Adfil Ignis 17/06 is a monofilament polypropylene microfibre supplied for dispersion in cementitious matrices, where the primary function is the reduction of explosive spalling during fire exposure. The model designation identifies a nominal filament diameter of 17 µm and a nominal cut length of 6 mm; the geometric ratio yields an aspect ratio of approximately 353. The product is introduced at mass dosages commonly between 1.0 kg/m³ and 3.0 kg/m³, although dosage selection is usually determined by section geometry, heating curve, concrete compressive strength and moisture condition. In this application the fibre is not specified to increase flexural toughness, shear capacity or ultimate tensile resistance; it is a sacrificial organic inclusion that acts after the onset of cement dehydration.

At a nominal density of 910 kg/m³, a single 17 µm × 6 mm filament has a calculated volume of 1.36 × 10⁻¹² m³ and a mass of approximately 1.24 × 10⁻⁹ kg. The corresponding fibre population is approximately 8.1 × 10⁸ fibres/kg. At a 2.0 kg/m³ addition, the theoretical number of fibres per cubic metre is about 1.6 × 10⁹. This high population is the main technical distinction between fire-protection microfibres and larger-diameter polymer fibres: it controls the density of potential melt channels that can relieve internal pore pressure. Because fibre count changes with the square of filament diameter, a 10% diameter deviation changes the calculated population by roughly 20%. Batch acceptance should therefore verify diameter and length against the supplier’s declared values.

Product conformity for polymer fibres intended for concrete is typically assessed against EN 14889-2:2006. Polypropylene microfibres of this type are normally regarded as Class II fibres because they are not relied upon for structural load-bearing. A Type III technical datasheet and downstream factory production control certificate should state nominal diameter, cut length, density, alkali resistance and the absence of substances that would adversely affect cement hydration. For fire-protection service, the fibre is also commonly evaluated within concrete specimens under ISO 834-1 or EN 1363-1 heating conditions, with spalling depth and mass loss recorded at specified exposure intervals.

Values listed are compiled from manufacturer-published typical data; batch-specific certificates may vary. The fibre is hydrophobic and does not require pre-drying under relative humidity above 60%. Storage should be in closed packaging below 50 °C and shielded from direct ultraviolet exposure to reduce oxidative surface degradation.

What Processing Boundaries Apply in High-Dosage Fire Protection Mixes?

In production-scale batching, the fibre should be added to the aggregate stream or a dry-mix stage before water is introduced. Addition to a flooded mixer is a documented cause of fibre balling, particularly at dosages above 2.0 kg/m³ in low-slump or high-strength concretes. Twin-shaft compulsory mixers with wet mixing times of 60 s to 120 s after fibre introduction are generally adequate for distribution. For planetary pan mixers used in dry-cast or semi-dry precast manufacture, an extension of 15 s to 30 s is typically required to eliminate clumps. Pneumatic transport from silo to weigh hopper should be checked for fibre loss at bends; an accessible inspection point after the last bend reduces unquantified dosing errors.

Rheological modification is expected at upper fire-protection dosages. Polypropylene microfibres raise plastic viscosity and can lower slump by 10 mm to 40 mm in concretes with normal aggregate gradings. The usual corrective measure is a polycarboxylate ether superplasticiser conforming to EN 934-2. Air content should be monitored by EN 12350-7 in freeze–thaw applications because the fibres can change air-void formation and spacing factor; trial mixes are required when both fire spalling resistance and XF exposure classes are specified under EN 206. The fibre is compatible with ordinary Portland cement, slag cement and fly ash systems, but its effect on water demand may be more noticeable in free-flowing self-compacting concrete than in stiff earth-moist mixes.

Mechanistically, spalling protection occurs when the polypropylene melts in the range 160 °C to 170 °C. Before melting, differential thermal contraction of the polymer relative to cement paste creates annular interfacial microcracks. After melting, the former fibre channels create pressure-relief paths for water vapour released by dehydration of calcium silicate hydrates and ettringite. In dense concrete with permeability below 1 × 10⁻¹⁸ m², the vapour-pressure rise can approach or exceed the tensile strength of the material; the melt-channel network is intended to increase effective gas-permeability sufficiently to prevent explosive spalling. Published product-specific data for this configuration is limited; design verification therefore should include fire testing of representative concrete specimens rather than reliance on fibre dosage alone.

