Cast-in-place industrial floor slab production requires a controlled addition sequence when Adfil Sinta 22/12 (SINTA VBA M2212) monofilament polypropylene microfiber is used at 0.9 kg/m³ to 1.2 kg/m³ in ready-mixed concrete placed by laser screed or power trowel. The product is charged into the mixer after the initial aggregate and water charge has formed a homogeneous paste because the 22 mm monofilament can develop electrostatic clusters when introduced into a dry cement–aggregate blend at relative humidity below 35%, particularly in winter batching plants with heated aggregates. For slab-on-grade and suspended floor mixes with a 20 mm nominal maximum crushed limestone aggregate, the reference concrete for trial batching should contain 320 kg/m³ CEM II/A-LL 42.5 N, 180 kg/m³ water, and a water–cement ratio of 0.48. Restrained plastic shrinkage testing conducted under ASTM C1579-21 on monofilament polypropylene microfiber concrete demonstrates lower crack width index values than an unreinforced reference mix of identical paste volume; published data for the exact M2212 variant in this test configuration is limited, so a plant trial against a reference slab remains the specified verification method before production placement.

Mixing in a twin-shaft compulsory mixer at 18 rpm to 22 rpm for 5 min after fiber addition is specified to disperse the filaments through the paste without exceeding the shear threshold that can fragment the monofilament and reduce its crack-bridging efficiency. If the fiber is added in the truck mixer on site, the drum must be charged at low speed and mixed for 2 min per cubic metre at mixing speed; charging dry fiber into a rapidly rotating drum causes fiber matting on the hopper and non-uniform distribution. The terminal product in this segment is a hard-trowelled interior logistics floor, an exterior hardstanding, or a suspended slab over metal decking, with crack control requirements tied to joint spacing and exposure classes in EN 206:2013/A2:2021. During finishing, the bleed water must remain on the surface until the first trowel pass; power-trowelling too early presses the top 1–2 mm of paste over fibers and can produce fine surface fuzz that is cosmetically visible under high-gloss coatings without reducing compressive strength.

Compliance for this application follows EN 14889-2:2006 Class I microfibre with nominal diameter below 0.3 mm and ASTM C1116/C1116M-10a Type III synthetic fiber-reinforced concrete. The polypropylene specific gravity of approximately 0.91 prevents the filaments from settling to the bottom of the slab under normal vibration. Because the microfiber is hydrophobic and inert in the alkaline pore solution at pH 12.5–13.5, it does not participate in the cement hydration reaction and does not require adjustments to the design cover for steel reinforcement. The operational boundary is the mixing moisture state: the product must be stored below 60% relative humidity, and pre-drying is required if bag storage has been exposed to condensation, because damp fibers do not separate in the mixer and can create agglomerates that survive the mixing cycle.

Table 1. Compliance and test method reference matrix for cast-in-place floor slab applications.

What Limits Wet-Mix Nozzle Carrying Capacity at Fibre Doses Above 1.2 kg/m³?

Rotor-type piston pumps with a 65 mm delivery line and production rates between 8 m³/h and 14 m³/h are the main placement equipment for wet-mix sprayed concrete in tunnel and underground shaft support. At 1.0 kg/m³ of Adfil Sinta 22/12, the high filament count of a 12 µm-class monofilament modifies the paste viscosity without materially changing the pump stroke pressure; at 1.2 kg/m³ and above, nozzle surging becomes observable when the aggregate packing is already optimized for an 8 mm nominal maximum size and the paste volume is below 380 L/m³. Published data for this specific product in wet-mix shotcrete is limited, but the response is consistent with the known relationship between fiber count per cubic metre, paste film thickness on aggregate surfaces, and delivery line resistance in dense-phase pumping.

Dosage for primary tunnel support and slope stabilization is normally 0.9 kg/m³ to 1.2 kg/m³ when the function is early-age crack control and green cohesion. This range does not replace steel fiber if EN 14487-2:2006 requires post-crack energy absorption above 500 J in panel tests to EN 14488-5:2006. In high-strength sprayed concrete for fire spalling control, the dosage is raised to 2.0 kg/m³ because the polypropylene filaments melt at 160–165 °C and generate interconnected channels for vapour pressure relief when the lining is exposed to hydrocarbon curve fire conditions. The terminal product includes temporary and permanent sprayed concrete linings for road tunnels, rock support in shafts, and erosion-resistant slope shells.

