Study Polypropylene Fiber Boosts Concrete Strength Post High Heat

As the cornerstone of modern construction, concrete's mechanical stability is paramount. However, extreme high-temperature environments like fires pose significant challenges to concrete structural safety. A critical engineering question emerges: how to maintain or even improve concrete's compressive strength after exposure to high temperatures? This study investigates the impact of polypropylene fibers on concrete's compressive performance under thermal stress, providing data-driven insights for optimizing fire-resistant structural designs.

Materials and Experimental Methods

The experiment utilized 42.5-grade ordinary Portland cement with detailed specifications documented in original reference tables. Natural river sand (fineness modulus 2.7-3.0) served as fine aggregate, while 5-20mm continuously graded basalt crushed stone functioned as coarse aggregate. Researchers prepared polypropylene fibers in three distinct lengths to examine length-related performance variations.

Experimental Process and Results

Thermal testing revealed progressive visual changes in concrete specimens. As temperatures increased to 300°C and 450°C, surfaces transitioned from gray to reddish hues, with visible cracking emerging above 300°C. Microscopic examination showed polypropylene fibers fully encapsulated in cement paste at room temperature, with strong aggregate-mortar bonding.

Impact of Polypropylene Fibers on Post-Fire Compressive Strength

Key findings emerged regarding fiber parameters:

• Dosage Effects: Optimal fiber concentrations effectively restrained thermal cracking, enhancing compressive strength. Excessive quantities caused uneven distribution, compromising performance.
• Length Considerations: Longer fibers better bridged microcracks but posed workability challenges. The study identified length thresholds where mechanical benefits outweighed practical drawbacks.

Thermal Effects on Fracture Characteristics

• Room-temperature fractures showed brittle patterns, while heated specimens exhibited extended, ductile fracture paths due to microcrack networks.
• Fibers improved aggregate-mortar interfacial bonding, counteracting thermal degradation of this critical transition zone.

Data Analysis and Interpretation

• Advanced analytical methods established quantitative relationships between:
• Compressive strength and thermal/fiber parameters
• Fracture morphology and material variables

Comparative analysis validated findings against existing literature, confirming polypropylene fibers' effectiveness in fire-damage mitigation.

Conclusions and Recommendations

• The research demonstrated that:
• Progressive color lightening (gray→white) and fracture path elongation reliably indicate thermal damage severity.
• Polypropylene fibers significantly enhance post-fire compressive strength and crack resistance when optimally proportioned.

Practical recommendations include:

• Precision-tuning fiber dosage and length for specific thermal exposure scenarios
• Implementing complementary fire-protection systems

Future Research Directions

• Promising investigative pathways include:
• Comparative studies of alternative fiber materials (carbon, steel)
• Synergistic effects between fibers and chemical admixtures
• Microstructural analysis using SEM technology
• Long-term performance under sustained thermal exposure

These advancements will further refine fire-resistant concrete design methodologies, ensuring structural integrity in extreme environments.