A high-surface-area fine monofilament polypropylene fiber for cementitious systems is introduced under the trade designation SikaFiber 112. The product is supplied in a water-soluble bag system and is intended primarily for the control of plastic shrinkage cracking in concrete and mortar. Published technical data list a nominal fiber length of 12 mm, a nominal diameter in the range of 28 µm to 32 µm, and a polypropylene matrix with a density of 0.91 g/cm³. The fiber is classified as a Class I polymer microfibre under EN 14889-2:2006 and is supplied in bags that dissolve during batch mixing, thereby reducing direct handling and airborne fibre discharge. The manufacturer specifies a typical addition rate of 0.6 kg/m³ to 0.9 kg/m³, with the higher value recommended for flatwork exposed to high evaporation rates, wind, or low relative humidity. At a dosage of 0.9 kg/m³, the calculated fiber count is approximately 1.3 × 10⁸ fibres/m³ when the diameter is taken as 28 µm; this high number density is the basis for crack-width suppression in the plastic state, not post-crack structural capacity.

How does a 12 mm, 28 µm monofilament suppress plastic shrinkage cracks?

Plastic shrinkage cracking occurs when the bleed-water supply at the concrete surface is exceeded by the evaporation flux. The resulting menisci in capillary pores generate negative pore-water pressure that can reach 30 kPa to 50 kPa in the first few hours after placement under high evaporation conditions. The fine monofilament geometry of SikaFiber 112 induces a dispersed network of high-count fibres that raises the tensile strain capacity of the fresh paste and increases the tortuosity of crack propagation. This mechanism is validated by restrained cracking tests such as ASTM C1579-21, in which fibre-bearing panels are compared with plain concretes under controlled wind and temperature exposure. The polymer fiber does not chemically participate in cement hydration; its crack-control function is purely mechanical and exerts no measurable pozzolanic or hydraulic activity.

The 28 µm diameter is sufficiently small to produce a high specific surface area without causing the clumping or baling observed with some fibrillated polypropylene tapes. When dispersed, the fibres bridge localized microcracks while the paste is still fluid. The low elastic modulus of polypropylene, approximately 3.5 kN/mm², means that the fibre yields locally at higher crack-opening displacements rather than sustaining structural load. For this reason, SikaFiber 112 is specified for concrete surface durability and early-age crack reduction, not for hardened-state residual flexural strength governed by EN 14651:2005+A1:2007 or ASTM C1609/C1609M-19.

In slab-on-grade placements with a surface area exceeding 500 m², plastic shrinkage crack control is often required when the evaporation rate exceeds 1.0 kg/m²/h according to hot-weather concreting guidance such as ACI 305.1. At a dosage of 0.9 kg/m³, SikaFiber 112 is batched directly into the agitator after the fine aggregate has been charged. Field data from large-area industrial floors show that the fibre reduces average crack area under ASTM C1579-21 test conditions by more than 60% relative to a plain control mix, although the exact reduction depends on aggregate grading, cement content, and evaporation rate. The addition increases the water demand by a measurable amount; if no water adjustment is made, slump measured by EN 12350-2 may drop by 10 mm to 20 mm at 0.9 kg/m³. A site trial remains necessary because crushed angular coarse aggregates with high void content can amplify workability loss more than rounded gravel.

Batching, Dispersion, and Mixer Shear Requirements

The water-soluble bag is designed to dissolve during the mixing cycle, and should not be opened manually unless the bag passes through a mechanical feeding hopper. In a twin-shaft compulsory mixer of 2.5 m³ batch capacity, a wet mixing period of 4 to 5 minutes at 20 rpm is generally sufficient to eliminate visible fibre agglomerations. In truck-mixed concrete, the bag is discharged onto the aggregate conveyor or into the drum prior to the addition of water; the drum speed is held at 12 rpm to 14 rpm for 2 minutes per m³ after all materials are charged. Lower drum speeds, below 8 rpm, result in incomplete bag dissolution and fibre clumping at the rear of the drum in stiff mixes with a water-cement ratio below 0.40.

Fibre distribution is influenced by aggregate surface area and paste volume. Lean mixes with a paste volume below 250 L/m³ present a higher risk of fibre balling because the reduced paste film thickness prevents filament separation. The use of superplasticizer to compensate for the mild increase in yield stress is preferable to adding water, because water addition changes the water-cement ratio and can negate the crack-control benefit by increasing bleeding and drying shrinkage. Air content should be rechecked after fibre addition using EN 12350-7 or ASTM C231/C231M; high-surface-area microfibres can reduce entrained air content by 0.5 to 1.0 percentage points in mixes containing air-entraining admixtures.

