In ground-supported floor slabs produced for logistics terminals, distribution centers, and high-bay racking installations, SikaFiber 155 is introduced as an embossed macro-synthetic crack-control fiber that is specified by dosage rather than by mesh area. The acceptance route shifts from the nominal welded wire fabric area recognized in ACI 302.1R-15 to the flexural residual strength measured under ASTM C1609/C1609M-19a. A dosage of 4.0 kg/m³ corresponds to approximately 0.44 vol% at a polyolefin density of 0.91 g/cm³; a dosage of 6.0 kg/m³ corresponds to approximately 0.66 vol%. The slab designer retains the subgrade-drag-based joint spacing calculation because the lower elastic modulus of the polyolefin fiber does not increase the pre-crack flexural stiffness of the slab; the fiber contribution begins after the cement paste cracks, where the embossed surface anchors the polymer strand across the fracture face and transfers tension through mechanical interlock and surrounding matrix shear. The specified acceptance criteria should be the residual strengths at net deflections of L/600 and L/150, which are 0.75 mm and 3.0 mm for a 450 mm span under ASTM C1609, not the number of fibers per cubic meter alone.

Processing on production-scale equipment shows that fiber batching sequence controls dispersion more than fiber feed rate. The concrete truck mixer or central batch plant should add SikaFiber 155 after the aggregates, cement, and water have formed a uniform paste, and mixing should continue for 4–5 minutes after the final fiber dose at a drum speed of 12–18 rpm for truck mixers. Adding the dry embossed fiber as the first constituent can generate fiber balls that wrap around mixer blades and collect behind the charging chute; wash-out testing according to EN 14889-2:2006, Annex A is recommended on the first production batches, with a coefficient of variation of fiber content below 10% for stable production. Field placement of welded wire mesh has a separate documented failure mode: mesh chairs are loaded by foot traffic and concrete placement until the mesh rests on the subbase, leaving the upper third of the slab unprotected. The integral fiber distribution avoids this placement risk. Power-trowel finishing should be carried out with low blade angle and minimal additional water because over-finishing can draw surface fibers upward and create a fuzzy surface that is not a hardened aggregate wearing course. Contraction joints are retained at the spacing calculated from the slab thickness and shrinkage gradient; the fiber does not eliminate the need for joint cutting or load-transfer mechanisms at construction joints.

For high-bay racking legs with concentrated loads above 4.5 tonnes per leg, the slab section must still be designed as a plain or conventionally reinforced concrete slab because macro-synthetic fiber does not provide a one-for-one substitute for continuous steel reinforcement in resisting flexural tension or punching shear. The fiber is not a structural load path in the design sense of ACI 318-19 or EN 1992-1-1:2004; it controls crack propagation after the concrete has reached its tensile capacity.

What Changes When Embossed Macro Fiber Enters the Wet-Mix Shotcrete Stream?

When the mixed concrete enters the delivery hose of a wet-mix shotcrete pump, SikaFiber 155 is subjected to shear in the pump, the 50–75 mm delivery line, and the nozzle assembly before the alkali-free accelerator is injected. The product is batched at the plant, and the mix must remain pumpable at a slump of 150–200 mm while providing enough early stiffness after accelerator addition to adhere to the rock or soil substrate without sloughing. The lower specific gravity of the embossed polymer fiber compared with steel fiber reduces fiber segregation in the pump hopper, but early addition of dry fiber to dry aggregates can still create dry fiber balls that block the hose at the nozzle coupling. The central mixer must therefore run for at least 5 minutes after the final fiber dose, and the batch should be visually checked for dispersed fibers before being transferred to the shotcrete pump. Material compliance is checked against ASTM C1436/C1436M for shotcrete materials and ACI 506R-16 for placement practice.

Acceptance of fiber-reinforced shotcrete is based on energy absorption measured on statically compacted round or square panels, not on compressive cylinder strength alone. The governing test methods and typical acceptance bands are listed in the following matrix.

Nozzleman technique remains the controlling placement variable. The nozzle is held 0.5–1.5 m from the receiving surface, with air volume at the nozzle in the range of 5–10 m³/min at an operating pressure near 7 bar. Excessive air above 10 m³/min increases rebound and carries embossed fibers away from the fresh layer, while insufficient air below 5 m³/min produces a dense stream that does not compact the material and can leave shadowing behind reinforcing bars. Rebound of macro-synthetic fiber is generally lower than steel fiber on a mass basis, but the hardened in-place fiber content should still be verified by coring or wash-out on sprayed test panels rather than assumed from the batch sheet. The nozzle is moved in small circular passes to build layers of 50–100 mm per pass, and the next pass is placed only after the previous layer has achieved enough early strength to resist sagging. Alkali-free accelerators typically produce final set in 2–5 minutes at 20 °C, but cold substrate below 10 °C retards setting and requires revalidation of the accelerator dose under site conditions. The terminal product is a primary tunnel lining or rock-support membrane with post-crack residual load capacity, used before the final cast-in-situ lining or as permanent support in low-risk rock units.

