In slab-on-grade construction for distribution centres and logistics terminals, MasterFiber MAC 2200 CB is charged at the batch plant after coarse aggregate and before final mixing water, at addition rates from 3.0 kg/m³ to 5.0 kg/m³. The batching sequence prevents fiber balling in a twin-shaft compulsory mixer with a wet mixing time of 5 minutes to 7 minutes after fiber introduction. A water-reducing admixture conforming to ASTM C494/C494M-19 Type A or Type F is used to maintain a slump of 150 mm ± 20 mm at the paver, because the chemically enhanced polypropylene surface increases paste demand by 5 kg/m³ to 10 kg/m³ of cementitious paste. Pumping through a 32 m boom pump with 125 mm line does not require changes to air entrainment, provided air content measured per ASTM C231/C231M-22 is held at 2.0% to 4.0% for interior slabs not exposed to freeze-thaw cycling. The terminal floor is typically a rack-supported slab with joint spacing limited to 4.5 m by saw-cutting within 8 hours to 12 hours of final finishing under ACI 360R-10 guidance. Residual flexural performance is verified after 28 days by ASTM C1609/C1609M-19, using third-point loading on 150 mm × 150 mm × 500 mm beams. At 3.0 kg/m³, the fiber contribution is usually limited to crack-width control after first crack; at 5.0 kg/m³, the specimen typically maintains rising load-carrying capacity past a deflection limit of L/600. Fiber distribution is checked by washing out 0.01 m³ samples at the discharge chute and inspecting for clumps larger than 25 mm, which must not exceed 1 clump per 0.5 m³ of placed concrete. When finished with a ride-on trowel, blade angle is reduced by 10° to 15° compared with plain concrete to avoid tearing surface fibers. ACI 302.1R-15 recommends a membrane-forming curing compound conforming to ASTM C309 applied at 0.20 L/m², and wet curing is extended by 24 hours when ambient relative humidity drops below 40%.

What Changes in Demoulding Cycle Times when Macrofiber Replaces Steel Mesh in Precast Panels?

Non-structural precast elements such as utility vaults, retaining wall panels, box culvert covers, and slatted flooring are cast with MasterFiber MAC 2200 CB at 4.0 kg/m³ to 6.0 kg/m³ to eliminate mesh cutting and fixing labour. The fiber is introduced into a planetary counter-current mixer after aggregate and cement are dry-blended for 30 seconds; the remaining mixing time is 90 seconds to 120 seconds at high speed after fiber addition. Formwork is filled using external vibrators operating at 12,000 vpm to 16,000 vpm, applied in 10-second intervals to avoid fiber orientation collapse near vertical faces. Stripping time is governed by the minimum demoulding strength of 10 MPa to 12 MPa measured by rebound hammer and correlated to cylinders per ASTM C39/C39M-21. Because macrofiber does not provide the same early-age flexural capacity as steel reinforcement, precast units with slenderness ratios above 20 still require lifting beam inserts and cannot rely on fiber alone during demoulding. The surface finish of vertical precast elements is checked after stripping for visible fiber clumps, and any clump exceeding 15 mm in length is rejected under the precaster’s own visual acceptance protocol. Curing is performed under a thermostatically controlled steam regime at 60 °C for 8 hours, followed by 3 days of ambient air curing before load transfer.

Tunnel Lining Shotcrete and Rebound Behaviour in Wet-Mix Application

Wet-mix sprayed concrete for permanent rock support in non-aggressive ground is produced with MasterFiber MAC 2200 CB at 7.0 kg/m³ to 9.0 kg/m³ to reduce plastic shrinkage and control early-age cracking around rock bolts and lattice girders. The concrete is batched at a slump of 180 mm to 200 mm, stabilised with a polycarboxylate ether superplasticiser conforming to EN 934-2:2009, and transported within 45 minutes to the shotcrete robot. The fiber is added at the batch plant, not at the nozzle, because post-nozzle fiber injection can disrupt the accelerator stream and create fiber-rich pockets in the sprayed layer. Hydration control is achieved with an alkali-free liquid accelerator dosed at 3% to 5% by cement weight, adjusted at the pump to maintain early strength of 1 MPa at 6 hours measured by needle penetration per EN 14488-2:2006. Rebound is controlled by nozzle distance of 1.0 m to 1.5 m, air flow of 5 m³/min to 8 m³/min, and wall overspray thickness removal before final layer application. Published data for rebound reduction in this specific fiber configuration is limited; therefore rebound acceptance must be established through on-site panel tests rather than transferred from steel fiber shotcrete records. The terminal sprayed lining is tested for flexural toughness using ASTM C1550-20 round panel tests on 75 mm thick specimens sprayed in the same orientation as the tunnel lining. At 7.0 kg/m³, the panel energy absorption at 40 mm central deflection is typically higher than early-age plastic shrinkage control levels but lower than steel fiber shotcrete at equivalent dosage; designers therefore maintain the steel lattice girder system for structural capacity. Fiber dispersion is verified at the nozzle by washing 10 L samples through a 4.75 mm sieve and counting retained fiber clumps, with a rejection limit of 3 clumps per 10 L. The concrete pressure at the nozzle is maintained between 0.5 MPa and 0.8 MPa to prevent segregation. Overspray containing macrofiber is not recirculated into the batch because variable fiber content cannot be homogenised within the wagon mixer.

