The brittleness of carbon plates is a material property, not a quality defect.

Many people believe that "carbon plate" is brittle, but this is essentially a confusion between "overall material properties" and "single mechanical properties." The "brittleness" of carbon plate specifically refers to its low shear strength (i.e., it easily breaks when subjected to lateral forces), but this does not equate to "overall weakness." Just as steel's "high toughness" doesn't mean it's more suitable than carbon plate in all scenarios.

From the perspective of material mechanics:

Carbon fiber plate: Made from a composite of carbon fiber and resin, its core advantages are high tensile strength (GB 50367 requires ≥3000 MPa) and high elastic modulus (≥240 GPa), but its shear strength is only 1/3 to 1/2 that of steel (approximately 30-50 MPa).

Ordinary steel: Its tensile strength is approximately 345-500 MPa, its elastic modulus is approximately 206 GPa, and its shear strength is approximately 180-250 MPa. Its advantages include superior shear and impact resistance, and high toughness (it easily deforms under external forces but is not prone to breaking).

Key conclusion: The brittleness of carbon plates is a result of a design that maximizes strengths and minimizes weaknesses. To maximize tensile strength (a core requirement for reinforcement), some shear resistance is sacrificed. Just like a pair of scissors, the blade must be brittle and hard to cut; if the blade were as flexible as rubber, it would be ineffective.

The "strongness" required in the solid scene is "tensile strength" rather than "shear strength"

Judging the strength of carbon panels cannot be separated from their application scenarios. Their core purpose is to reinforce concrete structures (such as floor slabs, beams, columns, and bridges). Concrete structures' weakness lies in their weak tensile strength, not their weak shear resistance.

1. Concrete's inherent flaws determine the suitability of carbon panels.

Concrete has a very high compressive strength (common C30 concrete has a compressive strength of ≥30 MPa), but its tensile strength is only 1/8 to 1/12 of that (approximately 2 to 4 MPa). This is like saying, "It can withstand the pressure of 10 strong men, but it can't withstand the pull of a child." Therefore, the core requirement for reinforcing concrete structures is to supplement their tensile strength to prevent cracking or fracture due to tension.

Now let’s look at the comparison between carbon plate and steel:

2. Reinforcement design can "circumvent" carbon plate's shear weakness and maximize its tensile strength.

Professional carbon plate reinforcement design uses three methods to avoid safety impacts from "shear weaknesses":

Load-bearing direction design: Carbon plates are used only in "tensile areas" (such as the bottom of beams and under floor slabs). Transverse load-bearing areas (such as the sides of beams) are supplemented with other materials (such as bonded steel and stirrups) to provide shear resistance, allowing the carbon plates to focus solely on their strengths.

Anchoring measures: Carbon fiber anchors or steel plate strips are installed at both ends of the carbon plate to prevent the plate from peeling due to excessive shear forces at the ends, effectively providing a protective sheath for the plate.

Thickness control: Carbon plates used for reinforcement are typically 1-5mm thick (ultra-thin design). With a small transverse cross-section, the carbon plates are subject to low shear forces, further reducing the risk of brittle fracture.

For example, during the reinforcement of a T-beam on a municipal bridge, a 2mm crack developed at the bottom of the beam due to tension. Engineers applied 3mm-thick carbon plates to the bottom (tension zone) of the beam, anchored the ends with steel plate strips, and added stirrups on the sides to provide additional shear resistance. Post-reinforcement testing showed the beam's tensile bearing capacity increased by 28%, and the crack width was reduced to less than 0.1mm. Five years of service have passed without any issues with the carbon plates breaking or peeling—a testament to the effectiveness of a design that leverages strengths and minimizes weaknesses.

The misconception that “carbon plates are not as strong as steel” stems from three cognitive biases

1. Using "everyday experience" instead of "engineering scenarios"

In everyday life, we think of "strength" as "unbreakable" (e.g., a dropped spoon is fine, but a carbon plate might break). However, in engineering, "strength" means "within the designed load range." Carbon plates only withstand tensile forces during reinforcement and are not subject to drops or impacts like everyday items, so they naturally won't fail due to "brittleness."

2. Confusing "material strength" with "structural strength"

Some people believe carbon plates are "weak" because they can be broken by hand. However, in actual reinforcement, carbon plates are bonded to concrete, forming a "concrete + carbon plate" composite structure. The tensile forces of the carbon plates are transferred to the concrete through a resin adhesive, making the overall structural strength far greater than that of either material alone. Just as a single chopstick breaks easily, a bundle of chopsticks is unbreakable. The combination of carbon plates and concrete has long since overcome the shortcomings of a single material.

3. Ignoring "Strongness" for "Long-Term Performance"

"Strongness" isn't just about short-term resistance; it also requires long-term durability. Steel is prone to rusting in humid, acidic, and alkaline environments (such as underground garages and coastal buildings), requiring maintenance every 3-5 years to prevent its strength from steadily declining. Carbon plates, on the other hand, are corrosion- and UV-resistant, with performance degradation of no more than 10% over 50 years in harsh environments. In the long term, carbon plates are actually more durable.

In 2018, a coastal factory building used both carbon plates and steel bonding to reinforce its columns. Inspections in 2023 revealed that the steel-bonded areas had developed localized rust and a 15% decrease in tensile strength. However, the carbon plate areas showed no corrosion and maintained essentially the same strength as when the reinforcement was first applied. This is the difference in long-term "strength."

Whether to choose carbon plate or steel depends on the application needs, not just the specific characteristics.

There's no such thing as an absolutely "stronger" material; there are only "more suitable" materials. How should we choose between carbon plate and steel in concrete reinforcement?

Scenarios where carbon plate is preferred:

• Needing additional tensile strength (e.g., beam bottoms, floor slabs, and bridge tension zones);

• Weight-sensitive applications (e.g., old buildings and high-rise buildings to avoid increasing structural loads);

• Harsh environments (humid, acidic, alkaline, coastal locations, requiring corrosion resistance);

• Tight construction schedules (carbon plate installation only takes 2-3 days, while steel reinforcement takes 7-10 days).

Scenarios where steel may be considered:

• Needing to withstand both tension and shear forces (e.g., beam-column joints, seismic reinforcement);

• Areas subject to high impact loads (e.g., factory equipment foundations, garage entrances);

• Extremely low budgets and dry environments (steel has slightly lower initial cost, but higher long-term maintenance costs).