What Flexural Strength in MPa Should Quality GRC Reach? What Is the Industry Standard? An In-Depth Interpretation of Qinglong GRC Mechanical Performance Standards

Flexural strength (also known as modulus of rupture) is a core indicator for evaluating the mechanical properties of GRC materials, particularly their toughness and load-bearing capacity. It directly reflects the reinforcing effect of glass fibers in the cement matrix and is the foundation for GRC's distinction from ordinary concrete and its ability to achieve lightweight thin-wall design. According to the Chinese building materials industry standard "Glass Fibre Reinforced Cement (GRC) Products" JC/T 940, there are explicit grading requirements for the flexural strength of GRC products. As an industry benchmark for quality, Qinglong GRC products typically perform far beyond the national standard baseline.

In the testing of unitized GRC curtain wall panels for the Qianhai International Financial Center in Shenzhen, a sample (15mm thick) submitted by Qinglong GRC underwent a three-point bending test at the National Building Materials Testing Center in accordance with the JC/T 940 standard, achieving a 28-day ultimate flexural strength (LOP) of 25.8MPa, far exceeding the standard's strength requirement of ≥15MPa for spray-up GRC panels. More importantly, its flexural toughness is excellent: after reaching ultimate strength, the load-bearing capacity declines slowly, exhibiting significant "pseudo-ductility" characteristics rather than brittle fracture. This data provides solid safety endorsement for the project's pioneering design featuring large panel divisions and minimal supports.

Strength Grading System in the Industry Standard (JC/T 940)

The standard sets different requirements for the flexural strength of GRC according to the forming process and fiber incorporation method. For the mainstream spray-up process, the 28-day flexural strength (LOP) should be no less than 15MPa. For the premix casting process, since fiber length and orientation are limited, the strength requirement is slightly lower but must still meet the corresponding grade. The standard also addresses both "first crack strength" and "ultimate strength": for quality GRC, the ultimate strength should be significantly higher than the first crack strength, and this difference reflects the fibers' bridging and toughening effect.

Qinglong GRC's Internal Strength Standards and How They Are Achieved

Qinglong GRC's internal corporate control standard typically sets the lower limit of the 28-day flexural strength of spray-up GRC at above 18MPa, and requires ≥20MPa or even 25MPa for high-end curtain walls, structural components, and similar products. Achieving high strength depends on: 1) High-quality alkali-resistant glass fibers (high zirconia content, excellent interfacial bonding); 2) A low water-cement ratio, highly dense matrix (achieved with high-range water reducers, with the water-cement ratio controlled at 0.30-0.33); 3) Scientific fiber dosage and distribution (4%-5% by volume, uniformly distributed in three-dimensional random orientation); 4) An optimized curing regime (ensuring full strength development).

The Relationship Between Flexural Strength and Other Properties

High flexural strength is a concentrated reflection of GRC's excellent overall performance. It is typically positively correlated with high impact resistance (good toughness), good crack resistance (fiber crack arrest), and excellent durability (dense matrix). In quality control, Qinglong GRC focuses not only on absolute strength values but also on the coefficient of variation of strength, keeping it within 8% to ensure highly consistent product performance — the foundation of safety and reliability in large-scale engineering applications.

Flexural strength is the "touchstone" of GRC performance. When selecting GRC products, one should not settle merely for meeting the minimum national standard requirements, but should pursue higher performance standards achieved through stable processes. With strength indicators far exceeding national standards and outstanding toughness, Qinglong GRC defines the mechanical performance benchmark for high-quality GRC.