Investigation on spalling resistance of ultra-high-strength concrete under rapid heating and rapid cooling

• Spalling resistance of ultra-high-strength concrete under rapid heating/cooling.
• Burst time is extended but spalling is unaffected by the addition of steel fiber.
• Spalling resistance is improved with addition of PP fiber or PP and steel fibers.
• Ultra-high-strength concrete with 0.20% PP fiber has excellent spalling resistance.
• Resistance to explosive spalling is enhanced with 12- or 19-mm-long PP fibers.

Effects of the fiber type, dosage and length on the explosive spalling of ultra-high-strength concrete under rapid heating and rapid cooling were experimentally investigated. The mechanism of spalling resistance was examined by comprehensive thermal analysis, X-ray diffraction analysis, scanning electron microscopy and mercury porosimetry. The burst time is extended but the spalling is unaffected by the addition of steel fiber. The spalling resistance is improved with the addition of polypropylene (PP) fiber or PP and steel fibers. Ultra-high-strength concrete with 0.20% (vol.) PP fiber has excellent spalling resistance. The resistance to explosive spalling is enhanced with 12- or 19-mm-long PP fibers. PP fiber improves the spalling resistance mainly through the formation of tubular channels.