If Composite Metal Deck Construction Limits Finishing Time, the Fiber Addition Sequence Becomes More Sensitive than Slab Thickness

Slabs cast on galvanised steel deck in composite floor systems are dosed with MasterFiber MAC 2200 CB at 1.8 kg/m³ to 3.0 kg/m³ to replace light-gauge welded wire reinforcement for crack control in negative moment regions above girders. The placement is pumped through a 50 mm rubber hose with concrete slump maintained at 140 mm ± 20 mm per ASTM C143/C143M-20. Because the fiber is hydrophobic and chemically enhanced, it disperses under the high shear of a truck-mounted pump without floating to the troweled surface if the finisher waits 15 minutes to 20 minutes after strike-off before first floating. In this application, the use of a bull float is limited to a single pass; repeated floating can draw fibers toward the top 6 mm and produce a hairy surface after burnishing. The terminal floor is a composite metal deck slab with a cover slab thickness of 65 mm to 90 mm over the deck ribs; flexural residual strength is tested by ASTM C1399/C1399M-10 at a net deflection of L/300, not ASTM C1609, because section depth is too small for beam testing. Published data for this specific composite section is limited, so qualification testing must use the specified deck profile and concrete cover rather than flat-slab specimens. Bond between the concrete cover and the steel deck is verified by visual inspection of the underside after deck removal for honeycombing, and the fiber content is rechecked after every 40 m³ of placement to ensure that pump pressure has not caused fiber accumulative loss in the hopper screen.

Unbonded concrete overlays for bus lanes and container yards receive MasterFiber MAC 2200 CB at 4.0 kg/m³ to 6.0 kg/m³ as a crack-width control agent in 120 mm to 180 mm thick slabs placed over a polyethylene separation layer. The concrete is specified with a maximum aggregate size of 10 mm to 14 mm, a water-cement ratio not exceeding 0.45, and a synthetic macrofiber that passes a boiling test in water at 100 °C for 1 hour with no visible degradation. Fiber addition at these rates requires a central mixer, not a transit mixer alone, because the short mixing period in a ready-mix truck cannot fully open the fiber bundles. The surface is textured longitudinally with a broom or tined float to produce a macrotexture of 0.5 mm to 0.8 mm without pulling fibers from the matrix. Joints are cut at intervals of 6.0 m, and the fiber content is verified by washout of a 20 kg fresh concrete sample against the mix design after every 50 m³ of placement. Compressive strength acceptance is based on ASTM C39/C39M-21 at 28 days and flexural performance on ASTM C1609/C1609M-19 beams sawn from the same batch. When ambient temperature exceeds 30 °C, the concrete is shaded and the surface is fog-sprayed before finishing to prevent early plastic shrinkage cracks that the macrofiber cannot fully close once crack widths exceed 0.5 mm.

Laser Screed Placement Disturbs Surface Fibers More than a Truss Screed in Very-Narrow-Aisle Slabs

Logistics buildings with very-narrow-aisle racking impose tight floor flatness and levelness requirements, typically FF 50 and FL 35 under ASTM E1155-20, and MasterFiber MAC 2200 CB is included at 5.0 kg/m³ to 7.0 kg/m³ to maintain crack control without mesh that interferes with laser screed operation. The concrete is placed at a slump of 160 mm ± 20 mm and struck off with a laser-guided paver capable of maintaining 3 mm elevation tolerance over 3 m. Fiber lumps are screened by a 50 mm vibrating grate at the pump hopper to prevent blocking the paver auger. Finishing uses a ride-on power trowel with pan floats, and the first floating pass is delayed until bleed water disappears from the surface; early troweling folds surface fibers and creates visible orange peel texture. The terminal slab is left without wet curing for more than 24 hours if the relative humidity is below 50%, and a curing compound conforming to ASTM C309 is applied at 0.15 L/m² to 0.20 L/m² within 2 hours after final troweling. Residual strength is measured by ASTM C1609/C1609M-19 using beams cast on site because saw-cut samples from a completed floor cannot provide the required dimensional tolerance. Joint filling is delayed until the moisture vapor emission rate measured per ASTM F2170-22 is below 3 lb/1,000 ft²/24 h, preventing trapped moisture from softening the filler material in high-rack wheel paths.

Precast drainage components such as catch basins, manhole risers, and culvert invert sections are cast with MasterFiber MAC 2200 CB at 4.0 kg/m³ to 6.0 kg/m³ to reduce cracking during form stripping and transport to the site. The concrete is mixed in a twin-shaft plant mixer for 4 minutes after fiber addition, and the fibers are introduced through the aggregate weigh hopper to disperse them before water contact. External form vibrators are operated at 9,000 vpm to 12,000 vpm for 5 seconds per position to avoid forming fiber orientation planes at the form face. The terminal element is cured under steam at 60 °C for 8 hours and then air-cured for 3 days before hydrostatic testing. The fiber does not replace the reinforcing cage required for earth loads; it is used as a secondary crack-control agent at zones of high stress concentration around lifting anchors. Compliance for stormwater contact is assessed through a migration test under EN 12873-1:2014 where required; published data for potable water contact in this specific fiber configuration is limited and must be confirmed before use in drinking water reservoirs. The precaster verifies fiber dispersion by splitting a 150 mm cube from the first batch each day and counting visible clumps on the fractured face, with a production limit of 2 clumps per 0.02 m² of fractured surface.