Product Description

Product Name：Unbound PC Steel Strand

Unbonded prestressed steel strands are composed of one or more high-strength steel wires twisted together (the most common is a seven-wire strand). The strands are coated along their entire length with a special rust-proof lubricant (such as asphalt, wax, or specialized grease) and sheathed in a high-density polyethylene (HDPE) plastic sheath, creating a permanent insulation barrier.

The key to being "unbonded" is that the strands can slide and move freely throughout the concrete structure, without any chemical bond (such as cement grout) or mechanical interlocking (such as the grain of ribbed rebar) between them.

Size: Φ9.50, Φ12.70, Φ15.20, Φ15.70, Φ17.80 or customized

Strength Grade: 1860 MPa, 1960 MPa, 2000 MPa.

Material: Q195、Q235、45、60、65、70、80、82B carbon steel and stainless steel materials

Anti-corrosion Grease Parameters
Grease is key to ensuring "no adhesion" and corrosion resistance.
Coating Requirements: A continuous, abundant, and even coating should be applied to the steel strand surface. The application rate per ton of steel strand is typically no less than 4.5 kg.
Working Cone Penetration: This reflects the hardness of the grease and affects lubrication effectiveness. It is typically between 250 and 350 mm (0.1 mm).
Dropping Point: This reflects the grease's high-temperature resistance and is required to be no less than 160°C to ensure it does not melt or dissipate in construction environments (such as concrete hydration heat).
Corrosivity: It must be non-corrosive to the steel strand and pass relevant corrosion tests.
Chemical Stability: It must exhibit excellent stability, be free of harmful substances, and have no adverse effects on the sheath and concrete.

Outer Sheath Parameters
The sheath is key to ensuring no adhesion and dual corrosion protection.
Material: It must be made of high-density polyethylene (HDPE) or polypropylene (PP). Thickness: Strict requirements apply to sheath thickness to ensure adequate durability and isolation.
For common specifications such as Φ15.20 mm, the sheath thickness is typically at least 1.0 mm.
The specific thickness may vary by standard and manufacturer, but must be uniform.
Appearance: The sheath should be smooth and continuous, free of cracks and holes.
Color: Typically black or a colored (such as blue or yellow) to facilitate identification of different prestressing tendons during construction.

Working Principle
This method differs fundamentally from traditional bonded prestressing in its working principle:

Bonded prestressing involves pouring concrete first and then pre-setting holes. After the concrete hardens, steel strands are inserted into the holes and tensioned. Finally, cement slurry is injected into the holes, bonding the strands to the concrete. Stress is transmitted through bonding forces.

Unbonded prestressing involves pre-sheathing and grease-coated unbonded strands, positioned in the formwork according to the design before pouring concrete. After the concrete has poured and hardened, the strands are tensioned directly. Because of the sheathing, the tensioning force is transmitted entirely to the concrete member through the anchors at each end.

Think of it like this:
A smooth rope (unbonded strand) is threaded through a string of beads (concrete member). You pull only at the ends of the rope (tensioning and anchoring). The rope itself can slide freely within the holes of the beads, but the tension compresses all the beads.

Main Application Areas

Floor slab systems: Cast-in-place concrete slabs in large-span office buildings, shopping malls, parking lots, and hospitals. This is its most classic and common application.

Foundation slabs: The foundation raft slabs of large buildings are used to resist concrete shrinkage and thermal stresses, preventing cracking.

Bridge structures: This technology is particularly used in segmental bridges.

Silos, tanks, etc.: Circular structures.

Soil anchoring: Slope support, foundation pit support, etc.

Customized Packing Options: We offer flexible packing options, including wooden reel, coil, roll, and Z2 packing, to meet the specific needs of our customers