The fiber is batch-mixed into the wet-mix before it is fed to the pump hopper. Dry addition at the nozzle is not recommended for this monofilament geometry because the low per-filament mass of a polypropylene product with density class 0.9 g/cm³ causes separation in the compressed-air stream and produces locally fiber-rich patches on the receiving surface. In a forced-action pan mixer, batch time of 3–4 min after fiber introduction is sufficient for visual dispersion; the sprayed surface is inspected under oblique light after the first pass for raised nodules that indicate undispersed fiber clumps. When ambient temperature drops below 5 °C or the aggregate moisture content exceeds 3% by mass, the dosage is held at 0.9 kg/m³ until fresh property tests to EN 12350-2:2019 for slump and EN 12350-7:2019 for air content confirm a stable mix.

Table 2. Sprayed concrete quality control methods under wet-mix application with monofilament PP fibre.

Precast segmental lining production is carried out in automated carousel plants where demoulding occurs at concrete cube strengths of 12–14 N/mm². Edge crumble and lift socket cracking are the primary early-age defects in this segment, and Adfil Sinta 22/12 is dosed at 0.6 kg/m³ to 0.9 kg/m³ into the pan mixer after the fine aggregate and before the cement slurry is discharged from the high-speed slurry mixer. The lower bound is used when external mould vibrators operate at 50–60 Hz and the mix must transfer from the skip into the battery mould without excessive air entrapment; the upper bound is permitted only if the flow of the self-compacting mix remains above 600 mm on the EN 12350-5:2019 flow table.

Mix design for segmental linings with a 0.34 water–cement ratio and 450 kg/m³ CEM I 52.5 N uses a 10 mm maximum aggregate size, polycarboxylate high-range water reducer at 1.0% by cement mass, and the microfiber at 0.6 kg/m³. Because the 22 mm monofilament is chemically inert, it does not alter the chloride ion migration coefficient measured by NT Build 492; however, trial mixes with the M2212 product are required when the fine aggregate contains more than 12% passing the 0.125 mm sieve, because fiber filaments can reduce filling ability by increasing paste yield stress. Demoulding performance is the functional target: at strengths below 15 N/mm², green concrete is susceptible to brittle tensile failure at sharp mould corners, and the monofilament network bridges microcracks before pull-out at low strain.

The final product is a segmental tunnel lining ring with a 100-year design service life under EN 1992-1-1 exposure classes XC2 or XD3. The polypropylene monofilament remains inert in the alkaline pore solution and does not generate corrosion staining at segment joints. This application does not use the microfiber as structural reinforcement, and the product must not replace steel bar reinforcement or steel fibers in tensile zones such as radial joints, lifting anchors, or gasket grooves. The specific operational boundary for the precast plant is demoulding at strengths below 8 N/mm²; in that case the fiber dosage is reduced to 0.3 kg/m³ and edge protection is maintained by retarding the mould release process rather than relying on the fiber network.

When Cementitious Underlayments Are Applied Over Low-Absorption Substrates

Self-levelling underlayment mixes that are pumped over power-floated concrete, ceramic tile backings, or steel decking tend to retain free water at the interfacial zone when substrate water absorption is below 0.5% by mass. Adfil Sinta 22/12 is incorporated at 0.6 kg/m³ to 0.9 kg/m³ to increase internal surface area and reduce upward free-water migration in thin layers of 3–10 mm. The polypropylene monofilament acts as a distributed bleed control medium rather than as a structural reinforcement, and this dosage range is selected to maintain the self-smoothing action of the mortar without increasing the plastic viscosity beyond the pumping window of a worm pump with 25 mm internal diameter hose.

The dry formulation for a pumpable underlayment contains 0.35–0.45 water–dry-mortar ratio, 25 kg bagged product, and 0.6 kg/m³ fiber, with a flow target of 280–300 mm on the ring-flow method in ASTM C1708/C1708M-19. Mixing is carried out with a high-shear mixer at 600 rpm for 90 s; the fiber is added to the dry blend before mixing water to prevent hydrophobic surface wetting inhibition. Above 1.0 kg/m³, pumpability through the 25 mm hose may become unstable when the underlayment is applied at a thickness below 5 mm, and the hopper should be fitted with a 6 mm mesh strainer to capture any dry fiber agglomerates. The terminal product is a smoothing and filling layer under vinyl, LVT, epoxy, or ceramic floor coverings, with shrinkage restraint verified by EN 13813:2002 and ASTM C1581/C1581M-18a.