In precast operations producing thin architectural panels with a slump of 100 mm to 150 mm, SikaFiber 112 has been used at 0.6 kg/m³ to reduce early-age edge cracking without altering surface finish. The fiber is compatible with standard mould-release agents and does not require chloride-containing accelerators. Because polypropylene is hydrophobic and has a low melting point of 160 °C, the product is not intended for applications where concrete is subjected to sustained temperatures above 80 °C during steam curing or long-term service. Published data for this specific configuration at higher curing temperatures is limited, and trial validation is advised before specifying the fiber in autoclaved aerated concrete or high-pressure steam curing regimes.

When a 0.9 kg/m³ addition rate is specified in pumped structural concrete

The combination of a 12 mm microfibre and a pumpable concrete mix requires attention to hose diameter and aggregate shape. Blockage risk is low in well-proportioned mixes with a maximum aggregate size of 20 mm, a minimum cementitious content of 350 kg/m³, and a slump of at least 160 mm before fibre addition. Field experience with truck-mounted concrete pumps indicates that the main bottleneck is not the fibre itself but the reduction in paste mobility caused by the high filament count. The pressure loss across a horizontal 125 mm delivery line is dominated by aggregate content and paste rheology rather than by fibre content; published data for the additional pressure loss at 0.9 kg/m³ in a specific mix is limited, and a site pump trial is required before establishing maximum pumping distance.

In high-rise placements exceeding 150 m vertical height, the mix is typically designed with a higher fine-paste volume and a polycarboxylate ether superplasticizer. Under these conditions, SikaFiber 112 does not require pre-drying at relative humidity below 60%. The water-soluble bags do, however, lose strength when stored at relative humidity above 80% or in direct contact with water before batching. Storage should be on pallets in dry, covered conditions at 5 °C to 35 °C.

In concrete walls with a placement height of 3.0 m to 4.0 m, plastic settlement cracking can occur over top reinforcement where the concrete has been held in a static state after casting. The addition of 0.9 kg/m³ SikaFiber 112 reduces the visible settlement crack length by creating a uniform internal filament network that resists differential movement between the paste and the top bars. The effect is more pronounced when the concrete has a slump of 180 mm to 220 mm and is placed without vibration delays. Because the fibre does not increase yield stress to the same degree as cellulose ethers or silica fume, it may be selected in architectural concrete where surface retardation is not permitted.

Comparative Position Against Steel and Macro-Synthetic Fibres

The table summarises the fundamental difference in density and stiffness between microsynthetic polypropylene and load-bearing reinforcement fibres. The 0.91 g/cm³ density of SikaFiber 112 delivers a high filament count at low mass dosage, but the modulus of elasticity of 3.5 kN/mm² to 4.0 kN/mm² is too low to replace steel at cracked section equilibrium. A structural steel fibre with 200 kN/mm² modulus and 35 mm to 60 mm length mobilises anchorage through yielding or pullout under EN 14651 testing, whereas a 12 mm microfibre cannot bridge cracks wider than 0.2 mm to 0.5 mm with significant residual force. The product therefore occupies a distinct specification function: plastic-shrinkage crack control, improved early-age surface integrity, and reduced plastic settlement cracking in deep sections, rather than partial replacement of conventional crack-control steel reinforcement.

Compared with fibrillated polypropylene microfibres, the fine monofilament construction of SikaFiber 112 reduces mechanical interlocking between filaments during dry feeding, so dispersion is more uniform in low-paste mixes. Fibrillated fibres can open into a net-like structure during mixing, which can be beneficial for crack control but may also entrap air and increase mixing torque. Monofilament geometry produces a smaller visible surface effect after finishing and is generally less prone to protruding fibres on the hardened surface when the slab is power-trowelled.

For CE marking under EN 14889-2:2006, the producer is required to declare the fiber class and the effect on plastic shrinkage cracking using a specified test method from the standard’s evaluation regime. The user is responsible for verifying that the delivered bags carry the correct CE label and batch number, and for recording the actual dosage per mixer load. In regulatory concrete production, dosage is typically checked by counting the number of water-soluble bags added per batch against the batch volume, rather than by post-placement extraction. No chemical incompatibility with calcium chloride, water-reducing admixtures, or air-entraining admixtures has been documented at the addition rates specified.

Limits in High-Temperature Steam Curing and Structural Use

Although polypropylene is resistant to alkalis and most salts, the melting point of 160 °C disqualifies the product from autoclaved aerated concrete production where saturation pressures correspond to temperatures of 180 °C to 200 °C. The product is also not a substitute for macro-synthetic or steel fibre reinforcement in elements requiring a specified restrained flexural residual strength. Published data for post-crack toughness of SikaFiber 112 is limited; therefore, if the structural specification requires a residual flexural strength class under EN 14651:2005+A1:2007 or a flexural toughness ratio under ASTM C1609/C1609M-19, the design must incorporate an appropriate structural fibre and treat the microfibre as a supplementary early-age crack-control system.