PSC Girder Stressing & Grouting Guide

IRC:112 & MoRTH Section 1800 Guidelines

PSC Girder Stressing & Grouting

From Tendon Tensioning to Long-Term Structural Durability

"Right Force + Correct Elongation + Complete Grouting = Durable Post-Tensioned Concrete Girder."

Geotechnical & Structural Field Guidelines

1. Pre-Stressing Field Checks & Execution Sequence

1 Before Stressing Protocols

• Verify concrete compressive strength has achieved the specified minimum stressing strength ($f_{cj}$, typically $\ge 0.8 f_{ck}$).
• Inspect tendon ducts using compressed air or mandrel pulling for alignment and blockage free passages.
• Clean anchorage plates, trumpet openings, and wedges; clear off rust, slurry, or debris.
• Validate hydraulic jack & pressure gauge calibration charts (must be within valid 6-month window).
• Establish clear exclusion safety zones behind live-end anchorages prior to pressurization.

2 Stressing Execution Sequence

1. Initial Seating: Apply 10% target force to take up slack and establish baseline mark ($L_0$).
2. Incremental Stressing: Raise pressure in 20% increments (e.g., 20%, 40%, 60%, 80%, 100%).
3. Elongation Measurement: Measure extension at each stage to monitor force-displacement linearity.
4. Target Force Verification: Hold target pressure for 5 minutes; verify maximum elongation variance ($\le \pm 5\%$).
5. Wedge Seating / Lock-Off: Release hydraulic pressure allowing wedges to bite and seat into anchor block.
6. Jack Release: Retract cylinder, measure final wedge draw-in/slip, and record final field logs.

2. Grouting Protocols & Corrosion Protection

Grouting serves a dual purpose: providing direct bond between prestressing steel and structural concrete, and shielding high-strength strands from aggressive environmental corrosion.

Corrosion Barrier

Composite Bond

Water Ingress Seal

Long-Term Life

Grouting Sequence:

Step 1 Clean & flush duct with clean water, followed by oil-free compressed air.

Step 2 Mix grout (w/c $\le 0.40$) using high-shear colloidal mixer for minimum 3 minutes.

Step 3 Perform fluidity (Cone test) and ambient/grout temperature verification prior to injection.

Step 4 Inject grout continuously from lowest point/inlet at steady speed ($6 - 12\text{ m/min}$).

Step 5 Sequentially close intermediate vents as air/water expels and thick grout streams continuously, hold $0.5\text{ MPa}$ pressure for 1 minute before lock-off.

3. End-to-End Field Execution Flowchart

graph TD A[Concrete Strength Check >= f_cj] --> B[Duct Clearance & Calibration Verification] B --> C[Set Up Jacking Rig & Initial Seating 10%] C --> D[Incremental Tensioning to 100% Target Force] D --> E{Elongation Tolerance Check +-5%} E -- Pass --> F[Lock-off Wedges & Measure Seating Slip] E -- Fail/Discrepancy --> G[HALT: Investigate Friction/Strand Slip] F --> H[Trim Strands & Seal Anchorage Caps] H --> I[Colloidal Grout Mixing & QA Fluidity Test] I --> J[Continuous Low-Pressure Grout Pumping] J --> K[Sequential Vent Closure & Pressure Hold] K --> L[Record Logs & Final Inspection Sign-off]

Interactive Elongation Calculator

$$\Delta L = \frac{P \cdot L}{A_p \cdot E_p}$$

Stressing Force $P$ (kN)

Tendon Length $L$ (m)

Strand Area $A_p$ ($\text{mm}^2$)

Elastic Modulus $E_p$ (MPa)

Measured Field Elongation (mm)

Wedge Draw-In / Slip (mm)

Theoretical Elongation: 569.8 mm

Net Measured Elongation: 554.0 mm

Variance Percentage: -2.77%

Within Allowable Tolerance ($\pm 5\%$)

Grout QA/QC Acceptance Limits (IRC:112)

Test / Property	Acceptance Limit
Water/Cement Ratio	$\le 0.40$ max
Grout Temperature	$10^\circ\text{C}$ to $25^\circ\text{C}$
7-Day Compressive Strength	$\ge 27\text{ MPa}$
28-Day Compressive Strength	$\ge 35\text{ MPa}$
28-Day Volume Change	$\le +0.2\%$ expansion
24-hr Free Bleeding	$\le 0.5\%$ (must re-absorb)
Cone Fluidity (Flow Time)	$11\text{ s} - 25\text{ s}$
Fluidity Retention (30 min)	$\le 20\%$ change
Chloride Content	$\le 0.10\%$ by cement wt

Critical Site Mistakes to Avoid

Stressing Solely by Pressure Gauge

Relying only on hydraulic pressure without verifying physical elongation hides structural friction losses and strand bind.

Ignoring Elongation Deviation

Proceeding when theoretical vs measured variance exceeds $\pm 5\%$ leads to under-stressing or strand breakage.

Adding Water to Improve Grout Flow

Diluting grout increases voids, severe bleeding, and micro-cracking, destroying corrosion protection.

Premature Vent Closure

Closing vents before full, air-free grout discharge creates trapped air pockets and localized strand corrosion.

Site Engineer's Key Takeaway

Verified Jack Calibration + Accurate Elongation Measurements + Full Lock-off Seating + High-Quality Colloidal Grouting = Long-Life Structural Integrity.

Yogendra Gopal Borse

Civil Engineer | Assistant Engineer Grade-I, Maharashtra PWD

B.Tech (Civil) from VJTI Mumbai. Experienced in bridge design, road works, estimation, project monitoring and digital engineering tools. Creator of YogiPWD – practical technical resources for civil engineers.

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