The microfiber does not contribute to the compressive strength class designation under EN 13813:2002; its function is confined to crack control during the first 24 h. The material specification must therefore list fiber content separately from binder performance, and the specified underlayment thickness must not be reduced because of the presence of fibers. Air content should be measured to EN 1015-7 when the mix is combined with polymer powder modification, because the monofilament can stabilise entrained air bubbles under high-shear mixing and shift the hardened density if mixer speed is not controlled across successive batches.

Machine-applied repair mortars and grouts depend on thixotropic yield stress for overhead placement and on low bleed for bond strength. Adfil Sinta 22/12 is incorporated at 0.3 kg/m³ to 0.5 kg/m³ in non-shrink grout and at 0.6 kg/m³ in machine-applied R4 repair mortar conforming to EN 1504-3:2005. The lower dosage in grout preserves capillary suction at the prepared concrete substrate; overdosing above 0.5 kg/m³ can reduce substrate wetting and may require a lower-solids primer to maintain the specified adhesion strength. In repair mortars, the 0.6 kg/m³ dosage controls plastic settlement cracks at the interface of horizontal and vertical repair patches without reducing the thixotropic buildup required for overhead spraying.

The mixing sequence is specific to the delivery method. Dry components including 0.6 kg/m³ of the 22/12 monofilament are pre-blended for 60 s in a horizontal shaft paddle mixer at 30 rpm; water is then added over 30 s at low speed, followed by high-speed dispersion at 600 rpm for 2 min. Spray application through a worm pump with a 15 mm nozzle and 2.5 bar compressed air deposits a dense paste rather than a high-velocity stream, which eliminates the rebound losses seen in dry-spray repair materials. The terminal product is an EN 1504-3 Class R4 structural repair layer applied in 10–20 mm lifts, or a non-structural surface fairing layer at 3–5 mm thickness where crack bridging is not the design intent.

Compliance for the repair segment references EN 1504-3:2005 for structural and non-structural repair mortars and ASTM C1581/C1581M-18a for restrained shrinkage of mortar. Polypropylene monofilament is inert with styrene–butadiene rubber and acrylic polymer powders used in repair mortars; polymer film formation at 23 °C and 50% RH proceeds unaffected. The microfiber does not conduct current and does not compromise the passivity of reinforcing steel when the repair is applied to chloride-contaminated concrete after substrate preparation. It is not a substitute for reinforcing bars where the structural design requires load transfer across the repair boundary, and it should not be used as the sole reinforcement in a patch that must satisfy load-bearing capacity under EN 1504-3:2005 structural requirements.

Low-Slump Dry-Cast Pipe Reinforcement and the Function of 22 mm Cut Length

Dry-cast pipe machines operate at zero slump and rely on immediate demoulding after vibro-compaction. The steepest process risk is vertical demoulding fracture when the green pipe is lifted from the core and outer jacket. Adfil Sinta 22/12 is distributed through the zero-slump mix at 0.4 kg/m³ to 0.7 kg/m³, with the upper bound reserved for pipe diameters above 600 mm and wall thickness below 100 mm. At these dosages the monofilament bridges plastic settlement cracks around the reinforcing cage during compaction but does not interfere with the mechanical bond between steel reinforcement and the dry-cast matrix.

Mixing is carried out in a planetary mixer at 12–15 rpm for 90 s after fiber addition. The free-water content is held between 6.5% and 8.0% by mass of cement, and compaction is achieved by eccentric vibration at 60–65 Hz for 12–18 s. The 22 mm cut length is more effective than fibers below 12 mm at bridging cracks that initiate at the tip of the compaction head, while fibers above 30 mm would have a higher probability of wrapping around the vibration shaft and forming localized fiber nests. The terminal products include stormwater and sanitary sewer pipes conforming to EN 1916:2002/AC:2008, jacking pipes, culverts, and manhole riser sections. Wet and dry acceptance testing follows ASTM C497-20; the presence of the microfiber does not change the specified hydrostatic leakage limit for the pipe class.

Polypropylene monofilament is hydrophobic, so water absorption of the dry-cast matrix is not affected at the stated dosages; this is relevant for frost-resistant pipe classes tested to CEN/TS 12390-9:2016. Field data on freeze–thaw salt-scaling resistance of M2212-containing dry-cast pipe is limited, and plant-specific trial mixes are recommended where exposure class XF3 or XF4 applies. The fiber is added after the aggregate but before the water to avoid hydrophobic floating on the mix surface during planetary mixing; if the plant uses recycled slurry water, the fiber dosage should be checked against the higher solids content because the filament can interact with the slurry and reduce the compacted green strength at dosages above 0.7 kg/m³.