Views: 0 Author: Site Editor Publish Time: 2026-02-18 Origin: Site
PC strand, or prestressed concrete steel strand, relies on a sophisticated bonding mechanism to transfer forces effectively between the steel and surrounding concrete. This bond ensures structural integrity in prestressed applications like bridges and high-rises.
PC strand consists of twisted high-strength steel wires, typically 2, 3, 7, or 19 in number, drawn from high-carbon steel rods. These strands undergo stress-relief processes and may feature coatings like epoxy or galvanization for durability.
In bonded systems, the strand integrates directly with concrete, unlike unbonded types that use grease or sheaths. Bonding allows compressive forces from prestressing to distribute evenly, countering tensile stresses.
TJ Wasungen supplies PC strands optimized for such bonding, meeting ASTM A416 standards for consistent performance in demanding projects.
Bonded PC strands form a chemical and mechanical interlock with concrete grout or direct encasement. Epoxy-coated variants enhance this by filling wire gaps, preventing corrosion and boosting adhesion.
Unbonded strands slide freely within ducts, but bonded ones achieve "firm connection with concrete" through grout injection post-tensioning. This grouting creates hydrostatic pressure and surface friction.
Key types include:
Epoxy-filled strands: Wires bonded internally with melted epoxy for fatigue resistance.
Galvanized bonded: Zinc-coated for corrosion protection while maintaining bond strength.
Standard bright strands: Rely on natural wire texture for mechanical grip.
Bonding begins during manufacturing. High-carbon wires are cold-drawn, stranded, and stabilized to minimize relaxation—typically under 2.5% after 1,000 hours.
In construction:
Strands are tensioned to 70-80% ultimate strength using jacks.
Concrete is cast around ducts containing the strands.
Post-tensioning, high-strength grout (cement-sand-water mix, 0.4-0.5 water-cement ratio) is injected, filling voids.
Curing forms crystalline bonds at the steel-concrete interface.
Mechanical interlocking dominates: Strand's helical profile grips grout, amplified by Poisson's effect under compression. Chemical adhesion from cement hydration adds ~20% strength.
Factors like embedment length (l_e) influence bond stress: τ = P_max / (π d_b l_e), where longer embeds reduce stress.
Bond strength hinges on cover depth (c/d_b ratio), where deeper concrete cover boosts performance by 15-30%.
Embedment length: Doubling l_e from 1 d_b to 2 d_b halves average bond stress but ensures full load transfer.
Initial prestress: Higher forces (up to 80%) enhance radial pressure, improving friction.
Strand diameter: Larger diameters (e.g., 15.2mm) show lower unit bond due to surface-area ratio.
Epoxy coatings maintain uniform thickness, allowing direct anchoring without stripping—critical for bond uniformity.
Grout quality matters: Low-bleed, high-flow mixes prevent voids, achieving 10-15 MPa bond stress.
Bonded PC strands offer high tensile strength (1,860-1,960 MPa) and low relaxation, reducing long-term deformations by 50% versus plain rebar.
They save material (20-30% less concrete), cut distortion, and boost stiffness/water resistance. In bridges, this extends service life beyond 100 years.
Fatigue resistance improves as epoxy eliminates wire fretting; structures withstand cyclic loads 4-6 times better.
Primarily used in prestressed beams, piles, and slabs for buildings/bridges. TJ Wasungen's PC strands excel in railway sleepers and nuclear containment.
In high-rises, bonding prevents shear lag, ensuring uniform stress. Recent 2025 projects highlight their role in seismic zones, per updated ASTM specs.
Suspension cables and stay-cables use coated bonded strands for corrosion-proof longevity.
Pull-out tests measure bond: Specimens fail at concrete crushing or strand slip, validating τ > 10 MPa.
Non-destructive methods like impact-echo assess grout voids. Standards mandate low-relaxation (<2.5%) and elongation >3.5%.
TJ Wasungen ensures compliance via ISO-certified testing, offering samples for site verification.
Epoxy advancements now include UV-stabilized polymers for exposed applications. Nano-silica grouts boost bond 25% via denser microstructure.
Hybrid unbonded-bonded systems emerge for repairable structures. With global infrastructure booms, demand rises 8% yearly.
TJ Wasungen provides bonded PC strands with specs tailored to local codes. Contact our for quotes, specs, or samples.
Their supply chain from China ensures competitive pricing for excavator parts and telecom alongside strands.
