by length, diameter, and surface treatment. MasterFiber MAC 360 uses a 54 mm length and embossed surface. Shorter macro fibres around 38 mm to 48 mm may disperse more easily in low-workability mixes but provide lower post-crack resistance at larger crack widths. Longer fibres above 60 mm may improve anchorage but increase the risk of balling in small hose diameters and congested formwork. The specific configuration of 0.8 mm diameter and 54 mm length is positioned for structural slab and shotcrete applications where pumpability and post-crack toughness must be balanced.

Exposure class limits for XC4 and XS2 service conditions

In concrete exposed to cyclic wetting and drying with chlorides, crack width limits govern the serviceability design. MasterFiber MAC 360 is used at 3 kg/m³ to 5 kg/m³ in slabs and walls to provide crack-width control after thermal and shrinkage loading. The fibre does not decrease the chloride diffusion coefficient determined by NT Build 443 or ASTM C1556, but it can reduce the continuity of shrinkage cracks that act as chloride ingress paths. In a crack width calculation under EN 1992-1-1, the contribution of macro fibre in the uncracked phase is not included; in the post-crack phase the residual tensile stress is used in the serviceability check. The exact residual stress value should be established by EN 14651 at the specified crack mouth opening displacement.

For XS2 marine splash exposures, the dosage should be selected from site-specific preconstruction testing rather than a default table. The fibre alone does not protect embedded steel from chloride-induced corrosion if the concrete cover is underspecified. In this context it is an auxiliary measure for crack control, not a corrosion protection system.