Batch-to-batch variation in cut length and diameter should be controlled because the derived fibre count depends on d² × L. A diameter shift from 17 µm to 18 µm reduces fibre count by approximately 11% at constant length. A length shift from 6 mm to 5.5 mm reduces individual fibre volume and increases count by approximately 9%. These changes can alter the spacing of pressure-relief channels in the heated concrete. Supplier batch certificates should state measured mean diameter, mean length and coefficient of variation, not only nominal values.

When Hydrocarbon or Modified Hydrocarbon Curves Govern Tunnel Lining Design

Tunnel segment linings exposed to the Rijkswaterstaat RWS curve, the HCM curve, or the modified hydrocarbon curve experience surface temperatures above 1000 °C within minutes. The severe thermal gradient drives moisture toward the interior and creates a quasi-saturated layer behind the drying front. In these applications, Adfil Ignis 17/06 is typically specified between 1.5 kg/m³ and 3.0 kg/m³, often in high-strength concrete with a water–cement ratio below 0.40. The product does not replace steel fibres or polypropylene macrofibres when post-crack flexural toughness or structural load capacity is required; it may be combined with steel fibres if the concrete specification separates spalling resistance from mechanical reinforcement.

Precast carousel plants producing tunnel segments generally use high-shear compulsory mixers of 1.0 m³ to 3.0 m³ capacity. Fibre introduction after coarse aggregate and before water reduces segregation and improves distribution. Wash-out tests on fresh concrete are common plant-level verification: a sample is washed through a 0.5 mm sieve, and retained fibre mass is compared with the nominal batched mass to detect fibre loss in conveying or balling in the mixer. Concrete placement by formwork-injection or tunnel-segment moulds should maintain concrete temperature below 30 °C during transport to avoid excessive slump loss and premature hydration.

Fire testing of tunnel segments is usually based on ISO 834-1 supplemented by hydrocarbon or RWS curves; spalling depth, temperature at reinforcement and residual concrete cross-section are recorded after defined durations. The fibre is not a substitute for minimum concrete cover, aggregate selection, or post-fire structural assessment. A detailed record of fibre dosage, mixing time, concrete temperature and air content should be maintained for each batch because deviations in any of these variables can alter dispersion and therefore the fire-protection result.

Compared with steel fibres, Adfil Ignis 17/06 has an elastic modulus approximately two orders of magnitude lower; it does not increase measured residual flexural tensile strength and is not considered structural reinforcement. Steel fibres retain their solid phase at fire temperatures and do not create the same controlled melt-channel network. Their higher thermal conductivity can also contribute to heat transfer into the concrete cover. Cellulose fibres decompose at temperatures below 200 °C, before the critical vapour-pressure peak in dense cement paste, and therefore do not provide reliable pressure relief under hydrocarbon heating. Coarser polypropylene macrofibres with diameter above 100 µm provide far fewer potential melt channels per unit mass; at 32 µm diameter and 6 mm length, the calculated fibre count is approximately 2.3 × 10⁸ fibres/kg, compared with 8.1 × 10⁸ fibres/kg for the 17 µm product.

For concretes requiring both spalling resistance and structural toughness, a hybrid system of Adfil Ignis 17/06 and steel fibres is sometimes used. The microfibre dosage is selected by fire testing or prescriptive guidance, while the steel fibre dosage is separately determined from flexural toughness classes in EN 14845-1 or slab design calculations. The two fibre types occupy different size scales and should be added sequentially to prevent entanglement: steel fibre first with aggregates, polypropylene microfibre before water. Production-scale experience indicates that combining fibres increases plastic viscosity more than either fibre alone, requiring additional water-reducing admixture and longer mixing time to reach uniform distribution.

Adfil Ignis 17/06 is therefore positioned as a fire-protection microfibre with a high filament population per unit mass, not as a reinforcement fibre. Its functional boundary is the heat-induced creation of dispersed pressure-relief channels in dense or moisture-saturated concrete. Mix design verification should include fire spalling tests, fresh-concrete fibre-content checks and hardened-state compressive strength tests under the relevant project specification, because the fibre alters rheology and may require adjustments to paste volume, superplasticiser dose and mixing sequence.