WEBINAR GFRP SEBAGAI TULANGAN TAHAN KOROSI: KAJIAN KARAKTERISTIK LEKATAN PADA BETON

Main Ideas / Concepts (Webinar Theme: GFRP as Corrosion-Resistant Reinforcement)

Introduction to GFRP (Glass Fiber Reinforced Polymer) Rebar

• GFRP rebar is presented as a durable reinforcement alternative designed to address the main limitation of conventional steel reinforcement: corrosion.
• In Indonesia, adoption is described as relatively recent, with claims that use began to enter the market around 2022, followed by accelerated expansion.

Why GFRP Instead of Steel Rebar

• Corrosion resistance
  • GFRP is non-metal, so it does not rust/corrode like steel.
• Tensile strength advantages (as stated)
  • Claimed tensile strength is roughly 2–3× that of steel.
• Lower density / weight
  • Claimed to be about ¼ the weight of conventional steel rebar, improving handling and potentially improving project efficiency.
• Durability implications
  • Reduced corrosion can mean lower maintenance cost and potentially less deterioration across the structure’s lifetime.

Core Technical Topic: Bond Characteristics Between GFRP and Concrete

Even if GFRP resists corrosion, the webinar emphasizes that its structural effectiveness depends on mechanical interaction with concrete, especially:

• Bond strength / adhesion
• Force transfer mechanism
• Cracking and failure modes
• Structural performance, especially when scaling from laboratory test specimens to real structural elements

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Methodology / Research Approach Described

A) Scope of Research: From Bond Tests to Structural Element Behavior

The study is described as a sequence of escalating investigations:

1. Bond characteristics (GFRP ↔ concrete) as the initial research step
2. Then escalation to structural elements, including:
   • Concrete slab reinforcement
   • Slab-on-ground (SOG) reinforcement

B) Bond Testing Variables and Specimen Design

Variables that were varied

• Bar diameter: 6 mm, 8 mm, 10 mm
  • Also discussed in relation to bond length scaling
• Rib / thread geometry effects
  • Variations include rib spacing and surface condition (e.g., some smooth, some with silica sand, etc.)
• Embedded vs. non-embedded length
  • Embedded area lengths varied as multiples of bar diameter:
    • 5×, 10×, 15× diameter (as described in the lecture)

Two main bond test types explicitly named

1. Flexible bond test (beam-based)
   • The reinforcement is placed on a beam so that:
     • The middle region is not clamped / not fully covered by concrete
     • The end regions allow evaluation of slip and comparison of force transfer behavior
2. Tensile / bond (standard-modified) test (based on SNI references)
   • Described as a modification from an SNI-related setup:
     • One side is fixed/dead
     • The other side is allowed to move
     • Slip is measured at the end to evaluate bond performance

C) Structural Element Testing Configurations

Structural element 1: One-way concrete slab

• Reinforcement comparisons
  • Some slabs reinforced with steel wire mesh (for certain diameters)
  • Others reinforced with GFRP
  • Reported diameter comparisons included:
    • GFRP: 6 mm, 8 mm (primary comparisons)
    • Steel equivalents: larger diameters such as 10 mm and 13 mm
• Control variables
  • Same reinforcement spacing and concrete quality/size criteria (to maintain fairness in comparison)
• Loading and measurement
  • 4-point loading (described as “two-point load / 4 point load”)
  • Captured deflection and load response
  • Observed crack pattern and failure mechanism

Structural element 2: Slab-on-ground (SOG)

• Scale / geometry
  • Described as 1:1 scale
• Loading area
  • Concentrated load over a small region (described as 10×10)
• Measurements
  • Load–deflection/stiffness comparison
  • Crack development and dominant damage location

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Key Findings / Conclusions Stated (Bond + Structural Performance)

Bond performance depends strongly on diameter and bond length

• Smaller-to-medium diameters (6–8 mm)
  • GFRP showed greater bond than steel (in the reported tests).
• Larger diameter (10 mm)
  • Bond performance varies
  • Failure behavior shifts depending on bond length and diameter

Failure / collapse mechanisms observed in bond tests

Two dominant bond failure modes were described:

1. Pull-out failure
   • Reinforcement is pulled from the concrete
   • Dominant for diameter 6–8 mm
2. Concrete splitting / splitting cracks
   • More prominent for larger diameters and sufficiently large bond lengths
   • Example described: around 10 mm with approximately 15× diameter bond length
   • Reason given: large tension along the embedded length causes concrete cracking/splitting around the reinforcement

From bond tests to structural behavior (slab and SOG)

Concrete slab results

• Load–bending behavior
  • GFRP is described as comparable to steel when diameter is appropriately matched.
• Capacity equivalence examples (as stated)
  • GFRP diameter 6 capacity ≈ steel diameter 8
  • GFRP diameter 8 capacity ≈ steel diameter 10
• Crack pattern
  • Described as similar between GFRP and steel.
• Deflection behavior
  • Deformation/deflection response was noted as not always linearly correlated with capacity.

Slab-on-ground (SOG) results

• Overall capacity
  • Described as almost the same between GFRP and steel at comparable diameters
• Stiffness
  • Tends to increase with changes in diameter (as described)
• Crack patterns
  • Similar, with dominant cracks around the loading area and vertical cracking behavior described

Final implications emphasized

• GFRP has potential as an alternative non-corrosive reinforcement in concrete structural elements.
• Good bond behavior enables reinforcement to participate in structural capacity—not only corrosion resistance.
• GFRP use may allow design tradeoffs (capacity equivalence vs diameter/spacing), potentially reducing overall reinforcement cost/material quantity (as argued later in discussion).

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Practical / Design-Related Guidance Mentioned in Q&A

Capacity calculation methods for GFRP

• Speaker referenced that ACI 440.1R provides design methods for GFRP.
• Because GFRP does not have a clear yield point like steel, design may use:
  • Ultimate tensile strength (FU)
  • Strain-based approaches derived from stress–strain behavior
  • Coefficient-based simplified assumptions (e.g., 0.8×FU in simplified concepts, as discussed)

Hybrid beams (GFRP + steel)

• Hybrid beams were described as conceptually allowed (as in academic practice).
• Requirement: recalculation using different stress–strain relationships for GFRP and steel.

Seismic / earthquake ductility concerns

• Discussion suggested ACI 440 sections on seismic ductility may not be fully covered in the referenced portions.
• Hybrid strategies and further research pathways were suggested, but no definitive seismic methodology was claimed from the webinar alone.

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High-Level List of Key Q&A Topics Addressed

• Can capacity formulas for GFRP be the same as steel?
• What tensile strength values were used for samples (FU by diameter)?
• Does bond weakness cause brittle failure due to slip/loose behavior?
• Can GFRP be combined with ordinary steel?
• Can GFRP be used for earthquake-prone structures requiring ductility?
• Optimum reinforcement ratio to avoid concrete crushing or GFRP rupture
• Durability in aggressive environments and whether bond degrades
• Recycling / end-of-life considerations
• Bending / rollability limits (small vs large diameters)
• Price and feasibility vs steel
• Substitution sizing (e.g., replacing 10 mm steel with 8 mm GFRP)

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Speakers / Sources Featured (Named)

1. Host / Moderator (names mentioned)

• Mrs. Dian
  • Appears as “Buudi Dian” in one place and later as Mrs. Dian from Kuria/KEA Composite Teknologi Indonesia in subtitles.
• A male host/participant voice is also implied (prompting transitions and asking questions).

2. Primary technical researcher

• Mrs. Indriani Puluhulawa
  • Head of the Material Testing Laboratory, Civil Engineering Department, Bengkalis State Polytechnic
  • Delivered the bond/structural research presentation.

3. Company representatives / organizational sources

• KEA Composite Technology Indonesia / Kuria Komposit Teknologi Indonesia
• PT Kuria Komposit Teknologi Indonesia
  • Mentioned as a supplier/testing source for GFRP properties.

4. Laboratory / university / collaboration sources

• Bengkalis State Polytechnic
• UNES
• UIS/UITM Malaysia (referenced via a project visit; expansion unclear)

5. Standards / codes referenced

• SNI 8975 (updated to 2025)
• ACI 440, ACI 440.1R, and ACI 440 IR15
• SNI (related to beam/bond testing): referenced in subtitles as “SNI … JFRP” (exact number not fully clear)