Demolding, Handling, and Edge Protection in Precast Concrete

Precast boxes, utility vaults, offset risers, and drainage channels are stripped after 16–24 h of curing, when the cement paste has reached enough compressive strength for form release but not enough tensile ductility to resist lifting and transport microcracks at the edges of lifting sockets and form reveals. SikaFiber 155 at 3.0–5.0 kg/m³ provides isotropic post-crack tensile capacity after microcracks have initiated, and the governing compliance path is ASTM C1116/C1116M Type III synthetic fiber-reinforced concrete with plant quality control under Precast/Prestressed Concrete Institute MNL-116. Flexural performance is verified on beams per ASTM C1609, with the test beam taken in the same orientation as the in-service load path because external vibration at 50–60 Hz can orient fibers parallel to vertical mold faces. Edge spalling during demolding is reduced only when proper draft angles, form release agents, and lifting inserts are already present; the fiber does not replace these requirements. The terminal precast element is still designed for the same service loads as a reinforced or unreinforced concrete section under ACI 318-19 or EN 1992-1-1:2004, and the fiber is not a substitute for reinforcement mandated for structural bending, shear, or anchorage.

Fiber Volume Fractions Above 0.3% Alter the Post-Crack Flexural Response

For embedded rail systems in tramways, light-rail corridors, and port crane pavements, the concrete infill between or below the rails is often unreinforced in the thin cover zones above the rail foot. SikaFiber 155 is dosed at 4.0–6.0 kg/m³, producing a volume fraction above 0.3%, which shifts the post-crack response from a deflection-softening matrix toward a pseudoplastic or deflection-hardening response depending on the cement paste toughness and aggregate interlock. The transition is measured by ASTM C1609 residual strength at 3.0 mm net deflection; in a low water-cement ratio mix with rounded siliceous aggregate of 10 mm top size, the residual strength may be 30–45% of the first-crack flexural strength, but published data for this exact embossed geometry in rail-track concrete are limited and project-specific beams are required. In self-consolidating infill mixes with a slump flow of 600–700 mm per EN 12350-8, the fiber must be added at the batch plant and the slump flow must be measured before and after fiber addition because the fibers typically reduce flow by 50–100 mm. The terminal embedded rail slab must meet the rail housing geometry tolerances on the approved installation drawing; the fiber contribution is confined to crack-width control and spall reduction under dynamic wheel loads, not to the flexural capacity of the slab as a structural element.

Repair concrete and structural overlays placed on deteriorated bridge decks, parking garage ramps, and industrial loading bays introduce a differential moisture sink at the interface between the old substrate and the new cementitious layer. SikaFiber 155 is suitable for thicker section repairs exceeding 75 mm, where it is dosed at 4.0–6.0 kg/m³ and provides post-crack tensile capacity that reduces the propagation of shrinkage cracks in the overlay. The practical lower thickness boundary is approximately 2.5–3.0 times the nominal fiber length; below this, the embossed macro fiber approaches the overlay thickness and trowel finishing can lift fiber ends through the surface. The governing material specification is EN 1504-3 for structural repair products or ASTM C928/C928M-20 for packaged dry repair concrete, and mechanical properties must be established on the actual repair mix rather than on a generic concrete.

Surface preparation is the controlling process variable. The substrate is roughened by hydrodemolition or captive shot blasting to a concrete surface profile of at least CSP 6 per ICRI 310.2R, and a bonding slurry is applied before the repair concrete is placed by low-velocity pumping or by hand. Wet curing with a curing compound meeting ASTM C309 is required for at least 7 days because plastic shrinkage can overwhelm the crack-control contribution of the fiber if the overlay dries too quickly. The terminal product is a bonded repair layer that remains attached to the old concrete and does not act as an independent structural element; the fiber content is not a replacement for reinforcing steel where the overlay spans over a delaminated or spalled area.

When Shotcrete Ground Support in Deep Mining Requires Energy Absorption Beyond 700 J

In deep mining ground support, the rock mass around an advancing heading is subject to stress redistribution that can generate fractures, bulking, and ejection of rock fragments before the final lining is installed. Fiber-reinforced shotcrete containing SikaFiber 155 is applied as a surface support layer to contain loose rock pieces and to transfer ground pressure to rock bolts. The energy-absorption requirement is selected from the EFNARC panel test classes, with class E700 or E1000 typical for burst-prone ground and class E500 used in blocky but stable ground. The dosage required to reach a given class is not a linear function of fiber content; it depends on compressive strength, aggregate top size, silica fume content, and accelerator type. Published data for this specific embossed macro-synthetic fiber in hard-rock mining are limited, so the mix must be pre-qualified by round panels per ASTM C1550 or square panels per EN 14488-5 at the actual spray thickness and curing temperature.

Application in a typical underground heading uses a robotic manipulator with the nozzle held 0.5–1.2 m from the rock face. The first layer is sprayed to a thickness of 40–60 mm and allowed to set before the next pass; subsequent layers are built up to a total thickness of 80–120 mm depending on the rock mass rating and the required support class. The low-density embossed fiber tends to follow the cement paste stream instead of bouncing off the rock face, but excessive air volume can trap fibers in rough rock apertures and remove them from the effective cross-section. Spray operators verify in-place fiber content by coring the hardened shotcrete and conducting wash-out or visual inspection of core fractures. The terminal product is a rock-support membrane with residual load-bearing capacity after cracking; it is not a replacement for rock bolts, wire mesh, or lattice girders where the ground control plan requires them, but it can reduce the time spent on manual mesh installation and improve support continuity in irregular rock profiles.